housecarl/internal/importer/importer.go

// Package importer turns an existing nftables ruleset (nft -j list
// ruleset) into Housecarl's configuration: zones, sets, services, rules,
// port forwards, source NAT and redirects, with the built-ins it
// recognises. What it can't express becomes a raw rule with the original
// text (from nft -a list ruleset), and every guess is explained in a note.
//
// The mapping keeps what the ruleset does: rules stay in order; a rule
// that looks like a built-in becomes the built-in only when it sits where
// the built-in goes (before every other rule of its chains), and stays a
// rule otherwise.
package importer

import (
	"encoding/json"
	"fmt"
	"regexp"
	"sort"
	"strconv"
	"strings"

	"housecarl/internal/model"
)

// Input is what to import.
type Input struct {
	// JSON is `nft -j list ruleset`.
	JSON []byte
	// Text is `nft -a list ruleset` (optional): the source of raw rules.
	Text string
	// Defines is the ruleset file (optional): its define lines name sets,
	// services and zones.
	Defines string
	// Table is the table to import ("inet main"); empty: the only table
	// that isn't Housecarl's.
	Table string
}

// Result is the imported configuration and what to know about it.
type Result struct {
	State *model.State
	Notes []string
	// Raw lists the rules that became raw rules.
	Raw []string
}

// ---- nftables JSON

type jsonDoc struct {
	Nftables []map[string]json.RawMessage `json:"nftables"`
}

type nftTable struct {
	Family string `json:"family"`
	Name   string `json:"name"`
}

type nftChain struct {
	Family string `json:"family"`
	Table  string `json:"table"`
	Name   string `json:"name"`
	Type   string `json:"type"`
	Hook   string `json:"hook"`
	Prio   int    `json:"prio"`
	Policy string `json:"policy"`
}

type nftRule struct {
	Family  string            `json:"family"`
	Table   string            `json:"table"`
	Chain   string            `json:"chain"`
	Handle  int               `json:"handle"`
	Comment string            `json:"comment"`
	Expr    []json.RawMessage `json:"expr"`
}

type nftSet struct {
	Family string            `json:"family"`
	Table  string            `json:"table"`
	Name   string            `json:"name"`
	Type   json.RawMessage   `json:"type"`
	Elem   []json.RawMessage `json:"elem"`
}

// nftMap is a named map: its elements are [key, value] pairs.
type nftMap struct {
	Family string            `json:"family"`
	Table  string            `json:"table"`
	Name   string            `json:"name"`
	Type   json.RawMessage   `json:"type"`
	Map    json.RawMessage   `json:"map"`
	Elem   []json.RawMessage `json:"elem"`
}

type nftFlowtable struct {
	Table string   `json:"table"`
	Name  string   `json:"name"`
	Dev   []string `json:"dev"`
}

type importer struct {
	in        Input
	table     nftTable
	chains    map[string]nftChain
	rules     map[string][]nftRule // by chain, in order
	sets      map[string]nftSet
	maps      map[string]nftMap
	flow      []nftFlowtable
	text      map[int]string // rule text by handle
	st        *model.State
	notes     []string
	raw       []string
	id        int64
	defines   map[string]string // name → value text
	addrNames map[string]string // canonical entry list → define name
	portNames map[string]string // canonical port list → define name
	ifNames   map[string]string // interface → define name
	used      map[string]bool   // sets created
	noted     map[string]bool
	positions map[string]float64
}

func (im *importer) note(format string, args ...any) {
	im.notes = append(im.notes, fmt.Sprintf(format, args...))
}

func (im *importer) newID() int64 { im.id++; return im.id }

// Import converts a ruleset.
func Import(in Input) (*Result, error) {
	var doc jsonDoc
	if err := json.Unmarshal(in.JSON, &doc); err != nil {
		return nil, fmt.Errorf("the input isn't nft's JSON (nft -j list ruleset): %v", err)
	}
	im := &importer{in: in, chains: map[string]nftChain{}, rules: map[string][]nftRule{}, sets: map[string]nftSet{}, maps: map[string]nftMap{},
		text: map[int]string{}, st: model.NewState(), used: map[string]bool{}, noted: map[string]bool{}, positions: map[string]float64{}}
	var tables []nftTable
	for _, item := range doc.Nftables {
		if raw, ok := item["table"]; ok {
			var t nftTable
			json.Unmarshal(raw, &t)
			if !(t.Family == "inet" && t.Name == "housecarl") {
				tables = append(tables, t)
			}
		}
	}
	switch {
	case in.Table != "":
		fam, name, _ := strings.Cut(strings.TrimSpace(in.Table), " ")
		found := false
		for _, t := range tables {
			if t.Family == fam && t.Name == name {
				im.table, found = t, true
			}
		}
		if !found {
			return nil, fmt.Errorf("there is no table %q in the ruleset (%s)", in.Table, tableList(tables))
		}
	case len(tables) == 0:
		return nil, fmt.Errorf("the ruleset has no table to import")
	case len(tables) > 1:
		return nil, fmt.Errorf("the ruleset has several tables (%s): say which to import (--table %q)", tableList(tables), tables[0].Family+" "+tables[0].Name)
	default:
		im.table = tables[0]
	}
	ours := func(fam, table string) bool { return fam == im.table.Family && table == im.table.Name }
	for _, item := range doc.Nftables {
		switch {
		case item["chain"] != nil:
			var c nftChain
			json.Unmarshal(item["chain"], &c)
			if ours(c.Family, c.Table) {
				im.chains[c.Name] = c
			}
		case item["rule"] != nil:
			var r nftRule
			json.Unmarshal(item["rule"], &r)
			if ours(r.Family, r.Table) {
				im.rules[r.Chain] = append(im.rules[r.Chain], r)
			}
		case item["set"] != nil:
			var s nftSet
			json.Unmarshal(item["set"], &s)
			if ours(s.Family, s.Table) {
				im.sets[s.Name] = s
			}
		case item["map"] != nil:
			var m nftMap
			json.Unmarshal(item["map"], &m)
			if ours(m.Family, m.Table) {
				im.maps[m.Name] = m
			}
		case item["flowtable"] != nil:
			var f nftFlowtable
			json.Unmarshal(item["flowtable"], &f)
			if f.Table == im.table.Name {
				im.flow = append(im.flow, f)
			}
		}
	}
	im.readText()
	im.readDefines()
	im.importSets()
	im.run()
	im.nameForwards()
	im.st.Renumber()
	return &Result{State: im.st, Notes: im.notes, Raw: im.raw}, nil
}

func tableList(ts []nftTable) string {
	var out []string
	for _, t := range ts {
		out = append(out, t.Family+" "+t.Name)
	}
	return strings.Join(out, ", ")
}

