kotlinlang #ktor

Arjan van Wieringen

04/17/2025, 5:31 AM

Can I create a PR for extending the Ktor Server docs on Routing? Because I am missing docs on typical usecases I find in other server libraries (e.g. ExpressJS etc) on middlewares. Especially adding auth guards on routing parts is pretty important. Having some clear docs on RouteSelector would be great because it is so powerful. And I have seen quite a few errors in blog posts related to auth guards for instance. Some usecases: • transparent routeselectors to show DSL example usages • route guards not only on authentication status

kodee loving 1

Aidan

04/18/2025, 6:31 PM

Hi folks, I understand that the CIO client engine for KTor supports native platforms, however I get this error when I'm using it on iOS (with KMP):

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failed with exception: kotlin.IllegalStateException: TLS sessions are not supported on Native platform.

Internet searches aren't giving me a ton of good info. Does anyone know if CIO is fully supported or not for iOS?

Sean Chin Jun Kai

04/19/2025, 6:29 AM

Hi guys, according to https://github.com/ktorio/ktor/blob/main/ktor-server/ktor-server-plugins/ktor-server-sse/common/src/io/ktor/server/sse/SSEServerContent.kt It says that : Please note that you generally shouldn't use this object directly but use [SSE] plugin with routing builders [sse] instead. Can I ask in what cases should we use this object?

Kuldar

04/19/2025, 1:12 PM

I'm currently using ktor 3.0.2 and I am unable to rotate session id. Eg: anon session turns into authenticated session.

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call.sessions.clear<UserSession>()
call.sessions.set(UserSession(...))

Any suggestions what should I try next?

✅ 1

Ville Orkas

04/20/2025, 6:48 AM

hey, I'm getting this weird logging error when a client request fails (I think there is an exception being thrown):

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java.lang.IllegalStateException: No instance for key AttributeKey: CallLogger
	at io.ktor.util.Attributes$DefaultImpls.get(Attributes.kt:77)
	at io.ktor.util.AttributesJvmBase.get(AttributesJvm.kt:17)
	at io.ktor.client.plugins.logging.LoggingKt$Logging$2$4.invokeSuspend(Logging.kt:622)
	at io.ktor.client.plugins.logging.LoggingKt$Logging$2$4.invoke(Unknown Source:15)
	at io.ktor.client.plugins.logging.LoggingKt$Logging$2$4.invoke(Unknown Source:6)
	at io.ktor.client.plugins.logging.ReceiveHook$install$1.invokeSuspend(Logging.kt:759)
	at io.ktor.client.plugins.logging.ReceiveHook$install$1.invoke(Unknown Source:11)
	at io.ktor.client.plugins.logging.ReceiveHook$install$1.invoke(Unknown Source:6)
	at io.ktor.util.pipeline.DebugPipelineContext.proceedLoop(DebugPipelineContext.kt:79)
	at io.ktor.util.pipeline.DebugPipelineContext.proceed(DebugPipelineContext.kt:57)
	at io.ktor.client.plugins.ReceiveError$install$1.invokeSuspend(HttpCallValidator.kt:165)
	at io.ktor.client.plugins.ReceiveError$install$1.invoke(Unknown Source:11)
	at io.ktor.client.plugins.ReceiveError$install$1.invoke(Unknown Source:6)
	at io.ktor.util.pipeline.DebugPipelineContext.proceedLoop(DebugPipelineContext.kt:79)
	at io.ktor.util.pipeline.DebugPipelineContext.proceed(DebugPipelineContext.kt:57)
	at io.ktor.util.pipeline.DebugPipelineContext.execute$ktor_utils(DebugPipelineContext.kt:63)
	at io.ktor.util.pipeline.Pipeline.execute(Pipeline.kt:92)
	at io.ktor.client.call.HttpClientCall.bodyNullable(HttpClientCall.kt:99)

I'm using 3.1.2, and I'm not doing anything more than calling GET on an API that returns JSON. Whats going on? I can't find anything on this online

Adam S

04/20/2025, 8:39 AM

Question about the multipart form data server docs https://ktor.io/docs/server-requests.html#form_data Isn't it strange that

var fileDescription

and

var fileName

are outside of the

post("/upload") { }

block? What if the form has multiple uploads? Or if the endpoint is called twice simultaneously - one request could overwrite the value from another?

