fix: don't block on unresponsive SSE receivers

Originally discovered, reported, and fixed by @ricmzn.

server/http.go

@@ -176,7 +176,11 @@ func (h *httpServer) streamServerEvents(w http.ResponseWriter, r *http.Request)
 
 	for {
 		select {
-		case msg := <-sub:
+		case msg, ok := <-sub:
+			if !ok {
+				return
+			}
+
 			outgoing := []byte("data: ")
 			outgoing = append(outgoing, msg...)
 			outgoing = append(outgoing, '\n', '\n')

server/session.go

@@ -111,8 +111,14 @@ func (s *serverSession) publish(event string, data interface{}) error {
 	}
 
 	s.Lock()
-	for _, sub := range s.subscribers {
-		sub <- encoded
+	for subId, sub := range s.subscribers {
+		select {
+		case sub <- encoded:
+			continue
+		default:
+			log.Printf("[session:%v] subscriber %v non-responsive, closing", s.server.Name, subId)
+			close(sub)
+		}
 	}
 	s.Unlock()
 	return nil