Handle an announcement without an origin like a replacement (closes #113)

An announcement whose AS path is empty or ends in AS 0 now deletes the
peer's route for the prefix, as a withdrawal does. Before, it was neither
stored nor applied: the peer's old route stayed live, and within one
batch it cancelled the peer's earlier withdrawal of the prefix.

Model: opus-5-5

README.md

@@ -36,6 +36,8 @@ DEBUG=routewatch ./routewatch
 
 ## HTTP Endpoints
 
+Every route answers `HEAD` as it answers `GET`, without the body.
+
 ### Web Interface
 
 - `GET /` - Home page (HTML): headline figures, and lookups by AS number and by
@@ -90,8 +92,11 @@ and 4 seconds for the database reads behind `/status.json` and `/api/v1/stats`.
 An AS number, prefix or mask length that does not parse answers 400, as does a
 mask length out of range for its IP version. An AS the database does not hold,
 or a prefix with no live route, answers 404. The HTML pages give these errors as
-plain text. A 500 answer says only `Internal server error`, and a host name that
-does not resolve only `could not resolve host name`; the detail goes to the log.
+plain text. Under `/api/v1` and `/ip/`, a path no route matches answers 404 with
+the message `Not found`, and `POST`, `PUT`, `PATCH`, `DELETE`, `OPTIONS`,
+`TRACE` or `CONNECT` answers 405 with `Method not allowed`. A 500 answer says
+only `Internal server error`, and a host name that does not resolve only
+`could not resolve host name`; the detail goes to the log.
 
 Every answer carries `Strict-Transport-Security`, `Content-Security-Policy`,
 `X-Frame-Options`, `X-Content-Type-Options`, `Referrer-Policy` and
@@ -190,10 +195,11 @@ routewatch/
     - **ASHandler**: Tracks all ASNs seen in AS paths
     - **PeerHandler**: Records BGP peer information
     - **PrefixHandler**: Maintains live routing table (upserts on announcement,
-      deletes on withdrawal, deletes all of a peer's routes when its BGP session
-      goes down). Routes are kept per peer IP, so when one peer IP has sessions
-      on two collectors, a session going down on one also removes the routes the
-      other still carries, until they are announced again.
+      deletes on withdrawal or on an announcement whose AS path is empty or ends
+      in AS 0, deletes all of a peer's routes when its BGP session goes down).
+      Routes are kept per peer IP, so when one peer IP has sessions on two
+      collectors, a session going down on one also removes the routes the other
+      still carries, until they are announced again.
     - **PeeringHandler**: Extracts AS peering relationships from AS paths
 
 5. **HTTP Request Flow**

internal/routewatch/app.go

@@ -116,17 +116,18 @@ func (rw *RouteWatch) Run(ctx context.Context) error {
 		return err
 	}
 
+	// Start ASN WHOIS fetcher for background updates. The HTTP handlers read
+	// the server's fetcher without a lock, so it is set before they run.
+	rw.asnFetcher = NewASNFetcher(rw.db, rw.logger.Logger)
+	rw.asnFetcher.Start(ctx)
+	rw.server.SetASNFetcher(rw.asnFetcher)
+
 	// Start HTTP server
 	err = rw.server.Start(ctx)
 	if err != nil {
 		return err
 	}
 
-	// Start ASN WHOIS fetcher for background updates
-	rw.asnFetcher = NewASNFetcher(rw.db, rw.logger.Logger)
-	rw.asnFetcher.Start(ctx)
-	rw.server.SetASNFetcher(rw.asnFetcher)
-
 	// Start database maintenance goroutine
 	rw.dbMaintainer = NewDBMaintainer(rw.db, rw.logger.Logger)
 	rw.dbMaintainer.Start(ctx)

internal/routewatch/prefixhandler.go

@@ -44,8 +44,9 @@ const (
 )
 
