Answer 504, not 408, when a request outlasts its time limit (closes #70)

The hand-written time limit middleware answered 408 and wrote that
answer from its own goroutine while the handler could still be writing.
It is replaced by chi's middleware.Timeout, placed after
JSONResponseMiddleware so its 504 is not lost behind a 200.

When a handler's database read or other lookup fails, it asks
deadlinePassed whether the request's time limit passed and, if so,
answers 504 instead of its 500 or 404. JSONValidationMiddleware answers
504 with the JSON error body when the limit has passed and the handler
wrote nothing. status.json and /api/v1/stats answer 504 when their
4-second database read runs out.

Model: opus-5-5

README.md

@@ -144,8 +144,9 @@ routewatch/
 - **Reconnection**: Exponential backoff (5s-320s) with reset after 30s of stable connection
 - **IP Lookup**: the most specific live route is found by looking up the
   address's prefix at each mask length, longest first, in the prefix index
-  (at most 33 lookups for IPv4, 129 for IPv6); prefixes are stored in the
-  text form Go's `net/netip` prints
+  (at most 25 lookups for IPv4, 113 for IPv6); prefixes are stored in the
+  text form Go's `net/netip` prints. Routes shorter than /8 for IPv4 or /16
+  for IPv6, such as a default route, are not used.
 
 ### Database Schema
 

internal/database/database.go

@@ -37,6 +37,14 @@ const (
 	ipv6Bits       = 128
 )
 
+// The IP lookup does not use routes shorter than these mask lengths. A default
+// route or a route this short only says where a peer sends traffic it has no
+// better route for; it does not say who holds the address.
+const (
+	minLookupMaskLengthV4 = 8
+	minLookupMaskLengthV6 = 16
+)
+
 // SQLite memory tuning. cache_size and busy_timeout go in the DSN so every
 // pooled connection gets them; the heap limits are process-wide and set once.
 const (
@@ -1876,11 +1884,12 @@ func (d *Database) GetIPInfo(ip string) (*IPInfo, error) {
 // GetIPInfoContext returns comprehensive IP information with context support.
 //
 // It finds the most specific live route for the address with point lookups on
-// the prefix index: for each mask length from the longest (32 or 128) down to 0
-// it looks up the address's network prefix at that length, and the first length
-// with a live route wins. That is at most 33 or 129 indexed lookups, however
-// many routes are live. The prefix is looked up in the text form net/netip
-// prints, which is the form the prefix handler stores.
+// the prefix index: for each mask length from the longest (32 or 128) down to
+// minLookupMaskLengthV4 or minLookupMaskLengthV6 it looks up the address's
+// network prefix at that length, and the first length with a live route wins.
+// That is at most 25 or 113 indexed lookups, however many routes are live. The
+// prefix is looked up in the text form net/netip prints, which is the form the
+// prefix handler stores.
 func (d *Database) GetIPInfoContext(ctx context.Context, ip string) (*IPInfo, error) {
 	addr, err := netip.ParseAddr(ip)
 	if err != nil {
@@ -1891,9 +1900,11 @@ func (d *Database) GetIPInfoContext(ctx context.Context, ip string) (*IPInfo, er
 
 	info := &IPInfo{IP: ip, IPVersion: ipVersionV6}
 	routesTable, prefixesTable := "live_routes_v6", "prefixes_v6"
+	minMaskLength := minLookupMaskLengthV6
 	if addr.Is4() {
 		info.IPVersion = ipVersionV4
 		routesTable, prefixesTable = "live_routes_v4", "prefixes_v4"
+		minMaskLength = minLookupMaskLengthV4
 	}
 
 	// Route info with peer count and prefix first_seen
@@ -1934,7 +1945,7 @@ func (d *Database) GetIPInfoContext(ctx context.Context, ip string) (*IPInfo, er
 	var whoisUpdatedAt sql.NullTime
 
 	found := false
-	for bits := addr.BitLen(); bits >= 0; bits-- {
+	for bits := addr.BitLen(); bits >= minMaskLength; bits-- {
 		prefix := netip.PrefixFrom(addr, bits).Masked().String()
 		err := stmt.QueryRowContext(ctx, prefix).Scan(
 			&info.Netblock,

internal/database/database_test.go

@@ -133,6 +133,78 @@ func TestGetIPInfoFindsMostSpecificLiveRoute(t *testing.T) {
 	lookup("2001:db8:1:2::3", "2001:db8:1::/48")
 }
 
