[BUG] WebSocket server does not send 426 Upgrade Required

[sirzooro]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

WebSocket server sends error 400 Bad Request when HTTP connection cannot be upgraded to WebSocket what is misleading - recently I had to exchange few emails with someone before I found that he was sending regular HTTP request instead of opening WS.

Expected Behavior

Send error 426 Upgrade Required as specified in RFCs:

RFC 9110 - HTTP Semantics:

The 426 (Upgrade Required) status code indicates that the server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol. The server MUST send an Upgrade header field in a 426 response to indicate the required protocol(s) (Section 7.8).

RFC 6455 - The WebSocket Protocol

   /version/
      The |Sec-WebSocket-Version| header field in the client's
      handshake includes the version of the WebSocket Protocol with
      which the client is attempting to communicate.  If this
      version does not match a version understood by the server, the
      server MUST abort the WebSocket handshake described in this
      section and instead send an appropriate HTTP error code (such
      as 426 Upgrade Required) and a |Sec-WebSocket-Version| header
      field indicating the version(s) the server is capable of
      understanding.

Steps To Reproduce

No response

Anything else?

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