Add blocking: blocklists and block/allow rules with BIND response policy zones

jarld downloads blocklists (Adblock, hosts or plain domains), checks them
daily and reloads named only when a list changed; your own block and
allow rules take precedence, and the most specific rule wins. Lists and
rules apply per view (default: every view that offers recursion). Web UI
Blocking page with name checks, jarl blocklist and jarl block, the
/blocking API, blocked counts in the statistics. Database schema 6.

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

internal/engine/engine.go

@@ -14,8 +14,10 @@ import (
 	"fmt"
 	"io/fs"
 	"log/slog"
+	"net/http"
 	"os"
 	"path/filepath"
+	"slices"
 	"sort"
 	"strings"
 	"sync"
@@ -23,6 +25,7 @@ import (
 
 	"jarl/internal/auth"
 	"jarl/internal/bind"
+	"jarl/internal/blocking"
 	"jarl/internal/dnsname"
 	"jarl/internal/model"
 	"jarl/internal/namedconf"
@@ -64,6 +67,12 @@ type Engine struct {
 	deploy *Deployer
 	mu     sync.Mutex // serializes applies
 	Now    func() time.Time
+
+	// Blocklist downloads (blocklists.go).
+	blMu   sync.Mutex    // serializes downloads
+	blKick chan struct{} // a list was added or changed
+	HTTP   *http.Client  // for downloads; nil: a default client
+	Limits BlocklistLimits
 }
 
 // New creates an engine.
@@ -78,6 +87,8 @@ func New(st *store.Store, tools *bind.Tools, cfg Config, log *slog.Logger) *Engi
 		store: st, tools: tools, cfg: cfg, log: log,
 		deploy: &Deployer{Group: cfg.FileGroup, NamedWritable: []string{cfg.Paths.ZoneDir, cfg.Paths.CacheDir}},
 		Now:    time.Now,
+		blKick: make(chan struct{}, 1),
+		Limits: DefaultBlocklistLimits(),
 	}
 }
 
@@ -383,6 +394,7 @@ type plan struct {
 	drift         []DriftEntry
 	configChanged bool
 	reloadZones   []*model.Zone
+	reloadPolicy  []render.PolicyZone // rules zones whose file changed
 	verify        map[int64]uint32
 	newZones      bool
 	backup        *Backup
@@ -446,7 +458,7 @@ func (e *Engine) makePlan(ctx context.Context, base, work *model.State, user str
 		}
 	}
 	for path, df := range deployed {
-		if pl.out.File(path) != nil || df.Kind != render.KindZone {
+		if pl.out.File(path) != nil || df.Kind != render.KindZone && df.Kind != render.KindPolicy {
 			continue
 		}
 		old, existed, _ := readFile(path)
@@ -484,6 +496,16 @@ func (e *Engine) makePlan(ctx context.Context, base, work *model.State, user str
 	if len(work.Zones) != len(base.Zones) {
 		pl.configChanged = true
 	}
+	// Rules zones whose content changed. New ones come with a change to
+	// named.conf, and reconfig loads them.
+	for _, z := range pl.out.Policy {
+		if z.ListID != 0 || !changedPaths[z.File] {
+			continue
+		}
+		if slices.Contains(baseOut.Policy, z) {
+			pl.reloadPolicy = append(pl.reloadPolicy, z)
+		}
+	}
 
 	if !e.cfg.SkipCheck {
 		if err := e.stagingCheck(ctx, pl); err != nil {
@@ -519,6 +541,16 @@ func (e *Engine) stagingCheck(ctx context.Context, pl *plan) error {
 			return err
 		}
 	}
+	// Blocklists as empty policy zones: their content is checked when
+	// they are downloaded.
+	for _, path := range sout.Blocklists {
+		if err := os.MkdirAll(filepath.Dir(path), 0o750); err != nil {
+			return err
+		}
+		if err := os.WriteFile(path, []byte(blocking.Placeholder()), 0o640); err != nil {
+			return err
+		}
+	}
 	main, err := e.stagingMain(dir, sp.MainConfig())
 	if err != nil {
 		return err
@@ -796,6 +828,12 @@ func (e *Engine) applyOps(ctx context.Context, cs *model.Changeset, reqs []Reque
 	res.ChangesetID = cs.ID
 	res.Applied = true
 	e.removeDerived(pl)
+	for _, op := range cs.Ops {
+		if strings.HasPrefix(op.Kind, "blocklist.") {
+			e.KickBlocklists()
+			break
+		}
+	}
 	e.log.Info("changeset applied", "changeset", cs.ID, "user", p.Name(), "ops", len(cs.Ops), "files", len(res.Files), "description", cs.Description)
 	return res, nil
 }
@@ -829,6 +867,9 @@ func (e *Engine) deployAndReload(ctx context.Context, pl *plan, res *Result, rel
 		return &Error{Kind: KindBIND, Message: "writing configuration files failed (nothing was changed): " + err.Error()}
 	}
 	pl.backup = backup
+	if err := e.ensureBlocklistFiles(pl.out.Blocklists); err != nil {
+		e.log.Warn("creating a blocklist's empty zone file failed", "err", err)
+	}
 	pl.reloaded = reload
 	if !reload {
 		return nil
@@ -860,6 +901,11 @@ func (e *Engine) rollback(ctx context.Context, pl *plan) {
 			e.log.Error("rndc reload after restore failed", "zone", z.Name, "err", err)
 		}
 	}
+	for _, z := range pl.reloadPolicy {
+		if err := e.tools.ReloadZone(ctx, z.Name, z.View); err != nil {
+			e.log.Error("rndc reload after restore failed", "zone", z.Name, "err", err)
+		}
+	}
 }
 
 // namedView returns the view name to pass to rndc for a zone ("" without
@@ -885,6 +931,16 @@ func (e *Engine) reload(ctx context.Context, pl *plan) ([]string, error) {
 		}
 		done = append(done, "reload "+zoneDesc(pl.work, z))
 	}
+	for _, z := range pl.reloadPolicy {
+		label := "blocking rules"
+		if z.View != "" {
+			label += " [view " + z.View + "]"
+		}
+		if err := e.tools.ReloadZone(ctx, z.Name, z.View); err != nil {
+			return done, fmt.Errorf("reloading %s failed: %v", label, err)
+		}
+		done = append(done, "reload "+label)
+	}
 	// named reloads zones asynchronously and reports load errors only in
 	// its log, so wait until it serves the new serials.
 	deadline := time.Now().Add(e.cfg.ReloadTimeout)
@@ -1003,6 +1059,12 @@ func (e *Engine) Resync(ctx context.Context, p *auth.Principal, opts ApplyOption
 			pl.verify[z.ID] = z.SOA.Serial
 		}
 	}
+	pl.reloadPolicy = nil
+	for _, z := range pl.out.Policy {
+		if z.ListID == 0 {
+			pl.reloadPolicy = append(pl.reloadPolicy, z)
+		}
+	}
 	reload := !e.cfg.NoReload && !opts.NoReload
 	if adopted, aerr := e.Adopted(); reload && (aerr != nil || !adopted) {
 		reload = false