ZIP Access &

Accessing Zip Archives with ZLib Decompression

The Library

The zziplib library 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

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 zip/unzip 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.

Using A Zip-File

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 achived by calling zzip_dir_open or zzip_dir_fdopen . The directory entries in the zip-archives can be obtained with zzip_dir_read . After being done, the zip-dir handle should be closed with zzip_dir_close .

 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);
 }

From the zip-dir handle a compressed file can be opened for reading. This is achieved by using zzip_file_open and providing it with the dir-handle and a name of the file. The function zzip_file_read is used to get pieces of uncompressed data from the file, and the file-handle should be closed with zzip_file_close

 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);
 } 

Magic Zipped Files

There is actually no need to directly use the zip-centric functions as described above. Instead there are magic replacements for the posix calls open/read/close and opendir/readdir/closedir. The prototypes of these functions had been the guideline for the design of their magic counterparts of the zziplib library.

The magic functions are described in a seperated document on Using Zipped Files . In general, the functions have a prefix zzip_ and their argument types have a prefix ZZIP_ 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.

To detect a real file (or directory), the info functions zzip_file_real and zzip_dir_real can be used. If these return a true value, the standard posix functions are more apropriate. The posix handles can be obtained with a call to zzip_realdir and zzip_realfd respectivly.

Errors & Infos

There are a set of error and info functions available. To handle error conditions specific to the zziplib library there are these functions: zzip_error , zzip_seterror and their string representations with zzip_strerror , zzip_strerror_of . The magic functions will map any of these specific library error conditions to the more generic system errno codes with zzip_errno .

More information on stream can be obtained with zzip_dir_stat and zzip_dirhandle. The latter is used to obtain the dir-handle that every zipped file handle has even if not explicitly opened.

The usage of many functions are shown in the example programs that come along with the zziplib library. See the files zzcat.c and zzdir.c . The zziptest.c program needs the private header file zzip.h whereas the library installer will only copy the public include file zziplib.h to your system's include directory.


guidod@gmx.de 1. June 2000