Help to port Socket.IO to Emscripten (WebAssembly)

[skhaz]

I am creating a Socket.IO implementation for Emscripten in C++, purely using WebSockets.

I followed the documentation for several days and even tried reverse-engineering the client for web browsers, but without success.

Below is a step-by-step description of what I am doing, and I would be very grateful to know what I did wrong to experience frequent disconnections.

WebSocket URL ws://localhost:3000/socket.io/?transport=websocket&EIO=4 (no HTTP!)

I connect and I receive

0{"sid":"w4NlzSj3BPm24GGDAAAX","upgrades":[],"pingInterval":25000,"pingTimeout":20000,"maxPayload":1000000}

Then I anwser with

0

Then the connection keeps for while...

If I try to send

42["messsage","hello world"]

I got disconnected immediately.

Also, if I receive

2

And anwser with

3

I got disconnected immediately too.

[darrachequesne]

Hi!

The protocol is split in two:

• the Engine.IO protocol
  • 0{"sid":"w4Nlz...} is the handshake sent by the server
  • 2 are indeed PING packets, and the client should respond with a PONG packet (3)

Reference: https://socket.io/docs/v4/engine-io-protocol/

• the Socket.IO protocol

Every Socket.IO packet must be prefixed by 4, indicating an Engine.IO MESSAGE packet.

So sending a CONNECT packet (0) becomes a 40 over the wire.

Then you will be able to send message with 42[...].

Reference: https://socket.io/docs/v4/socket-io-protocol/#format

[skhaz]

I see. Thank you!