Release 0.1.1-rc.12

Housecarl 0.1.1's twelfth release candidate. Since rc.11: quota usage
as a percentage; Statistics' quotas link to their rules and include
per-address quotas. make test and make e2e (304 checks) pass.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

AGENTS.md

@@ -30,6 +30,10 @@ Go module `housecarl`, `CGO_ENABLED=0`, Linux only for housecarld.
   on probation and rolled back unless confirmed (docs/design.md). An
   empty configuration applies nothing. But never force a rule that keeps
   SSH or the web UI open: the maintainer doesn't want one.
+* **Shadow mode changes no packet** (docs/shadow.md): anything new the
+  renderer writes that drops, rejects, translates or alters packets needs
+  its shadow form (counted, marked `[would …]`) or must be left out
+  there. `TestShadow` fails on what slips through.
 * **Stay within nftables 1.1.3** (Debian 13). The dev machine's newer nft
   accepts things 1.1.3 refuses; the tests with `HOUSECARL_NFT` and the
   e2e test use 1.1.3.

CHANGELOG.md

@@ -8,6 +8,68 @@ All notable changes to Housecarl are documented here. The format follows
 
 ### Added
 
+- **Quota usage as a share.** What a quota used shows its percentage
+  (`12.3 GB of 50.0 GB used (24%)`, each address's in the quota
+  dialog), on the Rules page, the dashboard and in `hc quotas`.
+- **Reset one address's quota, or give some back.** `hc rule
+  reset-quota ID --address ADDR` starts only that device's allowance
+  again; `--give 5gbytes` takes that much off what was used instead (one
+  address's, or everyone's): extra allowance until the next reset,
+  without changing the rule. In the web UI, a rule's quota is one
+  line (what it used, how it resets) that opens a dialog with the rest:
+  usage per address, last and next reset, and Reset and Give back for
+  everyone or one address. `POST /rules/{ref}/reset-quota` takes `address` and `give`.
+- **Names beside inside addresses.** Connections, the log, quota usage,
+  the dashboard's quotas and the statistics' devices and blocked
+  sources show each inside address's name, found by a reverse lookup:
+  `laptop 192.168.1.20` in the web UI, `192.168.1.20 (laptop)` in `hc`.
+  Only inside addresses are looked up (an inside zone's networks, and
+  private ones outside the external zones'). Names are cached for 10
+  minutes and never stored. `names.enabled`, `names.resolver` and
+  `names.cache` in housecarl.yaml; `hc --no-names`; `POST /names`.
+- **Quotas on the dashboard.** With any rule holding a quota, the
+  dashboard lists them all: the allowance, what is used (for a
+  per-address quota, how many addresses and the busiest) with a bar, and
+  the next reset. Each opens its rule.
+- **Links to a rule open it.** A rule named in the matrix, the log, the
+  tracer, statistics or the dashboard's busiest rules opens the Rules
+  page on its chain, scrolled to it and highlighted (`#/rules?rule=ID`).
+  The Rules page shows each rule's ID (`#410`, as `hc` and labels name
+  it) beside its order.
+- **A clearer zone matrix.** A cell reads allow, block, or **partly**
+  (some new connections let through, the rest not), with the exceptions
+  counted by what they do (`+3 -1` instead of `+4`), and what they let
+  through: services with the addresses they're limited to (`ssh from
+  trusted`, `5 port forwards`), under the grid in `hc matrix`, in each
+  cell on the Matrix page. A zone to itself is marked (only traffic routed
+  between its interfaces passes the firewall). The details list each
+  rule's hits. API: `summary`, `allowed`, `blocked`, `open`,
+  `same_zone`, `note`, `hits`, and `short` and `hits` per exception.
+  Raw rules that are a match and then accept, drop or reject (without
+  interfaces) are read instead of shown as unknown.
+- **Shadow mode** (`shadow.enabled` in housecarl.yaml; docs/shadow.md):
+  Housecarl's ruleset is loaded beside the firewall you have but blocks,
+  rejects and translates nothing. Drops and rejects are counted and accept
+  instead (an accept only ends Housecarl's chain), policies accept and
+  always log what they would drop, NAT only counts, MSS clamping and the
+  flowtable are left out, and raw rules that do more than accept, drop or
+  reject are left out with a warning (`shadow_raw_left_out`). Comments
+  mark what would happen (`[would drop]`). `shadow.position`: Housecarl's
+  filter chains run after the other firewall's (`filter + 10`, the
+  default: what it would drop is what switching would break) or before
+  (`- 10`); its NAT chains always first. Every change is checked by
+  nftables in both forms, so leaving shadow mode can't fail. No
+  probation; takeovers and closing connections are refused (409). The
+  boot ruleset is the shadow one, and its fallback filters nothing. When
+  a reload (`flush ruleset`) deletes Housecarl's table, housecarld puts it
+  back (it listens to nftables' netlink notifications). `mode` in
+  `/status`, `/healthz` and `/auth/whoami`; a banner in the web UI;
+  would-be drops marked in the log (`shadow`) and the tracer
+  (`would_drop`); `hc ruleset --enforcing` (`GET /ruleset?enforcing=1`)
+  shows the ruleset for after. `shadow_unprotected` warns when no other
+  table filters the input hook; `nftables_service` and `takeover_pending`
+  aren't raised in shadow mode. The e2e test imports in shadow mode
+  before taking over.
 - **Zone names at import:** `hc import --zone enp2s0=lan` (repeat;
   interfaces given one name share a zone; Zone names on the Import
   page), and a note listing each zone and where its name came from.
@@ -17,8 +79,40 @@ All notable changes to Housecarl are documented here. The format follows
 - Import: sets with `flags timeout` become dynamic sets; a DNAT of
   several ports becomes one port forward per port.
 
+### Changed
+
+- **Rules read as a direction.** A match's zones are written `lan → wan`,
+  `any but wan → any`, or with the firewall itself as the other end
+  (`lan → firewall` in input, `firewall → wan` in output), instead of
+  `in lan · out wan` and `in not wan`; exclusions read `from any but X`.
+  On the Rules and NAT pages and in `hc`; the flags and JSON stay as
+  they were.
+
 ### Fixed
 
+- Changing how a quota counts lost or muddled what it used: per address
+  to a total started at nothing, per source to per destination kept the
+  sources' use as if it were the destinations', and other groups left
+  the old entries behind. Now a total starts at the addresses' sum,
+  wider groups add up their addresses, and what can't be carried starts
+  again with a warning (`quota_restarts`) on the change.
+- Statistics' Quotas card linked every entry to the Rules page, not to
+  its rule; each now opens its rule, named. Per-address quotas were
+  missing from it (and from the `quota:rN` series): they count their
+  addresses' sum.
+- `hc stats top devices` listed each device twice (once for what it
+  received, once for what it sent); it is one row with both again.
+- `hc rule add --before/--after/--first` made two changes (create at the
+  end, then move), so two history entries, two probations, and the rule
+  briefly in force at the end of its chain; staged in a changeset, the
+  place was lost. The create now takes the place (`POST
+  /rules?before=ID`, `after`, `first`) and makes one change.
+- `hc matrix` in a terminal: the colours' escape codes threw the columns
+  out of line.
+- `hc counters` (`GET /counters`) kept listing the objects of a
+  configuration replaced since housecarld started (`hc import
+  --replace` gives every object a new ID), beside the current ones; the
+  totals of objects that no longer exist are now forgotten.
 - Import: two base chains on one hook had their rules imported twice,
   and the second chain's leading built-ins were moved above the first
   chain's rules; they now follow each other by priority (read in a

README.md

@@ -49,6 +49,10 @@ table of its own.
   ruleset into zones, sets, services, rules and port forwards, keeping the
   rules' order, and keeps what it can't translate as raw rules
   ([docs/import.md](docs/import.md)).
+* **Try it first, in shadow mode.** Housecarl's ruleset runs beside the
+  firewall you have, blocking nothing: its hits, log and tracer show what
+  it would drop, so you see what switching over would break before you do
+  ([docs/shadow.md](docs/shadow.md)).
 * **Easy to watch.** A zone matrix of what is allowed between zones,
   statistics over time (traffic per zone and device, drops, the sources
   blocked most, connections; [docs/stats.md](docs/stats.md)), hits per rule, a live log of what was dropped and
@@ -104,6 +108,7 @@ The web UI is on `http://127.0.0.1:8070/` (see `listen` in
 * [rules.md](docs/rules.md): zones, address sets, services, rules and the built-ins
 * [nat.md](docs/nat.md): port forwards, hairpin NAT, IPv6 pinholes, source NAT, redirects
 * [import.md](docs/import.md): moving from an existing nftables ruleset
+* [shadow.md](docs/shadow.md): shadow mode, Housecarl beside your firewall, changing nothing
 * [operations.md](docs/operations.md): probation, the boot and its fallback, hits and the log, monitoring, backups, troubleshooting
 * [flowtable.md](docs/flowtable.md): the fast path for forwarded traffic, and when (not) to use it
 * [certificates.md](docs/certificates.md): HTTPS with a certificate from Let's Encrypt, through Jarl
@@ -118,13 +123,14 @@ The web UI is on `http://127.0.0.1:8070/` (see `listen` in
 
 ## Status
 
-Housecarl 0.1.1 is in testing (0.1.1-rc.1): zones, address sets and
+Housecarl 0.1.1 is in testing (0.1.1-rc.12): zones, address sets and
 services with ordered rules, IPv4 and IPv6, port forwards with hairpin NAT
 and IPv6 pinholes, source NAT and redirects, built-ins, probation for
 network changes (confirmed by the client that made them), the ruleset
 at boot with a fail-closed fallback, hits and the drop log, nftables
 import, changesets reviewed with the ruleset's diff (as in Jarl),
-bandwidth limits and quotas, a web UI, REST API and CLI.
+bandwidth limits and quotas, shadow mode beside another firewall, a web
+UI, REST API and CLI.
 
 ## Licence
 

VERSION

@@ -1 +1 @@
-0.1.1-rc.1
+0.1.1-rc.12

cmd/hc/firewall.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"net/url"
 	"os"
 	"os/exec"
 	"sort"
@@ -30,6 +31,9 @@ func statusCmd() *cobra.Command {
 			}
 			return output(st, func(w io.Writer) {
 				fmt.Fprintf(w, "Housecarl:\t%s, up since %s\n", st.Build.Label, st.Started.Local().Format("2006-01-02 15:04"))
+				if st.Mode == api.ModeShadow {
+					fmt.Fprintf(w, "Mode:\tSHADOW: the ruleset blocks, rejects and translates nothing; the other firewall decides (Housecarl's chains run %s it)\n", st.ShadowPosition)
+				}
 				if st.Applied {
 					fmt.Fprintln(w, "Ruleset:\tin force (table inet housecarl)")
 				} else if st.Unconfigured {
@@ -237,21 +241,28 @@ func onOff(name, v string) (bool, error) {
 // ---- the ruleset, counters, the log
 
 func rulesetCmd() *cobra.Command {
-	return &cobra.Command{
+	var enforcing bool
+	cmd := &cobra.Command{
 		Use: "ruleset", Short: "Print the nftables ruleset Housecarl builds", Args: cobra.NoArgs,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			c, err := newClient()
 			if err != nil {
 				return err
 			}
+			var q url.Values
+			if enforcing {
+				q = url.Values{"enforcing": {"1"}}
+			}
 			var text string
-			if err := c.Do(ctx(), "GET", "/ruleset", nil, nil, &text); err != nil {
+			if err := c.Do(ctx(), "GET", "/ruleset", q, nil, &text); err != nil {
 				return err
 			}
 			fmt.Print(text)
 			return nil
 		},
 	}
+	cmd.Flags().BoolVar(&enforcing, "enforcing", false, "in shadow mode: the ruleset loaded once it is off")
+	return cmd
 }
 
 func countersCmd() *cobra.Command {
@@ -287,6 +298,13 @@ func quotasCmd() *cobra.Command {
 			if err != nil {
 				return err
 			}
+			var addrs []string
+			for _, q := range qs {
+				for _, a := range q.Addresses {
+					addrs = append(addrs, a.Address)
+				}
+			}
+			names := lookupNames(addrs...)
 			return output(qs, func(w io.Writer) {
 				fmt.Fprintln(w, "RULE\tUSED\tOF\tRESETS\tNEXT RESET")
 				for _, q := range qs {
@@ -304,9 +322,13 @@ func quotasCmd() *cobra.Command {
 					if q.Quota.PerSource || q.Quota.PerDestination {
 						of += " each"
 					}
-					fmt.Fprintf(w, "%s\t%s\t%s\t%s\t%s\n", q.Rule, humanBytes(q.Used), of, resets, next)
+					used := humanBytes(q.Used)
+					if !q.Quota.PerSource && !q.Quota.PerDestination {
+						used += " (" + percent(q.Used, q.Quota.Bytes) + ")"
+					}
+					fmt.Fprintf(w, "%s\t%s\t%s\t%s\t%s\n", q.Rule, used, of, resets, next)
 					for _, a := range q.Addresses {
-						fmt.Fprintf(w, "  %s\t%s\t\t\t\n", a.Address, humanBytes(a.Used))
+						fmt.Fprintf(w, "  %s\t%s (%s)\t\t\t\n", named(names, a.Address, a.Address), humanBytes(a.Used), percent(a.Used, q.Quota.Bytes))
 					}
 				}
 			})
@@ -314,6 +336,17 @@ func quotasCmd() *cobra.Command {
 	}
 }
 
+// percent writes used as a share of total: "25%", "<1%" for a little.
+func percent(used, total int64) string {
+	if total <= 0 || used <= 0 {
+		return "0%"
+	}
+	if used*100 < total {
+		return "<1%"
+	}
+	return fmt.Sprintf("%d%%", used*100/total)
+}
+
 func logCmd() *cobra.Command {
 	var follow bool
 	var limit int
@@ -330,6 +363,11 @@ func logCmd() *cobra.Command {
 			var last time.Time
 			print := func(es []api.LogEntry) {
 				sort.Slice(es, func(i, j int) bool { return es[i].Time.Before(es[j].Time) })
+				var addrs []string
+				for _, e := range es {
+					addrs = append(addrs, e.Source, e.Dest)
+				}
+				names := lookupNames(addrs...)
 				for _, e := range es {
 					last = e.Time
 					src, dst := e.Source, e.Dest
@@ -339,6 +377,7 @@ func logCmd() *cobra.Command {
 					if e.DestPort != 0 {
 						dst = joinPort(dst, e.DestPort)
 					}
+					src, dst = named(names, e.Source, src), named(names, e.Dest, dst)
 					what := e.Protocol
 					if e.ICMPType != "" {
 						what += " " + e.ICMPType
@@ -346,6 +385,9 @@ func logCmd() *cobra.Command {
 					if e.TCPFlags != "" {
 						what += " " + e.TCPFlags
 					}
+					if e.Shadow && (e.Verdict == "drop" || e.Verdict == "reject") {
+						what += "  (shadow mode: would " + e.Verdict + ", let through)"
+					}
 					fmt.Printf("%s  %-28s %-6s %-6s %s -> %s  %s\n", e.Time.Local().Format("15:04:05"), strings.TrimSpace(e.Prefix), orDash(e.In), orDash(e.Out), src, dst, what)
 				}
 			}

cmd/hc/main.go

@@ -46,6 +46,7 @@ var (
 	flagCACert    string
 	flagQuiet     bool
 	flagNoConfirm bool
+	flagNoNames   bool
 	// lastClient is the client the command made (to confirm a change by
 	// itself after it).
 	lastClient *client.Client
@@ -182,6 +183,7 @@ Exit codes: 0 ok, 1 error, 3 not authenticated or not allowed, 4 not found,
 	pf.StringVar(&flagCACert, "ca-cert", "", "PEM file with a CA to trust for the server's certificate")
 	pf.BoolVarP(&flagQuiet, "quiet", "q", false, "print only errors (and IDs of new objects)")
 	pf.BoolVar(&flagNoConfirm, "no-confirm", false, "leave a change on probation instead of confirming it once this client reaches Housecarl again")
+	pf.BoolVar(&flagNoNames, "no-names", false, "show inside addresses without their names (reverse lookups)")
 	pf.Int64VarP(&flagChangeset, "changeset", "C", 0, "stage configuration changes in this changeset instead of applying them (env HOUSECARL_CHANGESET)")
 	root.AddGroup(&cobra.Group{ID: "fw", Title: "Firewall:"}, &cobra.Group{ID: "changes", Title: "Changes:"}, &cobra.Group{ID: "admin", Title: "Administration:"})
 	add := func(group string, cmds ...*cobra.Command) {

cmd/hc/main_test.go

@@ -1,8 +1,11 @@
 package main
 
 import (
+	"regexp"
+	"strings"
 	"testing"
 
+	"housecarl/internal/matrix"
 	"housecarl/internal/model"
 )
 
@@ -32,11 +35,53 @@ func TestLimitAndDescribe(t *testing.T) {
 	if _, err := parseLimit("fast"); err == nil {
 		t.Error("a bad limit accepted")
 	}
-	m := model.Match{InZones: []string{"wan"}, NotSources: true, Sources: []string{"trusted"}, Services: []string{"ssh", "tcp/8080"}}
-	if got := describe(m); got != "in wan  from not trusted  ssh,tcp/8080" {
-		t.Errorf("describe: %q", got)
+	for _, c := range []struct {
+		m     model.Match
+		chain string
+		want  string
+	}{
+		{model.Match{InZones: []string{"wan"}, NotSources: true, Sources: []string{"trusted"}, Services: []string{"ssh", "tcp/8080"}}, "input",
+			"wan → firewall  from any but trusted  ssh,tcp/8080"},
+		{model.Match{InZones: []string{"wan"}, NotIn: true, Destinations: []string{"trusted_ips"}}, "forward", "any but wan → any  to trusted_ips"},
+		{model.Match{InZones: []string{"lan"}, OutZones: []string{"wan"}}, "forward", "lan → wan"},
+		{model.Match{OutZones: []string{"wan"}}, "output", "firewall → wan"},
+		{model.Match{OutZones: []string{"wan"}, Sources: []string{"10.0.0.0/8"}}, "", "any → wan  from 10.0.0.0/8"},
+		{model.Match{Sources: []string{"trusted"}}, "input", "from trusted"},
+		{model.Match{}, "forward", "everything"},
+	} {
+		if got := describe(c.m, c.chain); got != c.want {
+			t.Errorf("describe(%+v, %s) = %q, want %q", c.m, c.chain, got, c.want)
+		}
+	}
+	for used, want := range map[int64]string{0: "0%", 5: "<1%", 250: "25%", 1000: "100%", 1300: "130%"} {
+		if got := percent(used, 1000); got != want {
+			t.Errorf("percent(%d, 1000) = %q, want %q", used, got, want)
+		}
 	}
 	if got := editList([]string{"a", "b", "c"}, []string{"d"}, []string{"b"}); len(got) != 3 || got[1] != "c" || got[2] != "d" {
 		t.Errorf("editList: %v", got)
 	}
 }
+
+// TestMatrixAligned: the grid's columns line up in colour too (the
+// escape codes take no room on screen).
+func TestMatrixAligned(t *testing.T) {
+	st := model.NewState()
+	st.Zones = []*model.Zone{{ID: 1, Name: "lan", Interfaces: []string{"eth1"}}, {ID: 2, Name: "wan", Interfaces: []string{"wan"}, External: true}}
+	st.Rules = []*model.Rule{{ID: 3, Chain: model.ChainForward, Position: 1, Action: model.ActionAccept, Match: model.Match{InZones: []string{"lan"}, Services: []string{"https"}}}}
+	st.Settings.InputPolicy, st.Settings.ForwardPolicy = model.PolicyDrop, model.PolicyDrop
+	var b strings.Builder
+	writeMatrix(&b, matrix.Build(st), true)
+	esc := regexp.MustCompile("\x1b\\[[0-9]+m")
+	lines := strings.Split(esc.ReplaceAllString(b.String(), ""), "\n")
+	col := strings.Index(lines[0], "wan")
+	for _, l := range lines[1:4] {
+		if r := []rune(l); len(r) <= col || r[col-1] != ' ' || r[col] == ' ' {
+			t.Errorf("misaligned at column %d:\n%s", col, strings.Join(lines[:4], "\n"))
+			break
+		}
+	}
+	if !strings.Contains(b.String(), "\x1b[33mpartly +1") || !strings.Contains(b.String(), "lan → wan\thttps") {
+		t.Errorf("no partly cell, or no list of what's open:\n%s", b.String())
+	}
+}

cmd/hc/objects.go

@@ -49,6 +49,46 @@ func counters() map[string]api.Counter {
 	return cs.Counters
 }
 
+// lookupNames asks for inside addresses' names, for tables: none with
+// --no-names, another output format, or when they can't be had.
+func lookupNames(addrs ...string) map[string]string {
+	out := map[string]string{}
+	if flagNoNames || flagOutput != "table" {
+		return out
+	}
+	seen := map[string]bool{}
+	var list []string
+	for _, a := range addrs {
+		if a != "" && !seen[a] {
+			seen[a] = true
+			list = append(list, a)
+		}
+	}
+	if len(list) == 0 {
+		return out
+	}
+	c, err := newClient()
+	if err != nil {
+		return out
+	}
+	var ns api.Names
+	if c.Do(ctx(), "POST", "/names", nil, api.NamesInput{Addresses: list}, &ns) != nil {
+		return out
+	}
+	for a, n := range ns.Names {
+		out[a] = strings.SplitN(n, ".", 2)[0]
+	}
+	return out
+}
+
+// named adds an address's name to text (the address, or address:port).
+func named(names map[string]string, addr, text string) string {
+	if n := names[addr]; n != "" {
+		return text + " (" + n + ")"
+	}
+	return text
+}
+
 func hits(c map[string]api.Counter, marks ...string) string {
 	var p uint64
 	found := false

cmd/hc/rules.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"io"
+	"net/url"
 	"regexp"
 	"strconv"
 	"strings"
@@ -63,22 +64,40 @@ func (m *matchFlags) patch(fl *pflag.FlagSet, p patch) {
 	set("family", "family", m.family)
 }
 
-// describe sums up a match: "in lan  from trusted  ssh, dns".
-func describe(m model.Match) string {
+// describe sums up a match in a chain ("" for NAT): "lan → firewall
+// from trusted  ssh,dns". Zones are a direction; the firewall itself is
+// the other end of the input and output chains.
+func describe(m model.Match, chain string) string {
 	var parts []string
-	side := func(word string, not bool, list []string) {
-		if len(list) == 0 {
-			return
-		}
+	list := func(not bool, xs []string) string {
+		s := strings.Join(xs, ",")
 		if not {
-			word += " not"
+			return "any but " + s
 		}
-		parts = append(parts, word+" "+strings.Join(list, ","))
+		return s
+	}
+	if len(m.InZones) > 0 || len(m.OutZones) > 0 {
+		in, out := "any", "any"
+		if len(m.InZones) > 0 {
+			in = list(m.NotIn, m.InZones)
+		}
+		if len(m.OutZones) > 0 {
+			out = list(m.NotOut, m.OutZones)
+		}
+		switch chain {
+		case model.ChainInput:
+			out = "firewall"
+		case model.ChainOutput:
+			in = "firewall"
+		}
+		parts = append(parts, in+" → "+out)
+	}
+	if len(m.Sources) > 0 {
+		parts = append(parts, "from "+list(m.NotSources, m.Sources))
+	}
+	if len(m.Destinations) > 0 {
+		parts = append(parts, "to "+list(m.NotDests, m.Destinations))
 	}
-	side("in", m.NotIn, m.InZones)
-	side("out", m.NotOut, m.OutZones)
-	side("from", m.NotSources, m.Sources)
-	side("to", m.NotDests, m.Destinations)
 	if len(m.Services) > 0 {
 		parts = append(parts, strings.Join(m.Services, ","))
 	}
@@ -280,7 +299,7 @@ func ruleCmd() *cobra.Command {
 			return output(rs, func(w io.Writer) {
 				fmt.Fprintln(w, "CHAIN\tID\tMATCH\tACTION\tHITS\tCOMMENT")
 				for _, r := range rs {
-					what := describe(r.Match)
+					what := describe(r.Match, r.Chain)
 					if r.Raw != "" {
 						what = "raw: " + r.Raw
 					}
@@ -303,7 +322,7 @@ func ruleCmd() *cobra.Command {
 	cmd.AddCommand(ls)
 	cmd.AddCommand(showCmd("rules", "rule", func(w io.Writer, r model.Rule) {
 		if r.Raw == "" {
-			fmt.Fprintf(w, "ID:\t%d\nChain:\t%s\nMatch:\t%s%s\nAction:\t%s\n", r.ID, r.Chain, describe(r.Match), ruleExtras(r), r.Action)
+			fmt.Fprintf(w, "ID:\t%d\nChain:\t%s\nMatch:\t%s%s\nAction:\t%s\n", r.ID, r.Chain, describe(r.Match, r.Chain), ruleExtras(r), r.Action)
 		} else {
 			fmt.Fprintf(w, "ID:\t%d\nChain:\t%s\n", r.ID, r.Chain)
 		}
@@ -340,25 +359,20 @@ output (from it) or early (before connection tracking: cheap drops).
 			if err != nil {
 				return err
 			}
-			var resp api.MutationResponse
-			if err := c.Do(ctx(), "POST", "/rules", nil, r, &resp); err != nil {
-				return err
+			// Placed in the same change: one history entry, and never in
+			// force at the end of the chain.
+			q := url.Values{}
+			switch {
+			case rf.first:
+				q.Set("first", "1")
+			case rf.before != 0:
+				q.Set("before", fmt.Sprint(rf.before))
+			case rf.after != 0:
+				q.Set("after", fmt.Sprint(rf.after))
 			}
-			// Then place it.
-			if resp.Applied && (rf.first || rf.before != 0 || rf.after != 0) {
-				var created model.Rule
-				if err := jsonUnmarshal(resp.Object, &created); err == nil {
-					mv := api.MoveInput{Before: rf.before, After: rf.after}
-					if rf.first {
-						mv.To = "start"
-					}
-					var moved api.MutationResponse
-					if err := c.Do(ctx(), "POST", objPath("rules", fmt.Sprint(created.ID))+"/move", nil, mv, &moved); err != nil {
-						return err
-					}
-					resp.Changes = append(resp.Changes, moved.Changes...)
-					resp.ConfirmBy = moved.ConfirmBy
-				}
+			var resp api.MutationResponse
+			if err := c.Do(ctx(), "POST", "/rules", q, r, &resp); err != nil {
+				return err
 			}
 			return report(&resp)
 		},
@@ -426,22 +440,57 @@ output (from it) or early (before connection tracking: cheap drops).
 	move.Flags().BoolVar(&last, "last", false, "last in its chain")
 	move.Flags().StringVar(&chain, "chain", "", "to the end of another chain")
 	cmd.AddCommand(move)
-	cmd.AddCommand(&cobra.Command{
-		Use: "reset-quota ID", Short: "Start a rule's quota again now (every address's, for a per-address quota)", Args: cobra.ExactArgs(1),
+	var resetAddr, give string
+	resetCmd := &cobra.Command{
+		Use: "reset-quota ID [--address ADDR] [--give AMOUNT]", Short: "Start a rule's quota again now, or give some back until its next reset", Args: cobra.ExactArgs(1),
+		Long: `Starts a rule's quota again now: all of it (every address's, for a
+per-address quota), or with --address one address's. --give takes an
+amount off what was used instead: extra allowance until the quota's next
+reset, without changing the rule. Done at once, not staged or on
+probation.
+
+  hc rule reset-quota 31
+  hc rule reset-quota 31 --address 192.168.1.23
+  hc rule reset-quota 31 --give 5gbytes --address 192.168.1.23`,
 		RunE: func(cmd *cobra.Command, args []string) error {
+			in := api.QuotaReset{Address: resetAddr}
+			if give != "" {
+				bad := fmt.Errorf("--give %q: write it as 500mbytes or 5gbytes", give)
+				m := amountRe.FindStringSubmatch(strings.TrimSpace(give))
+				if m == nil {
+					return bad
+				}
+				unit, ok := byteUnit(m[2])
+				n, _ := strconv.ParseInt(m[1], 10, 64)
+				if !ok || unit == "" || n < 1 {
+					return bad
+				}
+				in.Give = n * model.ByteUnits[unit]
+			}
 			c, err := newClient()
 			if err != nil {
 				return err
 			}
-			if err := c.Do(ctx(), "POST", objPath("rules", args[0])+"/reset-quota", nil, nil, nil); err != nil {
+			if err := c.Do(ctx(), "POST", objPath("rules", args[0])+"/reset-quota", nil, in, nil); err != nil {
 				return err
 			}
 			if !flagQuiet {
-				fmt.Printf("reset the quota of rule %s\n", args[0])
+				who := ""
+				if resetAddr != "" {
+					who = " for " + resetAddr
+				}
+				if in.Give > 0 {
+					fmt.Printf("gave back %s of the quota of rule %s%s, until its next reset\n", humanBytes(in.Give), args[0], who)
+				} else {
+					fmt.Printf("reset the quota of rule %s%s\n", args[0], who)
+				}
 			}
 			return nil
 		},
-	})
+	}
+	resetCmd.Flags().StringVar(&resetAddr, "address", "", "only this address's (a per-address quota; an IPv6 address counts for its /64)")
+	resetCmd.Flags().StringVar(&give, "give", "", "take this much off what was used instead (5gbytes, 500mbytes)")
+	cmd.AddCommand(resetCmd)
 	for _, on := range []bool{true, false} {
 		verb, short := "disable", "Keep a rule but don't use it"
 		if on {
@@ -669,7 +718,7 @@ func snatCmd() *cobra.Command {
 					if to == "" {
 						to = "masquerade"
 					}
-					fmt.Fprintf(w, "%d\t%s\t%s\t%s\t%s\n", x.ID, describe(x.Match), to, hits(cs, fmt.Sprintf("s%d", x.ID)), x.Comment)
+					fmt.Fprintf(w, "%d\t%s\t%s\t%s\t%s\n", x.ID, describe(x.Match, ""), to, hits(cs, fmt.Sprintf("s%d", x.ID)), x.Comment)
 				}
 			})
 		},
@@ -749,7 +798,7 @@ func redirectCmd() *cobra.Command {
 			return output(xs, func(w io.Writer) {
 				fmt.Fprintln(w, "ID\tMATCH\tTO PORT\tHITS\tCOMMENT")
 				for _, x := range xs {
-					fmt.Fprintf(w, "%d\t%s\t%s\t%s\t%s\n", x.ID, describe(x.Match), orDash(x.ToPort), hits(cs, fmt.Sprintf("d%d", x.ID)), x.Comment)
+					fmt.Fprintf(w, "%d\t%s\t%s\t%s\t%s\n", x.ID, describe(x.Match, ""), orDash(x.ToPort), hits(cs, fmt.Sprintf("d%d", x.ID)), x.Comment)
 				}
 			})
 		},

cmd/hc/stats.go

@@ -283,6 +283,7 @@ func statsTopCmd() *cobra.Command {
 				for _, l := range [][]statEntry{down, up} {
 					for _, e := range l {
 						if _, ok := out[e.Key]; !ok {
+							out[e.Key] = [2]int64{}
 							order = append(order, e.Key)
 						}
 					}
@@ -297,10 +298,11 @@ func statsTopCmd() *cobra.Command {
 					v[1] = e.Count
 					out[e.Key] = v
 				}
+				names := lookupNames(order...)
 				return output(map[string]any{"up": up, "down": down}, func(w io.Writer) {
 					fmt.Fprintln(w, "DEVICE\tRECEIVED\tSENT")
 					for _, k := range order {
-						fmt.Fprintf(w, "%s\t%s\t%s\n", k, humanBytes(out[k][0]), humanBytes(out[k][1]))
+						fmt.Fprintf(w, "%s\t%s\t%s\n", named(names, k, k), humanBytes(out[k][0]), humanBytes(out[k][1]))
 					}
 				})
 			case "blocked", "tried":
@@ -309,10 +311,14 @@ func statsTopCmd() *cobra.Command {
 				if err != nil {
 					return err
 				}
+				var names map[string]string
+				if args[0] == "blocked" {
+					names = lookupNames(keys(es)...)
+				}
 				return output(es, func(w io.Writer) {
 					fmt.Fprintln(w, map[string]string{"blocked": "SOURCE", "tried": "WHAT"}[args[0]]+"\tPACKETS")
 					for _, e := range es {
-						fmt.Fprintf(w, "%s\t%d\n", e.Key, e.Count)
+						fmt.Fprintf(w, "%s\t%d\n", named(names, e.Key, e.Key), e.Count)
 					}
 				})
 			case "quota":
@@ -323,10 +329,11 @@ func statsTopCmd() *cobra.Command {
 				if err != nil {
 					return err
 				}
+				names := lookupNames(keys(es)...)
 				return output(es, func(w io.Writer) {
 					fmt.Fprintln(w, "ADDRESS\tUSED")
 					for _, e := range es {
-						fmt.Fprintf(w, "%s\t%s\n", e.Key, humanBytes(e.Count))
+						fmt.Fprintf(w, "%s\t%s\n", named(names, e.Key, e.Key), humanBytes(e.Count))
 					}
 				})
 			}
@@ -338,6 +345,15 @@ func statsTopCmd() *cobra.Command {
 	return cmd
 }
 
+// keys are a top list's keys.
+func keys(es []statEntry) []string {
+	var out []string
+	for _, e := range es {
+		out = append(out, e.Key)
+	}
+	return out
+}
+
 func statsRulesCmd() *cobra.Command {
 	var since string
 	var unused bool

cmd/hc/traffic.go

@@ -9,6 +9,7 @@ import (
 	"strconv"
 	"strings"
 	"time"
+	"unicode/utf8"
 
 	"github.com/spf13/cobra"
 
