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Room disconnects with `duplicateIdentity` after reconnecting from a single client: a timed-out signal connect leaves a live socket behind

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
30/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
dart, flutter
Domain
mobile-dev, networking

Research direction

Read lib/src/core/signal_client.dart around SignalClient.connect() and the engine handler near engine.dart:~1603; trace what happens when the timed-out WebSocket connection completes late. The issue says the author already has a local fix and plans a PR, so check for that work before starting. Done means the late socket is closed, S2 remains connected, and no duplicateIdentity disconnect is emitted.

Written by the indexing model from the issue text.

Description

Describe the bug

While a room recovers from a network drop, it can end with RoomDisconnectedEvent(reason: DisconnectReason.duplicateIdentity), even though only one client uses that identity. The reconnect had already succeeded, and the connection was healthy when the event arrived.

duplicateIdentity is supposed to mean another participant joined with the same identity, so apps treat it as "you were replaced" and don't retry. Here, the other session is one this client opened during its own reconnect.

The server is behaving correctly. The client ends up with two sessions for one identity, the server kicks the older one, and the SDK applies that kick to the session it is actually using.

Root cause

SignalClient.connect() (lib/src/core/signal_client.dart, main @ 2.13.0):

var future = _wsConnector(rtcUri, options: WebSocketEventHandlers(
  onData: _onSocketData, onDispose: _onSocketDispose, onError: _onSocketError), ...);
future = future.timeout(connectOptions.timeouts.connection);
_ws = await future;
  1. Future.timeout does not cancel io.WebSocket.connect. On a slow link the handshake can finish after the timeout. The server then has a live session S1 for that attempt.
  2. That socket is never assigned to _ws, so cleanUp() can never close it. LiveKitWebSocketIO has already subscribed it to the shared _onSocketData, so it keeps delivering messages as if it were current.
  3. The engine retries, and the next join creates session S2, which is the one we keep. The server sees two sessions for one identity and sends Leave(DISCONNECT, DUPLICATE_IDENTITY) to S1, which is the orphaned socket.
  4. The leave comes through _onSocketData as an ordinary SignalLeaveEvent. The engine handler (engine.dart:~1603) runs signalClient.cleanUp() and disconnect(), which tears down S2 and emits RoomDisconnectedEvent(reason: duplicateIdentity). Signal is already disconnected at that point, so no leave is sent for S2 either. The server keeps S2 as a stale participant until it times out, and other participants go on seeing it in the room.
To reproduce

Deterministic on an Android emulator (reproduced 5+ times):

  1. Use a short connect timeout so the race is easy to hit: ConnectOptions(timeouts: Timeouts(connection: Duration(seconds: 3), ...)).
  2. Turn on verbose logs: hierarchicalLoggingEnabled = true; Logger('livekit').level = Level.ALL;.
  3. Emulator: Wi-Fi off, so traffic goes over the emulated mobile-data link. adb emu network delay only affects that link.
  4. Join a room.
  5. Airplane mode on for ~40 s, so the server drops the session.
  6. adb emu network delay 5000. Every packet now takes longer than the connect timeout.
  7. Airplane mode off.

About 30 s later the logs show:

Leave received, action: RECONNECT, reason: STATE_MISMATCH   // resume rejected, server already dropped us
EngineFullRestartingEvent                                    // full rejoin #1
Received JoinResponse                                        // S1's handshake finished...
Connect Error TimeoutException after 0:00:03                 // ...but the attempt had already timed out
EngineFullRestartingEvent                                    // full rejoin #2 -> S2
Leave received, action: DISCONNECT, reason: DUPLICATE_IDENTITY   // meant for S1, handled as S2's
RoomDisconnectedEvent(reason: duplicateIdentity)

Expected: the room stays connected on S2, S1's socket is closed, and no RoomDisconnectedEvent is emitted.
Actual: RoomDisconnectedEvent(reason: duplicateIdentity) on a single client.

We also see this in production on phones with poor mobile data: one device, one identity, and a duplicateIdentity disconnect right after a run of reconnect attempts.

Relation to #1211

#1211 adds a per-socket generation so callbacks from a replaced socket are ignored. Once the retry bumps the generation, that would also drop the late leave above. This issue is a different trigger (a timed-out attempt instead of a disposed one), and two gaps remain:

  • the late socket is never closed, so it stays open and holds a server session until the server closes it;
  • between the timeout and the next connect() (e.g. during retry backoff), the orphan's callbacks still carry the current generation and are processed.

I have a fix with tests for this locally and plan to open a PR.

Environment
  • livekit_client 2.7.0 in production, same code on main (2.13.0)
  • Android (emulator repro) and iOS (production)
  • LiveKit server (self-hosted)
Dominant language
Dart
Stars
421
Forks
260
Avg merge
3d 9h
Merged PRs (30d)
11

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