How to use

JoinGroupRequest$ProtocolMetadata

in

org.apache.kafka.common.requests

@Override
protected List<JoinGroupRequest.ProtocolMetadata> metadata() {
  return Collections.singletonList(new JoinGroupRequest.ProtocolMetadata("dummy-subprotocol", EMPTY_DATA));
}

  @Override
  public boolean matches(AbstractRequest body) {
    JoinGroupRequest joinGroupRequest = (JoinGroupRequest) body;
    PartitionAssignor.Subscription subscription = ConsumerProtocol.deserializeSubscription(joinGroupRequest.groupProtocols().get(0).metadata());
    return subscribedTopics.equals(new HashSet<>(subscription.topics()));
  }
}, joinGroupFollowerResponse(assignor, 1, "memberId", "leaderId", Errors.NONE), coordinator);

private void handleJoinGroupRequest(ChannelHandlerContext ctx, Request request) {
  JoinGroupRequest joinGroupRequest = (JoinGroupRequest) request.getBody();
  ResponseHeader responseHeader = new ResponseHeader(request.getHeader().correlationId());
  List<ProtocolEntry> protocols = joinGroupRequest.groupProtocols().stream().map(protocol -> new ProtocolEntry(protocol.name(), Utils.toArray(protocol.metadata()))).collect(Collectors.toList());
  coordinator.handleJoinGroup(
      joinGroupRequest.groupId(),
      joinGroupRequest.memberId(),
      request.getHeader().clientId(),
      request.getClientAddress().toString(),
      joinGroupRequest.rebalanceTimeout(),
      joinGroupRequest.sessionTimeout(),
      joinGroupRequest.protocolType(),
      protocols,
      (joinResult) -> {
        Map<String, ByteBuffer> members = joinResult.getMembers().entrySet().stream().collect(Collectors.toMap(k -> k.getKey(), k -> ByteBuffer.wrap(k.getValue())));
        JoinGroupResponse responseBody = new JoinGroupResponse(request.getHeader().apiVersion(), joinResult.getErrorCode(), joinResult.getGenerationId(),
            joinResult.getSubProtocol(), joinResult.getMemberId(), joinResult.getLeaderId(), members);
        logger.trace(String.format("Sending join group response %s for correlation id %d to client %s.",
            responseBody, request.getHeader().correlationId(), request.getHeader().clientId()));
        sendResponse(ctx, new Response(responseHeader, responseBody));
      }
  );
}

@Override
public List<ProtocolMetadata> metadata() {
  configSnapshot = configStorage.snapshot();
  ConnectProtocol.WorkerState workerState = new ConnectProtocol.WorkerState(restUrl, configSnapshot.offset());
  ByteBuffer metadata = ConnectProtocol.serializeMetadata(workerState);
  return Collections.singletonList(new ProtocolMetadata(DEFAULT_SUBPROTOCOL, metadata));
}

@Override
public List<ProtocolMetadata> metadata() {
  configSnapshot = taskConfigManager.snapshot();
  DatalinkProtocol.WorkerState workerState = new DatalinkProtocol.WorkerState(restUrl, configSnapshot.version());
  ByteBuffer metadata = DatalinkProtocol.serializeMetadata(workerState);
  return Collections.singletonList(new ProtocolMetadata(DEFAULT_SUBPROTOCOL, metadata));
}

@Test
public void testProtocolMetadataOrder() {
  RoundRobinAssignor roundRobin = new RoundRobinAssignor();
  RangeAssignor range = new RangeAssignor();
  try (Metrics metrics = new Metrics(time)) {
    ConsumerCoordinator coordinator = buildCoordinator(metrics, Arrays.<PartitionAssignor>asList(roundRobin, range),
                              ConsumerConfig.DEFAULT_EXCLUDE_INTERNAL_TOPICS, false, true);
    List<ProtocolMetadata> metadata = coordinator.metadata();
    assertEquals(2, metadata.size());
    assertEquals(roundRobin.name(), metadata.get(0).name());
    assertEquals(range.name(), metadata.get(1).name());
  }
  try (Metrics metrics = new Metrics(time)) {
    ConsumerCoordinator coordinator = buildCoordinator(metrics, Arrays.<PartitionAssignor>asList(range, roundRobin),
                              ConsumerConfig.DEFAULT_EXCLUDE_INTERNAL_TOPICS, false, true);
    List<ProtocolMetadata> metadata = coordinator.metadata();
    assertEquals(2, metadata.size());
    assertEquals(range.name(), metadata.get(0).name());
    assertEquals(roundRobin.name(), metadata.get(1).name());
  }
}

public JoinGroupRequest(Struct struct, short versionId) {
  super(ApiKeys.JOIN_GROUP, versionId);
  groupId = struct.get(GROUP_ID);
  sessionTimeout = struct.getInt(SESSION_TIMEOUT_KEY_NAME);
  if (struct.hasField(REBALANCE_TIMEOUT_KEY_NAME))
    // rebalance timeout is added in v1
    rebalanceTimeout = struct.getInt(REBALANCE_TIMEOUT_KEY_NAME);
  else
    // v0 had no rebalance timeout but used session timeout implicitly
    rebalanceTimeout = sessionTimeout;
  memberId = struct.get(MEMBER_ID);
  protocolType = struct.getString(PROTOCOL_TYPE_KEY_NAME);
  groupProtocols = new ArrayList<>();
  for (Object groupProtocolObj : struct.getArray(GROUP_PROTOCOLS_KEY_NAME)) {
    Struct groupProtocolStruct = (Struct) groupProtocolObj;
    String name = groupProtocolStruct.getString(PROTOCOL_NAME_KEY_NAME);
    ByteBuffer metadata = groupProtocolStruct.getBytes(PROTOCOL_METADATA_KEY_NAME);
    groupProtocols.add(new ProtocolMetadata(name, metadata));
  }
}

@Override
public List<ProtocolMetadata> metadata() {
  this.joinedSubscription = subscriptions.subscription();
  List<ProtocolMetadata> metadataList = new ArrayList<>();
  for (PartitionAssignor assignor : assignors) {
    Subscription subscription = assignor.subscription(joinedSubscription);
    ByteBuffer metadata = ConsumerProtocol.serializeSubscription(subscription);
    metadataList.add(new ProtocolMetadata(assignor.name(), metadata));
  }
  return metadataList;
}

  @Override
  public boolean matches(AbstractRequest body) {
    JoinGroupRequest join = (JoinGroupRequest) body;
    ProtocolMetadata protocolMetadata = join.groupProtocols().iterator().next();
    PartitionAssignor.Subscription subscription = ConsumerProtocol.deserializeSubscription(protocolMetadata.metadata());
    protocolMetadata.metadata().rewind();
    return subscription.topics().containsAll(updatedSubscriptionSet);
  }
}, joinGroupLeaderResponse(2, consumerId, updatedSubscriptions, Errors.NONE));

private JoinGroupRequest createJoinGroupRequest(int version) {
  ByteBuffer metadata = ByteBuffer.wrap(new byte[] {});
  List<JoinGroupRequest.ProtocolMetadata> protocols = new ArrayList<>();
  protocols.add(new JoinGroupRequest.ProtocolMetadata("consumer-range", metadata));
  if (version == 0) {
    return new JoinGroupRequest.Builder("group1", 30000, "consumer1", "consumer", protocols).
        build((short) version);
  } else {
    return new JoinGroupRequest.Builder("group1", 10000, "consumer1", "consumer", protocols).
        setRebalanceTimeout(60000).build();
  }
}