Simplest WebSockets example "fails" with a 403

[dAnjou]

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Example Code

from fastapi import FastAPI

app = FastAPI()

@app.websocket("/foo")
async def foo(websocket):
    print("FOO")
    await websocket.accept()
    for line in ["line"]:
        await websocket.send_text(line)

Description

pip install fastapi==0.110.0 uvicorn==0.29.0 websockets==12.0
uvicorn main:app --log-level debug

python -m websockets ws://127.0.0.1:8000/foo

Uvicorn output:

INFO:     Started server process [22379]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
DEBUG:    = connection is CONNECTING
DEBUG:    < GET /foo HTTP/1.1
DEBUG:    < host: 127.0.0.1:8000
DEBUG:    < upgrade: websocket
DEBUG:    < connection: Upgrade
DEBUG:    < sec-websocket-key: pJNin2YFaLlhwD3jzinClQ==
DEBUG:    < sec-websocket-version: 13
DEBUG:    < sec-websocket-extensions: permessage-deflate; client_max_window_bits
DEBUG:    < user-agent: Python/3.12 websockets/12.0
INFO:     ('127.0.0.1', 53509) - "WebSocket /foo" 403
DEBUG:    > HTTP/1.1 403 Forbidden
DEBUG:    > Date: Sun, 24 Mar 2024 17:09:06 GMT
DEBUG:    > Content-Length: 0
DEBUG:    > Content-Type: text/plain
DEBUG:    > Connection: close
DEBUG:    > [body] (0 bytes)
INFO:     connection rejected (403 Forbidden)
DEBUG:    x closing TCP connection
DEBUG:    = connection is CLOSED
INFO:     connection closed

Client output:

Failed to connect to ws://127.0.0.1:8000/foo: server rejected WebSocket connection: HTTP 403.

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.110.0

Pydantic Version

2.6.4

Python Version

Python 3.12.2

Additional Context

No response

[Kludex]

Missing the type hint on websocket:

from fastapi import FastAPI, WebSocket

app = FastAPI()


@app.websocket('/foo')
async def foo(websocket: WebSocket):
    print('FOO')
    await websocket.accept()
    for line in ['line']:
        await websocket.send_text(line)

[dAnjou]

Huh, it relies on a type hint? That should be mentioned in the documentation, no?

[Trolldemorted]

wouldn't HTTP 400 be more fitting than HTTP 403?