 // PrefixHandler tracks BGP prefixes and maintains a live routing table in the
-// database. Routes are added on announcement and deleted on withdrawal, and all
-// routes of a peer are deleted when its BGP session goes down.
+// database. Routes are added on announcement and deleted on withdrawal or on an
+// announcement whose AS path is empty or ends in AS 0, and all routes of a peer
+// are deleted when its BGP session goes down.
 type PrefixHandler struct {
 	db      database.Store
 	logger  *logger.Logger
@@ -371,7 +372,11 @@ func (h *PrefixHandler) flushBatch() {
 	for _, update := range lastUpdates {
 		// An announcement is stored when its path gives an origin, or when it
 		// ends in an AS set of several members: that route is stored with
-		// origin 0 (none). An announcement with an empty path is not stored.
+		// origin 0 (none). Any other update deletes the peer's route for the
+		// prefix: a withdrawal, or an announcement whose path is empty or ends
+		// in AS 0. Such an announcement replaces the peer's route, as any
+		// announcement does, with none (RFC 7607 treats AS 0 in a path as a
+		// withdrawal).
 		if update.messageType == "announcement" &&
 			(update.originASN > 0 || update.endsInSet) {
 			// Create live route for batch upsert
@@ -379,11 +384,11 @@ func (h *PrefixHandler) flushBatch() {
 			if route != nil {
 				routesToUpsert = append(routesToUpsert, route)
 			}
-		} else if update.messageType == "withdrawal" {
+		} else {
 			// Parse CIDR to get IP version
 			_, ipVersion, err := parseCIDR(update.prefix)
 			if err != nil {
-				h.logger.Error("Failed to parse CIDR for withdrawal",
+				h.logger.Error("Failed to parse CIDR for route deletion",
 					"prefix", update.prefix, "error", err)
 
 				continue

internal/routewatch/prefixhandler_internal_test.go

@@ -378,6 +378,68 @@ func TestPrefixHandlerDoesNotStoreAnAnnouncementWithAnEmptyPath(t *testing.T) {
 	assertPeers(t, db, map[string][]string{testV4Prefix: nil})
 }
 
+// TestPrefixHandlerRemovesTheRouteOnAnAnnouncementWithoutAnOrigin runs, through
+// the prefix handler into a real database, a peer's announcement of a prefix
+// with origin AS testASNB and then the peer's announcement of the prefix with
+// an AS path that gives no origin: one whose last AS is 0, or an empty one. As
+// any later announcement from the peer does, the second replaces the peer's
+// route, here with none, whether it comes in a later batch or follows a
+// withdrawal in one batch. The in-memory route count and prefix distribution
+// must match the route table.
+func TestPrefixHandlerRemovesTheRouteOnAnAnnouncementWithoutAnOrigin(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	const prefixMaskLength = 24
+
+	noOrigin := func(path ristypes.ASPath) *ristypes.RISMessage {
+		msg := peerAnnouncement(testPeerIP, testV4Prefix)
+		msg.Path = path
+
+		return msg
+	}
+	endsInZero := ristypes.ASPath{Sequence: []int{testASNA, 0}}
+	withdrawal := &ristypes.RISMessage{
+		Type:            ristypes.MessageTypeUpdate,
+		Peer:            testPeerIP,
+		ParsedTimestamp: time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC),
+		Withdrawals:     []string{testV4Prefix},
+	}
+
+	tests := []struct {
+		name string
+		// Handled and flushed as one batch after the announcement with origin
+		// AS testASNB.
+		batch []*ristypes.RISMessage
+	}{
+		{
+			name:  "a path whose last AS is 0",
+			batch: []*ristypes.RISMessage{noOrigin(endsInZero)},
+		},
+		{
+			name:  "an empty path",
+			batch: []*ristypes.RISMessage{noOrigin(ristypes.ASPath{})},
+		},
+		{
+			name:  "a withdrawal and then a path whose last AS is 0",
+			batch: []*ristypes.RISMessage{withdrawal, noOrigin(endsInZero)},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			db := handleBatches(t, [][]*ristypes.RISMessage{
+				{peerAnnouncement(testPeerIP, testV4Prefix)},
+				tt.batch,
+			})
+			checkLivePeers(t, db, testV4Prefix, prefixMaskLength, nil)
+		})
+	}
+}
+
 // TestStateMessagesGoToThePrefixHandlerNotThePeerHandler checks that STATE
 // messages go to the prefix handler, which acts on a down, and not to the peer
 // handler, which would record a peer whose session never comes up as active.

internal/server/middleware.go

@@ -142,8 +142,9 @@ func deadlinePassed(ctx context.Context) bool {
 //
 // If a response is not valid JSON or is empty when JSON is expected, the middleware
 // 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
+// has passed, it answers 504 with the error message "Request timeout". A 4xx
+// keeps its status, with the status's standard text as the message. For other
+// errors, it returns "Internal server error", with status 500 if the original
 // status was 200.
 //
 // Non-JSON responses are passed through unchanged.
@@ -203,8 +204,13 @@ func JSONValidationMiddleware(next http.Handler) http.Handler {
 		w.WriteHeader(statusCode)
 