+// TestGetIPInfoIgnoresShortRoutes checks that the IP lookup does not report a
+// default route, or a route shorter than /8 for IPv4 or /16 for IPv6, as the
+// route for an address, and that a route of exactly /8 or /16, or longer, still
+// is. The prefixes are written out so that a wrong limit fails the test.
+func TestGetIPInfoIgnoresShortRoutes(t *testing.T) {
+	cfg := &config.Config{StateDir: t.TempDir()}
+
+	db, err := New(cfg, logger.New())
+	if err != nil {
+		t.Fatalf("failed to create database: %v", err)
+	}
+	defer func() { _ = db.Close() }()
+
+	ts := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
+	announce := func(prefix string, asn int) {
+		t.Helper()
+
+		err := db.UpsertLiveRouteBatch([]*LiveRoute{{
+			ID:          uuid.New(),
+			Prefix:      prefix,
+			MaskLength:  netip.MustParsePrefix(prefix).Bits(),
+			IPVersion:   detectIPVersion(prefix),
+			OriginASN:   asn,
+			PeerIP:      testPeerIP,
+			ASPath:      []int{asn},
+			NextHop:     testPeerIP,
+			LastUpdated: ts,
+		}})
+		if err != nil {
+			t.Fatalf("UpsertLiveRouteBatch(%s): %v", prefix, err)
+		}
+	}
+
+	// lookup checks that ip resolves to the live prefix netblock from asn.
+	lookup := func(ip, netblock string, asn int) {
+		t.Helper()
+
+		info, err := db.GetIPInfo(ip)
+		if err != nil {
+			t.Errorf("GetIPInfo(%s): %v", ip, err)
+
+			return
+		}
+		if info.Netblock != netblock || info.ASN != asn {
+			t.Errorf("GetIPInfo(%s) = %s AS%d, want %s AS%d", ip, info.Netblock, info.ASN, netblock, asn)
+		}
+	}
+
+	// Default and very short routes, and routes one bit shorter than each limit.
+	announce("2000::/3", 64500)
+	announce("0.0.0.0/0", 64500)
+	announce("2000::/15", 64500)
+	announce("192.0.0.0/7", 64500)
+
+	for _, ip := range []string{"2001:db8::1", "192.0.2.1"} {
+		if info, err := db.GetIPInfo(ip); !errors.Is(err, ErrNoRoute) {
+			t.Errorf("GetIPInfo(%s) with only short routes = %+v, %v; want ErrNoRoute", ip, info, err)
+		}
+	}
+
+	// Routes of exactly the minimum length are used.
+	announce("2001::/16", 64501)
+	announce("192.0.0.0/8", 64501)
+
+	lookup("2001:db8::1", "2001::/16", 64501)
+	lookup("192.0.2.1", "192.0.0.0/8", 64501)
+
+	announce("2001:db8::/32", 64502)
+
+	lookup("2001:db8::1", "2001:db8::/32", 64502)
+}
+
 // TestConnectionPoolPragmas holds several pooled connections open at once and
 // checks each one carries the per-connection settings from the DSN, plus the
 // process-wide hard heap limit, and sees the new file with auto_vacuum

internal/metrics/metrics.go

@@ -60,18 +60,23 @@ func New() *Tracker {
 	}
 }
 
-// SetConnected updates the connection status
+// SetConnected updates the connection status. Every connection after the
+// first counts one reconnect.
 func (t *Tracker) SetConnected(connected bool) {
-	wasConnected := t.isConnected.Swap(connected)
-	if connected {
+	t.isConnected.Store(connected)
+	if !connected {
+		return
+	}
+
 	t.mu.Lock()
+	// connectedSince is zero until the first connection.
+	connectedBefore := !t.connectedSince.IsZero()
 	t.connectedSince = time.Now()
 	t.mu.Unlock()
-		// Increment reconnect count (but not for the initial connection)
-		if wasConnected || t.reconnectCount.Load() > 0 {
+
+	if connectedBefore {
 		t.reconnectCount.Add(1)
 	}
-	}
 }
 
 // GetReconnectCount returns the number of reconnections since startup

internal/metrics/metrics_test.go

@@ -0,0 +1,21 @@
+package metrics
+
+import "testing"
+
+// TestReconnectCount connects three times with a disconnect between each, the
+// way the streamer does, and expects every connection after the first to count
+// one reconnect.
+func TestReconnectCount(t *testing.T) {
+	tracker := New()
+
+	tracker.SetConnected(true)
+	tracker.SetConnected(false)
+	tracker.SetConnected(true)
+	tracker.SetConnected(false)
+	tracker.SetConnected(true)
+
+	const wantReconnects = 2
+	if got := tracker.GetReconnectCount(); got != wantReconnects {
+		t.Fatalf("reconnect count = %d, want %d", got, wantReconnects)
+	}
+}

internal/routewatch/prefixhandler.go

@@ -105,7 +105,24 @@ func (h *PrefixHandler) HandleMessage(msg *ristypes.RISMessage) {
 	h.mu.Lock()
 	defer h.mu.Unlock()
 
-	// Process announcements
+	// Withdrawals are queued before announcements, because the batch keeps
+	// each peer's last update for a prefix: a message that lists a prefix as
+	// both withdrawn and announced keeps the route (RFC 4271 section 4.3).
+	for _, prefix := range msg.Withdrawals {
+		h.batch = append(h.batch, prefixUpdate{
+			prefix:      canonicalPrefix(prefix),
+			originASN:   originASN, // Use the originASN from path if available
+			peer:        msg.Peer,
+			messageType: "withdrawal",
+			timestamp:   timestamp,
+			path:        msg.Path,
+		})
+		// Record withdrawal in metrics
+		if h.metrics != nil {
+			h.metrics.RecordWithdrawal()
+		}
+	}
+
 	for _, announcement := range msg.Announcements {
 		for _, prefix := range announcement.Prefixes {
 			h.batch = append(h.batch, prefixUpdate{
@@ -123,22 +140,6 @@ func (h *PrefixHandler) HandleMessage(msg *ristypes.RISMessage) {
 		}
 	}
 
