[notmuch] RFC: output json from notmuch?

David Bremner david at tethera.net
Sun Dec 13 15:21:02 PST 2009

It would be nice to have more structured output from notmuch-show.  I
decided to investigate sexp (i.e. lisp) and json output.

Sexp has the obvious advantage that it is trivially parsable in emacs;
for other clients it is a little more work.  I started looking at
sfsexp (http://sexpr.sourceforge.net).  It looks ok; I got a little
irritated that it doesn't support cons cells (i.e. dotted pairs). 

Then I found that json parsing is provided by the library json.el
shipped with emacs23, so I decided to play with json a bit.

I settled on the jansson library (http://www.digip.org/jansson/)
because it seemed to have a sane api and documentation, but there are
many choices.  I'll follow up with the actual patch, but the idea is to
replace the printfs in show_message with calls to set (key,value) pairs
in a json object, and output it at the end.

This is not in any sense a production patch (e.g. it needs to actually
return a thread object rather than just dumping messages out; nothing at
all has been done on the emacs side), but it gives you some idea of
would be involved.

So, do people think this is a reasonable idea to persue?

    1) it adds a dependency, but not a heavy one. jansson is about 300k
    installed on debian/i386

    2) It might mean that people using emacs22 might have to score
    json.el from somewhere; I'm not sure.

    3) There is some increase in memory use since the whole thread has
    to be built as a json object before being output.

    4) Of course jansson is doing it's own reference counting memory
    managment, and not using talloc. But we already have glib...

Of course we won't really know if it is good idea until we try it, but
if it already looks like a no-go, I'll stop.

Attachments:  json output of a message from carl, and the equivalent
sexpr as parsed by json.el.  

David Bremner                                  Professor, UNB Computer Science
bremner at unb.ca			           
http://www.cs.unb.ca/~bremner               Cross Appointment, UNB Mathematics
http://www.mitacs.ca/			   MITACS Atlantic Scientific Director

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