fix: allowlist parent domain unblocks subdomains in blocklist

The allowlist walk-up was interleaved with the blocklist walk-up,
so an exact blocklist match on www.example.com short-circuited
before reaching example.com in the allowlist. Now allowlist is
checked at all parent levels before consulting the blocklist.

Deduplicate is_blocked/check via find_in_set helper; is_blocked
delegates to check. Adds 7 new blocklist tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/blocklist.rs

@@ -78,40 +78,9 @@ impl BlocklistStore {
     }
 
     pub fn is_blocked(&self, domain: &str) -> bool {
-        if !self.enabled {
+        self.check(domain).blocked
-            return false;
     }
 
-        if let Some(until) = self.paused_until {
-            if Instant::now() < until {
-                return false;
-            }
-        }
-
-        if self.allowlist.contains(domain) {
-            return false;
-        }
-
-        if self.domains.contains(domain) {
-            return true;
-        }
-
-        // Walk up: ads.tracker.example.com → tracker.example.com → example.com
-        let mut d = domain;
-        while let Some(dot) = d.find('.') {
-            d = &d[dot + 1..];
-            if self.allowlist.contains(d) {
-                return false;
-            }
-            if self.domains.contains(d) {
-                return true;
-            }
-        }
-
-        false
-    }
-
-    /// Check if a domain is blocked and return the reason.
     pub fn check(&self, domain: &str) -> BlockCheckResult {
         let domain = domain.to_lowercase();
 
@@ -119,28 +88,39 @@ impl BlocklistStore {
             return BlockCheckResult::disabled();
         }
 
-        if self.allowlist.contains(&domain) {
+        if let Some(until) = self.paused_until {
-            return BlockCheckResult::allowed(&domain, "exact match in allowlist");
+            if Instant::now() < until {
+                return BlockCheckResult::disabled();
+            }
         }
 
-        if self.domains.contains(&domain) {
+        if let Some(matched) = Self::find_in_set(&domain, &self.allowlist) {
-            return BlockCheckResult::blocked(&domain, "exact match in blocklist");
+            let reason = if matched == domain { "exact match in allowlist" } else { "parent domain in allowlist" };
+            return BlockCheckResult::allowed(matched, reason);
         }
 
-        let mut d = domain.as_str();
+        if let Some(matched) = Self::find_in_set(&domain, &self.domains) {
-        while let Some(dot) = d.find('.') {
+            let reason = if matched == domain { "exact match in blocklist" } else { "parent domain in blocklist" };
-            d = &d[dot + 1..];
+            return BlockCheckResult::blocked(matched, reason);
-            if self.allowlist.contains(d) {
-                return BlockCheckResult::allowed(d, "parent domain in allowlist");
-            }
-            if self.domains.contains(d) {
-                return BlockCheckResult::blocked(d, "parent domain in blocklist");
-            }
         }
 
         BlockCheckResult::not_blocked()
     }
 
+    fn find_in_set<'a>(domain: &'a str, set: &HashSet<String>) -> Option<&'a str> {
+        if set.contains(domain) {
+            return Some(domain);
+        }
+        let mut d = domain;
+        while let Some(dot) = d.find('.') {
+            d = &d[dot + 1..];
+            if set.contains(d) {
+                return Some(d);
+            }
+        }
+        None
+    }
+
     /// Atomically swap in a new domain set. Build the set outside the lock,
     /// then call this to swap — keeps lock hold time sub-microsecond.
     pub fn swap_domains(&mut self, domains: HashSet<String>, sources: Vec<String>) {
@@ -247,6 +227,78 @@ pub fn parse_blocklist(text: &str) -> HashSet<String> {
 mod tests {
     use super::*;
 
+    fn store_with(domains: &[&str], allowlist: &[&str]) -> BlocklistStore {
+        let mut store = BlocklistStore::new();
+        store.swap_domains(
+            domains.iter().map(|s| s.to_string()).collect(),
+            vec![],
+        );
+        for d in allowlist {
+            store.add_to_allowlist(d);
+        }
+        store
+    }
+
+    #[test]
+    fn exact_block() {
+        let store = store_with(&["ads.example.com"], &[]);
+        assert!(store.is_blocked("ads.example.com"));
+        assert!(!store.is_blocked("example.com"));
+    }
+
+    #[test]
+    fn parent_block_covers_subdomain() {
+        let store = store_with(&["tracker.com"], &[]);
+        assert!(store.is_blocked("tracker.com"));
+        assert!(store.is_blocked("www.tracker.com"));
+        assert!(store.is_blocked("deep.sub.tracker.com"));
+    }
+
+    #[test]
+    fn exact_allowlist_unblocks() {
+        let store = store_with(&["ads.example.com"], &["ads.example.com"]);
+        assert!(!store.is_blocked("ads.example.com"));
+    }
+
+    #[test]
+    fn parent_allowlist_unblocks_subdomain() {
+        let store = store_with(
+            &["example.com", "www.example.com"],
+            &["example.com"],
+        );
+        assert!(!store.is_blocked("example.com"));
+        assert!(!store.is_blocked("www.example.com"));
+        assert!(!store.is_blocked("sub.deep.example.com"));
+    }
+
+    #[test]
+    fn allowlist_does_not_unblock_sibling() {
+        let store = store_with(
+            &["www.example.com", "ads.example.com"],
+            &["www.example.com"],
+        );
+        assert!(!store.is_blocked("www.example.com"));
+        assert!(store.is_blocked("ads.example.com"));
+    }
+
+    #[test]
+    fn check_reports_parent_allowlist() {
+        let store = store_with(
+            &["goatcounter.com", "www.goatcounter.com"],
+            &["goatcounter.com"],
+        );
+        let result = store.check("www.goatcounter.com");
+        assert!(!result.blocked);
+        assert_eq!(result.matched_rule.as_deref(), Some("goatcounter.com"));
+    }
+
+    #[test]
+    fn disabled_never_blocks() {
+        let mut store = store_with(&["ads.example.com"], &[]);
+        store.set_enabled(false);
+        assert!(!store.is_blocked("ads.example.com"));
+    }
+
     #[test]
     fn heap_bytes_grows_with_domains() {
         let mut store = BlocklistStore::new();