[Bugifx] Shubhra/ Add buffer to FFI events #508

Shubhrakanti · 2025-07-18T20:14:46Z

This ports over a fix that was done in the python side, but never implemented in the node sdk (PR).

User reported that the Room would throw an error if there was already a participant inside and they tried to connect. This is because we were processing the participant_connected event before the trackSubscribed event.

Before fix:

call room.connect
receive trackSubscribed ← Tries to find participant that was never created!
throw participant not found error

After fix:

call room.connect
receive participants_updated
receive participant_connected ← Creates the participant
receive track_published
receive track_subscribed ← Works because participant exists

changeset-bot · 2025-07-18T20:14:50Z

🦋 Changeset detected

Latest commit: 772570f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@livekit/rtc-node	Patch
@livekit/rtc-node-darwin-arm64	Patch
@livekit/rtc-node-darwin-x64	Patch
@livekit/rtc-node-linux-arm64-gnu	Patch
@livekit/rtc-node-linux-x64-gnu	Patch
@livekit/rtc-node-win32-x64-msvc	Patch

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Shubhrakanti · 2025-07-18T20:17:58Z

tsconfig.json

@@ -1,6 +1,6 @@
 {
  "compilerOptions": {
-    "lib": ["es2015"],
+    "lib": ["es2015", "ES2021.WeakRef"],


We need this so that linter doesn't throw an error when using FinalizationRegistry

@lukasIO is there a reason this is es2015 can we just update it to something later.

Looks like we don't need FinalizationRegistry. But still would be good to upgrade this?

Shubhrakanti · 2025-07-18T20:18:21Z

tsconfig.json

@@ -1,6 +1,6 @@
 {
  "compilerOptions": {
-    "lib": ["es2015"],
+    "lib": ["es2015", "ES2021.WeakRef"],


@lukasIO is there a reason this is es2015 can we just update it to something later.

Shubhrakanti · 2025-07-18T20:22:39Z

packages/livekit-rtc/src/ffi_client.ts

+    }
+  }
+
+  subscribe(): ReadableStream<T> {


I chose this to be the equivalent of the asyncio's Queue we use in python. The main feature we care about is asynchronous reads and waiting for events while the stream is empty.

Shubhrakanti · 2025-07-18T20:25:01Z

packages/livekit-rtc/src/room.ts

@@ -88,8 +90,19 @@ export class Room extends (EventEmitter as new () => TypedEmitter<RoomCallbacks>
  remoteParticipants: Map<string, RemoteParticipant> = new Map();
  localParticipant?: LocalParticipant;

+  private static cleanupRegistry = new FinalizationRegistry((cleanup: () => void) => {


We use FinalizationRegistry (see docs) to act as an equivalent of python's __del__ method

There's also Symbol.dispose as defined in a ECMA proposal https://github.com/tc39/proposal-explicit-resource-management but I wasn't sure if this was merged in yet.

Shubhrakanti · 2025-07-18T20:27:58Z

packages/livekit-rtc/src/room.ts

+    } catch (error) {
+      log.debug(error, 'Listen task ended');
+    } finally {
+      this.listenTaskPromise = undefined;


is it better to type it as | null?

Shubhrakanti · 2025-07-18T20:34:51Z

@davidzhao this should fix the issues folks were having with inbound sip calls in agents js

Shubhrakanti · 2025-07-18T20:36:05Z

packages/livekit-rtc/src/ffi_client.ts

+      } catch (error: unknown) {
+        log.error(error, 'Error enqueuing item to stream');
+        toRemove.add(controller);
+      }
+    }
+
+    for (const controller of toRemove) {
+      this.subscribers.delete(controller);
+    }


is this overkill? Just want to make sure there are no memory leaks.

