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author | Maurus Cuelenaere <mcuelenaere@gmail.com> | 2008-07-11 15:50:46 +0000 |
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committer | Maurus Cuelenaere <mcuelenaere@gmail.com> | 2008-07-11 15:50:46 +0000 |
commit | 14c7f45cdae826f88dc539c8c38dd95caf305731 (patch) | |
tree | 832da054b7cfb2dc6fd63339af736625f31d21aa /utils/zenutils/libraries/zlib123/zlib/FAQ | |
parent | 7c84ede3781c27db73403bd6302f320c76a58c8c (diff) | |
download | rockbox-14c7f45cdae826f88dc539c8c38dd95caf305731.tar.gz rockbox-14c7f45cdae826f88dc539c8c38dd95caf305731.zip |
Add zook's ZenUtils to SVN
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@18010 a1c6a512-1295-4272-9138-f99709370657
Diffstat (limited to 'utils/zenutils/libraries/zlib123/zlib/FAQ')
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1 | |||
2 | Frequently Asked Questions about zlib | ||
3 | |||
4 | |||
5 | If your question is not there, please check the zlib home page | ||
6 | http://www.zlib.org which may have more recent information. | ||
7 | The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html | ||
8 | |||
9 | |||
10 | 1. Is zlib Y2K-compliant? | ||
11 | |||
12 | Yes. zlib doesn't handle dates. | ||
13 | |||
14 | 2. Where can I get a Windows DLL version? | ||
15 | |||
16 | The zlib sources can be compiled without change to produce a DLL. | ||
17 | See the file win32/DLL_FAQ.txt in the zlib distribution. | ||
18 | Pointers to the precompiled DLL are found in the zlib web site at | ||
19 | http://www.zlib.org. | ||
20 | |||
21 | 3. Where can I get a Visual Basic interface to zlib? | ||
22 | |||
23 | See | ||
24 | * http://www.dogma.net/markn/articles/zlibtool/zlibtool.htm | ||
25 | * contrib/visual-basic.txt in the zlib distribution | ||
26 | * win32/DLL_FAQ.txt in the zlib distribution | ||
27 | |||
28 | 4. compress() returns Z_BUF_ERROR. | ||
29 | |||
30 | Make sure that before the call of compress, the length of the compressed | ||
31 | buffer is equal to the total size of the compressed buffer and not | ||
32 | zero. For Visual Basic, check that this parameter is passed by reference | ||
33 | ("as any"), not by value ("as long"). | ||
34 | |||
35 | 5. deflate() or inflate() returns Z_BUF_ERROR. | ||
36 | |||
37 | Before making the call, make sure that avail_in and avail_out are not | ||
38 | zero. When setting the parameter flush equal to Z_FINISH, also make sure | ||
39 | that avail_out is big enough to allow processing all pending input. | ||
40 | Note that a Z_BUF_ERROR is not fatal--another call to deflate() or | ||
41 | inflate() can be made with more input or output space. A Z_BUF_ERROR | ||
42 | may in fact be unavoidable depending on how the functions are used, since | ||
43 | it is not possible to tell whether or not there is more output pending | ||
44 | when strm.avail_out returns with zero. | ||
45 | |||
46 | 6. Where's the zlib documentation (man pages, etc.)? | ||
47 | |||
48 | It's in zlib.h for the moment, and Francis S. Lin has converted it to a | ||
49 | web page zlib.html. Volunteers to transform this to Unix-style man pages, | ||
50 | please contact us (zlib@gzip.org). Examples of zlib usage are in the files | ||
51 | example.c and minigzip.c. | ||
52 | |||
53 | 7. Why don't you use GNU autoconf or libtool or ...? | ||
54 | |||
55 | Because we would like to keep zlib as a very small and simple | ||
56 | package. zlib is rather portable and doesn't need much configuration. | ||
57 | |||
58 | 8. I found a bug in zlib. | ||
59 | |||
60 | Most of the time, such problems are due to an incorrect usage of | ||
61 | zlib. Please try to reproduce the problem with a small program and send | ||
62 | the corresponding source to us at zlib@gzip.org . Do not send | ||
63 | multi-megabyte data files without prior agreement. | ||
64 | |||
65 | 9. Why do I get "undefined reference to gzputc"? | ||
66 | |||
67 | If "make test" produces something like | ||
68 | |||
69 | example.o(.text+0x154): undefined reference to `gzputc' | ||
70 | |||
71 | check that you don't have old files libz.* in /usr/lib, /usr/local/lib or | ||
72 | /usr/X11R6/lib. Remove any old versions, then do "make install". | ||
73 | |||
74 | 10. I need a Delphi interface to zlib. | ||
75 | |||
76 | See the contrib/delphi directory in the zlib distribution. | ||
77 | |||
78 | 11. Can zlib handle .zip archives? | ||
79 | |||
80 | Not by itself, no. See the directory contrib/minizip in the zlib | ||
81 | distribution. | ||
82 | |||
83 | 12. Can zlib handle .Z files? | ||
84 | |||