-	// Process withdrawals
-	for _, prefix := range msg.Withdrawals {
-		h.batch = append(h.batch, prefixUpdate{
-			prefix:      canonicalPrefix(prefix),
-			originASN:   originASN, // Use the originASN from path if available
-			peer:        msg.Peer,
-			messageType: "withdrawal",
-			timestamp:   timestamp,
-			path:        msg.Path,
-		})
-		// Record withdrawal in metrics
-		if h.metrics != nil {
-			h.metrics.RecordWithdrawal()
-		}
-	}
-
 	// Check if we need to flush
 	if len(h.batch) >= prefixBatchSize {
 		h.flushBatchLocked()
@@ -179,14 +180,14 @@ func (h *PrefixHandler) flushBatchLocked() {
 	startTime := time.Now()
 	batchSize := len(h.batch)
 
-	// Group updates by prefix to deduplicate
-	// For each prefix, keep the latest update
-	prefixMap := make(map[string]prefixUpdate)
+	// For each prefix and peer, keep only the last update the feed delivered.
+	// Updates from different peers for the same prefix are all kept. Arrival
+	// order decides, not the timestamp: timestamps are whole seconds, so
+	// updates within one second carry the same one.
+	type prefixAndPeer struct{ prefix, peer string }
+	lastUpdates := make(map[prefixAndPeer]prefixUpdate)
 	for _, update := range h.batch {
-		key := update.prefix
-		if existing, ok := prefixMap[key]; !ok || update.timestamp.After(existing.timestamp) {
-			prefixMap[key] = update
-		}
+		lastUpdates[prefixAndPeer{update.prefix, update.peer}] = update
 	}
 
 	// Collect routes to upsert and delete
@@ -196,7 +197,7 @@ func (h *PrefixHandler) flushBatchLocked() {
 	// Collect unique prefixes to update
 	prefixesToUpdate := make(map[string]time.Time)
 
-	for _, update := range prefixMap {
+	for _, update := range lastUpdates {
 		// Track prefix for both announcements and withdrawals
 		if _, exists := prefixesToUpdate[update.prefix]; !exists || update.timestamp.After(prefixesToUpdate[update.prefix]) {
 			prefixesToUpdate[update.prefix] = update.timestamp
@@ -255,7 +256,7 @@ func (h *PrefixHandler) flushBatchLocked() {
 	elapsed := time.Since(startTime)
 	h.logger.Debug("Flushed prefix batch",
 		"batch_size", batchSize,
-		"unique_prefixes", len(prefixMap),
+		"unique_prefixes", len(prefixesToUpdate),
 		"success", successCount,
 		"duration_ms", elapsed.Milliseconds(),
 	)

internal/routewatch/prefixhandler_test.go

@@ -1,7 +1,9 @@
 package routewatch
 
 import (
+	"context"
 	"errors"
+	"slices"
 	"testing"
 	"time"
 
