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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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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:
 *
 *   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 {
    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);
        }
    }
}