@@ -37,10 +38,16 @@ rules as it stands.
 			if err != nil {
 				return err
 			}
+			var addrs []string
+			for _, c := range cs {
+				addrs = append(addrs, c.Source, c.Destination)
+			}
+			names := lookupNames(addrs...)
 			return output(cs, func(w io.Writer) {
 				fmt.Fprintln(w, "PROTO\tFROM\tTO\tNAT\tSTATE\tEXPIRES")
 				for _, c := range cs {
-					fmt.Fprintf(w, "%s\t%s\t%s\t%s\t%s\t%s\n", c.Protocol, hostPort(c.Source, c.SourcePort), hostPort(c.Destination, c.DestinationPort), natText(c), c.State, fmtSeconds(c.Timeout))
+					fmt.Fprintf(w, "%s\t%s\t%s\t%s\t%s\t%s\n", c.Protocol, named(names, c.Source, hostPort(c.Source, c.SourcePort)),
+						named(names, c.Destination, hostPort(c.Destination, c.DestinationPort)), natText(c), c.State, fmtSeconds(c.Timeout))
 				}
 			})
 		},
@@ -205,6 +212,13 @@ func printPacket(w io.Writer, p api.TracePacket) {
 	} else {
 		fmt.Fprintf(w, "    => %s by %s\n", strings.ToUpper(p.Verdict), decided)
 	}
+	if wd := p.WouldDrop; wd != nil {
+		name := wd.Label
+		if name == "" {
+			name = strings.TrimSpace(wd.Chain + " " + wd.Mark)
+		}
+		fmt.Fprintf(w, "    => shadow mode: Housecarl would have dropped it, by %s\n", name)
+	}
 }
 
 func matrixCmd() *cobra.Command {
@@ -242,42 +256,112 @@ such as some services or addresses). With FROM and TO (a zone, or
 }
 
 func printMatrix(w io.Writer, m api.Matrix) {
+	writeMatrix(w, m, isTerminal(os.Stdout) && flagOutput == "table")
+}
+
+// writeMatrix writes the grid, in colour on a terminal.
+func writeMatrix(w io.Writer, m api.Matrix, color bool) {
 	cols := append(append([]string{}, m.Zones...), "firewall")
 	cells := map[[2]string]api.MatrixCell{}
 	for _, c := range m.Cells {
 		cells[[2]string{c.From, c.To}] = c
 	}
-	color := isTerminal(os.Stdout) && flagOutput == "table"
-	fmt.Fprint(w, "FROM \\ TO")
-	for _, c := range cols {
-		fmt.Fprintf(w, "\t%s", c)
-	}
-	fmt.Fprintln(w)
+	// The grid is padded by hand: tabwriter would count the colours'
+	// escape codes as text, and misalign the columns.
+	grid := [][]string{append([]string{"FROM \\ TO"}, cols...)}
+	kinds := [][]string{make([]string, len(cols)+1)}
+	same := false
 	for _, from := range cols {
-		fmt.Fprint(w, from)
+		row, kind := []string{from}, []string{""}
 		for _, to := range cols {
 			c, ok := cells[[2]string{from, to}]
-			text := "-"
-			if ok {
-				text = map[string]string{"allowed": "allow", "blocked": "block"}[c.Verdict]
-				if n := len(c.Exceptions); n > 0 {
-					text += fmt.Sprintf(" +%d", n)
-				}
-				if color {
-					text = map[string]string{"allowed": "\x1b[32m", "blocked": "\x1b[31m"}[c.Verdict] + text + "\x1b[0m"
-				}
+			if !ok {
+				row, kind = append(row, "-"), append(kind, "")
+				continue
 			}
-			fmt.Fprintf(w, "\t%s", text)
+			text := map[string]string{"allowed": "allow", "blocked": "block", "partly": "partly"}[c.Summary]
+			if c.Allowed > 0 {
+				text += fmt.Sprintf(" +%d", c.Allowed)
+			}
+			if c.Blocked > 0 {
+				text += fmt.Sprintf(" -%d", c.Blocked)
+			}
+			if c.SameZone {
+				text += " *"
+				same = true
+			}
+			row, kind = append(row, text), append(kind, c.Summary)
 		}
-		fmt.Fprintln(w)
+		grid, kinds = append(grid, row), append(kinds, kind)
+	}
+	width := make([]int, len(cols)+1)
+	for _, row := range grid {
+		for i, t := range row {
+			width[i] = max(width[i], utf8.RuneCountInString(t))
+		}
+	}
+	paint := map[string]string{"allowed": "\x1b[32m", "blocked": "\x1b[31m", "partly": "\x1b[33m"}
+	for r, row := range grid {
+		var b strings.Builder
+		for i, t := range row {
+			pad := strings.Repeat(" ", width[i]-utf8.RuneCountInString(t))
+			if i == len(row)-1 {
+				pad = ""
+			} else {
+				pad += "  "
+			}
+			if p := paint[kinds[r][i]]; color && p != "" {
+				t = p + t + "\x1b[0m"
+			}
+			b.WriteString(t + pad)
+		}
+		fmt.Fprintln(w, b.String())
+	}
+	// What the partly open pairs let through.
+	var open [][2]string
+	for _, from := range cols {
+		for _, to := range cols {
+			c, ok := cells[[2]string{from, to}]
+			if !ok || len(c.Open) == 0 || c.SameZone {
+				continue
+			}
+			items := c.Open
+			more := ""
+			if len(items) > 6 {
+				items, more = items[:6], fmt.Sprintf("; %d more", len(c.Open)-6)
+			}
+			open = append(open, [2]string{from + " → " + to, strings.Join(items, "; ") + more})
+		}
+	}
+	if len(open) > 0 {
+		fmt.Fprintln(w, "\nLet through for part of the traffic:")
+		for _, o := range open {
+			fmt.Fprintf(w, "  %s\t%s\n", o[0], o[1])
+		}
+	}
+	fmt.Fprintln(w, "\nallow, block: every new connection; partly: some are let through, some not.")
+	fmt.Fprintln(w, "+N: rules that let part of the traffic through; -N: rules that block part of it. 'hc matrix FROM TO' lists them.")
+	if same {
+		fmt.Fprintln(w, "*: a zone to itself: only traffic routed between its interfaces passes the firewall.")
 	}
-	fmt.Fprintln(w, "\nallow/block: new connections no exception covers; +N: rules deciding for part of the traffic first ('hc matrix FROM TO')")
 }
 
 func printCell(w io.Writer, c api.MatrixCell) {
-	fmt.Fprintf(w, "%s → %s (the %s chain), new connections:\n", c.From, c.To, c.Chain)
-	for _, e := range c.Exceptions {
-		fmt.Fprintf(w, "  %s\t%s\t%s\n", e.Verdict, e.What, e.Label)
+	summary := map[string]string{"allowed": "all allowed", "blocked": "all blocked", "partly": "partly allowed"}[c.Summary]
+	fmt.Fprintf(w, "%s → %s (the %s chain), new connections: %s\n", c.From, c.To, c.Chain, summary)
+	if c.Note != "" {
+		fmt.Fprintf(w, "  (%s)\n", c.Note)
 	}
-	fmt.Fprintf(w, "  %s\tthe rest\t%s\n", c.Verdict, c.DecidedBy)
+	hits := func(h *uint64) string {
+		if h == nil {
+			return "-"
+		}
+		return fmt.Sprintf("%d", *h)
+	}
+	fmt.Fprintln(w, "  VERDICT\tWHAT\tBY\tHITS")
+	for _, e := range c.Exceptions {
+		fmt.Fprintf(w, "  %s\t%s\t%s\t%s\n", e.Verdict, e.What, e.Label, hits(e.Hits))
+	}
+	fmt.Fprintf(w, "  %s\tthe rest\t%s\t%s\n", c.Verdict, c.DecidedBy, hits(c.Hits))
+	fmt.Fprintln(w, "\nHits: each rule's packets since housecarld started, in all its traffic (a rule can cover several pairs).")
 }

cmd/housecarld/main.go

@@ -32,12 +32,14 @@ import (
 	"housecarl/internal/jarl"
 	"housecarl/internal/linkwatch"
 	"housecarl/internal/model"
+	"housecarl/internal/names"
 	"housecarl/internal/nflog"
 	"housecarl/internal/nft"
 	"housecarl/internal/render"
 	"housecarl/internal/server"
 	"housecarl/internal/stats"
 	"housecarl/internal/store"
+	"housecarl/internal/tablewatch"
 	"housecarl/internal/trace"
 	"housecarl/internal/validate"
 	"housecarl/internal/version"
@@ -153,8 +155,12 @@ func serveCmd() *cobra.Command {
 			}
 			host := &hostif.Host{}
 			eng.Env = hostEnv(host)
-			fw := &nft.Firewall{Runner: &nft.Runner{Command: nft.Wrapper()}, Interfaces: host.Exists, BootFile: a.cfg.Ruleset}
+			fw := &nft.Firewall{Runner: &nft.Runner{Command: nft.Wrapper()}, Interfaces: host.Exists, BootFile: a.cfg.Ruleset,
+				Shadow: a.cfg.Shadow.Enabled, ShadowBefore: a.cfg.Shadow.Position == config.ShadowBefore}
 			eng.Firewall = fw
+			if fw.Shadow {
+				a.log.Warn("shadow mode: Housecarl's ruleset is loaded but blocks, rejects and translates nothing; the other firewall decides (docs/shadow.md)", "position", a.cfg.Shadow.Position)
+			}
 			for _, p := range eng.Problems() {
 				a.log.Warn("configuration problem: "+p.Message, "object", p.Object, "code", p.Code)
 			}
@@ -171,10 +177,15 @@ func serveCmd() *cobra.Command {
 				acme = certs.New(ctx, certs.Config{ACME: a.cfg.TLS.ACME, Version: version.Short()}, jc, a.store, a.log)
 				go acme.Run(ctx)
 			}
+			var resolver *names.Resolver
+			if a.cfg.Names.Enabled {
+				resolver = names.New(a.cfg.Names.Resolver, time.Duration(a.cfg.Names.Cache))
+			}
 			srv := server.New(server.Config{
 				Listen: a.cfg.Listen, TLSCertFile: a.cfg.TLS.CertFile, TLSKeyFile: a.cfg.TLS.KeyFile, TrustedProxies: a.cfg.Proxies(),
 				SessionLifetime: time.Duration(a.cfg.Session.Lifetime), SessionIdle: time.Duration(a.cfg.Session.IdleTimeout),
 				CookieSecure: a.cfg.Session.CookieSecure, Socket: a.cfg.Socket, ACME: acme,
+				Shadow: a.cfg.Shadow.Enabled, ShadowPosition: a.cfg.Shadow.Position, Names: resolver,
 			}, eng, fw, host, a.log, web.FS())
 			// Put the ruleset in force: what was on probation when
 			// housecarld stopped is rolled back first. An empty
@@ -182,12 +193,15 @@ func serveCmd() *cobra.Command {
 			// close the machine before any rule lets anyone in.
 			// What the quotas used before housecarld (or the machine)
 			// stopped comes back with the next apply.
-			if v, err := a.store.GetMeta(ctx, server.QuotaUsageKey); err == nil && v != "" {
-				var u nft.QuotaUsage
-				if json.Unmarshal([]byte(v), &u) == nil {
-					fw.RestoreQuotas(&u)
+			restoreQuotas := func() {
+				if v, err := a.store.GetMeta(ctx, server.QuotaUsageKey); err == nil && v != "" {
+					var u nft.QuotaUsage
+					if json.Unmarshal([]byte(v), &u) == nil {
+						fw.RestoreQuotas(&u)
+					}
 				}
 			}
+			restoreQuotas()
 			if !srv.ResumeProbation(ctx) {
 				if eng.State().Empty() {
 					a.log.Info("the configuration is empty: no ruleset is applied until the first change (or 'hc import')")
@@ -215,6 +229,29 @@ func serveCmd() *cobra.Command {
 					a.log.Warn("not watching the interfaces: a flowtable device that appears later is only added by the next change", "err", err)
 				}
 			}()
+			// In shadow mode the other firewall's ruleset is reloaded now
+			// and then, and a ruleset file usually starts with flush
+			// ruleset, which deletes Housecarl's table too: put it back.
+			if fw.Shadow {
+				go func() {
+					err := tablewatch.Watch(ctx, func() {
+						if _, err := fw.Table(ctx); !errors.Is(err, nft.ErrNoTable) || eng.State().Empty() {
+							return
+						}
+						// The quotas' usage went with the table: from
+						// what was last saved.
+						restoreQuotas()
+						if err := eng.ApplyCurrent(ctx); err != nil {
+							a.log.Error("Housecarl's table was deleted, and putting it back failed", "err", err)
+							return
+						}
+						a.log.Info("Housecarl's table was deleted (flush ruleset?): put it back")
+					})
+					if err != nil {
+						a.log.Warn("not watching nftables: if Housecarl's table is deleted, only the next change or a restart puts it back", "err", err)
+					}
+				}()
+			}
 			go nflog.Listen(ctx, render.LogGroup, a.log, srv.LogPacket)
 			go srv.RunQuotas(ctx)
 			srv.SetConntrack(conntrack.Client{})

docs/api.md

@@ -31,7 +31,7 @@ user name. [permissions.md](permissions.md) has what each call needs.
 | 401 | `unauthenticated`, `session_expired`, `login_failed` | |
 | 403 | `forbidden`, `csrf` | |
 | 404 | `not_found` | |
-| 409 | `conflict` | e.g. undoing a change after the objects changed again |
+| 409 | `conflict` | e.g. undoing a change after the objects changed again; a takeover or closing connections in shadow mode ([shadow.md](shadow.md)) |
 | 422 | `validation` | the change would make the configuration invalid; `problems` lists why ([validation.md](validation.md)) |
 | 422 | `firewall` | nftables refused the ruleset (`nft -c`), or applying it failed; the message has nftables' words. Nothing was changed |
 | 429 | `rate_limited` | |
@@ -50,7 +50,7 @@ Calls that change the configuration answer:
 
 * `confirm_by`: the change is on probation, and is rolled back at that
   time unless `POST /confirm` comes first. Missing for changes made
-  through the socket.
+  through the socket, and in shadow mode ([shadow.md](shadow.md)).
 * `confirm_token`: the client that made the change can confirm it by
   itself with `POST /confirm {"token"}`, from the same address, as the
   same user and token, over a new connection (the answer closes this
@@ -74,19 +74,20 @@ Creating answers 201, other changes 200.
 
 | | |
 |---|---|
-| `GET /healthz` | `ok`, `version`, `firewall` (`applied`, `unconfigured`, `fallback`, `missing`), `probation` (changes waiting to be confirmed), `warnings` (codes); HTTP 503 unless `ok`. Without authentication; read at most every five seconds ([operations.md](operations.md#monitoring)) |
-| `GET /status` | `build`, `started`, `applied` (the ruleset is in force), `apply_error`, `problems`, `probation`, `interfaces`, `counts` (objects by kind), `other_tables` (other nftables tables, `"inet main"`) |
+| `GET /healthz` | `ok`, `version`, `firewall` (`applied`, `unconfigured`, `fallback`, `missing`), `mode` (`enforcing`, or `shadow`: the ruleset blocks nothing, [shadow.md](shadow.md)), `probation` (changes waiting to be confirmed), `warnings` (codes); HTTP 503 unless `ok`. Without authentication; read at most every five seconds ([operations.md](operations.md#monitoring)) |
+| `GET /status` | `build`, `started`, `mode` (`enforcing` or `shadow`), `shadow_position` (`after` or `before`, in shadow mode), `applied` (the ruleset is in force), `apply_error`, `problems`, `probation`, `interfaces`, `counts` (objects by kind), `other_tables` (other nftables tables, `"inet main"`) |
 | `GET /interfaces` | the machine's interfaces: `name`, `up`, `addresses`, `zone` |
-| `GET /matrix[?changeset=ID]` | the zone matrix: `zones`, `cells` (`from`, `to` (a zone, or `firewall`), `chain`, `verdict` (allowed, blocked), `decided_by`, `rule_id`, `exceptions`: `rule_id`, `chain`, `label`, `verdict` (allowed, blocked, logged, unknown), `what`) ([rules.md](rules.md#the-zone-matrix)) |
-| `GET /ruleset` | the nftables ruleset Housecarl builds, as text |
+| `GET /matrix[?changeset=ID]` | the zone matrix: `zones`, `cells` (`from`, `to` (a zone, or `firewall`), `chain`, `summary` (allowed, blocked, partly), `verdict` (what the rest gets: allowed, blocked), `decided_by`, `rule_id`, `hits`, `allowed` and `blocked` (exceptions by verdict), `open` (what the allowing exceptions let through, in short), `same_zone` and `note`, `exceptions`: `rule_id`, `chain`, `label`, `verdict` (allowed, blocked, logged, unknown), `what`, `short`, `hits`). `hits` are the rule's or policy's packets since housecarld started, all its traffic (missing: no counter) ([rules.md](rules.md#the-zone-matrix)) |
+| `GET /ruleset[?enforcing=1]` | the nftables ruleset Housecarl builds, as text. In shadow mode it is the shadow ruleset; `enforcing=1` gives the one loaded once shadow mode is off |
 | `GET /counters` | `{"since", "counters": {"r12": {"packets", "bytes"}, ...}}`, by mark ([design.md](design.md#its-own-table-only)); totals since housecarld started |
 | `GET /quotas` | each rule's quota: `rule_id`, `rule`, `quota`, `used` (bytes), `addresses` (`[{"address", "used"}]` for a per-address quota), `last_reset`, `next_reset` |
 | `GET /connections[?q=&limit=]` | tracked connections: `family`, `protocol`, `source`, `source_port`, `destination`, `destination_port` (or `icmp_id`, `icmp_type`, `icmp_code`), `dnat_to`, `dnat_port`, `snat_to`, `state`, `assured`, `timeout` (seconds left), `packets` and `bytes` when the kernel counts them. `q`: all of its words in the addresses, `:port`, protocol, state |
-| `POST /connections/close` | `{"connections": [...]}` (as listed) or `{"search": "192.168.1.50"}`: delete their tracking entries (`config:write`, audited); answers `{"closed": N}` |
+| `POST /names` | `{"addresses": [...]}` (at most 2000): `{"enabled", "names": {"192.168.1.20": "laptop.example.net"}}`, the names of the inside addresses among them, by reverse lookup ([configuration.md](configuration.md#names)). Addresses without a name, outside ones, and those still being looked up after a second are left out; ask again for those. `log:read` |
+| `POST /connections/close` | `{"connections": [...]}` (as listed) or `{"search": "192.168.1.50"}`: delete their tracking entries (`config:write`, audited); answers `{"closed": N}`. 409 in shadow mode |
 | `POST /trace` | `{"address", "port", "protocol", "seconds"}` (5-600, default 60): start tracing (`config:write`, audited); 409 while one runs |
-| `GET /trace` | the trace running, or the last: `running`, `input`, `started`, `ends`, `error`, `packets`: each with `time`, `in`, `out`, `protocol`, addresses and ports, `tcp_flags`, `icmp_type`, `steps` (`table`, `chain`, `kind` rule or policy, `rule`, `mark`, `label`, `verdict`), `verdict` (accepted, dropped) and `decided_by` |
+| `GET /trace` | the trace running, or the last: `running`, `input`, `started`, `ends`, `error`, `packets`: each with `time`, `in`, `out`, `protocol`, addresses and ports, `tcp_flags`, `icmp_type`, `steps` (`table`, `chain`, `kind` rule or policy, `rule`, `mark`, `label`, `verdict`), `verdict` (accepted, dropped) and `decided_by`; in shadow mode `would_drop`, the step where Housecarl would have dropped it |
 | `DELETE /trace` | stop it |
-| `GET /log[?limit=&after=&q=]` | logged packets, newest first: `time`, `prefix`, `in`, `out`, `family`, `protocol`, `source`, `source_port`, `destination`, `destination_port`, `icmp_type`, `tcp_flags`, `length`, `mark` (the rule's). `after` (a time) for those since; `q` searches |
+| `GET /log[?limit=&after=&q=]` | logged packets, newest first: `time`, `prefix`, `in`, `out`, `family`, `protocol`, `source`, `source_port`, `destination`, `destination_port`, `icmp_type`, `tcp_flags`, `length`, `mark` (the rule's), `verdict`, `shadow` (logged in shadow mode: a drop or reject is what would have been done). `after` (a time) for those since; `q` searches |
 | `GET /catalog` | built-in services, chains, actions, roles, the log group |
 
 ### Settings
@@ -114,11 +115,11 @@ share one pattern, `/{kind}` with kind `zones`, `sets`, `services`,
 | | |
 |---|---|
 | `GET /{kind}` | all of them, in order; `GET /rules?chain=input` for one chain; `GET /services` includes the built-in ones |
-| `POST /{kind}` | create; rules, forwards and NAT rules go last unless given a `position` |
+| `POST /{kind}[?before=ID\|after=ID\|first=1]` | create; rules, forwards and NAT rules go last unless given a `position`, or placed before or after another of their chain, or first, in the same change (one history entry; staged in a changeset, the place goes with it) |
 | `GET /{kind}/{ref}` | by ID, or name for zones, sets, services and forwards |
 | `PATCH /{kind}/{ref}` | change the fields given (a JSON merge: `null` clears) |
 | `DELETE /{kind}/{ref}` | refused while something uses it |
-| `POST /rules/{ref}/reset-quota` | start a rule's quota again now (`config:write`; audited, not staged) |
+| `POST /rules/{ref}/reset-quota` | start a rule's quota again now (`config:write`; audited, not staged). Optional body: `{"address": "192.168.1.23"}` starts only that address's again (a per-address quota; an IPv6 address counts for its /64; 404 if it hasn't used the quota); `{"give": 5368709120}` takes that many bytes off what was used instead (the address's, or every address's), until the next reset |
 | `POST /{kind}/{ref}/move` | `{"before": ID}`, `{"after": ID}` or `{"to": "start"\|"end"}`; a rule can take `"chain"` too |
 
 The objects:
@@ -211,7 +212,7 @@ history, but are audited.
 | `GET /history/{id}` | one, with each object before and after |
 | `POST /history/{id}/revert` | undo it; 409 if an object it touched has changed since, or it was undone already |
 | `POST /import/nft` | `{"json": NFT_JSON, "text": "nft -a list ruleset output", "defines": "ruleset file", "table": "inet main", "zones": {"enp2s0": "lan"}, "replace": false}` ([import.md](import.md)); answers with `state` (the imported configuration), `notes` and `raw` too |
-| `POST /takeover` | `{"tables": ["inet main"]}`: delete these tables (administrators); on probation over the network |
+| `POST /takeover` | `{"tables": ["inet main"]}`: delete these tables (administrators); on probation over the network; 409 in shadow mode |
 
 ### Certificate
 

docs/cli.md

@@ -32,6 +32,7 @@ command and its flags.
 | `-C, --changeset ID` | `HOUSECARL_CHANGESET` (checked, see [Changesets](#changesets)) | stage configuration changes in this changeset instead of making them |
 | `-o, --output FORMAT` | | `table` (default), `json`, `yaml` or `id` |
 | `-q, --quiet` | | print only errors (and the IDs of new objects) |
+| `--no-names` | | show inside addresses without their names: tables show `192.168.1.20 (laptop)` ([configuration.md](configuration.md#names)) |
 
 Exit codes: 0 ok, 1 error, 3 not authenticated or not allowed, 4 not
 found, 5 conflict, 6 invalid or refused by validation or nftables, 7
@@ -131,15 +132,15 @@ by name.
 
 | Command | |
 |---|---|
-| `status` | the ruleset (in force or not), changes on probation, problems, interfaces, other tables |
+| `status` | the mode (in shadow mode), the ruleset (in force or not), changes on probation, problems, interfaces, other tables |
 | `interfaces` | the machine's interfaces, their addresses and zones |
-| `ruleset` | the nftables ruleset Housecarl builds |
+| `ruleset [--enforcing]` | the nftables ruleset Housecarl builds; in shadow mode, `--enforcing` shows the one loaded once it is off ([shadow.md](shadow.md)) |
 | `counters` | the hits of every rule, NAT rule, built-in and policy, by mark (`r12`, `f3`, `b-established`, `p-input`) |
 | `quotas` | what each rule's quota used (each address's, for per-address quotas), and when it resets |
 | `log [-f] [--search TEXT] [--limit N]` | the packets logged by rules and policies ([operations.md](operations.md#the-log)) |
-| `connections [--search TEXT] [--limit N]`, `connections close --search TEXT [-y]` | tracked connections; closing makes the rules check them again ([operations.md](operations.md#connections)) |
+| `connections [--search TEXT] [--limit N]`, `connections close --search TEXT [-y]` | tracked connections; closing makes the rules check them again ([operations.md](operations.md#connections)); not in shadow mode |
 | `stats [--since 24h]` | traffic per zone, drops, the busiest rules, blocked sources, devices; `stats status`, `stats traffic`, `stats top devices\|blocked\|tried\|quota ID`, `stats rules [--unused]`, `stats connections` ([stats.md](stats.md#the-cli)) |
-| `matrix [FROM TO]` | what the rules do to new connections between zones; with FROM and TO, that pair's rules in order ([rules.md](rules.md#the-zone-matrix)) |
+| `matrix [FROM TO]` | what the rules do to new connections between zones (allow, block or partly), and what is let through; with FROM and TO, that pair's rules in order, with their hits ([rules.md](rules.md#the-zone-matrix)) |
 | `trace [--address A] [--port N] [--protocol P] [--seconds S]` | follow packets through every table's rules ([operations.md](operations.md#tracing)) |
 
 ### zone, set, service
@@ -171,7 +172,7 @@ See [rules.md](rules.md).
 | `rule update ID [flags]` | only the flags given |
 | `rule move ID --before ID\|--after ID\|--first\|--last\|--chain CHAIN` | |
 | `rule enable\|disable ID` | |
-| `rule reset-quota ID` | start a rule's quota again now |
+| `rule reset-quota ID [--address ADDR] [--give 5gbytes]` | start a rule's quota again now, or one address's; `--give` takes an amount off what was used instead, until the next reset |
 | `rule delete ID` | |
 
 The match flags (`rule add`, `snat add`, `redirect add`):
@@ -220,7 +221,7 @@ See [nat.md](nat.md).
 | `history show ID` | each object before and after |
 | `history undo ID` | apply the change backwards (refused if something it touched has changed since) |
 | `import [FILE\|-] [--text FILE] [--defines FILE] [--table T] [--zone IFACE=NAME]... [--replace]` | [import.md](import.md) |
-| `takeover TABLE... [-y]` | delete tables Housecarl's ruleset replaces (administrators) |
+| `takeover TABLE... [-y]` | delete tables Housecarl's ruleset replaces (administrators); not in shadow mode |
 
 ### cert
 

docs/configuration.md

@@ -30,9 +30,36 @@ reads the file when it starts.
 | `stats.database` | `/var/lib/housecarl/stats.db` | the statistics' own database; deleting it is safe |
 | `stats.retention.minute`, `.hour`, `.day` | `7d`, `90d`, `730d` | how long per-minute, hourly and daily figures are kept |
 | `stats.top_n` | `100` | entries kept per top list, per hour and per day |
+| `shadow.enabled` | `false` | shadow mode: Housecarl's ruleset is loaded beside the firewall you have, but blocks, rejects and translates nothing; its counters, log and tracer show what it would do. No change is on probation, and takeovers and closing connections are refused ([shadow.md](shadow.md)) |
+| `shadow.position` | `after` | where Housecarl's filter chains run in shadow mode: `after` the other firewall's (`filter + 10`: it sees only what that one lets through, so what it would drop is what switching would break) or `before` them (`filter - 10`: it sees every packet) |
+| `names.enabled` | `true` | show inside addresses' names beside them, found by reverse lookups (below) |
+| `names.resolver` | `""` | the DNS server to ask, such as `10.10.0.1:53`; empty: the system's (`/etc/hosts`, then `/etc/resolv.conf`) |
+| `names.cache` | `10m` | how long a name, or the lack of one, is kept |
 
 Durations are written `15s`, `12h` or `30d`.
 
+Shadow mode is here, and not a firewall setting, so that no user or API
+token can switch enforcement off; restart housecarld to switch.
+
+### Names
+
+The web UI and `hc` show a name beside each **inside** address in
+connections, the log, quotas and traffic per device: `laptop
+192.168.1.20`. Housecarl finds it with a reverse (PTR) lookup, so the
+names are your reverse zones' (and `/etc/hosts`'). An address counts as
+inside when it is in a network connected to an inside zone's interface,
+or private (`10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16`, `fc00::/7`)
+and not in an external zone's network. Outside addresses get no name:
+their reverse zones belong to whoever holds the addresses, who would
+choose the names, and looking up every scanner is slow.
+
+Names are looked up when a page or `hc` asks, cached (a failed lookup is
+tried again after a minute), and never stored: statistics stay by
+address. With a split DNS (views), the server asked must answer the
+firewall as an inside client; set `names.resolver` if the system's
+resolver doesn't. IPv6 traffic per device is counted per /64, which has
+no name. `hc --no-names` leaves them out.
+
 The probation's length is a firewall setting, not here: `hc settings set
 --probation 5m`. So is counting traffic per device for the statistics:
 `hc settings set --stats-per-device on`.

docs/design.md

@@ -100,6 +100,32 @@ Every rule carries a comment `hc:<mark>`, such as `hc:r12` for rule 12,
 `hc:f3` for port forward 3, `hc:b-established` for a built-in. Counters
 and log lines are traced back to their object through it.
 
+## Shadow mode
+
+With `shadow.enabled` in the configuration file ([shadow.md](shadow.md)),
+the same configuration is rendered so that it changes nothing (render's
+`Options.Shadow`): drops and rejects accept instead, policies accept,
+NAT only counts, and what alters packets (MSS clamping, the flowtable)
+and raw rules that do more than accept, drop or reject are left out.
+This rests on how nftables runs base chains: an `accept` only ends its
+own chain, and the packet goes on to the next one on the hook, other
+tables' included; only a drop is final. Another table, the real
+firewall, decides.
+
+What would be dropped, rejected or translated is counted under the same
+marks, and its comment says so (`"hc:r12 [would drop] …"`), which is
+how the tracer tells it apart. The filter chains run at `filter + 10`
+(after the other firewall's: what Housecarl would drop is what switching
+over would break) or `- 10`; the NAT chains always at `- 10`, since the
+kernel asks NAT chains only until one translates.
+
+Every change is checked by nftables in both forms, so leaving shadow
+mode can't fail on the ruleset. There is no probation, since nothing
+can lock anyone out; takeovers and closing connections, which would
+change traffic, are refused. A ruleset reload elsewhere (`flush
+ruleset`) deletes Housecarl's table too: housecarld listens to nftables'
+netlink notifications (internal/tablewatch) and puts it back.
+
 ## Not locking yourself out
 
 A change made over the network is applied **on probation** (a changeset

docs/development.md

@@ -11,6 +11,8 @@ internal/
   render/             State → the nftables ruleset text, with each line's object
   nft/                runs nft: check, apply (keeping dynamic set entries and counters), list, the boot file
   nflog/              reads logged packets from netlink log group 4171
+  linkwatch/          netlink: interfaces that appear or go (the flowtable's devices)
+  tablewatch/         netlink: a table deleted (shadow mode puts Housecarl's back; docs/shadow.md)
   importer/           nft -j list ruleset → State, with notes and raw rules (docs/import.md)
   hostif/             the machine's interfaces
   store/              SQLite (modernc.org/sqlite, no cgo): configuration, history, users, tokens, sessions, audit
@@ -70,8 +72,11 @@ Newer nftables accepts things 1.1.3 doesn't (a meter with a timeout for
   `wan`, `enp2s0` and `wg0` inside it, IPv4 and IPv6;
 * "the internet" on the WAN side, a LAN client, and a "jellyfin" host.
 
-It imports a copy of the maintainer's ruleset (lab addresses), takes
-over the old table, and checks with real traffic: port forwards with
+It imports a copy of the maintainer's ruleset (lab addresses) with
+housecarld in shadow mode beside it (traffic unchanged, a would-be drop
+logged and let through, the table back after the old ruleset is
+reloaded), restarts it enforcing, takes over the old table, and checks
+with real traffic: port forwards with
 hairpin NAT and the IPv6 pinhole, masquerading, antispoofing, the drop
 log, a lockout change that rolls back by itself, a restart, the boot
 ruleset after a flush, and that other tables are left alone. It makes

docs/flowtable.md

@@ -58,6 +58,12 @@ over half of the forwarding cost, which shows up as speed only when the
 CPU was the limit, and otherwise as a cooler, quieter, more responsive
 machine.
 
+In shadow mode ([shadow.md](shadow.md)) Housecarl leaves its flowtable
+out: an offloaded connection skips every table's forward chain, the
+other firewall's too. If that firewall has a flowtable of its own, the
+same goes for Housecarl's forward chain: it only sees each connection's
+first packets.
+
 ## When not to use it
 
 **When the CPU keeps up anyway.** If the speed test already reaches your

docs/import.md

@@ -159,6 +159,11 @@ Housecarl's table is now in force **alongside** the old one: a packet
 must be accepted by both. Nothing should change for your traffic. If
 Housecarl already has a configuration, `--replace` replaces it.
 
+To be sure first, import in **shadow mode** ([shadow.md](shadow.md)):
+Housecarl's ruleset is then loaded but drops nothing, and its log shows
+each packet the old ruleset lets through that Housecarl would drop. When
+there are none you mind, leave shadow mode and take over.
+
 Imported over the network (not through the local socket), the import is
 on probation like any change: confirm it.
 

docs/install.md

@@ -85,6 +85,10 @@ you are changing the firewall you are connected through.
    sudo systemctl disable nftables.service
    ```
 
+   To try Housecarl beside your firewall first, turn on **shadow mode**
+   before the import: it loads Housecarl's ruleset but blocks nothing,
+   and shows what it would do ([shadow.md](shadow.md)).
+
    **Or start from scratch**, through the local socket (no probation).
    The first change puts the ruleset in force, and the input and forward
    policies drop what no rule accepts, so let yourself in first:

docs/nat.md

@@ -7,6 +7,10 @@ public port are sent to the host, and let through the forward chain.
 One object does what takes three rules by hand (the DNAT, the forward
 accept, and the hairpin masquerade).
 
+In shadow mode ([shadow.md](shadow.md)) NAT rules translate nothing:
+they count the connections they would translate, and the other
+firewall's NAT does the work.
+
 ```sh
 hc forward add 8443 --to 192.168.1.10:443 --public 203.0.113.10 --hairpin --name web
 hc forward add 27015-27030 --proto tcp,udp --to 192.168.1.20 --public 203.0.113.10 --hairpin --name game

docs/operations.md

@@ -28,7 +28,8 @@ edits) applies each edit at once instead. With hc, see
 ## Changes on probation
 
 Changes made over the network roll back unless confirmed
-([design.md](design.md#not-locking-yourself-out)). The web UI and `hc`
+([design.md](design.md#not-locking-yourself-out)); in shadow mode, where
+a change can't cut anyone off, none do ([shadow.md](shadow.md)). The web UI and `hc`
 confirm their own changes once they reach Housecarl again over a new
 connection, so normally nothing waits:
 
@@ -79,6 +80,9 @@ sudo cat /var/lib/housecarl/ruleset.nft
 sudo nft -c -f /var/lib/housecarl/ruleset.nft     # check it
 ```
 
+In shadow mode both files are shadow mode's, and the fallback filters
+nothing ([shadow.md](shadow.md#what-works-differently)).
+
 Dynamic sets start empty after a reboot. The saved ruleset has no
 flowtable, since its devices may not exist yet: housecarld adds it when
 it starts, and whenever a flowtable device appears
@@ -150,12 +154,15 @@ table on its hook, so a drop in any of them wins.
 Every rule, NAT rule, built-in and policy has a counter. `hc rule list`,
 `hc forward list` and the web UI show packets; `hc counters` shows them
 all, with bytes. They count from housecarld's start, and carry across
-changes to the ruleset.
+changes to the ruleset. A deleted object's counter goes with it; an
+import with `--replace` gives every object a new ID, so its counters
+start again. A disabled rule keeps its count for when it is enabled.
 
 ## Quotas
 
 `hc quotas` (and the rules page) show what each quota used and when it
-resets; `hc rule reset-quota ID` starts one again. housecarld resets
+resets; `hc rule reset-quota ID` starts one again (`--address` one device's,
+`--give 5gbytes` a top-up until the next reset). housecarld resets
 quotas at midnight when their period ends (late, if it was stopped then),
 and saves their usage every five minutes and when it stops; after a
 reboot it puts it back. A reboot without a clean stop loses at most the
@@ -177,6 +184,10 @@ hc log --search 198.51.100.7
 10:02:15  hc forward policy drop: wan  eth1  198.51.100.9:443 -> 192.168.1.20:51432  tcp
 ```
 
+In shadow mode ([shadow.md](shadow.md)) what the policies would drop is
+always logged, in all three chains, and drops are marked as what would
+have been done: the packets went on.
+
 The packets go to netlink log group 4171, where housecarld reads them;
 the last 2000 are kept in memory. They aren't written to the kernel log
 or the journal. A rule's log isn't rate-limited: on a busy rule, give it
@@ -281,13 +292,14 @@ it is asked):
 
 ```sh
 $ curl -s https://firewall.example.net:8070/healthz
-{"ok":true,"version":"0.1.0","firewall":"applied","probation":0,"warnings":[]}
+{"ok":true,"version":"0.1.0","firewall":"applied","mode":"enforcing","probation":0,"warnings":[]}
 ```
 
 | Field | |
 |---|---|
 | `ok` | `true` with HTTP 200 when the firewall is as it should be; `false` with HTTP **503** otherwise |
 | `firewall` | `applied` (Housecarl's ruleset is in force), `unconfigured` (nothing configured yet, so nothing to apply), `fallback` (the [boot fallback](#if-the-ruleset-fails-to-load-at-boot) is in force), `missing` (no Housecarl table: flushed, or never applied) |
+| `mode` | `enforcing`, or `shadow`: Housecarl's ruleset is loaded but blocks nothing, and another firewall decides ([shadow.md](shadow.md)). `ok` doesn't depend on it; to be told when a machine isn't enforcing, also expect `"mode":"enforcing"` |
 | `probation` | changes waiting to be confirmed, rolled back unless they are |
 | `warnings` | codes of problems with the machine, as `hc status` shows them (`nftables_service`) |
 

docs/rules.md

@@ -186,8 +186,22 @@ hc rule add forward --in lan --out wan --quota 50gbytes,over,per-source,monthly=
 hc rule add forward --in guest --out wan --quota 10gbytes,over,daily -a drop
 hc quotas                      # what each used, and the next reset
 hc rule reset-quota 31         # start again now
+hc rule reset-quota 31 --address 192.168.1.23            # one device only
+hc rule reset-quota 31 --give 5gbytes --address 192.168.1.23
 ```
 
+`--give` is a top-up: it takes that much off what was used (never below
+zero), so the device gets 5 GB more until the quota's next reset, and the
+rule stays as it is. In the web UI, the quota's line under the rule
+opens its dialog: usage (each address's), resets, and **Reset** and
+**Give back…** for everyone or one address. Like a reset, these are
+done at once (audited, not staged or on probation); Housecarl puts the
+ruleset in force again with the new figure.
+
+In the web UI each quota's use is on its rule (with **Reset**), all of
+them together on the dashboard, and their history under **Traffic →
+Statistics**.
+
 | | |
 |---|---|
 | `per-source`, `per-destination` | each address its own allowance; without, one allowance for everything the rule matches |
@@ -201,6 +215,20 @@ A per-address quota counts an address: a device that gets a new one
 starts again. With Steward's reservations IPv4 addresses stay; IPv6 is
 grouped by /64 (below).
 