@@ -72,3 +74,140 @@ func TestPrefixHandlerStoresPrefixesTheIPLookupFinds(t *testing.T) {
 		}
 	}
 }
+
+// TestPrefixHandlerAppliesEachPeersLastUpdateInABatch runs updates for one
+// prefix through the prefix handler into a real database. All updates carry the
+// same timestamp, as updates within one second of the feed do. Within a batch,
+// the last update each peer sent for the prefix decides whether that peer has a
+// live route for it, and updates from different peers are all applied. The
+// in-memory route count and prefix distribution must match the route table.
+func TestPrefixHandlerAppliesEachPeersLastUpdateInABatch(t *testing.T) {
+	const (
+		prefix           = "198.51.100.0/24"
+		prefixMaskLength = 24
+		otherPeerIP      = "2001:db8:ffff::2"
+	)
+
+	ts := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
+	announce := func(peer string) *ristypes.RISMessage {
+		return &ristypes.RISMessage{
+			Peer:            peer,
+			Path:            ristypes.ASPath{testASNA, testASNB},
+			ParsedTimestamp: ts,
+			Announcements:   []ristypes.RISAnnouncement{{NextHop: peer, Prefixes: []string{prefix}}},
+		}
+	}
+	withdraw := func(peer string) *ristypes.RISMessage {
+		return &ristypes.RISMessage{Peer: peer, ParsedTimestamp: ts, Withdrawals: []string{prefix}}
+	}
+	announceAndWithdraw := func(peer string) *ristypes.RISMessage {
+		msg := announce(peer)
+		msg.Withdrawals = []string{prefix}
+
+		return msg
+	}
+
+	tests := []struct {
+		name string
+		// Each inner list is handled and then flushed as one batch.
+		batches [][]*ristypes.RISMessage
+		// The peers left with a live route for the prefix, by peer IP.
+		wantPeers []string
+	}{
+		{
+			name:      "two peers announce the prefix",
+			batches:   [][]*ristypes.RISMessage{{announce(testPeerIP), announce(otherPeerIP)}},
+			wantPeers: []string{testPeerIP, otherPeerIP},
+		},
+		{
+			name: "two peers withdraw the prefix",
+			batches: [][]*ristypes.RISMessage{
+				{announce(testPeerIP)},
+				{announce(otherPeerIP)},
+				{withdraw(testPeerIP), withdraw(otherPeerIP)},
+			},
+		},
+		{
+			name:    "a peer announces and then withdraws the prefix",
+			batches: [][]*ristypes.RISMessage{{announce(testPeerIP), withdraw(testPeerIP)}},
+		},
+		{
+			name: "a peer withdraws and then re-announces the prefix",
+			batches: [][]*ristypes.RISMessage{
+				{announce(testPeerIP)},
+				{withdraw(testPeerIP), announce(testPeerIP)},
+			},
+			wantPeers: []string{testPeerIP},
+		},
+		{
+			// RFC 4271 section 4.3: the announcement counts, not the withdrawal.
+			name: "one message announces and withdraws the prefix",
+			batches: [][]*ristypes.RISMessage{
+				{announce(testPeerIP)},
+				{announceAndWithdraw(testPeerIP)},
+			},
+			wantPeers: []string{testPeerIP},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			db, err := database.New(&config.Config{StateDir: t.TempDir()}, logger.New())
+			if err != nil {
+				t.Fatalf("failed to create database: %v", err)
+			}
+			defer func() { _ = db.Close() }()
+
+			// Built without NewPrefixHandler's flush timer, so the test flushes itself.
+			h := &PrefixHandler{db: db, logger: logger.New()}
+			for _, batch := range tt.batches {
+				for _, msg := range batch {
+					h.HandleMessage(msg)
+				}
+				h.mu.Lock()
+				h.flushBatchLocked()
+				h.mu.Unlock()
+			}
+
+			ctx := context.Background()
+			routes, err := db.GetPrefixDetailsContext(ctx, prefix)
+			if err != nil && !errors.Is(err, database.ErrNoRoute) {
+				t.Fatalf("GetPrefixDetailsContext: %v", err)
+			}
+			var gotPeers []string
+			for _, route := range routes {
+				gotPeers = append(gotPeers, route.PeerIP)
+			}
+			if !slices.Equal(gotPeers, tt.wantPeers) {
+				t.Errorf("peers with a live route for %s = %v, want %v", prefix, gotPeers, tt.wantPeers)
+			}
+
+			stats, err := db.GetStatsContext(ctx)
+			if err != nil {
+				t.Fatalf("GetStatsContext: %v", err)
+			}
+			tableRoutesV4, _, err := db.GetLiveRouteCountsContext(ctx)
+			if err != nil {
+				t.Fatalf("GetLiveRouteCountsContext: %v", err)
+			}
+			if stats.IPv4Routes != len(tt.wantPeers) || tableRoutesV4 != len(tt.wantPeers) {
+				t.Errorf("IPv4 live routes: %d in memory, %d in the table, want %d",
+					stats.IPv4Routes, tableRoutesV4, len(tt.wantPeers))
+			}
+
+			var wantDistribution []database.PrefixDistribution
+			if len(tt.wantPeers) > 0 {
+				wantDistribution = []database.PrefixDistribution{{MaskLength: prefixMaskLength, Count: 1}}
+			}
+			queryDistributionV4, _, err := db.GetPrefixDistributionContext(ctx)
+			if err != nil {
+				t.Fatalf("GetPrefixDistributionContext: %v", err)
+			}
+			if !slices.Equal(stats.IPv4PrefixDistribution, wantDistribution) ||
+				!slices.Equal(queryDistributionV4, wantDistribution) {
+				t.Errorf("IPv4 prefix distribution: %v in memory, %v from the table, want %v",
+					stats.IPv4PrefixDistribution, queryDistributionV4, wantDistribution)
+			}
+		})
+	}
+}

internal/server/handlers.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"net"
 	"net/http"
+	"net/netip"
 	"runtime"
 	"sort"
 	"strconv"
@@ -200,12 +201,16 @@ func (s *Server) handleStatusJSON() http.HandlerFunc {
 		select {
 		case <-ctx.Done():
 			s.logger.Error("Database stats timeout in status.json")
-			writeJSONError(w, http.StatusRequestTimeout, "Database timeout")
+			writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
 
 			return
 		case err := <-errChan:
 			s.logger.Error("Failed to get database stats", "error", err)
+			if deadlinePassed(ctx) {
+				writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
+			} else {
 				writeJSONError(w, http.StatusInternalServerError, err.Error())
+			}
 
 			return
 		case dbStats = <-statsChan:
@@ -385,7 +390,7 @@ func (s *Server) handleStats() http.HandlerFunc {
 		// Check if context is already cancelled
 		select {
 		case <-ctx.Done():
-			http.Error(w, "Request timeout", http.StatusRequestTimeout)
+			writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
 
 			return
 		default:
@@ -414,11 +419,16 @@ func (s *Server) handleStats() http.HandlerFunc {
 		select {
 		case <-ctx.Done():
 			s.logger.Error("Database stats timeout")
-			// Don't write response here - timeout middleware already handles it
+			writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
+
 			return
 		case err := <-errChan:
 			s.logger.Error("Failed to get database stats", "error", err)
+			if deadlinePassed(ctx) {
+				writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
+			} else {
 				writeJSONError(w, http.StatusInternalServerError, err.Error())
+			}
 
 			return
 		case dbStats = <-statsChan:
@@ -621,6 +631,13 @@ func (s *Server) handleIPInfo() http.HandlerFunc {
 			}
 		}
 
+		// The time limit passed while resolving host names.
+		if deadlinePassed(ctx) {
+			writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
+
+			return
+		}
+
 		if len(ipsToLookup) == 0 {
 			writeJSONError(w, http.StatusBadRequest, "No valid IPs or hostnames provided")
 
@@ -663,6 +680,13 @@ func (s *Server) handleIPInfo() http.HandlerFunc {
 			}
 		}
 
