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   /*
    * Copyright 2016 The Netty Project
    *
    * The Netty Project 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:
    *
    * https://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 io.netty.example.http2.helloworld.multiplex.server;
  
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.example.http2.helloworld.server.HelloWorldHttp1Handler;
  import io.netty.handler.codec.http.HttpObjectAggregator;
  import io.netty.handler.codec.http.HttpServerCodec;
  import io.netty.handler.codec.http2.Http2FrameCodecBuilder;
  import io.netty.handler.codec.http2.Http2MultiplexHandler;
  import io.netty.handler.ssl.ApplicationProtocolNames;
  import io.netty.handler.ssl.ApplicationProtocolNegotiationHandler;
  
  /**
   * Negotiates with the browser if HTTP2 or HTTP is going to be used. Once decided, the Netty
   * pipeline is setup with the correct handlers for the selected protocol.
   */
  public class Http2OrHttpHandler extends ApplicationProtocolNegotiationHandler {
  
      private static final int MAX_CONTENT_LENGTH = 1024 * 100;
  
      protected Http2OrHttpHandler() {
          super(ApplicationProtocolNames.HTTP_1_1);
      }
  
      @Override
      protected void configurePipeline(ChannelHandlerContext ctx, String protocol) throws Exception {
          if (ApplicationProtocolNames.HTTP_2.equals(protocol)) {
              ctx.pipeline().addLast(Http2FrameCodecBuilder.forServer().build());
              ctx.pipeline().addLast(new Http2MultiplexHandler(new HelloWorldHttp2Handler()));
              return;
          }
  
          if (ApplicationProtocolNames.HTTP_1_1.equals(protocol)) {
              ctx.pipeline().addLast(new HttpServerCodec(),
                                     new HttpObjectAggregator(MAX_CONTENT_LENGTH),
                                     new HelloWorldHttp1Handler("ALPN Negotiation"));
              return;
          }
  
          throw new IllegalStateException("unknown protocol: " + protocol);
      }
  }