 		errorMsg := internalErrorMessage
-		if statusCode == http.StatusGatewayTimeout {
+
+		switch {
+		case statusCode == http.StatusGatewayTimeout:
 			errorMsg = requestTimeoutMessage
+		case statusCode >= http.StatusBadRequest &&
+			statusCode < http.StatusInternalServerError:
+			errorMsg = http.StatusText(statusCode)
 		}
 
 		response := map[string]any{

internal/server/middleware_internal_test.go

@@ -58,6 +58,34 @@ func TestResponsesCarrySecurityHeaders(t *testing.T) {
 	}
 }
 
+// TestJSONValidationKeeps4xxWithoutBody wraps a handler that answers 400
+// without a body in JSONValidationMiddleware and checks that the JSON error
+// body keeps the 400 and gives the status's own text. Before the fix it said
+// "Internal server error"
+// (https://git.eeqj.de/sneak/routewatch/issues/111).
+func TestJSONValidationKeeps4xxWithoutBody(t *testing.T) {
+	t.Parallel()
+
+	handler := JSONValidationMiddleware(http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.WriteHeader(http.StatusBadRequest)
+		}))
+
+	rec := httptest.NewRecorder()
+	handler.ServeHTTP(rec, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/", nil))
+
+	const name = "400 without a body"
+
+	if rec.Code != http.StatusBadRequest {
+		t.Errorf("%s: status %d, want %d; body %s",
+			name, rec.Code, http.StatusBadRequest, rec.Body)
+	}
+
+	checkJSONErrorCode(t, name, rec, http.StatusBadRequest)
+	checkJSONErrorMessage(t, name, rec, http.StatusText(http.StatusBadRequest))
+}
+
 // TestPagesCarryTheCSPNonce checks that every script and style block of each
 // page carries the nonce its Content-Security-Policy header names, so that the
 // browser runs and applies them, that each answer has a nonce of its own, and

internal/server/routes.go

@@ -1,18 +1,33 @@
 package server
 
 import (
+	"net/http"
 	"time"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
 )
 
+// The error messages the JSON routes under /api/v1 and /ip answer with when no
+// route matches the path, and when none takes the method.
+const (
+	notFoundMessage         = "Not found"
+	methodNotAllowedMessage = "Method not allowed"
+
+	// jsonRoutesAllow is the Allow header of their 405 answer: every one of
+	// them takes GET and HEAD, and no other method.
+	jsonRoutesAllow = "GET, HEAD"
+)
+
 // setupRoutes configures the HTTP routes
 func (s *Server) setupRoutes() {
 	r := chi.NewRouter()
 
 	// Middleware
 	r.Use(DecodedPathMiddleware)
+	// GetHead serves HEAD with the GET handler. It looks the route up by the
+	// path DecodedPathMiddleware sets, so it comes after it.
+	r.Use(middleware.GetHead)
 	r.Use(SecurityHeadersMiddleware)
 	r.Use(middleware.RequestID)
 	r.Use(RealIPMiddleware(s.trustedProxies))
@@ -40,16 +55,34 @@ func (s *Server) setupRoutes() {
 	r.Get("/prefixlength/{length}", s.handlePrefixLength())
 	r.Get("/prefixlength6/{length}", s.handlePrefixLength6())
 
+	// The JSON routes answer a path or method they do not take with the JSON
+	// error body, as they answer everything else.
+	jsonNotFound := func(w http.ResponseWriter, _ *http.Request) {
+		s.writeJSONError(w, http.StatusNotFound, notFoundMessage)
+	}
+	jsonMethodNotAllowed := func(w http.ResponseWriter, _ *http.Request) {
+		// chi's own 405 answer sets Allow; one set in its place must too.
+		w.Header().Set("Allow", jsonRoutesAllow)
+		s.writeJSONError(w, http.StatusMethodNotAllowed, methodNotAllowedMessage)
+	}
+
 	// IP info JSON endpoints (replaces old /ip redirect)
 	r.Route("/ip", func(r chi.Router) {
 		r.Use(JSONValidationMiddleware)
-		r.Get("/", s.handleIPInfo())       // Client IP
+		r.NotFound(jsonNotFound)
+		r.MethodNotAllowed(jsonMethodNotAllowed)
+		r.Get("/", s.handleIPInfo()) // Client IP
+		// GetHead does not reach this route: mounting the group registers
+		// /ip and /ip/ for every method, so HEAD arrives here as HEAD.
+		r.Head("/", s.handleIPInfo())
 		r.Get("/{addr}", s.handleIPInfo()) // Specified IP
 	})
 
