Google protocol Buffer Codec

["Trustin Lee (이희승)"]

Tom,

I would write a custom decoder instead of using ProtobufDecoder in such
a case; something like the following, which prepends the message type
and the message length field:

public class MyProtobufDecoder extends FrameDecoder {

  boolean waitingForHeader;
  int msgType;
  int msgLength;

  Message prototypeA =
      MessageA.getDefaultInstance().getDefaultInstanceForType();
  Message prototypeB =
      MessageB.getDefaultInstance().getDefaultInstanceForType();
  Message prototypeC =
      MessageC.getDefaultInstance().getDefaultInstanceForType();

  @Override
  protected Object decode(ctx, msg) {
    ChannelBuffer buf = (ChannelBuffer) msg;
    if (waitingForHeader) {
      // Wait until at least 5 bytes are received in the buffer
      if (buf.readableBytes() < 5) {
        return null;
      }
      msgType = buf.readByte();
      msgLength = buf.readInt();
      waitingForHeader = false;
    }

    if (!waitingForHeader) {
      ChannelBuffer pbmsg = buf.readBytes(msgLength);
      Message prototype;
      switch (msgType) {
      case 0: prototype = prototypeA; break;
      case 1: prototype = prototypeB; break;
      case 2: prototype = prototypeC; break;

      // This is a user defined exception.
      // Handle this exception in exceptionCaught()
      // in your terminal handler
      default: throw new ProtocolViolationException();
      }

      try {
        return prototype.newBuilderForType().mergeFrom(
                    new ChannelBufferInputStream(pbmsg)).build();
      } finally {
        waitingForHeader = true;
      }
    }
  }
}

You will have to learn how to write a decoder eventually to customize
the protocol to meet your need.  The user guide and the factorial
example is a good starting point.

However, I would still recommend the solution Jannick provided.

HTH,
Trustin

ritom wrote:
> Thanks for very much for the insight. If you do have multiple messages how to
> you handle them in the decoder. In the example looks like everything is
> based on one object what if you have two message type Foo and Bar instead of
> LocalTimeProtocol alone. Can you please give a example. Thanks a lot in
> advance.
> 
>   p.addLast("protobufDecoder", new
> ProtobufDecoder(LocalTimeProtocol.Locations.getDefaultInstance()));
> 
> 
> Thingfish wrote:
>> Hi
>>
>> The easiest solution is to wrap all your messages in a 'union type' as
>> described in this protobuf tutorial:
>> http://code.google.com/intl/da-DK/apis/protocolbuffers/docs/techniques.html#union
>>
>> Alternatively you will have to manually prepend some kind of command id to
>> identity the kind of protobuf message being sent, but unlikely to be worth
>> the trouble.
>>
>>
>> Regards
>> Jannick
>> <http://code.google.com/intl/da-DK/apis/protocolbuffers/docs/techniques.html#union>
>>
>> 2010/1/2 ritom <ritom at hotmail.com>
>>
>>> Can somebody please help me understand the google protobuf support within
>>> Netty.
>>> In the LocalTimeServerPipelineFactory example we have
>>>
>>> p.addLast("protobufDecoder", new
>>> ProtobufDecoder(LocalTimeProtocol.Locations.getDefaultInstance()));
>>>
>>> That would mean we can now receive the Locations message in
>>> TimeServerHandler.
>>>
>>>  public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
>>>        Locations locations = (Locations) e.getMessage();
>>>
>>> How would I implement support for multiple incoming message types where
>>> you
>>> might be receiving different types of request from the client. Lets say
>>> you
>>> are receiving Logon first then BalanceRequest, TransferRequest and so on.
>>> Also server will reply with multiple Message Types depending on the
>>> request.
>>> Can somebody please please help.
>>>
>>> Tom
>>> --
>>> View this message in context:
>>> http://n2.nabble.com/Google-protocol-Buffer-Codec-tp4241485p4241485.html
>>> Sent from the Netty User Group mailing list archive at Nabble.com.
>>> _______________________________________________
>>> netty-users mailing list
>>> netty-users at lists.jboss.org
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>> netty-users mailing list
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>>
> 

-- 
what we call human nature in actuality is human habit
http://gleamynode.net/


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