content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License. You may obtain a copy of the License at
   *
   *    http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.kafka.common.replica;
  
  import org.apache.kafka.common.TopicPartition;
  
  import java.util.Optional;
  import java.util.Set;
  import java.util.stream.Collectors;
  
  /**
   * Returns a replica whose rack id is equal to the rack id specified in the client request metadata. If no such replica
   * is found, returns the leader.
   */
  public class RackAwareReplicaSelector implements ReplicaSelector {
  
      @Override
      public Optional<ReplicaView> select(TopicPartition topicPartition,
                                          ClientMetadata clientMetadata,
                                          PartitionView partitionView) {
          if (clientMetadata.rackId() != null && !clientMetadata.rackId().isEmpty()) {
              Set<ReplicaView> sameRackReplicas = partitionView.replicas().stream()
                      .filter(replicaInfo -> clientMetadata.rackId().equals(replicaInfo.endpoint().rack()))
                      .collect(Collectors.toSet());
              if (sameRackReplicas.isEmpty()) {
                  return Optional.of(partitionView.leader());
              } else {
                  if (sameRackReplicas.contains(partitionView.leader())) {
                      // Use the leader if it's in this rack
                      return Optional.of(partitionView.leader());
                  } else {
                      // Otherwise, get the most caught-up replica
                      return sameRackReplicas.stream().max(ReplicaView.comparator());
                  }
              }
          } else {
              return Optional.of(partitionView.leader());
          }
      }
  }
  