// readText maps rule handles to their text, from nft -a list ruleset.
var handleRe = regexp.MustCompile(`^\s*(.*?)\s*# handle (\d+)$`)
var counterRe = regexp.MustCompile(`counter packets \d+ bytes \d+`)

func (im *importer) readText() {
	inTable := false
	for _, l := range strings.Split(im.in.Text, "\n") {
		if strings.HasPrefix(l, "table ") {
			inTable = strings.HasPrefix(l, "table "+im.table.Family+" "+im.table.Name+" ")
			continue
		}
		if !inTable {
			continue
		}
		m := handleRe.FindStringSubmatch(l)
		if m == nil || strings.HasSuffix(m[1], "{") {
			continue
		}
		h, _ := strconv.Atoi(m[2])
		im.text[h] = strings.TrimSpace(counterRe.ReplaceAllString(m[1], "counter"))
	}
}

// ---- defines

var defineRe = regexp.MustCompile(`(?m)^\s*define\s+([A-Za-z_][A-Za-z0-9_]*)\s*=\s*(.+?)\s*$`)

func (im *importer) readDefines() {
	im.defines, im.addrNames, im.portNames, im.ifNames = map[string]string{}, map[string]string{}, map[string]string{}, map[string]string{}
	for _, m := range defineRe.FindAllStringSubmatch(im.in.Defines, -1) {
		im.defines[m[1]] = m[2]
	}
	expand := func(v string) []string {
		var out []string
		for _, part := range strings.Split(strings.Trim(strings.TrimSpace(v), "{}"), ",") {
			part = strings.Trim(strings.TrimSpace(part), `"`)
			if strings.HasPrefix(part, "$") {
				if d, ok := im.defines[part[1:]]; ok {
					for _, x := range strings.Split(strings.Trim(strings.TrimSpace(d), "{}"), ",") {
						out = append(out, strings.Trim(strings.TrimSpace(x), `"`))
					}
					continue
				}
			}
			if part != "" {
				out = append(out, part)
			}
		}
		return out
	}
	names := make([]string, 0, len(im.defines))
	for n := range im.defines {
		names = append(names, n)
	}
	sort.Strings(names)
	for _, n := range names {
		vals := expand(im.defines[n])
		if len(vals) == 0 {
			continue
		}
		var addrs, ports []string
		for _, v := range vals {
			if a, err := model.NormalizeAddress(v); err == nil {
				addrs = append(addrs, a)
			} else if p, err := model.NormalizePorts(v); err == nil {
				ports = append(ports, p)
			}
		}
		switch {
		case len(addrs) == len(vals):
			// A set for a list, or for one prefix; one address stays as it is.
			if len(addrs) > 1 || strings.Contains(addrs[0], "/") {
				if _, taken := im.addrNames[key(addrs)]; !taken {
					im.addrNames[key(addrs)] = n
				}
			}
		case len(ports) == len(vals) && len(ports) > 1:
			im.portNames[key(ports)] = n
		case len(vals) == 1 && validIface(vals[0]):
			im.ifNames[vals[0]] = n
		}
	}
}

func key(vals []string) string {
	s := append([]string(nil), vals...)
	sort.Strings(s)
	return strings.Join(s, ",")
}

var ifaceRe = regexp.MustCompile(`^[A-Za-z][A-Za-z0-9_.@-]{0,14}\*?$`)

func validIface(s string) bool {
	return ifaceRe.MatchString(s) && !strings.ContainsAny(s, ".:") || s == "lo"
}

// ---- sets

// importSets turns the table's named address sets into sets.
func (im *importer) importSets() {
	names := make([]string, 0, len(im.sets))
	for n := range im.sets {
		names = append(names, n)
	}
	sort.Strings(names)
	for _, n := range names {
		s := im.sets[n]
		var typ string
		json.Unmarshal(s.Type, &typ)
		if typ != "ipv4_addr" && typ != "ipv6_addr" {
			im.note("set %s (%s) isn't an address set: not imported; rules using it become raw rules", n, string(s.Type))
			continue
		}
		var entries []string
		for _, e := range s.Elem {
			entries = append(entries, values(e)...)
		}
		if existing := im.st.Set(n); existing != nil {
			existing.Entries = append(existing.Entries, entries...)
			continue
		}
		im.st.Sets = append(im.st.Sets, &model.AddressSet{ID: im.newID(), Name: setName(n), Entries: entries})
		im.used[n] = true
	}
}

var nameRe = regexp.MustCompile(`[^A-Za-z0-9_-]+`)

func setName(s string) string {
	s = nameRe.ReplaceAllString(s, "_")
	if s == "" || !(s[0] >= 'A' && s[0] <= 'Z' || s[0] >= 'a' && s[0] <= 'z') {
		s = "s_" + s
	}
	if len(s) > 48 {
		s = s[:48]
	}
	return s
}

// namedSet returns a set name for a list of address entries: a define's
// name if one matches, else none ("" keeps them literal).
func (im *importer) namedSet(entries []string) string {
	n, ok := im.addrNames[key(entries)]
	if !ok {
		return ""
	}
	name := setName(n)
	if !im.used[name] {
		im.used[name] = true
		im.st.Sets = append(im.st.Sets, &model.AddressSet{ID: im.newID(), Name: name, Entries: append([]string(nil), entries...)})
	}
	return name
}

// zone returns the zone of an interface, making it on first use.
func (im *importer) zone(iface string) string {
	for _, z := range im.st.Zones {
		for _, i := range z.Interfaces {
			if i == iface {
				return z.Name
			}
		}
	}
	name := iface
	if d, ok := im.ifNames[iface]; ok {
		name = d
		for _, suf := range []string{"_interface", "_iface", "_int", "_if", "_dev"} {
			name = strings.TrimSuffix(name, suf)
		}
	}
	name = setName(strings.TrimSuffix(name, "*"))
	if im.st.Zone(name) != nil {
		name = setName(iface + "_zone")
	}
	im.st.Zones = append(im.st.Zones, &model.Zone{ID: im.newID(), Name: name, Interfaces: []string{iface}})
	return name
}

func (im *importer) external(iface string) {
	if z := im.st.Zone(im.zone(iface)); z != nil && !z.External {
		z.External = true
	}
}

