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/config/config.go

@@ -25,18 +25,39 @@ type Config struct {
 	TrustedProxies []string `yaml:"trusted_proxies"`
 	// Socket is a local unix socket for the API, where root and jarld's
 	// own user need no token ("" for none).
-	Socket     string  `yaml:"socket"`
-	Database   string  `yaml:"database"`
-	StagingDir string  `yaml:"staging_dir"`
-	Log        Log     `yaml:"log"`
-	Session    Session `yaml:"session"`
-	TOTP       TOTP    `yaml:"totp"`
-	BIND       BIND    `yaml:"bind"`
-	Audit      Audit   `yaml:"audit"`
-	Backup     Backup  `yaml:"backup"`
-	Stats      Stats   `yaml:"stats"`
-	ACME       ACME    `yaml:"acme"`
-	Porkbun    Porkbun `yaml:"porkbun"`
+	Socket     string   `yaml:"socket"`
+	Database   string   `yaml:"database"`
+	StagingDir string   `yaml:"staging_dir"`
+	Log        Log      `yaml:"log"`
+	Session    Session  `yaml:"session"`
+	TOTP       TOTP     `yaml:"totp"`
+	BIND       BIND     `yaml:"bind"`
+	Audit      Audit    `yaml:"audit"`
+	Backup     Backup   `yaml:"backup"`
+	Stats      Stats    `yaml:"stats"`
+	ACME       ACME     `yaml:"acme"`
+	Porkbun    Porkbun  `yaml:"porkbun"`
+	Blocking   Blocking `yaml:"blocking"`
+}
+
+// Blocking configures blocklist downloads (docs/blocking.md). The lists
+// and rules themselves are configuration in the database.
+type Blocking struct {
+	// Refresh is how often each list is checked for changes; a list is
+	// only downloaded again when it changed.
+	Refresh       Duration `yaml:"refresh"`
+	MaxDownloadMB int      `yaml:"max_download_mb"`
+	MaxEntries    int      `yaml:"max_entries"`
+}
+
+func (b *Blocking) check() error {
+	if b.Refresh < Duration(time.Hour) {
+		return fmt.Errorf("refresh must be at least 1h (list hosts ask not to be polled more often)")
+	}
+	if b.MaxDownloadMB < 1 || b.MaxEntries < 1 {
+		return fmt.Errorf("max_download_mb and max_entries must be at least 1")
+	}
+	return nil
 }
 
 // Porkbun lets Jarl manage domains' name servers, glue records and DNSSEC
@@ -300,8 +321,9 @@ func Default() *Config {
 			Retention:         StatsRetention{Minute: Duration(7 * 24 * time.Hour), Hour: Duration(90 * 24 * time.Hour), Day: Duration(730 * 24 * time.Hour)},
 			TopN:              100,
 		},
-		ACME:   ACME{HTTPReq: HTTPReq{RequireHTTPS: true}},
-		Backup: Backup{Dir: "/var/backups/jarl", Retention: Duration(30 * 24 * time.Hour), KeepAtLeast: 7, WarnAfter: Duration(2 * 24 * time.Hour)},
+		ACME:     ACME{HTTPReq: HTTPReq{RequireHTTPS: true}},
+		Blocking: Blocking{Refresh: Duration(24 * time.Hour), MaxDownloadMB: 64, MaxEntries: 1_000_000},
+		Backup:   Backup{Dir: "/var/backups/jarl", Retention: Duration(30 * 24 * time.Hour), KeepAtLeast: 7, WarnAfter: Duration(2 * 24 * time.Hour)},
 	}
 }
 
@@ -369,6 +391,9 @@ func (c *Config) check() error {
 	if err := c.Porkbun.check(); err != nil {
 		return fmt.Errorf("porkbun: %w", err)
 	}
+	if err := c.Blocking.check(); err != nil {
+		return fmt.Errorf("blocking: %w", err)
+	}
 	switch c.Log.Format {
 	case "text", "json":
 	default:
@@ -600,4 +625,12 @@ porkbun:
   api_key: ""          # pk1_...
   secret_api_key: ""   # sk1_...
   domains: []          # only these domains (default: any Jarl zone the key reaches)
+
+# Downloading blocklists (docs/blocking.md). The lists and rules are set up
+# in the web UI or with 'jarl blocklist' and 'jarl block'; this only sets
+# how jarld downloads them.
+blocking:
+  refresh: 24h           # check each list for changes this often (at least 1h)
+  max_download_mb: 64    # refuse larger downloads
+  max_entries: 1000000   # refuse lists with more domains
 `