[xianshijing-lk]

Port of livekit/client-sdk-js#2092.

The gap

DataReceivedEvent.participant is nullable, and the field's own comment says why:

/// Sender of the data. This may be null if data is sent from Server API.
final RemoteParticipant? participant;

When it is null — data sent via the Server API, or by a participant who has already left — the receiver has no way to tell who sent the data. The identity is not merely hard to get, it is absent from the event entirely.

The engine has it in hand at the construction site and simply drops it:

RemoteParticipant? senderParticipant;
if (dataPacketEvent.identity.isNotEmpty) {
  senderParticipant = getParticipantByIdentity(dataPacketEvent.identity) as RemoteParticipant?;
}

final event = DataReceivedEvent(
  participant: senderParticipant,   // <- dataPacketEvent.identity is right here
  data: dataPacketEvent.packet.payload,
  topic: dataPacketEvent.packet.topic,
);

The fix

Add a non-nullable participantIdentity to DataReceivedEvent, populated from the packet for every event — present whether or not the sender resolves to a RemoteParticipant.

Verification

Added test/core/data_received_identity_test.dart, which delivers an inbound packet from an identity that is not a room participant and asserts the identity still arrives. Before the change it does not compile, because the field does not exist:

Error: The getter 'participantIdentity' isn't defined for the type 'DataReceivedEvent'.

A second case covers a known participant, so both the resolved and unresolved paths are pinned.

flutter test 472/472, flutter analyze lib/ clean.

API note

This adds a required named parameter to the public DataReceivedEvent constructor. Nothing outside the SDK should be constructing these — the engine is the only producer — but it is technically breaking for anyone who does (a test fake, say). Happy to make it optional with a default of '' instead if you'd prefer to keep the constructor source-compatible.

🤖 Generated with Claude Code