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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 java.io.StreamCorruptedException;

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.handler.codec.frame.LengthFieldBasedFrameDecoder;
import org.jboss.netty.handler.codec.frame.TooLongFrameException;
/**
 * Decoder which MUST be used with {@link MarshallingEncoder}.
 *
 * A {@link LengthFieldBasedFrameDecoder} which use an {@link Unmarshaller} to read the Object out
 * of the {@link ChannelBuffer}.
 *
 */
public class MarshallingDecoder extends LengthFieldBasedFrameDecoder {

    private final UnmarshallerProvider provider;

    /**
     * Creates a new decoder whose maximum object size is {@code 1048576}
     * bytes.  If the size of the received object is greater than
     * {@code 1048576} bytes, a {@link StreamCorruptedException} will be
     * raised.
     *
     */
    public MarshallingDecoder(UnmarshallerProvider provider) {
        this(provider, 1048576);
    }

    /**
     * Creates a new decoder with the specified maximum object size.
     *
     * @param maxObjectSize  the maximum byte length of the serialized object.
     *                       if the length of the received object is greater
     *                       than this value, {@link TooLongFrameException}
     *                       will be raised.
     */
    public MarshallingDecoder(UnmarshallerProvider provider, int maxObjectSize) {
        super(maxObjectSize, 0, 4, 0, 4);
        this.provider = provider;
    }

    @Override
    protected Object decode(
            ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {

        ChannelBuffer frame = (ChannelBuffer) super.decode(ctx, channel, buffer);
        if (frame == null) {
            return null;
        }

        Unmarshaller unmarshaller = provider.getUnmarshaller(ctx);
        ByteInput input = new ChannelBufferByteInput(frame);

        try {
            unmarshaller.start(input);
            Object obj = unmarshaller.readObject();
            unmarshaller.finish();
            return obj;
        } 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 ChannelBuffer extractFrame(ChannelBuffer buffer, int index, int length) {
        return buffer.slice(index, length);
    }
}