source/libs/zziplib/zziplib-0.13.62/docs/zzip-extras.htm

   1 <section><date> 20. July 2002 </date>
   2 <h2> ZZIP API extras </h2>             The check/init API description.
   3
   4 <!--border-->
   5
   6 <section>
   7 <h3> Extras </h3>
   8
   9 <P>
  10   The next requests circulated around other file-extensions to
  11   automagically look inside filetypes that have zip-format too but
  12   carry other fileextensions - most famous might be the ".PK3"
  13   files of ID's Quake game. There have been a number of these
  14   requests and in a lot of cases it dawned to me that those guys
  15   may have overlooked the zzip_dir_open functions to travel
  16   through documents of zipformat under any name - that is that the
  17   "magic" was not actually needed but they just wanted to read
  18   files in zipformat with the zziplib.
  19 </P>
  20
  21 <P>
  22   Other requests circulated around encryption but I did reject
  23   those bluntly, always. Instead there have been always examples
  24   for doing some obfuscation around the zip-format so that the
  25   stock zip/unzip tools do not recognize them but a game
  26   software developer can pack/unpack his AI scripts and bitmaps
  27   into such a zipformat-like file.
  28 </P>
  29
  30 <P>
  31   After some dead-end patches (being shipped along with the
  32   zziplib as configure-time compile-options - greetings to
  33   Lutz Sammer and Andreas Schiffler), the general approach
  34   of _ext_io came up, and finally implemented (greetings go
  35   to Mike Nordell). The _open()-calls do now each have a
  36   cousin of _open_ext_io() with two/three additional arguments
  37   being a set of extensions to loop through our magic testing,
  38   a callback-handler plugin-table for obfuscation-means,
  39   and (often) a bit-mask for extra-options - this bitmask even
  40   has "PREFERZIP" and "ONLYZIP" options to skip the real-file
  41   test magic in those <code>zzip_*open</code> functions.
  42 </P>
  43
  44 <table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
  45   <tr><td width=50%> zzip_open(name,flags) </td>
  46       <td width=50%> zzip_open_ext_io(name,flags,mode,ext,io) </td></tr>
  47   <tr><td width=50%> zzip_opendir(name) </td>
  48       <td width=50%> zzip_opendir_ext_io(name,mode,ext,io) </td></tr>
  49   <tr><td width=50%> zzip_dir_open(name,errp) </td>
  50       <td width=50%> zzip_dir_open_ext_io(name,errp,ext,io) </td></tr>
  51   <tr><td width=50%> zzip_dir_fdopen(fd,errp) </td>
  52       <td width=50%> zzip_dir_fdopen_ext_io(fd,errp,ext,io) </td></tr>
  53   <tr><td width=50%> zzip_file_open(dir,name,mode) </td>
  54       <td width=50%> zzip_file_open_ext_io(dir,name,mode,ext,io) </td></tr>
  55 </table></td></tr></table>
  56
  57 <P>
  58   Oh, and note that the mode,ext,io extras are memorized
  59   in the respecitive ZZIP_DIR handle attached, so each
  60   of the other calls like <code>zzip_file_open()</code>
  61   and <code>zzip_read()</code> will be using them. There
  62   are a few helper routines to help setup a new io-plugin
  63   where the init_io will currently just memcopy the
  64   default_io entries into the user-supplied plugin-struct.
  65 </P>
  66
  67 <table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
  68   <tr><td width=50%> zzip_init_io </td>
  69       <td width=50%> the recommended way to do things </td></tr>
  70   <tr><td width=50%> zzip_get_default_io </td>
  71       <td width=50%> used internally whenever you supply a null
  72                      for the io-argument of a _ext_io()-call </td></tr>
  73   <tr><td width=50%> zzip_get_default_ext </td>
  74       <td width=50%> used internally but not exported </td></tr>
  75 </table></td></tr></table>
  76
  77
  78 <P>
  79   And last some stdio-like replacements were build but these
  80   happen to be actually just small wrappers around the other
  81   posix-like magic-calls. It just offers some convenience
  82   since wrappers like "SDL_rwops" tend to use a stringised
  83   open-mode - and I took the occasion to fold the zzip-bits
  84   for the _ext_io-calls right in there recognized via
  85   special extensions to the openmode-string of zzip_fopen().