// ---- expressions

// values reads a right-hand value: an address, prefix, range, number,
// string, or an anonymous set of them, as entries.
func values(raw json.RawMessage) []string {
	var s string
	if json.Unmarshal(raw, &s) == nil {
		return []string{s}
	}
	var n json.Number
	if json.Unmarshal(raw, &n) == nil {
		return []string{n.String()}
	}
	var list []json.RawMessage
	if json.Unmarshal(raw, &list) == nil {
		var out []string
		for _, x := range list {
			out = append(out, values(x)...)
		}
		return out
	}
	var obj map[string]json.RawMessage
	if json.Unmarshal(raw, &obj) != nil {
		return nil
	}
	if set, ok := obj["set"]; ok {
		return values(set)
	}
	if p, ok := obj["prefix"]; ok {
		var x struct {
			Addr string `json:"addr"`
			Len  int    `json:"len"`
		}
		json.Unmarshal(p, &x)
		return []string{fmt.Sprintf("%s/%d", x.Addr, x.Len)}
	}
	if r, ok := obj["range"]; ok {
		var x []json.RawMessage
		json.Unmarshal(r, &x)
		if len(x) == 2 {
			a, b := values(x[0]), values(x[1])
			if len(a) == 1 && len(b) == 1 {
				return []string{a[0] + "-" + b[0]}
			}
		}
	}
	if e, ok := obj["elem"]; ok {
		var x struct {
			Val json.RawMessage `json:"val"`
		}
		json.Unmarshal(e, &x)
		return values(x.Val)
	}
	return nil
}

// parsed is one rule, read.
type parsed struct {
	inIf, outIf        []string
	notIn, notOut      bool
	src, dst           []string // entries, or "@set"
	notSrc, notDst     bool
	family             string
	proto              string
	dports             []string
	icmp               []string
	icmpProto          string
	ctState, ctStatus  []string
	hop255             bool
	tcpSyn             bool
	limit              *model.Limit
	log                bool
	logPrefix          string
	verdict            string // accept, drop, reject, jump, goto, return
	rejectWith         string
	target             string
	dnatAddr, dnatPort string
	snatAddr           string
	masq               bool
	redirect           string
	mss, flowAdd       bool
	unsupported        []string
	comment            string
	handle             int
	// mapUse: a dnat to a map, or a verdict map, still to be expanded
	// into one rule per element (expandMaps).
	mapUse *mapUse
	// name: a port forward's name, when the rule's comment won't do
	// (one of a map's elements).
	name string
}

// mapUse is a lookup in a map: "dnat ip to tcp dport map @forwards" or
// "tcp dport vmap { 22 : accept }".
type mapUse struct {
	kind string          // dnat or vmap
	key  json.RawMessage // what is looked up: {"payload": ...}, {"meta": ...}
	data json.RawMessage // "@name", or {"set": [[key, value], ...]}
}

type match struct {
	Op    string          `json:"op"`
	Left  json.RawMessage `json:"left"`
	Right json.RawMessage `json:"right"`
}

func parse(r nftRule) *parsed {
	p := &parsed{comment: r.Comment, handle: r.Handle}
	for _, raw := range r.Expr {
		var e map[string]json.RawMessage
		json.Unmarshal(raw, &e)
		for k, v := range e {
			p.expr(k, v)
		}
	}
	return p
}

func (p *parsed) bad(what string) { p.unsupported = append(p.unsupported, what) }

func (p *parsed) expr(k string, v json.RawMessage) {
	switch k {
	case "match":
		var m match
		json.Unmarshal(v, &m)
		p.match(m)
	case "counter":
	case "accept", "drop", "return":
		p.verdict = k
	case "jump", "goto":
		var t struct{ Target string }
		json.Unmarshal(v, &t)
		p.verdict, p.target = k, t.Target
	case "reject":
		p.verdict = "reject"
		var x struct {
			Type string `json:"type"`
		}
		json.Unmarshal(v, &x)
		if x.Type == "tcp reset" {
			p.rejectWith = "tcp-reset"
		}
	case "log":
		var x struct {
			Prefix string `json:"prefix"`
		}
		json.Unmarshal(v, &x)
		p.log, p.logPrefix = true, x.Prefix
	case "limit":
		var x struct {
			Rate  int    `json:"rate"`
			Per   string `json:"per"`
			Burst int    `json:"burst"`
			Inv   bool   `json:"inv"`
			Unit  string `json:"rate_unit"`
		}
		json.Unmarshal(v, &x)
		if x.Unit != "" && x.Unit != "packets" {
			p.bad("a byte rate limit")
			return
		}
		p.limit = &model.Limit{Rate: x.Rate, Per: x.Per, Burst: x.Burst, Over: x.Inv}
	case "dnat", "snat":
		var x struct {
			Family string          `json:"family"`
			Addr   json.RawMessage `json:"addr"`
			Port   json.RawMessage `json:"port"`
		}
		json.Unmarshal(v, &x)
		var lookup struct {
			Map *struct {
				Key  json.RawMessage `json:"key"`
				Data json.RawMessage `json:"data"`
			} `json:"map"`
		}
		if k == "dnat" && json.Unmarshal(x.Addr, &lookup) == nil && lookup.Map != nil && len(x.Port) == 0 {
			p.mapUse = &mapUse{kind: "dnat", key: lookup.Map.Key, data: lookup.Map.Data}
			return
		}
		addr, port := values(x.Addr), values(x.Port)
		if len(addr) != 1 || len(port) > 1 {
			p.bad(k + " to a range or map")
			return
		}
		if k == "dnat" {
			p.dnatAddr = addr[0]
			if len(port) == 1 {
				p.dnatPort = port[0]
			}
		} else {
			p.snatAddr = addr[0]
		}
	case "masquerade":
		if string(v) != "null" {
			p.bad("masquerade with options")
		}
		p.masq = true
	case "redirect":
		var x struct {
			Port json.RawMessage `json:"port"`
		}
		json.Unmarshal(v, &x)
		if port := values(x.Port); len(port) == 1 {
			p.redirect = port[0]
		} else {
			p.redirect = "?"
		}
	case "mangle":
		if strings.Contains(string(v), `"maxseg"`) && strings.Contains(string(v), `"mtu"`) {
			p.mss = true
		} else {
			p.bad("mangle")
		}
	case "flow":
		p.flowAdd = true
	case "vmap":
		var x struct {
			Key  json.RawMessage `json:"key"`
			Data json.RawMessage `json:"data"`
		}
		json.Unmarshal(v, &x)
		p.mapUse = &mapUse{kind: "vmap", key: x.Key, data: x.Data}
	default:
		p.bad(k)
	}
}

