Re: grokking libgsf

[Allin Cottrell <cottrell wfu edu>]

On Mon, 4 May 2009, Jon K Hellan wrote:

> Allin Cottrell wrote:
> > I'm trying some tests with the hope of switching to libgsf in
> > place of low-level fiddling with pkzip structures in reading and
> > writing zipfiles.  So far I'm only partially successful and I'd
> > much appreciate any guidance.
> >
> > I have the following C source (with correct headers included, and
> > followed by a trivial main() function).  The idea is to print the
> > structure of a zipfile and then "unzip" it to a specified
> > location.
> >
> > The printing part, "print_kids", is working fine, but the
> > "unzipping" part is giving me an empty directory "foo".  I have
> > removed error-checking from the following for brevity, but no
> > errors were triggered when running the full version of the code.
>
> There is example code in the 'tests' subdirectory. You may
> already have discovered this. It looks like test-cp-zip.c should
> be a good starting point.

Thanks, you're right.  But I have a couple of questions about
test-cp-zip.c.

It contains a function "clone" which does a recursive read/write.
That's fine, but I'd have thought that gsf_input_copy() would
provide an automated route to the same result.  Apparently not.
So I'm not sure what gsf_input_copy() does.

Second, this test program writes out a new zip file, and I'd like
to write out an unzipped version.  It seems non-trivial to make
the change.  The trope in test-cp-zip.c is

 input = gsf_input_stdio_new (argv[1], &err);
 ...
 infile = gsf_infile_zip_new (input, &err);
 ...
 output = gsf_output_stdio_new (argv[2], &err);
 ...
 outfile = gsf_outfile_zip_new (output, &err);

By symmetry one might think that I could replace the last of
these lines with

 outfile = gsf_outfile_stdio_new (output, &err);

for stdio output, but that won't work.  Rather, I skip the
gsf_output_stdio_new() line and do

 outfile = gsf_outfile_stdio_new (argv[2], &err);

and pass outfile as the second argument to clone().  This works to
produce unzipped output, but it gives

GLib-GObject-WARNING **: invalid cast from `GsfOutputStdio' to
`GsfOutfile'

Having tried a few variants, I'm not sure of the right way to use
the API for this task.

Allin Cottrell