Inconsistent WebSocket subprotocol parsing compared to other ASGI servers

[david-sh-csiro]

I have observed an inconsistency in how WebSocket subprotocols are handled compared to other ASGI server implementations.
Specifically, Granian does not split the Sec-WebSocket-Protocol header into separate subprotocol strings. Instead, it returns a single combined string.

Client Websocket Opening Handshake
Sec-WebSocket-Protocol: bokeh, Token

Observed Behavior (Granian)

scope["subprotocols"] == ['bokeh, Token']

Expected / Common Behavior (Other ASGI servers)
Other ASGI servers such as Uvicorn, Hypercorn, and Daphne split the subprotocol header into a list of individual protocol strings:

scope["subprotocols"] == ['bokeh', 'Token']

This behavior was observed when using Django together with bokeh_django under Granian.

Other ASGI servers split the header value. Returning a single combined string may cause compatibility issues with frameworks or libraries that expect a list of individual subprotocols.

Is this behaviour intentional? If not, would it be possible to align Granian’s handling of WebSocket subprotocols with other ASGI server implementations?

[david-sh-csiro]

I'll add a minimal reproducible example repo shortly.

Edit - Repro example: https://github.com/david-sh-csiro/bokeh-django

[JaeHyuckSa]

I also needed this issue to be resolved, so I have submitted a PR with the necessary changes.