is there any good pattern to do the handling of websocket messages outside the `webSocket` block? I...

# ktor

[bbaldino]

is there any good pattern to do the handling of websocket messages outside the webSocket block? I’m trying to do something like:

webSocket("/ws") {
    val webSocketTransport = WebSocketTransport(this)
    eventHandler.newWebSocketConnected(webSocketTransport)
}

where the WebSocketTransport launches a coroutine to read the incoming messages:

scope.launch {
    for (msg in webSocketSession.incoming) {
        ...
    }
}

but when I try this, the websocket disconnects immediately, because it looks like it’s implemented in a way to close as soon as the passed handler returns. Is there any good pattern move that logic out? I did it one way where I added another channel, and the webSocket handler read messages and wrote them to that channel, and WebSocketTransport read from that channel, but was hoping to avoid having to create the intermediary.

[ephemient]

if scope is the current scope or a child then it will all work out

[bbaldino]

Ah great…so something like create a child scope and pass that to WebSocketTransport ?

[bbaldino]

and have it use that for its scope.launch

[ephemient]

yes, that will work, or refactor it to avoid the launch altogether

[bbaldino]

I now have:

webSocket("/ws") {
            coroutineScope {
                val webSocketTransport = WebSocketTransport(this@webSocket, this@coroutineScope)
                handler.newWebSocketConnection(sessionId, webSocketTransport)
            }
        }

which seems to be working right…does that look reasonable?

[bbaldino]

the scope.launch is done in the WebSocketTransport.init, so it kicks that off before coroutineScope closes, which I’m assuming is required to keep the parent webSocket scope “alive”

[ephemient]

so that's one way to do it, although this@webSocket should already implement CoroutineScope

[bbaldino]

Ah! That’s even better

[bbaldino]

Oh, hm. Using webSocketSession.launch doesn’t seem to keep it alive.

[ephemient]

hmm it doesn't? I'm not sure why that would be… but I guess an explicit coroutineScope {} works

[bbaldino]

from what i can tell it doesn’t. i can stick with the coroutineScope method…bit uglier but it seems to work.

[bbaldino]

perhaps because launch alone doesn’t create a child scope? (does it?)

[ephemient]

it does create a child scope, it must be something ktor is doing with the pipeline

[bbaldino]

ok

[bbaldino]

the relevant ktor block is here, i think

[bbaldino]

so as soon as handler finishes, it closes it

[Rustam Siniukov]

you can use client.webSocketSession(request) if you need manual control over closing

[bbaldino]

@Rustam Siniukov what’s “client” there/what scope is it available in? is that something available inside routing ?

[Rustam Siniukov]

Sorry, my fault. It’s a client API, not server.

[Aleksei Tirman [JB]]

Maybe, this answer helps you.