writeBytesTotal += toWrite
        outFinished = outFinishedOnLastFrame && toWrite == sendBuffer.size
      }

      writeTimeout.enter()
      try {
        connection.writeData(id, outFinished, sendBuffer, toWrite)
      } finally {
        writeTimeout.exitAndThrowIfTimedOut()
      }
    }

    @Throws(IOException::class)
    override fun flush() {
      lock.assertNotHeld()

   *
   * Zero [byteCount] writes are not subject to flow control and will not block. The only use case
   * for zero [byteCount] is closing a flushed output stream.
   */
  @Throws(IOException::class)
  fun writeData(
    streamId: Int,
    outFinished: Boolean,
    buffer: Buffer?,
    byteCount: Long,
  ) {
    // Empty data frames are not flow-controlled.
    if (byteCount == 0L) {

              override fun writeTo(sink: BufferedSink) {
                sink.write(postBytes) // push bytes into the stream's buffer
                sink.flush() // Http2Connection.writeData subject to write window
                sink.close() // Http2Connection.writeData empty frame
              }
            },
        ),
      )
    val response = call.execute()
    assertThat(response.body.string()).isEqualTo("ABCDE")

	for i := range w.buffer {
		delete(w.buffer, i)
	}
	w.wg.Wait()
	return err
}

type writerAt struct {
	w      *io.PipeWriter
	r      *io.PipeReader
	wg     *sync.WaitGroup
	buffer map[int64][]byte
	err    error

	nextOffset int64
	m          sync.Mutex
}

func (w *writerAt) WriteAt(b []byte, offset int64) (n int, err error) {
	w.m.Lock()
	defer w.m.Unlock()