1 <section> <date> 20. July 2002 </date>
2 <h2> ZZIP API Basics </h2> The open/close API description.
10 The naming schem of functions in this library follow a simple rule:
11 if you see a function with a <code>zzip_</code> prefix followed by
12 compact name representing otherwise a C library or posix function then
13 it is a magic wrapper that can automagically handle both real
14 files/directories or zip-contained files. This includes:
16 <table cellpadding=10 width=100%><tr><td><table width=100% border=1>
17 <tr><td width=50%> zzip_opendir </td><td width=50%> opendir </td></tr>
18 <tr><td width=50%> zzip_readdir </td><td width=50%> readdir </td></tr>
19 <tr><td width=50%> zzip_closedir </td><td width=50%> closedir </td></tr>
20 <tr><td width=50%> zzip_rewinddir </td><td width=50%> rewinddir </td></tr>
21 <tr><td width=50%> zzip_telldir </td><td width=50%> telldir </td></tr>
22 <tr><td width=50%> zzip_seekdir </td><td width=50%> seekdir </td></tr>
23 </table></td></tr></table>
25 The ZZIP_DIR handle can wrap both a real directory or a zip-file.
26 Note that you can not open a virtual directory <em>within</em> a
27 zip-file, the ZZIP_DIR is either a real DIR-handle of a real
28 directory or the reference of ZIP-file but never a DIR-handle
29 within a ZIP-file - there is no such schema of a SUB-DIR handle
30 implemented in this library. A ZZIP_DIR does actually represent
31 the central directory of a ZIP-file, so that each file entry in
32 this ZZIP-DIR can possibly have a subpath prepended.
36 This form of magic has historic reasons as originally the
37 magic wrappers of this library were not meant to wrap a complete
38 subtree of a real file tree but only a single directory being
39 wrapped with into a zip-file and placed instead. Later proposals
40 and patches were coming in to support subtree wrapping by not
41 only making a split between the dir-part and file-part but
42 going recursivly up through all "/"-dirseparators of a filepath
43 given to <code>zzip_open</code> and looking for zip-file there.
47 To open a zip-file unconditionally one should be using their
48 respective methods that would return a ZZIP_DIR handle being
49 the representant memory instance of a ZIP-DIR, the central
50 directory of a zip-file. From that ZZIP-DIR one can open a
51 compressed file entry which will be returned as a ZZIP_FILE
54 <table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
55 <tr><td width=50%> zzip_dir_open </td>
56 <td width=50%> open a zip-file and parse the central directory
57 to a memory shadow</td></tr>
58 <tr><td width=50%> zzip_dir_close </td>
59 <td width=50%> close a zip-file and free the memory shadow</td></tr>
60 <tr><td width=50%> zzip_dir_fdopen </td>
61 <td width=50%> aquire the given posix-file and try to parse it
62 as a zip-file.</td></tr>
63 <tr><td width=50%> zzip_dir_read </td>
64 <td width=50%> return the next info entry of a zip-file's central
65 directory - this would include a possible subpath </td></tr>
66 </table></td></tr></table>
69 To unconditionally access a zipped-file (as the counter-part of a
70 zip-file's directory) you should be using the functions having a
71 <code>zzip_file_</code> prefix which are the methods working on
72 ZZIP_FILE pointers directly and assuming those are references of
73 a zipped file with a ZZIP_DIR.
75 <table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
76 <tr><td width=50%> zzip_file_open </td>
77 <td width=50%> open a file within a zip and prepare a zlib
78 compressor for it - note the ZZIP_DIR argument,
79 multiple ZZIP_FILE's may share the same central
80 directory shadow.</td></tr>
81 <tr><td width=50%> zzip_file_close </td>
82 <td width=50%> close the handle of zippedfile
83 and free zlib compressor of it</td></tr>
84 <tr><td width=50%> zzip_file_read </td>
85 <td width=50%> decompress the next part of a compressed file
86 within a zip-file</td></tr>
87 </table></td></tr></table>
89 From here it is only a short step to the magic wrappers for
90 file-access - when being given a filepath to zzip_open then
91 the filepath is checked first for being possibly a real file
92 (we can often do that by a <code>stat</code> call) and if there is
93 a real file under that name then the returned ZZIP_FILE is
94 nothing more than a wrapper around a file-descriptor of the
95 underlying operating system. Any other calls like zzip_read
96 will see the realfd-flag in the ZZIP_FILE and forward the
97 execution to the read() function of the underlying operating system.
101 However if that fails then the filepath is cut at last directory
102 separator, i.e. a filepath of "this/test/README" is cut into the
103 dir-part "this/test" and a file-part "README". Then the possible
104 zip-extensions are attached (".zip" and ".ZIP") and we check if
105 there is a real file under that name. If a file "this/test.zip"
106 does exist then it is given to zzip_dir_open which will create
107 a ZZIP_DIR instance of it, and when that was successul (so it
108 was in zip-format) then we call zzip_file_open which will see
109 two arguments - the just opened ZZIP_DIR and the file-part. The
110 resulting ZZIP_FILE has its own copy of a ZZIP_DIR, so if you
111 open multiple files from the same zip-file than you will also
112 have multiple in-memory copies of the zip's central directory
113 whereas otherwise multiple ZZIP_FILE's may share a common
114 ZZIP_DIR when being opened with zzip_file_open directly - the
115 zzip_file_open's first argument is the ZZIP_DIR and the second
116 one the file-part to be looked up within that zip-directory.
119 <table cellpadding=10 width=100%><tr><td><table border=1 width=100%>
120 <tr><td width=50%> zzip_open </td>
121 <td width=50%> try the file-path as a real-file, and if not
122 there, look for the existance of ZZIP_DIR by
123 applying extensions, and open the file
124 contained within that one.</td></tr>
125 <tr><td width=50%> zzip_close </td>
126 <td width=50%> if the ZZIP_FILE wraps a real-file, then call
127 read(), otherwise call zzip_file_read() </td></tr>
128 <tr><td width=50%> zzip_close </td>
129 <td width=50%> if the ZZIP_FILE wraps a real-file, then call
130 close(), otherwise call zzip_file_close() </td></tr>
131 </table></td></tr></table>
134 Up to here we have the original functionality of the zziplib
135 when I (Guido Draheim) created the magic functions around the work from
136 Tomi Ollila who wrote the routines to read and decompress files from
137 a zip archive - unlike other libraries it was quite readable and
138 intelligible source code (after many changes there is not much
139 left of the original zip08x source code but that's another story).
140 Later however some request and proposals and patches were coming in.
144 Among the first extensions was the recursive zzip_open magic. In
145 the first instance, the library did just do as described above:
146 a file-path of "this/test/README" might be a zip-file known as
147 "this/test.zip" containing a compressed file "README". But if
148 there is neither a real file "this/test/README" and no real
149 zip-file "this/test.zip" then the call would have failed but
150 know the zzip_open call will recursivly check the parent
151 directories - so it can now find a zip-file "this.zip" which
152 contains a file-part "test/README".
156 This dissolves the original meaning of a ZZIP_DIR and it has lead
157 to some confusion later on - you can not create a DIRENT-like handle
158 for "this/test/" being within a "test.zip" file. And actually, I did
159 never see a reason to implement it so far (open "this.zip" and set
160 an initial subpath of "test" and let zzip_readdir skip all entries
161 that do not start with "test/"). This is left for excercie ;-)