fix: handle race between LocalTrackSubscribed signal and publishTrack completion (#1872)

Author: pabloFuente

.changeset/curvy-bugs-live.md

@@ -0,0 +1,5 @@
+---
+"livekit-client": patch
+---
+
+fix: handle race between `LocalTrackSubscribed` signal and `publishTrack` completion

src/room/Room.ts

@@ -588,22 +588,7 @@ class Room extends (EventEmitter as new () => TypedEmitter<RoomEventCallbacks>)
         this.emit(RoomEvent.DCBufferStatusChanged, status, kind);
       })
       .on(EngineEvent.LocalTrackSubscribed, (subscribedSid) => {
-        const trackPublication = this.localParticipant
-          .getTrackPublications()
-          .find(({ trackSid }) => trackSid === subscribedSid) as LocalTrackPublication | undefined;
-        if (!trackPublication) {
-          this.log.warn(
-            'could not find local track subscription for subscribed event',
-            this.logContext,
-          );
-          return;
-        }
-        this.localParticipant.emit(ParticipantEvent.LocalTrackSubscribed, trackPublication);
-        this.emitWhenConnected(
-          RoomEvent.LocalTrackSubscribed,
-          trackPublication,
-          this.localParticipant,
-        );
+        this.handleLocalTrackSubscribed(subscribedSid);
       })
       .on(EngineEvent.RoomMoved, (roomMoved) => {
         this.log.debug('room moved', roomMoved);
@@ -1626,6 +1611,65 @@ class Room extends (EventEmitter as new () => TypedEmitter<RoomEventCallbacks>)
     }
   }
 
+  private handleLocalTrackSubscribed(subscribedSid: string) {
+    const findPublication = () =>
+      this.localParticipant
+        .getTrackPublications()
+        .find(({ trackSid }) => trackSid === subscribedSid) as LocalTrackPublication | undefined;
+
+    const trackPublication = findPublication();
+    if (trackPublication) {
+      this.emitLocalTrackSubscribed(trackPublication);
+      return;
+    }
+
+    // the track publication may not be registered yet if the server signals
+    // the subscription before publishTrack has finished adding the publication.
+    // defer with a timeout until LocalTrackPublished fires for the matching trackSid
+    this.log.debug('deferring LocalTrackSubscribed, publication not yet available', {
+      ...this.logContext,
+      subscribedSid,
+    });
+
+    const TIMEOUT_MS = 10_000;
+    let timer: ReturnType<typeof setTimeout>;
+
+    const onPublished = (pub: LocalTrackPublication) => {
+      if (pub.trackSid === subscribedSid) {
+        cleanup();
+        this.emitLocalTrackSubscribed(pub);
+      }
+    };
+
+    const cleanup = () => {
+      clearTimeout(timer);
+      this.localParticipant.off(ParticipantEvent.LocalTrackPublished, onPublished);
+      this.off(RoomEvent.Disconnected, cleanup);
+    };
+
+    this.localParticipant.on(ParticipantEvent.LocalTrackPublished, onPublished);
+    this.once(RoomEvent.Disconnected, cleanup);
+
+    timer = setTimeout(() => {
+      cleanup();
+      // final attempt in case the publication was added without emitting the event
+      const pub = findPublication();
+      if (pub) {
+        this.emitLocalTrackSubscribed(pub);
+      } else {
+        this.log.warn(
+          'could not find local track publication for LocalTrackSubscribed event after timeout',
+          { ...this.logContext, subscribedSid },
+        );
+      }
+    }, TIMEOUT_MS);
+  }
+
+  private emitLocalTrackSubscribed(trackPublication: LocalTrackPublication) {
+    this.localParticipant.emit(ParticipantEvent.LocalTrackSubscribed, trackPublication);
+    this.emitWhenConnected(RoomEvent.LocalTrackSubscribed, trackPublication, this.localParticipant);
+  }
+
   private handleRestarting = () => {
     this.clearConnectionReconcile();
     // in case we went from resuming to full-reconnect, make sure to reflect it on the isResuming flag