I'm trying to get websockets working with a graphql backend (<http://graphql-java.readthedocs.io/en/...

# ktor

[danielm]

I'm trying to get websockets working with a graphql backend (http://graphql-java.readthedocs.io/en/latest/subscriptions.html).
How do I have to configure ktor to achieve this?
Thanks for any help

[Deactivated User]

If the websocket protocol is not explained, but only explained a higher level API. I guess your best bet is to either check the source-code, or use Chrome developer tools to check the WebSocket frames sent/received

[Deactivated User]

Once you have some samples, if it is JSON for example, you can serialize frames using Gson

[danielm]

In the meantime if found/realised that there's an WebSocket class in the graphql java example that's using servlets (https://github.com/graphql-java/graphql-java-subscription-example)
-> https://github.com/graphql-java/graphql-java-subscription-example/blob/master/src/main/java/com/graphql/example/http/StockTickerWebSocket.java

[danielm]

so I guess that this is what I need to map to ktor, correct?

[danielm]

what's the correct place to do this?

[Deactivated User]

What do you want is to use the library directly? Or to reimplement it using ktor?

[danielm]

I'd like to use the graphql functionality of this library to process requests coming in via ktor server.

[danielm]

for regular requests, i.e. not subscriptions/websockets, the integration looks something along this:``` val handler = GraphQLHandler(schema, resolvers)

val server = embeddedServer(Netty, port = 8888) {
install(ContentNegotiation) { jackson { } }
routing {
post("/graphql") {

val request = call.receive<Request>()
val result = handler.execute(request.query, ...)
call.respond(mapOf("data" to result.getData<Any>()))
}
}
}
```

[Deactivated User]

Ok. So you simply want to use the library and somehow consume its results inside a route

[Deactivated User]

You want to reverse proxy the websocket or something? Consume the results and publish to a websocket route of your ktor backend?

[danielm]

yes I guess that's correct (I'm not very familiar with websockets yet 😉 )

[danielm]

for the initial request an object that implements Publisher is being returned (https://github.com/graphql-java/graphql-java/blob/master/src/main/java/graphql/execution/reactive/CompletionStageMappingPublisher.java)

[Deactivated User]

Ok. It seems that that API returns a Publisher and a Subscription, and you can provide a object that will receive results in the onNext, method.
The idea is to call to se websocketSession.outgoing.send to send a frame with the content

[Deactivated User]

if you need to subscribe once, and then serve to several clientes, you will have to use a channel to produce results and read for each client

[Deactivated User]

You can read more about channels here: https://github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md#channels

[danielm]

how would the websocketSession and the Publisher be connected?

[danielm]

well I guess that I have to read my way through https://ktor.io/samples/websockets.html again with the information that you've given me. Thanks

[Deactivated User]

If you have a websocketSession instance, it has a outgoing property with a send method

[Deactivated User]

you can call it inside the onNext method

[Deactivated User]

that would be the easiest way of doing it, you could also try to convert the Subscription or something into a ktor channel, map and try to pipe it, but that would be more complex

[Deactivated User]

you can for example like a chat, store all the websocketSession instances that need to be notified inside a Set, and then when receiving in the onNext method, a message, iterate over all the websocketSession instances, and call session.outgoing.send(Frame(…)) to notify all the clients

[Deactivated User]

but I guess that the first step is to try it by yourself to get familiarized about stuff

[danielm]

yes, I guess that's the case