func (p *parsed) match(m match) {
	var left map[string]json.RawMessage
	json.Unmarshal(m.Left, &left)
	not := m.Op == "!="
	if m.Op != "==" && m.Op != "!=" && m.Op != "in" {
		p.bad("the operator " + m.Op)
		return
	}
	right := values(m.Right)
	if meta, ok := left["meta"]; ok {
		var x struct{ Key string }
		json.Unmarshal(meta, &x)
		switch x.Key {
		case "iifname":
			p.inIf, p.notIn = right, not
		case "oifname":
			p.outIf, p.notOut = right, not
		case "nfproto":
			if len(right) == 1 && !not {
				p.family = right[0]
			} else {
				p.bad("meta nfproto")
			}
		case "l4proto":
			if len(right) == 1 && !not {
				p.proto = right[0]
			} else {
				p.bad("meta l4proto with several protocols")
			}
		default:
			p.bad("meta " + x.Key)
		}
		return
	}
	if pl, ok := left["payload"]; ok {
		var x struct{ Protocol, Field string }
		json.Unmarshal(pl, &x)
		switch {
		case (x.Protocol == "ip" || x.Protocol == "ip6") && (x.Field == "saddr" || x.Field == "daddr"):
			if p.family == "" {
				p.family = map[string]string{"ip": "ipv4", "ip6": "ipv6"}[x.Protocol]
			}
			if x.Field == "saddr" {
				p.src, p.notSrc = right, not
			} else {
				p.dst, p.notDst = right, not
			}
		case (x.Protocol == "tcp" || x.Protocol == "udp" || x.Protocol == "sctp") && x.Field == "dport" && !not:
			p.proto, p.dports = x.Protocol, right
		case x.Protocol == "tcp" && x.Field == "flags" && len(right) == 1 && right[0] == "syn":
			p.tcpSyn = true
		case (x.Protocol == "icmp" || x.Protocol == "icmpv6") && x.Field == "type" && !not:
			p.icmpProto, p.icmp = x.Protocol, right
		case x.Protocol == "ip6" && x.Field == "hoplimit" && len(right) == 1 && right[0] == "255":
			p.hop255 = true
		default:
			p.bad(x.Protocol + " " + x.Field)
		}
		return
	}
	if ct, ok := left["ct"]; ok {
		var x struct{ Key string }
		json.Unmarshal(ct, &x)
		switch {
		case x.Key == "state" && !not:
			p.ctState = right
		case x.Key == "status" && !not:
			p.ctStatus = right
		default:
			p.bad("ct " + x.Key)
		}
		return
	}
	for k := range left {
		p.bad(k)
	}
}

// ---- converting

func (im *importer) run() {
	type base struct {
		name, kind string
	}
	var bases []base
	for name, c := range im.chains {
		switch {
		case c.Type == "filter" && c.Hook == "prerouting":
			bases = append(bases, base{name, model.ChainEarly})
		case c.Type == "filter" && (c.Hook == "input" || c.Hook == "forward" || c.Hook == "output"):
			bases = append(bases, base{name, c.Hook})
		case c.Type == "nat" && c.Hook == "prerouting":
			bases = append(bases, base{name, "dstnat"})
		case c.Type == "nat" && c.Hook == "postrouting":
			bases = append(bases, base{name, "srcnat"})
		case c.Hook != "":
			im.note("chain %s (%s %s) isn't imported: Housecarl doesn't manage that hook", name, c.Type, c.Hook)
		}
		set := &im.st.Settings
		switch {
		case c.Hook == "input" && c.Type == "filter":
			set.InputPolicy = c.Policy
		case c.Hook == "forward" && c.Type == "filter":
			set.ForwardPolicy = c.Policy
		case c.Hook == "output" && c.Type == "filter":
			set.OutputPolicy = c.Policy
		}
	}
	// NAT first: the filter chains' port-forward accepts are folded into
	// the port forwards.
	order := map[string]int{"dstnat": 0, "srcnat": 1, model.ChainEarly: 2, model.ChainInput: 3, model.ChainForward: 4, model.ChainOutput: 5}
	sort.SliceStable(bases, func(i, j int) bool { return order[bases[i].kind] < order[bases[j].kind] })
	im.st.Settings.Builtins = model.Builtins{}
	found := map[string]map[string]string{} // builtin → chain → "prefix" or "later"
	var deferred []func()
	for _, b := range bases {
		rules := im.flatten(b.name, nil, 0)
		switch b.kind {
		case "dstnat":
			for _, p := range rules {
				im.dstnat(p)
			}
		case "srcnat":
			for _, p := range rules {
				im.srcnat(p)
			}
		default:
			prefix := true
			for _, p := range rules {
				p := p
				if bi := im.builtinOf(b.kind, p); bi != "" {
					if found[bi] == nil {
						found[bi] = map[string]string{}
					}
					where := "later"
					if prefix {
						where = "prefix"
					}
					found[bi][b.kind] = where
					if prefix {
						continue
					}
				}
				prefix = false
				kind := b.kind
				deferred = append(deferred, func() { im.rule(kind, p) })
			}
		}
	}
	im.settleBuiltins(found)
	for _, f := range deferred {
		f()
	}
	if len(im.flow) > 0 {
		im.st.Settings.FlowtableDevices = im.flow[0].Dev
	}
	im.st.Sort()
}

// flatten reads a chain's rules, inlining jumps: each rule of the
// target chain gets the jump's own matches in front.
func (im *importer) flatten(chain string, prefix *parsed, depth int) []*parsed {
	var out []*parsed
	var rules []*parsed
	for _, r := range im.rules[chain] {
		rules = append(rules, im.expandMaps(parse(r))...)
	}
	for _, p := range rules {
		if prefix != nil {
			p = im.merge(prefix, p)
		}
		switch p.verdict {
		case "jump", "goto":
			if depth > 4 || im.chains[p.target].Hook != "" {
				p.bad("a jump too deep")
				out = append(out, p)
				continue
			}
			jumpMatch := *p
			jumpMatch.verdict, jumpMatch.target = "", ""
			out = append(out, im.flatten(p.target, &jumpMatch, depth+1)...)
			if p.verdict == "goto" {
				im.note("the goto to %s became the same rules followed by the rest of %s: check the order", p.target, chain)
			}
			continue
		case "return":
			if prefix != nil && len(p.unsupported) == 0 && !hasMatch(p, prefix) {
				return out // an unconditional return ends the jumped-to chain
			}
			p.bad("a conditional return")
		}
		out = append(out, p)
	}
	return out
}