+		// The time limit passed while looking up the IPs.
+		if deadlinePassed(ctx) {
+			writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
+
+			return
+		}
+
 		// Return response (even if no results, include errors)
 		if len(response.Results) == 0 && len(response.Errors) > 0 {
 			writeJSONError(w, http.StatusNotFound, "No routes found: "+response.Errors[0])
@@ -702,9 +726,12 @@ func (s *Server) handleASDetailJSON() http.HandlerFunc {
 
 		asInfo, prefixes, err := s.db.GetASDetailsContext(r.Context(), asn)
 		if err != nil {
-			if errors.Is(err, database.ErrNoRoute) {
+			switch {
+			case errors.Is(err, database.ErrNoRoute):
 				writeJSONError(w, http.StatusNotFound, err.Error())
-			} else {
+			case deadlinePassed(r.Context()):
+				writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
+			default:
 				writeJSONError(w, http.StatusInternalServerError, err.Error())
 			}
 
@@ -748,14 +775,24 @@ func (s *Server) handlePrefixDetailJSON() http.HandlerFunc {
 			return
 		}
 
-		// Combine prefix and length into CIDR notation
-		prefix := prefixParam + "/" + lenParam
+		// Look the prefix up in the text form net/netip prints, the form the
+		// tables store, so that any valid way of writing it finds the route.
+		parsed, err := netip.ParsePrefix(prefixParam + "/" + lenParam)
+		if err != nil {
+			writeJSONError(w, http.StatusBadRequest, err.Error())
+
+			return
+		}
+		prefix := parsed.Masked().String()
 
 		routes, err := s.db.GetPrefixDetailsContext(r.Context(), prefix)
 		if err != nil {
-			if errors.Is(err, database.ErrNoRoute) {
+			switch {
+			case errors.Is(err, database.ErrNoRoute):
 				writeJSONError(w, http.StatusNotFound, err.Error())
-			} else {
+			case deadlinePassed(r.Context()):
+				writeJSONError(w, http.StatusGatewayTimeout, requestTimeoutMessage)
+			default:
 				writeJSONError(w, http.StatusInternalServerError, err.Error())
 			}
 
@@ -795,9 +832,12 @@ func (s *Server) handleASDetail() http.HandlerFunc {
 
 		asInfo, prefixes, err := s.db.GetASDetailsContext(r.Context(), asn)
 		if err != nil {
-			if errors.Is(err, database.ErrNoRoute) {
+			switch {
+			case errors.Is(err, database.ErrNoRoute):
 				http.Error(w, "AS not found", http.StatusNotFound)
-			} else {
+			case deadlinePassed(r.Context()):
+				http.Error(w, requestTimeoutMessage, http.StatusGatewayTimeout)
+			default:
 				s.logger.Error("Failed to get AS details", "error", err)
 				http.Error(w, "Internal server error", http.StatusInternalServerError)
 			}
@@ -912,14 +952,24 @@ func (s *Server) handlePrefixDetail() http.HandlerFunc {
 			return
 		}
 
-		// Combine prefix and length into CIDR notation
-		prefix := prefixParam + "/" + lenParam
+		// Look the prefix up in the text form net/netip prints, the form the
+		// tables store, so that any valid way of writing it finds the route.
+		parsed, err := netip.ParsePrefix(prefixParam + "/" + lenParam)
+		if err != nil {
+			http.Error(w, "Invalid prefix", http.StatusBadRequest)
+
+			return
+		}
+		prefix := parsed.Masked().String()
 
 		routes, err := s.db.GetPrefixDetailsContext(r.Context(), prefix)
 		if err != nil {
-			if errors.Is(err, database.ErrNoRoute) {
+			switch {
+			case errors.Is(err, database.ErrNoRoute):
 				http.Error(w, "Prefix not found", http.StatusNotFound)
-			} else {
+			case deadlinePassed(r.Context()):
+				http.Error(w, requestTimeoutMessage, http.StatusGatewayTimeout)
+			default:
 				s.logger.Error("Failed to get prefix details", "error", err)
 				http.Error(w, "Internal server error", http.StatusInternalServerError)
 			}
@@ -1073,8 +1123,12 @@ func (s *Server) handlePrefixLength() http.HandlerFunc {
 		const maxPrefixes = 500
 		prefixes, err := s.db.GetRandomPrefixesByLengthContext(r.Context(), maskLength, ipVersion, maxPrefixes)
 		if err != nil {
+			if deadlinePassed(r.Context()) {
+				http.Error(w, requestTimeoutMessage, http.StatusGatewayTimeout)
+			} else {
 				s.logger.Error("Failed to get prefixes by length", "error", err)
 				http.Error(w, "Internal server error", http.StatusInternalServerError)
+			}
 
 			return
 		}
@@ -1164,8 +1218,12 @@ func (s *Server) handlePrefixLength6() http.HandlerFunc {
 		const maxPrefixes = 500
 		prefixes, err := s.db.GetRandomPrefixesByLengthContext(r.Context(), maskLength, ipVersion, maxPrefixes)
 		if err != nil {
+			if deadlinePassed(r.Context()) {
+				http.Error(w, requestTimeoutMessage, http.StatusGatewayTimeout)
+			} else {
 				s.logger.Error("Failed to get prefixes by length", "error", err)
 				http.Error(w, "Internal server error", http.StatusInternalServerError)
+			}
 
 			return
 		}

internal/server/handlers_test.go

@@ -148,6 +148,231 @@ func TestStatsHandlersAnswerFromMemory(t *testing.T) {
 	}
 }
 
