Hey guys, trying to basic async endpoint with `kto...

# ktor

[Sergey Chikin]

Hey guys, trying to basic async endpoint with `ktor`:

override val route: Routing.() -> Unit
        get() = {
            get("healthz") {
                val dbState = asyncGetDatabaseState()

                var res = HealthModel(
                        status = Server.status,
                        database = dbState.await(),
                        redis = RedisHealth("null", 0)
                )

                call.respond(res)
            }
        }

    suspend fun getDatabaseState(): DatabaseHealth {
        delay(500) //sleep for 500ms

        return DatabaseHealth(
                host = Config.config[DatabaseConfig.host],
                database = Config.config[DatabaseConfig.database],
                latencyMs = 500
        )
    }

    fun asyncGetDatabaseState() = async {
        getDatabaseState()
    }

But I keep getting Caused by: io.ktor.server.engine.BaseApplicationResponse$ResponseAlreadySentException: Response has already been sent even though actual content is sent back to client with HTTP 200. What am I doing wrong?

[orangy]

Do you mean that HealthModel is being correctly sent, and then something else is attempting to send another respond? We would need more information to help…

[Sergey Chikin]

HealthModel is being correctly sent but in the log I can see the exception. I don't think there's something else trying to respond

[Sergey Chikin]

it seems like BaseApplicationResponse is intercepting the call after it was responded:

Caused by: io.ktor.server.engine.BaseApplicationResponse$ResponseAlreadySentException: Response has already been sent
	at io.ktor.server.engine.BaseApplicationResponse$$special$$inlined$apply$lambda$1.doResume(BaseApplicationResponse.kt:30)

[Sergey Chikin]

@orangy FYI. Changing backend from netty to jetty helped. It seems like with netty even this https://github.com/ktorio/ktor/tree/master/ktor-samples/ktor-samples-async is logging the same exception I had

[orangy]

Will check it. What version are you using?

[Sergey Chikin]

0.9.0

[orangy]

Try latest alpha, please

[Sergey Chikin]

same with 0.9.1-alpha-8. I'll try to run the sample but at least my code works ok with jetty and throws exception with netty

[Sergey Chikin]

sample works ok with netty. now I'm completely out of ideas what's wrong about my code

[orangy]

I might need more code to see what’s going on or even debug…

[Sergey Chikin]

@orangy I simplified snippet to this:

suspend fun testSuspend(): Int {
    delay(500)

    val random = java.util.Random()
    return random.nextInt(100)
}

fun main(args : Array<String>) {
    embeddedServer(Netty, 9000) {
        install(Routing) {
            get("/healthz") {
                val start = System.currentTimeMillis()

                val calcResult = async { testSuspend() }.await()

                val end = System.currentTimeMillis()

                call.respond("Runtime ${end - start}ms Result ${calcResult}")
            }
        }
    }.start(wait = true)
}

[orangy]

Thanks! Will try to repro and report back

[Sergey Chikin]

call.respondText works ok though

[orangy]

I cannot reproduce it on master. However I’ve found a different problem (and fixed). We are going to release a build tomorrow, so let’s wait till then and try on your side, it might already be fixed.

[noncom]

isn't this the same as the issue I've logged some time ago? https://github.com/ktorio/ktor/issues/268

[orangy]

No, it isn’t. See example above, there are no second handler.

[orangy]

Second handler warning is still on my list (soon)

[orangy]

@Sergey Chikin 0.9.1-alpha-9 has been published, please try it with your case

[Sergey Chikin]

@orangy same here. it's quite interesting that changing call.respond to call.respondText is resolving this problem. but in my case I need it to responding with JSON so need call.respond(Any)

[orangy]

Weird. Your sample works fine for me. You said you need JSON, do you install ContentNegotiation with JSON?

[Sergey Chikin]

Yep

[orangy]

But does simplified snipped you posted works for you now? I can’t reproduce the problem and don’t understand what can go wrong… One guess I have is an exception is thrown that is not tracked/reported, and that causes 500 Internal Server Error to be attempted.

[orangy]

Can you please put a breakpoint here: https://github.com/ktorio/ktor/blob/master/ktor-server/ktor-server-host-common/src/io/ktor/server/engine/BaseApplicationResponse.kt#L31
And tell what is the value of subject?

[Sergey Chikin]

Hm

[Sergey Chikin]

Sec

[Sergey Chikin]

Cannot find local variable: name = this I guess I'm doing something wrong

[orangy]

Nope, it’s debugger issues…

[orangy]

Huh, I don’t know…

[Sergey Chikin]

I'll setup a gradle project for the whole case

[orangy]

Thanks a lot! I hope that’s not something specific to your OS setup or something…

[Sergey Chikin]

https://github.com/schikin/ktor-netty-exception

[Sergey Chikin]

I have macOS High Sierra

[orangy]

I will check it tomorrow. I have macOS High Sierra too.

[orangy]

I have no exceptions when I run the project and open <http://localhost:9000/healthz> in browser