+Changing the amount, `over` or the resets keeps what was used. Changing
+how the quota counts carries what can be carried:
+
+| Change | What was used |
+|---|---|
+| per address to one total | the addresses' sum |
+| to wider groups (IPv6 /64 to /56) | added up per new group |
+| a total to per address | starts again: a total can't be split |
+| per source to per destination (or back) | starts again |
+| to finer groups (/64 to /128) | starts again: a group can't be split |
+
+A change that starts a quota again says so (warning `quota_restarts`),
+when it is staged for review and in `hc` (also with `-n`).
+
 **Rules with a quota or a byte rate count every packet.** The built-in
 that accepts established connections comes before your rules, so a rule
 there only sees each connection's first packet. Rules that count traffic
@@ -235,6 +263,11 @@ nftables names (`@trusted_v4`). The importer makes raw rules from
 what it can't translate. It goes into the ruleset as written: add
 `counter` to it to count its packets.
 
+In shadow mode ([shadow.md](shadow.md)) a raw rule's final `drop` or
+`reject` becomes `accept`; a raw rule that does anything else to packets
+(NAT, `meta mark set`, `jump`, `notrack`, a verdict map…) is left out,
+with a warning (`shadow_raw_left_out`).
+
 ## Built-ins
 
 Housecarl adds the rules every firewall needs before yours. Each can be
@@ -273,31 +306,67 @@ chain; from it: output; zone to zone: forward).
 
 ```
 $ hc matrix
-FROM \ TO  guest     lan       wan       firewall
-guest      block     block     block +1  block +3
-lan        block     block     allow     block +4
-wan        block +2  block +2  block +1  block +3
-firewall   allow     allow     allow     -
+FROM \ TO  guest         lan           wan         firewall
+guest      block *       block         partly +1   partly +4
+lan        block         block *       allow       partly +4
+wan        partly +1 -1  partly +1 -1  block -1 *  partly +3 -1
+firewall   allow         allow         allow       -
+
+Let through for part of the traffic:
+  guest → wan       http, https
+  guest → firewall  ICMPv6; ping; ssh from admins; dns
+  lan → firewall    ICMPv6; ping; ssh from admins; dns
+  wan → guest       1 port forward
+  wan → lan         1 port forward
+  wan → firewall    ICMPv6; DHCPv6; ssh from admins
+
+allow, block: every new connection; partly: some are let through, some not.
++N: rules that let part of the traffic through; -N: rules that block part of it. 'hc matrix FROM TO' lists them.
+*: a zone to itself: only traffic routed between its interfaces passes the firewall.
 ```
 
 Each cell walks that pair's rules in order, as nftables would, with the
 built-ins that act on new connections (ping from internal zones,
 ICMPv6, the DHCPv6 client, antispoofing, port forwards):
 
-* a rule that applies to the whole pair decides it ("allow", "block");
+* a rule that applies to the whole pair decides it;
 * a rule that applies to part of its traffic (some addresses, services,
-  times, rates, a quota) is an **exception** (+N), and the walk goes on;
+  times, rates, a quota) is an **exception**, and the walk goes on;
 * what's left falls to the deciding rule or the chain's policy.
 
+A cell reads **allow** or **block** when every new connection gets the
+same, and **partly** when exceptions let some through while the rest is
+blocked (or block some while the rest is allowed). **+N** counts the
+exceptions that let traffic through, **-N** those that block it. Under
+the grid (in the web UI, in each cell) is what the exceptions let
+through: their services, with the addresses they are limited to.
+
+A zone to itself (`*`, faded in the web UI) is mostly traffic that never
+reaches the firewall: within one interface's network it goes straight
+from host to host. Only what is routed between the zone's interfaces (or
+back out of the one it came in on) passes.
+
 `hc matrix guest wan` (or clicking the cell) lists the exceptions in
-order:
+order, with each rule's hits:
 
 ```
-guest → wan (the forward chain), new connections:
-  allowed  http, https   rule forward #14
-  blocked  the rest      forward policy
+guest → wan (the forward chain), new connections: partly allowed
+  VERDICT  WHAT         BY                HITS
+  allowed  http, https  rule forward #14  1520
+  blocked  the rest     forward policy    37
 ```
 
+The hits are the rule's packets since housecarld started, in all of its
+traffic: a rule without zones counts for every pair it covers. They are
+how you tell an exception that is used from one that isn't.
+
+A raw rule is read when it is a match followed by `accept`, `drop` or
+`reject` (with `counter` and `log` if you like): it counts as an exception
+for every pair of its chain, shown as `raw: …`. One that matches
+interfaces (the matrix can't tell which zones), jumps, translates, sets
+something or uses a verdict map shows as **unknown**: check it yourself.
+Raw rules have hits only if they say `counter`.
+
 A rule whose addresses all lie in networks directly connected to other
 zones is left out of a pair: traffic between those zones can't have them
 (`from wg_net` doesn't concern traffic coming in on the LAN). Routed

docs/shadow.md

@@ -0,0 +1,171 @@
+# Shadow mode
+
+In shadow mode Housecarl runs beside the firewall you have now and
+changes nothing. Its ruleset is loaded, so its counters, log, tracer and
+statistics show what it *would* do with your real traffic, but it blocks,
+rejects and translates nothing. Your current firewall keeps deciding.
+
+Use it to:
+
+* **try Housecarl** on the real machine before you trust it with the
+  firewall: the web UI, the API, `hc`, changesets, history;
+* **check an import**: import your ruleset ([import.md](import.md)) and
+  watch whether Housecarl would drop anything your firewall lets through;
+* **develop against the API**: Steward, scripts or fail2ban can fill
+  dynamic sets and see them used, with nothing at stake.
+
+## Turning it on
+
+Shadow mode is set in `/etc/housecarl/housecarl.yaml`
+([configuration.md](configuration.md)), not through the API, so no user
+or token can switch enforcement off:
+
+```yaml
+shadow:
+  enabled: true
+  position: after     # or before; see below
+```
+
+housecarld reads the file when it starts:
+
+```sh
+sudo systemctl restart housecarl
+sudo hc status        # Mode: SHADOW …
+```
+
+The web UI shows a banner on every page, `hc status` a `Mode:` line, and
+`/healthz` `"mode": "shadow"`.
+
+## Why it can't let anything through
+
+In nftables, `accept` only ends the chain it is in. The packet then
+goes on to the next base chain on the same hook, and other tables' chains
+are among those. Only a drop is final. Housecarl's table in shadow mode
+never drops, so it can't let through anything your firewall drops, and it
+can't block anything your firewall accepts.
+
+## What changes in the ruleset
+
+The same configuration is rendered, with everything that acts on packets
+turned into counting:
+
+| | Enforcing | Shadow mode |
+|---|---|---|
+| Rules that drop or reject | `drop`, `reject` | counted, then `accept` (Housecarl's chain ends as it would have). Their comment says `[would drop]` or `[would reject]` |
+| The built-ins that drop (invalid packets, antispoofing) | `drop` | counted, `[would drop]` |
+| Policies | as configured | `accept`. What a drop policy would drop is counted and **always logged**, rate-limited, in all three chains |
+| Port forwards, source NAT, redirects | translate | counted only (`[would dnat]`, `[would masquerade]`, `[would snat]`, `[would redirect]`) |
+| MSS clamping | changes SYN packets | left out |
+| The flowtable | offloads connections | left out: offloaded connections skip *every* table's forward chain, your firewall's too |
+| Raw rules | as written | as written if they only match, count, log or accept. A final `drop` or `reject` becomes `accept`. Anything else that acts on packets (NAT, `set`, `jump`, `notrack`, a verdict map…) is left out, with a warning (`shadow_raw_left_out`) |
+| Everything else | | the same: accepts, rate limits, connection limits, quotas, dynamic sets, per-device counters, logging |
+
+`hc ruleset` prints the shadow ruleset, the one loaded now.
+`hc ruleset --enforcing` prints the ruleset that will be loaded once
+shadow mode is off.
+
+**Every change is checked by nftables twice**: the shadow ruleset, and the
+enforcing one. A change that nftables would refuse once shadow mode is off
+is refused now, so leaving shadow mode can't fail on that.
+
+## Where Housecarl's chains run
+
+Your firewall's chains are usually at priority `filter` (0), its raw
+chains at `raw`. `shadow.position` puts Housecarl's filter chains just
+next to them:
+
+* **`after`** (the default) runs them at `filter + 10` (and `raw + 10`).
+  Housecarl only sees what your firewall let through. So **every would-drop
+  is traffic that would break if you switched over**: the list to work
+  through before you do. What your firewall drops and Housecarl would
+  accept (a hole) doesn't show; compare the rules for that.
+* **`before`** runs them at `filter - 10` (and `raw - 10`). Housecarl sees
+  every packet, as it would when enforcing, and its hits and drops are the
+  numbers you would get. Its would-drops include everything your firewall
+  drops too (the internet's background noise).
+
+If your firewall uses other priorities, say `filter + 20`, "after" is
+relative to `filter`, not to it: check with `nft list ruleset`.
+
+NAT chains are different: the kernel asks NAT chains in turn only until
+one translates. Housecarl's NAT chains always run first (`dstnat - 10`,
+`srcnat - 10`), whatever the position, or they would never see a
+connection your firewall translates. They translate nothing, so your
+firewall's NAT still does the work.
+
+## What you see
+
+* **Hits** (`hc counters`, the Rules page): a drop rule's hits are what it
+  would have dropped. NAT counters count connections (only a connection's
+  first packet reaches the NAT chains).
+* **The log** (`hc log`, the Log page): every packet a drop policy would
+  have dropped, and what rules with logging would have dropped, marked
+  *would drop*. `hc log` adds "(shadow mode: would drop, let through)".
+* **The tracer** (`hc trace`, the Trace page): the verdict is your
+  firewall's, the real one. When Housecarl would have dropped the packet,
+  the trace says by which rule ("shadow mode: Housecarl would have
+  dropped it, by …").
+* **Statistics** ([stats.md](stats.md)): drops, drops per chain and the
+  blocked sources are what Housecarl would have dropped.
+
+## What works differently
+
+* **No probation.** A change can't cut anyone off, so changes from the
+  network are applied and saved at once, with no confirmation. Changesets
+  work as usual; their ruleset diff is of the shadow ruleset.
+* **No takeover, no closing connections.** `hc takeover` (deleting your
+  firewall's tables) and `hc connections close` are refused (409,
+  `hc` exits with 5): both would change your traffic.
+* **The boot.** `housecarl-ruleset.service` loads the shadow ruleset at
+  boot. Its fallback ([operations.md](operations.md#if-the-ruleset-fails-to-load-at-boot))
+  is an empty table that filters nothing, since your firewall protects the
+  machine.
+* **Your firewall reloading.** A ruleset file such as `/etc/nftables.conf`
+  usually starts with `flush ruleset`, and Debian's `nftables.service`
+  runs `nft flush ruleset` when it stops or restarts. Both delete
+  Housecarl's table too. housecarld watches nftables' notifications and
+  puts its table back within a few seconds (the journal says "Housecarl's
+  table was deleted … put it back"). Dynamic sets lose their entries, and
+  quotas go back to what was last saved (every five minutes).
+* **Warnings.** `nftables_service` and `takeover_pending` aren't raised:
+  another firewall beside Housecarl is the point. Instead:
+  `shadow_unprotected` when no other table has a filter chain on the input
+  hook (nothing protects the machine), and `shadow_raw_left_out` for each
+  raw rule left out ([validation.md](validation.md#the-machine)).
+* **Quotas count** what passes in shadow mode, and keep counting when
+  you switch over.
+
+## A trial, step by step
+
+From a machine whose firewall is `/etc/nftables.conf` with `table inet main`:
+
+1. Install Housecarl and create the administrator
+   ([install.md](install.md)).
+2. Turn shadow mode on in `/etc/housecarl/housecarl.yaml`, and start
+   housecarld: `sudo systemctl enable --now housecarl`.
+3. Import your ruleset: `sudo hc import --defines /etc/nftables.conf`
+   ([import.md](import.md)). Leave `nftables.service` as it is.
+4. Use your network for a while, and watch `hc log -f`, `hc counters` and
+   the dashboard. With `position: after`, each would-drop is something
+   your firewall allows and Housecarl wouldn't: fix the rule in Housecarl,
+   or decide it doesn't matter. `hc status` lists the raw rules left out.
+5. When nothing you need would be dropped, leave shadow mode.
+
+## Leaving shadow mode
+
+1. Look at what will be loaded: `sudo hc ruleset --enforcing`.
+2. Set `shadow.enabled: false` (or remove the section), and
+   `sudo systemctl restart housecarl`. Housecarl's ruleset is now in
+   force **alongside** your firewall: a packet must be accepted by both.
+   The restart applies it at once, not on probation, but your old firewall
+   is still there and still decides too.
+3. Take over: `sudo hc takeover "inet main"` deletes the old table (on
+   probation over the network), and `sudo systemctl disable nftables`
+   (without `--now`) retires it ([import.md](import.md#3-take-over)).
+
+## Going back
+
+Set `shadow.enabled: true` and restart housecarld. If Housecarl was your
+only firewall, **the machine is now unprotected**: load your other
+firewall first. Until one filters the input hook, `hc status` and
+`/healthz` warn (`shadow_unprotected`).

docs/stats.md

@@ -100,6 +100,10 @@ The blocked lists only see what is **logged**: the input and forward
 policies' drops with `hc settings set --log-drops on`, and rules with
 logging. The drop counts above see everything.
 
+In shadow mode ([shadow.md](shadow.md)) the drops, and the blocked
+lists, are what Housecarl would have dropped: the packets went on. What
+the policies would drop is always logged there.
+
 A counter that goes down (an interface that came back, a quota reset)
 counts again from zero. What happens while housecarld is stopped isn't
 counted.

docs/validation.md

@@ -97,6 +97,7 @@ These apply to rules, source NAT and redirects.
 | `rule_group` | error | a grouping prefix outside 1-32 (IPv4) or 1-128 (IPv6) |
 | `rule_traffic_accept` | error | a rule with a quota or a byte rate that accepts: it is checked before established connections are accepted, so it can only drop, reject or log |
 | `rule_every_packet_accept` | error | a rule checked against every packet (`every_packet`) that accepts: it comes before established connections are accepted, so it can only drop, reject or log |
+| `quota_restarts` | warning | a change makes a rule count its quota so that what it used can't carry over (a total to per address, per source to per destination, finer groups): it starts again. Only on the change that does it |
 | `flowtable_traffic` | warning | a forward rule checked against every packet (a quota, a byte rate, `every_packet`) while the flowtable is on: it only sees each connection's first packets |
 | `reject_with` | error | `tcp-reset` on a rule that matches more than TCP, or with an action other than reject |
 | `log_prefix` | error | a log prefix over 100 characters |
@@ -132,3 +133,8 @@ configuration: the dashboard and `hc status` show them.
 | `nftables_service` | warning, *host* | Debian's `nftables.service` is enabled: at boot it loads `/etc/nftables.conf`, and stopping or restarting it runs `nft flush ruleset`, deleting Housecarl's table too. Disable it with `systemctl disable nftables` (without `--now`) |
 | `conntrack_full` | warning, *host* | the connection tracking table is over 80% full; once it is full, the kernel drops new connections. Raise `net.netfilter.nf_conntrack_max`, or find what opens so many ([stats.md](stats.md#warnings)) |
 | `takeover_pending` | warning, *host* | the table you imported from is still in force beside Housecarl's, so a packet must get past both; `hc takeover TABLE` deletes it once Housecarl's rules are right |
+| `shadow_unprotected` | warning, *host* | shadow mode, and no other table has a filter chain on the input hook: Housecarl's ruleset blocks nothing, and nothing else protects the machine. Load your firewall, or leave shadow mode ([shadow.md](shadow.md)) |
+| `shadow_raw_left_out` | warning, *host* | shadow mode leaves this raw rule out: it does more to packets than accept, drop or reject (NAT, setting a mark or field, a jump, a verdict map…). Its hits aren't counted, and the rules after it see what it would have taken ([shadow.md](shadow.md#what-changes-in-the-ruleset)) |
+
+In shadow mode `nftables_service` and `takeover_pending` aren't raised:
+another firewall beside Housecarl is the point there.

internal/api/types.go

@@ -40,8 +40,18 @@ type Whoami struct {
 	TokenID   int64         `json:"token_id,omitempty"`
 	CSRFToken string        `json:"csrf_token,omitempty"`
 	Build     version.Build `json:"build"`
+	// Mode is enforcing, or shadow (docs/shadow.md).
+	Mode string `json:"mode"`
 }
 
+// Modes: housecarld's ruleset decides, or (shadow mode, the
+// configuration file's shadow.enabled) it only shows what it would do,
+// beside another firewall.
+const (
+	ModeEnforcing = "enforcing"
+	ModeShadow    = "shadow"
+)
+
 // Login is the login request.
 type Login struct {
 	Username string `json:"username"`
@@ -155,15 +165,23 @@ type LogEntry struct {
 	TCPFlags string    `json:"tcp_flags,omitempty"`
 	RuleMark string    `json:"mark,omitempty"`
 	Verdict  string    `json:"verdict,omitempty"`
+	// Shadow: logged in shadow mode, where a drop or reject is what would
+	// have been done; the packet went on.
+	Shadow bool `json:"shadow,omitempty"`
 }
 
 // Status is the dashboard's overview.
 type Status struct {
-	Build      version.Build `json:"build"`
-	Started    time.Time     `json:"started"`
-	Database   string        `json:"database,omitempty"`
-	Applied    bool          `json:"applied"`
-	ApplyError string        `json:"apply_error,omitempty"`
+	Build    version.Build `json:"build"`
+	Started  time.Time     `json:"started"`
+	Database string        `json:"database,omitempty"`
+	// Mode is enforcing or shadow; ShadowPosition (shadow mode) after or
+	// before: where Housecarl's filter chains run beside the other
+	// firewall's.
+	Mode           string `json:"mode"`
+	ShadowPosition string `json:"shadow_position,omitempty"`
+	Applied        bool   `json:"applied"`
+	ApplyError     string `json:"apply_error,omitempty"`
 	// Unconfigured: the configuration is empty, and no ruleset was
 	// applied yet.
 	Unconfigured bool               `json:"unconfigured,omitempty"`
@@ -308,6 +326,16 @@ type CertificateResponse struct {
 	Status *CertStatus `json:"status,omitempty"`
 }
 
+// QuotaReset is POST /rules/{ref}/reset-quota's optional body. Without
+// one the whole quota starts again. Address starts one address of a
+// per-address quota again (any address in its group: 10.0.10.23, or an
+// IPv6 address for its /64); Give takes that many bytes off what was used
+// instead (the address's, or every address's), until the next reset.
+type QuotaReset struct {
+	Address string `json:"address,omitempty"`
+	Give    int64  `json:"give,omitempty"`
+}
+
 // QuotaInfo is a rule's quota and what it used.
 type QuotaInfo struct {
 	RuleID int64       `json:"rule_id"`
@@ -366,6 +394,19 @@ type Connection struct {
 	Bytes   uint64 `json:"bytes,omitempty"`
 }
 
+// NamesInput asks for the names of addresses (POST /names).
+type NamesInput struct {
+	Addresses []string `json:"addresses"`
+}
+
+// Names are the names found for the inside addresses asked about, by
+// address; those without one (or still being looked up) are left out.
+// Enabled is false when names are off (names.enabled).
+type Names struct {
+	Enabled bool              `json:"enabled"`
+	Names   map[string]string `json:"names"`
+}
+
 // CloseConnections closes connections: these, or every one Search finds
 // (as GET /connections?q= does).
 type CloseConnections struct {
@@ -414,6 +455,9 @@ type TracePacket struct {
 	// Verdict is accepted or dropped; DecidedBy the step that decided.
 	Verdict   string    `json:"verdict"`
 	DecidedBy TraceStep `json:"decided_by"`
+	// WouldDrop, in shadow mode, is the step of Housecarl's where it
+	// would have dropped (or rejected) the packet, had it been enforcing.
+	WouldDrop *TraceStep `json:"would_drop,omitempty"`
 }
 
 // TraceStatus is the trace running (or the last one).
@@ -446,6 +490,26 @@ type MatrixCell struct {
 	DecidedBy  string            `json:"decided_by"`
 	RuleID     int64             `json:"rule_id,omitempty"` // the deciding rule
 	Exceptions []MatrixException `json:"exceptions"`
+	// Summary is the pair at a glance: allowed or blocked when every new
+	// connection gets the same, partly when some are let through and
+	// some not.
+	Summary string `json:"summary"`
+	// Allowed and Blocked count the exceptions that let part of the
+	// traffic through, and that block part of it.
+	Allowed int `json:"allowed"`
+	Blocked int `json:"blocked"`
+	// Open sums up what the allowing exceptions let through, shortest
+	// first in their order: "ssh", "dns", "5 port forwards".
+	Open []string `json:"open"`
+	// SameZone: from a zone to itself. Note says what of that traffic
+	// passes the firewall at all.
+	SameZone bool   `json:"same_zone,omitempty"`
+	Note     string `json:"note,omitempty"`
+	// Hits are the deciding rule's (or policy's) packets, all of its
+	// traffic since housecarld started (nil: no counter).
+	Hits *uint64 `json:"hits,omitempty"`
+	// Marks are the counters behind Hits.
+	Marks []string `json:"-"`
 }
 
 // MatrixException is a rule (or built-in) that decides for part of a
@@ -459,4 +523,12 @@ type MatrixException struct {
 	Verdict string `json:"verdict"`
 	// What it covers: "from trusted · ssh", "Monday 08:00–17:00".
 	What string `json:"what"`
+	// Short is What in a word or two, for the overview: its services,
+	// or else its first condition.
+	Short string `json:"short"`
+	// Hits are its packets, all of its traffic since housecarld started
+	// (a rule may apply to several pairs; nil: no counter).
+	Hits *uint64 `json:"hits,omitempty"`
+	// Marks are the counters behind Hits ("r12", "b-ping", "f3").
+	Marks []string `json:"-"`
 }

internal/config/config.go

@@ -41,8 +41,40 @@ type Config struct {
 	Ruleset string `yaml:"ruleset"`
 	// Stats keeps traffic, hits and drops over time (docs/stats.md).
 	Stats Stats `yaml:"stats"`
+	// Shadow loads the ruleset without letting it block, reject or
+	// translate anything, beside the firewall in force (docs/shadow.md).
+	Shadow Shadow `yaml:"shadow"`
+	// Names shows inside addresses' names, by reverse lookups
+	// (docs/configuration.md).
+	Names Names `yaml:"names"`
 }
 
+// Names configures the reverse lookups that put names beside inside
+// addresses in the web UI and hc.
+type Names struct {
+	Enabled bool `yaml:"enabled"`
+	// Resolver is a DNS server ("10.10.0.1:53"; "": the system's).
+	Resolver string `yaml:"resolver"`
+	// Cache is how long a name is kept.
+	Cache Duration `yaml:"cache"`
+}
+
+// Shadow is shadow mode: Housecarl's ruleset is loaded and counts, logs
+// and traces what it would do, while another firewall decides.
+type Shadow struct {
+	Enabled bool `yaml:"enabled"`
+	// Position is where Housecarl's filter chains run: after the other
+	// firewall's (it sees what that one lets through, so what it would
+	// drop is what switching would break) or before (it sees everything).
+	Position string `yaml:"position"`
+}
+
+// Shadow positions.
+const (
+	ShadowAfter  = "after"
+	ShadowBefore = "before"
+)
+
 // Stats configures statistics: a database of their own, aggregates
 // only, pruned by age.
 type Stats struct {
@@ -204,7 +236,9 @@ func Default() *Config {
 		Backup:         Backup{Dir: "/var/backups/housecarl", Retention: Duration(30 * 24 * time.Hour), KeepAtLeast: 7},
 		Stats: Stats{Enabled: true, Database: "/var/lib/housecarl/stats.db", TopN: 100,
 			Retention: StatsRetention{Minute: Duration(7 * 24 * time.Hour), Hour: Duration(90 * 24 * time.Hour), Day: Duration(730 * 24 * time.Hour)}},
-		TLS: TLS{ACME: ACME{Directory: "letsencrypt-staging", Resolvers: []string{"1.1.1.1:53", "9.9.9.9:53", "8.8.8.8:53"}, CheckPropagation: true}},
+		Shadow: Shadow{Position: ShadowAfter},
+		Names:  Names{Enabled: true, Cache: Duration(10 * time.Minute)},
+		TLS:    TLS{ACME: ACME{Directory: "letsencrypt-staging", Resolvers: []string{"1.1.1.1:53", "9.9.9.9:53", "8.8.8.8:53"}, CheckPropagation: true}},
 	}
 }
 
@@ -275,6 +309,17 @@ func (c *Config) check() error {
 	default:
 		return fmt.Errorf("log.level must be debug, info, warn or error")
 	}
+	if c.Shadow.Position != ShadowAfter && c.Shadow.Position != ShadowBefore {
+		return fmt.Errorf("shadow.position must be after or before")
+	}
+	if c.Names.Resolver != "" {
+		if _, err := netip.ParseAddrPort(c.Names.Resolver); err != nil {
+			return fmt.Errorf("names.resolver must be an address and port, such as 10.10.0.1:53")
+		}
+	}
+	if c.Names.Cache <= 0 {
+		return fmt.Errorf("names.cache must be a duration, such as 10m")
+	}
 	return nil
 }
 
@@ -427,4 +472,16 @@ stats:
     hour: 90d      # hourly figures and top lists
     day: 730d      # daily figures and top lists
   top_n: 100       # entries kept per top list, per hour and day
+
+# Shadow mode (docs/shadow.md): Housecarl's ruleset is loaded beside the
+# firewall you have now, but blocks, rejects and translates nothing. Its
+# counters, log and tracer show what it would do. No change is on
+# probation, and takeovers and closing connections are refused. housecarld
+# reads this when it starts: restart it to switch.
+shadow:
+  enabled: false
+  # after: Housecarl's filter chains run after the other firewall's, and
+  # see only what it lets through: what Housecarl would drop is what
+  # switching over would break. before: they see every packet.
+  position: after
 `

internal/config/config_test.go

@@ -35,6 +35,7 @@ func TestErrors(t *testing.T) {
 		"{tls: {acme: {domain: '*.example.com'}}, jarl: {server: https://j, token: x}}":                            "full name",
 		"{tls: {acme: {domain: d.example.com, directory: http://x}}, jarl: {server: https://j, token: x}}":         "https://",
 		"ruleset: relative.nft": "ruleset",
+		"shadow: {position: x}": "shadow.position",
 	}
 	for yml, want := range cases {
 		path := filepath.Join(t.TempDir(), "s.yaml")

internal/engine/engine.go

@@ -191,6 +191,7 @@ func (e *Engine) commit(ctx context.Context, p *auth.Principal, description stri
 	// Only report warnings the change brings; old ones are on the status
 	// page.
 	res.Warnings = newProblems(validate.Check(e.state, e.env()), problems)
+	res.Warnings = append(res.Warnings, quotaRestarts(e.state, next)...)
 	if e.Firewall != nil {
 		if err := e.Firewall.Check(ctx, next); err != nil {
 			return res, &Error{Kind: KindFirewall, Message: "nftables refused the ruleset: " + err.Error()}
@@ -230,6 +231,23 @@ func (e *Engine) commit(ctx context.Context, p *auth.Principal, description stri
 	return res, nil
 }
 
+// quotaRestarts warns of the rules whose quota starts again because they
+// now count it in a way what they used can't be carried to.
+func quotaRestarts(before, after *model.State) []validate.Problem {
+	was := map[int64]*model.Rule{}
+	for _, r := range before.Rules {
+		was[r.ID] = r
+	}
+	var out []validate.Problem
+	for _, r := range after.Rules {
+		if carry, why := model.QuotaCarry(was[r.ID], r); carry == model.QuotaRestarts {
+			out = append(out, validate.Problem{Severity: validate.Warning, Code: "quota_restarts", Object: r.Label(),
+				Message: "its quota starts again: " + why})
+		}
+	}
+	return out
+}
+
 func newProblems(before, after []validate.Problem) []validate.Problem {
 	seen := map[string]bool{}
 	for _, p := range before {

internal/engine/engine_test.go

@@ -173,3 +173,49 @@ func TestPositionsStayStableUntilCrowded(t *testing.T) {
 		t.Errorf("order %v", order)
 	}
 }
+
+// TestQuotaRestartsWarns: a change that counts a quota so what it used
+// can't carry over warns; one that can (to a total, wider groups) doesn't.
+func TestQuotaRestartsWarns(t *testing.T) {
+	e := newEngine(t)
+	ctx := context.Background()
+	var id int64
+	if _, err := e.Apply(ctx, admin, "", Options{}, func(st *model.State, newID func() int64) error {
+		id = newID()
+		st.Rules = append(st.Rules, &model.Rule{ID: id, Chain: "forward", Action: "drop", Quota: &model.Quota{Bytes: 1 << 30, Over: true, PerSource: true}})
+		return nil
+	}); err != nil {
+		t.Fatal(err)
+	}
+	change := func(f func(r *model.Rule)) []string {
+		res, err := e.Apply(ctx, admin, "", Options{DryRun: true}, func(st *model.State, _ func() int64) error {
+			f(st.ByID(model.KindRule, id).(*model.Rule))
+			return nil
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+		var codes []string
+		for _, w := range res.Warnings {
+			if w.Code == "quota_restarts" {
+				codes = append(codes, w.Message)
+			}
+		}
+		return codes
+	}
+	if w := change(func(r *model.Rule) { r.Quota.PerSource, r.Quota.PerDestination = false, true }); len(w) != 1 || !strings.Contains(w[0], "per source can't be counted per destination") {
+		t.Errorf("per source to per destination: %v", w)
+	}
+	if w := change(func(r *model.Rule) { r.Quota.PerSource = false }); len(w) != 0 {
+		t.Errorf("to a total (summed): %v", w)
+	}
+	if w := change(func(r *model.Rule) { r.GroupV6 = 56 }); len(w) != 0 {
+		t.Errorf("wider groups: %v", w)
+	}
+	if w := change(func(r *model.Rule) { r.GroupV6 = 128 }); len(w) != 1 {
+		t.Errorf("finer groups: %v", w)
+	}
+	if w := change(func(r *model.Rule) { r.Quota.Bytes = 2 << 30 }); len(w) != 0 {
+		t.Errorf("another amount: %v", w)
+	}
+}

internal/matrix/matrix.go

@@ -9,6 +9,7 @@ package matrix
 import (
 	"fmt"
 	"net/netip"
+	"regexp"
 	"strings"
 
 	"housecarl/internal/api"
@@ -63,6 +64,50 @@ func Cell(st *model.State, o Options, from, to string) (api.MatrixCell, bool) {
 }
 
 func cell(st *model.State, o Options, chain, from, to string) api.MatrixCell {
+	c := walkCell(st, o, chain, from, to)
+	sum(&c)
+	if from == to && chain == model.ChainForward {
+		c.SameZone, c.Note = true, sameZoneNote(st.Zone(from))
+	}
+	return c
+}
+
+// sum fills in the overview: the summary, the exceptions counted by
+// verdict, and what the allowing ones let through.
+func sum(c *api.MatrixCell) {
+	c.Open = []string{}
+	seen := map[string]bool{}
+	for _, e := range c.Exceptions {
+		switch e.Verdict {
+		case "allowed":
+			c.Allowed++
+			if !seen[e.Short] {
+				seen[e.Short] = true
+				c.Open = append(c.Open, e.Short)
+			}
+		case "blocked":
+			c.Blocked++
+		}
+	}
+	c.Summary = c.Verdict
+	if c.Verdict == "blocked" && c.Allowed > 0 || c.Verdict == "allowed" && c.Blocked > 0 {
+		c.Summary = "partly"
+	}
+}
+
+// sameZoneNote says what of a zone's traffic to itself the firewall sees:
+// only what it routes between the zone's interfaces.
+func sameZoneNote(z *model.Zone) string {
+	if z == nil {
+		return ""
+	}
+	if len(z.Interfaces) == 1 && !strings.HasSuffix(z.Interfaces[0], "*") {
+		return fmt.Sprintf("traffic within %s stays on its own network: it passes the firewall only if routed back out of %s", z.Name, z.Interfaces[0])
+	}
+	return fmt.Sprintf("only traffic routed between %s's interfaces (%s) passes the firewall; within one of them it stays on its own network", z.Name, strings.Join(z.Interfaces, ", "))
+}
+
+func walkCell(st *model.State, o Options, chain, from, to string) api.MatrixCell {
 	c := api.MatrixCell{From: from, To: to, Chain: chain, Exceptions: []api.MatrixException{}}
 	b := st.Settings.Builtins
 	fromZone := st.Zone(from)
@@ -71,7 +116,7 @@ func cell(st *model.State, o Options, chain, from, to string) api.MatrixCell {
 	if chain != model.ChainOutput {
 		if b.Antispoof && external {
 			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: model.ChainEarly, Label: "built-in: antispoof", Verdict: "blocked",
-				What: "sources that can't come from outside (private ranges, your own prefixes)"})
+				What: "sources that can't come from outside (private ranges, your own prefixes)", Short: "spoofed sources", Marks: []string{"b-antispoof", "b-antispoof6"}})
 		}
 		if decided := walk(st, o, &c, model.ChainEarly, from, ""); decided {
 			return c
@@ -81,22 +126,26 @@ func cell(st *model.State, o Options, chain, from, to string) api.MatrixCell {
 	switch chain {
 	case model.ChainInput:
 		if b.ICMPv6 {
-			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "built-in: icmpv6", Verdict: "allowed", What: "ICMPv6 errors, echo, neighbour discovery, MLD"})
+			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "built-in: icmpv6", Verdict: "allowed", What: "ICMPv6 errors, echo, neighbour discovery, MLD",
+				Short: "ICMPv6", Marks: []string{"b-icmpv6", "b-icmpv6-nd", "b-icmpv6-mld"}})
 		}
 		if b.PingInternal && !external {
-			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "built-in: ping", Verdict: "allowed", What: "ping (ICMP echo)"})
+			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "built-in: ping", Verdict: "allowed", What: "ping (ICMP echo)", Short: "ping", Marks: []string{"b-ping"}})
 		}
 		if b.DHCPv6Client && external {
-			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "built-in: dhcpv6-client", Verdict: "allowed", What: "DHCPv6 replies to the firewall"})
+			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "built-in: dhcpv6-client", Verdict: "allowed", What: "DHCPv6 replies to the firewall",
+				Short: "DHCPv6", Marks: []string{"b-dhcpv6-client"}})
 		}
 	case model.ChainForward:
-		if n := forwards(st); n > 0 && external && !st.Zone(to).External {
+		if marks := forwards(st); len(marks) > 0 && external && !st.Zone(to).External {
+			n := fmt.Sprintf("%d port forward%s", len(marks), map[bool]string{true: "", false: "s"}[len(marks) == 1])
 			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "port forwards", Verdict: "allowed",
-				What: fmt.Sprintf("%d port forward%s to inside hosts", n, map[bool]string{true: "", false: "s"}[n == 1])})
+				What: n + " to inside hosts", Short: n, Marks: marks})
 		}
 	case model.ChainOutput:
 		if st.Settings.OutputPolicy == model.PolicyDrop && b.ICMPv6 {
-			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "built-in: icmpv6", Verdict: "allowed", What: "ICMPv6 errors, echo, neighbour discovery, MLD"})
+			c.Exceptions = append(c.Exceptions, api.MatrixException{Chain: chain, Label: "built-in: icmpv6", Verdict: "allowed", What: "ICMPv6 errors, echo, neighbour discovery, MLD",
+				Short: "ICMPv6", Marks: []string{"b-icmpv6"}})
 		}
 	}
 	if walk(st, o, &c, chain, from, to) {
@@ -104,17 +153,22 @@ func cell(st *model.State, o Options, chain, from, to string) api.MatrixCell {
 	}
 	policy := map[string]string{model.ChainInput: st.Settings.InputPolicy, model.ChainForward: st.Settings.ForwardPolicy, model.ChainOutput: st.Settings.OutputPolicy}[chain]
 	c.Verdict, c.DecidedBy = verdictOf(policy), chain+" policy"
+	if policy == model.PolicyDrop {
+		c.Marks = []string{"p-" + chain} // only a drop policy is counted
+	}
 	return c
 }
 
