code: // Licensed to the Software Freedom Conservancy (SFC) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The SFC 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.openqa.selenium.remote.http;
  
  import static com.google.common.net.HttpHeaders.CONTENT_TYPE;
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import com.google.common.collect.ArrayListMultimap;
  import com.google.common.collect.ImmutableSet;
  import com.google.common.collect.Multimap;
  import com.google.common.net.MediaType;
  import java.io.InputStream;
  import java.nio.charset.Charset;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Objects;
  import java.util.function.Supplier;
  import java.util.stream.Collectors;
  import org.openqa.selenium.internal.Require;
  
  abstract class HttpMessage<M extends HttpMessage<M>> {
  
    private final Multimap<String, String> headers = ArrayListMultimap.create();
    private final Map<String, Object> attributes = new HashMap<>();
    private Supplier<InputStream> content = Contents.empty();
  
    /**
     * Retrieves a user-defined attribute of this message. Attributes are stored as simple key-value
     * pairs and are not included in a message's serialized form.
     *
     * @param key attribute name
     * @return attribute object
     */
    public Object getAttribute(String key) {
      return attributes.get(key);
    }
  
    public M setAttribute(String key, Object value) {
      attributes.put(key, value);
      return self();
    }
  
    public M removeAttribute(String key) {
      attributes.remove(key);
      return self();
    }
  
    public Iterable<String> getAttributeNames() {
      return ImmutableSet.copyOf(attributes.keySet());
    }
  
    public Iterable<String> getHeaderNames() {
      return headers.keySet();
    }
  
    public Iterable<String> getHeaders(String name) {
      return headers.entries().stream()
          .filter(e -> Objects.nonNull(e.getKey()))
          .filter(e -> e.getKey().equalsIgnoreCase(name.toLowerCase()))
          .map(Map.Entry::getValue)
          .collect(Collectors.toList());
    }
  
    public String getHeader(String name) {
      Iterable<String> initialHeaders = getHeaders(name);
      if (initialHeaders == null) {
        return null;
      }
  
      Iterator<String> headers = initialHeaders.iterator();
      if (headers.hasNext()) {
        return headers.next();
      }
      return null;
    }
  
    public M setHeader(String name, String value) {
      return removeHeader(name).addHeader(name, value);
    }
  
    public M addHeader(String name, String value) {
      headers.put(name, value);
      return self();
    }
  
    public M removeHeader(String name) {
      String toRemove =
          headers.keySet().stream()
              .filter(header -> header.equalsIgnoreCase(name))
              .findFirst()
              .orElse(name);
      headers.removeAll(toRemove);
      return self();
    }
  
    public Charset getContentEncoding() {
      Charset charset = UTF_8;
      try {
        String contentType = getHeader(CONTENT_TYPE);
        if (contentType != null) {
          MediaType mediaType = MediaType.parse(contentType);
          charset = mediaType.charset().or(UTF_8);
        }
      } catch (IllegalArgumentException ignored) {
        // Do nothing.
      }
      return charset;
    }
  
    public M setContent(Supplier<InputStream> supplier) {
      this.content = Require.nonNull("Supplier", supplier);
      return self();
    }
  
    public Supplier<InputStream> getContent() {
      return content;
    }
  
    @SuppressWarnings("unchecked")
    private M self() {
      return (M) this;
    }
  }
  