ZZIP_FILE can serve as a replacement
for a normal file descriptor. As long as it is only used
for reading a file, the zzlib-user can actually replace
the posix functions
by their counterparts from the
As long as the filename path given to
refers to a real file in the filesystem, it will almost
directly forward the call to the respective posix
call. The returned file descriptor is then stored in
a member-variable of the
Any subsequent calls to
zzip_read will then
be forwarded to the posix
read call on the
memorized file descriptor. The same about
which will call the posix
close function and then
The real benefit of the
comes about when the filename argument does actually refer
to a file that is zipped in a zip-archive. It happens that
even both a real file and a zipped file can live under the
same pathname given to the
whereas the real file is used in preference.
Suppose you have subdirectory called 'test/'. In
this directory is just one file, called 'README'.
zzip_open function with an
argument of 'optional-path/ test/README',
then it will open that file for subsequent reading with
zzip_read. In this case the real (stat'able)
file is opened.
Now you can go to the 'test/' directory and zip up
the files in there by calling
zzip_open will still succeed.
The reason is that the part of the path saying
'test/README' will be replaced by sth. like
'test.zip:README' - that is the real file 'test.zip'
is opened and searched for a contained file 'README'.
zzip_read on the zipped 'README' file
will return the very same data as if it is a real file in a
real directory. If the zipped file is compressed it will be
decompressed on the fly.
The same applies to the use of
which can safely be replaced with their counterparts from the
zziplib library - again their prototype
follows the scheme of the original calls, just prepend zzip_
to the function calls and ZZIP_ to the struct-typedefs.
zzip_opendir on a real directory will then
ZZIP_DIR whose member-variable
realdir points to the actual
returned by the underlying posix
If a real directory 'test' does not exist, then the
zzip_opendir will try to open a file 'test.zip'
with a call to
Subsequent calls to
zzip_readdir will then return
information as being obtained from the central archive directory
of the zip-file.
There are no differences between the posix calls and their counterparts from the zziplib library - well, just as long as the zip-file contains just the plain files from a directory.
If the zip-file contains directory entries you may be prompted with
some awkward behaviour, since in zip-file a directory happens to be
just an empty file. Note that the posix function
may also open a directory for reading - it will only return
EISDIR if the
open mode-argument included
What the current of version of the zziplib library can definitly not do: calling zzip_opendir on a directory zippend inside a zip-file.
To prevent the enrollment of directories into the zip-archive, you
can use the -D option of the zip program. That
is in any Makefile you may want to use
Distribution of a set of files is much easier if it just means to wrap up a group of files into a zip-archive - and copy that zip-archive to the respective destination directory. Even more the files can be compressed and unlike a tar.gz archive there is no need to decompress the archive in temporary location before accessing a member-file.
On the other hand, there is no chance to scatter files around
on the disk like it could easily happen with a set of gzip'ed
man-pages in a single `man`-directory. The reader
application does not specifically need to know that the file
is compressed, so that reading a script like
`share/guile/x.x.x/ice-9/popen.scm` is done by simple
zzip_read which works on zip-file named
A version mismatch between different files in a group is now obvious: either the opened file belongs to the distribution archive, or otherwise in resides in a real directory just next to the zip-archive that contains the original.
The zziplib library does not
use any code piece from the
zip programs, neither
pkzip nor infozip, so there is no license
issue here. The decompression is done by using the free
zlib library which has no special
issues with respect to licensing.
The rights to the zziplib library
are reserved to the copyright holders, there is a public
license that puts most the sources themselves under
the GNU Lesser General Public License,
so that the use of a shared library instance of the
has no restrictions of interest to application programmers.
For more details and hints about static linking, check
the COPYING information.
The only issue you have with the zziplib library is the fact that you can only read the contained files. Writing/Compression is not implemented. Even more, a compressed file is not seekable at the moment although I hope that someone will stand up to implement that functionality someday.