david dereba

04/21/2025, 6:19 AM

hello there. Am using Gson and am implementing my own custom serializers specifically for the Instant class but am getting this error. 2025-04-21 091355.340 [eventLoopGroupProxy-4-1] ERROR i.k.server.application.Application - Error occurred: JsonIOException || Failed making field 'java.time.Instant#seconds' accessible; either increase its visibility or write a custom TypeAdapter for its declaring type. See https://github.com/google/gson/blob/main/Troubleshooting.md#reflection-inaccessible com.google.gson.JsonIOException: Failed making field 'java.time.Instant#seconds' accessib. let me share the impl

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package com.root.plugins


import com.google.gson.*
import com.google.gson.FieldNamingPolicy
import com.google.gson.Strictness
import com.google.gson.stream.JsonReader
import com.google.gson.stream.JsonToken
import com.google.gson.stream.JsonWriter
import com.root.utility.UtilityFunctions
import io.ktor.http.ContentType
import io.ktor.serialization.gson.*
import io.ktor.serialization.kotlinx.json.json
import io.ktor.server.application.*
import io.ktor.server.plugins.contentnegotiation.*
import io.ktor.server.response.*
import io.ktor.server.routing.*
import io.ktor.util.Encoder
import kotlinx.serialization.ExperimentalSerializationApi
import kotlinx.serialization.KSerializer
import kotlinx.serialization.descriptors.PrimitiveKind
import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
import kotlinx.serialization.descriptors.SerialDescriptor
import kotlinx.serialization.encoding.Decoder
import kotlinx.serialization.json.Json
import kotlinx.serialization.json.JsonNamingStrategy
import kotlinx.serialization.modules.SerializersModule
import java.lang.reflect.Type
import java.time.Instant
import kotlinx.datetime.Instant as KtxInstant

@OptIn(ExperimentalSerializationApi::class)
fun Application.configureSerialization() {
    // Create the fully configured Gson instance
    val gson = GsonBuilder()
        .setPrettyPrinting()
        .setStrictness(Strictness.LENIENT)
        .serializeNulls()
        .registerTypeAdapter(UtilityFunctions.ApiResponseGsonSerializer::class.java, UtilityFunctions.ApiResponseGsonSerializer())
        .registerTypeAdapter(Instant::class.java, object : JsonSerializer<Instant>, JsonDeserializer<Instant> {
            override fun serialize(src: Instant, typeOfSrc: Type, context: JsonSerializationContext): JsonElement {
                return JsonPrimitive(src.toString())
            }

            override fun deserialize(json: JsonElement, typeOfT: Type, context: JsonDeserializationContext): Instant {
                return Instant.parse(json.asString)
            }
        })
        .registerTypeAdapter(Instant::class.java, object : TypeAdapter<Instant>() {
            override fun write(out: JsonWriter, value: Instant?) {
                if (value == null) {
                    out.nullValue()
                } else {
                    out.value(value.toString()) // ISO-8601
                }
            }

            override fun read(reader: JsonReader): Instant? {
                return if (reader.peek() == JsonToken.NULL) {
                    reader.nextNull(); null
                } else {
                    Instant.parse(reader.nextString())
                }
            }
        }.nullSafe())
        .registerTypeAdapter(KtxInstant::class.java, object : JsonSerializer<KtxInstant>, JsonDeserializer<KtxInstant> {
            override fun serialize(src: KtxInstant, typeOfSrc: Type, context: JsonSerializationContext): JsonElement {
                return JsonPrimitive(src.toString())
            }

            override fun deserialize(json: JsonElement, typeOfT: Type, context: JsonDeserializationContext): KtxInstant {
                return KtxInstant.parse(json.asString)
            }
        })
        .setDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'")
        .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
        .create()

    install(ContentNegotiation) {
        // Apply the pre-configured Gson instance
            register(ContentType.Application.Json, GsonConverter(gson))
        

        json(Json {
            isLenient = true
            prettyPrint = true
            encodeDefaults = true
            ignoreUnknownKeys = true
            coerceInputValues = true
            namingStrategy = JsonNamingStrategy.SnakeCase
            serializersModule = SerializersModule {
                contextual(KtxInstant::class) {
                    KotlinxInstantSerializer
                }
            }
        })
    }

    routing {
        get("/json/kotlinx-serialization") {
            call.respond(mapOf("hello" to "world"))
        }
        get("/json/gson") {
            call.respond(mapOf("hello" to "world"))
        }
    }
}

