Error during WebSocket handshake: Unexpected response code: 400 (anonymous) @ (index):16

Checklist

• The bug is reproducible against the latest release and/or master.
• There are no similar issues or pull requests to fix it yet.

Describe the bug

I am following the Fastapi websockets tutorial (https://fastapi.tiangolo.com/advanced/websockets/#await-for-messages-and-send-messages). With the exact code given (see link) I start uvicorn with uvicorn main:app --reload visit http://127.0.0.1:8000/. I get this error in my chrome console:

(index):16 WebSocket connection to 'ws://localhost:8000/ws' failed: Error during WebSocket handshake: Unexpected response code: 400

To reproduce

Expected behavior

When I click “send” I expect to see the message I typed appear on the screen

Actual behavior

When I click “send” nothing happens

Debugging material

Environment

• OS / Python / Uvicorn version: just run uvicorn --version macos 10.15.5 python 3.8.2 uvicorn 0.12.1

• The exact command you’re running uvicorn with, all flags you passed included. If you run it with gunicorn please do the same. If there is a reverse-proxy involved and you cannot reproduce without it please give the minimal config of it to reproduce. uvicorn main:app --reload

Additional context

[KoehlerClem]

Fixed it with: pip3 install websockets

[euri10]

ok the new packaging does not install websocket or h11 by default so with a simple pip install uvicorn no ws will be handled.

to fix this. install with pip install uvicorn[standard].

we need to either provide a gentle message on ws usage if the latter installation was used or update docs, or both