// expandMaps turns a rule that looks something up in a map into one rule
// per element, each matching the element's key and doing what its value
// says: "tcp dport vmap { 22 : accept, 23 : drop }" becomes "tcp dport 22
// accept" and "tcp dport 23 drop"; "dnat ip to tcp dport map @forwards"
// one dnat (later a port forward) per element. A lookup finds at most one
// element, and their keys don't overlap, so the rules do the same in
// order. A map that can't be expanded leaves the rule unsupported.
func (im *importer) expandMaps(p *parsed) []*parsed {
	u := p.mapUse
	if u == nil {
		return []*parsed{p}
	}
	p.mapUse = nil
	fail := func(why string) []*parsed {
		p.bad(why)
		return []*parsed{p}
	}
	var keyObj map[string]json.RawMessage
	json.Unmarshal(u.key, &keyObj)
	if keyObj["concat"] != nil {
		return fail("a map keyed by several fields (" + u.kind + ")")
	}
	// The elements: a named map's, or the anonymous one's.
	var elems []json.RawMessage
	mapName := ""
	var ref string
	if json.Unmarshal(u.data, &ref) == nil && strings.HasPrefix(ref, "@") {
		m, ok := im.maps[ref[1:]]
		if !ok {
			return fail("the map " + ref + ", which isn't in the table")
		}
		mapName, elems = m.Name, m.Elem
	} else {
		var anon struct {
			Set []json.RawMessage `json:"set"`
		}
		if json.Unmarshal(u.data, &anon) != nil || anon.Set == nil {
			return fail("a " + u.kind + " map Housecarl can't read")
		}
		elems = anon.Set
	}
	if len(elems) == 0 {
		im.note("rule handle %d looks up the empty map %s: left out", p.handle, map[bool]string{true: "@" + mapName, false: "{}"}[mapName != ""])
		return nil
	}
	var out []*parsed
	for _, e := range elems {
		var pair []json.RawMessage
		if json.Unmarshal(e, &pair) != nil || len(pair) != 2 {
			return fail("a map element Housecarl can't read")
		}
		q := *p
		q.unsupported = append([]string{}, p.unsupported...)
		q.match(match{Op: "==", Left: u.key, Right: pair[0]})
		switch u.kind {
		case "dnat":
			addr, port := mapTarget(pair[1])
			if addr == "" {
				return fail("a dnat map whose values aren't addresses (or address . port)")
			}
			q.dnatAddr, q.dnatPort = addr, port
			if mapName != "" {
				if k := values(pair[0]); len(k) == 1 {
					q.name = mapName + "-" + k[0]
				}
			}
		case "vmap":
			var verdict map[string]json.RawMessage
			if json.Unmarshal(pair[1], &verdict) != nil || len(verdict) != 1 {
				return fail("a verdict map value Housecarl can't read")
			}
			for k, v := range verdict {
				q.expr(k, v)
			}
		}
		out = append(out, &q)
	}
	if mapName != "" {
		what := map[string]string{"dnat": "port forward", "vmap": "rule"}[u.kind]
		if !im.noted["map "+mapName] {
			im.noted["map "+mapName] = true
			if len(elems) == 1 {
				im.note("map %s: its element became a %s", mapName, what)
			} else {
				im.note("map %s: its %d elements became %d %ss, one each", mapName, len(elems), len(elems), what)
			}
		}
	}
	return out
}

// mapTarget reads a dnat map's value: an address, or address . port.
func mapTarget(raw json.RawMessage) (addr, port string) {
	var obj struct {
		Concat []json.RawMessage `json:"concat"`
	}
	if json.Unmarshal(raw, &obj) == nil && len(obj.Concat) == 2 {
		a, b := values(obj.Concat[0]), values(obj.Concat[1])
		if len(a) == 1 && len(b) == 1 {
			return a[0], b[0]
		}
		return "", ""
	}
	if a := values(raw); len(a) == 1 {
		return a[0], ""
	}
	return "", ""
}

// hasMatch reports whether p matches more than the jump's own matches.
func hasMatch(p, prefix *parsed) bool {
	return len(p.dports) != len(prefix.dports) || len(p.src) != len(prefix.src) || len(p.dst) != len(prefix.dst) ||
		len(p.inIf) != len(prefix.inIf) || len(p.outIf) != len(prefix.outIf) || len(p.ctState) != len(prefix.ctState) || len(p.icmp) != len(prefix.icmp)
}

// merge puts a jump's matches in front of a jumped-to rule's. When both
// match the same field, the rule's own (narrower, usually) is kept and
// noted.
func (im *importer) merge(prefix, p *parsed) *parsed {
	q := *p
	q.unsupported = append(append([]string{}, prefix.unsupported...), p.unsupported...)
	fill := func(what string, dst *[]string, not *bool, src []string, srcNot bool) {
		if len(*dst) == 0 && len(src) > 0 {
			*dst, *not = src, srcNot
		} else if len(*dst) > 0 && len(src) > 0 && key(*dst) != key(src) {
			im.note("rule handle %d: both the jump to it and the rule match %s; the rule's own (%s) are kept, the jump's (%s) dropped: check it",
				p.handle, what, strings.Join(*dst, ", "), strings.Join(src, ", "))
		}
	}
	fill("interfaces in", &q.inIf, &q.notIn, prefix.inIf, prefix.notIn)
	fill("interfaces out", &q.outIf, &q.notOut, prefix.outIf, prefix.notOut)
	fill("sources", &q.src, &q.notSrc, prefix.src, prefix.notSrc)
	fill("destinations", &q.dst, &q.notDst, prefix.dst, prefix.notDst)
	if q.family == "" {
		q.family = prefix.family
	}
	if len(q.ctState) == 0 {
		q.ctState = prefix.ctState
	}
	if q.proto == "" {
		q.proto, q.dports = prefix.proto, prefix.dports
	}
	return &q
}

