feat: add COALESCED query path and coalescing tests

Followers in the inflight coalescing path now log as COALESCED instead
of RECURSIVE, making it visible in the dashboard when queries were
deduplicated vs independently resolved. Adds 10 tests covering
InflightGuard cleanup, broadcast mechanics, and concurrent handle_query
coalescing through a mock TCP DNS server.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

site/dashboard.html

@@ -285,6 +285,7 @@ body {
 .path-tag.OVERRIDE { background: rgba(82, 122, 82, 0.12); color: var(--emerald); }
 .path-tag.SERVFAIL { background: rgba(181, 68, 58, 0.12); color: var(--rose); }
 .path-tag.BLOCKED { background: rgba(163, 152, 136, 0.15); color: var(--text-dim); }
+.path-tag.COALESCED { background: rgba(138, 104, 158, 0.12); color: var(--violet-dim); }
 
 /* Sidebar panels */
 .sidebar {
@@ -547,6 +548,8 @@ body {
           <select id="logFilterPath" onchange="applyLogFilter()"
             style="font-family:var(--font-mono);font-size:0.7rem;padding:0.25rem 0.4rem;border:1px solid var(--border);border-radius:4px;background:var(--bg-surface);color:var(--text-secondary);outline:none;">
             <option value="">all paths</option>
+            <option value="RECURSIVE">recursive</option>
+            <option value="COALESCED">coalesced</option>
             <option value="FORWARD">forward</option>
             <option value="CACHED">cached</option>
             <option value="BLOCKED">blocked</option>

src/api.rs

@@ -182,6 +182,7 @@ struct QueriesStats {
     total: u64,
     forwarded: u64,
     recursive: u64,
+    coalesced: u64,
     cached: u64,
     local: u64,
     overridden: u64,
@@ -499,6 +500,7 @@ async fn stats(State(ctx): State<Arc<ServerCtx>>) -> Json<StatsResponse> {
             total: snap.total,
             forwarded: snap.forwarded,
             recursive: snap.recursive,
+            coalesced: snap.coalesced,
             cached: snap.cached,
             local: snap.local,
             overridden: snap.overridden,

src/ctx.rs

@@ -201,7 +201,7 @@ pub async fn handle_query(
                         match rx.recv().await {
                             Ok(Some(mut resp)) => {
                                 resp.header.id = query.header.id;
-                                (resp, QueryPath::Recursive, DnssecStatus::Indeterminate)
+                                (resp, QueryPath::Coalesced, DnssecStatus::Indeterminate)
                             }
                             _ => (
                                 DnsPacket::response_from(&query, ResultCode::SERVFAIL),
@@ -442,6 +442,20 @@ impl Drop for InflightGuard<'_> {
     }
 }
 