 	// API routes
 	r.Route("/api/v1", func(r chi.Router) {
 		r.Use(JSONValidationMiddleware)
+		r.NotFound(jsonNotFound)
+		r.MethodNotAllowed(jsonMethodNotAllowed)
 		r.Get("/stats", s.handleStats())
 		r.Get("/ip/{ip}", s.handleIPLookup())
 		r.Get("/as/{asn}", s.handleASDetailJSON())

internal/server/routes_internal_test.go

@@ -0,0 +1,100 @@
+package server
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// TestRoutesAnswerHEAD sends HEAD for a page and JSON routes through the
+// server's router and checks that each answers as GET does. /ip and /ip/, the
+// lookup of the caller's own address, are in the list because chi's GetHead
+// does not reach them. Before the fix every route answered HEAD with 405
+// (https://git.eeqj.de/sneak/routewatch/issues/111).
+func TestRoutesAnswerHEAD(t *testing.T) {
+	t.Parallel()
+
+	s := newServerWithTestRoutes(t)
+
+	for _, path := range []string{"/", statsPath, "/ip", "/ip/"} {
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), http.MethodHead, path, nil))
+
+		if rec.Code != http.StatusOK {
+			t.Errorf("HEAD %s: status %d, want %d; body %s",
+				path, rec.Code, http.StatusOK, rec.Body)
+		}
+	}
+}
+
+// TestJSONRoutesAnswerUnmatchedRequestsWithJSONErrors sends a method the JSON
+// routes do not take, and a path none of them matches, to each group of JSON
+// routes through the server's router. Each must answer with the JSON error
+// body, and a 405 must name the methods the routes take in its Allow header.
+// Before the fix a 405 said "Internal server error" and a 404 was chi's plain
+// text answer (https://git.eeqj.de/sneak/routewatch/issues/111).
+func TestJSONRoutesAnswerUnmatchedRequestsWithJSONErrors(t *testing.T) {
+	t.Parallel()
+
+	s := newServerWithTestRoutes(t)
+
+	tests := []struct {
+		method   string
+		path     string
+		wantCode int
+		wantMsg  string
+	}{
+		{http.MethodPost, statsPath, http.StatusMethodNotAllowed, methodNotAllowedMessage},
+		{http.MethodPost, "/ip/", http.StatusMethodNotAllowed, methodNotAllowedMessage},
+		{http.MethodGet, "/api/v1/nothing", http.StatusNotFound, notFoundMessage},
+		{http.MethodGet, "/ip/192.0.2.1/nothing", http.StatusNotFound, notFoundMessage},
+	}
+
+	for _, tt := range tests {
+		name := tt.method + " " + tt.path
+
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), tt.method, tt.path, nil))
+
+		if rec.Code != tt.wantCode {
+			t.Errorf("%s: status %d, want %d; body %s",
+				name, rec.Code, tt.wantCode, rec.Body)
+		}
+
+		checkJSONErrorCode(t, name, rec, tt.wantCode)
+		checkJSONErrorMessage(t, name, rec, tt.wantMsg)
+
+		allow := rec.Header().Get("Allow")
+		if tt.wantCode == http.StatusMethodNotAllowed && allow != jsonRoutesAllow {
+			t.Errorf("%s: Allow %q, want %q", name, allow, jsonRoutesAllow)
+		}
+	}
+}
+
+// checkJSONErrorMessage checks that rec holds the JSON error body with the
+// given message.
+func checkJSONErrorMessage(
+	t *testing.T, name string, rec *httptest.ResponseRecorder, want string,
+) {
+	t.Helper()
+
+	var body struct {
+		Error struct {
+			Msg string `json:"msg"`
+		} `json:"error"`
+	}
+
+	err := json.Unmarshal(rec.Body.Bytes(), &body)
+	if err != nil {
+		t.Errorf("%s: decoding the answer %q: %v", name, rec.Body, err)
+
+		return
+	}
+
+	if body.Error.Msg != want {
+		t.Errorf("%s: error message %q, want %q", name, body.Error.Msg, want)
+	}
+}

internal/server/server.go

@@ -139,7 +139,8 @@ func (s *Server) Stop(ctx context.Context) error {
 	return nil
 }
 
