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.header;
  
  public interface Headers extends Iterable<Header> {
      
      /**
       * Adds a header (key inside), to the end, returning if the operation succeeded.
       * 
       * @param header the Header to be added
       * @return this instance of the Headers, once the header is added.
       * @throws IllegalStateException is thrown if headers are in a read-only state.
       */
      Headers add(Header header) throws IllegalStateException;
  
      /**
       * Creates and adds a header, to the end, returning if the operation succeeded.
       *
       * @param key of the header to be added.
       * @param value of the header to be added.
       * @return this instance of the Headers, once the header is added.
       * @throws IllegalStateException is thrown if headers are in a read-only state.
       */
      Headers add(String key, byte[] value) throws IllegalStateException;
  
      /**
       * Removes all headers for the given key returning if the operation succeeded.
       * 
       * @param key to remove all headers for.
       * @return this instance of the Headers, once the header is removed.
       * @throws IllegalStateException is thrown if headers are in a read-only state.
       */
      Headers remove(String key) throws IllegalStateException;
  
      /**
       * Returns just one (the very last) header for the given key, if present.
       * 
       * @param key to get the last header for.
       * @return this last header matching the given key, returns null if not present.
       */
      Header lastHeader(String key);
  
      /**
       * Returns all headers for the given key, in the order they were added in, if present.
       *
       * @param key to return the headers for.
       * @return all headers for the given key, in the order they were added in, if NO headers are present an empty iterable is returned. 
       */
      Iterable<Header> headers(String key);
  
      /**
       * Returns all headers as an array, in the order they were added in.
       *
       * @return the headers as a Header[], mutating this array will not affect the Headers, if NO headers are present an empty array is returned.
       */
      Header[] toArray();
  
  }
  