SSE stands for Server-Sent Events.
SSE is a browser API that allows a server to push updates to the client over a single HTTP connection. Unlike WebSocket which is bidirectional, SSE only supports server-to-client messages.
SSE for WebRTC signaling
SSE can be used as a signaling transport for WebRTC:
- Server-to-client: SSE delivers SDP answers and ICE candidates from the server
- Client-to-server: Regular HTTP POST requests send SDP offers and ICE candidates to the server
SSE vs WebSocket for signaling
| Feature | SSE | WebSocket |
|---|---|---|
| Direction | Server-to-client only | Bidirectional |
| Protocol | HTTP | WebSocket (upgraded HTTP) |
| Reconnection | Automatic | Manual |
| Firewall friendly | Yes (plain HTTP) | Usually (port 443) |
| Complexity | Simpler | More features |
SSE is a reasonable choice for WebRTC signaling when combined with HTTP POST for the client-to-server direction. It is simpler to implement than WebSocket and works well behind proxies. WHIP and WHEP use a similar HTTP-based approach.