+/// Build a wire-format DNS query packet for the given domain and type.
+#[cfg(test)]
+fn build_wire_query(id: u16, domain: &str, qtype: QueryType) -> BytePacketBuffer {
+    let mut pkt = DnsPacket::new();
+    pkt.header.id = id;
+    pkt.header.recursion_desired = true;
+    pkt.header.questions = 1;
+    pkt.questions
+        .push(crate::question::DnsQuestion::new(domain.to_string(), qtype));
+    let mut buf = BytePacketBuffer::new();
+    pkt.write(&mut buf).unwrap();
+    BytePacketBuffer::from_bytes(buf.filled())
+}
+
 fn special_use_response(query: &DnsPacket, qname: &str, qtype: QueryType) -> DnsPacket {
     use std::net::{Ipv4Addr, Ipv6Addr};
     if qname == "ipv4only.arpa" {
@@ -475,3 +489,334 @@ fn special_use_response(query: &DnsPacket, qname: &str, qtype: QueryType) -> Dns
         DnsPacket::response_from(query, ResultCode::NXDOMAIN)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashMap;
+    use std::net::{Ipv4Addr, SocketAddr};
+    use std::sync::{Arc, Mutex, RwLock};
+    use tokio::sync::broadcast;
+
+    // ---- InflightGuard unit tests ----
+
+    #[test]
+    fn inflight_guard_removes_key_on_drop() {
+        let map: Mutex<InflightMap> = Mutex::new(HashMap::new());
+        let key = ("example.com".to_string(), QueryType::A);
+        let (tx, _) = broadcast::channel::<Option<DnsPacket>>(1);
+        map.lock().unwrap().insert(key.clone(), tx);
+
+        assert_eq!(map.lock().unwrap().len(), 1);
+        {
+            let _guard = InflightGuard {
+                inflight: &map,
+                key: key.clone(),
+            };
+        } // guard dropped here
+        assert!(map.lock().unwrap().is_empty());
+    }
+
+    #[test]
+    fn inflight_guard_only_removes_own_key() {
+        let map: Mutex<InflightMap> = Mutex::new(HashMap::new());
+        let key_a = ("a.com".to_string(), QueryType::A);
+        let key_b = ("b.com".to_string(), QueryType::A);
+        let (tx_a, _) = broadcast::channel::<Option<DnsPacket>>(1);
+        let (tx_b, _) = broadcast::channel::<Option<DnsPacket>>(1);
+        map.lock().unwrap().insert(key_a.clone(), tx_a);
+        map.lock().unwrap().insert(key_b.clone(), tx_b);
+
+        {
+            let _guard = InflightGuard {
+                inflight: &map,
+                key: key_a,
+            };
+        }
+        let m = map.lock().unwrap();
+        assert_eq!(m.len(), 1);
+        assert!(m.contains_key(&key_b));
+    }
+
+    #[test]
+    fn inflight_guard_same_domain_different_qtype_independent() {
+        let map: Mutex<InflightMap> = Mutex::new(HashMap::new());
+        let key_a = ("example.com".to_string(), QueryType::A);
+        let key_aaaa = ("example.com".to_string(), QueryType::AAAA);
+        let (tx_a, _) = broadcast::channel::<Option<DnsPacket>>(1);
+        let (tx_aaaa, _) = broadcast::channel::<Option<DnsPacket>>(1);
+        map.lock().unwrap().insert(key_a.clone(), tx_a);
+        map.lock().unwrap().insert(key_aaaa.clone(), tx_aaaa);
+
+        {
+            let _guard = InflightGuard {
+                inflight: &map,
+                key: key_a,
+            };
+        }
+        let m = map.lock().unwrap();
+        assert_eq!(m.len(), 1);
+        assert!(m.contains_key(&key_aaaa));
+    }
+
+    // ---- Coalescing disposition tests ----
+
+    #[test]
+    fn leader_follower_disposition() {
+        // First caller becomes leader, second becomes follower
+        let map: Mutex<InflightMap> = Mutex::new(HashMap::new());
+        let key = ("test.com".to_string(), QueryType::A);
+
+        // First: no entry → insert and become leader
+        let is_leader = {
+            let mut m = map.lock().unwrap();
+            if m.get(&key).is_some() {
+                false
+            } else {
+                let (tx, _) = broadcast::channel::<Option<DnsPacket>>(1);
+                m.insert(key.clone(), tx);
+                true
+            }
+        };
+        assert!(is_leader);
+
+        // Second: entry exists → become follower
+        let is_follower = {
+            let m = map.lock().unwrap();
+            m.get(&key).is_some()
+        };
+        assert!(is_follower);
+    }
+
+    #[tokio::test]
+    async fn broadcast_delivers_result_to_follower() {
+        let (tx, _) = broadcast::channel::<Option<DnsPacket>>(1);
+        let mut rx = tx.subscribe();
+
+        let mut resp = DnsPacket::new();
+        resp.header.id = 42;
+        resp.answers.push(DnsRecord::A {
+            domain: "test.com".into(),
+            addr: Ipv4Addr::new(1, 2, 3, 4),
+            ttl: 300,
+        });
+
