Package io.netty.handler.codec.protobuf

Source Code of io.netty.handler.codec.protobuf.ProtobufDecoder

/*
* Copyright 2011 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 io.netty.handler.codec.protobuf;

import io.netty.buffer.ChannelBuffer;
import io.netty.buffer.ChannelBufferInputStream;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.MessageEvent;
import io.netty.handler.codec.frame.FrameDecoder;
import io.netty.handler.codec.frame.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.frame.LengthFieldPrepender;
import io.netty.handler.codec.oneone.OneToOneDecoder;

import com.google.protobuf.ExtensionRegistry;
import com.google.protobuf.Message;
import com.google.protobuf.MessageLite;

/**
* Decodes a received {@link ChannelBuffer} into a
* <a href="http://code.google.com/p/protobuf/">Google Protocol Buffers</a>
* {@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:
* <pre>
* {@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}());
* </pre>
* and then you can use a {@code MyMessage} instead of a {@link ChannelBuffer}
* as a message:
* <pre>
* 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);
* }
* </pre>
* @apiviz.landmark
*/
@Sharable
public class ProtobufDecoder extends OneToOneDecoder {

    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;
        if (buf.hasArray()) {
            final int offset = buf.readerIndex();
            if (extensionRegistry == null) {
                return prototype.newBuilderForType().mergeFrom(
                        buf.array(), buf.arrayOffset() + offset, buf.readableBytes()).build();
            } else {
                return prototype.newBuilderForType().mergeFrom(
                        buf.array(), buf.arrayOffset() + offset, buf.readableBytes(), extensionRegistry).build();
            }
        } else {
            if (extensionRegistry == null) {
                return prototype.newBuilderForType().mergeFrom(
                        new ChannelBufferInputStream((ChannelBuffer) msg)).build();
            } else {
                return prototype.newBuilderForType().mergeFrom(
                        new ChannelBufferInputStream((ChannelBuffer) msg), extensionRegistry).build();
            }
        }
    }
}
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