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   /*
    * Copyright 2012 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.factorial;
  
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.SimpleChannelInboundHandler;
  
  import java.math.BigInteger;
  import java.util.concurrent.BlockingQueue;
  import java.util.concurrent.LinkedBlockingQueue;
  
  /**
   * Handler for a client-side channel.  This handler maintains stateful
   * information which is specific to a certain channel using member variables.
   * Therefore, an instance of this handler can cover only one channel.  You have
   * to create a new handler instance whenever you create a new channel and insert
   * this handler to avoid a race condition.
   */
  public class FactorialClientHandler extends SimpleChannelInboundHandler<BigInteger> {
  
      private ChannelHandlerContext ctx;
      private int receivedMessages;
      private int next = 1;
      final BlockingQueue<BigInteger> answer = new LinkedBlockingQueue<BigInteger>();
  
      public BigInteger getFactorial() {
          boolean interrupted = false;
          try {
              for (;;) {
                  try {
                      return answer.take();
                  } catch (InterruptedException ignore) {
                      interrupted = true;
                  }
              }
          } finally {
              if (interrupted) {
                  Thread.currentThread().interrupt();
              }
          }
      }
  
      @Override
      public void channelActive(ChannelHandlerContext ctx) {
          this.ctx = ctx;
          sendNumbers();
      }
  
      @Override
      public void channelRead0(ChannelHandlerContext ctx, final BigInteger msg) {
          receivedMessages ++;
          if (receivedMessages == FactorialClient.COUNT) {
              // Offer the answer after closing the connection.
              ctx.channel().close().addListener(new ChannelFutureListener() {
                  @Override
                  public void operationComplete(ChannelFuture future) {
                      boolean offered = answer.offer(msg);
                      assert offered;
                  }
              });
          }
      }
  
      @Override
      public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
          cause.printStackTrace();
          ctx.close();
      }
  
      private void sendNumbers() {
          // Do not send more than 4096 numbers.
          ChannelFuture future = null;
          for (int i = 0; i < 4096 && next <= FactorialClient.COUNT; i++) {
              future = ctx.write(Integer.valueOf(next));
              next++;
          }
          if (next <= FactorialClient.COUNT) {
              assert future != null;
              future.addListener(numberSender);
          }
          ctx.flush();
      }
  
      private final ChannelFutureListener numberSender = new ChannelFutureListener() {
         @Override
         public void operationComplete(ChannelFuture future) throws Exception {
             if (future.isSuccess()) {
                 sendNumbers();
             } else {
                 future.cause().printStackTrace();
                 future.channel().close();
             }
         }
     };
 }