-func forwards(st *model.State) int {
-	n := 0
+// forwards returns the counters' marks of the port forwards that send
+// connections inside.
+func forwards(st *model.State) []string {
+	var marks []string
 	for _, f := range st.Forwards {
 		if !f.Disabled && f.To != "" {
-			n++
+			marks = append(marks, fmt.Sprintf("f%d", f.ID))
 		}
 	}
-	return n
+	return marks
 }
 
 // walk goes through a chain's rules for the pair, as nftables checks
@@ -130,8 +184,22 @@ func walk(st *model.State, o Options, c *api.MatrixCell, chain, from, to string)
 		}
 	}
 	for _, r := range rules {
+		mark := []string{fmt.Sprintf("r%d", r.ID)}
 		if r.Raw != "" {
-			c.Exceptions = append(c.Exceptions, api.MatrixException{RuleID: r.ID, Chain: chain, Label: "rule " + r.Label(), Verdict: "unknown", What: "a raw rule: " + r.Raw})
+			rr := readRaw(r.Raw)
+			switch {
+			case !rr.ok:
+				c.Exceptions = append(c.Exceptions, api.MatrixException{RuleID: r.ID, Chain: chain, Label: "rule " + r.Label(), Verdict: "unknown", What: "a raw rule: " + r.Raw,
+					Short: "a raw rule", Marks: mark})
+			case !rr.forNew || chain == model.ChainEarly && rr.verdict == "allowed":
+				// Not for new connections; an early accept decides nothing.
+			case rr.match == "":
+				c.Verdict, c.DecidedBy, c.RuleID, c.Marks = rr.verdict, "rule "+r.Label(), r.ID, mark
+				return true
+			default:
+				c.Exceptions = append(c.Exceptions, api.MatrixException{RuleID: r.ID, Chain: chain, Label: "rule " + r.Label(), Verdict: rr.verdict, What: "raw: " + rr.match,
+					Short: rr.short, Marks: mark})
+			}
 			continue
 		}
 		if !zones(r, from, to) || !forNew(r) {
@@ -151,10 +219,11 @@ func walk(st *model.State, o Options, c *api.MatrixCell, chain, from, to string)
 			if what == "" {
 				what = "everything"
 			}
-			c.Exceptions = append(c.Exceptions, api.MatrixException{RuleID: r.ID, Chain: chain, Label: "rule " + r.Label(), Verdict: v, What: what})
+			c.Exceptions = append(c.Exceptions, api.MatrixException{RuleID: r.ID, Chain: chain, Label: "rule " + r.Label(), Verdict: v, What: what,
+				Short: short(r, what), Marks: mark})
 			continue
 		}
-		c.Verdict, c.DecidedBy, c.RuleID = v, "rule "+r.Label(), r.ID
+		c.Verdict, c.DecidedBy, c.RuleID, c.Marks = v, "rule "+r.Label(), r.ID, mark
 		return true
 	}
 	return false
@@ -265,6 +334,160 @@ func forNew(r *model.Rule) bool {
 	return false
 }
 
+// raw is what the matrix can read of a raw rule.
+type raw struct {
+	ok      bool   // read: it applies to every pair of its chain
+	forNew  bool   // it can match a new connection
+	verdict string // allowed or blocked
+	match   string // what it matches ("" for everything)
+	short   string
+}
+
+// rawStops are words that make a raw rule's reach or effect unclear to
+// the matrix: interfaces (which zones?), jumps, NAT, changes, verdict maps.
+var rawStops = map[string]bool{
+	"iifname": true, "oifname": true, "iif": true, "oif": true, "iiftype": true, "oiftype": true,
+	"jump": true, "goto": true, "return": true, "vmap": true, "queue": true, "continue": true,
+	"dnat": true, "snat": true, "masquerade": true, "redirect": true, "tproxy": true,
+	"set": true, "notrack": true, "dup": true, "fwd": true, "synproxy": true, "flow": true,
+}
+
+// readRaw reads a raw rule that is a match and then accept, drop or
+// reject: the verdict is the last word (but a reject's "with …"); counter
+// and log only count and log.
+func readRaw(text string) raw {
+	toks := fields(text)
+	for i, t := range toks {
+		if t == "comment" {
+			toks = toks[:i]
+			break
+		}
+	}
+	verdict := -1
+	for i, t := range toks {
+		if strings.HasPrefix(t, `"`) {
+			continue
+		}
+		w := strings.Trim(t, ",{}")
+		if rawStops[w] {
+			return raw{}
+		}
+		if w == "accept" || w == "drop" || w == "reject" {
+			verdict = i
+		}
+	}
+	if verdict < 0 || verdict != len(toks)-1 && !(toks[verdict] == "reject" && toks[verdict+1] == "with") {
+		return raw{}
+	}
+	rr := raw{ok: true, forNew: true, verdict: verdictOf(toks[verdict])}
+	var match []string
+	for i := 0; i < verdict; i++ {
+		switch toks[i] {
+		case "counter":
+			continue
+		case "log":
+			// Its options run up to the next match.
+			for i+1 < verdict && map[string]bool{"prefix": true, "level": true, "group": true, "flags": true}[toks[i+1]] {
+				i += 2
+			}
+			continue
+		}
+		match = append(match, toks[i])
+	}
+	rr.match = strings.Join(match, " ")
+	// ct state without new: not for new connections. The states are one
+	// word ("established,related") or a set ("{ established, related }").
+	for i := 0; i+2 < len(match); i++ {
+		if match[i] != "ct" || match[i+1] != "state" {
+			continue
+		}
+		list := match[i+2]
+		if list == "{" || strings.HasPrefix(list, "{") {
+			var b []string
+			for j := i + 2; j < len(match); j++ {
+				b = append(b, match[j])
+				if strings.HasSuffix(match[j], "}") {
+					break
+				}
+			}
+			list = strings.Join(b, " ")
+		}
+		rr.forNew = false
+		for _, st := range strings.FieldsFunc(list, func(c rune) bool { return c == ',' || c == ' ' || c == '{' || c == '}' }) {
+			rr.forNew = rr.forNew || st == "new"
+		}
+	}
+	rr.short = rr.match
+	if m := icmpRe.FindStringSubmatch(rr.match); m != nil {
+		rr.short = m[1]
+	}
+	if len(rr.short) > 40 {
+		rr.short = rr.short[:39] + "…"
+	}
+	return rr
+}
+
+// fields splits a rule into words, a quoted string being one.
+func fields(s string) []string {
+	var out []string
+	var cur strings.Builder
+	quoted := false
+	for _, c := range s {
+		switch {
+		case c == '"':
+			quoted = !quoted
+			cur.WriteRune(c)
+		case !quoted && (c == ' ' || c == '\t'):
+			if cur.Len() > 0 {
+				out = append(out, cur.String())
+				cur.Reset()
+			}
+		default:
+			cur.WriteRune(c)
+		}
+	}
+	if cur.Len() > 0 {
+		out = append(out, cur.String())
+	}
+	return out
+}
+
+// icmpRe finds an ICMP type match in a raw rule: shown as just icmp or
+// icmpv6.
+var icmpRe = regexp.MustCompile(`\b(icmpv6|icmp) type\b`)
+
+// short sums up an exception for the overview: its services (ICMP types
+// as just icmp or icmpv6), with the addresses it is limited to, which
+// matter as much ("tcp/22 from trusted"); times and rates are left to
+// the details.
+func short(r *model.Rule, what string) string {
+	var parts []string
+	if len(r.Services) > 0 {
+		var svcs []string
+		seen := map[string]bool{}
+		for _, s := range r.Services {
+			if p, _, ok := strings.Cut(s, "/"); ok && (p == "icmp" || p == "icmpv6") {
+				s = p
+			}
+			if !seen[s] {
+				seen[s] = true
+				svcs = append(svcs, s)
+			}
+		}
+		parts = append(parts, strings.Join(svcs, ", "))
+	}
+	for _, c := range strings.Split(what, " · ") {
+		if strings.HasPrefix(c, "from ") || strings.HasPrefix(c, "to ") {
+			parts = append(parts, c)
+		}
+	}
+	if len(parts) == 0 {
+		first, _, _ := strings.Cut(what, " · ")
+		return first
+	}
+	return strings.Join(parts, " ")
+}
+
 // conditions says what limits a rule to part of a pair's traffic ("" for
 // none: it decides the pair).
 func conditions(st *model.State, r *model.Rule) string {

internal/matrix/matrix_test.go

@@ -110,3 +110,90 @@ func TestConnected(t *testing.T) {
 		t.Errorf("guest → lan: %v", ids(guestLan)) // not "to a guest": it is in guest, not lan
 	}
 }
+
+// TestSummary: each pair at a glance, what its exceptions let through,
+// and the counters behind each line.
+func TestSummary(t *testing.T) {
+	st := state()
+	st.Settings.InputPolicy = model.PolicyDrop
+	m := Build(st)
+	for _, c := range []struct {
+		from, to, summary string
+		allowed, blocked  int
+		open              string
+	}{
+		{"lan", "wan", "allowed", 0, 0, ""},
+		{"guest", "wan", "partly", 1, 0, "http, https"},
+		{"wan", "lan", "partly", 1, 1, "1 port forward"},
+		{"lan", "guest", "blocked", 0, 0, ""},
+		{"lan", Firewall, "partly", 4, 0, "ICMPv6|ping|ssh from admins|dns"},
+	} {
+		got := find(m, c.from, c.to)
+		if got.Summary != c.summary || got.Allowed != c.allowed || got.Blocked != c.blocked || strings.Join(got.Open, "|") != c.open {
+			t.Errorf("%s → %s: %s +%d -%d %q; want %s +%d -%d %q", c.from, c.to, got.Summary, got.Allowed, got.Blocked, got.Open, c.summary, c.allowed, c.blocked, c.open)
+		}
+	}
+	if c := find(m, "lan", "lan"); !c.SameZone || !strings.Contains(c.Note, "out of eth1") {
+		t.Errorf("same zone: %+v", c)
+	}
+	if c := find(m, "lan", "wan"); c.SameZone || c.Note != "" {
+		t.Errorf("not the same zone: %+v", c)
+	}
+	wl := find(m, "wan", "lan")
+	if strings.Join(wl.Exceptions[0].Marks, ",") != "b-antispoof,b-antispoof6" || strings.Join(wl.Exceptions[1].Marks, ",") != "f30" || strings.Join(wl.Marks, ",") != "r15" {
+		t.Errorf("marks: %+v", wl)
+	}
+	icmp := &model.Rule{Match: model.Match{Services: []string{"icmp/echo-request", "icmp/echo-reply", "icmpv6/echo-request", "ssh"}}}
+	if s := short(icmp, "x"); s != "icmp, icmpv6, ssh" {
+		t.Errorf("short: %q", s)
+	}
+	ssh := &model.Rule{Match: model.Match{Sources: []string{"trusted"}, Services: []string{"ssh"}}, Days: []string{"mon"}}
+	if s := short(ssh, conditions(st, ssh)); s != "ssh from trusted" {
+		t.Errorf("short with a source: %q", s)
+	}
+	if s := short(&model.Rule{Days: []string{"mon"}}, "mon"); s != "mon" {
+		t.Errorf("short of a time: %q", s)
+	}
+	if c := find(m, "lan", Firewall); strings.Join(c.Marks, ",") != "p-input" {
+		t.Errorf("a drop policy's mark: %v", c.Marks)
+	}
+}
+
+// TestRaw: raw rules that are a match and a verdict are read; others stay
+// unknown.
+func TestRaw(t *testing.T) {
+	for _, c := range []struct {
+		raw, verdict, short string
+		ok, forNew          bool
+	}{
+		{"icmpv6 type { nd-router-solicit, nd-neighbor-advert } ip6 hoplimit 255 accept", "allowed", "icmpv6", true, true},
+		{`tcp dport 22 counter log prefix "ssh: " drop comment "x"`, "blocked", "tcp dport 22", true, true},
+		{"ip saddr 10.0.0.1 reject with icmpx type admin-prohibited", "blocked", "ip saddr 10.0.0.1", true, true},
+		{"ct state established,related accept", "allowed", "ct state established,related", true, false},
+		{"ct state { new, untracked } tcp dport 80 accept", "allowed", "ct state { new, untracked } tcp dport 80", true, true},
+		{"counter accept", "allowed", "", true, true},
+		{`iifname "wan" tcp dport 22 accept`, "", "", false, false},
+		{"tcp dport vmap { 22 : accept }", "", "", false, false},
+		{"meta mark set 1 accept", "", "", false, false},
+		{"tcp dport 22 counter", "", "", false, false},
+	} {
+		rr := readRaw(c.raw)
+		if rr.ok != c.ok || c.ok && (rr.verdict != c.verdict || rr.short != c.short || rr.forNew != c.forNew) {
+			t.Errorf("%q: %+v", c.raw, rr)
+		}
+	}
+	// In a pair: an exception that lets ND in, not "unknown".
+	st := state()
+	st.Rules = append(st.Rules, &model.Rule{ID: 90, Chain: "input", Position: 0.5, Raw: "icmpv6 type { nd-router-solicit } ip6 hoplimit 255 accept"})
+	st.Sort()
+	e := find(Build(st), "wan", Firewall).Exceptions
+	found := false
+	for _, x := range e {
+		if x.RuleID == 90 {
+			found = x.Verdict == "allowed" && x.Short == "icmpv6" && strings.HasPrefix(x.What, "raw: icmpv6 type")
+		}
+	}
+	if !found {
+		t.Errorf("the raw ND rule: %+v", e)
+	}
+}

internal/model/changeset.go

@@ -53,7 +53,10 @@ type Op struct {
 	ID int64 `json:"id,omitempty"`
 	// Data is the object (create), the fields to change (update,
 	// settings) or where to move it (move).
-	Data    json.RawMessage `json:"data,omitempty"`
+	Data json.RawMessage `json:"data,omitempty"`
+	// Place is where a create puts the object in its order (a move's
+	// data); none: at the end.
+	Place   json.RawMessage `json:"place,omitempty"`
 	Summary string          `json:"summary"`
 	AddedAt time.Time       `json:"added_at"`
 }

internal/model/objects.go

@@ -274,6 +274,45 @@ func (r *Rule) Groups() (v4, v6 int) {
 	return v4, v6
 }
 
+// What becomes of what a rule's quota used when the rule changes
+// (QuotaCarry).
+const (
+	QuotaKept      = ""          // counted as before: carried as it is
+	QuotaSummed    = "summed"    // per address to a total: the addresses' sum
+	QuotaRegrouped = "regrouped" // per address in wider groups: added up per group
+	QuotaRestarts  = "restarts"  // can't be carried: starts again
+)
+
+// QuotaCarry says what becomes of what old's quota used when the rule
+// becomes new (both the same rule, with quotas), and for QuotaRestarts
+// why. The amount, over and the resets don't matter: only how it counts.
+func QuotaCarry(old, new *Rule) (carry, why string) {
+	if old == nil || new == nil || old.Quota == nil || new.Quota == nil {
+		return QuotaKept, ""
+	}
+	was, is := old.Quota.PerAddress(), new.Quota.PerAddress()
+	words := map[string]string{"saddr": "per source", "daddr": "per destination", "": "in total"}
+	switch {
+	case was == "" && is == "":
+		return QuotaKept, ""
+	case is == "":
+		return QuotaSummed, ""
+	case was == "":
+		return QuotaRestarts, "a total can't be split by address, so each address starts at nothing"
+	case was != is:
+		return QuotaRestarts, "what was counted " + words[was] + " can't be counted " + words[is]
+	}
+	o4, o6 := old.Groups()
+	n4, n6 := new.Groups()
+	switch {
+	case o4 == n4 && o6 == n6:
+		return QuotaKept, ""
+	case n4 > o4 || n6 > o6:
+		return QuotaRestarts, "addresses are grouped more finely now, and a group's use can't be split"
+	}
+	return QuotaRegrouped, ""
+}
+
 // PortForward publishes a service on an inside host: incoming connections
 // to a public address and port are sent on (DNAT) to To[:ToPort], let
 // through the forward chain, and, with Hairpin, also work from inside.

internal/model/quota_test.go

@@ -0,0 +1,26 @@
+package model
+
+import "testing"
+
+func TestQuotaCarry(t *testing.T) {
+	rule := func(per string, v4, v6 int) *Rule {
+		return &Rule{GroupV4: v4, GroupV6: v6, Quota: &Quota{Bytes: 1, PerSource: per == "src", PerDestination: per == "dst"}}
+	}
+	for _, c := range []struct {
+		old, new *Rule
+		want     string
+	}{
+		{rule("", 0, 0), rule("", 0, 0), QuotaKept},
+		{rule("src", 0, 0), rule("src", 32, 64), QuotaKept}, // the defaults, written out
+		{rule("src", 0, 0), rule("", 0, 0), QuotaSummed},
+		{rule("", 0, 0), rule("src", 0, 0), QuotaRestarts},
+		{rule("src", 0, 0), rule("dst", 0, 0), QuotaRestarts},
+		{rule("src", 0, 0), rule("src", 24, 56), QuotaRegrouped},
+		{rule("src", 0, 0), rule("src", 24, 128), QuotaRestarts},
+		{nil, rule("src", 0, 0), QuotaKept},
+	} {
+		if got, _ := QuotaCarry(c.old, c.new); got != c.want {
+			t.Errorf("%+v -> %+v: %q, want %q", c.old, c.new, got, c.want)
+		}
+	}
+}

internal/names/names.go

@@ -0,0 +1,152 @@
+// Package names finds the names of addresses by reverse lookups, for
+// showing them beside the addresses (connections, the log, quotas,
+// traffic per device). Names are cached and never stored: statistics stay
+// keyed by address.
+package names
+
+import (
+	"context"
+	"errors"
+	"net"
+	"net/netip"
+	"strings"
+	"sync"
+	"time"
+)
+
+// Lookups running at once, and the most names kept.
+const (
+	parallel = 16
+	maxCache = 20000
+)
+
+// Resolver looks up and caches addresses' names.
+type Resolver struct {
+	lookup func(ctx context.Context, addr string) ([]string, error)
+	// ttl is how long a name (or its absence) is kept; a lookup that
+	// failed (a timeout, a server error) is tried again after retry.
+	ttl, retry time.Duration
+	timeout    time.Duration
+	now        func() time.Time
+
+	mu      sync.Mutex
+	cache   map[netip.Addr]entry
+	pending map[netip.Addr]chan struct{}
+	sem     chan struct{}
+}
+
+type entry struct {
+	name    string
+	expires time.Time
+}
+
+// New makes a resolver asking server ("10.10.0.1:53"; "" for the
+// system's, /etc/hosts then /etc/resolv.conf), keeping names for ttl.
+func New(server string, ttl time.Duration) *Resolver {
+	res := &net.Resolver{PreferGo: true}
+	if server != "" {
+		res.Dial = func(ctx context.Context, network, _ string) (net.Conn, error) {
+			var d net.Dialer
+			return d.DialContext(ctx, network, server)
+		}
+	}
+	return NewFunc(res.LookupAddr, ttl)
+}
+
+// NewFunc makes a resolver with its own lookup (tests).
+func NewFunc(lookup func(ctx context.Context, addr string) ([]string, error), ttl time.Duration) *Resolver {
+	return &Resolver{lookup: lookup, ttl: ttl, retry: time.Minute, timeout: 2 * time.Second, now: time.Now,
+		cache: map[netip.Addr]entry{}, pending: map[netip.Addr]chan struct{}{}, sem: make(chan struct{}, parallel)}
+}
+
+// Names returns the names of addrs: those cached, and those looked up
+// within wait. Lookups still running then carry on and are cached for
+// the next call. An address without a name is left out.
+func (r *Resolver) Names(ctx context.Context, addrs []netip.Addr, wait time.Duration) map[netip.Addr]string {
+	out := map[netip.Addr]string{}
+	var waiting []netip.Addr
+	var done []chan struct{}
+	now := r.now()
+	r.mu.Lock()
+	for _, a := range addrs {
+		if e, ok := r.cache[a]; ok && now.Before(e.expires) {
+			if e.name != "" {
+				out[a] = e.name
+			}
+			continue
+		}
+		ch, ok := r.pending[a]
+		if !ok {
+			ch = make(chan struct{})
+			r.pending[a] = ch
+			go r.resolve(a, ch)
+		}
+		waiting = append(waiting, a)
+		done = append(done, ch)
+	}
+	r.mu.Unlock()
+	if len(waiting) == 0 {
+		return out
+	}
+	t := time.NewTimer(wait)
+	defer t.Stop()
+	for _, ch := range done {
+		select {
+		case <-ch:
+		case <-t.C:
+			return r.collect(out, waiting)
+		case <-ctx.Done():
+			return r.collect(out, waiting)
+		}
+	}
+	return r.collect(out, waiting)
+}
+
+// collect adds what the lookups found for addrs.
+func (r *Resolver) collect(out map[netip.Addr]string, addrs []netip.Addr) map[netip.Addr]string {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	for _, a := range addrs {
+		if e, ok := r.cache[a]; ok && e.name != "" {
+			out[a] = e.name
+		}
+	}
+	return out
+}
+
+func (r *Resolver) resolve(a netip.Addr, done chan struct{}) {
+	r.sem <- struct{}{}
+	ctx, cancel := context.WithTimeout(context.Background(), r.timeout)
+	ns, err := r.lookup(ctx, a.String())
+	cancel()
+	<-r.sem
+	e := entry{expires: r.now().Add(r.ttl)}
+	var dnsErr *net.DNSError
+	switch {
+	case err == nil && len(ns) > 0:
+		e.name = strings.TrimSuffix(ns[0], ".")
+	case err != nil && !(errors.As(err, &dnsErr) && dnsErr.IsNotFound):
+		e.expires = r.now().Add(r.retry)
+	}
+	r.mu.Lock()
+	if len(r.cache) >= maxCache {
+		r.prune()
+	}
+	r.cache[a] = e
+	delete(r.pending, a)
+	r.mu.Unlock()
+	close(done)
+}
+
+// prune drops expired names, or all of them when none has expired.
+func (r *Resolver) prune() {
+	now := r.now()
+	for a, e := range r.cache {
+		if !now.Before(e.expires) {
+			delete(r.cache, a)
+		}
+	}
+	if len(r.cache) >= maxCache {
+		clear(r.cache)
+	}
+}

internal/names/names_test.go

@@ -0,0 +1,57 @@
+package names
+
+import (
+	"context"
+	"errors"
+	"net"
+	"net/netip"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+func TestNames(t *testing.T) {
+	var calls atomic.Int32
+	slow := make(chan struct{})
+	r := NewFunc(func(ctx context.Context, addr string) ([]string, error) {
+		calls.Add(1)
+		switch addr {
+		case "10.0.0.1":
+			return []string{"nas.example.net."}, nil
+		case "10.0.0.2":
+			return nil, &net.DNSError{Err: "no such host", Name: addr, IsNotFound: true}
+		case "10.0.0.3":
+			return nil, errors.New("server failure")
+		case "10.0.0.4":
+			<-slow
+			return []string{"slow.example.net."}, nil
+		}
+		return nil, nil
+	}, time.Hour)
+	a := netip.MustParseAddr
+	all := []netip.Addr{a("10.0.0.1"), a("10.0.0.2"), a("10.0.0.3"), a("10.0.0.4")}
+
+	got := r.Names(context.Background(), all, 200*time.Millisecond)
+	if len(got) != 1 || got[a("10.0.0.1")] != "nas.example.net" {
+		t.Fatalf("first call: %v", got)
+	}
+	// The slow lookup finishes later and is there next time; the others
+	// come from the cache, the failure too until it is retried.
+	close(slow)
+	time.Sleep(50 * time.Millisecond)
+	got = r.Names(context.Background(), all, 200*time.Millisecond)
+	if len(got) != 2 || got[a("10.0.0.4")] != "slow.example.net" {
+		t.Fatalf("second call: %v", got)
+	}
+	if n := calls.Load(); n != 4 {
+		t.Fatalf("%d lookups, want 4 (cached)", n)
+	}
+
+	// A failure is tried again after retry, a missing name after ttl.
+	now := time.Now().Add(2 * time.Minute)
+	r.now = func() time.Time { return now }
+	r.Names(context.Background(), all, 200*time.Millisecond)
+	if n := calls.Load(); n != 5 {
+		t.Fatalf("%d lookups, want 5 (the failure again)", n)
+	}
+}

internal/nft/nft.go

@@ -15,6 +15,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"net/netip"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -409,6 +410,10 @@ type Firewall struct {
 	// BootFile is where the confirmed ruleset is saved for the boot unit
 	// (housecarl-ruleset.service; "" for none).
 	BootFile string
+	// Shadow is shadow mode: the ruleset changes nothing, beside another
+	// firewall (render.Options; docs/shadow.md). ShadowBefore runs its
+	// filter chains before that one's.
+	Shadow, ShadowBefore bool
 
 	// Replacing the table resets its counters: base keeps the totals of
 	// the tables replaced since housecarld started.
@@ -418,6 +423,11 @@ type Firewall struct {
 	// restore is the quota usage saved before housecarld (or the machine)
 	// stopped, put back by the next apply.
 	restore *QuotaUsage
+	// adjust are quota changes the next apply makes (AdjustQuota).
+	adjust []QuotaAdjust
+	// quotaRules are the rules with a quota in the ruleset in force, by
+	// ID: what their usage was counted by (nil before the first apply).
+	quotaRules map[int64]*model.Rule
 	// flowDevs are the flowtable's devices in the ruleset in force, by
 	// name, with their interface index then (0: left out, missing).
 	flowDevs map[string]int
@@ -458,6 +468,119 @@ func (f *Firewall) RestoreQuotas(u *QuotaUsage) {
 	f.restore = u
 }
 
+// QuotaAdjust takes Give bytes off what a quota used (never below zero):
+// the named quota Name, or the entries of the per-address sets Name_v4
+// and Name_v6, Addr's alone if given (the set's key, as listed).
+type QuotaAdjust struct {
+	Name string
+	Addr string
+	Give int64
+}
+
+// AdjustQuota has the next apply change what a quota used.
+func (f *Firewall) AdjustQuota(a QuotaAdjust) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.adjust = append(f.adjust, a)
+}
+
+// apply takes what a's say off u. An entry with nothing left used is
+// dropped, so its quota starts again with its next packet.
+func (u *QuotaUsage) apply(adj []QuotaAdjust) {
+	less := func(used, give int64) int64 {
+		if give >= used {
+			return 0
+		}
+		return used - give
+	}
+	for _, a := range adj {
+		if used, ok := u.Quotas[a.Name]; ok {
+			u.Quotas[a.Name] = less(used, a.Give)
+		}
+		for _, set := range []string{a.Name + "_v4", a.Name + "_v6"} {
+			var kept []render.Element
+			for _, e := range u.QuotaSets[set] {
+				if a.Addr == "" || e.Addr == a.Addr {
+					e.Used = less(e.Used, a.Give)
+				}
+				if e.Used > 0 {
+					kept = append(kept, e)
+				}
+			}
+			if _, ok := u.QuotaSets[set]; ok {
+				u.QuotaSets[set] = kept
+			}
+		}
+	}
+}
+
+// carry keeps what quotas used when their rules now count differently
+// (model.QuotaCarry): per address to a total, the sum; to wider groups,
+// the groups' sums; what can't be carried starts again. was are the
+// rules in force before (nil: nothing to compare with).
+func (u *QuotaUsage) carry(was map[int64]*model.Rule, st *model.State) {
+	for _, r := range st.Rules {
+		old := was[r.ID]
+		carry, _ := model.QuotaCarry(old, r)
+		if carry == model.QuotaKept {
+			continue
+		}
+		name := render.QuotaName(r.ID)
+		sets := []string{name + "_v4", name + "_v6"}
+		switch carry {
+		case model.QuotaSummed:
+			var sum int64
+			for _, set := range sets {
+				for _, e := range u.QuotaSets[set] {
+					sum += e.Used
+				}
+			}
+			if u.Quotas == nil {
+				u.Quotas = map[string]int64{}
+			}
+			u.Quotas[name] = sum
+		case model.QuotaRegrouped:
+			v4, v6 := r.Groups()
+			for _, set := range sets {
+				byKey := map[string]int64{}
+				var order []string
+				for _, e := range u.QuotaSets[set] {
+					a, err := netip.ParseAddr(e.Addr)
+					if err != nil {
+						continue
+					}
+					bits := v4
+					if a.Is6() {
+						bits = v6
+					}
+					p, _ := a.Prefix(bits)
+					k := p.Addr().String()
+					if _, ok := byKey[k]; !ok {
+						order = append(order, k)
+					}
+					byKey[k] += e.Used
+				}
+				if len(order) == 0 {
+					continue
+				}
+				var es []render.Element
+				for _, k := range order {
+					es = append(es, render.Element{Addr: k, Used: byKey[k]})
+				}
+				u.QuotaSets[set] = es
+			}
+			continue
+		}
+		// What was counted the other way goes: a total, or the entries.
+		if carry != model.QuotaSummed {
+			delete(u.Quotas, name)
+		}
+		for _, set := range sets {
+			delete(u.QuotaSets, set)
+		}
+	}
+}
+
 // ResetQuota starts a rule's quota again: the named quota, or the
 // per-address quota sets (both families).
 func (f *Firewall) ResetQuota(ctx context.Context, ruleID int64, perAddress bool) error {
@@ -478,7 +601,7 @@ func (f *Firewall) ResetQuota(ctx context.Context, ruleID int64, perAddress bool
 }
 
 func (f *Firewall) options() render.Options {
-	var o render.Options
+	o := render.Options{Shadow: f.Shadow, ShadowBefore: f.ShadowBefore}
 	if f.Interfaces != nil {
 		o.Interfaces = f.Interfaces()
 	}
@@ -488,9 +611,26 @@ func (f *Firewall) options() render.Options {
 // Render builds the ruleset for st as Apply would.
 func (f *Firewall) Render(st *model.State) *render.Ruleset { return render.Render(st, f.options()) }
 
-// Check implements engine.Firewall.
+// RenderEnforcing builds the ruleset for st as Apply would outside shadow
+// mode.
+func (f *Firewall) RenderEnforcing(st *model.State) *render.Ruleset {
+	o := f.options()
+	o.Shadow, o.ShadowBefore = false, false
+	return render.Render(st, o)
+}
+
+// Check implements engine.Firewall. In shadow mode it checks the
+// enforcing ruleset too, so that leaving shadow mode can't fail.
 func (f *Firewall) Check(ctx context.Context, st *model.State) error {
-	return f.Runner.Check(ctx, render.Render(st, f.options()))
+	if err := f.Runner.Check(ctx, render.Render(st, f.options())); err != nil {
+		return err
+	}
+	if f.Shadow {
+		if err := f.Runner.Check(ctx, f.RenderEnforcing(st)); err != nil {
+			return fmt.Errorf("the ruleset for when shadow mode is off: %w", err)
+		}
+	}
+	return nil
 }
 
 // Apply implements engine.Firewall.
@@ -510,6 +650,9 @@ func (f *Firewall) Apply(ctx context.Context, st *model.State) error {
 		usage = old.QuotaUsage
 	}
 	usage.merge(f.restore)
+	usage.carry(f.quotaRules, st)
+	usage.apply(f.adjust)
+	f.adjust = nil
 	opt.Quotas, opt.QuotaSets = usage.Quotas, usage.QuotaSets
 	if old != nil {
 		opt.DeviceSets = old.DeviceSets
@@ -518,6 +661,14 @@ func (f *Firewall) Apply(ctx context.Context, st *model.State) error {
 		return err
 	}
 	f.restore = nil
+	f.quotaRules = map[int64]*model.Rule{}
+	for _, r := range st.Rules {
+		if r.Quota != nil {
+			c, q := *r, *r.Quota // only the quota and the grouping are read
+			c.Quota = &q
+			f.quotaRules[r.ID] = &c
+		}
+	}
 	f.flowDevs = map[string]int{}
 	for _, d := range st.Settings.FlowtableDevices {
 		if opt.Interfaces == nil || opt.Interfaces[d] {
@@ -535,14 +686,45 @@ func (f *Firewall) Apply(ctx context.Context, st *model.State) error {
 			f.base[k] = b
 		}
 	}
+	pruneCounters(f.base, st)
 	return nil
 }
 
+// pruneCounters forgets the totals of objects st no longer has (deleted,
+// or replaced by an import with new IDs), so they aren't listed beside
+// the current ones. A disabled object keeps its totals for when it comes
+// back; built-ins and policies are always kept.
+func pruneCounters(base map[string]Counter, st *model.State) {
+	ids := map[string]bool{}
+	for _, r := range st.Rules {
+		ids[fmt.Sprintf("r%d", r.ID)] = true
+	}
+	for _, x := range st.Forwards {
+		ids[fmt.Sprintf("f%d", x.ID)] = true
+	}
+	for _, x := range st.SNATs {
+		ids[fmt.Sprintf("s%d", x.ID)] = true
+	}
+	for _, x := range st.Redirects {
+		ids[fmt.Sprintf("d%d", x.ID)] = true
+	}
+	for mark := range base {
+		obj, _, _ := strings.Cut(mark, "-") // f3-hairpin, f3-6 are f3's
+		if len(obj) < 2 || !strings.ContainsRune("rfsd", rune(obj[0])) || strings.Trim(obj[1:], "0123456789") != "" {
+			continue // b-established, p-input
+		}
+		if !ids[obj] {
+			delete(base, mark)
+		}
+	}
+}
+
 // SaveBoot writes the ruleset of st for the boot unit, and the fallback
 // it loads if that fails (FallbackFile), atomically. The boot ruleset has
 // no flowtable: it loads before the network comes up, when its devices
 // (ppp0, wg0) don't exist yet and nftables would refuse the whole file;
-// housecarld adds it once they do.
+// housecarld adds it once they do. In shadow mode both are shadow mode's:
+// the fallback then filters nothing.
 func (f *Firewall) SaveBoot(st *model.State) error {
 	if f.BootFile == "" {
 		return nil
@@ -550,10 +732,14 @@ func (f *Firewall) SaveBoot(st *model.State) error {
 	if err := os.MkdirAll(filepath.Dir(f.BootFile), 0o750); err != nil {
 		return err
 	}
-	if err := writeAtomic(FallbackFile(f.BootFile), render.Fallback(st)); err != nil {
+	fallback := render.Fallback(st)
+	if f.Shadow {
+		fallback = render.ShadowFallback()
+	}
+	if err := writeAtomic(FallbackFile(f.BootFile), fallback); err != nil {
 		return err
 	}
-	rs := render.Render(st, render.Options{Interfaces: map[string]bool{}})
+	rs := render.Render(st, render.Options{Interfaces: map[string]bool{}, Shadow: f.Shadow, ShadowBefore: f.ShadowBefore})
 	return writeAtomic(f.BootFile, rs.Text)
 }
 

internal/nft/nft_test.go

@@ -6,6 +6,8 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"reflect"
+	"sort"
 	"strings"
 	"testing"
 
