Linz RB wrote:
Just looking for some confirmation on my thoughts (and understanding) of
writing ProtocolCodecs
Before I start - congratulations to the MINA team - MINA 2,0 is great and
the separation of repsonsibilities is a joy to work with.
I am primarily concerned with the construction of decoder codecs (as
converting a POJO to an IO Buffer is straight forward).
I have three protocols that I am looking at - and planning to convert to
using MINA. These are DHCP, TFTP, and a bespoke protocol.
So DHCP:
I took a look at the codec provided for Apache DS - but was not confident
that it would work. The decoder codec seems to assume that an entire DHCP
message would be present in the IOBuffer. But from what I have read - you
cannot make this assumption.
Have I understoodd this correctly ?
I suspect you are right. I have not checked the ApacheDS DHCP codec
though, so I trust you on that.
So I have implemented a version that uses an internal state machine (not the
mina-statemachine - learning one thing at a time!) that process as much of
the received DHCP message as possible in stages : for example - process the
'static' part (first 236 bytes), then the magic cookie and lastly options
(variable length).
Sounds the way to go.
So TFTP:
Again - I have read the 'static' portion of the message header - and then
process the rest of the message.
The rest of the message is 0 byte terminated - so I have to look at the
IOBuffer - at the limit() position for a 0 - which indicates that the entire
message is available and can be processed (since TFTP is a strict handshake
style protocol I do no have to worry about a second message in the buffer -
I think !!)
Sounds ok too
How am I doing so far ? Is my approach incorrect - and not what MINA gurus
would recommend.
Well, that's the way I would have handled those protocol. May be someone
else has a better idea ?
I am getting the feeling that it would be helpful to find a way to describe
a protocol and then provide a codec framework that is a close fit - is this
intention of MINA ? - so, codecs for synchronous (handshake) based protocols
(where you can only every expect a single message per IOBuffer) v
asynchronous (streaming-like) protocols (where you may find more than one
message per IOBUffer).
There are a few interesting approaches so far to solve this problem, and
some peeps have developped some Codec generators. One of them is based
on Google Protocol Buffer (thomasz blachowicz).
I have also thought that we should have an ASN.1 compiler generating
code for any kind of codec, but it's a very long task ...
Last, not least, we discussed a bit about creating a codec library,
containing the most well known protocols (as we already have a few of
them, it should not be a problem)
So this is still an open area, where those who want to play can join us !
--
--
cordialement, regards,
Emmanuel Lécharny
www.iktek.com
directory.apache.org
