Code for the article: "Uploading a file with progress in Kotlin"

AttachmentUploader.kt

private fun createUploadRequest(
    filename: String,
    file: File,
    mimeType: String,
    progressEmitter: PublishSubject<Double>
): Single<AttachmentUploadedRemoteDto> {
    val requestBody = createUploadRequestBody(file, mimeType, progressEmitter)
    return remoteApi.attachFile(
        filename = filename.toPlainTextBody(),
        mimeType = mimeType.toPlainTextBody(),
        fileSize = file.length().toString().toPlainTextBody(),
        filePart = MultipartBody.Part.createFormData(
            name = "files[]",
            filename = filename,
            body = requestBody
        )
    )
}

private fun String.toPlainTextBody() = toRequestBody("text/plain".toMediaType())