Re: Look for data serialisation format to implement communication between Emacs and external program.

[Oleksandr Gavenko]

On 2013-01-07, Thien-Thi Nguyen wrote:

> () Oleksandr Gavenko <gavenkoa@gmail.com>
> () Sun, 06 Jan 2013 23:44:46 +0200
>
>    Another formats like JSON or sexp also look nice but I don't know
>    about Emacs support for this formats.
>
> Go with sexp.  If you must touch XML, at least dress it up as SXML,
> which, aside from being less ugly, extends interop to include Scheme.
> E.g., sexp + SXML is the approach IXIN uses.  Latest announcement:
> <http://lists.gnu.org/archive/html/help-texinfo/2013-01/msg00000.html>.
>
One thing stop me from using sexp - my Python code can be possible used in
another cases where sexp parser can be absent.

> If you absolutely need a binary (non-text) format, then i would next
> recommend bindat.el (info "(elisp) Byte Packing") for the job.  Perhaps
> ASN.1 can be layered on top of bindat.el, but that doesn't sound so fun.
> (But what do i know about ASN.1 and/or fun?)
>
Thank for suggestion. I completed simple type-length-value example:

  (setq bin-str (unibyte-string ?s 4 ?h ?a ?l ?o))
  (setq bin-header '((:type u8) (:len u8) (:val vec (:len))))
  (setq bin-data (bindat-unpack bin-header bin-str))
  (bindat-pack bin-header bin-data)

But as input come from external process I need manually check for input end
because parsing of incomplete input take error "args-out-of-range".

I don't know how to resolve this issue.

I expect to find a way to get data validation for free (like XSD/RNC for XML).

Also I don't see have can I split data into packets with "bindat" (Emacs send
request and Python send response in a loop without dropping connection while
returned data is valid). As solution - make 10 attempt with 1 sec delay and
then report error - incomplete or invalid packet...

> Lastly, on the other side of the pipe, why not consider Emacs itself, or
> Guile, or something that can ‘read’ a sexp?

-- 
Best regards!