85 | No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt | ||
86 | the code of uncompress on your own. | ||
87 | |||
88 | 13. How can I make a Unix shared library? | ||
89 | |||
90 | make clean | ||
91 | ./configure -s | ||
92 | make | ||
93 | |||
94 | 14. How do I install a shared zlib library on Unix? | ||
95 | |||
96 | After the above, then: | ||
97 | |||
98 | make install | ||
99 | |||
100 | However, many flavors of Unix come with a shared zlib already installed. | ||
101 | Before going to the trouble of compiling a shared version of zlib and | ||
102 | trying to install it, you may want to check if it's already there! If you | ||
103 | can #include <zlib.h>, it's there. The -lz option will probably link to it. | ||
104 | |||
105 | 15. I have a question about OttoPDF. | ||
106 | |||
107 | We are not the authors of OttoPDF. The real author is on the OttoPDF web | ||
108 | site: Joel Hainley, jhainley@myndkryme.com. | ||
109 | |||
110 | 16. Can zlib decode Flate data in an Adobe PDF file? | ||
111 | |||
112 | Yes. See http://www.fastio.com/ (ClibPDF), or http://www.pdflib.com/ . | ||
113 | To modify PDF forms, see http://sourceforge.net/projects/acroformtool/ . | ||
114 | |||
115 | 17. Why am I getting this "register_frame_info not found" error on Solaris? | ||
116 | |||
117 | After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib | ||
118 | generates an error such as: | ||
119 | |||
120 | ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so: | ||
121 | symbol __register_frame_info: referenced symbol not found | ||
122 | |||
123 | The symbol __register_frame_info is not part of zlib, it is generated by | ||
124 | the C compiler (cc or gcc). You must recompile applications using zlib | ||
125 | which have this problem. This problem is specific to Solaris. See | ||
126 | http://www.sunfreeware.com for Solaris versions of zlib and applications | ||
127 | using zlib. | ||
128 | |||
129 | 18. Why does gzip give an error on a file I make with compress/deflate? | ||
130 | |||
131 | The compress and deflate functions produce data in the zlib format, which | ||
132 | is different and incompatible with the gzip format. The gz* functions in | ||
133 | zlib on the other hand use the gzip format. Both the zlib and gzip | ||
134 | formats use the same compressed data format internally, but have different | ||
135 | headers and trailers around the compressed data. | ||
136 | |||
137 | 19. Ok, so why are there two different formats? | ||
138 | |||
139 | The gzip format was designed to retain the directory information about | ||
140 | a single file, such as the name and last modification date. The zlib | ||
141 | format on the other hand was designed for in-memory and communication | ||
142 | channel applications, and has a much more compact header and trailer and | ||
143 | uses a faster integrity check than gzip. | ||
144 | |||
145 | 20. Well that's nice, but how do I make a gzip file in memory? | ||
146 | |||
147 | You can request that deflate write the gzip format instead of the zlib | ||
148 | format using deflateInit2(). You can also request that inflate decode | ||
149 | the gzip format using inflateInit2(). Read zlib.h for more details. | ||
150 | |||
151 | 21. Is zlib thread-safe? | ||
152 | |||
153 | Yes. However any library routines that zlib uses and any application- | ||
154 | provided memory allocation routines must also be thread-safe. zlib's gz* | ||
155 | functions use stdio library routines, and most of zlib's functions use the | ||
156 | library memory allocation routines by default. zlib's Init functions allow | ||
157 | for the application to provide custom memory allocation routines. | ||
158 | |||
159 | Of course, you should only operate on any given zlib or gzip stream from a | ||
160 | single thread at a time. | ||
161 | |||
162 | 22. Can I use zlib in my commercial application? | ||
163 | |||
164 | Yes. Please read the license in zlib.h. | ||
165 | |||
166 | 23. Is zlib under the GNU license? | ||
167 | |||
168 | No. Please read the license in zlib.h. | ||
169 | |||
170 | 24. The license says that altered source versions must be "plainly marked". So | ||
171 | what exactly do I need to do to meet that requirement? | ||
172 | |||
173 | You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In | ||
174 | particular, the final version number needs to be changed to "f", and an | ||
175 | identification string should be appended to ZLIB_VERSION. Version numbers | ||
176 | x.x.x.f are reserved for modifications to zlib by others than the zlib | ||
