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

CountingRequestBody.kt

class CountingRequestBody(
    private val requestBody: RequestBody,
    private val onProgressUpdate: CountingRequestListener
) : RequestBody() {
    override fun contentType() = requestBody.contentType()

    @Throws(IOException::class)
    override fun contentLength() = requestBody.contentLength()

    ...
}