Je me souviens

Everything here is my personal opinion. I do not speak for my employer.
Back: July 2004
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2004-08-07 »

(Super)freeswan Super Sucks

...but the world is a better place thanks to ipsec_tunnel and patch that makes isakmpd work with it.

IPsec is a grotesque horror story which barely works and is too complicated to be provably secure. That's bad enough, but when crazy bad-quality programmers get into the picture, you get total nastiness - that is, Freeswan.

On the other hand, ipsec_tunnel is downright straightforward, but only because it skips the key negotiation stuff, expecting you to do it yourself. And isakmpd is actually pretty wonky, but only because it has to do a truly startlingly huge amount of complicated negotiation just to make things work out. I'm pretty sure they made it as configurable as they did just so you have to suffer a little bit, just like they did. But other than the big long boilerplate config file (containing words like "QM-ESP-3DES-SHA-PFS-SUITE"), the programmers are pretty certifiably Not Insane.

And after spending more hours today fighting with bugs in freeswan's pluto daemon, I could definitely use some of that.

Meanwhile, we're thinking of taking my age-old Tunnel Vision and making it use IPsec (ie. ipsec_tunnel, in this case) as the packet-transfer layer. That could have the major advantages of throwing out stupid horrible IKE, plus it would let you auto-negotiate routes like Tunnel Vision always does and IPsec never did. The ESP (tunnel) part of the IPsec standard isn't so bad; it's the key negotiation that sucks, so why not let SSL do it for me? Of course, it wouldn't really be IPsec-compatible then.

The other choice is to keep IKE and add a layer on top of that. The advantage there is that you can gracefully fall back to plain IPsec if the other guy doesn't have Tunnel Vision. But that solution makes me feel guilty, because then I'm just making a bad thing even worse. Oh well...

August 07, 2004 23:54

2004-08-11 »

Embed me some HTML, Please

I was sitting today, thinking how unfortunate it is that C/C++ don't have any string quoting operators other than double-quote. I mean, designers of all sorts of languages since then (perl, in the especially extreme case) have figured out that if you want to print double quotes, that's just no fun at all.

Then I realized I was wrong.

#define qq(s) #s

int main()
{
    printf(qq(blah blah\n "quoted" stuff (and some parens)
        with newlines));
    return 0;
}

Try it. It works.

August 11, 2004 14:35

2004-08-18 »

Manifesto Writing

At Ozzy's suggestion, watched Pirates of Silicon Valley tonight for inspiration. Slightly depressed that I am neither a slimy poker-faced business supergeek negotiator (Gates) nor a crazy slave-driving hippie artist (Jobs), and will therefore probably never amount to much. On the up side, probably nobody will make a movie featuring my pathetic roller-skating antics or illegitimate children. It could be worse.

August 19, 2004 01:38

2004-08-22 »

IDL Compilers

Perhaps foolishly, I told pphaneuf that I might help him with his XPLC IDL compiler if he would send me some "before and after" examples of what he wanted it to look like. He sent me some pretty crappy examples written by the XPCOM people (WOW! Bad documentation!), but I got motivated anyway, probably due to my still-sucky-but-upcoming manifesto, and like magic... we now have an IDL compiler.

Before, I thought that IDL ("Interface Definition Language") was a general term for languages that define interfaces, and an IDL compiler was a general term for something that turns your general language into a real language (like C++, perl, etc). But it turns out, for those who didn't know, that IDL is itself a well-defined language (by the CORBA people), and it's actually both straightforward and well done. The rest of CORBA turned into a mess, but IDL is a nice little gem hidden inside. Plus, there's a libIDL that even turns it into a parse tree for me.

Anyway, once I got the parser working (using the crazy magic of WvCont to convert the ugly state machine into a simple procedural program, heh heh), producing C++ output was pretty easy - IDL is based on C++ anyway, it seems. Then it wasn't too hard to write C bindings by making very, very dangerous evil assumptions about the format of the C++ vtable (so shoot me). Result: now, like magic, I can access my C++ classes transparently from C with zero overhead compared to C++. It's neat. (The overhead in C++ is also minimal; just the cost of a virtual function call. XPLC doesn't get in the way of plain C++ programming here.)

But that's all normal stuff that people have been doing (badly) for years. I could write a whole rant about how ridiculously bad COM and XPCOM are for no apparent reason, but I won't.

Instead, I will reveal to you the amazing secret I discovered about IDL: it thinks like I do. That's right, while in UniConf I made the simplifying assumption that "everything is a string" and it made everything easy, IDL allows us to make almost the same assumption. Everything is a string or an object. And, as we know, monikers are strings that map into objects.

So I added a feature to my IDL compiler to write wrapper functions for your interfaces. The wrappers only pass around "strings" and "objects" (actually, they pass around union objects that are both). You can look up a function by name, then match against its signature to see if the objects you have are the ones it wants, just in case there's more than one function with that name (ie. in different types of interface).

The magic: objects have interfaces, and functions take a "this" pointer that's always an object; but when it comes down to it, that's all objects do. You don't poke around inside them. You don't "serialize" them. They're opaque. You simply try to run functions on them and check the return values to see if they work.

CORBA (and others) screwed up by assuming I wanted to "do stuff" with objects, like ship them around transparently from computer to computer. Big mistake: real life says that I ship strings around from computer to computer, not objects, and I have nothing against making that transparent. And hey, if my objects want to have functions to convert themselves to strings and back, that's fine with me - but it's not transparent. It's for them to worry about.

Anyway, it turns out that this model is pretty trivial to get working, and functions that take and return strings and/or pointers to objects happen to be really well supported by SWIG, so I can now access my C++ objects from tcl and (probably) perl and a bunch of other languages, essentially for free. (I only need one plugin per language, not one per language+interface, and SWIG will write most of the plugins for me!)

What amazes me is that it's always been done so badly before. XPCOM claims to do this, but after all this time, I have no idea how to load XPCOM components into tcl or run a command-line javascript interpreter. Why? It should be easy. In XPLC, it'll be easy. (By the way, the XPLC runtime is still only about 26k. Now that we have scripting, there will be an extra cost of a few kbytes for each language binding we want. For reference, the tcl bindings are about 10k.)

I really want to write a "sh" binding to demonstrate how powerful this model is. After all, the shell is great at dealing with strings, and since I don't ship my objects back and forth, I can just have them all live in another process that my shell can talk to. Nobody else's component model has shell plugins.

Anybody who wants to follow along can grab my very-alpha-quality code from open.nit.ca's anonymous CVS (project 'xplcidl').

August 23, 2004 02:53
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