// And define your serializer
object KotlinxInstantSerializer : KSerializer<KtxInstant> {
    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("KotlinxInstant", PrimitiveKind.STRING)

    override fun serialize(encoder: kotlinx.serialization.encoding.Encoder, value: KtxInstant) {
        encoder.encodeString(value.toString())
    }

    override fun deserialize(decoder: Decoder): KtxInstant {
        return KtxInstant.parse(decoder.decodeString())
    }
}

then this is the full error log

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2025-04-21 09:13:55.340 [eventLoopGroupProxy-4-1] ERROR i.k.server.application.Application - Error occurred: JsonIOException || Failed making field 'java.time.Instant#seconds' accessible; either increase its visibility or write a custom TypeAdapter for its declaring type.
See <https://github.com/google/gson/blob/main/Troubleshooting.md#reflection-inaccessible> 
com.google.gson.JsonIOException: Failed making field 'java.time.Instant#seconds' accessible; either increase its visibility or write a custom TypeAdapter for its declaring type.
See <https://github.com/google/gson/blob/main/Troubleshooting.md#reflection-inaccessible>
        at com.google.gson.internal.reflect.ReflectionHelper.makeAccessible(ReflectionHelper.java:76)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:388)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:161)
        at com.google.gson.Gson.getAdapter(Gson.java:628)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:201)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:395)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:161)
        at com.google.gson.Gson.getAdapter(Gson.java:628)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:201)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:395)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:161)
        at com.google.gson.Gson.getAdapter(Gson.java:628)
        at com.google.gson.Gson.toJson(Gson.java:928)
        at com.google.gson.Gson.toJsonTree(Gson.java:802)
        at com.google.gson.Gson.toJsonTree(Gson.java:779)
        at com.root.routing.LeasesRoutesKt.handleLeaseCreation(LeasesRoutes.kt:53)
        at com.root.routing.LeasesRoutesKt.access$handleLeaseCreation(LeasesRoutes.kt:1)
        at com.root.routing.LeasesRoutesKt$handleLeaseCreation$1.invokeSuspend(LeasesRoutes.kt)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.internal.DispatchedContinuation.resumeWith(DispatchedContinuation.kt:197)
        at io.ktor.util.pipeline.SuspendFunctionGun.resumeRootWith(SuspendFunctionGun.kt:146)
        at io.ktor.util.pipeline.SuspendFunctionGun.loop(SuspendFunctionGun.kt:120)
        at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(SuspendFunctionGun.kt:11)
        at io.ktor.util.pipeline.SuspendFunctionGun$continuation$1.resumeWith(SuspendFunctionGun.kt:70)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:46)
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
        at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:173)
        at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:166)
        at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:569)
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998)
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
        at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make field private final long java.time.Instant.seconds accessible: module java.base does not "opens java.time" to unnamed module @10315254
        at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:354)
        at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
        at java.base/java.lang.reflect.Field.checkCanSetAccessible(Field.java:178)
        at java.base/java.lang.reflect.Field.setAccessible(Field.java:172)
        at com.google.gson.internal.reflect.ReflectionHelper.makeAccessible(ReflectionHelper.java:68)

What could be the issue. please assist.

🧵 4

Yassine Abou

04/23/2025, 9:48 PM

Hey everyone! I’m building a Compose Multiplatform app targeting android/iOS/Desktop Kotlin-Wasm. When calling REST APIs via the Ktor client in the Wasm target, I’m stuck with two errors: 1. *Original Error*`: warning: Node.js net module is not available. Please verify that you are using Node.js` (Happens when using the

CIO

engine) 2. After Removing

CIO

Engine:`Uncaught runtime errors: ERROR wasm validation error: at offset 5557696: type mismatch: expression has type (ref null 1950) but expected externref` 3. Here is my setup:

my ktor version is 3.1.0

and

compose version is 1.7.3.

Dependencies (commonMain):

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implementation(libs.ktor.client.core)
implementation(libs.ktor.client.content.negotiation)
implementation(libs.ktor.serialization.kotlinx.json)
implementation(libs.ktor.client.cio)

Koin DI Configuration:

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single {  Json { ignoreUnknownKeys = true isLenient ; = true encodeDefaults = false } }
// 2. HTTP Client Configuration 
single<HttpClient> { HttpClient(CIO) { engine { requestTimeout = 0 } 
install(ContentNegotiation) { json( json = get(), contentType = ContentType.Application.Json ) } }

here is the repository link for more context: https://github.com/yassineAbou/LLMS

Austin Pederson

04/25/2025, 7:48 PM

Hey all, I'm trying to upload a data class to S3 as JSON using a presigned URL, but I am experiencing issues with the

ContentNegotiation

plugin. It looks like the

ContentNegotiation

plugin always uses

Transfer-Encoding: chunked

which is a problem for S3. This limits me to having to manually serializes this object before uploading it. Is there any way to turn off this behavior? I've scoured the web but found no way to do this as of yet...

