tl;dr: fa20ae35b8ac53b28dde4fc333aba21f :-)
Up until now, Mozilla’s Weave add-on has been living with an awkward implementation detail: a binary component. When I wrote Weave’s current cryptographic component back in 2008, in order to use the crypto code that’s already in Mozilla (ie, NSS) there was no choice but to write C++ code. NSS doesn’t export any scriptable interfaces at all, and its partner-in-crime (PSM) exposes only a limited set of high-level functions — none of which was useful for Weave.
The C++ code has been working fine, but has a number of serious drawbacks… A binary component has to be compiled for each supported platform (originally just Windows, Linux, Mac x86 and Mac PowerPC). That results in a bigger download, and makes it a pain to support new platforms (like 64-bit Windows, 64-bit Linux, 64-bit Mac, Maemo, Windows CE/Mobile, Android, etc). It’s also a barrier to new developers — compiling a binary component requires a build environment and XULRunner SDK, whereas hacking on most extensions requires nothing more than a text editor. Luckily the C++ code has been quite stable, so Weave was able to hack around this by including pre-compiled binaries in the Mercurial repository.
But enough is enough.
I should also mention that unit tests were a HUGE help in getting the new code completed. I wrote extensive tests for the C++ version of WeaveCrypto, and once the JS-CTypes version was working with those tests I was able to make a full-up Weave sync work with the new code on the first try. Easy-peasy!
If you’re interested in seeing what this new code does, take a look at the bug and the code in the Mercurial repository. Note that the XPCOM interfaces are fairly specific to what Weave wants to do — it’s not a general-purpose JS crypto API. But it’s a huge step towards making it easier to do crypto code in JS extensions — and perhaps in the future we’ll look at making a real general-purpose crypto API for extensions; it’s certainly an interesting problem! If folks are interested in helping out with such a project, let me know.