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Improper `Payload#hasMetadata` behavior.

See original GitHub issue

I was debugging some rust codes which send a REQUEST_RESPONSE without metadata. Unexpectedly, I received a PAYLOAD frame with a metadata (blank string). ServerSide is very simple:

package com.example.rsocket;

import io.rsocket.AbstractRSocket;
import io.rsocket.Payload;
import io.rsocket.RSocketFactory;
import io.rsocket.transport.netty.server.TcpServerTransport;
import io.rsocket.util.DefaultPayload;
import java.lang.invoke.MethodHandles;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Mono;

/**
 * Echo
 *
 * @author jeffsky
 * @since 2020-03-29
 */
public class Echo {

  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());

  public static void main(String[] args) {
    RSocketFactory.receive()
        .fragment(1024)
        .acceptor(
            (setup, sendingSocket) ->
                Mono.just(
                    new AbstractRSocket() {
                      @Override
                      public Mono<Payload> requestResponse(Payload payload) {
                        log.info(
                            "> data={}, meta={}, has_metadata={}",
                            payload.getDataUtf8(),
                            payload.getMetadataUtf8(),
                            payload.hasMetadata());
                        return Mono.just(payload);
                      }
                    }))
        .transport(TcpServerTransport.create(7878))
        .start()
        .block()
        .onClose()
        .block();
  }
}

Console show below:

20:50:42.703 [reactor-tcp-nio-2] DEBUG io.rsocket.FrameLogger - receiving -> 
Frame => Stream ID: 1 Type: REQUEST_RESPONSE Flags: 0b0 Length: 15
Data:
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 65 6c 6c 6f 52 75 73 74                      |HelloRust       |
+--------+-------------------------------------------------+----------------+
20:50:42.705 [reactor-tcp-nio-2] INFO  com.example.rsocket.Echo - > data=HelloRust, meta=, has_metadata=true

The problem I thought is that has_metadata should be false because the frame flags is 0b0 already.