Kev

04/26/2025, 7:50 AM

Hello. I'm trying to use the routing library but it fails to download. Any ideas?

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Could not find io.ktor:ktor-server-routing:3.1.2.
Searched in the following locations:
  - <https://repo.maven.apache.org/maven2/io/ktor/ktor-server-routing/3.1.2/ktor-server-routing-3.1.2.pom>

Arjan van Wieringen

04/27/2025, 7:14 AM

Is there a reason that

createApplicationPlugin

createRouteScopedPlugin

are typically instantiated as values with a configuration block? In a lot of cases it is much easier to just do:

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fun MyCustomPlugin(val myDeps: MyDeps) = createRouteScopedPlugin("MyCustomPlugin") {
     ...use myDeps
}

instead of a configuration class with mutable variables.

➕ 2

ursus

04/29/2025, 2:35 PM

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webSocketSession.send(frame)

this suspends until it's actually sent? or only until enqueued (and will be sent later)? if it's the later - is there a way to tell it's actually been delivered? -- I need to update my entity's state from

SENDING

SENT

Colton Idle

04/30/2025, 1:19 AM

Feel like I'm losing my marbles... I have a kmp/cmp app. android/ios/wasm.

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commonMain.dependencies {
            implementation("io.ktor:ktor-client:3.0.0")

Android works iOS works Running wasm comes with a

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Could not determine the dependencies of task ':kotlinNpmInstall'.
> Could not resolve all dependencies for configuration ':composeApp:wasmJsNpmAggregated'.
   > Could not resolve io.ktor:ktor-client:3.0.0.
     Required by:
         project :composeApp
      > No matching variant of io.ktor:ktor-client:3.0.0 was found. The consumer was configured to find a library for use during 'kotlin-runtime', preferably optimized for non-jvm, as well as attribute 'org.jetbrains.kotlin.js.public.package.json' with value 'public-package-json', attribute 'org.jetbrains.kotlin.platform.type' with value 'wasm', attribute 'org.jetbrains.kotlin.wasm.target' with value 'js' but:

Jay

05/01/2025, 10:32 AM

anyway to enable support for brotli in a client? only have access to gzip and deflate

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install(plugin = ContentEncoding) {
    gzip()
    deflate()
}

Jay

05/01/2025, 11:12 AM

I've also noticed I hit 429 way more often when using OkHttp for my Engine. anyone know why?

ursus

05/02/2025, 4:09 PM

If I want websocket to not be active when app goes to background

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appInForeground
    .collectLatest { isInForeground ->
        if (isInForeground) {
            val webSocketSession = ktorClient.webSocketSession(..)
            webSocketSession listenAndSend(webSocketSession)
        }
    }

is this enough? or does it need cancelling / closing explicitly? Since the WebSocketSession implements CoroutineScope im not sure

Marc

05/02/2025, 5:47 PM

did anyone faced this error with the swaggerUI plugin?

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ERROR io.ktor.server.Application - Unhandled: GET - /swagger
java.lang.ClassCastException: class kotlinx.html.DIV cannot be cast to class kotlinx.html.CoreAttributeGroupFacade (kotlinx.html.DIV and kotlinx.html.CoreAttributeGroupFacade are in unnamed module of loader 'app')
	at io.ktor.server.plugins.swagger.SwaggerKt$swaggerUI$5$2.invokeSuspend$lambda$9(Swagger.kt:103) [...] etc

I’m not doing anything misterious, just followed the doccumentation steps 😕

Dejan Lozanovic

05/04/2025, 1:17 PM

Is it possible for Ktor Sever and Oauth module to use custom states?

Charann

05/06/2025, 3:44 AM

I came across the Ktor collection utils https://api.ktor.io/ktor-utils/io.ktor.util.collections/-concurrent-map/index.html where this thread-safe concurrentMap was marked with "Please do not use it" warning. Is there any specific reason? Because I am in need of a few multiplatform thread-safe collections

Eugen Martynov

05/06/2025, 7:04 AM

New member question - can I through monitoring pipeline print server certificate?

arnaud.giuliani

05/06/2025, 1:34 PM

Hey all 👋 A question about Ktor plugin registry, does the

version.ktor.yaml

file mean that it takes all versions from 2.0 to all superior ones?

