I do something similar, using a binary protocol where messages vary in
length based on data-length values in the message. And yes, I use a
custom subclass of CumulativeProtocolDecoder for this.
The code's a bit ugly, but it works. Essentially your decoder needs to
handle 3 possible cases:
* full, syntactically correct message received
* part of a syntactically correct message received, and
* syntactically incorrect message received
Not sure what more info you're looking for, so if you email back
specific questions, I'll respond with further explanations and/or code.
HTH,
DR
Chowdhury, Shubhankar [WHQKA] wrote:
Thanks Emanuel but actually I the message lengths vary in each
message - that's part of the message itself. If you see the message
format "14-2-Data_length" - so starting at 14th byte and I will have
an short value giving me the data length.
Once I receive the whole message then only I can apply the byte
off-sets to extract the message body and header etc. but with
in.available() I would have to know the message length before hand
isn't it? Am I missing something?
Thanks, Shubhankar 847-700-4452 -----Original Message----- From:
Emmanuel Lecharny [mailto:[email protected]] On Behalf Of Emmanuel
Lecharny Sent: Friday, June 19, 2009 5:46 PM To:
[email protected] Subject: Re: Handling variable length
request/response in MINA
Chowdhury, Shubhankar [WHQKA] wrote:
o o the whole format got garbled - let me try in plain text
----------------------------------------------------------
----------------------------------------------------------
This might be a very dumb post but please help.
I have already used MINA for a few projects mainly using the
CumulativeProtocolDecoder and RequestResponseFilter for the client
applications and using TextlineCodec for a few server instances.
But my next attempt is a bit complex where the data that comes is a
structured data of variable length basically of the following
format-
Offset-LengthInByte-FieldName ------------------------------
0-8-application_id 8-2-Version 10-2-Type 12-2-message_id_number
14-2-Data_length 16-4-Reserved 20-data_length-Data
The application would be a server listening to a port (TCP) and
also would return back some response based on the type field. So
the client would initiate by sending a "login-request" - in
response we have to send "accept" or "reject", then the data would
be flowing, then log-out, keep-alive etc and all of them would
follow the above structure.
How do I handle this using MINA? Is there anyway I can use the
CumulativeProtocolDecoder?
Actually, it will easy. As you know the length of your message, it's
just a matter of storing what has already been received in the
session, until you got all the message.
The decoder must be able to stop in the middle of an int, for
instance, which is not that complicated, assuming that an int is a
fixed size element. You just have to check that you have 4 bytes
available in the buffer to decode the int, otherwise, you just store
the buffer in the session, and wait for the next bytes to come.
Sounds complicated, but it's not.
The real issue is if you have very long messages : in this case, you
may want to stream to a file the incoming data, to avoid a OOM.
When you have received everything, then you can push the resulting
eleme,t to your handler (if of course you built a data structure on
the fly).
Hope it helps.