// ---- built-ins

var essentials6 = map[string]bool{"destination-unreachable": true, "packet-too-big": true, "time-exceeded": true, "parameter-problem": true, "echo-request": true, "echo-reply": true}
var nd6 = map[string]bool{"nd-router-solicit": true, "nd-router-advert": true, "nd-neighbor-solicit": true, "nd-neighbor-advert": true}

func plain(p *parsed) bool {
	return len(p.unsupported) == 0 && p.limit == nil && !p.log && len(p.src) == 0 && len(p.dst) == 0 && len(p.outIf) == 0
}

// builtinOf names the built-in a rule is, or "".
func (im *importer) builtinOf(chain string, p *parsed) string {
	only := func(items []string, allowed map[string]bool) bool {
		for _, i := range items {
			if !allowed[i] {
				return false
			}
		}
		return len(items) > 0
	}
	switch {
	case chain == model.ChainInput && p.verdict == "accept" && len(p.inIf) == 1 && p.inIf[0] == "lo" && !p.notIn && plain(p) && p.proto == "":
		return "loopback"
	case p.verdict == "accept" && key(p.ctState) == "established,related" && plain(p) && len(p.inIf) == 0 && p.proto == "":
		return "established"
	case p.verdict == "drop" && key(p.ctState) == "invalid" && plain(p) && len(p.inIf) == 0 && p.proto == "":
		return "invalid"
	case chain == model.ChainInput && p.verdict == "accept" && p.icmpProto == "icmpv6" && only(p.icmp, essentials6) && plain(p) && len(p.inIf) == 0 && !p.hop255:
		return "icmpv6"
	case chain == model.ChainInput && p.verdict == "accept" && p.icmpProto == "icmpv6" && only(p.icmp, nd6) && p.hop255 && plain(p) && len(p.inIf) == 0:
		return "icmpv6-nd"
	case chain == model.ChainInput && p.verdict == "accept" && p.icmpProto == "icmp" && only(p.icmp, map[string]bool{"echo-request": true, "echo-reply": true}) &&
		plain(p) && p.notIn && len(p.inIf) > 0:
		for _, i := range p.inIf {
			im.external(i)
		}
		return "ping"
	case chain == model.ChainInput && p.verdict == "accept" && p.proto == "udp" && key(p.dports) == "546" && len(p.inIf) > 0 && !p.notIn &&
		p.limit == nil && !p.log && len(p.dst) == 0 && key(p.src) == "fe80::/10":
		for _, i := range p.inIf {
			im.external(i)
		}
		return "dhcpv6-client"
	case chain == model.ChainForward && p.mss && p.tcpSyn && len(p.outIf) > 0 && !p.notOut:
		for _, i := range p.outIf {
			im.external(i)
		}
		return "mss-clamp"
	case chain == model.ChainForward && p.flowAdd:
		return "flowtable"
	case chain == model.ChainEarly && p.verdict == "drop" && len(p.inIf) > 0 && !p.notIn && len(p.src) > 0 && !p.notSrc &&
		len(p.dst) == 0 && p.proto == "" && len(p.unsupported) == 0:
		for _, i := range p.inIf {
			im.external(i)
		}
		for _, s := range p.src {
			if strings.HasPrefix(s, "@") {
				return ""
			}
		}
		set := &im.st.Settings
		if p.family == "ipv6" {
			set.OwnPrefixes = append(set.OwnPrefixes, p.src...)
			im.st.Settings.AntispoofV6 = nil
		} else {
			set.AntispoofV4 = p.src
		}
		return "antispoof"
	}
	return ""
}

// settleBuiltins turns on the built-ins found where they go, in every
// chain they apply to; the others stay off, and the rules that looked
// like them are kept as rules.
func (im *importer) settleBuiltins(found map[string]map[string]string) {
	b := &im.st.Settings.Builtins
	on := func(name string, chains ...string) bool {
		for _, c := range chains {
			if found[name][c] != "prefix" {
				return false
			}
		}
		return true
	}
	b.Loopback = on("loopback", model.ChainInput)
	b.Established = on("established", model.ChainInput, model.ChainForward)
	b.DropInvalid = on("invalid", model.ChainInput, model.ChainForward)
	b.ICMPv6 = on("icmpv6", model.ChainInput) && on("icmpv6-nd", model.ChainInput)
	b.PingInternal = on("ping", model.ChainInput)
	b.DHCPv6Client = on("dhcpv6-client", model.ChainInput)
	b.MSSClamp = on("mss-clamp", model.ChainForward)
	b.Antispoof = on("antispoof", model.ChainEarly)
	if !b.Antispoof {
		im.st.Settings.AntispoofV4, im.st.Settings.AntispoofV6, im.st.Settings.OwnPrefixes = nil, nil, nil
	} else if im.st.Settings.AntispoofV6 == nil {
		im.st.Settings.AntispoofV6 = []string{}
	}
	if b.ICMPv6 {
		im.note("the ICMPv6 built-in also accepts MLD from link-local addresses, and lets ICMPv6 errors through the forward chain (RFC 4890)")
	}
	// The ones found in one chain's head but not another's: explicit rules
	// in the chains where they were found.
	for name, chains := range found {
		for chain, where := range chains {
			if where != "prefix" {
				continue
			}
			kept := map[string]bool{"loopback": b.Loopback, "established": b.Established, "invalid": b.DropInvalid, "icmpv6": b.ICMPv6, "icmpv6-nd": b.ICMPv6,
				"ping": b.PingInternal, "dhcpv6-client": b.DHCPv6Client, "mss-clamp": b.MSSClamp, "antispoof": b.Antispoof, "flowtable": true}[name]
			if !kept {
				im.note("%s in the %s chain stays a rule (it isn't in every chain the built-in covers, or comes after other rules)", name, chain)
				im.builtinRule(name, chain)
			}
		}
	}
}

// builtinRule writes a built-in that stays off as a rule of its chain.
func (im *importer) builtinRule(name, chain string) {
	r := &model.Rule{ID: im.newID(), Chain: chain, Position: im.nextPos(chain) - 1000}
	switch name {
	case "established":
		r.CtState, r.Action = []string{"established", "related"}, model.ActionAccept
	case "invalid":
		r.CtState, r.Action = []string{"invalid"}, model.ActionDrop
	case "loopback":
		r.Raw, r.Action = `iifname "lo" accept`, model.ActionAccept
	default:
		im.note("built-in %s of the %s chain couldn't be kept; add it by hand", name, chain)
		return
	}
	im.st.Rules = append(im.st.Rules, r)
}

func (im *importer) nextPos(chain string) float64 {
	im.positions[chain]++
	return im.positions[chain]
}

