val f = { channel: Channel =>
      request: Req =>
        guavaFuture2ScalaFuture(ClientCalls.futureUnaryCall(channel.newCall(method, CallOptions.DEFAULT), request))
    }

requests.map { x =>
    println(x)
    Thread.sleep(500)

    Try(requestObserver.onNext(x)).recover {
      case exception => requestObserver.onError(exception)
    }

  }

  requestObserver.onCompleted()

while ((tmp = inputstream.read(buffer, 0, bufferSize)) != -1) {
  LOGGER.info("In chunker: {}", tmp);
        ByteString byteString = ByteString.copyFrom(buffer, 0, tmp);
  File m = builder.setBinary(byteString).build();
  Thread.sleep(80); // if not set, on first iteration in client side, all chunks are sent without any control on flow .... 
  responseObserver.onNext(m);
}
responseObserver.onCompleted();