TODO.md

@@ -23,6 +23,10 @@ runs make check on main.
 
 # Completed Steps
 
+- 2026-09-28: stopping the daemon while the feed is flowing no longer
+  panics with "send on closed channel": the read loop checks for a stop
+  just before handing a message to the handler queues, and a second
+  `Stop` no longer closes the queues again (closes #34)
 - 2026-09-28: `docker stop` no longer kills the daemon 2 seconds after the
   stop signal: the entrypoint switches to the `routewatch` user with
   `setpriv` instead of `runuser`, so the daemon receives the signal itself

internal/streamer/streamer.go

@@ -210,9 +210,14 @@ func (s *Streamer) Start() error {
 // the connection status in metrics. This method is safe to call multiple times.
 func (s *Streamer) Stop() {
 	s.mu.Lock()
-	if s.cancel != nil {
+	if s.cancel == nil {
-		s.cancel()
+		// Not started, or already stopped: closing the queues again would panic.
+		s.mu.Unlock()
+
+		return
 	}
+	s.cancel()
+	s.cancel = nil
 	// Close all handler queues to signal workers to stop
 	for _, info := range s.handlers {
 		close(info.queue)
@@ -660,8 +665,15 @@ func (s *Streamer) stream(ctx context.Context) error {
 			continue
 		}
 
-		// Dispatch to interested handlers
+		// Dispatch to interested handlers. Stop cancels ctx and closes the
+		// queues under the write lock, so if ctx is cancelled here, under the
+		// read lock, the queues are closed and must not be sent to.
 		s.mu.RLock()
+		if ctx.Err() != nil {
+			s.mu.RUnlock()
+
+			return ctx.Err()
+		}
 		for _, info := range s.handlers {
 			if !info.handler.WantsMessage(msg.Type) {
 				continue

internal/streamer/streamer_test.go

@@ -2,6 +2,8 @@ package streamer
 
 import (
 	"context"
+	"errors"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"runtime"
@@ -10,6 +12,7 @@ import (
 
 	"git.eeqj.de/sneak/routewatch/internal/logger"
 	"git.eeqj.de/sneak/routewatch/internal/metrics"
+	"git.eeqj.de/sneak/routewatch/internal/ristypes"
 )
 
 func TestNewStreamer(t *testing.T) {
@@ -75,6 +78,45 @@ func TestStreamDoesNotLeakTickersAcrossReconnects(t *testing.T) {
 	}
 }
 
+// updateHandler wants UPDATE messages and does nothing with them.
+type updateHandler struct{}
+
+func (updateHandler) WantsMessage(messageType string) bool { return messageType == "UPDATE" }
+func (updateHandler) HandleMessage(*ristypes.RISMessage)   {}
+func (updateHandler) QueueCapacity() int                   { return 10 }
+
+// TestStopBeforeMessageReachesQueues stops the streamer after the read loop
+// has checked for cancellation but before it hands the message to the handler
+// queues. That is the gap a stop from another goroutine can land in, and it
+// used to end in "send on closed channel". The raw handler runs in that gap on
+// the read loop itself, so calling Stop from it hits the gap every time.
+func TestStopBeforeMessageReachesQueues(t *testing.T) {
+	const line = `{"type":"ris_message","data":{"type":"UPDATE","peer":"192.0.2.1",` +
+		`"peer_asn":"64496","timestamp":1700000000}}` + "\n"
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		_, _ = io.WriteString(w, line)
+	}))
+	defer srv.Close()
+
+	s := New(logger.New(), metrics.New())
+	s.url = srv.URL
+	s.RegisterHandler(updateHandler{})
+	s.RegisterRawHandler(func(string) { s.Stop() })
+
+	// Start would run the stream in the background, where the test cannot
+	// wait for it. Setting cancel as Start does lets Stop cancel the stream
+	// run here instead.
+	ctx, cancel := context.WithCancel(context.Background())
+	s.cancel = cancel
+
+	if err := s.stream(ctx); !errors.Is(err, context.Canceled) {
+		t.Fatalf("stream returned %v, want %v", err, context.Canceled)
+	}
+
+	// A second Stop must not close the queues again.
+	s.Stop()
+}
+
 // settledGoroutineCount lets transient goroutines finish, then reports the
 // current count.
 func settledGoroutineCount() int {