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Posted to dev@mina.apache.org by Frederic Soulier <fr...@wallaby.uklinux.net> on 2007/12/11 20:27:50 UTC

CumulativeProtocolDecoder and UDP

Hi

I have an issue with Datagrams and the CumulativeProtocolDecoder  
which doesn't seem to cumulate!
(working just fine with TCP).

I have a Decoder extending CumulativeProtocolDecoder.

protected boolean doDecode(IoSession session, ByteBuffer in,  
ProtocolDecoderOutput out)
	throws Exception
     {
         int startIndex = in.position(); // Save buffer position
         boolean done = doDecodeWithoutBackingUp(session, in, out);
         if (!done)
         {
             // Reset buffer to start as-if doDecodeWithoutBackingUp  
had never run
             in.position(startIndex);
         }
         return done;
     }


protected boolean doDecodeWithoutBackingUp(IoSession ioSession,  
ByteBuffer in, ProtocolDecoderOutput out)
	 throws Exception
{
         if (in.remaining() < TYPE_SIZE)
         {
             return false; // Need more data, we don't have the type  
of the message
         }
         else
         {
             type = in.get();
             if (type == TYPE_MSG)
             {
                 if (in.remaining() < TRANSACTION_ID_SIZE)
                 {
                     return false; // Need more data, we don't have  
the transaction id
                 }
                 else
                 {
                     transactionId = in.getInt();

                     // do we have the message length?
                     if (in.remaining() <  
CodecUtils.MESSAGE_LENGTH_SIZE)
                     {
	                    return false; // Need more data, we don't have  
the message length
                     }
                     else
                     {
         	            int dataLength = in.getInt(); // Read 4-byte  
int data length

                             // do we have all the data?
                             if (in.remaining() < dataLength)
                             {
                                     // Here we're already read 9  
bytes (1 byte + 1 int + 1 int) but
   ==>                               // we don't have all we need so  
we return false and next time
                                     // around we'll have more
                                     return false; // Need more data,  
we don't have the complete data
                             }
                             else
                             {
                                     ** HERE WE PROCESS A FULL  
MESSAGE **

	                            return true; // Please carry on giving  
us more data to decode
                             }
                     }
		}
	    }
             else
	    {
                  throw new MySuperDuperException();
             }
        }
}

The buffer (in.remaining = 30)
I read 9 bytes from the buffer to be able to decide whether to read  
more or not.
in.remaining = 20 but my data length is 50 so I need more bytes and  
return false.
Another datagram is received in the meantime, I expect the new  
datagram to be accumulated behind what I haven't processed  
(considering I returned true).

Instead I only get the new datagram and the previous stuff I haven't  
processed yet is gone to the big bit bucket in the sky!

Is the Cumulative stuff supposed to work with UDP the same way it  
works with TCP? As I wrote at the top it works prefectly with TCP.

Thx.

--
Frederic P. Soulier
OpenPGP key available on http://pgpkeys.mit.edu/
1024D/BA6700ED   49A6 8E8E 4230 8D41 1ADE  B649 3203 1DD2 BA67 00ED

Re: CumulativeProtocolDecoder and UDP

Posted by Chad Beaulac <ca...@gmail.com>.

UDP datagrams are fragmented on MTU size. So if your messages are bigger than MTU size, you need to handle multiple callbacks for MTU size in your decoder. So, it doesn't work very well with UDP. 

Sent from my iPhone

> On Mar 1, 2016, at 11:37 AM, Ashish <pa...@gmail.com> wrote:
> 
> TCP handles fragmentation at its level, but for UDP you have to do it
> at application layer meaning UDP data has to carry message sequences
> and then you merge them at receiving end. Here you packets can come in
> different order do you got to keep them somewhere before complete
> message is constructed.
> 
> 
> 
>> On Tue, Mar 1, 2016 at 7:58 AM, tunca <at...@gmail.com> wrote:
>> Our customer has strange requirement about merging multiple udp/TCP packages
>> to create a single  message.
>> There is a well defined protocol that defines message boundaries.
>> The decoder is working good with TCP packages.  It can create a single
>> message from multiple TCP packages.
>> However when a message is fragmented into multiple packages the do doDecode
>> method always gives the same ioBuffer.
>> I'll try 2.0.13 next day.
>> Thanks
>> 
>> 
>> 
>> 
>> --
>> View this message in context: http://apache-mina.10907.n7.nabble.com/CumulativeProtocolDecoder-and-UDP-tp18927p50274.html
>> Sent from the Apache MINA Developer Forum mailing list archive at Nabble.com.
> 
> 
> 
> -- 
> thanks
> ashish
> 
> Blog: http://www.ashishpaliwal.com/blog
> My Photo Galleries: http://www.pbase.com/ashishpaliwal