@@ -185,6 +187,31 @@ func TestQuotasInContainer(t *testing.T) {
 	if t2, d2 := used(); t2 < total || d2 < dev {
 		t.Errorf("after a reload: total %d (was %d), per destination %d (was %d)", t2, total, d2, dev)
 	}
+	// Some given back, and one address started again, by the next apply.
+	total, dev = used()
+	fw.AdjustQuota(QuotaAdjust{Name: "quota_r1", Give: 1000})
+	fw.AdjustQuota(QuotaAdjust{Name: "quota_r2", Addr: "127.0.0.3", Give: 1 << 62})
+	if err := fw.Apply(ctx, st); err != nil {
+		t.Fatal(err)
+	}
+	if t2, d2 := used(); t2 > total-1000 || t2 < total-2000 || d2 != 0 {
+		t.Errorf("after giving back: total %d (was %d, gave 1000), per destination %d (was %d, reset)", t2, total, d2, dev)
+	}
+	// Counted in total now: what the addresses used carries over.
+	ping("127.0.0.3")
+	_, dev = used()
+	st.Rules[1].Quota.PerDestination = false
+	if err := fw.Apply(ctx, st); err != nil {
+		t.Fatal(err)
+	}
+	tb, _ := fw.Table(ctx)
+	if tb.Quotas["quota_r2"] < dev || dev == 0 {
+		t.Errorf("per destination to a total: %d, was %d", tb.Quotas["quota_r2"], dev)
+	}
+	st.Rules[1].Quota.PerDestination = true
+	if err := fw.Apply(ctx, st); err != nil {
+		t.Fatal(err)
+	}
 	// Reset by hand.
 	if err := fw.ResetQuota(ctx, 1, false); err != nil {
 		t.Fatal(err)
@@ -199,7 +226,7 @@ func TestQuotasInContainer(t *testing.T) {
 	// saved usage comes back.
 	ping("127.0.0.2")
 	ping("127.0.0.3")
-	tb, _ := fw.Table(ctx)
+	tb, _ = fw.Table(ctx)
 	saved := tb.QuotaUsage
 	exec.Command("docker", "exec", name, "nft", "delete", "table", "inet", "housecarl").Run()
 	fw.RestoreQuotas(&saved)
@@ -211,6 +238,62 @@ func TestQuotasInContainer(t *testing.T) {
 	}
 }
 
+// TestQuotaAdjust: giving back takes off what was used, never below
+// zero; an entry with nothing left goes.
+func TestQuotaAdjust(t *testing.T) {
+	u := QuotaUsage{Quotas: map[string]int64{"quota_r1": 5000, "quota_r9": 10},
+		QuotaSets: map[string][]render.Element{"quota_r2_v4": {{Addr: "10.0.0.1", Used: 3000}, {Addr: "10.0.0.2", Used: 4000}},
+			"quota_r2_v6": {{Addr: "2001:db8::", Used: 100}}}}
+	u.apply([]QuotaAdjust{{Name: "quota_r1", Give: 2000}, {Name: "quota_r9", Give: 2000}, {Name: "quota_r2", Addr: "10.0.0.2", Give: 1500},
+		{Name: "quota_r2", Give: 100}})
+	if u.Quotas["quota_r1"] != 3000 || u.Quotas["quota_r9"] != 0 {
+		t.Errorf("named: %v", u.Quotas)
+	}
+	want := map[string][]render.Element{"quota_r2_v4": {{Addr: "10.0.0.1", Used: 2900}, {Addr: "10.0.0.2", Used: 2400}}, "quota_r2_v6": nil}
+	if !reflect.DeepEqual(u.QuotaSets, want) {
+		t.Errorf("sets: %+v", u.QuotaSets)
+	}
+}
+
+// TestQuotaCarry: usage follows a rule counting its quota differently.
+func TestQuotaCarry(t *testing.T) {
+	perSource := &model.Rule{ID: 2, Quota: &model.Quota{Bytes: 1 << 30, PerSource: true}}
+	usage := func() QuotaUsage {
+		return QuotaUsage{Quotas: map[string]int64{}, QuotaSets: map[string][]render.Element{
+			"quota_r2_v4": {{Addr: "10.0.0.1", Used: 100}, {Addr: "10.0.0.2", Used: 50}},
+			"quota_r2_v6": {{Addr: "2001:db8:0:1::", Used: 7}, {Addr: "2001:db8:0:2::", Used: 3}}}}
+	}
+	was := map[int64]*model.Rule{2: perSource}
+	with := func(f func(r *model.Rule)) *model.State {
+		r := *perSource
+		q := *perSource.Quota
+		r.Quota = &q
+		f(&r)
+		return &model.State{Rules: []*model.Rule{&r}}
+	}
+	u := usage()
+	u.carry(was, with(func(r *model.Rule) { r.Quota.PerSource = false }))
+	if u.Quotas["quota_r2"] != 160 || len(u.QuotaSets["quota_r2_v4"]) != 0 {
+		t.Errorf("to a total: %+v", u)
+	}
+	u = usage()
+	u.carry(was, with(func(r *model.Rule) { r.GroupV4, r.GroupV6 = 24, 48 }))
+	want := map[string][]render.Element{"quota_r2_v4": {{Addr: "10.0.0.0", Used: 150}}, "quota_r2_v6": {{Addr: "2001:db8::", Used: 10}}}
+	if !reflect.DeepEqual(u.QuotaSets, want) {
+		t.Errorf("wider groups: %+v", u.QuotaSets)
+	}
+	u = usage()
+	u.carry(was, with(func(r *model.Rule) { r.Quota.PerSource, r.Quota.PerDestination = false, true }))
+	if len(u.QuotaSets) != 0 {
+		t.Errorf("per destination now: %+v", u.QuotaSets)
+	}
+	u = usage()
+	u.carry(nil, with(func(r *model.Rule) { r.Quota.PerSource = false }))
+	if len(u.QuotaSets["quota_r2_v4"]) != 2 || u.Quotas["quota_r2"] != 0 {
+		t.Errorf("nothing to compare with (the first apply): %+v", u)
+	}
+}
+
 // TestDeviceCountsInContainer: the per-device counters are read back and
 // survive a reload.
 func TestDeviceCountsInContainer(t *testing.T) {
@@ -365,3 +448,98 @@ func TestBootInContainer(t *testing.T) {
 		t.Errorf("the fallback stayed after an apply: %+v %v", tb, err)
 	}
 }
+
+// TestShadowInContainer: in shadow mode a drop counts but doesn't drop,
+// the ruleset for leaving shadow mode is checked too, and the boot files
+// are shadow mode's.
+func TestShadowInContainer(t *testing.T) {
+	image := os.Getenv("HOUSECARL_NFT_IMAGE")
+	if image == "" {
+		t.Skip("HOUSECARL_NFT_IMAGE not set")
+	}
+	name := "housecarl-nft-shadow-test"
+	exec.Command("docker", "rm", "-f", name).Run()
+	if out, err := exec.Command("docker", "run", "-d", "--name", name, "--cap-add", "NET_ADMIN", image, "sleep", "300").CombinedOutput(); err != nil {
+		t.Fatalf("starting the container: %v %s", err, out)
+	}
+	t.Cleanup(func() { exec.Command("docker", "rm", "-f", name).Run() })
+	dir := t.TempDir()
+	fw := &Firewall{Runner: &Runner{Command: []string{"docker", "exec", "-i", name, "nft"}}, Shadow: true, BootFile: filepath.Join(dir, "ruleset.nft")}
+	ctx := context.Background()
+	st := model.NewState()
+	st.Settings.OutputPolicy = model.PolicyDrop
+	st.Settings.InputPolicy = model.PolicyAccept
+	st.Settings.Builtins.Loopback = false // it would accept the ping first
+	st.Rules = []*model.Rule{{ID: 3, Chain: model.ChainOutput, Position: 1, Action: model.ActionReject, Match: model.Match{Destinations: []string{"127.0.0.2"}}}}
+	if err := fw.Apply(ctx, st); err != nil {
+		t.Fatalf("apply: %v", err)
+	}
+	ping := func() error {
+		return exec.Command("docker", "exec", name, "ping", "-c", "2", "-W", "1", "127.0.0.2").Run()
+	}
+	if err := ping(); err != nil {
+		t.Errorf("shadow mode blocked a ping: %v", err)
+	}
+	tb, err := fw.Table(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if tb.Counters["r3"].Packets == 0 {
+		t.Errorf("what would be rejected isn't counted: %+v", tb.Counters)
+	}
+	// A rule shadow mode leaves out, which nftables refuses when enforcing.
+	broken := st.Clone()
+	broken.Rules = append(broken.Rules, &model.Rule{ID: 4, Chain: model.ChainInput, Position: 1, Raw: "tcp dport 22 jump nowhere", Comment: "jump"})
+	if err := fw.Check(ctx, broken); err == nil || !strings.Contains(err.Error(), "shadow mode is off") || !strings.Contains(err.Error(), "input #4 (jump)") {
+		t.Errorf("the ruleset for leaving shadow mode wasn't checked: %v", err)
+	}
+	// Enforcing, the same rule rejects.
+	enforcing := &Firewall{Runner: fw.Runner}
+	if err := enforcing.Apply(ctx, st); err != nil {
+		t.Fatal(err)
+	}
+	if ping() == nil {
+		t.Error("enforcing didn't reject")
+	}
+	// The boot files: both load, and filter nothing.
+	if err := fw.SaveBoot(st); err != nil {
+		t.Fatal(err)
+	}
+	for _, f := range []string{"ruleset.nft", "ruleset-fallback.nft"} {
+		b, _ := os.ReadFile(filepath.Join(dir, f))
+		c := exec.Command("docker", "exec", "-i", name, "nft", "-f", "/dev/stdin")
+		c.Stdin = strings.NewReader(string(b))
+		if out, err := c.CombinedOutput(); err != nil {
+			t.Fatalf("%s doesn't load: %v %s", f, err, out)
+		}
+		if err := ping(); err != nil {
+			t.Errorf("%s blocked a ping: %v", f, err)
+		}
+	}
+	if tb, err := fw.Table(ctx); err != nil || !tb.Fallback {
+		t.Errorf("the shadow fallback isn't recognised: %+v %v", tb, err)
+	}
+}
+
+// TestPruneCounters: the totals of objects gone (an import with --replace
+// gives every object a new ID) are forgotten; built-ins, policies and
+// disabled objects keep theirs.
+func TestPruneCounters(t *testing.T) {
+	base := map[string]Counter{}
+	for _, m := range []string{"r1", "r2", "r3", "f4", "f4-hairpin", "f4-6", "f5-hairpin", "s6", "d7", "d8", "b-established", "p-input", "fallback-input"} {
+		base[m] = Counter{Packets: 1}
+	}
+	st := model.NewState()
+	st.Rules = []*model.Rule{{ID: 1}, {ID: 3, Disabled: true}}
+	st.Forwards = []*model.PortForward{{ID: 4}}
+	st.Redirects = []*model.Redirect{{ID: 8}}
+	pruneCounters(base, st)
+	var got []string
+	for m := range base {
+		got = append(got, m)
+	}
+	sort.Strings(got)
+	if strings.Join(got, " ") != "b-established d8 f4 f4-6 f4-hairpin fallback-input p-input r1 r3" {
+		t.Errorf("kept %v", got)
+	}
+}

internal/render/render.go

@@ -8,6 +8,14 @@
 // counter and a comment "hc:<kind><id>", which is how counters are read
 // back, and Ruleset.Lines maps each line to its object, for nftables'
 // error messages.
+//
+// In shadow mode (Options.Shadow, docs/shadow.md) the same rules are
+// written so that they change nothing: drops and rejects accept instead
+// (an accept only ends Housecarl's chain; the packet goes on to other
+// tables' chains, which decide), policies accept, NAT only counts, and
+// what alters packets (MSS clamping, the flowtable) is left out. What
+// would be dropped, rejected or translated carries a marker in its
+// comment ("[would drop]"), which the tracer reads.
 package render
 
 import (
@@ -42,8 +50,18 @@ type Options struct {
 	// DeviceSets are the per-device traffic counters' entries
 	// (stats_up_v4 …), so a reload keeps them.
 	DeviceSets map[string][]Element
+	// Shadow renders for shadow mode: nothing is blocked, rejected,
+	// translated or changed (see the package comment).
+	Shadow bool
+	// ShadowBefore runs the filter chains just before other tables' on
+	// their hooks (priority - 10) instead of just after (+ 10).
+	ShadowBefore bool
 }
 
+// Would marks, in shadow mode, a rule's comment with what it would do:
+// "[would drop]".
+func Would(action string) string { return "[would " + action + "]" }
+
 // Element is a dynamic set's entry with its remaining lifetime, or a
 // per-address quota's entry with what it used.
 type Element struct {
@@ -112,6 +130,9 @@ type renderer struct {
 func (r *renderer) render() {
 	w := r.w
 	w.emit("", "# Built by Housecarl from its database; changes made here are lost.")
+	if r.opt.Shadow {
+		w.emit("", "# Shadow mode: nothing here drops, rejects or translates; other tables decide.")
+	}
 	w.emit("", "table inet %s {}", Table)
 	w.emit("", "delete table inet %s", Table)
 	w.emit("", "table inet %s {", Table)
@@ -265,6 +286,10 @@ func addrType(v6 bool) string {
 }
 
 func (r *renderer) flowtableDevices() []string {
+	if r.opt.Shadow {
+		// Offloaded connections skip every table's forward chain.
+		return nil
+	}
 	var out []string
 	for _, d := range r.st.Settings.FlowtableDevices {
 		if r.opt.Interfaces == nil || r.opt.Interfaces[d] {
@@ -277,8 +302,19 @@ func (r *renderer) flowtableDevices() []string {
 // ---- chains
 
 func (r *renderer) chain(name, hook, prio, policy string) {
+	nat := prio == "dstnat" || prio == "srcnat"
+	if r.opt.Shadow {
+		// NAT chains are asked in turn only until one translates: to
+		// count anything, Housecarl's must come first.
+		if nat || r.opt.ShadowBefore {
+			prio += " - 10"
+		} else {
+			prio += " + 10"
+		}
+		policy = model.PolicyAccept
+	}
 	r.w.emit("", "\tchain %s {", name)
-	r.w.emit("", "\t\ttype %s hook %s priority %s; policy %s;", map[bool]string{true: "nat", false: "filter"}[prio == "dstnat" || prio == "srcnat"], hook, prio, policy)
+	r.w.emit("", "\t\ttype %s hook %s priority %s; policy %s;", map[bool]string{true: "nat", false: "filter"}[nat], hook, prio, policy)
 }
 
 func (r *renderer) end() { r.w.emit("", "\t}") }
@@ -287,6 +323,16 @@ func (r *renderer) builtin(name, format string, args ...any) {
 	r.w.emit("built-in: "+name, "\t\t"+format+" comment \"hc:b-%s\"", append(args, name)...)
 }
 
+// builtinDrop writes a built-in that drops what it matches, or in shadow
+// mode counts it.
+func (r *renderer) builtinDrop(name, format string, args ...any) {
+	if r.opt.Shadow {
+		r.w.emit("built-in: "+name, "\t\t"+format+" counter accept comment \"hc:b-%s %s\"", append(args, name, Would("drop"))...)
+		return
+	}
+	r.builtin(name, format+" counter drop", args...)
+}
+
 func (r *renderer) early() {
 	st := r.st
 	r.chain("early", "prerouting", "raw", "accept")
@@ -302,10 +348,10 @@ func (r *renderer) early() {
 			}
 		}
 		if len(v4) > 0 {
-			r.builtin("antispoof", "iifname %s ip saddr { %s } counter drop", ifaces(ext), strings.Join(v4, ", "))
+			r.builtinDrop("antispoof", "iifname %s ip saddr { %s }", ifaces(ext), strings.Join(v4, ", "))
 		}
 		if len(v6) > 0 {
-			r.builtin("antispoof6", "iifname %s ip6 saddr { %s } counter drop", ifaces(ext), strings.Join(v6, ", "))
+			r.builtinDrop("antispoof6", "iifname %s ip6 saddr { %s }", ifaces(ext), strings.Join(v6, ", "))
 		}
 	}
 	r.rules(model.ChainEarly, true)
@@ -325,7 +371,7 @@ func (r *renderer) connBuiltins() {
 		r.builtin("established", "ct state established,related counter accept")
 	}
 	if b.DropInvalid {
-		r.builtin("invalid", "ct state invalid counter drop")
+		r.builtinDrop("invalid", "ct state invalid")
 	}
 }
 
@@ -366,7 +412,8 @@ func (r *renderer) forward(flowtable bool) {
 	b := st.Settings.Builtins
 	r.chain("forward", "forward", "filter", st.Settings.ForwardPolicy)
 	ext := st.ExternalInterfaces()
-	if b.MSSClamp && len(ext) > 0 {
+	// Shadow mode changes no packet.
+	if b.MSSClamp && len(ext) > 0 && !r.opt.Shadow {
 		r.builtin("mss-clamp", "oifname %s tcp flags syn tcp option maxseg size set rt mtu", ifaces(ext))
 	}
 	r.rules(model.ChainForward, true)
@@ -404,15 +451,21 @@ func (r *renderer) output() {
 	r.end()
 }
 
-// policyTail counts (and optionally logs) what reaches the policy.
+// policyTail counts (and optionally logs) what reaches the policy. In
+// shadow mode, where the policy accepts, that is what it would drop, and
+// it is always logged: the log is how shadow mode shows it.
 func (r *renderer) policyTail(chain, policy string) {
 	if policy != model.PolicyDrop {
 		return
 	}
 	obj := "policy: " + chain
-	if r.st.Settings.LogPolicyDrops && chain != "output" {
+	if r.opt.Shadow || r.st.Settings.LogPolicyDrops && chain != "output" {
 		r.w.emit(obj, "\t\tlimit rate 10/second burst 20 packets log prefix %s group %d", quote("hc "+chain+" policy drop: "), LogGroup)
 	}
+	if r.opt.Shadow {
+		r.w.emit(obj, "\t\tcounter comment \"hc:p-%s %s\"", chain, Would("drop"))
+		return
+	}
 	r.w.emit(obj, "\t\tcounter comment \"hc:p-%s\"", chain)
 }
 
@@ -428,7 +481,15 @@ func (r *renderer) rules(chain string, traffic bool) {
 		obj := rule.Label()
 		mark := fmt.Sprintf("r%d", rule.ID)
 		if rule.Raw != "" {
-			r.w.emit(obj, "\t\t%s", rule.Raw)
+			raw := rule.Raw
+			if r.opt.Shadow {
+				var ok bool
+				if raw, ok = ShadowRaw(raw); !ok {
+					r.w.emit(obj, "\t\t# left out in shadow mode: %s", rule.Raw)
+					continue
+				}
+			}
+			r.w.emit(obj, "\t\t%s", raw)
 			continue
 		}
 		var tail []string
@@ -478,17 +539,22 @@ func (r *renderer) verdict(rule *model.Rule, mark string) string {
 		}
 		v = append(v, fmt.Sprintf("log prefix %s group %d", quote(prefix), LogGroup))
 	}
-	switch rule.Action {
-	case model.ActionAccept, model.ActionDrop:
+	text := rule.Comment
+	switch {
+	case r.opt.Shadow && (rule.Action == model.ActionDrop || rule.Action == model.ActionReject):
+		// It ends Housecarl's chain as the drop would, and no more.
+		v = append(v, model.ActionAccept)
+		text = Would(rule.Action) + " " + text
+	case rule.Action == model.ActionAccept, rule.Action == model.ActionDrop:
 		v = append(v, rule.Action)
-	case model.ActionReject:
+	case rule.Action == model.ActionReject:
 		if rule.RejectWith == "tcp-reset" {
 			v = append(v, "reject with tcp reset")
 		} else {
 			v = append(v, "reject")
 		}
 	}
-	v = append(v, "comment "+comment(mark, rule.Comment))
+	v = append(v, "comment "+comment(mark, text))
 	return strings.Join(v, " ")
 }
 
@@ -781,7 +847,7 @@ func (r *renderer) dstnat() {
 					}
 				}
 			}
-			r.w.emit(obj, "\t\t%s counter redirect to :%s comment %s", strings.Join(nonEmpty(line.parts), " "), to, comment(mark, x.Comment))
+			r.w.emit(obj, "\t\t%s counter %s", strings.Join(nonEmpty(line.parts), " "), r.nat("redirect to :"+to, mark, x.Comment))
 		}
 	}
 	ext := st.ExternalInterfaces()
@@ -811,7 +877,7 @@ func (r *renderer) dstnat() {
 		for _, wh := range where {
 			for _, sa := range srcAlts {
 				for _, p := range f.Protocols {
-					r.w.emit(obj, "\t\t%s counter dnat ip to %s comment %s", strings.Join(nonEmpty([]string{wh, sa, p + " dport " + f.Ports}), " "), to, comment(mark, f.Name+" "+f.Comment))
+					r.w.emit(obj, "\t\t%s counter %s", strings.Join(nonEmpty([]string{wh, sa, p + " dport " + f.Ports}), " "), r.nat("dnat ip to "+to, mark, f.Name+" "+f.Comment))
 				}
 			}
 		}
@@ -885,7 +951,7 @@ func (r *renderer) srcnat() {
 		}
 		for _, sa := range srcAlts {
 			for _, p := range f.Protocols {
-				r.w.emit(obj, "\t\t%s counter masquerade comment %s", strings.Join(nonEmpty([]string{sa, "ip daddr " + f.To, p + " dport " + ports, "ct status dnat"}), " "), comment(mark, f.Name))
+				r.w.emit(obj, "\t\t%s counter %s", strings.Join(nonEmpty([]string{sa, "ip daddr " + f.To, p + " dport " + ports, "ct status dnat"}), " "), r.nat("masquerade", mark, f.Name))
 			}
 		}
 	}
@@ -917,12 +983,21 @@ func (r *renderer) srcnat() {
 					action = "snat ip to " + x.To
 				}
 			}
-			r.w.emit(obj, "\t\t%s counter %s comment %s", strings.Join(nonEmpty(line.parts), " "), action, comment(mark, x.Comment))
+			r.w.emit(obj, "\t\t%s counter %s", strings.Join(nonEmpty(line.parts), " "), r.nat(action, mark, x.Comment))
 		}
 	}
 	r.end()
 }
 
+// nat writes a NAT rule's statement and comment; in shadow mode only the
+// comment, saying what it would do ("[would dnat]").
+func (r *renderer) nat(action, mark, text string) string {
+	if r.opt.Shadow {
+		return "comment " + comment(mark, Would(strings.Fields(action)[0])+" "+text)
+	}
+	return action + " comment " + comment(mark, text)
+}
+
 // ---- helpers
 
 // hours writes a time window. nftables can't take a range past midnight,

internal/render/render_test.go

@@ -2,6 +2,7 @@ package render
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"os/exec"
 	"strings"
@@ -254,15 +255,25 @@ func TestRenderedRulesetPassesNft(t *testing.T) {
 	vlan.Settings.FlowtableDevices = []string{"lo", "enp2s0.20"}
 	for name, st := range map[string]*model.State{"router": router(), "empty": model.NewState(), "stats": stats, "vlan": vlan} {
 		q, qs := quotaOptions(st)
-		rs := Render(st, Options{Elements: map[string][]Element{"guests": {{Addr: "10.0.30.5", Timeout: 1700}, {Addr: "2a02:8013:7f3d:30::5"}}}, Quotas: q, QuotaSets: qs,
-			DeviceSets: map[string][]Element{"stats_up_v4": {{Addr: "10.0.10.5", Timeout: 3000, Packets: 7, Bytes: 7000}}, "stats_down_v6": {{Addr: "2001:db8:1:2::", Packets: 1, Bytes: 100}}}})
-		c := exec.CommandContext(context.Background(), cmd[0], append(cmd[1:], "-c", "-f", "/dev/stdin")...)
-		c.Stdin = strings.NewReader(rs.Text)
-		if out, err := c.CombinedOutput(); err != nil {
-			t.Errorf("%s: nft -c: %v\n%s", name, err, out)
-			for i, l := range strings.Split(rs.Text, "\n") {
-				t.Logf("%3d %s", i+1, l)
-			}
+		// Enforcing, and in shadow mode after and before other tables.
+		for _, mode := range []Options{{}, {Shadow: true}, {Shadow: true, ShadowBefore: true}} {
+			opt := Options{Elements: map[string][]Element{"guests": {{Addr: "10.0.30.5", Timeout: 1700}, {Addr: "2a02:8013:7f3d:30::5"}}}, Quotas: q, QuotaSets: qs,
+				DeviceSets: map[string][]Element{"stats_up_v4": {{Addr: "10.0.10.5", Timeout: 3000, Packets: 7, Bytes: 7000}}, "stats_down_v6": {{Addr: "2001:db8:1:2::", Packets: 1, Bytes: 100}}},
+				Shadow:     mode.Shadow, ShadowBefore: mode.ShadowBefore}
+			nftCheck(t, cmd, fmt.Sprintf("%s (shadow %v, before %v)", name, mode.Shadow, mode.ShadowBefore), Render(st, opt).Text)
+		}
+	}
+	nftCheck(t, cmd, "shadow fallback", ShadowFallback())
+}
+
+func nftCheck(t *testing.T, cmd []string, name, text string) {
+	t.Helper()
+	c := exec.CommandContext(context.Background(), cmd[0], append(cmd[1:], "-c", "-f", "/dev/stdin")...)
+	c.Stdin = strings.NewReader(text)
+	if out, err := c.CombinedOutput(); err != nil {
+		t.Errorf("%s: nft -c: %v\n%s", name, err, out)
+		for i, l := range strings.Split(text, "\n") {
+			t.Logf("%3d %s", i+1, l)
 		}
 	}
 }

internal/render/shadow.go

@@ -0,0 +1,127 @@
+package render
+
+import (
+	"fmt"
+	"strings"
+
+	"housecarl/internal/model"
+)
+
+// effects are the words of a raw rule's statements that act on packets
+// (or jump away). In shadow mode a raw rule with any of them is left out,
+// unless its only one is a final drop or reject, which becomes an accept.
+var effects = map[string]bool{
+	"drop": true, "reject": true, "queue": true,
+	"dnat": true, "snat": true, "masquerade": true, "redirect": true, "tproxy": true,
+	"notrack": true, "dup": true, "fwd": true, "synproxy": true, "flow": true, "offload": true,
+	"set": true, "reset": true, "jump": true, "goto": true, "return": true,
+}
+
+// ShadowRaw rewrites a raw rule for shadow mode: as written when it only
+// matches, counts, logs or accepts; with its final drop or reject made an
+// accept (marked "[would drop]" in its comment); ok is false when it does
+// anything else to packets (NAT, setting a mark or header field, a jump,
+// a verdict map…), and must be left out.
+func ShadowRaw(raw string) (out string, ok bool) {
+	toks := tokens(raw)
+	verdict := -1
+	for i := 0; i < len(toks); i++ {
+		w := word(toks[i])
+		if w == "comment" {
+			i++ // its text
+			continue
+		}
+		if !effects[w] {
+			continue
+		}
+		if verdict >= 0 || (w != "drop" && w != "reject") {
+			return "", false
+		}
+		verdict = i
+		// What follows a verdict, up to the comment, must be a reject's
+		// "with …".
+		j := i + 1
+		for j < len(toks) && word(toks[j]) != "comment" {
+			j++
+		}
+		if j > i+1 && (w == "drop" || word(toks[i+1]) != "with") {
+			return "", false
+		}
+		i = j - 1
+	}
+	if verdict < 0 {
+		return raw, true
+	}
+	mark := Would(word(toks[verdict]))
+	head := append(append([]string{}, toks[:verdict]...), "accept")
+	for i := verdict + 1; i < len(toks); i++ {
+		if word(toks[i]) != "comment" {
+			continue
+		}
+		if i+1 < len(toks) {
+			text := strings.Trim(toks[i+1], `"`)
+			return strings.Join(append(head, "comment", quote(strings.TrimSpace(mark+" "+text))), " "), true
+		}
+	}
+	return strings.Join(append(head, "comment", quote(mark)), " "), true
+}
+
+// tokens splits a rule into words, a quoted string being one.
+func tokens(s string) []string {
+	var out []string
+	var cur strings.Builder
+	quoted := false
+	for _, c := range s {
+		switch {
+		case c == '"':
+			quoted = !quoted
+			cur.WriteRune(c)
+		case !quoted && (c == ' ' || c == '\t'):
+			if cur.Len() > 0 {
+				out = append(out, cur.String())
+				cur.Reset()
+			}
+		default:
+			cur.WriteRune(c)
+		}
+	}
+	if cur.Len() > 0 {
+		out = append(out, cur.String())
+	}
+	return out
+}
+
+// word is a token as a keyword: without the punctuation of sets and maps
+// around it; a quoted string is no keyword.
+func word(t string) string {
+	if strings.HasPrefix(t, `"`) {
+		return ""
+	}
+	return strings.ToLower(strings.Trim(t, ",{}:()"))
+}
+
+// ShadowLeftOut lists the raw rules shadow mode leaves out (ShadowRaw).
+func ShadowLeftOut(st *model.State) []*model.Rule {
+	var out []*model.Rule
+	for _, r := range st.Rules {
+		if r.Raw == "" || r.Disabled {
+			continue
+		}
+		if _, ok := ShadowRaw(r.Raw); !ok {
+			out = append(out, r)
+		}
+	}
+	return out
+}
+
+// ShadowFallback is the boot fallback in shadow mode: the other firewall
+// protects the machine, so it is an empty table that filters nothing,
+// with a rule outside every hook that tells housecarld it is in force.
+func ShadowFallback() string {
+	var b strings.Builder
+	fmt.Fprintf(&b, "# Housecarl's fallback in shadow mode: loaded at boot only if ruleset.nft\n")
+	fmt.Fprintf(&b, "# fails to load. It filters nothing; the other firewall decides.\n")
+	fmt.Fprintf(&b, "table inet %s {}\ndelete table inet %s\n", Table, Table)
+	fmt.Fprintf(&b, "table inet %s {\n\tchain fallback {\n\t\tcounter comment \"hc:%s-shadow\"\n\t}\n}\n", Table, FallbackMark)
+	return b.String()
+}

internal/render/shadow_test.go

@@ -0,0 +1,91 @@
+package render
+
+import (
+	"regexp"
+	"strings"
+	"testing"
+
+	"housecarl/internal/model"
+)
+
+// TestShadow: in shadow mode nothing in the ruleset drops, rejects,
+// translates or changes a packet, and what would is counted and marked.
+func TestShadow(t *testing.T) {
+	st := router()
+	st.Rules = append(st.Rules,
+		&model.Rule{ID: 950, Chain: model.ChainInput, Position: 99, Raw: `tcp dport 9999 counter reject with tcp reset comment "old"`},
+		&model.Rule{ID: 951, Chain: model.ChainForward, Position: 99, Raw: "meta mark set 0x1 accept"})
+	st.Settings.OutputPolicy = model.PolicyDrop
+	text := Render(st, Options{Shadow: true}).Text
+	// What acts on packets: verdicts, NAT, changes, the flowtable.
+	acts := regexp.MustCompile(`(?m)(\b(drop|reject|dnat|snat|masquerade|redirect)\b|maxseg size set|flow add|flowtable|policy drop)[^"\n]*$`)
+	for _, l := range strings.Split(text, "\n") {
+		code, _, _ := strings.Cut(l, "comment ")
+		code = strings.ReplaceAll(code, "ct status dnat", "") // a match
+		if strings.HasPrefix(strings.TrimSpace(l), "#") {
+			continue
+		}
+		if m := acts.FindString(code); m != "" && !strings.Contains(code, "log prefix") {
+			t.Errorf("acts on packets in shadow mode: %s", l)
+		}
+	}
+	for _, want := range []string{
+		"type filter hook input priority filter + 10; policy accept;",
+		"type filter hook prerouting priority raw + 10; policy accept;",
+		"type nat hook prerouting priority dstnat - 10; policy accept;",
+		"type nat hook postrouting priority srcnat - 10; policy accept;",
+		`ct state invalid counter accept comment "hc:b-invalid [would drop]"`,
+		`counter comment "hc:p-input [would drop]"`,
+		`counter comment "hc:p-output [would drop]"`,
+		`log prefix "hc output policy drop: "`,
+		`[would reject]`,
+		`[would dnat] jellyfin`,
+		`[would masquerade]`,
+		`[would redirect]`,
+		`tcp dport 9999 counter accept comment "[would reject] old"`,
+		"# left out in shadow mode: meta mark set 0x1 accept",
+		"# Shadow mode:",
+	} {
+		if !strings.Contains(text, want) {
+			t.Errorf("no %q in\n%s", want, text)
+		}
+	}
+	before := Render(st, Options{Shadow: true, ShadowBefore: true}).Text
+	for _, want := range []string{"priority filter - 10;", "priority raw - 10;", "priority dstnat - 10;"} {
+		if !strings.Contains(before, want) {
+			t.Errorf("before: no %q", want)
+		}
+	}
+	// Enforcing is unchanged by it.
+	if strings.Contains(Render(st, Options{}).Text, "would") {
+		t.Error("shadow markers when enforcing")
+	}
+	if got := ShadowLeftOut(st); len(got) != 1 || got[0].ID != 951 {
+		t.Errorf("left out: %v", got)
+	}
+}
+
+func TestShadowRaw(t *testing.T) {
+	cases := []struct{ in, out string }{
+		{"meta skuid 0 counter accept", "meta skuid 0 counter accept"},
+		{"tcp dport 22 drop", `tcp dport 22 accept comment "[would drop]"`},
+		{`tcp dport 22 counter drop comment "no ssh"`, `tcp dport 22 counter accept comment "[would drop] no ssh"`},
+		{"ip saddr 10.0.0.1 reject with icmpx type admin-prohibited", `ip saddr 10.0.0.1 accept comment "[would reject]"`},
+		{"tcp dport 22 reject with tcp reset", `tcp dport 22 accept comment "[would reject]"`},
+		{`log prefix "drop me: " group 5 accept`, `log prefix "drop me: " group 5 accept`},
+		{"ip saddr { 10.0.0.1, 10.0.0.2 } counter", "ip saddr { 10.0.0.1, 10.0.0.2 } counter"},
+		{"tcp dport vmap { 22 : drop, 80 : accept }", ""},
+		{"meta mark set 1", ""},
+		{"ip daddr 1.2.3.4 dnat ip to 10.0.0.1", ""},
+		{"tcp dport 22 jump other", ""},
+		{"drop accept", ""},
+		{"meta nftrace set 1", ""},
+		{"ct state new notrack", ""},
+	}
+	for _, c := range cases {
+		out, ok := ShadowRaw(c.in)
+		if ok != (c.out != "") || out != c.out {
+			t.Errorf("%q: got %q %v, want %q", c.in, out, ok, c.out)
+		}
+	}
+}

internal/server/authn.go

@@ -275,7 +275,7 @@ func (s *Server) logout(w http.ResponseWriter, r *http.Request, p *auth.Principa
 }
 
 func (s *Server) whoamiOf(p *auth.Principal, se *model.Session) api.Whoami {
-	out := api.Whoami{User: p.User, Admin: p.IsAdmin(), Method: p.Method, Permissions: p.Permissions(), Build: version.Info()}
+	out := api.Whoami{User: p.User, Admin: p.IsAdmin(), Method: p.Method, Permissions: p.Permissions(), Build: version.Info(), Mode: s.mode()}
 	if se != nil {
 		out.CSRFToken = se.CSRFToken
 	}

internal/server/h_config.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"net/netip"
 	"sort"
+	"strconv"
 	"strings"
 
 	udiff "github.com/aymanbagabas/go-udiff"
@@ -15,6 +16,7 @@ import (
 	"housecarl/internal/engine"
 	"housecarl/internal/matrix"
 	"housecarl/internal/model"
+	"housecarl/internal/nft"
 	"housecarl/internal/store"
 )
 
