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/validate/blocking.go

@@ -0,0 +1,93 @@
+package validate
+
+import (
+	"strings"
+
+	"jarl/internal/model"
+)
+
+// checkBlocking checks blocklists and block/allow rules (docs/blocking.md).
+func (c *checker) checkBlocking() {
+	viewNames := func(ids []int64) string {
+		var names []string
+		for _, id := range ids {
+			if v := c.s.Views[id]; v != nil {
+				names = append(names, v.Name)
+			}
+		}
+		return strings.Join(names, ", ")
+	}
+	used := map[int64]bool{} // views (0: the server) with blocking
+	// what describes where something applies, and warns when it can't
+	// have any effect.
+	effective := func(objType string, id int64, label string, ids []int64) []int64 {
+		for _, vid := range ids {
+			if c.s.Views[vid] == nil {
+				c.errf("blocking_view_missing", objType, id, "%s names view %d, which doesn't exist", label, vid)
+			}
+		}
+		views := c.s.BlockingViews(ids)
+		if len(views) == 0 {
+			c.warnf("blocking_no_view", objType, id, "%s has no effect: no view offers recursion, and blocking only changes answers to recursive queries", label)
+		}
+		var idle []int64
+		for _, vid := range views {
+			if !c.s.RecursionOn(vid) {
+				idle = append(idle, vid)
+			}
+		}
+		if len(idle) > 0 {
+			c.warnf("blocking_no_recursion", objType, id, "%s has no effect in view %s: it doesn't offer recursion, and blocking only changes answers to recursive queries", label, viewNames(idle))
+		}
+		for _, vid := range views {
+			used[vid] = true
+		}
+		return views
+	}
+	for _, b := range c.s.SortedBlocklists() {
+		if !b.Disabled {
+			effective("blocklist", b.ID, "blocklist "+b.Name, b.ViewIDs)
+		}
+	}
+	// One rule per name and view: two would compete for the same entries
+	// of the policy zone.
+	seen := map[string]*model.BlockRule{} // view|name -> first rule
+	for _, r := range c.s.SortedBlockRules() {
+		label := "the rule for " + r.Name
+		for _, vid := range effective("blockrule", r.ID, label, r.ViewIDs) {
+			key := c.blockingScope(vid) + "|" + r.Name
+			if first := seen[key]; first != nil && first.ID != r.ID {
+				where := ""
+				if v := c.s.Views[vid]; v != nil {
+					where = " in view " + v.Name
+				}
+				c.errf("blocking_rule_duplicate", "blockrule", r.ID, "there are two rules for %s%s (%s and %s); keep one", r.Name, where, first.Action, r.Action)
+				continue
+			}
+			seen[key] = r
+		}
+	}
+	// Jarl writes the response-policy statement where blocking is used;
+	// named allows one per view (or for the server).
+	for vid := range used {
+		if o := c.s.FindOption(model.ScopeView, vid, "response-policy"); vid != 0 && o != nil {
+			p := c.errf("blocking_response_policy", "option", o.ID, "view %s has a response-policy option, but Jarl's blocking writes that statement there; remove the option (or the blocking that applies to this view)", c.s.Views[vid].Name)
+			p.View = c.s.Views[vid].Name
+		}
+	}
+	if o := c.s.FindOption(model.ScopeOptions, 0, "response-policy"); o != nil && len(used) > 0 {
+		c.errf("blocking_response_policy", "option", o.ID, "the server has a response-policy option, which Jarl's blocking replaces wherever it is used; remove the option, or set up your policy zones with Jarl's blocking instead")
+	}
+	for _, z := range c.s.Zones {
+		if n := strings.TrimSuffix(z.Name, "."); n == "jarl.invalid" || strings.HasSuffix(n, ".jarl.invalid") {
+			c.zoneProblem(z, Error, "zone_name_reserved", "zone names under jarl.invalid are reserved for Jarl's blocking")
+		}
+	}
+}
+
+func (c *checker) blockingScope(viewID int64) string {
+	if v := c.s.Views[viewID]; v != nil {
+		return v.Name
+	}
+	return ""
+}