source/libs/zziplib/zziplib-0.13.62/docs/faq.htm

   1 <section> <date> 2004 </date>
   2 <H2> FAQ </H2> (non)frequently asked questions
   3
   4 <BLOCKQUOTE>
   5   While using the zziplib some people come up with questions and
   6   problems that need a little longer to be explained. So here is
   7   a list of these notes for your information. Keep it up.
   8 </BLOCKQUOTE>
   9 <ul>
  10 <li> <a href="#latin-1">extended ascii characters in names of zipped files </a>
  11 </li>
  12 <li> <a href="#utf-8">unicode support for names of zipped files </a>
  13 </li>
  14 <li> <a href="#timestamps">timestamps of zipped files </a>
  15 </li>
  16 <li> <a href="#install">installation instructions </a>
  17 </li>
  18 <li> <a href="#php">php zip module installation </a>
  19 </li>
  20 <li> <a href="#license">commercial support </a>
  21 </li>
  22 </ul>
  23
  24 <DL>
  25 <DT><a name="latin-1" />
  26  zziplib does not support extended ascii characaters, winzip does</DT>
  27 <DD><P>
  28   That's somehow incorrect - the ascii range is the 7bit lower plane of
  29   an 8bit character encoding. The upper plane had been non-standard for
  30   decades including the age when the ZIP file format was invented. The
  31   first instances of pkware's zip compressor were used on DOS with a
  32   codepage 437 which has a way different encoding for the upper plane
  33   than todays latin-1 encoding which in fact used in <em>all</em>
  34   modern operating systems. So what really see is a mismatch of
  35   character encodings that you are used to.
  36 </P><P>
  37   Even more than that the character encoding had never been specified
  38   at all for the filenames in the central directory part. An alert
  39   reader will however recognize that <em>each</em> file entry does
  40   also have version-info field telling about the compressor that did
  41   create the file entry. That version-info has an upper byte telling
  42   about the host OS being in use while packaging. A heavy-weight
  43   zip decoder might use that value to infer the character encoding
  44   on the host OS (while compressing), to detect a mismatch to the
  45   current OS (while decompressing), and going to re-code the filename
  46   accordingly.
  47 </P><P>
  48   Even more than that the zip file format has seen various extensions
  49   over time that have found their place in an extra info block. There
  50   are info blocks telling more about the filename / codeset. However
  51   the zziplib library does not even attempt to decode a single extra
  52   info block as zziplib is originally meant to be a light-weight library.
  53   However one might want to put a layer on top of the structure decoding
  54   of zziplib that does the necessary detection of character encodings and
  55   re-coding of name entries. Such a layer has not been written so far.
  56 </P></DD>
  57 <DT><a name="utf-8" />
  58  zziplib does not support any unicode plane for filenames </DT>
  59 <DD><P>
  60   The pkware's appnote.text has an extra info block (id-8) for the
  61   unicode name of the file entry but it was never actually being
  62   used AFAICS. This might be related to the current developments of
  63   older systems to drop usage of latin-1 encoding in the upper plane
  64   of 8bit characters and instead choosing the multibyte encoding
  65   according to UTF-8. This is again highly system specific.
  66 </P><P>
  67   Basically, you would need to instruct the compressor to use
  68   UTF-8 encoding for the file-entries to arrive at a zip archive
  69   with filenames in that specific character encoding. Along with
  70   this zip archive one can switch the application into utf-8 usage
  71   as well and take advantage of filename matches in that encoding.
  72   This will make it so there is not mismatch in character encoding
  73   and implicit re-coding being needed.
  74 </P></DD>
  75 <DT><a name="timestamps" />
  76  zziplib does not return stat values for file timestamps </DT>
  77 <DD><P>
  78   That's correct and again a re-coding problem. The original
  79   timestamp in each file entry is in DOS format (i.e. old-FAT).
  80   The stat value is usually expected to be in POSIX format. The
  81   win32 API has an extra function for conversion but none of the
  82   unix compatibles has one, so it would be needed to ship a
  83   conversion function along with zziplib.
  84 </P><P>
  85   However the zziplib is intended to be light-weight system and
  86   used largely for packaging data for an application. There it
  87   is not used strictly as a variant of Virtual File System (vfs)
  88   that would need to map any information from the zip file system
  89   to native host system. Of course applications are free to cut
  90   out the DOS file timestamp and re-code it on their own. It's
  91   just that zziplib does not provide that re-coding originally.
