Okay deleted old question. Currently trying to return a MultipartForm from a contract route but does not seem to work (errors in thread). Have something like this, which I would assume should work, however getting errors when loading the swagger:

fun downloadDocument(documentService: DocumentService): ContractRoute =
    "document" / Path.uuid().of("documentId") meta {
        summary = "Download document"
        returning(OK, formBody to formExample)
    } bindContract Method.GET to
            { documentId ->
                { 
                        val doc = documentService.getDocument(documentId))

                        Response(OK)
                            .with(
                                formBody of MultipartForm()
                                    .with(outputFile of MultipartFormFile(filename = doc.filename, contentType = ContentType(doc.mimeType), content = doc.data.inputStream()))
                            )
                }
            }




private val outputFile = MultipartFormFile.required("outputFile")
private val formBody = Body.multipartForm(Validator.Strict, outputFile).toLens()

private val formExample = MultipartForm()
    .with(outputFile of MultipartFormFile(filename = "test_file.txt", contentType = ContentType.TEXT_PLAIN, content = createTempFileWithName("byteBufferExample", suffix = ".txt")
        .also { it.writeText("example") }
        .inputStream()))

for multipart you need to disable the PreExtraction check in the route

Still getting the weird behaviour of it not actually returning anything until stopping the application. As a complete baseless guess, is there some stream which isn’t being closed?