Behavior on `WebSocket.Send` on disconnection

[Kludex]

Behavior on `WebSocket.Send` on disconnection

[andrewgodwin]

I'm shocked we never specified this to be honest - you'd think it would have come up before now!

I'm inclined to say that an exception is the best behaviour here, as silent failure sending things down a socket seems like a way to make people's debugging very annoying. I can think of other behaviours when this might occur, though - HTTP connections where you try to send some body after sending previous body with more_body=False.

Probably makes the most sense to define a common error type that gets raised in these scenarios? We could define one in asgiref, but that kind of irks me as it means you'd need the package to implement the spec, whereas right now you don't. Maybe just saying you get something like IOError would be better.

[Kludex]

I'm shocked we never specified this to be honest - you'd think it would have come up before now!

It actually came up some years ago in the FastAPI discussions. I didn't know enough by then. 😁

HTTP connections where you try to send some body after sending previous body with more_body=False.

Hmm... I didn't understand this case - or how it's similar to the current.

Probably makes the most sense to define a common error type that gets raised in these scenarios? We could define one in asgiref, but that kind of irks me as it means you'd need the package to implement the spec, whereas right now you don't.

This seems like it will create a barrier for package maintainers to be fully compliant with ASGI.

Maybe just saying you get something like IOError would be better.

Yes, it will. But... Can we be more generic here instead? Would it be bad to write something like the following?

The `send` event may raise an `Exception` in case the client is disconnected.

Maybe even... (to be improved)

The ASGI framework should be in charge of catching the exception.

[Kludex]

I had an idea!

What if we enable the application and the server to communicate about those scenarios beforehand?

One way could be being an ASGI extension:

"scope": {
    ...
    "extensions": {
        "websockets.send.exceptions": {
            "exceptions": [
                 websockets.WebSocketException,
                 wsproto.LocalProtocolError,
             ]
         },
    },
}

Details, and API to be defined (it can be more generic, more specific), but you get the idea.

[Kludex]

Well... I see that @tomchristie created an issue here about WebSocket.send exceptions years ago: #66. 😅

[Kludex]

• I'm going to close this in favor of #66.