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<section><date> 1. June 2000 </date>
<h2> ZIP Access </h2> Accessing Zip Archives with ZLib Decompression
<!--border-->
<section>
<h3> The Library </h3>
<P>
The <a href="zziplib.html">zziplib library</a> offers users the
ability to easily extract data from files archived in a single
zip file. This way, programs that use many "read-only" files from
a program specific source directory can have a single zip
archive
</P>
<P>
This library offers only a (free) subset of compression methods
provided in a full implementation but that is well enough. The
idea here is that <tt>zip/unzip</tt> utilities can be used
to create archives that will later be read by using this library.
Yet those programmes (or a library with their functionality)
is not needed in that final operation.
</P>
</section><section>
<h3> Using A Zip-File </h3>
<P>
Before a file in the zip-archive is accessed, the application
must first get a handle to the central directory contained in the
zip-file. This is achieved by calling
<a href="zziplib.html#zzip_dir_open"> zzip_dir_open </a>
or
<a href="zziplib.html#zzip_dir_fdopen"> zzip_dir_fdopen </a>.
The directory entries in the zip-archives can be obtained
with
<a href="zziplib.html#zzip_dir_read"> zzip_dir_read </a>.
After being done, the zip-dir handle should be closed with
<a href="zziplib.html#zzip_dir_close"> zzip_dir_close </a>.
</P>
<p><pre> ZZIP_DIR* dir = zzip_dir_open("test.zip",0);
if (dir) {
ZZIP_DIRENT dirent;
if (zzip_dir_read(dir,&dirent) {
/* show info for first file */
print("%s %i/%i", dirent.d_name, dirent.d_csize, dirent.st_size);
}
zzip_dir_close(dir);
}
</pre></p>
<P>
From the zip-dir handle a compressed file can be opened
for reading. This is achieved by using
<a href="zziplib.html#zzip_file_open"> zzip_file_open </a>
and providing it with the dir-handle and a name of the file.
The function
<a href="zziplib.html#zzip_file_read"> zzip_file_read </a>
is used to get pieces of uncompressed data from the file, and
the file-handle should be closed with
<a href="zziplib.html#zzip_file_close"> zzip_file_close </a>
</P>
<p><pre> ZZIP_FILE* fp = zzip_file_open(dir,"README",0);
if (fp) {
char buf[10];
zzip_ssize_t len = zzip_file_read(fp, buf, 10);
if (len) {
/* show head of README */
write(1, buf, len);
}
zzip_file_close(fp);
}
</pre></p>
</section><section>
<h3> Magic Zipped Files </h3>
<P>
There is actually no need to directly use the zip-centric functions
as described above. Instead there are magic replacements for the
posix calls <code>open/read/close</code> and
<code>opendir/readdir/closedir</code>. The prototypes of these
functions had been the guideline for the design of their magic
counterparts of the
<a href="zziplib.html">zziplib library</a>.
</P>
<P>
The magic functions are described in a separated document on
<a href="zzip-file.html"> Using Zipped Files </a>. In general,
the functions have a prefix <tt>zzip_</tt> and their argument
types have a prefix <tt>ZZIP_</tt> where appropriate. Calls
to the magic functions and the direct functions above can
be mixed as long as the magic functions have not been opening
a real file.
</P>
<P>
To detect a real file (or directory), the info functions
<a href="zziplib.html#zzip_file_real"> zzip_file_real </a>
and
<a href="zziplib.html#zzip_dir_real"> zzip_dir_real </a>
can be used.
If these return a true value, the standard posix functions
are more appropriate. The posix handles can be obtained with
a call to
<a href="zziplib.html#zzip_realdir"> zzip_realdir </a> and
<a href="zziplib.html#zzip_realfd"> zzip_realfd </a> respectively.
</P>
</section><section>
<h3> Errors & Infos </h3>
<P>
There are a set of error and info functions available. To handle
error conditions specific to the
<a href="zziplib.html">zziplib library</a>
there are these functions:
<a href="zziplib.html#zzip_error"> zzip_error </a>,
<a href="zziplib.html#zzip_seterror"> zzip_seterror </a>
and their string representations with
<a href="zziplib.html#zzip_strerror"> zzip_strerror </a>,
<a href="zziplib.html#zzip_strerror_of"> zzip_strerror_of </a>.
The magic functions will map any of these specific library
error conditions to the more generic system <code>errno</code>
codes with
<a href="zziplib.html#zzip_errno"> zzip_errno </a>.
</P>
<P>
More information on stream can be obtained with
<a href="zziplib.html#zzip_dir_stat"> zzip_dir_stat </a> and
<a href="zziplib.html#zzip_dirhandle"> zzip_dirhandle. </a>
The latter is used to obtain the dir-handle that every zipped file
handle has even if not explicitly opened.
</P>
<P>
The usage of many functions are shown in the example programs
that come along with the
<a href="zziplib.html">zziplib library</a>. See the files
<a href="zzcat.c"> zzcat.c </a> and
<a href="zzdir.c"> zzdir.c </a>. The
<a href="zziptest.c"> zziptest.c </a> program needs the
private header file
<a href="zzip.h"> zzip.h </a> whereas the library installer
will only copy the public include file
<a href="zziplib.h"> zziplib.h </a> to your system's
<tt>include</tt> directory.
</P>
</section></section>
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