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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.protobuf;

import com.google.protobuf.ExtensionRegistry;
import com.google.protobuf.Message;
import com.google.protobuf.MessageLite;
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.channel.ChannelPipeline;
import org.jboss.netty.channel.MessageEvent;
import org.jboss.netty.handler.codec.frame.FrameDecoder;
import org.jboss.netty.handler.codec.frame.LengthFieldBasedFrameDecoder;
import org.jboss.netty.handler.codec.frame.LengthFieldPrepender;
import org.jboss.netty.handler.codec.oneone.OneToOneDecoder;

/**
 * Decodes a received {@link ChannelBuffer} into a
 * Google Protocol Buffers
 * {@link Message} and {@link MessageLite}.  Please note that this decoder must
 * be used with a proper {@link FrameDecoder} such as {@link ProtobufVarint32FrameDecoder}
 * or {@link LengthFieldBasedFrameDecoder} if you are using a stream-based
 * transport such as TCP/IP.  A typical setup for TCP/IP would be:
 *  * {@link ChannelPipeline} pipeline = ...;
 *
 * // Decoders
 * pipeline.addLast("frameDecoder",
 *                  new {@link LengthFieldBasedFrameDecoder}(1048576, 0, 4, 0, 4));
 * pipeline.addLast("protobufDecoder",
 *                  new {@link ProtobufDecoder}(MyMessage.getDefaultInstance()));
 *
 * // Encoder
 * pipeline.addLast("frameEncoder", new {@link LengthFieldPrepender}(4));
 * pipeline.addLast("protobufEncoder", new {@link ProtobufEncoder}());
 * 
 * and then you can use a {@code MyMessage} instead of a {@link ChannelBuffer}
 * as a message:
 *  * void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
 *     MyMessage req = (MyMessage) e.getMessage();
 *     MyMessage res = MyMessage.newBuilder().setText(
 *                               "Did you say '" + req.getText() + "'?").build();
 *     ch.write(res);
 * }
 * 
 *
 * @apiviz.landmark
 */
@Sharable
public class ProtobufDecoder extends OneToOneDecoder {
    private static final boolean HAS_PARSER;

    static {
        boolean hasParser = false;
        try {
            // MessageLite.getParsetForType() is not available until protobuf 2.5.0.
            MessageLite.class.getDeclaredMethod("getParserForType");
            hasParser = true;
        } catch (Throwable t) {
            // Ignore
        }

        HAS_PARSER = hasParser;
    }
    private final MessageLite prototype;
    private final ExtensionRegistry extensionRegistry;

    /**
     * Creates a new instance.
     */
    public ProtobufDecoder(MessageLite prototype) {
        this(prototype, null);
    }

    public ProtobufDecoder(MessageLite prototype, ExtensionRegistry extensionRegistry) {
        if (prototype == null) {
            throw new NullPointerException("prototype");
        }
        this.prototype = prototype.getDefaultInstanceForType();
        this.extensionRegistry = extensionRegistry;
    }

    @Override
    protected Object decode(
            ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
        if (!(msg instanceof ChannelBuffer)) {
            return msg;
        }

        ChannelBuffer buf = (ChannelBuffer) msg;
        final byte[] array;
        final int offset;
        final int length = buf.readableBytes();

        if (buf.hasArray()) {
            array = buf.array();
            offset = buf.arrayOffset() + buf.readerIndex();
        } else {
            array = new byte[length];
            buf.getBytes(buf.readerIndex(), array, 0, length);
            offset = 0;
        }

        if (extensionRegistry == null) {
            if (HAS_PARSER) {
                return prototype.getParserForType().parseFrom(array, offset, length);
            } else {
                return prototype.newBuilderForType().mergeFrom(array, offset, length).build();
            }
        } else {
            if (HAS_PARSER) {
                return prototype.getParserForType().parseFrom(array, offset, length, extensionRegistry);
            } else {
                return prototype.newBuilderForType().mergeFrom(array, offset, length, extensionRegistry).build();
            }
        }
    }
}