Websocket Routes overides uvicorns default Server header

[iudeen]

This is a continuation of a discussion happened in FastAPI Discord Channel after an issue was reported by Salaz#7667.

When a Websocket route is created, there is a Server header that is present. Currently the server header has the python version.

Sample:

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: SCtyBF9CdOAnFbass9dkRn6ZX0U=
Sec-WebSocket-Extensions: permessage-deflate
Date: Thu, 14 Jul 2022 07:15:48 GMT
Server: Python/3.10 websockets/10.3

On tracing it back, it was found that the websocket library adds this header.

Interesting part is, for normal routes (http), the default headers added by Uvicorn looks like this:

HTTP/1.1 200 OK
date: Thu, 14 Jul 2022 07:22:35 GMT
server: uvicorn
content-length: 4
content-type: application/json

This behavior exits even if --no-server-header is passed, only for Websockets route.

One way I found to remove the Server header is to replace it by doing this:

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept(headers=[(b"Server", b"")])
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(f"Message text was: {data}")

Test Scenario:

Webserver: uvicorn 0.18.2 with CPython 3.10.4 on Windows
Framework: FastAPI 0.78
OS: Windows
Websocket Client: Simple Web Socket Client

Code Snippet

from starlette.websockets import WebSocket
from fastapi import FastAPI, Form

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(f"Message text was: {data}")

[iudeen]

IMHO, it should be considered a bug (minor) in Uvicorn simply for the fact that Uvicorn behaves differently for HTTP routes.

I went through the code. Not exactly sure where we can set the appropriate server header before passing on to Web Sockets.

As I mentioned in the question, setting the header (rather replacing header - as pointed by @Kludex in discord) during websocket.accept works. We just need to do it internally.

[iudeen]

Not able to find :/

[iudeen]

I searched with keywords header, server_header and even default_header. May be I overlooked 😔

[iudeen]

I went through 07c6c18, I think headers were left out. Not exactly sure why..

[iudeen]

I have started a PR for this. #1581 #1606

I'd need some insights from you @Kludex if this makes sense or it'd be ideal to stall the PR till we have a clear idea on this implementation.

[iudeen]

I went through 07c6c18, I think headers were left out. Not exactly sure why..

I this the original commit left out headers because Websockets did not provide an API for it. Just my wild guess. Any thoughts? @Kludex ?

[iudeen]

This is fixed in #1606