// ---- rules

// addrRefs turns address entries into references: "@set" → the set, a
// list matching a define → its set, else the literal entries.
func (im *importer) addrRefs(entries []string) []string {
	var out, lit []string
	for _, e := range entries {
		if strings.HasPrefix(e, "@") {
			out = append(out, setName(e[1:]))
			continue
		}
		if n, err := model.NormalizeAddress(e); err == nil {
			lit = append(lit, n)
		} else {
			lit = append(lit, e)
		}
	}
	if len(lit) > 0 {
		if name := im.namedSet(lit); name != "" {
			out = append(out, name)
		} else {
			out = append(out, lit...)
		}
	}
	return out
}

func (im *importer) services(p *parsed) ([]string, bool) {
	var out []string
	if p.icmpProto != "" {
		for _, t := range p.icmp {
			out = append(out, p.icmpProto+"/"+t)
		}
	}
	if p.proto != "" {
		if len(p.dports) == 0 {
			if p.proto != "tcp" && p.proto != "udp" && p.proto != "sctp" {
				return nil, false
			}
			return append(out, p.proto+"/1-65535"), true
		}
		var ports []string
		for _, d := range p.dports {
			if strings.HasPrefix(d, "@") {
				return nil, false
			}
			n, err := model.NormalizePorts(d)
			if err != nil {
				return nil, false
			}
			ports = append(ports, n)
		}
		if name, ok := im.portNames[key(ports)]; ok {
			svc := setName(name)
			if im.st.Service(svc) == nil || im.st.Service(svc).Builtin {
				var entries []string
				for _, x := range ports {
					entries = append(entries, p.proto+"/"+x)
				}
				im.st.Services = append(im.st.Services, &model.Service{ID: im.newID(), Name: svc, Entries: entries})
			}
			return append(out, svc), true
		}
		for _, x := range ports {
			out = append(out, p.proto+"/"+x)
		}
	}
	return out, true
}

func (im *importer) zones(ifaces []string) []string {
	var out []string
	for _, i := range ifaces {
		out = append(out, im.zone(i))
	}
	return out
}

// toMatch builds a Match; ok is false when something can't be said.
func (im *importer) toMatch(p *parsed) (model.Match, bool) {
	svcs, ok := im.services(p)
	if !ok || len(p.unsupported) > 0 {
		return model.Match{}, false
	}
	m := model.Match{InZones: im.zones(p.inIf), NotIn: p.notIn, OutZones: im.zones(p.outIf), NotOut: p.notOut,
		Sources: im.addrRefs(p.src), NotSources: p.notSrc, Destinations: im.addrRefs(p.dst), NotDests: p.notDst, Services: svcs}
	if len(p.src) == 0 && len(p.dst) == 0 && p.icmpProto == "" && p.family != "" {
		m.Family = p.family
	}
	return m, true
}

// rule converts a filter rule (or keeps it raw).
func (im *importer) rule(chain string, p *parsed) {
	if chain == model.ChainForward && im.absorbForward(p) {
		return
	}
	r := &model.Rule{ID: im.newID(), Chain: chain, Position: im.nextPos(chain), Comment: p.comment, CtState: p.ctState, CtStatus: p.ctStatus,
		Limit: p.limit, Log: p.log, LogPrefix: p.logPrefix, RejectWith: p.rejectWith}
	switch p.verdict {
	case "accept", "drop", "reject":
		r.Action = p.verdict
	case "":
		switch {
		case len(p.unsupported) > 0:
			// The verdict may be in what couldn't be read (a verdict map).
			im.rawRule(r, p)
			return
		case !p.log:
			im.note("a %s rule with no verdict (handle %d) was left out", chain, p.handle)
			return
		}
		r.Action = model.ActionLog
	default:
		p.bad(p.verdict)
	}
	m, ok := im.toMatch(p)
	if ok && !p.hop255 && !p.mss && !p.tcpSyn && !p.flowAdd && p.dnatAddr == "" && !p.masq {
		r.Match = m
		im.st.Rules = append(im.st.Rules, r)
		return
	}
	im.rawRule(r, p)
}

var mapRefRe = regexp.MustCompile(`@([A-Za-z0-9_]+)`)

func (im *importer) rawRule(r *model.Rule, p *parsed) {
	text, ok := im.text[p.handle]
	if !ok {
		im.note("rule handle %d of chain %s couldn't be expressed (%s), and there is no text to keep it raw: add it by hand (import with the nft -a list ruleset text)", p.handle, r.Chain, strings.Join(p.unsupported, ", "))
		return
	}
	// The original's comment goes into Housecarl's.
	if i := strings.LastIndex(text, ` comment "`); i >= 0 {
		text = strings.TrimSpace(text[:i])
	}
	// A named map isn't carried over: a raw rule naming it would make
	// nftables refuse the whole ruleset.
	for _, ref := range mapRefRe.FindAllStringSubmatch(text, -1) {
		if _, ok := im.maps[ref[1]]; ok {
			im.note("rule handle %d of chain %s uses the map @%s, which couldn't be expanded (%s): left out, add it by hand: %s",
				p.handle, r.Chain, ref[1], strings.Join(p.unsupported, ", "), text)
			return
		}
	}
	if r.Action == "" {
		r.Action = model.ActionAccept
	}
	r.Match, r.Raw = model.Match{}, text
	im.st.Rules = append(im.st.Rules, r)
	why := strings.Join(p.unsupported, ", ")
	if why == "" {
		why = "a match Housecarl has no field for"
	}
	im.raw = append(im.raw, fmt.Sprintf("%s: %s (%s)", r.Chain, text, why))
	if strings.Contains(text, "@") {
		im.note("raw rule %q names a set of the old table: Housecarl's sets are NAME_v4 and NAME_v6", text)
	}
}

