Cliff Hacks Things.

Saturday, February 24, 2007

The wheel of hobbies spins on.

This is a sort of omnibus update for all my various projects, in case anyone's watching. :-)

My spare-time projects tend to be fueled by interest from others. If I'm doing them just for me, I'll hack on it to solve some interesting set of problems, and then leave them unfinished. The partially-finished systems are useful to me, and solve my problems; packaging and publishing them is only worth it if they'll be useful to others. I do enough software-polishing in my day job that I have a hard time making it a hobby unless I'm helping people in the process.

Speaking of the day job, my workload has increased dramatically since about October. My team has shrunk, but our responsibilities haven't. I'm enjoying it, but it cuts into my spare time.

PropellerForth has stalled due to profound lack of interest from the Propeller community, though I've suddenly (past week or so) gotten a bunch of emails about it. Thus, I may pick it back up, or at least publish the sources so others can carry the torch. (I never got around to publishing before.) I still don't know of anyone using propasm, which is ironic, since I actually packaged it -- the sources are available, and have near-100% test coverage.

I've done a lot of rethinking of Mongoose. I've been working with some of the new batch of next-generation multi-paradigmatic languages, like Scala, but none of them are heading in the direction I want. I'm still using Mongoose primarily to prove some points, and not intending it to be the "next big thing" -- but at the same time, I've been looking at targeting it to existing VMs, with the hopes of achieving interoperability with some last-gen languages. (And not having to maintain my own VM. I hate C++.)

The robots have been dormant lately, but DPR still boots and works (imagine, a Linux system that still works after several months of inattention). I've been learning a lot about machine learning lately in my day job, and I'm hoping to rewrite some of DPR's personality using new techniques like fuzzy associative memories. I'll post here if I get around to it.

So, what have I been hacking on? Strangely enough, Cesta -- my network analyzer, which I've left untouched for nearly a year. My brain keeps coming back to it, because it lets me do the sort of stuff I don't get to do at work (like UI and interaction design), while still presenting a lot of juicy hard problems (like my fuzzy protocol decoding ideas). I'm applying what I learned from the Mongoose compiler to reworking Cesta's protocol decoding layer, enabling it to synthesize new decoders on the fly.

For example, take TCP. TCP connections contain no indication of the protocol they're carrying -- sure, the connection is to port 80, but that's not a guarantee that it's carrying HTTP.

Previously, my solution was brute-force: try to decode every known TCP protocol, eliminating them one by one as they reject the data as malformed. Two years ago I was already looking at more efficient ways to do this, but got caught up in the fun stuff like graph rendering and UI design.

In my reworking of the protocol decoding, I came across a better way. Protocols are defined declaratively using a protocol definition file, which Cesta compiles into decoder code -- and by synthesizing the constraints and layouts of all protocols known to be carried in TCP connections, it can generate a state machine that allows quick and efficient payload-type detection. (And, thanks to the dynamic code generation techniques I learned for Mongoose, I think I can compile the code on the fly without e.g. calling out to gcc.)

If this sounds like massive overkill, you're right -- which is where the machine learning comes in. Using the fuzzy associative memory techniques I've learned recently, Cesta can learn what protocols are most likely to be sent over a given port, and optimize the decoder appropriately. For example, a TCP connection to port 80 is pretty likely to be HTTP, so we can try decoding it as such until proven wrong -- a technique I call speculative decoding. If the guess proves wrong, we can try the next-most-likely protocol, or fall back to the synthetic every-protocol decoder I described above.

As a side effect, we get service-type identification. If Cesta learns that a port on a particular host seems to be speaking HTTP or SSHv2, it records this in the fuzzy memory, and we can present this to the user.

Multiplexed ports or changes in service don't present a problem for this either: it has no difficulty describing a port as "80% HTTP, 20% SSH" if something weird is going on (such as dynamic port mappings on a NAT).

This is complicated -- rather more complicated, in fact, than any network analyzer I've ever used -- but I understand all the techniques involved, and I think I can pull it off. Once there's code, I'll post it here.

Labels: , ,