Error during WebSocket handshake: Unexpected response code: 400

Why error after migrate from v2.2.0 to v2.4.0 ??? Error during WebSocket handshake: Unexpected response code: 400

[willyprayogo26]

Hi, we also encountered the same error yesterday, indeed it was linked to CORS. We updated socket.io from 2.3 to 2.4, and suddenly we had an error 400: Bad request. After fixing CORS everything worked fine. One interesting thing: by coincidence we had transports set to only ['websocket'], so it took a while to figure out that the problem was CORS: if the pooling fallback is enabled it is displayed on the console of the browser an error of the type Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:3030/socket.io/?EIO=3&transport=polling&t=NROEP-d. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). , so it is easy to understand that the problem are missing CORS headers. But if you have only the websocket transport enabled, a generic error 400: Bad request is raised. I don’t know if it would be possible to have a more descriptive error to point users in the right direction even if they are using only the websocket trasport. Cheers

Thanks for the information 👍

[darrachequesne]

The change included in socket.io@2.4.0 was reverted in socket.io@2.4.1: https://github.com/socketio/socket.io/releases/tag/2.4.1