Fast JSON codec based on YAJL

[Julian Scheid <julians37@gmail.com>]

Hi,

I'm getting close to finishing a first version of an interface to YAJL,
"a small event-driven (SAX-style) JSON parser written in ANSI C, and a
small validating JSON generator."  See http://lloyd.github.com/yajl/

I've started working on this interface because json.el proves to be a
bottleneck in another project of mine.

A few unscientific benchmarks suggest that YAJL (via my interface) is
roughly 5 to 25 times as fast as byte-compiled json.el, on average about
an order of magnitude faster.  Memory usage is about on par.

With a few minor exceptions it's fully compatible to json.el and can be
used as a drop-in replacement in most situations. [*]

The interface also exposes a number of useful YAJL features not found in
json.el, such as optional pretty-printing.

It comes with a comprehensive ERT-based unit test suite, a small
stress-test and benchmarking suite, full TexInfo documentation, and the
usual detection code and switches for the configure script.

I've looked at a number of JSON libraries and chose YAJL mainly because
it's mature, clean and fast, and its event-driven architecture means a
redundant document tree won't have to be kept in memory.

YAJL is available in most major package repositories such as Debian, Red
Hat, Arch Linux, and MacPorts.

Is there interest in adding this interface to Emacs mainline?  If so,
I'd polish it a bit more and send over my code for review soon.

As for the legal side, YAJL (the underlying library, not my interface)
uses the ISC license but is only linked against.  The interface itself
doesn't include any ISC-licensed code, or any third-party code for that
matter.  I'd be happy to sign over copyright.

Julian


[*] The minor incompatibilities boil down to the fact that json.el can
emit invalid JSON in some cases when YAJL refuses to do so.  Example:
(json-encode '((1 . 1))) will yield invalid JSON output.  json.el also
has issues with characters on the astral plane and some to do with NaN
and Inf, which YAJL handles slightly different (and closer to the JSON
specification.)