SID in the connect endpoint and in the HTTP query params do not match

[guneemwelloeux]

I've been investigating issues with my socket.io powered service for a while now, but only realised that the sid= part of the URL does not match what the connect event handler is reporting as sid (the first parameter).
For example, with this connect event handler:

async def connect(sid, _, auth: Optional[Dict[str, Optional[str]]] = None):
    lock = locks.setdefault(sid, asyncio.Lock())
    async with server.session(sid) as session, lock:
        session.update({'r': {}, 'user_id': res.get("uid")})
    logging.info({"msg": "Client connected", "sid": sid, "uid": res.get("uid")})
    return True

I'm seeing this in the logs:

INFO:     127.0.0.1:50982 - "GET /socket.io/?EIO=4&transport=polling&t=l2b9udo8 HTTP/1.1" 200 OK
INFO:root:{'msg': 'Client connected', 'sid': '2CkxGCyEyUnzUYNyAAAB', 'uid': 'n0wfkIiv6OED73Q3ct3vaVhEoTca'}
INFO:     127.0.0.1:50982 - "POST /socket.io/?EIO=4&transport=polling&t=l2c2a6pk&sid=gB93-W2WdSa1DzOLAAAA HTTP/1.1" 200 OK

This clearly shows that the SID that python-socketio "sees" is different from that which is returned to the client, which we can see in the next request on the third line above.

What gives? How can I explain that, and more importantly, how can I fix my code so that the same SID is displayed and I can link my logs together properly?

[miguelgrinberg]

This is actually working as designed. For each Socket.IO client you will normally find at least 2 SIDs.

The SID that you see in the connection URL in the logs is the Engine.IO SID. This is the low-level transport on which all the Socket.IO namespaces are multiplexed. Then the client connects to one or more Socket.IO namespaces, and each of these logical connections receives its own SID. These are the SIDs that you receive in your connection event handler.

[guneemwelloeux]

Thanks for the reply. I figured it wasn't a bug, because my service is actually working (unless it isn't), but I was very confused that I couldn't find the HTTP requests with the same sid, given that it has the same name.
After I enabled logging for both EngineIO and SocketIO, and saw both ids, and which layer was responsible for which id.

Would you be able to tell me how to get to the EngineIO sid though, so I can improve my logging, and hopefully have complete traces? Thanks

[miguelgrinberg]

With the warning that this is undocumented functionality, so it is not guaranteed to be supported in future versions, here is how you can do the conversion:

eio_sid = sio.manager.eio_sid_from_sid(sid, namespace)

If you are not using namespaces, then set the namespace argument to '/'.