@@ -309,7 +311,19 @@ func (s *Server) createObject(w http.ResponseWriter, r *http.Request, p *auth.Pr
 	if _, err := decodeObject(kind, raw); err != nil {
 		return err
 	}
-	return s.change(w, r, p, model.Op{Op: model.OpCreate, Kind: kind, Data: raw})
+	op := model.Op{Op: model.OpCreate, Kind: kind, Data: raw}
+	// ?before=ID, ?after=ID or ?first=1: where it goes in its order.
+	q := r.URL.Query()
+	var place api.MoveInput
+	place.Before, _ = strconv.ParseInt(q.Get("before"), 10, 64)
+	place.After, _ = strconv.ParseInt(q.Get("after"), 10, 64)
+	if queryBool(r, "first") {
+		place.To = "start"
+	}
+	if place.Before != 0 || place.After != 0 || place.To != "" {
+		op.Place, _ = json.Marshal(place)
+	}
+	return s.change(w, r, p, op)
 }
 
 func (s *Server) updateObject(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
@@ -471,10 +485,39 @@ func (s *Server) zoneMatrix(w http.ResponseWriter, r *http.Request, p *auth.Prin
 	if err != nil {
 		return err
 	}
-	writeJSON(w, http.StatusOK, matrix.Build(st, matrix.Options{Connected: s.connected(st)}))
+	m := matrix.Build(st, matrix.Options{Connected: s.connected(st)})
+	if t, err := s.fw.Table(r.Context()); err == nil {
+		matrixHits(&m, t.Counters)
+	}
+	writeJSON(w, http.StatusOK, m)
 	return nil
 }
 
+// matrixHits fills in the hits of the matrix's rules, built-ins and
+// policies from the counters.
+func matrixHits(m *api.Matrix, counters map[string]nft.Counter) {
+	hits := func(marks []string) *uint64 {
+		var n uint64
+		found := false
+		for _, mk := range marks {
+			if c, ok := counters[mk]; ok {
+				n, found = n+c.Packets, true
+			}
+		}
+		if !found {
+			return nil
+		}
+		return &n
+	}
+	for i := range m.Cells {
+		c := &m.Cells[i]
+		c.Hits = hits(c.Marks)
+		for j := range c.Exceptions {
+			c.Exceptions[j].Hits = hits(c.Exceptions[j].Marks)
+		}
+	}
+}
+
 // connected maps the networks on the firewall's interfaces (link-local
 // and loopback aside) to their zones.
 func (s *Server) connected(st *model.State) map[netip.Prefix]string {
@@ -505,6 +548,10 @@ func (s *Server) ruleset(w http.ResponseWriter, r *http.Request, p *auth.Princip
 		return err
 	}
 	rs := s.fw.Render(st)
+	// In shadow mode: what would be loaded once it is off.
+	if queryBool(r, "enforcing") {
+		rs = s.fw.RenderEnforcing(st)
+	}
 	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 	w.Write([]byte(rs.Text))
 	return nil

internal/server/h_health.go

@@ -19,6 +19,8 @@ type health struct {
 	OK       bool   `json:"ok"`
 	Version  string `json:"version"`
 	Firewall string `json:"firewall"` // applied, unconfigured, fallback, missing
+	// Mode is enforcing, or shadow: the ruleset blocks nothing.
+	Mode string `json:"mode"`
 	// Probation: changes waiting to be confirmed, rolled back otherwise.
 	Probation int `json:"probation"`
 	// Warnings are the codes of the machine's problems (nftables_service).
@@ -49,7 +51,7 @@ func (s *Server) healthz(w http.ResponseWriter, r *http.Request) {
 }
 
 func (s *Server) checkHealth(r *http.Request) health {
-	out := health{Version: version.String(), Warnings: []string{}}
+	out := health{Version: version.String(), Warnings: []string{}, Mode: s.mode()}
 	t, err := s.fw.Table(r.Context())
 	switch {
 	case err != nil && s.eng.State().Empty():
@@ -63,7 +65,12 @@ func (s *Server) checkHealth(r *http.Request) health {
 	}
 	pr := s.probationStatus()
 	out.Probation = len(pr.Pending) + pr.Takeovers
-	for _, p := range s.hostProblems(r.Context(), nil) {
+	// The other tables matter in shadow mode (shadow_unprotected).
+	var ruleset []byte
+	if s.cfg.Shadow {
+		ruleset, _ = s.fw.ListRuleset(r.Context())
+	}
+	for _, p := range s.hostProblems(r.Context(), ruleset) {
 		out.Warnings = append(out.Warnings, p.Code)
 	}
 	return out

internal/server/h_import.go

@@ -53,7 +53,8 @@ func (s *Server) importNft(w http.ResponseWriter, r *http.Request, p *auth.Princ
 	s.afterChange(r.Context(), p, er)
 	if er.Applied {
 		// Until it is taken over, the old table still applies too: the
-		// status warns (takeover_pending).
+		// status warns (takeover_pending; not in shadow mode, where that
+		// is the point).
 		s.store.SetMeta(r.Context(), importedTableKey, res.Table)
 	}
 	out.MutationResponse = api.MutationResponse{Applied: er.Applied, DryRun: er.DryRun, HistoryID: er.HistoryID, Changes: er.Changes, Warnings: er.Warnings}
@@ -117,6 +118,9 @@ func (s *Server) takeover(w http.ResponseWriter, r *http.Request, p *auth.Princi
 	if err := notStaged(r, "a takeover"); err != nil {
 		return err
 	}
+	if err := s.refuseInShadow("delete other tables (the firewall in force)"); err != nil {
+		return err
+	}
 	var in api.TakeoverInput
 	if err := decodeJSON(r, &in); err != nil {
 		return err

internal/server/h_status.go

@@ -27,7 +27,10 @@ func (s *Server) status(w http.ResponseWriter, r *http.Request, p *auth.Principa
 	}
 	st := s.eng.State()
 	out := api.Status{Build: version.Info(), Started: s.started, Problems: s.eng.Problems(), Probation: s.probationStatus(),
-		Interfaces: s.hostInterfaces(st), Counts: map[string]int{}, OtherTables: []string{}}
+		Interfaces: s.hostInterfaces(st), Counts: map[string]int{}, OtherTables: []string{}, Mode: s.mode()}
+	if s.cfg.Shadow {
+		out.ShadowPosition = s.cfg.ShadowPosition
+	}
 	if out.Problems == nil {
 		out.Problems = []validate.Problem{}
 	}
@@ -46,10 +49,11 @@ func (s *Server) status(w http.ResponseWriter, r *http.Request, p *auth.Principa
 	} else {
 		out.Applied = true
 	}
-	if data, err := s.fw.ListRuleset(r.Context()); err == nil {
+	data, err := s.fw.ListRuleset(r.Context())
+	if err == nil {
 		out.OtherTables = otherTables(data)
 	}
-	out.Problems = append(out.Problems, s.hostProblems(r.Context(), out.OtherTables)...)
+	out.Problems = append(out.Problems, s.hostProblems(r.Context(), data)...)
 	out.Problems = append(out.Problems, s.statsProblems()...)
 	writeJSON(w, http.StatusOK, out)
 	return nil
@@ -57,6 +61,20 @@ func (s *Server) status(w http.ResponseWriter, r *http.Request, p *auth.Principa
 
 const importedTableKey = "imported_table"
 
+// shadowProblems are shadow mode's warnings about the machine.
+func (s *Server) shadowProblems(ruleset []byte) []validate.Problem {
+	var out []validate.Problem
+	if ruleset != nil && len(inputFilters(ruleset)) == 0 {
+		out = append(out, validate.Problem{Severity: validate.Warning, Code: "shadow_unprotected", Object: "shadow mode",
+			Message: "housecarld is in shadow mode, where its ruleset blocks nothing, and no other table filters what reaches this machine (none has a filter chain on the input hook): nothing protects it; load your firewall, or leave shadow mode"})
+	}
+	for _, r := range render.ShadowLeftOut(s.eng.State()) {
+		out = append(out, validate.Problem{Severity: validate.Warning, Code: "shadow_raw_left_out", Object: r.Label(),
+			Message: "shadow mode leaves this raw rule out: it does more to packets than accept, drop or reject (NAT, setting a mark or field, a jump, a verdict map…), so its hits aren't counted and later rules see what it would have taken"})
+	}
+	return out
+}
+
 // nftablesUnitLinks are where an enabled nftables.service shows (Debian
 // enables it for sysinit.target).
 var nftablesUnitLinks = []string{
@@ -66,8 +84,15 @@ var nftablesUnitLinks = []string{
 
 // hostProblems are warnings about the machine rather than the
 // configuration: another ruleset that still loads at boot, or the table
-// an import came from, still in force beside Housecarl's.
-func (s *Server) hostProblems(ctx context.Context, others []string) []validate.Problem {
+// an import came from, still in force beside Housecarl's. ruleset is the
+// machine's (nft -j list ruleset; nil: not read). In shadow mode those
+// are expected; the warnings are that nothing else filters, and the raw
+// rules left out.
+func (s *Server) hostProblems(ctx context.Context, ruleset []byte) []validate.Problem {
+	if s.cfg.Shadow {
+		return s.shadowProblems(ruleset)
+	}
+	others := otherTables(ruleset)
 	var out []validate.Problem
 	for _, link := range s.unitLinks {
 		if _, err := os.Lstat(link); err == nil {
@@ -300,6 +325,7 @@ func (l *logRing) Latest(n int, after time.Time, keep func(api.LogEntry) bool) [
 // LogPacket records a packet the firewall logged (internal/nflog calls
 // it).
 func (s *Server) LogPacket(e api.LogEntry) {
+	e.Shadow = s.cfg.Shadow
 	s.logs.Add(e)
 	if s.stats != nil {
 		s.stats.Packet(e)

internal/server/h_traffic.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"net/netip"
 	"sort"
 	"strconv"
 	"strings"
@@ -88,12 +89,92 @@ func (s *Server) listConnections(w http.ResponseWriter, r *http.Request, p *auth
 	return nil
 }
 
+// lookupNames finds the names of the inside addresses asked about
+// (docs/configuration.md#names), waiting at most a second for lookups.
+func (s *Server) lookupNames(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
+	if err := require(p, auth.ResLog, false); err != nil {
+		return err
+	}
+	var in api.NamesInput
+	if err := decodeJSON(r, &in); err != nil {
+		return err
+	}
+	if len(in.Addresses) > maxNames {
+		return badRequest("ask for at most %d addresses at once", maxNames)
+	}
+	out := api.Names{Enabled: s.cfg.Names != nil, Names: map[string]string{}}
+	if s.cfg.Names == nil {
+		writeJSON(w, http.StatusOK, out)
+		return nil
+	}
+	inside := s.insideNetworks(s.eng.State())
+	asked := map[netip.Addr][]string{}
+	var addrs []netip.Addr
+	for _, a := range in.Addresses {
+		ad, err := netip.ParseAddr(a)
+		if err != nil || !inside(ad.Unmap()) {
+			continue
+		}
+		ad = ad.Unmap()
+		if _, ok := asked[ad]; !ok {
+			addrs = append(addrs, ad)
+		}
+		asked[ad] = append(asked[ad], a)
+	}
+	for a, n := range s.cfg.Names.Names(r.Context(), addrs, time.Second) {
+		for _, as := range asked[a] {
+			out.Names[as] = n
+		}
+	}
+	writeJSON(w, http.StatusOK, out)
+	return nil
+}
+
+// maxNames is the most addresses one POST /names may ask about.
+const maxNames = 2000
+
+// insideNetworks tells inside addresses: in a network connected to an
+// inside zone's interface, or private and not in an external zone's.
+func (s *Server) insideNetworks(st *model.State) func(netip.Addr) bool {
+	external := map[string]bool{}
+	for _, z := range st.Zones {
+		external[z.Name] = z.External
+	}
+	var in, out []netip.Prefix
+	for p, zone := range s.connected(st) {
+		if external[zone] {
+			out = append(out, p)
+		} else {
+			in = append(in, p)
+		}
+	}
+	return func(a netip.Addr) bool {
+		if a.IsLoopback() || a.IsUnspecified() || a.IsMulticast() || a.IsLinkLocalUnicast() {
+			return false
+		}
+		for _, p := range in {
+			if p.Contains(a) {
+				return true
+			}
+		}
+		for _, p := range out {
+			if p.Contains(a) {
+				return false
+			}
+		}
+		return a.IsPrivate()
+	}
+}
+
 // closeConnections deletes tracking entries: the rules check those
 // connections again with their next packet.
 func (s *Server) closeConnections(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
 	if err := require(p, auth.ResConfig, true); err != nil {
 		return err
 	}
+	if err := s.refuseInShadow("close connections"); err != nil {
+		return err
+	}
 	ct, err := s.conntrack()
 	if err != nil {
 		return err
@@ -227,6 +308,12 @@ func (s *Server) traceStatus() api.TraceStatus {
 			p.Steps[j].Label = markLabel(st, p.Steps[j])
 		}
 		p.DecidedBy.Label = markLabel(st, p.DecidedBy)
+		if p.WouldDrop != nil {
+			// A copy: the tracer still holds the step.
+			wd := *p.WouldDrop
+			wd.Label = markLabel(st, wd)
+			p.WouldDrop = &wd
+		}
 	}
 	return out
 }

internal/server/ops.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net/http"
 	"sort"
+	"strconv"
 	"strings"
 
 	"housecarl/internal/api"
@@ -63,7 +64,16 @@ func createOp(st *model.State, op *model.Op) (int64, error) {
 		*pos = lastPosition(st, op.Kind, chainOf(o))
 	}
 	data, _ := json.Marshal(o)
-	return op.ID, st.Put(op.Kind, op.ID, data)
+	if err := st.Put(op.Kind, op.ID, data); err != nil {
+		return 0, err
+	}
+	// Placed in the same change, so it is never in force anywhere else.
+	if len(op.Place) > 0 {
+		if _, err := moveOp(st, &model.Op{Op: model.OpMove, Kind: op.Kind, Ref: strconv.FormatInt(op.ID, 10), Data: op.Place}); err != nil {
+			return 0, err
+		}
+	}
+	return op.ID, nil
 }
 
 func updateOp(st *model.State, op *model.Op) (int64, error) {

internal/server/probation.go

@@ -81,7 +81,8 @@ func (s *Server) startProbation(ctx context.Context, p *auth.Principal, historyI
 	pr := &s.probation
 	pr.mu.Lock()
 	defer pr.mu.Unlock()
-	if p.Method == "socket" && len(pr.pending) == 0 && len(pr.restores) == 0 {
+	// In shadow mode a change can't cut anyone off: it blocks nothing.
+	if s.cfg.Shadow || p.Method == "socket" && len(pr.pending) == 0 && len(pr.restores) == 0 {
 		s.saveBoot()
 		return
 	}

internal/server/quota.go

@@ -4,8 +4,11 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"math"
 	"net/http"
+	"net/netip"
 	"sort"
+	"strings"
 	"time"
 
 	"housecarl/internal/api"
@@ -237,7 +240,8 @@ func (s *Server) listQuotas(w http.ResponseWriter, r *http.Request, p *auth.Prin
 	return nil
 }
 
-// resetQuota starts a rule's quota again now.
+// resetQuota starts a rule's quota again now: all of it, or one
+// address's; or gives some of what it used back, until its next reset.
 func (s *Server) resetQuota(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
 	if err := require(p, auth.ResConfig, true); err != nil {
 		return err
@@ -250,14 +254,103 @@ func (s *Server) resetQuota(w http.ResponseWriter, r *http.Request, p *auth.Prin
 	if rule.Quota == nil {
 		return badRequest("%s has no quota", rule.Label())
 	}
-	if err := s.fw.ResetQuota(r.Context(), rule.ID, rule.Quota.PerAddress() != ""); err != nil {
+	var in api.QuotaReset
+	if err := decodeOptional(r, &in); err != nil {
 		return err
 	}
-	resets := s.quotaResets(r.Context())
-	resets[fmt.Sprintf("r%d", rule.ID)] = s.nowFn()
-	s.saveQuotaResets(r.Context(), resets)
-	s.forgetQuotaUsage(r.Context(), rule.ID)
-	s.eng.Audit(r.Context(), p, "quota.reset", rule.Label(), "success", "")
-	writeJSON(w, http.StatusOK, map[string]any{"reset": rule.Label()})
+	if in.Give < 0 {
+		return badRequest("give a number of bytes to give back, 1 or more")
+	}
+	if in.Address == "" && in.Give == 0 {
+		if err := s.fw.ResetQuota(r.Context(), rule.ID, rule.Quota.PerAddress() != ""); err != nil {
+			return err
+		}
+		resets := s.quotaResets(r.Context())
+		resets[fmt.Sprintf("r%d", rule.ID)] = s.nowFn()
+		s.saveQuotaResets(r.Context(), resets)
+		s.forgetQuotaUsage(r.Context(), rule.ID)
+		s.eng.Audit(r.Context(), p, "quota.reset", rule.Label(), "success", "")
+		writeJSON(w, http.StatusOK, map[string]any{"reset": rule.Label()})
+		return nil
+	}
+	name := render.QuotaName(rule.ID)
+	adj := nft.QuotaAdjust{Name: name, Give: in.Give}
+	if in.Address != "" {
+		if rule.Quota.PerAddress() == "" {
+			return badRequest("%s has one quota for everything it matches, not one per address: leave out the address", rule.Label())
+		}
+		key, err := quotaKey(rule, in.Address)
+		if err != nil {
+			return err
+		}
+		if !s.quotaHas(r.Context(), name, key) {
+			return notFound("%s hasn't used the quota of %s since its last reset", in.Address, rule.Label())
+		}
+		adj.Addr = key
+	}
+	if adj.Give == 0 {
+		adj.Give = math.MaxInt64 // all of it: the address starts again
+	}
+	// The next apply writes the quota's new usage into the ruleset.
+	s.fw.AdjustQuota(adj)
+	if err := s.eng.ApplyCurrent(r.Context()); err != nil {
+		return fmt.Errorf("putting the ruleset in force with the quota's new usage: %w", err)
+	}
+	s.SaveQuotaUsage(r.Context())
+	detail, out := "", map[string]any{}
+	if in.Give > 0 {
+		detail = fmt.Sprintf("gave back %d bytes", in.Give)
+		out["given"] = in.Give
+	}
+	if in.Address != "" {
+		detail = strings.TrimSpace(detail + " " + in.Address)
+		out["address"] = in.Address
+	}
+	action := "quota.reset"
+	if in.Give > 0 {
+		action = "quota.give"
+	}
+	s.eng.Audit(r.Context(), p, action, rule.Label(), "success", detail)
+	out["reset"] = rule.Label()
+	writeJSON(w, http.StatusOK, out)
 	return nil
 }
+
+// quotaKey is the entry of a per-address quota an address counts under:
+// the address, or its group's first address (10.0.10.0 for a /24; an
+// IPv6 address's /64).
+func quotaKey(rule *model.Rule, s string) (string, error) {
+	var a netip.Addr
+	if p, err := netip.ParsePrefix(s); err == nil {
+		a = p.Addr()
+	} else if a, err = netip.ParseAddr(s); err != nil {
+		return "", badRequest("%q isn't an address", s)
+	}
+	a = a.Unmap()
+	v4, v6 := rule.Groups()
+	bits := v4
+	if a.Is6() {
+		bits = v6
+	}
+	p, err := a.Prefix(bits)
+	if err != nil {
+		return "", badRequest("%q: %v", s, err)
+	}
+	return p.Addr().String(), nil
+}
+
+// quotaHas reports whether a per-address quota has an entry for key.
+func (s *Server) quotaHas(ctx context.Context, name, key string) bool {
+	t, err := s.fw.Table(ctx)
+	if err != nil {
+		return false
+	}
+	for _, set := range []string{name + "_v4", name + "_v6"} {
+		for _, e := range t.QuotaSets[set] {
+			if e.Addr == key {
+				return true
+			}
+		}
+	}
+	return false
+}

internal/server/routes.go

@@ -41,6 +41,7 @@ func (s *Server) routes() {
 	m.HandleFunc("GET "+p+"/quotas", s.authed(s.listQuotas))
 	m.HandleFunc("GET "+p+"/connections", s.authed(s.listConnections))
 	m.HandleFunc("POST "+p+"/connections/close", s.authed(s.closeConnections))
+	m.HandleFunc("POST "+p+"/names", s.authed(s.lookupNames))
 	m.HandleFunc("GET "+p+"/trace", s.authed(s.getTrace))
 	m.HandleFunc("POST "+p+"/trace", s.authed(s.startTrace))
 	m.HandleFunc("DELETE "+p+"/trace", s.authed(s.stopTrace))

internal/server/routes_cfg.go

@@ -8,6 +8,29 @@ import (
 
 // otherTables lists the tables in an `nft -j list ruleset` other than
 // Housecarl's ("inet main").
+// inputFilters lists the tables other than Housecarl's with a filter
+// chain on the input hook: what filters the machine in shadow mode.
+func inputFilters(data []byte) []string {
+	var doc struct {
+		Nftables []map[string]json.RawMessage `json:"nftables"`
+	}
+	out := []string{}
+	if json.Unmarshal(data, &doc) != nil {
+		return out
+	}
+	for _, item := range doc.Nftables {
+		raw, ok := item["chain"]
+		if !ok {
+			continue
+		}
+		var c struct{ Family, Table, Type, Hook string }
+		if json.Unmarshal(raw, &c) == nil && c.Type == "filter" && c.Hook == "input" && !(c.Family == "inet" && (c.Table == "housecarl" || c.Table == trace.Table)) {
+			out = append(out, c.Family+" "+c.Table)
+		}
+	}
+	return out
+}
+
 func otherTables(data []byte) []string {
 	var doc struct {
 		Nftables []map[string]json.RawMessage `json:"nftables"`

internal/server/server.go

@@ -18,10 +18,12 @@ import (
 	"syscall"
 	"time"
 
+	"housecarl/internal/api"
 	"housecarl/internal/auth"
 	"housecarl/internal/certs"
 	"housecarl/internal/engine"
 	"housecarl/internal/model"
+	"housecarl/internal/names"
 	"housecarl/internal/nft"
 	"housecarl/internal/render"
 	"housecarl/internal/stats"
@@ -45,6 +47,13 @@ type Config struct {
 	// ACME keeps the certificate housecarld obtains itself (tls.acme; nil
 	// when off).
 	ACME *certs.Manager
+	// Shadow is shadow mode (docs/shadow.md): nothing goes on probation,
+	// takeovers and closing connections are refused. ShadowPosition is
+	// after or before, for the status.
+	Shadow         bool
+	ShadowPosition string
+	// Names looks up inside addresses' names (nil: names are off).
+	Names *names.Resolver
 }
 
 // Interfaces lists the host's interfaces with their addresses, and
@@ -58,6 +67,8 @@ type Interfaces interface {
 // engine (internal/nft.Firewall).
 type Firewall interface {
 	Render(st *model.State) *render.Ruleset
+	// RenderEnforcing is the ruleset outside shadow mode.
+	RenderEnforcing(st *model.State) *render.Ruleset
 	Table(ctx context.Context) (*nft.Table, error)
 	AddElement(ctx context.Context, set, addr string, timeout int) error
 	DeleteElement(ctx context.Context, set, addr string) error
@@ -68,6 +79,8 @@ type Firewall interface {
 	SaveBoot(st *model.State) error
 	// ResetQuota starts a rule's quota again (perAddress: its sets).
 	ResetQuota(ctx context.Context, ruleID int64, perAddress bool) error
+	// AdjustQuota has the next apply change what a quota used.
+	AdjustQuota(a nft.QuotaAdjust)
 	// Trace follows packets (internal/trace) until ctx ends.
 	Trace(ctx context.Context, script string, line func(string)) error
 }
@@ -131,6 +144,22 @@ func New(cfg Config, eng *engine.Engine, fw Firewall, ifaces Interfaces, log *sl
 	return s
 }
 
+// mode is housecarld's mode: enforcing, or shadow.
+func (s *Server) mode() string {
+	if s.cfg.Shadow {
+		return api.ModeShadow
+	}
+	return api.ModeEnforcing
+}
+
+// refuseInShadow refuses what would change traffic in shadow mode.
+func (s *Server) refuseInShadow(what string) error {
+	if !s.cfg.Shadow {
+		return nil
+	}
+	return conflict("housecarld is in shadow mode, where it changes nothing about traffic, so it doesn't %s; leave shadow mode first (shadow.enabled in housecarl.yaml, docs/shadow.md)", what)
+}
+
 // Handler returns the HTTP handler with all middleware.
 func (s *Server) Handler() http.Handler {
 	return s.recoverer(s.securityHeaders(s.logRequests(s.mux)))

internal/server/server_test.go

@@ -7,11 +7,13 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"math"
 	"net/http"
 	"net/http/cookiejar"
 	"net/http/httptest"
 	"net/netip"
 	"os"
+	"reflect"
 	"strings"
 	"sync"
 	"testing"
@@ -21,6 +23,7 @@ import (
 	"housecarl/internal/auth"
 	"housecarl/internal/engine"
 	"housecarl/internal/model"
+	"housecarl/internal/names"
 	"housecarl/internal/nft"
 	"housecarl/internal/render"
 	"housecarl/internal/stats"
@@ -41,6 +44,10 @@ type fakeFW struct {
 	traced     string
 	traceLines []string
 	fallback   bool // the boot fallback is in force
+	shadow     bool
+	ruleset    string // nft -j list ruleset ("": a default)
+	quotas     nft.QuotaUsage
+	adjusted   []nft.QuotaAdjust
 }
 
 func (f *fakeFW) Check(_ context.Context, st *model.State) error { return nil }
@@ -58,14 +65,24 @@ func (f *fakeFW) last() *model.State {
 	defer f.mu.Unlock()
 	return f.applied[len(f.applied)-1]
 }
-func (f *fakeFW) Render(st *model.State) *render.Ruleset { return render.Render(st, render.Options{}) }
+func (f *fakeFW) Render(st *model.State) *render.Ruleset {
+	return render.Render(st, render.Options{Shadow: f.shadow})
+}
+func (f *fakeFW) RenderEnforcing(st *model.State) *render.Ruleset {
+	return render.Render(st, render.Options{})
+}
 func (f *fakeFW) Table(context.Context) (*nft.Table, error) {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 	if len(f.applied) == 0 {
 		return nil, errors.New("No such file or directory: list table inet housecarl")
 	}
-	return &nft.Table{Counters: map[string]nft.Counter{"r1": {Packets: 3, Bytes: 180}}, Elements: f.elements, Fallback: f.fallback}, nil
+	return &nft.Table{Counters: map[string]nft.Counter{"r1": {Packets: 3, Bytes: 180}}, Elements: f.elements, Fallback: f.fallback, QuotaUsage: f.quotas}, nil
+}
+func (f *fakeFW) AdjustQuota(a nft.QuotaAdjust) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.adjusted = append(f.adjusted, a)
 }
 func (f *fakeFW) AddElement(_ context.Context, set, addr string, timeout int) error {
 	f.mu.Lock()
@@ -86,6 +103,9 @@ func (f *fakeFW) DeleteElement(_ context.Context, set, addr string) error {
 	return nil
 }
 func (f *fakeFW) ListRuleset(context.Context) ([]byte, error) {
+	if f.ruleset != "" {
+		return []byte(f.ruleset), nil
+	}
 	return []byte(`{"nftables":[{"table":{"family":"inet","name":"main"}},{"table":{"family":"inet","name":"housecarl"}}]}`), nil
 }
 func (f *fakeFW) DeleteTable(_ context.Context, fam, name string) error {
@@ -142,6 +162,11 @@ type env struct {
 }
 
 func newEnv(t *testing.T) *env {
+	t.Helper()
+	return newEnvWith(t, Config{})
+}
+
+func newEnvWith(t *testing.T, cfg Config) *env {
 	t.Helper()
 	ctx := context.Background()
 	st, err := store.Open(":memory:")
@@ -159,10 +184,10 @@ func newEnv(t *testing.T) *env {
 	if err != nil {
 		t.Fatal(err)
 	}
-	fw := &fakeFW{elements: map[string][]render.Element{}}
+	fw := &fakeFW{elements: map[string][]render.Element{}, shadow: cfg.Shadow}
 	eng.Firewall = fw
 	ifs := hostIfaces{"wan": {netip.MustParsePrefix("217.155.8.194/32")}, "eth1": {netip.MustParsePrefix("10.0.10.1/24")}}
-	srv := New(Config{}, eng, fw, ifs, nil, nil)
+	srv := New(cfg, eng, fw, ifs, nil, nil)
 	ts := httptest.NewServer(srv.Handler())
 	t.Cleanup(ts.Close)
 	return &env{t: t, ts: ts, srv: srv, eng: eng, fw: fw, token: tok}
@@ -733,9 +758,38 @@ func TestQuotaResets(t *testing.T) {
 	if len(qs) != 1 || qs[0].NextReset == nil || qs[0].NextReset.Day() != 21 {
 		t.Errorf("quotas %+v", qs)
 	}
-	if code := e.call(e.token, "POST", "/rules/"+itoa(created.ID)+"/reset-quota", nil, nil); code != 200 || len(e.fw.resets) != 2 {
+	reset := "/rules/" + itoa(created.ID) + "/reset-quota"
+	if code := e.call(e.token, "POST", reset, nil, nil); code != 200 || len(e.fw.resets) != 2 {
 		t.Errorf("reset by hand: %d %v", code, e.fw.resets)
 	}
+
+	// One address started again, or some given back: the next apply
+	// (made at once) writes the new usage.
+	name := render.QuotaName(created.ID)
+	e.fw.quotas = nft.QuotaUsage{QuotaSets: map[string][]render.Element{name + "_v4": {{Addr: "10.0.10.23", Used: 6 << 30}},
+		name + "_v6": {{Addr: "2001:db8:1:2::", Used: 1 << 30}}}}
+	applies := len(e.fw.applied)
+	if code := e.call(e.token, "POST", reset, api.QuotaReset{Address: "10.0.10.23"}, nil); code != 200 {
+		t.Errorf("reset one address: %d", code)
+	}
+	if code := e.call(e.token, "POST", reset, api.QuotaReset{Address: "2001:db8:1:2:aaaa::7", Give: 2 << 30}, nil); code != 200 {
+		t.Errorf("give back to an IPv6 address (its /64): %d", code)
+	}
+	if code := e.call(e.token, "POST", reset, api.QuotaReset{Give: 1 << 30}, nil); code != 200 {
+		t.Errorf("give back to everyone: %d", code)
+	}
+	want3 := []nft.QuotaAdjust{{Name: name, Addr: "10.0.10.23", Give: math.MaxInt64}, {Name: name, Addr: "2001:db8:1:2::", Give: 2 << 30}, {Name: name, Give: 1 << 30}}
+	if !reflect.DeepEqual(e.fw.adjusted, want3) || len(e.fw.applied) != applies+3 || len(e.fw.resets) != 2 {
+		t.Errorf("adjusted %+v, applied %d more, resets %v", e.fw.adjusted, len(e.fw.applied)-applies, e.fw.resets)
+	}
+	for _, c := range []struct {
+		in   api.QuotaReset
+		code int
+	}{{api.QuotaReset{Address: "10.0.10.99"}, 404}, {api.QuotaReset{Address: "nonsense"}, 400}, {api.QuotaReset{Give: -5}, 400}} {
+		if code := e.call(e.token, "POST", reset, c.in, nil); code != c.code {
+			t.Errorf("%+v: %d, want %d", c.in, code, c.code)
+		}
+	}
 }
 
 // TestAutoConfirm: the client that made a change confirms it by itself:
@@ -876,6 +930,13 @@ func TestMatrixEndpoint(t *testing.T) {
 	if c := cell("lan", "wan"); c.Verdict != "allowed" {
 		t.Errorf("lan → wan with the changeset: %+v", c)
 	}
+	// Hits: summed over an object's counters; none without a counter.
+	hm := api.Matrix{Cells: []api.MatrixCell{{Marks: []string{"p-forward"}, Exceptions: []api.MatrixException{
+		{Marks: []string{"b-antispoof", "b-antispoof6"}}, {Marks: []string{"r9"}}}}}}
+	matrixHits(&hm, map[string]nft.Counter{"p-forward": {Packets: 4}, "b-antispoof": {Packets: 2}, "b-antispoof6": {Packets: 3}})
+	if c := hm.Cells[0]; c.Hits == nil || *c.Hits != 4 || c.Exceptions[0].Hits == nil || *c.Exceptions[0].Hits != 5 || c.Exceptions[1].Hits != nil {
+		t.Errorf("hits: %+v", c)
+	}
 }
 
 // TestHostProblems: an enabled nftables.service, and an imported table
@@ -960,6 +1021,41 @@ func TestConnections(t *testing.T) {
 	}
 }
 
