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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.serialization;

import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.util.concurrent.atomic.AtomicReference;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBufferFactory;
import org.jboss.netty.buffer.ChannelBufferOutputStream;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;

/**
 * An encoder which serializes a Java object into a {@link ChannelBuffer}
 * (interoperability version).
 * 
 * This encoder is interoperable with the standard Java object streams such as
 * {@link ObjectInputStream} and {@link ObjectOutputStream}.
 */
public class CompatibleObjectEncoder extends OneToOneEncoder {

    private final AtomicReference buffer =
        new AtomicReference();
    private final int resetInterval;
    private volatile ObjectOutputStream oout;
    private int writtenObjects;

    /**
     * Creates a new instance with the reset interval of {@code 16}.
     */
    public CompatibleObjectEncoder() {
        this(16); // Reset at every sixteen writes
    }

    /**
     * Creates a new instance.
     *
     * @param resetInterval
     *        the number of objects between {@link ObjectOutputStream#reset()}.
     *        {@code 0} will disable resetting the stream, but the remote
     *        peer will be at the risk of getting {@link OutOfMemoryError} in
     *        the long term.
     */
    public CompatibleObjectEncoder(int resetInterval) {
        if (resetInterval < 0) {
            throw new IllegalArgumentException(
                    "resetInterval: " + resetInterval);
        }
        this.resetInterval = resetInterval;
    }

    /**
     * Creates a new {@link ObjectOutputStream} which wraps the specified
     * {@link OutputStream}.  Override this method to use a subclass of the
     * {@link ObjectOutputStream}.
     */
    protected ObjectOutputStream newObjectOutputStream(OutputStream out) throws Exception {
        return new ObjectOutputStream(out);
    }

    @Override
    protected Object encode(ChannelHandlerContext context, Channel channel, Object msg) throws Exception {
        ChannelBuffer buffer = buffer(context);
        ObjectOutputStream oout = this.oout;
        if (resetInterval != 0) {
            // Resetting will prevent OOM on the receiving side.
            writtenObjects ++;
            if (writtenObjects % resetInterval == 0) {
                oout.reset();

                // Also discard the byproduct to avoid OOM on the sending side.
                buffer.discardReadBytes();
            }
        }
        oout.writeObject(msg);
        oout.flush();

        ChannelBuffer encoded = buffer.readBytes(buffer.readableBytes());
        return encoded;
    }

    private ChannelBuffer buffer(ChannelHandlerContext ctx) throws Exception {
        ChannelBuffer buf = buffer.get();
        if (buf == null) {
            ChannelBufferFactory factory = ctx.getChannel().getConfig().getBufferFactory();
            buf = ChannelBuffers.dynamicBuffer(factory);
            if (buffer.compareAndSet(null, buf)) {
                boolean success = false;
                try {
                    oout = newObjectOutputStream(new ChannelBufferOutputStream(buf));
                    success = true;
                } finally {
                    if (!success) {
                        oout = null;
                    }
                }
            } else {
                buf = buffer.get();
            }
        }
        return buf;
    }
}