Re: using libmagic in Emacs?

[Eli Zaretskii <eliz@gnu.org>]

> From: joakim@verona.se
> Date: Fri, 21 Aug 2009 11:55:45 +0200
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>,
> 	Emacs Development <emacs-devel@gnu.org>
> 
> Is autoheader supposed to generate config.in?

Yes.

> When does that happen?

Either run autoheader by hand, or run autoreconf (which AFAIK is
supposed to run autoheader as well).

> +DEFUN ("libmagic-file-internal", Flibmagic_file_internal, Slibmagic_file_internal, 1,1,0,
> +       doc: /* Return (MIME_TYPE MIME_ENCODING DESCRIPTION) for FILENAME_OR_BUFFER.
> +Return nil on error. */)

This doc string "needs work"(TM).  Please use the doc string of
visited-file-name as an example.

> +  (filename_or_buffer)
> +     Lisp_Object filename_or_buffer;

Using a `_' in an argument is un-Lisp'y (IMO).

> +{
> +  CHECK_STRING_OR_BUFFER (filename_or_buffer);
> +  magic_t cookie=NULL;
> +  char* f = NULL;
> +  const char* rvs;
> +
> +  if (STRINGP (filename_or_buffer))
> +    f = SDATA (filename_or_buffer);
> +  if (BUFFERP (filename_or_buffer))
> +    f = SDATA (XBUFFER (filename_or_buffer)->filename);
> +  cookie = magic_open (MAGIC_ERROR);
> +  if (cookie == NULL) goto libmagic_error;  
> +  magic_load (cookie, NULL); //load default database
> +
> +  magic_setflags (cookie, MAGIC_MIME_TYPE | MAGIC_ERROR);  
> +  rvs = magic_file (cookie, f);

You need to encode file names before you pass them to C APIs.  Use
ENCODE_FILE to do that; see file-attributes for an example of how this
is done.

> +  if (rvs == NULL) goto libmagic_error;
> +  Lisp_Object file_mime = intern (rvs);

You cannot declare variables in the middle of a block: Emacs does not
require a C99 compiler yet and need to support C90 or even older
compilers, which will reject this code.

> +  magic_setflags (cookie, MAGIC_MIME_ENCODING | MAGIC_ERROR);
> +  rvs=magic_file (cookie, f);
> +  if (rvs == NULL) goto libmagic_error;
> +  Lisp_Object file_encoding = intern(rvs);  

Is file_encoding supposed to be a valid encoding, one of those for
which Emacs has a coding-system?  If so, perhaps you should make sure
you indeed return a valid coding-system or its alias, or otherwise
tell in the doc string that it's not guaranteed to be valid (so that
the caller should validate it before using).