+// TestNames: names only for inside addresses (an inside zone's network,
+// or private outside the external zones'), under the address as asked.
+func TestNames(t *testing.T) {
+	var asked []string
+	var mu sync.Mutex
+	e := newEnvWith(t, Config{Names: names.NewFunc(func(_ context.Context, a string) ([]string, error) {
+		mu.Lock()
+		asked = append(asked, a)
+		mu.Unlock()
+		return []string{"host-" + strings.ReplaceAll(a, ".", "-") + ".example.net."}, nil
+	}, time.Hour)})
+	e.call(e.token, "POST", "/zones", model.Zone{Name: "wan", Interfaces: []string{"wan"}, External: true}, nil)
+	e.call(e.token, "POST", "/zones", model.Zone{Name: "lan", Interfaces: []string{"eth1"}}, nil)
+	var out api.Names
+	e.call(e.token, "POST", "/names", api.NamesInput{Addresses: []string{"10.0.10.5", "::ffff:10.0.10.5", "192.168.7.7", "217.155.8.194", "8.8.8.8", "fe80::1", "nonsense"}}, &out)
+	want := map[string]string{"10.0.10.5": "host-10-0-10-5.example.net", "::ffff:10.0.10.5": "host-10-0-10-5.example.net", "192.168.7.7": "host-192-168-7-7.example.net"}
+	if !out.Enabled || !reflect.DeepEqual(out.Names, want) {
+		t.Errorf("names: %+v", out)
+	}
+	if len(asked) != 2 {
+		t.Errorf("looked up %v, want the two inside addresses once each", asked)
+	}
+	var tok api.Token
+	e.call(e.token, "POST", "/me/tokens", api.TokenInput{Name: "monitor", Role: "log"}, &tok)
+	var one, none api.Names
+	if code := e.call(tok.Secret, "POST", "/names", api.NamesInput{Addresses: []string{"10.0.10.5"}}, &one); code != 200 || len(one.Names) != 1 {
+		t.Errorf("with log:read: %d %+v", code, one)
+	}
+	off := newEnv(t)
+	off.call(off.token, "POST", "/names", api.NamesInput{Addresses: []string{"10.0.10.5"}}, &none)
+	if none.Enabled || len(none.Names) != 0 {
+		t.Errorf("names off: %+v", none)
+	}
+}
+
 // TestTrace: a trace runs with the filter's table, collects packets named
 // after Housecarl's objects, and stops when asked; one at a time.
 func TestTrace(t *testing.T) {
@@ -1060,3 +1156,151 @@ func TestStatsEndpoints(t *testing.T) {
 		}
 	}
 }
+
+// TestShadowMode: in shadow mode changes aren't on probation, what would
+// change traffic is refused, and the status, health and log say so.
+func TestShadowMode(t *testing.T) {
+	e := newEnvWith(t, Config{Shadow: true, ShadowPosition: "after"})
+	e.srv.SetConntrack(&fakeConns{})
+	link := t.TempDir() + "/nftables.service"
+	os.Symlink("/usr/lib/systemd/system/nftables.service", link)
+	e.srv.unitLinks = []string{link}
+	e.srv.store.SetMeta(context.Background(), importedTableKey, "inet main")
+	var mr api.MutationResponse
+	if code := e.call(e.token, "POST", "/zones", model.Zone{Name: "wan", Interfaces: []string{"wan"}, External: true}, &mr); code != 201 || mr.ConfirmToken != "" || mr.ConfirmBy != nil {
+		t.Errorf("a change: %d %+v", code, mr)
+	}
+	var pr api.Probation
+	e.call(e.token, "GET", "/probation", nil, &pr)
+	if len(pr.Pending) != 0 || e.fw.boot == nil {
+		t.Errorf("on probation in shadow mode: %+v (saved for the boot: %v)", pr, e.fw.boot != nil)
+	}
+	var er api.ErrorBody
+	if code := e.call(e.token, "POST", "/takeover", api.TakeoverInput{Tables: []string{"inet main"}}, &er); code != 409 || !strings.Contains(er.Error.Message, "shadow mode") || len(e.fw.deleted) != 0 {
+		t.Errorf("takeover: %d %+v %v", code, er, e.fw.deleted)
+	}
+	if code := e.call(e.token, "POST", "/connections/close", api.CloseConnections{Search: "tcp"}, &er); code != 409 {
+		t.Errorf("closing connections: %d", code)
+	}
+	if code := e.call(e.token, "POST", "/rules", model.Rule{Chain: model.ChainInput, Raw: "meta mark set 1"}, &er); code != 201 {
+		t.Fatalf("a raw rule: %d %+v", code, er)
+	}
+	var st api.Status
+	e.call(e.token, "GET", "/status", nil, &st)
+	var codes []string
+	for _, p := range st.Problems {
+		codes = append(codes, p.Code)
+	}
+	c := strings.Join(codes, " ")
+	if st.Mode != api.ModeShadow || st.ShadowPosition != "after" {
+		t.Errorf("status mode: %q %q", st.Mode, st.ShadowPosition)
+	}
+	// Expected in shadow mode: the other firewall, and its service.
+	if strings.Contains(c, "nftables_service") || strings.Contains(c, "takeover_pending") || !strings.Contains(c, "shadow_unprotected") || !strings.Contains(c, "shadow_raw_left_out") {
+		t.Errorf("warnings: %s", c)
+	}
+	e.fw.ruleset = `{"nftables":[{"chain":{"family":"inet","table":"main","name":"input","type":"filter","hook":"input","prio":0,"policy":"drop"}}]}`
+	e.call(e.token, "GET", "/status", nil, &st)
+	for _, p := range st.Problems {
+		if p.Code == "shadow_unprotected" {
+			t.Error("unprotected while inet main filters")
+		}
+	}
+	var h health
+	resp, err := http.Get(e.ts.URL + "/healthz")
+	if err != nil {
+		t.Fatal(err)
+	}
+	json.NewDecoder(resp.Body).Decode(&h)
+	resp.Body.Close()
+	if h.Mode != api.ModeShadow || !h.OK {
+		t.Errorf("healthz: %+v", h)
+	}
+	var who api.Whoami
+	e.call(e.token, "GET", "/auth/whoami", nil, &who)
+	if who.Mode != api.ModeShadow {
+		t.Errorf("whoami: %+v", who)
+	}
+	e.srv.LogPacket(api.LogEntry{Time: time.Now(), Prefix: "hc input policy drop: ", Verdict: "drop"})
+	var logs []api.LogEntry
+	e.call(e.token, "GET", "/log", nil, &logs)
+	if len(logs) != 1 || !logs[0].Shadow {
+		t.Errorf("log: %+v", logs)
+	}
+	shadow := e.text("/ruleset")
+	enforcing := e.text("/ruleset?enforcing=1")
+	if !strings.Contains(shadow, "Shadow mode") || strings.Contains(enforcing, "Shadow mode") {
+		t.Errorf("rulesets:\n%s\n---\n%s", shadow, enforcing)
+	}
+	// Enforcing, the same change goes on probation.
+	n := newEnv(t)
+	n.call(n.token, "POST", "/zones", model.Zone{Name: "wan", Interfaces: []string{"wan"}, External: true}, nil)
+	n.call(n.token, "GET", "/probation", nil, &pr)
+	if len(pr.Pending) != 1 {
+		t.Errorf("not on probation enforcing: %+v", pr)
+	}
+	n.call(n.token, "GET", "/status", nil, &st)
+	if st.Mode != api.ModeEnforcing {
+		t.Errorf("enforcing status mode: %q", st.Mode)
+	}
+}
+
+// text GETs a plain-text answer.
+func (e *env) text(path string) string {
+	e.t.Helper()
+	req, _ := http.NewRequest("GET", e.ts.URL+api.Prefix+path, nil)
+	req.Header.Set("Authorization", "Bearer "+e.token)
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		e.t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	b, _ := io.ReadAll(resp.Body)
+	return string(b)
+}
+
+// TestCreatePlaced: a rule created ?before= another is placed in the same
+// change (one history entry), also when staged in a changeset.
+func TestCreatePlaced(t *testing.T) {
+	e := newEnv(t)
+	var a, b, c api.MutationResponse
+	e.call(e.token, "POST", "/rules", model.Rule{Chain: "input", Match: model.Match{Services: []string{"ssh"}}}, &a)
+	e.call(e.token, "POST", "/rules", model.Rule{Chain: "input", Match: model.Match{Services: []string{"dns"}}}, &b)
+	var first model.Rule
+	json.Unmarshal(a.Object, &first)
+	if code := e.call(e.token, "POST", "/rules?before="+itoa(first.ID), model.Rule{Chain: "input", Match: model.Match{Services: []string{"http"}}, Comment: "placed"}, &c); code != 201 {
+		t.Fatalf("create placed: %d %+v", code, c)
+	}
+	order := func() string {
+		var out []string
+		for _, r := range e.eng.State().Rules {
+			out = append(out, strings.Join(r.Services, ""))
+		}
+		return strings.Join(out, ",")
+	}
+	if o := order(); o != "http,ssh,dns" {
+		t.Errorf("order: %s", o)
+	}
+	var hs []model.HistoryEntry
+	e.call(e.token, "GET", "/history", nil, &hs)
+	if len(hs) != 3 || len(hs[0].Changes) != 1 || hs[0].Changes[0].Action() != "create" {
+		t.Errorf("history: %d entries, newest %+v", len(hs), hs[0])
+	}
+	// Staged, the place goes with it.
+	var cs model.Changeset
+	e.call(e.token, "POST", "/changesets", nil, &cs)
+	e.call(e.token, "POST", "/rules?first=1&changeset="+itoa(cs.ID), model.Rule{Chain: "input", Match: model.Match{Services: []string{"ntp"}}}, nil)
+	if code := e.call(e.token, "POST", "/changesets/"+itoa(cs.ID)+"/apply", nil, nil); code != 200 {
+		t.Fatalf("apply: %d", code)
+	}
+	if o := order(); o != "ntp,http,ssh,dns" {
+		t.Errorf("order after the changeset: %s", o)
+	}
+	// A bad place: refused, nothing created.
+	if code := e.call(e.token, "POST", "/rules?before=99999", model.Rule{Chain: "input"}, nil); code != 400 {
+		t.Errorf("before a rule that isn't there: %d", code)
+	}
+	if n := len(e.eng.State().Rules); n != 4 {
+		t.Errorf("%d rules", n)
+	}
+}

internal/stats/collector.go

@@ -402,7 +402,10 @@ func (c *Collector) sample(ctx context.Context, minute int64) map[string]int64 {
 			for set, es := range t.QuotaSets {
 				kind := strings.TrimSuffix(strings.TrimSuffix(set, "_v4"), "_v6")
 				for _, e := range es {
-					addTop(kind, e.Addr, c.table.of(set+"/"+e.Addr, e.Used))
+					d := c.table.of(set+"/"+e.Addr, e.Used)
+					addTop(kind, e.Addr, d)
+					// A per-address quota's series is its addresses' sum.
+					add("quota:"+strings.TrimPrefix(kind, "quota_"), d)
 				}
 			}
 			for set, es := range t.DeviceSets {

internal/stats/collector_test.go

@@ -85,6 +85,10 @@ func TestCollector(t *testing.T) {
 	h.table.Counters["r1"] = nft.Counter{Packets: 10, Bytes: 1000}
 	h.table.Counters["r2"] = nft.Counter{Packets: 100, Bytes: 9000}
 	h.table.Quotas["quota_r5"] = 1 << 20
+	if h.table.QuotaSets == nil {
+		h.table.QuotaSets = map[string][]render.Element{}
+	}
+	h.table.QuotaSets["quota_r6_v4"] = []render.Element{{Addr: "10.0.10.5", Used: 1000}}
 	h.table.DeviceSets["stats_up_v4"] = []render.Element{{Addr: "10.0.10.5", Bytes: 5000}}
 
 	store, err := OpenStore(":memory:")
@@ -104,6 +108,7 @@ func TestCollector(t *testing.T) {
 	h.table.Counters["r1"] = nft.Counter{Packets: 25, Bytes: 2500}
 	h.table.Counters["p-input"] = nft.Counter{Packets: 3, Bytes: 180} // a new counter counts whole
 	h.table.Quotas["quota_r5"] = 3 << 20
+	h.table.QuotaSets["quota_r6_v4"] = []render.Element{{Addr: "10.0.10.5", Used: 2000}, {Addr: "10.0.10.6", Used: 500}} // a new entry counts whole
 	h.table.DeviceSets["stats_up_v4"] = []render.Element{{Addr: "10.0.10.5", Bytes: 8000}}
 	h.table.DeviceSets["stats_down_v6"] = []render.Element{{Addr: "2001:db8:1:2::", Bytes: 70000}}
 	for range 2 {
@@ -142,6 +147,7 @@ func TestCollector(t *testing.T) {
 	check("drop:forward", sum("drop:")["forward"], 15)
 	check("drop:input", sum("drop:")["input"], 3)
 	check("quota:r5", sum("quota:")["r5"], 2<<20)
+	check("quota:r6 (per address: the sum)", sum("quota:")["r6"], 1500)
 
 	s, err := q.Summary(ctx, time.Hour, 10)
 	if err != nil {

internal/tablewatch/tablewatch.go

@@ -0,0 +1,100 @@
+// Package tablewatch tells when an nftables table is deleted: by
+// `nft flush ruleset` (which a ruleset file such as /etc/nftables.conf
+// usually starts with, and which nftables.service runs when it stops), or
+// by hand. It listens to nftables' netlink notifications, as `nft monitor`
+// does, and calls back once they have been quiet for a moment, since a
+// ruleset reload brings many. In shadow mode housecarld then puts its
+// table back (docs/shadow.md).
+package tablewatch
+
+import (
+	"context"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"os"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+// Settle is how long the notifications must be quiet before the callback.
+const Settle = 2 * time.Second
+
+// Watch calls deleted after a table was deleted, until ctx ends. It
+// returns an error only if it can't listen at all.
+func Watch(ctx context.Context, deleted func()) error {
+	fd, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW|unix.SOCK_CLOEXEC|unix.SOCK_NONBLOCK, unix.NETLINK_NETFILTER)
+	if err != nil {
+		return fmt.Errorf("opening a netlink socket: %w", err)
+	}
+	if err := unix.Bind(fd, &unix.SockaddrNetlink{Family: unix.AF_NETLINK, Groups: 1 << (unix.NFNLGRP_NFTABLES - 1)}); err != nil {
+		unix.Close(fd)
+		return fmt.Errorf("listening to nftables' changes: %w", err)
+	}
+	// A non-blocking descriptor goes through Go's poller, so closing the
+	// file ends a Read in progress.
+	f := os.NewFile(uintptr(fd), "nfnetlink")
+	go func() {
+		<-ctx.Done()
+		f.Close()
+	}()
+	events := make(chan struct{}, 1)
+	go func() {
+		buf := make([]byte, 256<<10)
+		for {
+			n, err := f.Read(buf)
+			switch {
+			case err != nil && ctx.Err() != nil:
+				close(events)
+				return
+			case errors.Is(err, unix.ENOBUFS):
+				// Notifications were lost: one may have been a deletion.
+			case err != nil:
+				time.Sleep(time.Second)
+				continue
+			case !DeletesTable(buf[:n]):
+				continue
+			}
+			select {
+			case events <- struct{}{}:
+			default:
+			}
+		}
+	}()
+	var timer <-chan time.Time
+	for {
+		select {
+		case _, ok := <-events:
+			if !ok {
+				return nil
+			}
+			timer = time.After(Settle)
+		case <-timer:
+			timer = nil
+			deleted()
+		}
+	}
+}
+
+// DeletesTable reports whether a netlink datagram holds a table being
+// deleted.
+func DeletesTable(b []byte) bool {
+	want := uint16(unix.NFNL_SUBSYS_NFTABLES<<8 | unix.NFT_MSG_DELTABLE)
+	for len(b) >= unix.NLMSG_HDRLEN {
+		size := int(binary.NativeEndian.Uint32(b[0:4]))
+		typ := binary.NativeEndian.Uint16(b[4:6])
+		if size < unix.NLMSG_HDRLEN || size > len(b) {
+			return false
+		}
+		if typ == want {
+			return true
+		}
+		size = (size + unix.NLMSG_ALIGNTO - 1) &^ (unix.NLMSG_ALIGNTO - 1)
+		if size >= len(b) {
+			return false
+		}
+		b = b[size:]
+	}
+	return false
+}

internal/tablewatch/tablewatch_test.go

@@ -0,0 +1,37 @@
+package tablewatch
+
+import (
+	"encoding/binary"
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+// msg is a netlink message of a type, with a few bytes of payload.
+func msg(typ uint16) []byte {
+	b := make([]byte, unix.NLMSG_HDRLEN+4)
+	binary.NativeEndian.PutUint32(b[0:4], uint32(len(b)))
+	binary.NativeEndian.PutUint16(b[4:6], typ)
+	return b
+}
+
+func TestDeletesTable(t *testing.T) {
+	nft := func(m uint16) uint16 { return unix.NFNL_SUBSYS_NFTABLES<<8 | m }
+	newRule, delTable, delChain := msg(nft(unix.NFT_MSG_NEWRULE)), msg(nft(unix.NFT_MSG_DELTABLE)), msg(nft(unix.NFT_MSG_DELCHAIN))
+	cases := []struct {
+		b    []byte
+		want bool
+	}{
+		{delTable, true},
+		{append(append([]byte{}, newRule...), delTable...), true},
+		{append(append([]byte{}, newRule...), delChain...), false},
+		{newRule, false},
+		{delTable[:10], false},
+		{nil, false},
+	}
+	for i, c := range cases {
+		if got := DeletesTable(c.b); got != c.want {
+			t.Errorf("%d: %v", i, got)
+		}
+	}
+}

internal/trace/trace.go

@@ -194,8 +194,21 @@ func (t *Tracer) Line(line string) {
 	}
 }
 
-// decide notes a packet's fate: the first drop (or reject) ends it.
+// wouldRe finds shadow mode's marker in a rule's comment (render.Would):
+// "[would drop]", "[would reject]".
+var wouldRe = regexp.MustCompile(`"hc:\S+ \[would (drop|reject)\]|"\[would (drop|reject)\]`)
+
+// decide notes a packet's fate: the first drop (or reject) ends it. In
+// shadow mode Housecarl's rules accept what they would drop: that is
+// noted apart, and decides nothing.
 func decide(p *api.TracePacket, s api.TraceStep) {
+	if s.Kind == "rule" && wouldRe.MatchString(s.Rule) {
+		if p.WouldDrop == nil && p.Verdict != "dropped" {
+			step := s
+			p.WouldDrop = &step
+		}
+		return
+	}
 	if p.Verdict == "dropped" {
 		return
 	}

internal/trace/trace_test.go

@@ -87,3 +87,34 @@ func TestScript(t *testing.T) {
 		t.Error("ICMP with a port")
 	}
 }
+
+// In shadow mode Housecarl's rules accept what they would drop: the
+// packet's fate is the other table's, and the would-be drop is noted.
+func TestShadowTrace(t *testing.T) {
+	var tr Tracer
+	for _, l := range strings.Split(`trace id 9 ip main input packet: iif "wan" ip saddr 198.51.100.7 ip daddr 203.0.113.10 tcp sport 4000 tcp dport 9999 tcp flags == syn
+trace id 9 ip main input rule tcp dport 9999 accept (verdict accept)
+trace id 9 inet housecarl input rule tcp dport 9999 counter packets 1 bytes 60 accept comment "hc:r12 [would drop] block 9999" (verdict accept)
+trace id 10 ip main input packet: iif "wan" ip saddr 198.51.100.7 ip daddr 203.0.113.10 tcp sport 4001 tcp dport 7000 tcp flags == syn
+trace id 10 ip main input rule tcp dport 7000 accept (verdict accept)
+trace id 10 inet housecarl input rule counter packets 1 bytes 60 comment "hc:p-input [would drop]" (verdict continue)
+trace id 10 inet housecarl input policy accept
+trace id 11 ip main input packet: iif "wan" ip saddr 198.51.100.7 ip daddr 203.0.113.10 tcp sport 4002 tcp dport 22 tcp flags == syn
+trace id 11 ip main input rule tcp dport 22 accept (verdict accept)
+trace id 11 inet housecarl input rule tcp dport 22 counter packets 1 bytes 60 accept comment "hc:r3 ssh" (verdict accept)`, "\n") {
+		tr.Line(l)
+	}
+	ps := tr.Packets()
+	if len(ps) != 3 {
+		t.Fatalf("packets: %+v", ps)
+	}
+	if p := ps[0]; p.Verdict != "accepted" || p.WouldDrop == nil || p.WouldDrop.Mark != "r12" || p.DecidedBy.Table != "ip main" {
+		t.Errorf("first: %+v", p)
+	}
+	if p := ps[1]; p.Verdict != "accepted" || p.WouldDrop == nil || p.WouldDrop.Mark != "p-input" {
+		t.Errorf("second: %+v", p)
+	}
+	if p := ps[2]; p.WouldDrop != nil || p.DecidedBy.Mark != "r3" {
+		t.Errorf("third: %+v", p)
+	}
+}

internal/web/static/assets/app.js

@@ -134,7 +134,11 @@ function layout() {
         me.admin ? h("a", { href: "#/users" }, "Users") : null,
         h("button", { type: "button", class: "menu-item", onclick: logout }, "Log out"),
       ], { right: true, active: ["account", "users"].includes(current.nav), label: "Account menu" })));
-  mount(app, h("div", { class: "shell" }, header, barEl, bannerEl, mainEl, footer(me.build)));
+  // Shadow mode (housecarl.yaml): say so on every page.
+  const shadow = me.mode === "shadow" ? h("div", { class: "probation-banner shadow-banner", role: "status" },
+    h("strong", null, "Shadow mode:"), " Housecarl's ruleset is loaded but blocks, rejects and translates nothing; the other firewall decides. ",
+    "What its counters, log, tracer and statistics call drops are what Housecarl would drop. Changes aren't on probation.") : null;
+  mount(app, h("div", { class: "shell" }, header, shadow, barEl, bannerEl, mainEl, footer(me.build)));
   renderNav();
   refreshProbation();
 }

internal/web/static/assets/charts.js

@@ -331,7 +331,7 @@ export function heatmapTable(hm, unit) {
 // so the list is its own table view.
 // extra(key), when given, adds something after an entry's label (e.g. a
 // link that excludes it).
-export function barList(entries, { total, label = (k) => k, empty = "No data yet.", href, extra, format = compact } = {}) {
+export function barList(entries, { total, label = (k) => k, empty = "No data yet.", href, extra, format = compact, share: showShare = true } = {}) {
   if (!entries.length) return h("div", { class: "empty" }, empty);
   // Entries may be in a natural order (e.g. latency buckets), not by size.
   const peak = Math.max(1, ...entries.map((e) => e.count));
@@ -345,7 +345,7 @@ export function barList(entries, { total, label = (k) => k, empty = "No data yet
     return h("li", { title: (e.name ? e.name + " (" + name + ")" : name) + ": " + format(e.count) + " (" + share.toFixed(1) + "%)" },
       h("div", { class: "bar-text" },
         link ? h("a", { href: link, class: "bar-label" }, shown) : h("span", { class: "bar-label" }, shown),
-        h("span", { class: "bar-value" }, extra ? [extra(e.key), " "] : null, format(e.count), h("span", { class: "muted" }, " · " + share.toFixed(share < 10 ? 1 : 0) + "%"))),
+        h("span", { class: "bar-value" }, extra ? [extra(e.key), " "] : null, format(e.count), showShare ? h("span", { class: "muted" }, " · " + share.toFixed(share < 10 ? 1 : 0) + "%") : null)),
       h("div", { class: "bar-track" }, h("div", { class: "bar-fill", style: { width: Math.max(0.5, (e.count / peak) * 100) + "%" } })));
   }));
 }

internal/web/static/assets/pages/connections.js

@@ -3,7 +3,7 @@
 import { h, mount, input, debounce, toast, confirmDialog, badge } from "../ui.js";
 import { get, api, can } from "../api.js";
 import { onLeave } from "../app.js";
-import { fmtSeconds } from "../widgets.js";
+import { fmtSeconds, lookupNames, named } from "../widgets.js";
 
 export async function render(el, params, query) {
   const search = input({ type: "search", placeholder: "address, :port, protocol, state…", value: query.get("q") || "" });
@@ -22,14 +22,15 @@ export async function render(el, params, query) {
   };
   const draw = async () => {
     shown = await get("/connections", { q: search.value.trim(), limit: 500 });
+    const names = await lookupNames(shown.flatMap((c) => [c.source, c.destination, c.dnat_to]));
     count.textContent = shown.length === 1 ? "1 connection" : shown.length + " connections";
     mount(out, shown.length ? h("div", { class: "table-wrap" }, h("table", null,
       h("thead", null, h("tr", null, ["Protocol", "From", "To", "NAT", "State", "Expires", ""].map((t) => h("th", null, t)))),
       h("tbody", null, shown.map((c) => h("tr", null,
         h("td", null, c.protocol),
-        h("td", { class: "mono" }, hostPort(c.source, c.source_port)),
-        h("td", { class: "mono" }, hostPort(c.destination, c.destination_port)),
-        h("td", { class: "mono small" }, c.dnat_to ? "to " + hostPort(c.dnat_to, c.dnat_port || c.destination_port) : "", c.snat_to ? (c.dnat_to ? ", " : "") + "as " + c.snat_to : ""),
+        h("td", { class: "mono" }, named(names, c.source, hostPort(c.source, c.source_port))),
+        h("td", { class: "mono" }, named(names, c.destination, hostPort(c.destination, c.destination_port))),
+        h("td", { class: "mono small" }, c.dnat_to ? ["to ", named(names, c.dnat_to, hostPort(c.dnat_to, c.dnat_port || c.destination_port))] : "", c.snat_to ? (c.dnat_to ? ", " : "") + "as " + c.snat_to : ""),
         h("td", null, c.state || "", c.assured ? null : [" ", badge("one way", "")]),
         h("td", { class: "small" }, fmtSeconds(c.timeout)),
         h("td", { class: "actions-cell" }, write ? h("button", { class: "small reveal", onclick: () => close([c], "this connection") }, "Close") : null)))))) :

internal/web/static/assets/pages/dashboard.js

@@ -1,9 +1,9 @@
-// Dashboard: the ruleset's state, problems, interfaces, the busiest rules
-// and the latest drops.
-import { h, mount, table, badge, problemsList, time } from "../ui.js";
+// Dashboard: the ruleset's state, problems, interfaces, the busiest rules,
+// the quotas and the latest drops.
+import { h, mount, table, badge, problemsList, time, plural } from "../ui.js";
 import { get, can } from "../api.js";
 import { onLeave } from "../app.js";
-import { describe, hits, humanCount } from "../widgets.js";
+import { describe, hits, humanCount, fmtBytes, usageBar, lookupNames, named, pct } from "../widgets.js";
 import { lineChart, chartCard, legend, timeTable, stepSeconds } from "../charts.js";
 import { bytes } from "./stats.js";
 
@@ -11,12 +11,13 @@ export async function render(el) {
   const draw = async () => {
     const st = await get("/status");
     const config = can("config", false), logs = can("log", false);
-    const [rules, cs, log, tl, zones] = await Promise.all([
+    const [rules, cs, log, tl, zones, quotas] = await Promise.all([
       config ? get("/rules") : [],
       logs ? get("/counters").then((c) => c.counters).catch(() => ({})) : {},
       logs ? get("/log", { limit: 8 }).catch(() => []) : [],
       logs ? get("/stats/timeline", { since: "24h", step: "1h", keys: "zrx:*,ztx:*,drops" }).catch(() => null) : null,
       config ? get("/zones").catch(() => []) : [],
+      logs ? get("/quotas").catch(() => []) : [],
     ]);
     const busiest = rules.filter((r) => cs["r" + r.id] && cs["r" + r.id].packets > 0)
       .sort((a, b) => cs["r" + b.id].packets - cs["r" + a.id].packets).slice(0, 8);
@@ -49,11 +50,12 @@ export async function render(el) {
         h("div", { class: "panel-head" }, h("h2", null, "Busiest rules"), h("a", { class: "button small", href: "#/rules" }, "All rules")),
         table([
           { label: "Chain", render: (r) => r.chain },
-          { label: "Rule", render: (r) => r.raw || describe(r) },
+          { label: "Rule", render: (r) => h("a", { href: "#/rules?chain=" + r.chain + "&rule=" + r.id }, "#" + r.id + " ", r.raw || describe(r)) },
           { label: "Action", render: (r) => badge(r.action, { accept: "ok", drop: "err", reject: "warn" }[r.action]) },
           { label: "Hits", render: (r) => hits(cs, "r" + r.id) },
           { label: "Comment", render: (r) => r.comment },
         ], busiest)) : null,
+      quotas.length ? quotaPanel(quotas, await lookupNames(quotas.map((q) => (q.addresses || [])[0]).filter(Boolean).map((a) => a.address))) : null,
       log.length ? h("div", { class: "panel" },
         h("div", { class: "panel-head" }, h("h2", null, "Latest logged packets"), h("a", { class: "button small", href: "#/log" }, "The log")),
         table([
@@ -69,6 +71,24 @@ export async function render(el) {
   onLeave(() => clearInterval(t));
 }
 
+// quotaPanel lists every rule's quota with what it used: the total, or
+// for a per-address quota the busiest address (the rest are on the rule).
+function quotaPanel(quotas, names) {
+  const perAddress = (q) => q.quota.per_source || q.quota.per_destination;
+  const used = (q) => perAddress(q) ? ((q.addresses || [])[0] || { used: 0 }).used : q.used;
+  return h("div", { class: "panel" },
+    h("div", { class: "panel-head" }, h("h2", null, "Quotas"), h("a", { class: "button small", href: "#/stats" }, "Statistics")),
+    table([
+      { label: "Rule", render: (q) => h("a", { href: "#/rules?rule=" + q.rule_id }, q.rule) },
+      { label: "Allowance", render: (q) => fmtBytes(q.quota.bytes) + (q.quota.per_source ? " each source" : q.quota.per_destination ? " each destination" : "") },
+      { label: "Used", render: (q) => perAddress(q)
+        ? [plural((q.addresses || []).length, "address", "addresses"), q.addresses && q.addresses.length ? [", busiest ", named(names, q.addresses[0].address), " " + fmtBytes(used(q)) + " (" + pct(used(q), q.quota.bytes) + ")"] : ""]
+        : fmtBytes(q.used) + " (" + pct(q.used, q.quota.bytes) + ")" },
+      { label: "", render: (q) => usageBar(used(q), q.quota.bytes) },
+      { label: "Next reset", render: (q) => q.next_reset ? time(q.next_reset) : h("span", { class: "muted" }, "by hand") },
+    ], quotas));
+}
+
 // statsCharts: the last 24 hours' traffic with the internet and drops,
 // per hour (the Statistics page has the rest).
 function statsCharts(tl, zones) {

internal/web/static/assets/pages/log.js

@@ -1,8 +1,9 @@
 // The log: packets rules (with logging on) and the policies logged,
 // refreshed every few seconds.
-import { h, mount, input, debounce } from "../ui.js";
-import { get } from "../api.js";
+import { h, mount, input, debounce, badge } from "../ui.js";
+import { get, state } from "../api.js";
 import { onLeave } from "../app.js";
+import { lookupNames, named } from "../widgets.js";
 
 export async function render(el, params, query) {
   const search = input({ type: "search", placeholder: "address, interface, rule…", value: query.get("q") || "" });
@@ -12,15 +13,20 @@ export async function render(el, params, query) {
   const addr = (a, port) => port ? (a.includes(":") ? "[" + a + "]:" + port : a + ":" + port) : a;
   const draw = async () => {
     const es = await get("/log", { limit: 300, q: search.value.trim() });
+    const names = await lookupNames(es.flatMap((e) => [e.source, e.destination]));
     mount(out, es.length ? h("div", { class: "table-wrap" }, h("table", { class: "activity" },
       h("thead", null, h("tr", null, ["Time", "Why", "In", "Out", "From", "To", "Protocol"].map((t) => h("th", null, t)))),
       h("tbody", null, es.map((e) => h("tr", null,
         h("td", { class: "mono small" }, new Date(e.time).toLocaleTimeString(undefined, { hourCycle: "h23" })),
-        h("td", null, e.mark && e.mark.startsWith("r") ? h("a", { href: "#/rules", title: "rule " + e.mark.slice(1) }, e.prefix) : e.prefix),
+        h("td", null, e.mark && e.mark.startsWith("r") ? h("a", { href: "#/rules?rule=" + e.mark.slice(1), title: "rule #" + e.mark.slice(1) }, e.prefix) : e.prefix,
+          e.shadow && /^(drop|reject)$/.test(e.verdict) ? [" ", badge("would " + e.verdict, "warn")] : null),
         h("td", { class: "mono" }, e.in || ""), h("td", { class: "mono" }, e.out || ""),
-        h("td", { class: "mono" }, addr(e.source, e.source_port)), h("td", { class: "mono" }, addr(e.destination, e.destination_port)),
+        h("td", { class: "mono" }, named(names, e.source, addr(e.source, e.source_port))),
+        h("td", { class: "mono" }, named(names, e.destination, addr(e.destination, e.destination_port))),
         h("td", null, e.protocol, e.icmp_type ? " " + e.icmp_type : "", e.tcp_flags ? h("span", { class: "muted small" }, " " + e.tcp_flags) : null)))))) :
-      h("div", { class: "empty" }, "Nothing logged yet. Turn logging on for a rule (Edit → Log), or for what the policies drop (Settings)."));
+      h("div", { class: "empty" }, state.me.mode === "shadow"
+        ? "Nothing logged yet. In shadow mode, what the policies would drop is logged; turn logging on for a rule with Edit → Log."
+        : "Nothing logged yet. Turn logging on for a rule (Edit → Log), or for what the policies drop (Settings)."));
   };
   search.addEventListener("input", debounce(draw, 300));
   mount(el,

internal/web/static/assets/pages/matrix.js

@@ -11,7 +11,7 @@ export async function render(el) {
   const name = (z) => z === "firewall" ? h("em", null, "firewall") : z;
   mount(el,
     h("div", { class: "page-head" }, h("div", { class: "grow" }, h("h1", null, "Zone matrix"),
-      h("div", { class: "muted" }, "What happens to a new connection from a zone (rows) to a zone (columns), or to and from the firewall itself, worked out from the rules in order: allowed or blocked, and how many rules decide for part of the traffic first (some services, addresses, times). Click a cell for the rules."))),
+      h("div", { class: "muted" }, "What happens to a new connection from a zone (rows) to a zone (columns), or to and from the firewall itself, worked out from the rules in order: all allowed, all blocked, or partly (some services, addresses or times let through, the rest not). Click a cell for the rules."))),
     pending ? h("div", { class: "msg info" }, "Shown with your pending changes.") : null,
     !m.zones.length ? h("div", { class: "panel" }, h("div", { class: "empty" }, "No zones yet: add them under Objects → Zones.")) :
     h("div", { class: "panel" }, h("div", { class: "table-wrap" }, h("table", { class: "matrix" },
@@ -19,20 +19,32 @@ export async function render(el) {
       h("tbody", null, cols.map((from) => h("tr", null, h("th", null, name(from)), cols.map((to) => {
         const c = cells.get(from + "\u0000" + to);
         if (!c) return h("td", { class: "matrix-none" }, "–");
-        const n = c.exceptions.length;
-        return h("td", { class: "matrix-" + c.verdict + (n ? " matrix-some" : ""), title: c.verdict + " by " + c.decided_by + (n ? ", " + n + " exception" + (n === 1 ? "" : "s") + " first" : "") },
-          h("button", { type: "button", class: "matrix-cell", onclick: () => detail(c) }, c.verdict, n ? h("span", { class: "matrix-n" }, "+" + n) : null));
+        const open = c.open || [];
+        const counts = [c.allowed ? "+" + c.allowed : "", c.blocked ? "−" + c.blocked : ""].filter(Boolean).join(" ");
+        const title = (c.same_zone ? c.note + ". " : "") + "The rest: " + c.verdict + " by " + c.decided_by +
+          (c.allowed ? "; " + c.allowed + " rule(s) let part of it through" : "") + (c.blocked ? "; " + c.blocked + " block part of it" : "");
+        return h("td", { class: "matrix-" + c.summary + (c.same_zone ? " matrix-same" : ""), title },
+          h("button", { type: "button", class: "matrix-cell", onclick: () => detail(c) },
+            c.summary === "partly" ? "partly" : c.verdict, counts ? h("span", { class: "matrix-n" }, counts) : null,
+            open.length && !c.same_zone ? h("span", { class: "matrix-open" }, open.slice(0, 3).join(" · ") + (open.length > 3 ? " · +" + (open.length - 3) + " more" : "")) : null));
       })))))),
-      h("p", { class: "muted small" }, "Zone to zone is the forward chain; to the firewall, input; from it, output. Exceptions are rules (and built-ins such as ping or port forwards) that decide for some of the traffic before the rest falls to the deciding rule or the policy. Replies and established connections aren't shown: the built-in lets those through.")));
+      h("p", { class: "muted small" }, "Zone to zone is the forward chain; to the firewall, input; from it, output. +N: rules (and built-ins such as ping or port forwards) that let part of the traffic through before the rest falls to the deciding rule or the policy; −N: those that block part of it. Under each cell, what is let through. A zone to itself (faded): only traffic routed between its interfaces passes the firewall. Replies and established connections aren't shown: the built-in lets those through.")));
 }
 
 function detail(c) {
-  const ruleLink = (id, chain, label) => id ? h("a", { href: "#/rules?chain=" + chain, onclick: () => document.querySelector(".modal-back") && document.querySelector(".modal-back").remove() }, label) : label;
+  const ruleLink = (id, chain, label) => id ? h("a", { href: "#/rules?chain=" + chain + "&rule=" + id, onclick: () => document.querySelector(".modal-back") && document.querySelector(".modal-back").remove() }, label) : label;
   const v = (verdict) => badge(verdict, { allowed: "ok", blocked: "err", logged: "", unknown: "warn" }[verdict]);
+  const hits = (n) => h("td", { class: "small num" }, n === undefined || n === null ? "–" : n.toLocaleString());
+  const summary = { allowed: "all allowed", blocked: "all blocked", partly: "partly allowed" }[c.summary];
   modal(c.from + " → " + c.to, h("div", null,
-    h("p", { class: "muted" }, "New connections, checked in this order (the " + c.chain + " chain):"),
-    h("div", { class: "table-wrap" }, h("table", null, h("tbody", null,
-      c.exceptions.map((e) => h("tr", null, h("td", null, v(e.verdict)), h("td", null, e.what), h("td", { class: "small" }, ruleLink(e.rule_id, e.chain, e.label)))),
-      h("tr", { class: "matrix-rest" }, h("td", null, v(c.verdict)), h("td", null, h("strong", null, c.exceptions.length ? "the rest" : "everything")),
-        h("td", { class: "small" }, ruleLink(c.rule_id, c.chain, c.decided_by))))))), [{ label: "Close", value: null }], { wide: true });
+    h("p", null, h("strong", null, summary), h("span", { class: "muted" }, " · new connections, checked in this order (the " + c.chain + " chain):")),
+    c.note ? h("div", { class: "msg info" }, c.note[0].toUpperCase() + c.note.slice(1) + ".") : null,
+    h("div", { class: "table-wrap" }, h("table", null,
+      h("thead", null, h("tr", null, h("th", null, ""), h("th", null, "What"), h("th", null, "By"), h("th", { class: "num" }, "Hits"))),
+      h("tbody", null,
+        c.exceptions.map((e) => h("tr", null, h("td", null, v(e.verdict)), h("td", null, e.what), h("td", { class: "small" }, ruleLink(e.rule_id, e.chain, e.label)), hits(e.hits))),
+        h("tr", { class: "matrix-rest" }, h("td", null, v(c.verdict)), h("td", null, h("strong", null, c.exceptions.length ? "the rest" : "everything")),
+          h("td", { class: "small" }, ruleLink(c.rule_id, c.chain, c.decided_by)), hits(c.hits))))),
+    h("p", { class: "muted small" }, "Hits: each rule's packets since housecarld started, in all its traffic: a rule can cover several pairs.")),
+    [{ label: "Close", value: null }], { wide: true });
 }

internal/web/static/assets/pages/rules.js

@@ -2,7 +2,7 @@
 import { h, mount, table, modal, errorBox, field, input, select, checkbox, confirmDialog, badge, textarea, toast } from "../ui.js";
 import { get, api, change, can } from "../api.js";
 import { rerender } from "../app.js";
-import { names, matchEditor, describe, hits, counters, listEditor, rowClass, live, fmtBytes, quotas } from "../widgets.js";
+import { names, matchEditor, describe, hits, counters, listEditor, rowClass, live, fmtBytes, quotas, usageBar, lookupNames, named, pct } from "../widgets.js";
 
 const chains = [
   ["input", "Input", "Traffic to the firewall itself."],
@@ -24,7 +24,14 @@ const builtins = {
 };
 
 export async function render(el, params, query) {
-  const chain = query.get("chain") || "input";
+  // ?rule=ID (from the matrix, the log, the tracer, statistics): show
+  // that rule, in its chain, highlighted.
+  const target = Number(query.get("rule")) || 0;
+  let chain = query.get("chain");
+  if (!chain && target) {
+    try { chain = (await get("/rules/" + target)).chain; } catch { /* gone: the default chain */ }
+  }
+  chain = chain || "input";
   const [all, settings, cs, qs] = await Promise.all([get("/rules", { chain }), get("/settings"), counters(), quotas()]);
   // As nftables checks them: the rules that count traffic first.
   const rules = [...all.filter(everyPacket), ...all.filter((r) => !everyPacket(r))];
@@ -40,7 +47,8 @@ export async function render(el, params, query) {
     h("div", { class: "panel" },
       builtinsRow(chain, settings, cs),
       table([
-        { label: "#", render: (r) => r.pending === "deleted" ? "" : String(live(rules).indexOf(r) + 1) },
+        { label: "Order", render: (r) => r.pending === "deleted" ? "" : String(live(rules).indexOf(r) + 1) },
+        { label: "ID", render: (r) => r.id ? h("span", { class: "muted mono small" }, "#" + r.id) : "" },
         { label: "Match", render: (r) => r.raw ? [badge("raw", ""), " ", h("span", { class: "mono small" }, r.raw)]
           : [everyPacket(r) ? [badge("every packet", "accent"), " "] : null, describe(r), extras(r, qs[r.id])] },
         { label: "Action", render: actionBadge },
@@ -59,10 +67,15 @@ export async function render(el, params, query) {
           h("button", { class: "small reveal", onclick: () => del(r) }, "Delete"),
         ];
         } } : null,
-      ].filter(Boolean), rules, { empty: "No rules in this chain yet.", rowClass }),
+      ].filter(Boolean), rules, { empty: "No rules in this chain yet.", rowClass: (r) => rowClass(r) + (target && r.id === target ? " row-target" : "") }),
       rules.some(everyPacket) ? h("div", { class: "muted small" }, "Rules marked “every packet” are checked before established connections are accepted: they see all of a connection's traffic, not only its first packet, so a quota counts all of it and a block stops connections already open. They can drop, reject or log, not accept.") : null,
       h("div", { class: "policy small" }, "Then the policy: ", badge(policy, policy === "drop" ? "err" : "ok"),
         policy === "drop" ? [" — ", hits(cs, "p-" + chain), " packets reached it"] : null)));
+  if (target) {
+    const row = el.querySelector("tr.row-target");
+    if (row) requestAnimationFrame(() => row.scrollIntoView({ block: "center" }));
+    else el.querySelector(".tabs").after(h("div", { class: "msg warn" }, "There is no rule #" + target + " (any more)."));
+  }
 }
 