Re: CumulativeProtocolDecoder and UDP

Posted by Ashish <pa...@gmail.com>.

Agree, that's why the protocol shift to Application layer, meaning you
emulate what TCP does like how many packets and their sequence to
order them at receiving layer for meaningful interpretation.

On Tue, Mar 1, 2016 at 11:01 AM, Mondain <mo...@gmail.com> wrote:
> Ashish, just be aware that with UDP, some of your data may never arrive;
> that's the nature of the protocol.
>
> Paul
>
> On Tue, Mar 1, 2016 at 1:48 PM Ashish <pa...@gmail.com> wrote:
>
>> TCP handles fragmentation at its level, but for UDP you have to do it
>> at application layer meaning UDP data has to carry message sequences
>> and then you merge them at receiving end. Here you packets can come in
>> different order do you got to keep them somewhere before complete
>> message is constructed.
>>
>>
>>
>> On Tue, Mar 1, 2016 at 7:58 AM, tunca <at...@gmail.com> wrote:
>> > Our customer has strange requirement about merging multiple udp/TCP
>> packages
>> > to create a single  message.
>> > There is a well defined protocol that defines message boundaries.
>> > The decoder is working good with TCP packages.  It can create a single
>> > message from multiple TCP packages.
>> > However when a message is fragmented into multiple packages the do
>> doDecode
>> > method always gives the same ioBuffer.
>> > I'll try 2.0.13 next day.
>> > Thanks
>> >
>> >
>> >
>> >
>> > --
>> > View this message in context:
>> http://apache-mina.10907.n7.nabble.com/CumulativeProtocolDecoder-and-UDP-tp18927p50274.html
>> > Sent from the Apache MINA Developer Forum mailing list archive at
>> Nabble.com.
>>
>>
>>
>> --
>> thanks
>> ashish
>>
>> Blog: http://www.ashishpaliwal.com/blog
>> My Photo Galleries: http://www.pbase.com/ashishpaliwal
>>



-- 
thanks
ashish

Blog: http://www.ashishpaliwal.com/blog
My Photo Galleries: http://www.pbase.com/ashishpaliwal

Re: CumulativeProtocolDecoder and UDP

Posted by Mondain <mo...@gmail.com>.

Ashish, just be aware that with UDP, some of your data may never arrive;
that's the nature of the protocol.

Paul

On Tue, Mar 1, 2016 at 1:48 PM Ashish <pa...@gmail.com> wrote:

> TCP handles fragmentation at its level, but for UDP you have to do it
> at application layer meaning UDP data has to carry message sequences
> and then you merge them at receiving end. Here you packets can come in
> different order do you got to keep them somewhere before complete
> message is constructed.
>
>
>
> On Tue, Mar 1, 2016 at 7:58 AM, tunca <at...@gmail.com> wrote:
> > Our customer has strange requirement about merging multiple udp/TCP
> packages
> > to create a single  message.
> > There is a well defined protocol that defines message boundaries.
> > The decoder is working good with TCP packages.  It can create a single
> > message from multiple TCP packages.
> > However when a message is fragmented into multiple packages the do
> doDecode
> > method always gives the same ioBuffer.
> > I'll try 2.0.13 next day.
> > Thanks
> >
> >
> >
> >
> > --
> > View this message in context:
> http://apache-mina.10907.n7.nabble.com/CumulativeProtocolDecoder-and-UDP-tp18927p50274.html
> > Sent from the Apache MINA Developer Forum mailing list archive at
> Nabble.com.
>
>
>
> --
> thanks
> ashish
>
> Blog: http://www.ashishpaliwal.com/blog
> My Photo Galleries: http://www.pbase.com/ashishpaliwal
>