2004
(non)frequently asked questions
While using the zziplib some people come up with questions and problems that need a little longer to be explained. So here is a list of these notes for your information. Keep it up.
- extended ascii characters in names of zipped files
- unicode support for names of zipped files
- timestamps of zipped files
- installation instructions
- php zip module installation
- commercial support
[latin-1]:
That's somehow incorrect - the ascii range is the 7bit lower plane of an 8bit character encoding. The upper plane had been non-standard for decades including the age when the ZIP file format was invented. The first instances of pkware's zip compressor were used on DOS with a codepage 437 which has a way different encoding for the upper plane than today's latin-1 encoding which in fact used in all modern operating systems. So what really see is a mismatch of character encodings that you are used to.
Even more than that the character encoding had never been specified at all for the filenames in the central directory part. An alert reader will however recognize that each file entry does also have version-info field telling about the compressor that did create the file entry. That version-info has an upper byte telling about the host OS being in use while packaging. A heavy-weight zip decoder might use that value to infer the character encoding on the host OS (while compressing), to detect a mismatch to the current OS (while decompressing), and going to re-code the filename accordingly.
Even more than that the zip file format has seen various extensions over time that have found their place in an extra info block. There are info blocks telling more about the filename / codeset. However the zziplib library does not even attempt to decode a single extra info block as zziplib is originally meant to be a light-weight library. However one might want to put a layer on top of the structure decoding of zziplib that does the necessary detection of character encodings and re-coding of name entries. Such a layer has not been written so far.
[utf-8]:
The pkware's appnote.text has an extra info block (id-8) for the unicode name of the file entry but it was never actually being used AFAICS. This might be related to the current developments of older systems to drop usage of latin-1 encoding in the upper plane of 8bit characters and instead choosing the multibyte encoding according to UTF-8. This is again highly system specific.
Basically, you would need to instruct the compressor to use UTF-8 encoding for the file-entries to arrive at a zip archive with filenames in that specific character encoding. Along with this zip archive one can switch the application into utf-8 usage as well and take advantage of filename matches in that encoding. This will make it so there is not mismatch in character encoding and implicit re-coding being needed.
[timestamps]:
That's correct and again a re-coding problem. The original timestamp in each file entry is in DOS format (i.e. old-FAT). The stat value is usually expected to be in POSIX format. The win32 API has an extra function for conversion but none of the unix compatibles has one, so it would be needed to ship a conversion function along with zziplib.
However the zziplib is intended to be light-weight system and used largely for packaging data for an application. There it is not used strictly as a variant of Virtual File System (vfs) that would need to map any information from the zip file system to native host system. Of course applications are free to cut out the DOS file timestamp and re-code it on their own. It's ust that zziplib does not provide that re-coding originally.
[install]:
The zziplib project is opensource which effectly gives two ways of installing the package: one can download the source archive and use a C compiler to derive a binary executable for whatever computer it needs to be on (see the platform compatibility list). This is the preferred way but for convenience one can download a binary installation archive with precompiled executables.
The current project uses autoconf/automake for cross platform support which includes most unix compatible systems and their native C compilers. The derivates of the GNU C compiler (gcc) have replaced most of these native C compilers in the past years. The mingw32 project has ported a unix born C compiler to win32 and zziplib can be compiled with it for the various win32 platforms.
There exist some C compilers which can not be embedded easily into a unix compilation framework. The zziplib source archive ships with project files for MSVC6 and MSVC6 (Microsoft Visual C). Adapting these project files might help with installation problems of the DLL hell on win32 platforms. There exist no sufficient guidelines to mix binary helper libraries for many applications on windows.
There exists win32 binary archives as zip files on the download area of zziplib (MSI is always on my wishlist). Including the project as a helper library however you should not use it but instead compile from source. The general library installation on unix are better, the zziplib download area contains regularly some linux binary archives (rpm). Many vendors of unix compatible systems provide precompiled binary packages of zziplib on their own.
[php]:
Now that is one of the most frequently asked questions that I do receive. There is just one major problem with it: I did not write the php zip module (which uses zziplib) and I have no idea how php modules work or how to tell apache's php sandbox to make it work. Really, I do not have the slightest clue on that.
I was posting to some php developer sites to spread awareness of the fact and hopefully to find a guy that I could forward any questions on the php zip module installation. But so far there is nothing, it merily seems that such installation problems are in no way related to zziplib anyway but exists with any other module with a third party library dependency as well. So the answers on php forum sites will ask for details of the current php and apache configuration.
Since I do not run a php zip whatever nor any other php stuff, it's just that those hints were not quite helpful to me. It would be really really great if someone with a php zip background could be so nice to write a short roundup of the areas to check when a php zip module installation fails, so that I could post it here. Where are you? Yours desperatly... ;-)
[license]:
The zziplib has been created as a spare time project and it is put under a very easy free public license. Even for commercial projects there is hardly any need to negotiate a separate license since the restrictions of the GNU LGPL or MPL can be matched easily. As a general hint, if the zziplib is shipped unmodified with your project then you are right within the limits of the free public license.
Sometimes the question for a personal license comes up for very different reason - the need for a support contract and/or the setting of functionality guarantees. The free public licenses include a safeguard clause to that end, "in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose." Since the project was developed as a spare time project however there have never been personal licenses going beyond.
In general you can still try to negotiate a support contract but it will be very costly. It is much more profitable for you to tell one of your developers to have a look at the source code and ensure the required functionality is there, with hands on. The source code is written to be very readable, maintainable and extensible. Just be reminded that the free public licenses have restrictions on shipping modified binaries but I can give you a cheap personal license to escape these. (Such licenses can be obtained in return for tax-deductible donations to organisations supporting opensource software).
... and as always - ** Patches are welcome ** -