Shubhrakanti · 2025-07-18T20:36:30Z

packages/livekit-rtc/src/ffi_client.ts

+  /**
+   * @throws "TypeError: Invalid state: ReadableStream is locked"
+   * if the stream is locked, make sure the stream is not being read from
+   * before calling this method.
+   */
+  unsubscribe(stream: ReadableStream<T>): void {
+    stream.cancel();
+  }
+}


I don't love this, but it works for now.

theomonnom · 2025-07-18T22:04:21Z

packages/livekit-rtc/src/room.ts

  constructor() {
    super();
+    // Register a finalizer to disconnect the room when it's garbage collected
+    Room.cleanupRegistry.register(this, () => {


I don't think we need this. If the FfiHandle is dropped, the Rust side will already close the room

Good to know. I saw in the python side so that's why I implemented it - but had a felling we didn't need this.

theomonnom · 2025-07-18T22:05:00Z

packages/livekit-rtc/src/room.ts

@@ -180,6 +193,9 @@ export class Room extends (EventEmitter as new () => TypedEmitter<RoomCallbacks>
      options,
    });

+    // subscribe before connecting so we don't miss any events
+    this.ffiQueue = FfiClient.instance.queue.subscribe();


On JS it may be simpler, just hooking into the FfiEvent using on. We could just append to a list?

Maybe it's fine, but IIRC that was the only difference. JS using events, but python using queues

On JS it may be simpler, just hooking into the FfiEvent using on that's exactly what this is doing.

We grab the events and append them to a queue. The only reason it's a stream is so reads are async and we don't block the main event loop.

Do you mean get rid of FfiClient.instance.queue all together. Replace this with

connect(){ // wire up the event listener first FfiClient.instance.on(FfiClientEvent.FfiEvent, this.onFfiEvent) // send the connection request const res = FfiClient.instance.request<ConnectResponse>({ ...... }) } // onEvent(event): { this.buffer.push(event) // only start processing the events once we've connected. if (connected) { this.proccessEvent(event) ...

As I understand it the order of operations are.

Create a buffer for all the events coming in

Connect to the room

Immediately populate the buffer so we don't drop events

Start processing events

Right now step 1 is done with this.ffiQueue = FfiClient.instance.queue.subscribe(); if we replace it with FfiClient.instance.on(FfiClientEvent.FfiEvent, this.onFfiEvent) we still need to buffer the events to process until we receive the ConnectResponse?

Shubhrakanti · 2025-07-21T21:14:31Z

Discussed offline with @theomonnom - we're just going to buffer the events that come in before the connect in room.ts. Once we have connected - we will process them in batch.

init

628ef2d

Shubhrakanti changed the title ~~Shubhra/ Add buffer to FFI events~~ [Bugifx] Shubhra/ Add buffer to FFI events Jul 18, 2025

remove unused code

80769e5

Shubhrakanti commented Jul 18, 2025

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update comments

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Shubhrakanti commented Jul 18, 2025

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changeset

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Shubhrakanti requested review from lukasIO and theomonnom July 18, 2025 20:35

Shubhrakanti commented Jul 18, 2025

View reviewed changes

Shubhrakanti requested review from toubatbrian and davidzhao July 18, 2025 20:36

theomonnom reviewed Jul 18, 2025

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Shubhrakanti requested a review from theomonnom July 19, 2025 19:31

Shubhrakanti added 6 commits July 19, 2025 12:33

remove garbage collection hadle

8975a20

simpler solution

fca0fe0

init solution

7389f7d

clean up

c2b8b76

clean up

1e5a64e

fix builds

772570f

theomonnom approved these changes Jul 21, 2025

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Shubhrakanti merged commit 37211ca into main Jul 22, 2025
17 checks passed

Shubhrakanti deleted the shubhra/add-buffer-to-ffi-events branch July 22, 2025 03:47

github-actions bot mentioned this pull request Jul 22, 2025

Version Packages #511

Merged

[Bugifx] Shubhra/ Add buffer to FFI events #508

[Bugifx] Shubhra/ Add buffer to FFI events #508

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Shubhrakanti commented Jul 21, 2025

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