// ---- NAT

func (im *importer) dstnat(p *parsed) {
	switch {
	case p.dnatAddr != "" && len(p.unsupported) == 0 && p.proto != "" && len(p.dports) == 1 && !p.notDst && !p.notSrc:
		ports, err := model.NormalizePorts(p.dports[0])
		if err != nil {
			break
		}
		f := &model.PortForward{Protocols: []string{p.proto}, Ports: ports, To: p.dnatAddr, ToPort: p.dnatPort, Comment: p.comment, Name: forwardName(p.comment)}
		if p.name != "" {
			f.Name = strings.ToLower(nameRe.ReplaceAllString(p.name, "-"))
		}
		if f.ToPort == ports {
			f.ToPort = ""
		}
		f.PublicAddresses = im.addrRefs(p.dst)
		f.Sources = im.addrRefs(p.src)
		for _, i := range p.inIf {
			im.external(i)
		}
		// The same forward for another protocol: one forward, both.
		for _, o := range im.st.Forwards {
			if o.Ports == f.Ports && o.To == f.To && o.ToPort == f.ToPort && key(o.PublicAddresses) == key(f.PublicAddresses) && key(o.Sources) == key(f.Sources) {
				o.Protocols = append(o.Protocols, p.proto)
				return
			}
		}
		f.ID, f.Position = im.newID(), float64(len(im.st.Forwards)+1)
		im.st.Forwards = append(im.st.Forwards, f)
		return
	case p.redirect != "" && p.redirect != "?" && len(p.unsupported) == 0:
		m, ok := im.toMatch(p)
		if ok {
			im.st.Redirects = append(im.st.Redirects, &model.Redirect{ID: im.newID(), Position: float64(len(im.st.Redirects) + 1), Match: m, ToPort: p.redirect, Comment: p.comment})
			return
		}
	}
	im.note("the dstnat rule handle %d couldn't be imported (%s): %s", p.handle, strings.Join(p.unsupported, ", "), im.text[p.handle])
}

var forwardWords = regexp.MustCompile(`(?i)^\s*port\s*forward(ing)?\s*[:-]?\s*`)

func forwardName(comment string) string {
	n := strings.TrimSpace(forwardWords.ReplaceAllString(comment, ""))
	return strings.Trim(strings.ToLower(nameRe.ReplaceAllString(n, "-")), "-")
}

// nameForwards makes the forwards' names (from their comments) valid and
// unique: "8096 to jellyfin" becomes "fwd-8096-to-jellyfin", a second
// "web" becomes "web-2".
func (im *importer) nameForwards() {
	seen := map[string]bool{}
	for _, f := range im.st.Forwards {
		n := f.Name
		if n == "" {
			continue
		}
		if !(n[0] >= 'a' && n[0] <= 'z') {
			n = "fwd-" + n
		}
		if len(n) > 44 {
			n = strings.TrimRight(n[:44], "-")
		}
		base := n
		for i := 2; seen[n]; i++ {
			n = fmt.Sprintf("%s-%d", base, i)
		}
		seen[n] = true
		f.Name = n
	}
}

func (im *importer) srcnat(p *parsed) {
	if len(p.unsupported) > 0 {
		im.note("the srcnat rule handle %d couldn't be imported (%s): %s", p.handle, strings.Join(p.unsupported, ", "), im.text[p.handle])
		return
	}
	// Hairpin: masquerading connections that were port forwarded, to the
	// forwards' hosts.
	if p.masq && key(p.ctStatus) == "dnat" && len(p.dst) > 0 && !p.notDst {
		matched := 0
		for _, f := range im.st.Forwards {
			for _, d := range p.dst {
				if d == f.To {
					f.Hairpin, f.HairpinSources = true, im.addrRefs(p.src)
					if p.notSrc {
						f.HairpinSources = nil
						im.note("hairpin for %s: the original excluded sources; Housecarl's hairpin covers all inside sources", f.Label())
					}
					matched++
				}
			}
		}
		if matched > 0 {
			return
		}
	}
	m, ok := im.toMatch(p)
	if !ok || !p.masq && p.snatAddr == "" {
		im.note("the srcnat rule handle %d couldn't be imported: %s", p.handle, im.text[p.handle])
		return
	}
	for _, i := range p.outIf {
		if !p.notOut && p.masq {
			im.external(i)
		}
	}
	if p.family == "ipv6" && len(p.src) == 0 {
		m.Family = model.FamilyIPv6
	}
	for _, s := range p.src {
		if a, err := model.ParseAddress(s); err == nil && a.IsV6() {
			m.Family = model.FamilyIPv6
		}
	}
	im.st.SNATs = append(im.st.SNATs, &model.SourceNAT{ID: im.newID(), Position: float64(len(im.st.SNATs) + 1), Match: m, To: p.snatAddr, Comment: p.comment})
}

// absorbForward folds a port forward's own forward-chain accept (and an
// IPv6 pinhole on its port) into the port forward.
func (im *importer) absorbForward(p *parsed) bool {
	if p.verdict != "accept" || len(p.unsupported) > 0 || len(p.dst) != 1 || p.notDst || len(p.dports) != 1 || p.proto == "" || len(p.src) > 0 || len(p.outIf) > 0 {
		return false
	}
	port, err := model.NormalizePorts(p.dports[0])
	if err != nil {
		return false
	}
	dst := p.dst[0]
	if p.family == "ipv4" || !strings.Contains(dst, ":") {
		for _, f := range im.st.Forwards {
			inside := f.ToPort
			if inside == "" {
				inside = f.Ports
			}
			if f.To == dst && inside == port && contains(f.Protocols, p.proto) {
				if len(p.inIf) > 0 && !im.noted["forward-iif"] {
					im.noted["forward-iif"] = true
					im.note("port forwards' own accepts aren't limited to arriving on %s any more: they only let port-forwarded connections through (ct status dnat), which hairpin needs from inside too", strings.Join(p.inIf, ", "))
				}
				return true
			}
		}
		return false
	}
	// IPv6: a pinhole for the one forward on that port.
	var cands []*model.PortForward
	for _, f := range im.st.Forwards {
		inside := f.ToPort
		if inside == "" {
			inside = f.Ports
		}
		if inside == port && contains(f.Protocols, p.proto) && f.To6 == "" {
			cands = append(cands, f)
		}
	}
	if len(cands) == 1 && len(p.ctStatus) == 0 {
		cands[0].To6 = dst
		im.note("the IPv6 rule to %s port %s became %s's IPv6 pinhole", dst, port, cands[0].Label())
		return true
	}
	return false
}

func contains(list []string, s string) bool {
	for _, x := range list {
		if x == s {
			return true
		}
	}
	return false
}