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.streams.processor.internals;
  
  import org.apache.kafka.clients.producer.internals.BuiltInPartitioner;
  import org.apache.kafka.common.serialization.Serializer;
  import org.apache.kafka.streams.processor.StreamPartitioner;
  
  import java.util.Collections;
  import java.util.Optional;
  import java.util.Set;
  
  public class DefaultStreamPartitioner<K, V> implements StreamPartitioner<K, V> {
  
      private final Serializer<K> keySerializer;
  
      public DefaultStreamPartitioner(final Serializer<K> keySerializer) {
          this.keySerializer = keySerializer;
      }
  
      @Override
      public Optional<Set<Integer>> partitions(final String topic, final K key, final V value, final int numPartitions) {
          final byte[] keyBytes = keySerializer.serialize(topic, key);
  
          // if the key bytes are not available, we just return empty optional to let the producer decide
          // which partition to send internally; otherwise stick with the same built-in partitioner
          // util functions that producer used to make sure its behavior is consistent with the producer
          if (keyBytes == null) {
              return Optional.empty();
          } else {
              return Optional.of(Collections.singleton(BuiltInPartitioner.partitionForKey(keyBytes, numPartitions)));
          }
      }
  }
  