MalformedInputException: Input length = 1, when uploading an image multipart

Ktor Version and Engine Used (client or server and name) Ktor 1.3.2, Kotlin 1.3.70, Netty server, ContentNegotiation, Jackson parser, Exposed.

I simply used the Ktor project generator for Gradle, and checked a few boxes for modules as mentioned above. After which I managed to connect a database & a few endpoints, but my core endpoint for uploading images doesn’t work.

Describe the bug When trying to upload a simple image using Retrofit & Multipart support in Android, I get a MalformedInputException on my server.

Retrofit/Android code:

@Multipart
@POST("/api/upload")
suspend fun uploadImages(@Part("image") imageFile: RequestBody): UploadResponse

Upload code:

val requestBody: RequestBody = MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("title", "Image Upload")
        .addFormDataPart(
            "image", // part name
            file.path.split("/").last(), // file name
            file.asRequestBody("image/jpg".toMediaType()) // Content-Type: image/jpg
        )
        .build()

    return apiService.uploadImages(requestBody)

Using the new way of creating RequestBody objects in OkHttp. I followed the documentation to receive the multipart data, and I’ve formed a MalformedInputException.

To Reproduce Steps to reproduce the behavior:

1. Use Retrofit to Upload an image to a Ktor server.
2. call receiveMultipart() to receive MP on the Ktor side.
3. See error

Expected behavior Multipart data should be received correctly.

Stack trace:

[nioEventLoopGroup-4-1] ERROR Application - Unhandled: POST - /api/upload
io.ktor.utils.io.charsets.MalformedInputException: Input length = 1
	at io.ktor.utils.io.charsets.CharsetJVMKt.throwExceptionWrapped(CharsetJVM.kt:323)
	at io.ktor.utils.io.charsets.CharsetJVMKt.decodeImplSlow(CharsetJVM.kt:289)
	at io.ktor.utils.io.charsets.CharsetJVMKt.decodeExactBytes(CharsetJVM.kt:254)
	at io.ktor.utils.io.core.StringsKt.readTextExactBytes(Strings.kt:293)
	at io.ktor.utils.io.core.StringsKt.readTextExactBytes$default(Strings.kt:292)
	at io.ktor.utils.io.core.AbstractInput.readText(AbstractInput.kt:468)
	at io.ktor.utils.io.core.AbstractInput.readText$default(AbstractInput.kt:465)
	at io.ktor.http.cio.CIOMultipartDataBase.partToData(CIOMultipartData.kt:127)
	at io.ktor.http.cio.CIOMultipartDataBase$partToData$1.invokeSuspend(CIOMultipartData.kt)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:56)
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:164)
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:500)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
	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:844)

[fluidsonic]

Same for me with different stack trace (logging feature). In my case disabling the logging feature is a suitable workaround.

io.ktor.utils.io.charsets.MalformedInputException: Input length = 1
    at io.ktor.utils.io.charsets.CharsetJVMKt.throwExceptionWrapped(CharsetJVM.kt:323)
    at io.ktor.utils.io.charsets.CharsetJVMKt.decode(CharsetJVM.kt:199)
    at io.ktor.utils.io.charsets.EncodingKt.decode(Encoding.kt:101)
    at io.ktor.utils.io.core.StringsKt.readText(Strings.kt:251)
    at io.ktor.utils.io.core.StringsKt.readText$default(Strings.kt:250)
    at io.ktor.client.features.logging.Logging$logRequestBody$2$1.invokeSuspend(Logging.kt:111)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:56)
    at kotlinx.coroutines.EventLoop.processUnconfinedEvent(EventLoop.common.kt:69)
    at kotlinx.coroutines.DispatchedTaskKt.resumeUnconfined(DispatchedTask.kt:184)
    at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:108)
    at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:307)
    at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl(CancellableContinuationImpl.kt:317)
    at kotlinx.coroutines.CancellableContinuationImpl.resumeWith(CancellableContinuationImpl.kt:249)
    at io.ktor.utils.io.ByteBufferChannel.resumeWriteOp(ByteBufferChannel.kt:2210)
    at io.ktor.utils.io.ByteBufferChannel.bytesRead(ByteBufferChannel.kt:930)
    at io.ktor.utils.io.ByteBufferChannel.readAsMuchAsPossible(ByteBufferChannel.kt:544)
    at io.ktor.utils.io.ByteBufferChannel.readAvailable$suspendImpl(ByteBufferChannel.kt:606)
    at io.ktor.utils.io.ByteBufferChannel.readAvailable(Unknown Source:0)
    at io.ktor.utils.io.jvm.javaio.WritingKt.copyTo(Writing.kt:21)
    at io.ktor.utils.io.jvm.javaio.WritingKt.copyTo$default(Writing.kt:12)
    at io.ktor.client.engine.android.AndroidClientEngineKt.writeTo(AndroidClientEngine.kt:112)
    at io.ktor.client.engine.android.AndroidClientEngine.execute(AndroidClientEngine.kt:79)
    at io.ktor.client.engine.HttpClientEngine$executeWithinCallContext$2.invokeSuspend(HttpClientEngine.kt:83)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:56)
    at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:738)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665)```

[AlexShniperson-INO]

In the course of researching the problem, I saw that if the boundary body does not contain the name of the filename, then this error occurs. after adding unique filename to boundary body the problem went away