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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.Marshaller;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandler.Sharable;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;

/**
 * {@link OneToOneEncoder} implementation which uses JBoss Marshalling to marshal
 * an Object. Be aware that this {@link OneToOneEncoder} is not compatible with
 * an other client that just use JBoss Marshalling as it includes the size of every
 * {@link Object} that gets serialized in front of the {@link Object} itself.
 *
 * Use this with {@link MarshallingDecoder}
 *
 * See JBoss Marshalling website
 * for more informations
 *
 */
@Sharable
public class MarshallingEncoder extends OneToOneEncoder {
    private static final byte[] LENGTH_PLACEHOLDER = new byte[4];
    private final MarshallerProvider provider;

    private final int estimatedLength;

    /**
     * Creates a new encoder with the estimated length of 512 bytes.
     *
     * @param provider the {@link MarshallerProvider} to use
     */
    public MarshallingEncoder(MarshallerProvider provider) {
        this(provider, 512);
    }

    /**
     * Creates a new encoder.
     *
     * @param provider
     *        the {@link MarshallerProvider} to use
     * @param estimatedLength
     *        the estimated byte length of the serialized form of an object.
     *        If the length of the serialized form exceeds this value, the
     *        internal buffer will be expanded automatically at the cost of
     *        memory bandwidth.  If this value is too big, it will also waste
     *        memory bandwidth.  To avoid unnecessary memory copy or allocation
     *        cost, please specify the properly estimated value.
     */
    public MarshallingEncoder(MarshallerProvider provider, int estimatedLength) {
        if (estimatedLength < 0) {
            throw new IllegalArgumentException(
                    "estimatedLength: " + estimatedLength);
        }
        this.estimatedLength = estimatedLength;
        this.provider = provider;
    }

    @Override
    protected Object encode(ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
        Marshaller marshaller = provider.getMarshaller(ctx);
        ChannelBufferByteOutput output = new ChannelBufferByteOutput(
                ctx.getChannel().getConfig().getBufferFactory(), estimatedLength);
        output.getBuffer().writeBytes(LENGTH_PLACEHOLDER);
        marshaller.start(output);
        marshaller.writeObject(msg);
        marshaller.finish();
        marshaller.close();

        ChannelBuffer encoded = output.getBuffer();
        encoded.setInt(0, encoded.writerIndex() - 4);

        return encoded;
    }

}