fix(async): handle WebSocket binary frames and attachment collection race condition

[bneigher]

Summary

Fixes two bugs that cause the async Socket.IO client to crash when receiving binary events (e.g. Socket.IO v4 binary attachments sent as WebSocket binary frames):

1. Binary frame misidentification (InvalidUtf8 / InvalidPacketId)

WebSocket binary frames were prefixed with PacketId::Message (0x34 = '4'), causing the Engine.IO packet parser to treat raw binary attachment data as a UTF-8 text message. This produced InvalidUtf8 or InvalidPacketId errors on any binary event.

Fix: Binary frames are now prefixed with a 'B' (0x42) marker byte that the packet parser recognizes and maps to PacketId::MessageBinary, bypassing text/base64 decoding entirely.

Files:

• engineio/src/asynchronous/async_transports/websocket_general.rs — use 'B' marker instead of PacketId::Message for binary WebSocket frames
• engineio/src/packet.rs — recognize b'B' as PacketId::MessageBinary; handle raw binary path in TryFrom<Bytes>
• engineio/src/asynchronous/async_socket.rs — short-circuit parse_payload for raw binary and single packets

2. Attachment collection race condition (EngineIO Error / lost packets)

handle_engineio_packet collected binary attachments via client.clone(), creating a second consumer on the same underlying stream. The outer iteration loop and the attachment loop then raced for incoming packets, causing binary frames to be consumed by the wrong loop and misinterpreted as Socket.IO text packets.

Fix: handle_engineio_packet is removed. Its logic is inlined directly into stream() using &mut client, so attachment packets are consumed sequentially from the same stream without contention.

Files:

• socketio/src/asynchronous/socket.rs — inline attachment collection into stream(), remove handle_engineio_packet

Additional improvements

• socketio/src/asynchronous/client/client.rs — handle_binary_event now properly extracts the event name from quoted strings (e.g. "tts:audio") instead of stripping all quotes from the entire data field, which broke event routing for binary events with metadata.
• socketio/src/error.rs — IncompleteResponseFromEngineIo now includes the inner Engine.IO error in its display message ("EngineIO Error: {0}" instead of just "EngineIO Error").

Reproduction

Connect a rust_socketio async client (WebSocket transport) to a Socket.IO v4 server that emits binary events (e.g. socket.emit("audio", Buffer.from(...))). Without this fix, the client panics or errors with:

• EngineIO Error (no details)
• InvalidPacketId(66) (byte 0x42 from binary data interpreted as packet type)
• InvalidUtf8 (binary data parsed as text)

Test plan

• Verified against a Socket.IO v4 server (Go, zishang520/socket.io) emitting binary events with audio data
• Verified text events, ack events, and disconnect/reconnect still work correctly
• Existing CI test suite (binary event tests in socketio/src/asynchronous/client/client.rs)

Made with Cursor