-// SetASNFetcher sets the ASN WHOIS fetcher for on-demand lookups.
+// SetASNFetcher sets the ASN WHOIS fetcher for on-demand lookups. Call it
+// before Start: the handlers read the fetcher without a lock.
 func (s *Server) SetASNFetcher(fetcher ASNFetcher) {
 	s.asnFetcher = fetcher
 }

internal/streamer/streamer.go

@@ -106,12 +106,12 @@ type RawMessageHandler func(line string)
 // handlerMetrics tracks performance metrics for a handler
 type handlerMetrics struct {
 	processedCount     uint64        // Total messages processed
-	droppedCount       uint64        // Total messages dropped
+	droppedCount       atomic.Uint64 // Total messages dropped; not under mu
 	totalTime          time.Duration // Total processing time (for average calculation)
 	minTime            time.Duration // Minimum processing time
 	maxTime            time.Duration // Maximum processing time
 	queueHighWaterMark int           // Maximum queue length seen
-	mu                 sync.Mutex    // Protects the metrics
+	mu                 sync.Mutex    // Protects the other metrics
 }
 
 // handlerInfo wraps a handler with its queue and metrics
@@ -371,7 +371,7 @@ func (s *Streamer) GetHandlerStats() []HandlerStats {
 			QueueCapacity:      cap(info.queue),
 			QueueHighWaterMark: info.metrics.queueHighWaterMark,
 			ProcessedCount:     info.metrics.processedCount,
-			DroppedCount:       info.metrics.droppedCount,
+			DroppedCount:       info.metrics.droppedCount.Load(),
 			MinProcessTime:     info.metrics.minTime,
 			MaxProcessTime:     info.metrics.maxTime,
 		}
@@ -488,7 +488,7 @@ func (s *Streamer) logMetrics() {
 				"queue_len", len(info.queue),
 				"queue_cap", cap(info.queue),
 				"processed", info.metrics.processedCount,
-				"dropped", info.metrics.droppedCount,
+				"dropped", info.metrics.droppedCount.Load(),
 				"avg_time", avgTime,
 				"min_time", info.metrics.minTime,
 				"max_time", info.metrics.maxTime,
@@ -858,7 +858,7 @@ func (s *Streamer) dispatchMessage(
 		}
 
 		if !s.queueMessage(info, msg) {
-			atomic.AddUint64(&info.metrics.droppedCount, 1)
+			info.metrics.droppedCount.Add(1)
 			s.totalDropped.Add(1)
 
 			continue

internal/streamer/streamer_internal_test.go

@@ -621,6 +621,68 @@ func TestStreamReadsLongLine(t *testing.T) {
 	}
 }
 
+// blockedHandler wants UPDATE messages, has room on its queue for one, and
+// does not return from HandleMessage until release is closed.
+type blockedHandler struct {
+	release chan struct{}
+}
+
+func (blockedHandler) WantsMessage(messageType string) bool {
+	return messageType == ristypes.MessageTypeUpdate
+}
+
+func (blockedHandler) QueueCapacity() int { return 1 }
+
+func (h blockedHandler) HandleMessage(*ristypes.RISMessage) { <-h.release }
+
+// TestHandlerStatsReadWhileMessagesAreDropped has the server send a few UPDATE
+// lines to a blockedHandler, so the read loop drops all but the one the
+// handler holds and the one on its queue, while the test reads the handler's
+// statistics. The drop count must reach the number dropped, and the race
+// detector must find the count read and written safely.
+func TestHandlerStatsReadWhileMessagesAreDropped(t *testing.T) {
+	t.Parallel()
+
+	const (
+		lines       = 5
+		wantDropped = lines - 2
+		maxWait     = 5 * time.Second
+	)
+
+	srv := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			_, _ = io.WriteString(w, strings.Repeat(updateLine, lines))
+
+			flush(w)
+			<-r.Context().Done()
+		}))
+	defer srv.Close()
+
+	s := New(logger.New(), metrics.New())
+	s.url = srv.URL
+	handler := blockedHandler{release: make(chan struct{})}
+	s.RegisterHandler(handler)
+
+	err := s.Start(t.Context())
+	if err != nil {
+		t.Fatalf("Start returned error: %v", err)
+	}
+	defer s.Stop(t.Context())
+	defer close(handler.release)
+
+	// The test polls instead of waiting for a signal from the read loop: a
+	// signal would order the drops before the reads here, and the race
+	// detector would have nothing to report.
+	deadline := time.Now().Add(maxWait)
+
+	for s.GetHandlerStats()[0].DroppedCount < wantDropped {
+		if time.Now().After(deadline) {
+			t.Fatalf("fewer than %d messages counted as dropped within %s",
+				wantDropped, maxWait)
+		}
+	}
+}
+
 // TestPeerCountCountsEveryPeerHeardFrom has the server send an UPDATE from
 // stateDownPeer and a KEEPALIVE from another peer, with no OPEN from either,
 // and then a message that ends stateDownPeer's session: a NOTIFICATION, or a