// MetadataRequest requests metadata from Kafka.
MetadataRequest => key 3, max version 12, flexible v9+
  // Topics is a list of topics to return metadata about. If this is null
  // in v1+, all topics are included. If this is empty, no topics are.
  // For v0 (<Kafka 0.10.0.0), if this is empty, all topics are included.
  Topics: nullable-v1+[=>]
    // The topic ID. Only one of either topic ID or topic name should be used.
    // If using the topic name, this should just be the default empty value.
    TopicID: uuid // v10+
    // Topic is the topic to request metadata for. Version 10 switched this
    // from a string to a nullable string; if using a topic ID, this field
    // should be null.
    Topic: nullable-string-v10+
  // AllowAutoTopicCreation, introduced in Kafka 0.11.0.0, allows topic
  // auto creation of the topics in this request if they do not exist.
  AllowAutoTopicCreation: bool // v4+
  // IncludeClusterAuthorizedOperations, introduced in Kakfa 2.3.0, specifies
  // whether to return a bitfield of AclOperations that this client can perform
  // on the cluster. See KIP-430 for more details.
  //
  // This field was removed in Kafka 2.8.0 in favor of the new DescribeClusterRequest.
  IncludeClusterAuthorizedOperations: bool // v8-v10
  // IncludeTopicAuthorizedOperations, introduced in Kakfa 2.3.0, specifies
  // whether to return a bitfield of AclOperations that this client can perform
  // on individual topics. See KIP-430 for more details.
  //
  // This field was removed in Kafka 2.8.0 in favor of the new DescribeClusterRequest.
  IncludeTopicAuthorizedOperations: bool // v8+

// MetadataResponse is returned from a MetdataRequest.
MetadataResponse =>
  ThrottleMillis(6) // v3+
  // Brokers is a set of alive Kafka brokers.
  Brokers: [=>]
    // NodeID is the node ID of a Kafka broker.
    NodeID: int32
    // Host is the hostname of a Kafka broker.
    Host: string
    // Port is the port of a Kafka broker.
    Port: int32
    // Rack is the rack this Kafka broker is in.
    Rack: nullable-string // v1+
  // ClusterID, proposed in KIP-78 and introduced in Kafka 0.10.1.0, is a
  // unique string specifying the cluster that the replying Kafka belongs to.
  ClusterID: nullable-string // v2+
  // ControllerID is the ID of the controller broker (the admin broker).
  ControllerID: int32(-1) // v1+
  // Topics contains metadata about each topic requested in the
  // MetadataRequest.
  Topics: [=>]
    // ErrorCode is any error for a topic in a metadata request.
    //
    // TOPIC_AUTHORIZATION_FAILED is returned if the client is not authorized
    // to describe the topic, or if the metadata request specified topic auto
    // creation, the topic did not exist, and the user lacks permission to create.
    //
    // UNKNOWN_TOPIC_OR_PARTITION is returned if a topic does not exist and
    // the request did not specify autocreation.
    //
    // LEADER_NOT_AVAILABLE is returned if a new topic is created successfully
    // (since there is no leader on an immediately new topic).
    //
    // There can be a myriad of other errors for unsuccessful topic creation.
    ErrorCode: int16
    // Topic is the topic this metadata corresponds to.
    Topic: nullable-string-v12+
    // The topic ID.
    TopicID: uuid // v10+
    // IsInternal signifies whether this topic is a Kafka internal topic.
    IsInternal: bool // v1+
    // Partitions contains metadata about partitions for a topic.
    Partitions: [=>]
      // ErrorCode is any error for a partition in topic metadata.
      //
      // LEADER_NOT_AVAILABLE is returned if a leader is unavailable for this
      // partition. For v0 metadata responses, this is also returned if a
      // partition leader's listener does not exist.
      //
      // LISTENER_NOT_FOUND is returned if a leader ID is known but the
      // listener for it is not (v1+).
      //
      // REPLICA_NOT_AVAILABLE is returned in v0 responses if any replica is
      // unavailable.
      //
      // UNKNOWN_TOPIC_ID is returned if using a topic ID and the ID does not
      // exist.
      ErrorCode: int16
      // Partition is a partition number for a topic.
      Partition: int32
      // Leader is the broker leader for this partition. This will be -1
      // on leader / listener error.
      Leader: int32
      // LeaderEpoch, proposed in KIP-320 and introduced in Kafka 2.1.0 is the
      // epoch of the broker leader.
      LeaderEpoch: int32(-1) // v7+
      // Replicas returns all broker IDs containing replicas of this partition.
      Replicas: [int32]
      // ISR returns all broker IDs of in-sync replicas of this partition.
      ISR: [int32]
      // OfflineReplicas, proposed in KIP-112 and introduced in Kafka 1.0,
      // returns all offline broker IDs that should be replicating this partition.
      OfflineReplicas: [int32] // v5+
    // AuthorizedOperations, proposed in KIP-430 and introduced in Kafka 2.3.0,
    // is a bitfield (corresponding to AclOperation) containing which operations
    // the client is allowed to perform on this topic.
    // This is only returned if requested.
    AuthorizedOperations: int32(-2147483648) // v8+
  // AuthorizedOperations is a bitfield containing which operations the client
  // is allowed to perform on this cluster.
  AuthorizedOperations: int32(-2147483648) // v8-v10