+        let _ = tx.send(Some(resp));
+        let received = rx.recv().await.unwrap().unwrap();
+        assert_eq!(received.header.id, 42);
+        assert_eq!(received.answers.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn broadcast_none_signals_failure() {
+        let (tx, _) = broadcast::channel::<Option<DnsPacket>>(1);
+        let mut rx = tx.subscribe();
+        let _ = tx.send(None);
+
+        let received = rx.recv().await.unwrap();
+        assert!(received.is_none());
+    }
+
+    #[tokio::test]
+    async fn multiple_followers_all_receive_result() {
+        let (tx, _) = broadcast::channel::<Option<DnsPacket>>(1);
+        let mut rx1 = tx.subscribe();
+        let mut rx2 = tx.subscribe();
+        let mut rx3 = tx.subscribe();
+
+        let mut resp = DnsPacket::new();
+        resp.answers.push(DnsRecord::A {
+            domain: "multi.com".into(),
+            addr: Ipv4Addr::new(10, 0, 0, 1),
+            ttl: 60,
+        });
+        let _ = tx.send(Some(resp));
+
+        for rx in [&mut rx1, &mut rx2, &mut rx3] {
+            let r = rx.recv().await.unwrap().unwrap();
+            assert_eq!(r.answers.len(), 1);
+        }
+    }
+
+    // ---- Integration: concurrent handle_query coalescing ----
+
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    use tokio::net::TcpListener;
+
+    /// Spawn a slow TCP DNS server that delays `delay` before responding.
+    /// Returns (addr, query_count) where query_count is an Arc<AtomicU32>
+    /// tracking how many queries were actually resolved (not coalesced).
+    async fn spawn_slow_dns_server(
+        delay: Duration,
+    ) -> (SocketAddr, Arc<std::sync::atomic::AtomicU32>) {
+        let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let addr = listener.local_addr().unwrap();
+        let count = Arc::new(std::sync::atomic::AtomicU32::new(0));
+        let count_clone = count.clone();
+
+        tokio::spawn(async move {
+            loop {
+                let (mut stream, _) = match listener.accept().await {
+                    Ok(c) => c,
+                    Err(_) => break,
+                };
+                let count = count_clone.clone();
+                let delay = delay;
+                tokio::spawn(async move {
+                    let mut len_buf = [0u8; 2];
+                    if stream.read_exact(&mut len_buf).await.is_err() {
+                        return;
+                    }
+                    let len = u16::from_be_bytes(len_buf) as usize;
+                    let mut data = vec![0u8; len];
+                    if stream.read_exact(&mut data).await.is_err() {
+                        return;
+                    }
+
+                    let mut buf = BytePacketBuffer::from_bytes(&data);
+                    let query = match DnsPacket::from_buffer(&mut buf) {
+                        Ok(q) => q,
+                        Err(_) => return,
+                    };
+
+                    count.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
+
+                    // Deliberate delay to create coalescing window
+                    tokio::time::sleep(delay).await;
+
+                    let mut resp = DnsPacket::response_from(&query, ResultCode::NOERROR);
+                    resp.header.authoritative_answer = true;
+                    if let Some(q) = query.questions.first() {
+                        resp.answers.push(DnsRecord::A {
+                            domain: q.name.clone(),
+                            addr: Ipv4Addr::new(10, 0, 0, 1),
+                            ttl: 300,
+                        });
+                    }
+
+                    let mut resp_buf = BytePacketBuffer::new();
+                    if resp.write(&mut resp_buf).is_err() {
+                        return;
+                    }
+                    let resp_bytes = resp_buf.filled();
+                    let mut out = Vec::with_capacity(2 + resp_bytes.len());
+                    out.extend_from_slice(&(resp_bytes.len() as u16).to_be_bytes());
+                    out.extend_from_slice(resp_bytes);
+                    let _ = stream.write_all(&out).await;
+                });
+            }
+        });
+        (addr, count)
+    }
+
+    async fn test_recursive_ctx(root_hint: SocketAddr) -> Arc<ServerCtx> {
+        let socket = tokio::net::UdpSocket::bind("127.0.0.1:0").await.unwrap();
+        Arc::new(ServerCtx {
+            socket,
+            zone_map: HashMap::new(),
+            cache: RwLock::new(crate::cache::DnsCache::new(100, 60, 86400)),
+            stats: Mutex::new(crate::stats::ServerStats::new()),