+// TestPrefixDetailHandlersParsePrefix checks that both prefix pages find a
+// stored route whatever valid text form the URL writes its prefix in, and
+// answer 400 for a prefix that does not parse. The tables store the form
+// net/netip prints. Before the fix the URL text was looked up as typed, so
+// "2001:DB8:0:0::/32" was not found although "2001:db8::/32" was stored, and
+// "foo/24" answered 500 (https://git.eeqj.de/sneak/routewatch/issues/71).
+func TestPrefixDetailHandlersParsePrefix(t *testing.T) {
+	db, err := database.New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("database.New: %v", err)
+	}
+	t.Cleanup(func() { _ = db.Close() })
+
+	ts := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
+	if err := db.UpsertLiveRouteBatch([]*database.LiveRoute{
+		{
+			ID: uuid.New(), Prefix: "192.0.2.0/24", MaskLength: 24, IPVersion: 4,
+			OriginASN: 64500, PeerIP: "198.51.100.1", ASPath: []int{64500}, NextHop: "198.51.100.1",
+			LastUpdated: ts,
+		},
+		{
+			ID: uuid.New(), Prefix: "2001:db8::/32", MaskLength: 32, IPVersion: 6,
+			OriginASN: 64501, PeerIP: "2001:db8::1", ASPath: []int{64501}, NextHop: "2001:db8::1",
+			LastUpdated: ts,
+		},
+	}); err != nil {
+		t.Fatalf("UpsertLiveRouteBatch: %v", err)
+	}
+
+	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	tests := []struct {
+		path string
+		want int
+	}{
+		{"/api/v1/prefix/foo/24", http.StatusBadRequest},
+		{"/prefix/foo/24", http.StatusBadRequest},
+		{"/api/v1/prefix/2001:DB8:0:0::/32", http.StatusOK},
+		{"/prefix/2001:DB8:0:0::/32", http.StatusOK},
+		{"/api/v1/prefix/192.0.2.1/24", http.StatusOK},
+		{"/prefix/192.0.2.1/24", http.StatusOK},
+	}
+
+	for _, tt := range tests {
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, tt.path, nil))
+		if rec.Code != tt.want {
+			t.Errorf("%s: status %d, want %d; body %s", tt.path, rec.Code, tt.want, rec.Body)
+		}
+	}
+}
+
+// shortRequestDeadline is the deadline the tests below give a request. The
+// server's 30-second limit and the stats handlers' 4-second limit inherit it,
+// so the tests do not wait for either.
+const shortRequestDeadline = 50 * time.Millisecond
+
+// TestRequestPastTimeLimitAnswers504 sends a request through the server's
+// router to a page and to a JSON route whose handlers wait for the time limit
+// to pass and return without answering. The page answers 504; the JSON route
+// answers 504 with the JSON error body. Before the fix both answered 408,
+// written by the time limit middleware from its own goroutine while the
+// handler could still be writing.
+func TestRequestPastTimeLimitAnswers504(t *testing.T) {
+	s := New(nil, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	waitForTimeLimit := func(_ http.ResponseWriter, r *http.Request) {
+		<-r.Context().Done()
+	}
+	// Registered the way setupRoutes registers pages and JSON routes.
+	s.router.Get("/slow-page", waitForTimeLimit)
+	s.router.Get("/slow.json", JSONValidationMiddleware(http.HandlerFunc(waitForTimeLimit)).ServeHTTP)
+
+	tests := []struct {
+		path         string
+		wantJSONBody bool
+	}{
+		{path: "/slow-page"},
+		{path: "/slow.json", wantJSONBody: true},
+	}
+
+	for _, tt := range tests {
+		ctx, cancel := context.WithTimeout(context.Background(), shortRequestDeadline)
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, tt.path, nil).WithContext(ctx))
+		cancel()
+
+		if rec.Code != http.StatusGatewayTimeout {
+			t.Errorf("%s: status %d, want %d; body %s", tt.path, rec.Code, http.StatusGatewayTimeout, rec.Body)
+		}
+		if tt.wantJSONBody {
+			checkJSONErrorCode(t, tt.path, rec, http.StatusGatewayTimeout)
+		}
+	}
+}
+
+// TestStatsHandlersAnswer504WhenDatabaseReadRunsOut calls each stats handler
+// with a store that does not answer before the handler's 4-second limit runs
+// out, and checks that the handler itself answers 504 with the JSON error
+// body. Before the fix status.json answered 408, and /api/v1/stats wrote
+// nothing, which the JSON check on its route turned into 500.
+func TestStatsHandlersAnswer504WhenDatabaseReadRunsOut(t *testing.T) {
+	release := make(chan struct{})
+	defer close(release)