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"[2.0,)":
  - io.insert-koin:koin-ktor:$koin
  - io.insert-koin:koin-logger-slf4j:$koin

✅ 1

Umesh Solanki

05/06/2025, 3:50 PM

Any idea how to upload Blob using

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submitFormWithBinaryData

I'm using HttpClient(Js)? formData.append didn't work. Thread in Slack Conversation

dayanruben

05/06/2025, 3:52 PM

Ktor 3.1.3 released https://ktor.io/changelog/3.1/

🔥 5

kodee loving 3

🚀 1

Hong Phuc

05/07/2025, 3:34 AM

Are all requests coming to an ktor application handled on the same Application's coroutine? Since when I print out the CoroutineContext when a request hit an endpoint I get the same context. Thanks in advance

frevib

05/07/2025, 12:45 PM

Hi there, what would be the best approach to run a Kafka consumer (or any message listener) next to Ktor? I know Ktor is a http library only, but most backend developers need to have some Kafka, MQTT or message consumer running next to their HTTP server. For instance, is it recommended to run the Kafka consumer next to the Ktor server, like:

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fun main() = runBlocking {
  launch(<http://Dispatchers.IO|Dispatchers.IO>) {
    embeddedServer(CIO, port = 8080, module = Application::modules)
    .start(wait = true)
  }

  launch(<http://Dispatchers.IO|Dispatchers.IO>) {
    startKafkaConsumer()
  }
}

or have the Kafka consumer be a module of Ktor, e.g.:

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fun main() {
  embeddedServer(CIO, port = 8080, module = Application::modules)
    .start(wait = true)
}

fun Application.modules() {
  kafkaModule()
  ktorModules()
}

fun Application.kafkaModule() {
  launch(<http://Dispatchers.IO|Dispatchers.IO>) {
    startKafkaConsumer()
  }
}

Approach 1 seems more architecturally correct, having both Ktor server and Kafka consumer running in a coroutine on the same level. The 2nd approach makes Ktor managing the lifecycle of the Kafka consumer, which is arguably less good.

Hong Phuc

05/08/2025, 3:10 AM

Hi all, is the

httpClient

thread-safe? From the answer in here and here, I inferred that using

httpClient

with the

OkHttp

engine is thread-safe. Still can someone confirm if this is true? Thanks in advance Also is the

httpClient

supposed to be used as a singleton? Is it possible to change to a specific engine so that I can create multiple instance of

httpClient

👀 1

Ulf

05/08/2025, 2:33 PM

Hi all, we're using Ktor client with

HttpCache

plugin. We've also made a custom logging plugin based on similar code as in the

Logging

plugin. However, one difference from the

Logging

plugin is that we would like to log the response even if nothing is sent over the network, ie the cached item is valid and returned directly (see for example

HttpCache.proceedWithCache

). Logging the response body becomes problematic and I'm unsure how to solve that. In the

Logging

plugin the

ResponseObserver

which is running in the

receivePipeline

is used to split the ByteReadChannel that contains the

rawContent

so that one is used for logging, but when response comes from cache the

receivePipeline

will never run. I can intercept the response in the

responsePipeline

though, but am unsure how to handle it here so that i can both log it and have the channel possible to consume later when reading the body, i've tried to something similar with

split( )

as in

ResponseObserver

but so far failed... (the response body is there but hidden as
responseBody
in
SavedHttpCall
, so if one could access it directly things would be quite simple...)

hellman

05/09/2025, 7:33 AM

We're facing some problems with using Ktor in AWS Fargate behind a load balancer. We want HTTP/2 as the application protocol, but we're getting a Netty exception that looks strange:

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2025-05-09 07:18:11.727 [eventLoopGroupProxy-4-1] TRACE io.ktor.server.Application - Failed to decode request
java.lang.IllegalArgumentException: text is empty (possibly HTTP/0.9)

Has anyone seen this and know what we're doing wrong?

hellman

05/12/2025, 7:13 AM

Hi! I found a weird behavior with

sse()

routes. If we want to send a HTTP response instead of emitting events (e.g.,

call.respond(HttpStatusCode.BadRequest)

), that response code is simply ignored and we always get HTTP 200. Is this an expected behavior? I feel it makes error handling for SSE endpoints difficult.

romainbsl

05/12/2025, 10:00 AM

Hi, I have a silly question about intercepting HTTP calls with Ktor client. I see the documentation (https://ktor.io/docs/client-http-send.html) suggest to jump onto HttpSend plugin after configuring the client. But, using a custom plugin (https://ktor.io/docs/client-custom-plugins.html#example-custom-header) seems to lead to the same result using

onRequest

. Maybe there is a semantic explanation for both usage, but at the end what do you suggest to use ?