Can the v3 client connect to Socket.IO v2 servers?

[NarvaloBanouu]

My Go client needs to connect to multiple Socket.IO servers. Some servers are running Socket.IO v2 (EIO=3) and others are running Socket.IO v3+ (EIO=4).
I understand that this library's server can accept both v2 and v3 clients by detecting the EIO parameter. However, I'm unsure if the client can do the same.
My question: Can I configure the v3 client to connect to Socket.IO v2 servers by setting EIO=3 in the query parameters?
Is it possible for the v3 client to speak the v2 protocol? Or do I need to use the v2 client for v2 servers?
Thanks!

[anntnzrb]

Short answer: No, the v3 client only supports EIO=4 (Socket.IO v4+ protocol).

Looking at the code, the client hardcodes Protocol = 4 in the parser and sends EIO={protocol} in the connection query. There's no option to configure the protocol version.

The server has AllowEIO3 option to accept connections from both v2 and v4 clients (backward compat), but the client itself doesn't support speaking EIO=3.

Your options:

1. Upgrade all servers to Socket.IO v4 — cleanest solution
2. Use two different client libraries — this one for v4 servers, find an older Go client for v2 servers (messy)
3. Check if your v2 servers can accept v4 clients — some configs may allow this

Realistically, if you control the servers, upgrading them to v4 is the way to go. If you don't control them, you'd need a separate client library that implements the older protocol.