  92 </P></DD>
  93 <DT><a name="install" />
  94  how can one install the zziplib package </DT>
  95 <DD><P>
  96  The zziplib project is opensource which effectly gives two ways of
  97  installing the package: one can download the source archive and use
  98  a C compiler to derive a binary executable for whatever computer
  99  it needs to be on (see the platform compatibility list). This is
 100  the preferred way but for convenience one can download a binary
 101  installation archive with precompiled executables.
 102 </P><P>
 103  The current project uses autoconf/automake for cross platform
 104  support which includes most unix compatible systems and their
 105  native C compilers. The derivates of the GNU C compiler (gcc) have
 106  replaced most of these native C compilers in the past years. The
 107  <a href="http://www.mingw.org">mingw32</a> project has ported a
 108  unix born C compiler to win32 and zziplib can be compiled with
 109  it for the various win32 platforms.
 110 </P><P>
 111  There exist some C compilers which can not be embedded easily into
 112  a unix compilation framework. The zziplib source archive ships with
 113  project files for MSVC6 and MSVC6 (Microsoft Visual C). Adapting
 114  these project files might help with installation problems of the
 115  DLL hell on win32 platforms. There exist no sufficient guidelines to
 116  mix binary helper libraries for many applications on windows.
 117 </P><P>
 118  There exists win32 binary archives as zip files on the download area
 119  of zziplib (MSI is always on my wishlist). Including the project as
 120  a helper library however you should not use it but instead compile
 121  from source. The general library installation on unix are better,
 122  the zziplib download area contains regularly some linux binary
 123  archives (rpm). Many vendors of unix compatible systems provide
 124  precompiled binary packages of zziplib on their own.
 125 </P></DD>
 126 <DT><a name="php" />
 127  after installing zziplib the php zip module still does not work </DT>
 128 <DD><P>
 129  Now that is one of <b>the most</b> frequently asked questions that
 130  I do receive. There is just one major problem with it: I did not
 131  write the php zip module (which uses zziplib) and I have no idea
 132  how php modules work or how to tell apache's php sandbox to make
 133  it work. Really, I do not have the slightest clue on that.
 134 </P><P>
 135  I was posting to some php developer sites to spread awareness of
 136  the fact and hopefully to find a guy that I could forward any
 137  questions on the php zip module installation. But so far there is
 138  nothing, it merily seems that such installation problems are in no
 139  way related to zziplib anyway but exists <b>with any other module with a
 140  third party library dependency</b> as well. So the answers on php forum
 141  sites will ask for details of the current php and apache configuration.
 142 </P><P>
 143  Since I do not run a php zip whatever nor any other php stuff, it's
 144  just that those hints were not quite helpful to me. It would be really
 145  really great if someone with a php zip background could be so nice to
 146  write a short roundup of the areas to check when a php zip module
 147  installation fails, so that I could post it here. Where are you?
 148  Yours desperatly...&nbsp;;-)
 149 </P></DD>
 150 <DT><a name="license" />
 151  how to obtain a license and support contract for a commercial project </DT>
 152 <DD><P>
 153  The zziplib has been created as a spare time project and it is put
 154  under a very easy free public license. Even for commercial projects
 155  there is hardly any need to negotiate a separate license since the
 156  restrictions of the GNU LGPL or MPL can be matched easily. As a
 157  general hint, if the zziplib is shipped unmodified with your project
 158  then you are right within the limits of the free public license.
 159 </P><P>
 160  Sometimes the question for a personal license comes up for very
 161  different reason - the need for a support contract and/or the setting
 162  of functionality guarantees. The free public licenses include a safeguard
 163  clause to that end, "in the hope that it will be useful,
 164  but <em>without any warranty</em>; without even the implied warranty of
 165  <em>merchantability</em> or <em>fitness for a particular purpose</em>."
 166  Since the project was developed as a spare time project however there
 167  have never been personal licenses going beyond.
 168 </P><P>
 169  In general you can still try to negotiate a support contract but it
 170  will be very costly. It is much more profitable for you to tell one
 171  of your developers to have a look at the source code and ensure the
 172  required functionality is there, with hands on. The source code is
 173  written to be very readable, maintainable and extensible. Just be
 174  reminded that the free public licenses have restrictions on shipping
 175  modified binaries but I can give you a cheap personal license to
 176  escape these. (Such licenses can be obtained in return for tax-deductible
 177  donations to organisations supporting opensource software).
 178 </P></DD>
 179 </DL>
 180
 181 <P> and as always - <em> Patches are welcome </em> - </P>
 182 </section>