+	db := blockingStatsDB{release: release}
+	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	handlers := map[string]http.HandlerFunc{
+		"status.json": s.handleStatusJSON(),
+		"stats":       s.handleStats(),
+	}
+
+	for name, handler := range handlers {
+		ctx, cancel := context.WithTimeout(context.Background(), shortRequestDeadline)
+		rec := httptest.NewRecorder()
+		handler(rec, httptest.NewRequest(http.MethodGet, "/", nil).WithContext(ctx))
+		cancel()
+
+		if rec.Code != http.StatusGatewayTimeout {
+			t.Errorf("%s: status %d, want %d; body %s", name, rec.Code, http.StatusGatewayTimeout, rec.Body)
+		}
+		checkJSONErrorCode(t, name, rec, http.StatusGatewayTimeout)
+	}
+}
+
+// slowDB embeds database.Store (left nil) and overrides the reads the routes
+// in TestRoutesAnswer504WhenDatabaseReadIsCutOff make. Each read waits until
+// its context ends and returns the context's error, as a slow database read
+// cut off by a time limit does.
+type slowDB struct {
+	database.Store
+}
+
+func (slowDB) GetStatsContext(ctx context.Context) (database.Stats, error) {
+	<-ctx.Done()
+
+	return database.Stats{}, ctx.Err()
+}
+
+func (slowDB) GetIPInfoContext(ctx context.Context, _ string) (*database.IPInfo, error) {
+	<-ctx.Done()
+
+	return nil, ctx.Err()
+}
+
+func (slowDB) GetASDetailsContext(ctx context.Context, _ int) (*database.ASN, []database.LiveRoute, error) {
+	<-ctx.Done()
+
+	return nil, nil, ctx.Err()
+}
+
+func (slowDB) GetPrefixDetailsContext(ctx context.Context, _ string) ([]database.LiveRoute, error) {
+	<-ctx.Done()
+
+	return nil, ctx.Err()
+}
+
+func (slowDB) GetRandomPrefixesByLengthContext(ctx context.Context, _, _, _ int) ([]database.LiveRoute, error) {
+	<-ctx.Done()
+
+	return nil, ctx.Err()
+}
+
+// TestRoutesAnswer504WhenDatabaseReadIsCutOff sends a request through the
+// server's router for each route that reads the database, with a store whose
+// reads fail when the request's time limit passes. Each route answers 504, the
+// JSON routes with the JSON error body. Before the fix they answered 408 or,
+// when the handler wrote first, its own error: 500, or 404 on the IP lookups.
+// The health check is left out: it answers 503 when its own 2-second ping runs
+// out.
+func TestRoutesAnswer504WhenDatabaseReadIsCutOff(t *testing.T) {
+	s := New(slowDB{}, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	tests := []struct {
+		path         string
+		wantJSONBody bool
+	}{
+		{path: "/as/64500"},
+		{path: "/prefix/192.0.2.0/24"},
+		{path: "/prefixlength/24"},
+		{path: "/prefixlength6/48"},
+		{path: "/status.json", wantJSONBody: true},
+		{path: "/ip/192.0.2.1", wantJSONBody: true},
+		{path: "/api/v1/stats", wantJSONBody: true},
+		{path: "/api/v1/ip/192.0.2.1", wantJSONBody: true},
+		{path: "/api/v1/as/64500", wantJSONBody: true},
+		{path: "/api/v1/prefix/192.0.2.0/24", wantJSONBody: true},
+	}
+
+	for _, tt := range tests {
+		ctx, cancel := context.WithTimeout(context.Background(), shortRequestDeadline)
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, tt.path, nil).WithContext(ctx))
+		cancel()
+
+		if rec.Code != http.StatusGatewayTimeout {
+			t.Errorf("%s: status %d, want %d; body %s", tt.path, rec.Code, http.StatusGatewayTimeout, rec.Body)
+		}
+		if tt.wantJSONBody {
+			checkJSONErrorCode(t, tt.path, rec, http.StatusGatewayTimeout)
+		}
+	}
+}
+
+// checkJSONErrorCode checks that rec holds the JSON error body with the given
+// code.
+func checkJSONErrorCode(t *testing.T, name string, rec *httptest.ResponseRecorder, want int) {
+	t.Helper()
+
+	var body struct {
+		Status string `json:"status"`
+		Error  struct {
+			Code int `json:"code"`
+		} `json:"error"`
+	}
+	if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
+		t.Errorf("%s: decoding the answer %q: %v", name, rec.Body, err)
+
+		return
+	}
+	if body.Status != "error" || body.Error.Code != want {
+		t.Errorf("%s: answer %s, want status \"error\" and error code %d", name, rec.Body, want)
+	}
+}
+
 // settledGoroutineCount lets transient goroutines finish, then reports the
 // current count.
 func settledGoroutineCount() int {

