Retrofit gzip interceptor with content length

Retrofit-gzip-interceptor

class GzipRequestInterceptor implements Interceptor {
  @Override public Response intercept(Chain chain) throws IOException {
    Request originalRequest = chain.request();
    if (originalRequest.body() == null || originalRequest.header("Content-Encoding") != null) {
      return chain.proceed(originalRequest);
    }

    Request compressedRequest = originalRequest.newBuilder()
        .header("Content-Encoding", "gzip")
        .method(originalRequest.method(), forceContentLength(gzip(originalRequest.body())))
        .build();
    return chain.proceed(compressedRequest);
  }

  /** https://github.com/square/okhttp/issues/350 */
  private RequestBody forceContentLength(final RequestBody requestBody) throws IOException {
    final Buffer buffer = new Buffer();
    requestBody.writeTo(buffer);
    return new RequestBody() {
      @Override
      public MediaType contentType() {
        return requestBody.contentType();
      }

      @Override
      public long contentLength() {
        return buffer.size();
      }

      @Override
      public void writeTo(BufferedSink sink) throws IOException {
        sink.write(buffer.snapshot());
      }
    };
  }

  private RequestBody gzip(final RequestBody body) {
    return new RequestBody() {
      @Override public MediaType contentType() {
        return body.contentType();
      }

      @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();
      }
    };
  }
}