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   /*
    * Copyright 2015 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.handler.ssl;
  
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInboundHandlerAdapter;
  import io.netty.channel.ChannelInitializer;
  import io.netty.channel.ChannelPipeline;
  import io.netty.channel.socket.ChannelInputShutdownEvent;
  import io.netty.handler.codec.DecoderException;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.RecyclableArrayList;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import javax.net.ssl.SSLException;
  
  /**
   * Configures a {@link ChannelPipeline} depending on the application-level protocol negotiation result of
   * {@link SslHandler}.  For example, you could configure your HTTP pipeline depending on the result of ALPN:
   * <pre>
   * public class MyInitializer extends {@link ChannelInitializer}&lt;{@link Channel}&gt; {
   *     private final {@link SslContext} sslCtx;
   *
   *     public MyInitializer({@link SslContext} sslCtx) {
   *         this.sslCtx = sslCtx;
   *     }
   *
   *     protected void initChannel({@link Channel} ch) {
   *         {@link ChannelPipeline} p = ch.pipeline();
   *         p.addLast(sslCtx.newHandler(...)); // Adds {@link SslHandler}
   *         p.addLast(new MyNegotiationHandler());
   *     }
   * }
   *
   * public class MyNegotiationHandler extends {@link ApplicationProtocolNegotiationHandler} {
   *     public MyNegotiationHandler() {
   *         super({@link ApplicationProtocolNames}.HTTP_1_1);
   *     }
   *
   *     protected void configurePipeline({@link ChannelHandlerContext} ctx, String protocol) {
   *         if ({@link ApplicationProtocolNames}.HTTP_2.equals(protocol) {
   *             configureHttp2(ctx);
   *         } else if ({@link ApplicationProtocolNames}.HTTP_1_1.equals(protocol)) {
   *             configureHttp1(ctx);
   *         } else {
   *             throw new IllegalStateException("unknown protocol: " + protocol);
   *         }
   *     }
   * }
   * </pre>
   */
  public abstract class ApplicationProtocolNegotiationHandler extends ChannelInboundHandlerAdapter {
  
      private static final InternalLogger logger =
              InternalLoggerFactory.getInstance(ApplicationProtocolNegotiationHandler.class);
  
      private final String fallbackProtocol;
      private final RecyclableArrayList bufferedMessages = RecyclableArrayList.newInstance();
      private ChannelHandlerContext ctx;
      private boolean sslHandlerChecked;
  
      /**
       * Creates a new instance with the specified fallback protocol name.
       *
       * @param fallbackProtocol the name of the protocol to use when
       *                         ALPN/NPN negotiation fails or the client does not support ALPN/NPN
       */
      protected ApplicationProtocolNegotiationHandler(String fallbackProtocol) {
          this.fallbackProtocol = ObjectUtil.checkNotNull(fallbackProtocol, "fallbackProtocol");
      }
  
      @Override
      public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
          this.ctx = ctx;
          super.handlerAdded(ctx);
      }
  
      @Override
      public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
          fireBufferedMessages();
          bufferedMessages.recycle();
          super.handlerRemoved(ctx);
      }
  
     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
         // Let's buffer all data until this handler will be removed from the pipeline.
         bufferedMessages.add(msg);
         if (!sslHandlerChecked) {
             sslHandlerChecked = true;
             if (ctx.pipeline().get(SslHandler.class) == null) {
                 // Just remove ourself if there is no SslHandler in the pipeline and so we would otherwise
                 // buffer forever.
                 removeSelfIfPresent(ctx);
             }
         }
     }
 
     /**
      * Process all backlog into pipeline from List.
      */
     private void fireBufferedMessages() {
         if (!bufferedMessages.isEmpty()) {
             for (int i = 0; i < bufferedMessages.size(); i++) {
                 ctx.fireChannelRead(bufferedMessages.get(i));
             }
             ctx.fireChannelReadComplete();
             bufferedMessages.clear();
         }
     }
 
     @Override
     public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
         if (evt instanceof SslHandshakeCompletionEvent) {
             SslHandshakeCompletionEvent handshakeEvent = (SslHandshakeCompletionEvent) evt;
             try {
                 if (handshakeEvent.isSuccess()) {
                     SslHandler sslHandler = ctx.pipeline().get(SslHandler.class);
                     if (sslHandler == null) {
                         throw new IllegalStateException("cannot find an SslHandler in the pipeline (required for "
                                 + "application-level protocol negotiation)");
                     }
                     String protocol = sslHandler.applicationProtocol();
                     configurePipeline(ctx, protocol != null ? protocol : fallbackProtocol);
                 } else {
                     // if the event is not produced because of an successful handshake we will receive the same
                     // exception in exceptionCaught(...) and handle it there. This will allow us more fine-grained
                     // control over which exception we propagate down the ChannelPipeline.
                     //
                     // See https://github.com/netty/netty/issues/10342
                 }
             } catch (Throwable cause) {
                 exceptionCaught(ctx, cause);
             } finally {
                 // Handshake failures are handled in exceptionCaught(...).
                 if (handshakeEvent.isSuccess()) {
                     removeSelfIfPresent(ctx);
                 }
             }
         }
 
         if (evt instanceof ChannelInputShutdownEvent) {
             fireBufferedMessages();
         }
 
         ctx.fireUserEventTriggered(evt);
     }
 
     @Override
     public void channelInactive(ChannelHandlerContext ctx) throws Exception {
         fireBufferedMessages();
         super.channelInactive(ctx);
     }
 
     private void removeSelfIfPresent(ChannelHandlerContext ctx) {
         ChannelPipeline pipeline = ctx.pipeline();
         if (!ctx.isRemoved()) {
             pipeline.remove(this);
         }
     }
 
     /**
      * Invoked on successful initial SSL/TLS handshake. Implement this method to configure your pipeline
      * for the negotiated application-level protocol.
      *
      * @param protocol the name of the negotiated application-level protocol, or
      *                 the fallback protocol name specified in the constructor call if negotiation failed or the client
      *                 isn't aware of ALPN/NPN extension
      */
     protected abstract void configurePipeline(ChannelHandlerContext ctx, String protocol) throws Exception;
 
     /**
      * Invoked on failed initial SSL/TLS handshake.
      */
     protected void handshakeFailure(ChannelHandlerContext ctx, Throwable cause) throws Exception {
         logger.warn("{} TLS handshake failed:", ctx.channel(), cause);
         ctx.close();
     }
 
     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
         Throwable wrapped;
         if (cause instanceof DecoderException && ((wrapped = cause.getCause()) instanceof SSLException)) {
             try {
                 handshakeFailure(ctx, wrapped);
                 return;
             } finally {
                 removeSelfIfPresent(ctx);
             }
         }
         logger.warn("{} Failed to select the application-level protocol:", ctx.channel(), cause);
         ctx.fireExceptionCaught(cause);
         ctx.close();
     }
 }