177 | maintainers. For example, if the version of the base zlib you are altering | ||
178 | is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and | ||
179 | ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3". You can also | ||
180 | update the version strings in deflate.c and inftrees.c. | ||
181 | |||
182 | For altered source distributions, you should also note the origin and | ||
183 | nature of the changes in zlib.h, as well as in ChangeLog and README, along | ||
184 | with the dates of the alterations. The origin should include at least your | ||
185 | name (or your company's name), and an email address to contact for help or | ||
186 | issues with the library. | ||
187 | |||
188 | Note that distributing a compiled zlib library along with zlib.h and | ||
189 | zconf.h is also a source distribution, and so you should change | ||
190 | ZLIB_VERSION and ZLIB_VERNUM and note the origin and nature of the changes | ||
191 | in zlib.h as you would for a full source distribution. | ||
192 | |||
193 | 25. Will zlib work on a big-endian or little-endian architecture, and can I | ||
194 | exchange compressed data between them? | ||
195 | |||
196 | Yes and yes. | ||
197 | |||
198 | 26. Will zlib work on a 64-bit machine? | ||
199 | |||
200 | It should. It has been tested on 64-bit machines, and has no dependence | ||
201 | on any data types being limited to 32-bits in length. If you have any | ||
202 | difficulties, please provide a complete problem report to zlib@gzip.org | ||
203 | |||
204 | 27. Will zlib decompress data from the PKWare Data Compression Library? | ||
205 | |||
206 | No. The PKWare DCL uses a completely different compressed data format | ||
207 | than does PKZIP and zlib. However, you can look in zlib's contrib/blast | ||
208 | directory for a possible solution to your problem. | ||
209 | |||
210 | 28. Can I access data randomly in a compressed stream? | ||
211 | |||
212 | No, not without some preparation. If when compressing you periodically | ||
213 | use Z_FULL_FLUSH, carefully write all the pending data at those points, | ||
214 | and keep an index of those locations, then you can start decompression | ||
215 | at those points. You have to be careful to not use Z_FULL_FLUSH too | ||
216 | often, since it can significantly degrade compression. | ||
217 | |||
218 | 29. Does zlib work on MVS, OS/390, CICS, etc.? | ||
219 | |||
220 | We don't know for sure. We have heard occasional reports of success on | ||
221 | these systems. If you do use it on one of these, please provide us with | ||
222 | a report, instructions, and patches that we can reference when we get | ||
223 | these questions. Thanks. | ||
224 | |||
225 | 30. Is there some simpler, easier to read version of inflate I can look at | ||
226 | to understand the deflate format? | ||
227 | |||
228 | First off, you should read RFC 1951. Second, yes. Look in zlib's | ||
229 | contrib/puff directory. | ||
230 | |||
231 | 31. Does zlib infringe on any patents? | ||
232 | |||
233 | As far as we know, no. In fact, that was originally the whole point behind | ||
234 | zlib. Look here for some more information: | ||
235 | |||
236 | http://www.gzip.org/#faq11 | ||
237 | |||
238 | 32. Can zlib work with greater than 4 GB of data? | ||
239 | |||
240 | Yes. inflate() and deflate() will process any amount of data correctly. | ||
241 | Each call of inflate() or deflate() is limited to input and output chunks | ||
242 | of the maximum value that can be stored in the compiler's "unsigned int" | ||
243 | type, but there is no limit to the number of chunks. Note however that the | ||
244 | strm.total_in and strm_total_out counters may be limited to 4 GB. These | ||
245 | counters are provided as a convenience and are not used internally by | ||
246 | inflate() or deflate(). The application can easily set up its own counters | ||
247 | updated after each call of inflate() or deflate() to count beyond 4 GB. | ||
248 | compress() and uncompress() may be limited to 4 GB, since they operate in a | ||
249 | single call. gzseek() and gztell() may be limited to 4 GB depending on how | ||
250 | zlib is compiled. See the zlibCompileFlags() function in zlib.h. | ||
251 | |||
252 | The word "may" appears several times above since there is a 4 GB limit | ||
253 | only if the compiler's "long" type is 32 bits. If the compiler's "long" | ||
254 | type is 64 bits, then the limit is 16 exabytes. | ||
255 | |||
256 | 33. Does zlib have any security vulnerabilities? | ||
257 | |||
258 | The only one that we are aware of is potentially in gzprintf(). If zlib | ||
