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#ktor
Title
# ktor
s

Shubham Singh

03/08/2023, 5:35 PM
Is there a way to collect a flow inside the
webSocket
block in Ktor Server and
sendSerialized
the values collected from that flow? In my case, I am observing the changes inside my PostgreSQL DB and returning the changes as a flow from the repository. Now I want to send this flow of values through a websocket connection so that whenever the value inside the flow changes, my websocket also sends a new frame, but right now when I try to do the following:
Copy code
webSocket(getObservable) {
                    safeCall {
                        val id = call.parameters["id"]
                        repository.getObservable(id = UUID(id)).collect { value ->
                            sendSerialized(value)
                        }
                    }
                }
the websocket connection closes as soon as I connect to it.
🦻 1
🦻🏾 1
What does this👂mean @Jonah Stiennon @Andromadus Naruto?
a

Andromadus Naruto

03/11/2023, 11:14 AM
In my case, it means that I would love to hear how the conversation is going. Maybe I should have just used the 'watch for replies' feature.
s

Shubham Singh

03/11/2023, 12:12 PM
Understood.. thanks for explaining 🙂
a

Aleksei Tirman [JB]

03/13/2023, 12:05 PM
The problem may be that the
safeCall
returns immediately. Here is an example where a mutable state flow is collected inside a websocket handler:
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val flow = MutableStateFlow(0)

GlobalScope.launch {
    while (true) {
        delay(2000)
        flow.update {
            it + 1
        }
    }
}

embeddedServer(Netty, port = 8082) {
    install(WebSockets)

    routing {
        webSocket("/ws") {
            flow.collect {
                send(Frame.Text(it.toString()))
            }
        }
    }
}.start(wait = true)
👍🏾 1
j

Jonah Stiennon

03/13/2023, 7:47 PM
@Shubham Singh I'm testing an AI Q&A bot that I installed in this server. When I react with that emoji, the bot tries to answer the question, but sends the answer to me in a DM so that it doesn't pollute the channel with wrong answers. If the answer is right, I post it back to the thread, but in this case it was unhelpful 😞
s

Shubham Singh

03/14/2023, 6:27 AM
@Aleksei Tirman [JB]
safeCall
wasn't the issue, it is just a try-catch block internally. The thing was that I was getting only a
Flow
from the repository (that is cold by nature), when I converted it into a SharedFlow using the
shareIn
convenience function, it doesn't close immediately anymore, but now I'm facing another issue i.e. maybe the Apollo graphql client is not able to parse a UUID string as Json and hence throws the error in the image attached below. I'll maybe try to post this in the Apollo GraphQL slack channel.
Still, thank you for taking out time to help The only thing I wanted to know from you if there is official documentation or an example that teaches us how to work with Flows inside a WebSocket in Ktor? Or maybe a WebSocket isn't even meant to perform such operations and there's something else that helps.
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