 // everyPacket: checked before established connections are accepted (as
@@ -145,46 +158,86 @@ function extras(r, q) {
   return out;
 }
 
-// quotaLine shows a quota, and what it used: in total, or per address
-// (the busiest, and the rest in a dialog).
+// quotaLine sums up a quota on the rule's row: what it used (in total,
+// or how many addresses and the busiest); the rest is in its dialog.
 function quotaLine(r, q) {
   const qt = r.quota;
   const each = qt.per_source ? " each source" : qt.per_destination ? " each destination" : "";
-  const resets = qt.reset === "monthly" ? "monthly on day " + (qt.day || 1) : qt.reset || "by hand";
-  let used = null;
-  if (q && !qt.per_source && !qt.per_destination) {
-    used = [h("strong", null, fmtBytes(q.used)), " of " + fmtBytes(qt.bytes) + " used"];
-  } else if (q) {
+  const resets = qt.reset === "monthly" ? "monthly" : qt.reset || "reset by hand";
+  let used = fmtBytes(qt.bytes) + each;
+  if (q && !each) used = fmtBytes(q.used) + " of " + fmtBytes(qt.bytes) + " used (" + pct(q.used, qt.bytes) + ")";
+  else if (q) {
     const n = (q.addresses || []).length;
-    used = [n === 1 ? "1 address" : n + " addresses", n ? [", busiest ", h("strong", null, fmtBytes(q.addresses[0].used))] : null, " ",
-      n ? h("button", { class: "small", onclick: () => usageDialog(r, q) }, "Usage…") : null];
+    used += " · " + (n === 1 ? "1 address" : n + " addresses") + (n ? ", busiest " + fmtBytes(q.addresses[0].used) + " (" + pct(q.addresses[0].used, qt.bytes) + ")" : "");
   }
-  return h("div", { class: "muted small" }, (qt.over ? "quota over " : "quota ") + fmtBytes(qt.bytes) + each + ", resets " + resets,
-    used ? [" · ", used] : null,
-    q && q.next_reset ? " · next reset " + new Date(q.next_reset).toLocaleString() : null,
-    can("config", true) && q && r.pending !== "new" ? [" ", h("button", { class: "small", onclick: () => resetQuota(r) }, "Reset")] : null);
+  const text = "quota " + used + " · " + resets;
+  return h("div", { class: "muted small" }, q && r.pending !== "new"
+    ? h("button", { class: "link small", title: "Usage, reset and give back", onclick: () => quotaDialog(r, q) }, text) : text);
 }
 
-async function usageDialog(r, q) {
-  await modal("Quota usage of " + (r.comment || "rule #" + r.id), h("div", null,
-    h("p", { class: "muted" }, "Each " + (r.quota.per_source ? "source" : "destination") + " has " + fmtBytes(r.quota.bytes) + "."),
-    table([
-      { label: "Address", render: (a) => h("span", { class: "mono" }, a.address) },
+// quotaDialog shows a quota in full: what it used (each address's, for a
+// per-address one), its resets, and resetting or giving back.
+async function quotaDialog(r, q) {
+  const qt = r.quota;
+  const perAddress = qt.per_source || qt.per_destination;
+  const write = can("config", true);
+  const resets = qt.reset === "monthly" ? "monthly on day " + (qt.day || 1) : qt.reset || "only by hand";
+  const when = (t) => t ? new Date(t).toLocaleString() : "–";
+  const names = perAddress ? await lookupNames((q.addresses || []).map((a) => a.address)) : {};
+  // A row's action closes this dialog first: it opens one of its own.
+  const then = (f) => (e) => { e.target.closest(".modal").querySelector(".buttons button:last-child").click(); f(); }; // Close
+  const v = await modal("Quota of " + (r.comment || "rule #" + r.id), h("div", null,
+    h("p", null, fmtBytes(qt.bytes) + (perAddress ? (qt.per_source ? " for each source" : " for each destination") : " in all") + "; the rule matches " +
+      (qt.over ? "once it is used up" : "while it lasts") + ". Resets " + resets + "."),
+    h("p", { class: "muted small" }, "Last reset " + when(q.last_reset) + " · next reset " + when(q.next_reset)),
+    perAddress ? table([
+      { label: "Address", render: (a) => h("span", { class: "mono" }, named(names, a.address)) },
       { label: "Used", render: (a) => fmtBytes(a.used) },
-      { label: "", render: (a) => h("div", { class: "usage" }, h("div", { class: "usage-bar" + (a.used >= r.quota.bytes ? " full" : "") }, bar(a.used / r.quota.bytes))) },
-    ], q.addresses)), [{ label: "Close", value: null }], { wide: true });
+      { label: "", class: "num", tdClass: "num", render: (a) => pct(a.used, qt.bytes) },
+      { label: "", render: (a) => usageBar(a.used, qt.bytes) },
+      write ? { label: "", render: (a) => h("span", { class: "nowrap" },
+        h("button", { class: "small", onclick: then(() => resetQuota(r, a.address)) }, "Reset"), " ",
+        h("button", { class: "small", onclick: then(() => giveBack(r, a.address)) }, "Give back…")) } : null,
+    ].filter(Boolean), q.addresses || [], { empty: "No address has used it since the last reset." })
+      : h("div", null, h("strong", null, fmtBytes(q.used)), " of " + fmtBytes(qt.bytes) + " used (" + pct(q.used, qt.bytes) + ")", usageBar(q.used, qt.bytes))),
+  [
+    ...(write ? [{ label: perAddress ? "Reset all" : "Reset", value: "reset" }, { label: perAddress ? "Give back to all…" : "Give back…", value: "give" }] : []),
+    { label: "Close", value: null },
+  ], { wide: perAddress });
+  if (v === "reset") resetQuota(r);
+  if (v === "give") giveBack(r);
 }
 
-function bar(f) {
-  const seg = h("div", { class: "seg leased" });
-  seg.style.width = Math.min(100, f * 100) + "%";
-  return seg;
+// giveBack takes an amount off what a quota used (one address's, or
+// everyone's): extra allowance until its next reset.
+async function giveBack(r, address) {
+  const amount = input({ type: "number", min: 1, value: "1", class: "short" });
+  const unit = select([["mb", "MB"], ["gb", "GB"]], "gb", { class: "inline" });
+  const perAddress = r.quota.per_source || r.quota.per_destination;
+  const who = address ? " for " + address : perAddress ? " for every address" : "";
+  await modal("Give back quota", h("div", null,
+    h("p", null, "Take this much off what " + (r.comment || "rule #" + r.id) + "'s quota used" + who + ": extra allowance until its next reset, without changing the rule. This is done at once, not staged."),
+    field("Amount", h("div", null, amount, " ", unit))), [
+    { label: "Cancel", value: null },
+    { label: "Give back", kind: "primary", onclick: async () => {
+      const n = parseInt(amount.value, 10);
+      if (!(n > 0)) { toast("Give an amount of 1 or more", "err"); return false; }
+      const give = n * (unit.value === "gb" ? 1 << 30 : 1 << 20);
+      try {
+        await api("POST", "/rules/" + r.id + "/reset-quota", { body: address ? { give, address } : { give } });
+        toast("Gave back " + fmtBytes(give)); rerender();
+      } catch (e) { modal("Not given back", errorBox(e)); return false; }
+    } },
+  ]);
 }
 
-async function resetQuota(r) {
+async function resetQuota(r, address) {
   if (!await confirmDialog("Reset the quota", "Start the quota of " + (r.comment || "rule #" + r.id) + " again now" +
-    (r.quota.per_source || r.quota.per_destination ? ", for every address" : "") + "? This is done at once, not staged.", "Reset")) return;
-  try { await api("POST", "/rules/" + r.id + "/reset-quota"); toast("Quota reset"); rerender(); } catch (e) { modal("Not reset", errorBox(e)); }
+    (address ? " for " + address : r.quota.per_source || r.quota.per_destination ? ", for every address" : "") + "? This is done at once, not staged.", "Reset")) return;
+  try {
+    await api("POST", "/rules/" + r.id + "/reset-quota", address ? { body: { address } } : {});
+    toast("Quota reset"); rerender();
+  } catch (e) { modal("Not reset", errorBox(e)); }
 }
 
 async function move(r, where) {

internal/web/static/assets/pages/stats.js

@@ -3,6 +3,7 @@
 import { h, mount, fmtTime, errorBox } from "../ui.js";
 import { get } from "../api.js";
 import { lineChart, chartCard, legend, timeTable, heatmap, heatmapTable, barList, compact, stepSeconds, endLabelWidth } from "../charts.js";
+import { withNames } from "../widgets.js";
 
 const ranges = [["1h", "1 hour"], ["6h", "6 hours"], ["24h", "24 hours"], ["7d", "7 days"], ["30d", "30 days"], ["90d", "90 days"], ["365d", "a year"]];
 const rangeSecs = { "1h": 3600, "6h": 6 * 3600, "24h": 86400, "7d": 7 * 86400, "30d": 30 * 86400, "90d": 90 * 86400, "365d": 365 * 86400 };
@@ -103,7 +104,7 @@ export async function render(el, params, query) {
     listCard("What they tried", "the logged drops' protocol and port", barList(s.blocked_ports, { empty: "No logged drops " + rangeLabel + "." })),
     listCard("Devices, received", "bytes from external zones, by inside address (IPv6 per /64)", s.devices_down.length ? barList(s.devices_down, { format: bytes, href: connHref }) : devHint),
     listCard("Devices, sent", "bytes to external zones", s.devices_up.length ? barList(s.devices_up, { format: bytes, href: connHref }) : devHint.cloneNode(true)),
-    d.quotas.length ? listCard("Quotas", "bytes counted against each rule's quota, " + rangeLabel, barList(d.quotas, { format: bytes, label: (k) => "rule #" + k.slice(1), href: () => "#/rules" })) : null,
+    d.quotas.length ? listCard("Quotas", "bytes counted against each rule's quota, " + rangeLabel, barList(d.quotas, { format: bytes, label: (k) => (d.hits.find((x) => x.key === k) || {}).name || "rule #" + k.slice(1), href: ruleHref, share: false })) : null,
     listCard("Rules that matched nothing", "in the last 30 days (or since statistics started): candidates to remove",
       unused.length ? h("div", null, h("ul", { class: "plain-list" }, unused.slice(0, 12).map((e) => h("li", null, h("a", { href: ruleHref(e.key) }, e.name || e.key)))),
         unused.length > 12 ? h("div", { class: "muted small" }, "and " + (unused.length - 12) + " more: hc stats rules --unused") : null) : h("div", { class: "empty" }, "Every rule matched something."))));
@@ -142,6 +143,7 @@ async function loadAll(since, heatSince) {
     get("/stats/timeline", { since, keys: "g:conntrack,g:conntrack_max,g:mem,g:rss,g:load,g:cpu" }),
     get("/stats/timeline", { since, keys: "quota:*" }),
   ]);
+  await withNames(summary.devices_down, summary.devices_up, summary.blocked_sources);
   return { summary, zones, traffic, drops, heat, hits, gauges,
     quotas: quotas.series.map((x) => ({ key: x.key.slice(6), count: x.values.reduce((a, v) => a + Math.max(v, 0), 0) })).filter((e) => e.count > 0).sort((a, b) => b.count - a.count) };
 }
@@ -180,7 +182,7 @@ function rangeRow(since) {
 // ruleHref: a counter's mark to its page ("r12" → the rules, "b-…" → the
 // built-ins under Settings).
 function ruleHref(mark) {
-  if (/^r\d/.test(mark)) return "#/rules";
+  if (/^r\d+$/.test(mark)) return "#/rules?rule=" + mark.slice(1);
   if (mark.startsWith("b-") || mark.startsWith("p-")) return "#/settings";
   if (mark.startsWith("f")) return "#/nat";
   return null;

internal/web/static/assets/pages/trace.js

@@ -56,9 +56,11 @@ export async function render(el, params, query) {
         h("span", { class: "muted" }, head, p.in ? " · in " + p.in : "", p.out ? " · out " + p.out : ""),
         h("span", { class: "muted small trace-time" }, new Date(p.time).toLocaleTimeString())),
       decided ? h("div", { class: "small" }, p.verdict === "dropped" ? "Dropped by " : "Accepted by ", h("strong", null, decided)) : null,
-      h("table", { class: "trace-steps" }, h("tbody", null, p.steps.map((s) => h("tr", { class: /^(drop|reject)/.test(s.verdict) ? "step-drop" : s.verdict === "accept" ? "step-accept" : "" },
+      p.would_drop ? h("div", { class: "small" }, badge("shadow mode", "warn"), " Housecarl would have dropped it: ",
+        h("strong", null, p.would_drop.label || [p.would_drop.chain, p.would_drop.mark].filter(Boolean).join(" "))) : null,
+      h("table", { class: "trace-steps" }, h("tbody", null, p.steps.map((s) => h("tr", { class: /^(drop|reject)/.test(s.verdict) || /\[would (drop|reject)\]/.test(s.rule || "") ? "step-drop" : s.verdict === "accept" ? "step-accept" : "" },
         h("td", { class: "muted small" }, s.table + " " + s.chain),
-        h("td", null, s.label ? (s.mark && s.mark.startsWith("r") ? h("a", { href: "#/rules?chain=" + s.chain }, s.label) : s.label)
+        h("td", null, s.label ? (s.mark && s.mark.startsWith("r") ? h("a", { href: "#/rules?chain=" + s.chain + "&rule=" + s.mark.slice(1).split("-")[0] }, s.label) : s.label)
           : s.kind === "policy" ? s.chain + " policy" : h("span", { class: "mono small" }, s.rule)),
         h("td", { class: "small" }, s.verdict))))));
   }

internal/web/static/assets/style.css

@@ -85,6 +85,7 @@ h1 { font-size: 20px; margin: 0 0 4px; }
 h2 { font-size: 16px; margin: 18px 0 8px; }
 h3 { font-size: 14px; margin: 14px 0 6px; }
 .muted { color: var(--muted); }
+.host-name { font-weight: 600; }
 .small { font-size: 12px; }
 .nowrap { white-space: nowrap; }
 .warn-text { color: var(--warn); }
@@ -373,6 +374,7 @@ pre.wrap { white-space: pre-wrap; word-break: break-all; font-size: 12px; }
 /* The probation banner: changes roll back unless confirmed. */
 .probation-banner { background: var(--warn-soft); color: var(--text); border-bottom: 1px solid var(--warn); padding: 10px 24px; font-size: 14px; }
 .probation-banner .banner-actions { margin-left: 12px; white-space: nowrap; }
+.shadow-banner { background: var(--panel); border-bottom-color: var(--border); }
 /* List editors (zones, addresses, services). */
 .list-rows { display: flex; flex-direction: column; gap: 6px; margin-bottom: 6px; }
 .list-row { display: flex; gap: 6px; align-items: center; }
@@ -424,10 +426,18 @@ table.matrix th, table.matrix td { text-align: center; }
 table.matrix tbody th { text-align: left; }
 table.matrix th.corner { font-weight: 400; color: var(--muted); text-transform: none; }
 table.matrix td { padding: 4px; }
-.matrix-cell { width: 100%; min-width: 7em; border: 0; background: transparent; color: inherit; font-weight: 600; padding: 6px 8px; cursor: pointer; }
+table.matrix { table-layout: fixed; width: 100%; min-width: 640px; }
+table.matrix thead th:first-child, table.matrix tbody th { width: 8em; }
+.matrix-cell { display: block; width: 100%; min-width: 7em; border: 0; background: transparent; color: inherit; font-weight: 600; padding: 6px 8px; cursor: pointer; white-space: normal; text-align: center; }
 td.matrix-allowed { background: var(--add); color: var(--add-text); }
 td.matrix-blocked { background: var(--del); color: var(--del-text); }
-.matrix-n { margin-left: 6px; font-weight: 400; font-size: 12px; color: var(--warn); }
+.matrix-n { margin-left: 6px; font-weight: 400; font-size: 12px; }
+td.matrix-partly { background: var(--warn-soft); color: var(--text); }
+td.matrix-same { opacity: 0.55; }
+/* The rule a link pointed at (?rule=ID). */
+tr.row-target td { background: var(--accent-soft); font-weight: 600; }
+tr.row-target td:first-child { box-shadow: inset 3px 0 0 var(--accent); }
+.matrix-open { display: block; font-weight: 400; font-size: 12px; opacity: 0.85; margin-top: 2px; }
 td.matrix-none { color: var(--muted); }
 tr.matrix-rest td { border-top: 2px solid var(--border); }
 

internal/web/static/assets/widgets.js

@@ -1,7 +1,7 @@
 // Widgets shared by several pages: list editors with suggestions, the
 // match editor of rules and NAT, descriptions, hit counts, durations.
 import { h, input, select, field, checkbox } from "./ui.js";
-import { get } from "./api.js";
+import { get, api } from "./api.js";
 
 // ---- durations
 
@@ -98,11 +98,16 @@ export function matchEditor(m, n, opts = {}) {
 // describe sums up a match: "in lan · from trusted · ssh, dns".
 export function describe(m) {
   const parts = [];
-  const side = (word, not, list) => { if (list && list.length) parts.push(word + (not ? " not " : " ") + list.join(", ")); };
-  side("in", m.not_in, m.in_zones);
-  side("out", m.not_out, m.out_zones);
-  side("from", m.not_sources, m.sources);
-  side("to", m.not_destinations, m.destinations);
+  const list = (not, xs) => (not ? "any but " : "") + xs.join(", ");
+  // Zones are a direction, "lan → wan"; the firewall itself is the other
+  // end of the input and output chains.
+  const ins = m.in_zones || [], outs = m.out_zones || [];
+  if (ins.length || outs.length) {
+    parts.push((m.chain === "output" ? "firewall" : ins.length ? list(m.not_in, ins) : "any") + " → " +
+      (m.chain === "input" ? "firewall" : outs.length ? list(m.not_out, outs) : "any"));
+  }
+  if (m.sources && m.sources.length) parts.push("from " + list(m.not_sources, m.sources));
+  if (m.destinations && m.destinations.length) parts.push("to " + list(m.not_destinations, m.destinations));
   if (m.services && m.services.length) parts.push(m.services.join(", "));
   if (m.family) parts.push(m.family + " only");
   return parts.length ? parts.join(" · ") : "everything";
@@ -156,6 +161,41 @@ export function fmtBytes(n) {
   return n + " bytes";
 }
 
+// pct writes used as a share of total: "25%", "<1%" for a little.
+export function pct(used, total) {
+  if (!total || used <= 0) return "0%";
+  const p = used / total * 100;
+  return p < 1 ? "<1%" : Math.floor(p) + "%";
+}
+
+// usageBar draws used out of total as a bar, red once it is all used.
+export function usageBar(used, total) {
+  const seg = h("div", { class: "seg leased" });
+  seg.style.width = Math.min(100, used / total * 100) + "%";
+  return h("div", { class: "usage" }, h("div", { class: "usage-bar" + (used >= total ? " full" : "") }, seg));
+}
+
+// lookupNames asks for inside addresses' names (docs/configuration.md):
+// {address: name}, {} when names are off or can't be had.
+export async function lookupNames(addrs) {
+  const list = [...new Set(addrs.filter(Boolean))];
+  if (!list.length) return {};
+  try { return (await api("POST", "/names", { body: { addresses: list } })).names || {}; } catch { return {}; }
+}
+
+// named shows an address (or text with it, such as address:port) after
+// its name's first label; the whole name is in the tooltip.
+export function named(names, addr, text = addr) {
+  const n = names[addr];
+  return n ? h("span", { title: n + " (" + addr + ")" }, h("span", { class: "host-name" }, n.split(".")[0]), " ", h("span", { class: "muted" }, text)) : text;
+}
+
+// withNames sets each top-list entry's name from its key (an address).
+export async function withNames(...lists) {
+  const names = await lookupNames(lists.flat().map((e) => e.key));
+  for (const e of lists.flat()) if (names[e.key]) e.name = names[e.key].split(".")[0];
+}
+
 // quotas loads what the rules' quotas used, by rule ID ({} without
 // log:read).
 export async function quotas() {

scripts/e2e.sh

@@ -2,12 +2,12 @@
 # End-to-end test with real traffic: a Debian 13 router container (nftables
 # 1.1.3) between an "internet" network and a LAN, IPv4 and IPv6, runs
 # housecarld. The maintainer's own router ruleset (internal/importer/
-# testdata/router.nft, with lab addresses) is loaded as it is today, imported,
-# taken over, and then checked with connections: port forwards, hairpin NAT,
-# the IPv6 pinhole, masquerading, antispoofing, the drop log, a change on
-# probation that cuts the client off and rolls itself back, a restart and the
-# boot ruleset. Needs Docker; no root on the host. Run from the repository
-# root:
+# testdata/router.nft, with lab addresses) is loaded as it is today,
+# imported with housecarld in shadow mode beside it, taken over, and then
+# checked with connections: port forwards, hairpin NAT, the IPv6 pinhole,
+# masquerading, antispoofing, the drop log, a change on probation that cuts
+# the client off and rolls itself back, a restart and the boot ruleset.
+# Needs Docker; no root on the host. Run from the repository root:
 #
 #   make e2e        or        scripts/e2e.sh
 #
@@ -55,6 +55,9 @@ docker run -d --name ${P}-router --hostname router --cap-add NET_ADMIN $sysctls
 	--network ${P}-wan --ip $WAN4 --ip6 $WAN6 -v "$WORK:/w" "$IMAGE" sleep infinity >/dev/null || exit 1
 docker network connect --ip $LAN4 --ip6 $LAN6 ${P}-lan ${P}-router || exit 1
 docker network connect --ip 10.88.50.1 ${P}-wg ${P}-router || exit 1
+# The client has a name for housecarld's reverse lookups (/etc/hosts
+# here, a PTR record in real life); the addresses outside get none.
+docker exec ${P}-router sh -c "echo '$CLIENT4 e2e-client.lab' >> /etc/hosts" || exit 1
 # The router's interfaces get the names of the real one: wan, enp2s0, wg0
 # (attached in that order: eth0, eth1, eth2).
 docker exec ${P}-router sh -c 'for p in eth0:wan eth1:enp2s0 eth2:wg0; do i=${p%:*} n=${p#*:}; ip link set $i down && ip link set $i name $n && ip link set $n up; done
@@ -102,7 +105,10 @@ backup: {dir: /w/backups}
 log: {level: debug}
 stats: {database: /w/data/stats.db}
 EOF
-start() { R sh -c '(HOUSECARL_STATS_INTERVAL=3s /w/housecarld -c /w/housecarl.yaml serve >> /w/srv.log 2>&1 &); for i in $(seq 1 30); do [ -S /run/housecarl/housecarl.sock ] && exit 0; sleep 0.3; done; exit 1'; }
+{ cat "$WORK/housecarl.yaml"; echo "shadow: {enabled: true}"; } > "$WORK/housecarl-shadow.yaml"
+CONF=housecarl.yaml
+start() { R sh -c "(HOUSECARL_STATS_INTERVAL=3s /w/housecarld -c /w/$CONF serve >> /w/srv.log 2>&1 &); for i in \$(seq 1 30); do [ -S /run/housecarl/housecarl.sock ] && exit 0; sleep 0.3; done; exit 1"; }
+stop() { docker exec ${P}-router sh -c 'kill $(pidof housecarld)'; sleep 1; }
 
 # ---- today's router: the hand-written ruleset
 
@@ -113,11 +119,13 @@ R nft add table ip other
 run "the port forward works under it" 0 connect net $WAN4 8096
 contains "jellyfin"
 
-# ---- import and take over
+# ---- import in shadow mode: beside today's ruleset, changing nothing
 
 run "init" 0 R sh -c 'echo secret-pass-123 | /w/housecarld -c /w/housecarl.yaml init --password-stdin'
-run "start housecarld" 0 start
+CONF=housecarl-shadow.yaml
+run "start housecarld in shadow mode" 0 start
 run "status" 0 H status
+contains "Mode:.*SHADOW"
 contains "Other tables:.*inet main"
 run "two tables: say which" 6 H import --defines /w/router.nft -n
 contains "several tables"
@@ -130,8 +138,56 @@ contains "lan (enp2s0: as given)"
 contains "vpn (wg0: as given)"
 run "import" 0 H import --table "inet main" --defines /w/router.nft
 contains "applied and saved"
+run "the shadow ruleset is in force" 0 R nft list table inet housecarl
+contains "would dnat\] jellyfin"
+contains "priority filter + 10; policy accept;"
+not_contains "dnat ip to"
+not_contains "maxseg size set"
+not_contains "flowtable"
+run "nothing in it drops, rejects or translates" 1 R sh -c "nft list table inet housecarl | grep -v 'log prefix' | sed 's/comment.*//; s/ct status dnat//' | grep -wE 'drop|reject|dnat|snat|masquerade|redirect'"
+run "no warning about today's ruleset beside it" 0 H status
+not_contains "takeover_pending"
+not_contains "shadow_unprotected"
+run "what it loads once shadow mode is off" 0 H ruleset --enforcing
+contains "dnat ip to 10.88.10.57:443"
+run "the port forward works, by today's ruleset" 0 connect net $WAN4 8096
+contains "jellyfin"
+run "and Housecarl's would-be DNAT counted it" 0 R nft list chain inet housecarl dstnat
+contains 'packets [1-9][0-9]* bytes [0-9]* comment "hc:f[0-9]* \[would dnat\] jellyfin'
+# A drop Housecarl has and today's ruleset doesn't: logged, let through.
+SR=$(H -o id rule add forward --from $CLIENT4 --service tcp/9000 -a drop --log --first --comment "e2e shadow")
+: > "$WORK/net.log"
+run "a shadow drop lets the connection through" 0 docker exec ${P}-client sh -c "echo hi | nc -N -w 3 $NET4 9000"
+sleep 1
+run "it reached the internet" 0 grep -q "$WAN4" "$WORK/net.log"
+run "the log says it would have been dropped" 0 H log
+contains "would drop, let through"
+run "the shadow rule goes" 0 H rule delete -y "$SR"
+run "no takeover in shadow mode" 5 H takeover "inet main" -y
+contains "shadow mode"
+run "healthz" 0 R curl -sf http://127.0.0.1:8070/healthz
+contains '"mode":"shadow"'
+run "the boot ruleset is the shadow one" 0 R grep -q "would dnat" /w/data/ruleset.nft
+run "the boot fallback filters nothing" 1 R grep -wE "drop|masquerade" /w/data/ruleset-fallback.nft
+# Today's ruleset starts with flush ruleset: reloading it deletes
+# Housecarl's table, which housecarld puts back.
+run "today's ruleset reloaded" 0 R nft -f /w/router.nft
+R nft add table ip other
+sleep 4
+run "Housecarl's table is back" 0 R nft list table inet housecarl
+contains "would dnat"
+run "and logged" 0 R grep -q "put it back" /w/srv.log
+
+# ---- enforcing, and take over
+
+stop
+CONF=housecarl.yaml
+run "start housecarld enforcing" 0 start
+run "status" 0 H status
+not_contains "SHADOW"
 run "the ruleset is in force" 0 R nft list table inet housecarl
 contains "dnat ip to 10.88.10.57:443"
+not_contains "would"
 run "zones" 0 H zone list
 contains "wan.*wan.*yes"
 contains "dhcp.*enp2s0"
@@ -266,28 +322,52 @@ send 2000000 >/dev/null 2>&1
 run "used up: the device is cut off" 1 send 1000
 run "the usage" 0 H quotas
 contains "e2e quota.*1.0 MB each.*by hand"
-contains "$CLIENT4  *1\.[0-9] MB"
-docker exec ${P}-router sh -c 'kill $(pidof housecarld)'; sleep 1; start
+contains "$CLIENT4 (e2e-client)  *1\.[0-9] MB (1[0-9][0-9]%)"
+stop; start
 run "after a restart, still used up" 1 send 1000
 run "the usage after a restart" 0 H quotas
-contains "$CLIENT4  *1\.[0-9] MB"
+contains "$CLIENT4 (e2e-client)  *1\.[0-9] MB"
+# A top-up: some given back (more than the cut-off packets added), then
+# used up again; one address started again; then the whole quota.
+run "a top-up for the device" 0 H rule reset-quota "$QR" --give 10mbytes --address $CLIENT4
+contains "gave back 10.0 MB"
+run "topped up: the device is back" 0 send 1000
+send 30000000 >/dev/null 2>&1
+run "used up again" 1 send 1000
+run "an address that used nothing" 4 H rule reset-quota "$QR" --address 10.88.10.99
+run "one address started again" 0 H rule reset-quota "$QR" --address $CLIENT4
+run "back again" 0 send 1000
 run "reset by hand" 0 H rule reset-quota "$QR"
 run "the device is back" 0 send 1000
 run "the reset is audited" 0 H audit --action quota.
 contains "quota.reset"
+contains "quota.give"
+# Counted in total now: what the device used carries over; per
+# destination can't take it, and says so.
+run "within the quota" 0 send 300000
+run "to one total" 0 H rule update "$QR" --quota 1mbytes,over
+not_contains "quota_restarts"
+run "the total carried over" 0 H quotas
+contains "e2e quota)  *[0-9.]* KB ([0-9]*%)"
+run "per destination starts again" 0 H rule update "$QR" --quota 1mbytes,over,per-destination
+contains "quota_restarts"
 run "the quota rule goes" 0 H rule delete -y "$QR"
 
 # ---- the zone matrix, of the imported ruleset
 
 run "the matrix" 0 H matrix
 contains "^firewall  *allow"
+contains "^dhcp  *partly +[0-9]"
+contains "dhcp → wan  *.*from trusted_ips"
 run "LAN to the internet" 0 H matrix dhcp wan
-contains "allowed  *from trusted_ips  *rule forward #[0-9]* (Forward from trusted IPs)"
-contains "blocked  *the rest  *forward policy"
+contains "new connections: partly allowed"
+contains "allowed  *from trusted_ips  *rule forward #[0-9]* (Forward from trusted IPs)  *[0-9]"
+contains "blocked  *the rest  *forward policy  *[0-9]"
 not_contains "wg0_net"
 run "the internet to the firewall" 0 H matrix wan firewall
 contains "blocked  *sources that can't come from outside"
 contains "allowed  *udp/51820"
+contains "allowed  *raw: icmpv6 type"
 
 # ---- statistics (sampled every 3 seconds here)
 
@@ -305,7 +385,8 @@ contains "Dropped:  *[1-9]"
 run "traffic per zone over time" 0 H stats traffic --since 1h --step 1m
 contains "wan ↓"
 run "the devices" 0 H stats top devices --since 1h
-contains "^$CLIENT4  *[0-9.]* KB  *[0-9.]* KB"
+contains "^$CLIENT4 (e2e-client)  *[0-9.]* KB  *[0-9.]* KB"
+run "each device once" 0 sh -c "docker exec ${P}-router /w/hc stats top devices --since 1h | grep -c '^$CLIENT4 ' | grep -qx 1"
 run "the sources blocked" 0 H stats top blocked --since 1h
 contains "^$NET4  *[1-9]"
 run "what they tried" 0 H stats top tried --since 1h
@@ -322,6 +403,8 @@ contains "^[0-9-]* [0-9:]*  *[0-9]*  *[0-9]*"
 docker exec -d ${P}-client sh -c "sleep 30 | nc $NET4 9000"
 sleep 1
 run "the connection is tracked" 0 H connections --search "$CLIENT4 :9000"
+contains "$CLIENT4:[0-9]* (e2e-client)  *$NET4:9000  *as $WAN4"
+run "without names" 0 H connections --search "$CLIENT4 :9000" --no-names
 contains "$CLIENT4:[0-9]*  *$NET4:9000  *as $WAN4"
 run "closed" 0 H connections close --search "$CLIENT4 :9000" -y
 contains "closed [1-9][0-9]* connection"
@@ -408,7 +491,7 @@ contains 'iifname "enp2s0" udp dport 67'
 
 # ---- restart and boot
 
-docker exec ${P}-router sh -c 'kill $(pidof housecarld)'; sleep 1
+stop
 run "the ruleset stays without housecarld" 0 connect net $WAN4 8096
 contains "jellyfin"
 run "restart housecarld" 0 start
@@ -446,7 +529,7 @@ contains '"firewall":"fallback"'
 contains " 503"
 run "status says so" 0 H status
 contains "NOT in force: the boot fallback"
-docker exec ${P}-router sh -c 'kill $(pidof housecarld)'; sleep 1
+stop
 run "housecarld starts" 0 start
 run "and puts the real ruleset back" 0 connect net $WAN4 8096
 contains "jellyfin"