Hello, everyone I am using the ktor 1.6.3 client and serialization to send requests Before that, everything worked correctly, but now I need to send an image to the chat of the application that I am doing For client settings,

defaultRequest

uses

header(HttpHeaders.ContentType, ContentType.Application.Json)

When sending via

submitFormWithBinaryData

, it returns the error

kotlinx. serialization. SerializationException: Serializer for class 'MultipartFormDataContent' is not found

I tried to change

header

for the request to send an image with

contentType

, but I get another error

io.ktor. http.UnsafeHeaderException: Header(s) [Content-Type] are controlled by the engine and cannot be set explicitly

Judging by https://youtrack.jetbrains.com/issue/KTOR-620, I can't do this Setting

contentType

for

MultipartFormDataContent

does not give anything How can I send a request with a serializable class of type

AddImageToMessage (val messageId: Int)

and attach an image to this request?

need more code to diagnose, but in general, content type is supposed to be set by

body

if I use the code from the official website. he doesn't work for me because

defaultRequest

is set in

header(HttpHeaders.ContentType, ContentType.Application.Json)

I get an error

kotlinx. serialization. SerializationException: Serializer for class 'MultipartFormDataContent' is not found

client settings

fun getClient(): HttpClient {

        return HttpClient(CIO) {

            install(JsonFeature) {

                serializer = KotlinxSerializer(

                    Json {
                        prettyPrint = true
                        isLenient = true
                        ignoreUnknownKeys = true
                        coerceInputValues = true
                    }
                )
            }

            expectSuccess = false

            defaultRequest {

                host = BuildConfig.REST_API_ADDRESS
                url.protocol = URLProtocol.HTTPS

                header(HttpHeaders.ContentType, ContentType.Application.Json)
            }
        }
    }

request

suspend fun addImageToMessage(
        messageId: Int,
        path: String,
        image: File
    ) {

        client.submitFormWithBinaryData<Unit>(
            formData = formData {
                append(
                    "image", image.readBytes(), Headers.build {
                        append(HttpHeaders.ContentType, "image/png")
                        append(HttpHeaders.ContentDisposition, "filename=image.png")
                    }
                )
//                append("messageId", messageId)
            }
        ) {
            url.encodedPath = path
//            body = AddImageToMessage(messageId = messageId)
        }
    }

I would also like to add

AddImageToMessage

to this request

append("messageId", messageId)

does not work in my case

The only thing I can suggest is to not put the

application/json

content-type in the

defaultRequest

because this header triggers content converter execution (

UnsafeHeaderException

is not thrown because because

ContentNegotiation

removes this header before the check).

I tried this option, but I couldn't add the

messageId

parameter to the request body as if I sent them through the serializable

AddImageToMessage

class most likely, this should be added to the

formData

, but I do not know how

You can serialize it manually and append a string but I agree this is not convenient.

please tell me, what value I need to put for the 

key

 parameter?

suspend fun addImageToMessage(
        messageId: Int,
        path: String,
        image: File
    ) {

        client.submitFormWithBinaryData<Unit>(
            formData = formData {
                append(
                    "image", image.readBytes(), Headers.build {
                        append(HttpHeaders.ContentType, "image/png")
                        append(HttpHeaders.ContentDisposition, "filename=image.png")
                    }
                )

                val messageIdJson = JSONObject().apply {
                    put("messageId", messageId)
                }

                append(key = "?",value = messageIdJson.toString())
            }
        ) {
            url.encodedPath = path
        }
    }

@Evgeny Berezovsky, what HTTP request do you want to construct? The key is the name of a part.

for example, if I send just a 

messageId

 with 

ContentType=application/json

 without an attached image, then in the logs it will look like this but when I attach an image and change 

ContentType=multipart/form-data

, I do not know how to add information about the 

messageId

 so that the server sees it