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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.frame.server;
  
  import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
  
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInboundHandlerAdapter;
  import io.netty.channel.ChannelInitializer;
  import io.netty.channel.ChannelPipeline;
  import io.netty.channel.SimpleChannelInboundHandler;
  import io.netty.channel.socket.SocketChannel;
  import io.netty.example.http2.helloworld.server.HelloWorldHttp1Handler;
  import io.netty.handler.codec.http.HttpMessage;
  import io.netty.handler.codec.http.HttpObjectAggregator;
  import io.netty.handler.codec.http.HttpServerCodec;
  import io.netty.handler.codec.http.HttpServerUpgradeHandler;
  import io.netty.handler.codec.http.HttpServerUpgradeHandler.UpgradeCodec;
  import io.netty.handler.codec.http.HttpServerUpgradeHandler.UpgradeCodecFactory;
  import io.netty.handler.codec.http2.Http2CodecUtil;
  import io.netty.handler.codec.http2.Http2FrameCodecBuilder;
  import io.netty.handler.codec.http2.Http2ServerUpgradeCodec;
  import io.netty.handler.ssl.SslContext;
  import io.netty.util.AsciiString;
  import io.netty.util.ReferenceCountUtil;
  
  /**
   * Sets up the Netty pipeline for the example server. Depending on the endpoint config, sets up the
   * pipeline for NPN or cleartext HTTP upgrade to HTTP/2.
   */
  public class Http2ServerInitializer extends ChannelInitializer<SocketChannel> {
  
      private static final UpgradeCodecFactory upgradeCodecFactory = new UpgradeCodecFactory() {
          @Override
          public UpgradeCodec newUpgradeCodec(CharSequence protocol) {
              if (AsciiString.contentEquals(Http2CodecUtil.HTTP_UPGRADE_PROTOCOL_NAME, protocol)) {
                  return new Http2ServerUpgradeCodec(
                          Http2FrameCodecBuilder.forServer().build(), new HelloWorldHttp2Handler());
              } else {
                  return null;
              }
          }
      };
  
      private final SslContext sslCtx;
      private final int maxHttpContentLength;
  
      public Http2ServerInitializer(SslContext sslCtx) {
          this(sslCtx, 16 * 1024);
      }
  
      public Http2ServerInitializer(SslContext sslCtx, int maxHttpContentLength) {
          this.sslCtx = sslCtx;
          this.maxHttpContentLength = checkPositiveOrZero(maxHttpContentLength, "maxHttpContentLength");
      }
  
      @Override
      public void initChannel(SocketChannel ch) {
          if (sslCtx != null) {
              configureSsl(ch);
          } else {
              configureClearText(ch);
          }
      }
  
      /**
       * Configure the pipeline for TLS NPN negotiation to HTTP/2.
       */
      private void configureSsl(SocketChannel ch) {
          ch.pipeline().addLast(sslCtx.newHandler(ch.alloc()), new Http2OrHttpHandler());
      }
  
      /**
       * Configure the pipeline for a cleartext upgrade from HTTP to HTTP/2.0
       */
      private void configureClearText(SocketChannel ch) {
          final ChannelPipeline p = ch.pipeline();
          final HttpServerCodec sourceCodec = new HttpServerCodec();
  
          p.addLast(sourceCodec);
          p.addLast(new HttpServerUpgradeHandler(sourceCodec, upgradeCodecFactory));
          p.addLast(new SimpleChannelInboundHandler<HttpMessage>() {
              @Override
              protected void channelRead0(ChannelHandlerContext ctx, HttpMessage msg) throws Exception {
                  // If this handler is hit then no upgrade has been attempted and the client is just talking HTTP.
                 System.err.println("Directly talking: " + msg.protocolVersion() + " (no upgrade was attempted)");
                 ChannelPipeline pipeline = ctx.pipeline();
                 pipeline.addAfter(ctx.name(), null, new HelloWorldHttp1Handler("Direct. No Upgrade Attempted."));
                 pipeline.replace(this, null, new HttpObjectAggregator(maxHttpContentLength));
                 ctx.fireChannelRead(ReferenceCountUtil.retain(msg));
             }
         });
 
         p.addLast(new UserEventLogger());
     }
 
     /**
      * Class that logs any User Events triggered on this channel.
      */
     private static class UserEventLogger extends ChannelInboundHandlerAdapter {
         @Override
         public void userEventTriggered(ChannelHandlerContext ctx, Object evt) {
             System.out.println("User Event Triggered: " + evt);
             ctx.fireUserEventTriggered(evt);
         }
     }
 }