ktor upload file based on curl example

I have following example which works well using curl:

curl -X 'POST' \
  'https://example.com/rest/someservice?oauth_token=<token>' \
  -H 'accept: application/json' \
  -H 'Content-Type: multipart/form-data' \
  -F 'file=@docs_recognize_ok.jpg;type=image/jpeg' \
  -F 'meta={
  "images": [
    {
      "name": "file"
    }
  ]
}'

Can't figure out how to handle it using ktor client in Java/Kotlin?

For the moment I'm trying to handle it as:

        val json = "{\n" +
                "  \"images\": [\n" +
                "    {\n" +
                "      \"name\": \"file\"\n" +
                "    }\n" +
                "  ]\n" +
                "}"
        val filesList = mutableListOf<PartData>()
        val partData = formData {
            append(key = "meta", value = json, headers = Headers.build {
                append(HttpHeaders.ContentType, "application/json; charset=utf-8")
            })
            request.images.forEach { file ->
                append(
                    "file",
                    InputProvider { File(file.imageFileName).inputStream().asInput() },
                    Headers.build {
                        append(HttpHeaders.ContentType, "image/jpeg")
                    }
                )
            }
        }
        filesList.addAll(partData)
        httpClient.post("rest/someservice") {
            setBody(MultiPartFormDataContent(parts = filesList))
            parameters {
                append("oauth_token", apiKey)
            }
        }

Any ideas?

The information about sending multipart/form-data requests with the Ktor client can be found in the documentation. Here is a more or less direct translation of your curl command:

val client = HttpClient(CIO)

client.post("https://example.com/rest/someservice?oauth_token=<token>") {
    header(HttpHeaders.Accept, "application/json")
    setBody(
        MultiPartFormDataContent(
            formData {
                append(
                    "meta", """{
                      "images": [
                        {
                          "name": "file"
                        }
                      ]
                    }""".trimIndent()
                )
                append("file", File("docs_recognize_ok.jpg").readBytes(), Headers.build {
                    append(HttpHeaders.ContentType, "image/jpeg")
                    append(HttpHeaders.ContentDisposition, "filename=\"docs_recognize_ok.jpg\"")
                })
            },
        )
    )
}

Also, here is a code generated by my tool c2k for Ktor 3.*:

import io.ktor.client.HttpClient
import io.ktor.client.request.forms.ChannelProvider
import io.ktor.client.request.forms.MultiPartFormDataContent
import io.ktor.client.request.forms.formData
import io.ktor.client.request.post
import io.ktor.client.request.setBody
import io.ktor.client.statement.bodyAsText
import io.ktor.http.Headers
import io.ktor.http.HttpHeaders
import io.ktor.util.cio.readChannel
import java.io.File
import kotlinx.coroutines.runBlocking

fun main() = runBlocking {
    val client = HttpClient {
        followRedirects = false
    }
    val response = client.post("https://example.com/rest/someservice?oauth_token=<token>") {
        headers.append("accept", "application/json")
        headers.append("Content-Type", "multipart/form-data")

        setBody(MultiPartFormDataContent(formData {
            val docs_recognize_ok = File("docs_recognize_ok.jpg")
            append("file", ChannelProvider(size = docs_recognize_ok.length()) { docs_recognize_ok.readChannel() }, Headers.build {
                append(HttpHeaders.ContentType, "image/jpeg")
                append(HttpHeaders.ContentDisposition, "filename=\"${docs_recognize_ok.name}\"")
            })

            append("meta", """{
              "images": [
                {
                  "name": "file"
                }
              ]
            }""".trimIndent())
        }))
    }
    print(response.bodyAsText())
}