  86 </P>
  87
  88 <table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
  89   <tr><td width=50%> zzip_fopen </td>
  90       <td width=50%> convert stringmode and call zzip_open_ext_io </td></tr>
  91   <tr><td width=50%> zzip_fread </td>
  92       <td width=50%> slower way to say zzip_read </td></tr>
  93   <tr><td width=50%> zzip_fclose </td>
  94       <td width=50%> a synonym of zzip_close </td></tr>
  95 </table></td></tr></table>
  96
  97 <P>
  98   For some reason, people did need the full set of function-calls()
  99   to be working on zzip-wrappers too, so here they are - if the
 100   ZZIP_FILE instance did wrap a real file, then the real posix-call
 101   will be used, otherwise it is simulated on the compressed stream
 102   with a zip-contained file - especially <code>seek()</code> can be
 103   a slow operation:
 104   if the new point is later then just read out more bytes till we
 105   hit that position but if it is an earlier point then rewind to the
 106   beginning of the compressed data and start reading/decompression
 107   until the position is met.
 108 </P>
 109
 110 <table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
 111   <tr><td width=50%> zzip_rewind </td>
 112       <td width=50%> magic for rewind() </td></tr>
 113   <tr><td width=50%> zzip_tell </td>
 114       <td width=50%> magic for tell() </td></tr>
 115   <tr><td width=50%> zzip_seek </td>
 116       <td width=50%> magic for seek() </td></tr>
 117 </table></td></tr></table>
 118
 119 <P>
 120   And last not least, there are few informative functions to
 121   use function-calls to read parts of the opaque structures
 122   of zzip-objects and their zzip-factory.
 123 </P>
 124
 125 <table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
 126   <tr><td width=50%> zzip_dir_stat </td>
 127       <td width=50%> a stat()-like thing on a file within a ZZIP_DIR </td></tr>
 128   <tr><td width=50%> zzip_dir_real </td>
 129       <td width=50%> check if ZZIP_DIR wraps a stat'able posix-dirent</td></tr>
 130   <tr><td width=50%> zzip_file_real </td>
 131       <td width=50%> check if ZZIP_FILE wraps a stat'able posix-file </td></tr>
 132   <tr><td width=50%> zzip_realdir </td>
 133       <td width=50%> if zzip_dir_real then return the posix-dirent </td></tr>
 134   <tr><td width=50%> zzip_realfd </td>
 135       <td width=50%> if zzip_file_real then return the posix-file </td></tr>
 136   <tr><td width=50%> zzip_dirhandle </td>
 137       <td width=50%> the attached ZZIP_DIR of compressed ZZIP_FILE </td></tr>
 138   <tr><td width=50%> zzip_dirfd </td>
 139       <td width=50%> the attached posix-file of ZZIP_DIR zip-file </td></tr>
 140   <tr><td width=50%> zzip_set_error </td>
 141       <td width=50%> set the last ZZIP_DIR error-code </td></tr>
 142   <tr><td width=50%> zzip_error </td>
 143       <td width=50%> get the last ZZIP_DIR error-code </td></tr>
 144   <tr><td width=50%> zzip_strerror </td>
 145       <td width=50%> convert a zzip_error into a readable string </td></tr>
 146   <tr><td width=50%> zzip_strerror_of </td>
 147       <td width=50%> combine both above zzip_strerror of zzip_error </td></tr>
 148   <tr><td width=50%> zzip_errno </td>
 149       <td width=50%> helper to wrap a zzip-error to a posix-errno </td></tr>
 150   <tr><td width=50%> zzip_compr_str </td>
 151       <td width=50%> helper to wrap a compr-number to a readable string
 152                      </td></tr>
 153   <tr><td width=50%> zzip_dir_free </td>
 154       <td width=50%> internally called by zzip_dir_close if the ref-count
 155                      of the ZZIP_DIR has gone zero</td></tr>
 156   <tr><td width=50%> zzip_freopen </td>
 157       <td width=50%> to reuse the ZZIP_DIR from another ZZIP_FILE so it does
 158                      not need to be parsed again </td></tr>
 159   <tr><td width=50%> zzip_open_shared_io </td>
 160       <td width=50%> the ext/io cousin but it does not close the old ZZIP_FILE
 161                      and instead just shares the ZZIP_DIR if possible</td></tr>
 162 </table></td></tr></table>
 163
 164 </section></section>