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.connect.storage;
  
  import org.apache.kafka.common.Configurable;
  import org.apache.kafka.common.config.ConfigDef;
  import org.apache.kafka.connect.data.Schema;
  import org.apache.kafka.connect.data.SchemaAndValue;
  import org.apache.kafka.connect.header.Header;
  
  import java.io.Closeable;
  
  /**
   * The HeaderConverter interface provides support for translating between Kafka Connect's runtime data format
   * and byte[]. This is similar to the {@link Converter} interface, but specifically for
   * {@link org.apache.kafka.connect.header.Headers Headers}.
   * <p>Kafka Connect may discover implementations of this interface using the Java {@link java.util.ServiceLoader} mechanism.
   * To support this, implementations of this interface should also contain a service provider configuration file in
   * {@code META-INF/services/org.apache.kafka.connect.storage.HeaderConverter}.
   *
   * <p>Implement {@link org.apache.kafka.common.metrics.Monitorable} to enable the converter to register metrics.
   * The following tags are automatically added to all metrics registered: <code>connector</code> set to connector name,
   * <code>task</code> set to the task id and <code>converter</code> set to <code>header</code>.
   */
  public interface HeaderConverter extends Configurable, Closeable {
  
      /**
       * Convert the header name and byte array value into a {@link Header} object.
       * @param topic the name of the topic for the record containing the header
       * @param headerKey the header's key; may not be null
       * @param value the header's raw value; may be null
       * @return the {@link SchemaAndValue}; may not be null
       */
      SchemaAndValue toConnectHeader(String topic, String headerKey, byte[] value);
  
      /**
       * Convert the {@link Header}'s {@link Header#value() value} into its byte array representation.
       * @param topic the name of the topic for the record containing the header
       * @param headerKey the header's key; may not be null
       * @param schema the schema for the header's value; may be null
       * @param value the header's value to convert; may be null
       * @return the byte array form of the Header's value; may be null if the value is null
       */
      byte[] fromConnectHeader(String topic, String headerKey, Schema schema, Object value);
  
      /**
       * Configuration specification for this set of header converters.
       * @return the configuration specification; may not be null
       */
      ConfigDef config();
  }
  