/*
    * 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:
    *
    *   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.jboss.netty.handler.codec.marshalling;
  
  import org.jboss.marshalling.ByteInput;
  import org.jboss.marshalling.Unmarshaller;
  import org.jboss.netty.buffer.ChannelBuffer;
  import org.jboss.netty.channel.Channel;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.channel.ExceptionEvent;
  import org.jboss.netty.handler.codec.frame.TooLongFrameException;
  import org.jboss.netty.handler.codec.replay.ReplayingDecoder;
  import org.jboss.netty.handler.codec.replay.VoidEnum;
  
  import java.io.ObjectStreamConstants;
  
  /**
   * {@link ReplayingDecoder} which use an {@link Unmarshaller} to read the Object out of the {@link ChannelBuffer}.
   *
   * If you can you should use {@link MarshallingDecoder}.
   *
   *
   *
   */
  public class CompatibleMarshallingDecoder extends ReplayingDecoder<VoidEnum> {
      protected final UnmarshallerProvider provider;
      protected final int maxObjectSize;
      private boolean discardingTooLongFrame;
  
      /**
       * Create a new instance of {@link CompatibleMarshallingDecoder}.
       *
       * @param provider
       *        the {@link UnmarshallerProvider} which is used to obtain the {@link Unmarshaller}
       *        for the {@link Channel}
       * @param maxObjectSize
       *        the maximal size (in bytes) of the {@link Object} to unmarshal. Once the size is
       *        exceeded the {@link Channel} will get closed. Use a a maxObjectSize of
       *        {@link Integer#MAX_VALUE} to disable this. You should only do this if you are sure
       *        that the received Objects will never be big and the sending side are trusted, as
       *        this opens the possibility for a DOS-Attack due an {@link OutOfMemoryError}.
       */
      public CompatibleMarshallingDecoder(UnmarshallerProvider provider, int maxObjectSize) {
          this.provider = provider;
          this.maxObjectSize = maxObjectSize;
      }
  
      @Override
      protected Object decode(
              ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer, VoidEnum state) throws Exception {
          if (discardingTooLongFrame) {
              buffer.skipBytes(actualReadableBytes());
              checkpoint();
              return null;
          }
  
          Unmarshaller unmarshaller = provider.getUnmarshaller(ctx);
          ByteInput input = new ChannelBufferByteInput(buffer);
          if (maxObjectSize != Integer.MAX_VALUE) {
              input = new LimitingByteInput(input, maxObjectSize);
          }
          try {
              unmarshaller.start(input);
              Object obj = unmarshaller.readObject();
              unmarshaller.finish();
              return obj;
          } catch (LimitingByteInput.TooBigObjectException e) {
              discardingTooLongFrame = true;
              throw new TooLongFrameException();
          } finally {
              // Call close in a finally block as the ReplayingDecoder will throw an Error if not enough bytes are
              // readable. This helps to be sure that we do not leak resource
              unmarshaller.close();
          }
      }
  
      @Override
      protected Object decodeLast(ChannelHandlerContext ctx, Channel channel,
              ChannelBuffer buffer, VoidEnum state)
              throws Exception {
          switch (buffer.readableBytes()) {
          case 0:
              return null;
          case 1:
              // Ignore the last TC_RESET
              if (buffer.getByte(buffer.readerIndex()) == ObjectStreamConstants.TC_RESET) {
                 buffer.skipBytes(1);
                 return null;
             }
         }
 
         Object decoded = decode(ctx, channel, buffer, state);
         return decoded;
     }
 
     /**
      * Calls {@link Channel#close()} if a TooLongFrameException was thrown
      */
     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) throws Exception {
         if (e.getCause() instanceof TooLongFrameException) {
             e.getChannel().close();
         } else {
             super.exceptionCaught(ctx, e);
         }
     }
 }