Hi Guys, I have a plugin written to expose a Heal...

# ktor

[Mark Malik]

Hi Guys,

I have a plugin written to expose a HealthCheck endpoint. It all works, and responds correctly, but I noticed I also get the following error:

java.lang.UnsupportedOperationException: Headers can no longer be set because response was already completed
	at io.ktor.server.netty.http1.NettyHttp1ApplicationResponse$headers$1.engineAppendHeader(NettyHttp1ApplicationResponse.kt:42)
	at io.ktor.server.response.ResponseHeaders.append(ResponseHeaders.kt:57)
	at io.ktor.server.response.ResponseHeaders.append$default(ResponseHeaders.kt:48)
	at io.ktor.server.response.ApplicationResponsePropertiesKt.header(ApplicationResponseProperties.kt:14)
	at io.ktor.server.plugins.cors.CORSKt.corsVary(CORS.kt:226)

This is the plugin code:

val HealthChecks: ApplicationPlugin<HealthConfig> = createApplicationPlugin("HealthChecks", ::HealthConfig) {
    on(CallSetup) { call ->
        if (call.request.path() != "/monitoring/health-check" && call.request.httpMethod != HttpMethod.Get) return@on

        var healthCheckStatus: Map<String, Boolean>
        runBlocking {
            healthCheckStatus = pluginConfig.performChecks()
        }

        val statusCode = when (healthCheckStatus.all { it.value }) {
            true -> HttpStatusCode.OK
            false -> HttpStatusCode.InternalServerError
        }
        call.respondText(Json.encodeToString(healthCheckStatus), ContentType.Application.Json, statusCode)
    }
}

I thought that I could use the plugin to expose request handlers not requiring to create a routing. Is there something invalid about this setup ?

FYI.
I have CORS enabled with anyHosts() option.
The error is thrown in

private fun ApplicationCall.corsVary() {
        val vary = response.headers[HttpHeaders.Vary]
        if (vary == null) {
            response.header(HttpHeaders.Vary, HttpHeaders.Origin)
        } else {
            response.header(HttpHeaders.Vary, vary + ", " + HttpHeaders.Origin)
        }
    }

[Rustam Siniukov]

This is a bug on our side. Please create ticket.

[Mark Malik]

https://youtrack.jetbrains.com/issue/KTOR-4433/UnsupportedOperationException-thrown-when-handling-requests-in-Custom-Plugins