fun ByteString.commonToRequestBody(contentType: MediaType?): RequestBody {
  return object : RequestBody() {
    override fun contentType() = contentType

    override fun contentLength() = size.toLong()

    override fun writeTo(sink: BufferedSink) {
      sink.write(this@commonToRequestBody)
    }
  }

import java.io.IOException
import okhttp3.internal.chooseCharset
import okhttp3.internal.commonContentLength
import okhttp3.internal.commonIsDuplex
import okhttp3.internal.commonIsOneShot
import okhttp3.internal.commonToRequestBody
import okio.BufferedSink
import okio.ByteString
import okio.FileSystem
import okio.GzipSink
import okio.Path
import okio.buffer
import okio.source

abstract class RequestBody {