+            overrides: RwLock::new(crate::override_store::OverrideStore::new()),
+            blocklist: RwLock::new(crate::blocklist::BlocklistStore::new()),
+            query_log: Mutex::new(crate::query_log::QueryLog::new(100)),
+            services: Mutex::new(crate::service_store::ServiceStore::new()),
+            lan_peers: Mutex::new(crate::lan::PeerStore::new(90)),
+            forwarding_rules: Vec::new(),
+            upstream: Mutex::new(crate::forward::Upstream::Udp(
+                "127.0.0.1:53".parse().unwrap(),
+            )),
+            upstream_auto: false,
+            upstream_port: 53,
+            lan_ip: Mutex::new(Ipv4Addr::LOCALHOST),
+            timeout: Duration::from_secs(3),
+            proxy_tld: "numa".to_string(),
+            proxy_tld_suffix: ".numa".to_string(),
+            lan_enabled: false,
+            config_path: "/tmp/test-numa.toml".to_string(),
+            config_found: false,
+            config_dir: std::path::PathBuf::from("/tmp"),
+            data_dir: std::path::PathBuf::from("/tmp"),
+            tls_config: None,
+            upstream_mode: crate::config::UpstreamMode::Recursive,
+            root_hints: vec![root_hint],
+            srtt: RwLock::new(crate::srtt::SrttCache::new(true)),
+            inflight: Mutex::new(HashMap::new()),
+            dnssec_enabled: false,
+            dnssec_strict: false,
+        })
+    }
+
+    #[tokio::test]
+    async fn concurrent_queries_coalesce_to_single_resolution() {
+        // Force TCP-only so mock server works
+        crate::recursive::UDP_DISABLED.store(true, std::sync::atomic::Ordering::Release);
+
+        let (server_addr, query_count) = spawn_slow_dns_server(Duration::from_millis(200)).await;
+        let ctx = test_recursive_ctx(server_addr).await;
+        let src: SocketAddr = "127.0.0.1:9999".parse().unwrap();
+
+        // Fire 5 concurrent queries for the same (domain, A)
+        let mut handles = Vec::new();
+        for i in 0..5u16 {
+            let ctx = ctx.clone();
+            let buf = build_wire_query(100 + i, "coalesce-test.example.com", QueryType::A);
+            handles.push(tokio::spawn(async move {
+                handle_query(buf, src, &ctx).await
+            }));
+        }
+
+        for h in handles {
+            h.await.unwrap().unwrap();
+        }
+
+        // Only 1 resolution should have reached the upstream server
+        let actual = query_count.load(std::sync::atomic::Ordering::Relaxed);
+        assert_eq!(actual, 1, "expected 1 upstream query, got {}", actual);
+
+        // Inflight map must be empty after all queries complete
+        assert!(ctx.inflight.lock().unwrap().is_empty());
+
+        crate::recursive::reset_udp_state();
+    }
+
+    #[tokio::test]
+    async fn different_qtypes_not_coalesced() {
+        crate::recursive::UDP_DISABLED.store(true, std::sync::atomic::Ordering::Release);
+
+        let (server_addr, query_count) = spawn_slow_dns_server(Duration::from_millis(100)).await;
+        let ctx = test_recursive_ctx(server_addr).await;
+        let src: SocketAddr = "127.0.0.1:9999".parse().unwrap();
+
+        // Fire A and AAAA concurrently — should NOT coalesce
+        let ctx_ref = ctx.clone();
+        let ctx_ref2 = ctx.clone();
+        let buf_a = build_wire_query(200, "different-qt.example.com", QueryType::A);
+        let buf_aaaa = build_wire_query(201, "different-qt.example.com", QueryType::AAAA);
+
+        let h1 = tokio::spawn(async move { handle_query(buf_a, src, &ctx_ref).await });
+        let h2 = tokio::spawn(async move { handle_query(buf_aaaa, src, &ctx_ref2).await });
+
+        h1.await.unwrap().unwrap();
+        h2.await.unwrap().unwrap();
+
+        let actual = query_count.load(std::sync::atomic::Ordering::Relaxed);
+        assert!(actual >= 2, "A and AAAA should resolve independently, got {}", actual);
+        assert!(ctx.inflight.lock().unwrap().is_empty());
+
+        crate::recursive::reset_udp_state();
+    }
+
+    #[tokio::test]
+    async fn inflight_map_cleaned_after_upstream_error() {
+        // Server that rejects everything — no server running at all
+        let bogus_addr: SocketAddr = "127.0.0.1:1".parse().unwrap();
+        let ctx = test_recursive_ctx(bogus_addr).await;
+        let src: SocketAddr = "127.0.0.1:9999".parse().unwrap();
+
+        let buf = build_wire_query(300, "will-fail.example.com", QueryType::A);
+        let _ = handle_query(buf, src, &ctx).await;
+
+        // Map must be clean even after error
+        assert!(ctx.inflight.lock().unwrap().is_empty());
+    }
+}