internal/server/middleware.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log/slog"
 	"net/http"
@@ -109,142 +110,24 @@ func JSONResponseMiddleware(next http.Handler) http.Handler {
 	})
 }
 
-// timeoutWriter wraps ResponseWriter to prevent concurrent writes after timeout
-type timeoutWriter struct {
-	http.ResponseWriter
-	mu      sync.Mutex
-	written bool
-	header  http.Header // cached header to prevent concurrent access
-}
+// requestTimeoutMessage is the error message sent with 504 Gateway Timeout.
+const requestTimeoutMessage = "Request timeout"
 
-func (tw *timeoutWriter) Write(b []byte) (int, error) {
-	tw.mu.Lock()
-	defer tw.mu.Unlock()
-
-	if tw.written {
-		return 0, nil // Discard writes after timeout
-	}
-
-	return tw.ResponseWriter.Write(b)
-}
-
-func (tw *timeoutWriter) WriteHeader(statusCode int) {
-	tw.mu.Lock()
-	defer tw.mu.Unlock()
-
-	if tw.written {
-		return // Discard writes after timeout
-	}
-
-	tw.ResponseWriter.WriteHeader(statusCode)
-}
-
-func (tw *timeoutWriter) Header() http.Header {
-	tw.mu.Lock()
-	defer tw.mu.Unlock()
-
-	if tw.written {
-		// Return a copy to prevent modifications after timeout
-		if tw.header == nil {
-			tw.header = make(http.Header)
-		}
-
-		return tw.header
-	}
-
-	return tw.ResponseWriter.Header()
-}
-
-func (tw *timeoutWriter) markWritten() {
-	tw.mu.Lock()
-	defer tw.mu.Unlock()
-	tw.written = true
-}
-
-// TimeoutMiddleware creates an HTTP middleware that enforces a request timeout.
-// If the handler does not complete within the specified duration, the middleware
-// returns a JSON error response with HTTP status 408 (Request Timeout).
-//
-// The timeout parameter specifies the maximum duration allowed for request processing.
-// The returned middleware handles panics from the wrapped handler by re-panicking
-// after cleanup, and prevents concurrent writes to the response after timeout occurs.
-func TimeoutMiddleware(timeout time.Duration, logger *slog.Logger) func(http.Handler) http.Handler {
-	return func(next http.Handler) http.Handler {
-		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			startTime := time.Now()
-
-			ctx, cancel := context.WithTimeout(r.Context(), timeout)
-			defer cancel()
-
-			tw := &timeoutWriter{
-				ResponseWriter: w,
-				header:         make(http.Header),
-			}
-
-			done := make(chan struct{})
-			panicChan := make(chan interface{}, 1)
-
-			go func() {
-				defer func() {
-					if p := recover(); p != nil {
-						panicChan <- p
-					}
-				}()
-
-				next.ServeHTTP(tw, r.WithContext(ctx))
-				close(done)
-			}()
-
-			select {
-			case p := <-panicChan:
-				panic(p)
-			case <-done:
-				return
-			case <-ctx.Done():
-				tw.markWritten() // Prevent the handler from writing after timeout
-				execTime := time.Since(startTime)
-
-				// Log the timeout as a warning
-				logger.Warn("Request timeout",
-					"method", r.Method,
-					"path", r.URL.Path,
-					"duration_ms", execTime.Milliseconds(),
-					"remote_addr", r.RemoteAddr,
-				)
-
-				// Write directly to the underlying writer since we've marked tw as written
-				// This is safe because markWritten() prevents the handler from writing
-				tw.mu.Lock()
-				w.Header().Set("Content-Type", "application/json")
-				w.WriteHeader(http.StatusRequestTimeout)
-				tw.mu.Unlock()
-
-				response := map[string]interface{}{
-					"status": "error",
-					"error": map[string]interface{}{
-						"msg":  "Request timeout",
-						"code": http.StatusRequestTimeout,
-					},
-					"@meta": map[string]interface{}{
-						"time_zone":      "UTC",
-						"api_version":    1,
-						"execution_time": fmt.Sprintf("%d ms", execTime.Milliseconds()),
-					},
-				}
-
-				_ = json.NewEncoder(w).Encode(response)
-			}
-		})
-	}
+// deadlinePassed reports whether ctx ended because its deadline passed. When
+// a handler's database read or other lookup fails, it uses this to tell a
+// request cut off by its time limit, which answers 504, from other failures.
+func deadlinePassed(ctx context.Context) bool {
+	return errors.Is(ctx.Err(), context.DeadlineExceeded)
 }
 
 // JSONValidationMiddleware is an HTTP middleware that validates JSON API responses.
 // It ensures that responses with Content-Type "application/json" contain valid JSON.
 //
 // If a response is not valid JSON or is empty when JSON is expected, the middleware
-// returns a properly formatted JSON error response. For timeout errors (status 408),
-// the error message will be "Request timeout". For other errors, it returns
-// "Internal server error" with status 500 if the original status was 200.
+// returns a properly formatted JSON error response. If the request's time limit
+// has passed, it answers 504 with the error message "Request timeout". For other
+// errors, it returns "Internal server error" with status 500 if the original
+// status was 200.
 //
 // Non-JSON responses are passed through unchanged.
 func JSONValidationMiddleware(next http.Handler) http.Handler {
@@ -293,11 +176,14 @@ func JSONValidationMiddleware(next http.Handler) http.Handler {
 		if statusCode == http.StatusOK {
 			statusCode = http.StatusInternalServerError
 		}
+		if deadlinePassed(r.Context()) {
+			statusCode = http.StatusGatewayTimeout
+		}
 		w.WriteHeader(statusCode)
 
 		errorMsg := "Internal server error"
-		if statusCode == http.StatusRequestTimeout {
-			errorMsg = "Request timeout"
+		if statusCode == http.StatusGatewayTimeout {
+			errorMsg = requestTimeoutMessage
 		}
 
 		response := map[string]interface{}{

internal/server/routes.go

@@ -16,9 +16,12 @@ func (s *Server) setupRoutes() {
 	r.Use(middleware.RealIP)
 	r.Use(RequestLoggerMiddleware(s.logger.Logger)) // Structured request logging
 	r.Use(middleware.Recoverer)
-	const requestTimeout = 30 * time.Second // Increased from 8s for slow queries
-	r.Use(TimeoutMiddleware(requestTimeout, s.logger.Logger))
 	r.Use(JSONResponseMiddleware)
+	// Timeout must come after JSONResponseMiddleware, which sends its answer
+	// when the handler returns and would send a 200 ahead of Timeout's 504 for
+	// a handler that wrote nothing.
+	const requestTimeout = 30 * time.Second // Increased from 8s for slow queries
+	r.Use(middleware.Timeout(requestTimeout))
 
 	// Routes
 	r.Get("/", s.handleIndex())