Describe the bug

When Proxying to a WebSocket service in local development the socket connection can rejected by the server as the Host and Origin header values do not match. This Origin-limiting behaviour is recommended in RFC 6455 and is implemented in the Java websockets API and the Gorillas websocket package.

The Vite proxy is intended as a convenience for local development rather than use in production. I therefore think Vite proxy should support it out-of-the-box.

I don't have a reproduction I can share but have been able to verify that upstream socket servers that implement RFC-6455 return a 403 and this causes the Vite proxy to error on initial connection.

I'm happy to raise a PR.

Reproduction

n/a

Steps to reproduce

With a vite project that connects to a remote RFC-6455 compliant websocket server without using CORS.

Steps:

1. In vite.config.ts set a ws proxy that points to the websocket server
2. Run npm start
3. Open browser dev tools > network

Expected:

ws request responds with a 101 Upgrade and the socket is established

Actual:

ws request receives no response and its status is Finished

System Info

System:
    OS: macOS 14.4.1
    CPU: (8) arm64 Apple M2
    Memory: 64.20 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 18.19.1
    npm: 10.2.4
  Browsers:
    Chrome: 124.0.6367.93
  npmPackages:
    @vitejs/plugin-react: ^4.2.1 => 4.2.1 
    vite: ^5.2.10 => 5.2.10

Used Package Manager

npm

Logs

> vite -d proxy --port 1693
  VITE v5.2.10  ready in 108 ms

  ➜  Local:   http://localhost:1693/
  ➜  Network: use --host to expose
  ➜  press h + enter to show help

  vite:proxy /ws -> ws https://proxied.dev.server +63ms
5:50:22 PM [vite] ws proxy socket error:
Error: read ECONNRESET
    at TCP.onStreamRead (node:internal/stream_base_commons:217:20)

Validations

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• The provided reproduction is a minimal reproducible example of the bug.