src/recursive.rs

@@ -21,7 +21,7 @@ const UDP_FAIL_THRESHOLD: u8 = 3;
 
 static QUERY_ID: AtomicU16 = AtomicU16::new(1);
 static UDP_FAILURES: std::sync::atomic::AtomicU8 = std::sync::atomic::AtomicU8::new(0);
-static UDP_DISABLED: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
+pub(crate) static UDP_DISABLED: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
 
 fn next_id() -> u16 {
     QUERY_ID.fetch_add(1, Ordering::Relaxed)

src/stats.rs

@@ -4,6 +4,7 @@ pub struct ServerStats {
     queries_total: u64,
     queries_forwarded: u64,
     queries_recursive: u64,
+    queries_coalesced: u64,
     queries_cached: u64,
     queries_blocked: u64,
     queries_local: u64,
@@ -18,6 +19,7 @@ pub enum QueryPath {
     Cached,
     Forwarded,
     Recursive,
+    Coalesced,
     Blocked,
     Overridden,
     UpstreamError,
@@ -30,6 +32,7 @@ impl QueryPath {
             QueryPath::Cached => "CACHED",
             QueryPath::Forwarded => "FORWARD",
             QueryPath::Recursive => "RECURSIVE",
+            QueryPath::Coalesced => "COALESCED",
             QueryPath::Blocked => "BLOCKED",
             QueryPath::Overridden => "OVERRIDE",
             QueryPath::UpstreamError => "SERVFAIL",
@@ -45,6 +48,8 @@ impl QueryPath {
             Some(QueryPath::Forwarded)
         } else if s.eq_ignore_ascii_case("RECURSIVE") {
             Some(QueryPath::Recursive)
+        } else if s.eq_ignore_ascii_case("COALESCED") {
+            Some(QueryPath::Coalesced)
         } else if s.eq_ignore_ascii_case("BLOCKED") {
             Some(QueryPath::Blocked)
         } else if s.eq_ignore_ascii_case("OVERRIDE") {
@@ -69,6 +74,7 @@ impl ServerStats {
             queries_total: 0,
             queries_forwarded: 0,
             queries_recursive: 0,
+            queries_coalesced: 0,
             queries_cached: 0,
             queries_blocked: 0,
             queries_local: 0,
@@ -85,6 +91,7 @@ impl ServerStats {
             QueryPath::Cached => self.queries_cached += 1,
             QueryPath::Forwarded => self.queries_forwarded += 1,
             QueryPath::Recursive => self.queries_recursive += 1,
+            QueryPath::Coalesced => self.queries_coalesced += 1,
             QueryPath::Blocked => self.queries_blocked += 1,
             QueryPath::Overridden => self.queries_overridden += 1,
             QueryPath::UpstreamError => self.upstream_errors += 1,
@@ -106,6 +113,7 @@ impl ServerStats {
             total: self.queries_total,
             forwarded: self.queries_forwarded,
             recursive: self.queries_recursive,
+            coalesced: self.queries_coalesced,
             cached: self.queries_cached,
             local: self.queries_local,
             overridden: self.queries_overridden,
@@ -121,11 +129,12 @@ impl ServerStats {
         let secs = uptime.as_secs() % 60;
 
         log::info!(
-            "STATS | uptime {}h{}m{}s | total {} | fwd {} | recursive {} | cached {} | local {} | override {} | blocked {} | errors {}",
+            "STATS | uptime {}h{}m{}s | total {} | fwd {} | recursive {} | coalesced {} | cached {} | local {} | override {} | blocked {} | errors {}",
             hours, mins, secs,
             self.queries_total,
             self.queries_forwarded,
             self.queries_recursive,
+            self.queries_coalesced,
             self.queries_cached,
             self.queries_local,
             self.queries_overridden,
@@ -140,6 +149,7 @@ pub struct StatsSnapshot {
     pub total: u64,
     pub forwarded: u64,
     pub recursive: u64,
+    pub coalesced: u64,
     pub cached: u64,
     pub local: u64,
     pub overridden: u64,