object : RequestBody() {
      override fun contentType(): MediaType? = "text/plain".toMediaTypeOrNull()

      @Throws(IOException::class)
      override fun writeTo(sink: BufferedSink) {
        try {
          sink.writeUtf8("abc")
          sink.flush()
          Thread.sleep(sleepMillis.toLong())
          sink.writeUtf8("def")
        } catch (e: InterruptedException) {

      @Override public long contentLength() {
        return -1; // We don't know the compressed length in advance!
      }

      @Override public void writeTo(BufferedSink sink) throws IOException {
        BufferedSink gzipSink = Okio.buffer(new GzipSink(sink));
        body.writeTo(gzipSink);
        gzipSink.close();
      }
    };
  }
}
```

### Rewriting Responses

    setLevel(Level.HEADERS)
    server.enqueue(MockResponse())
    val body: RequestBody =
      object : RequestBody() {
        override fun contentType() = PLAIN

        override fun writeTo(sink: BufferedSink) {
          sink.writeUtf8("Hi!")
        }
      }
    val response = client.newCall(request().post(body).build()).execute()
    response.body.close()
    applicationLogs

	i := copy(b2, b)
	return b2[:i]
}

// WriteTo writes data to w until the buffer is drained or an error occurs.
// The return value n is the number of bytes written; it always fits into an
// int, but it is int64 to match the [io.WriterTo] interface. Any error
// encountered during the write is also returned.
func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
	b.lastRead = opInvalid

pkg runtime/trace, method (*FlightRecorder) Enabled() bool #63185
pkg runtime/trace, method (*FlightRecorder) Start() error #63185
pkg runtime/trace, method (*FlightRecorder) Stop() #63185
pkg runtime/trace, method (*FlightRecorder) WriteTo(io.Writer) (int64, error) #63185
pkg runtime/trace, type FlightRecorder struct #63185
pkg runtime/trace, type FlightRecorderConfig struct #63185
pkg runtime/trace, type FlightRecorderConfig struct, MaxBytes uint64 #63185

    override fun contentType() = delegate.contentType()

    override fun isDuplex() = true

    override fun writeTo(sink: BufferedSink) {
      executorService.schedule({
        try {
          delegate.writeTo(sink)
          sink.close()
        } catch (e: IOException) {
          throw RuntimeException(e)
        }
      }, delayMillis, TimeUnit.MILLISECONDS)

          url = server.url("/"),
          body =
            object : ForwardingRequestBody(transferKind.newRequestBody("def")) {
              override fun writeTo(sink: BufferedSink) {
                sinkReference.set(sink)
                super.writeTo(sink)
              }
            },
        ),
      )
    assertThat(readAscii(response.body.byteStream(), Int.MAX_VALUE))
      .isEqualTo("abc")

            object : RequestBody() {
              override fun contentType(): MediaType? = null

              @Throws(
                IOException::class,
              )
              override fun writeTo(sink: BufferedSink) {
                for (i in 0..9) {
                  sink.writeByte(0)
                  sink.flush()
                  sleep(100)
                }

            override fun writeTo(sink: BufferedSink) {
              val a1024x1024 = "a".repeat(1024 * 1024)
              repeat(100) {
                sink.writeUtf8(a1024x1024)
              }
            }
          },
        ).build()
    val buffer = Buffer()
    multipartBody.writeTo(buffer)

    val multipartReader = MultipartReader(buffer, "foo")

				}
			case testWriteTo:
				f := &testFile{ops: tf.ops}
				got, err := fr.WriteTo(f)
				if _, ok := err.(testError); ok {
					t.Errorf("test %d.%d, WriteTo(): %v", i, j, err)
				} else if got != tf.wantCnt || err != tf.wantErr {
					t.Errorf("test %d.%d, WriteTo() = (%d, %v), want (%d, %v)", i, j, got, err, tf.wantCnt, tf.wantErr)
				}
				if len(f.ops) > 0 {