259 | is compiled to use sprintf() or vsprintf(), then there is no protection | ||
260 | against a buffer overflow of a 4K string space, other than the caller of | ||
261 | gzprintf() assuring that the output will not exceed 4K. On the other | ||
262 | hand, if zlib is compiled to use snprintf() or vsnprintf(), which should | ||
263 | normally be the case, then there is no vulnerability. The ./configure | ||
264 | script will display warnings if an insecure variation of sprintf() will | ||
265 | be used by gzprintf(). Also the zlibCompileFlags() function will return | ||
266 | information on what variant of sprintf() is used by gzprintf(). | ||
267 | |||
268 | If you don't have snprintf() or vsnprintf() and would like one, you can | ||
269 | find a portable implementation here: | ||
270 | |||
271 | http://www.ijs.si/software/snprintf/ | ||
272 | |||
273 | Note that you should be using the most recent version of zlib. Versions | ||
274 | 1.1.3 and before were subject to a double-free vulnerability. | ||
275 | |||
276 | 34. Is there a Java version of zlib? | ||
277 | |||
278 | Probably what you want is to use zlib in Java. zlib is already included | ||
279 | as part of the Java SDK in the java.util.zip package. If you really want | ||
280 | a version of zlib written in the Java language, look on the zlib home | ||
281 | page for links: http://www.zlib.org/ | ||
282 | |||
283 | 35. I get this or that compiler or source-code scanner warning when I crank it | ||
284 | up to maximally-pedantic. Can't you guys write proper code? | ||
285 | |||
286 | Many years ago, we gave up attempting to avoid warnings on every compiler | ||
287 | in the universe. It just got to be a waste of time, and some compilers | ||
288 | were downright silly. So now, we simply make sure that the code always | ||
289 | works. | ||
290 | |||
291 | 36. Valgrind (or some similar memory access checker) says that deflate is | ||
292 | performing a conditional jump that depends on an uninitialized value. | ||
293 | Isn't that a bug? | ||
294 | |||
295 | No. That is intentional for performance reasons, and the output of | ||
296 | deflate is not affected. This only started showing up recently since | ||
297 | zlib 1.2.x uses malloc() by default for allocations, whereas earlier | ||
298 | versions used calloc(), which zeros out the allocated memory. | ||
299 | |||
300 | 37. Will zlib read the (insert any ancient or arcane format here) compressed | ||
301 | data format? | ||
302 | |||
303 | Probably not. Look in the comp.compression FAQ for pointers to various | ||
304 | formats and associated software. | ||
305 | |||
306 | 38. How can I encrypt/decrypt zip files with zlib? | ||
307 | |||
308 | zlib doesn't support encryption. The original PKZIP encryption is very weak | ||
309 | and can be broken with freely available programs. To get strong encryption, | ||
310 | use GnuPG, http://www.gnupg.org/ , which already includes zlib compression. | ||
311 | For PKZIP compatible "encryption", look at http://www.info-zip.org/ | ||
312 | |||
313 | 39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings? | ||
314 | |||
315 | "gzip" is the gzip format, and "deflate" is the zlib format. They should | ||
316 | probably have called the second one "zlib" instead to avoid confusion | ||
317 | with the raw deflate compressed data format. While the HTTP 1.1 RFC 2616 | ||
318 | correctly points to the zlib specification in RFC 1950 for the "deflate" | ||
319 | transfer encoding, there have been reports of servers and browsers that | ||
320 | incorrectly produce or expect raw deflate data per the deflate | ||
321 | specficiation in RFC 1951, most notably Microsoft. So even though the | ||
322 | "deflate" transfer encoding using the zlib format would be the more | ||
323 | efficient approach (and in fact exactly what the zlib format was designed | ||
324 | for), using the "gzip" transfer encoding is probably more reliable due to | ||
325 | an unfortunate choice of name on the part of the HTTP 1.1 authors. | ||
326 | |||
327 | Bottom line: use the gzip format for HTTP 1.1 encoding. | ||
328 | |||
329 | 40. Does zlib support the new "Deflate64" format introduced by PKWare? | ||
330 | |||
331 | No. PKWare has apparently decided to keep that format proprietary, since | ||
332 | they have not documented it as they have previous compression formats. | ||
333 | In any case, the compression improvements are so modest compared to other | ||
334 | more modern approaches, that it's not worth the effort to implement. | ||
335 | |||
336 | 41. Can you please sign these lengthy legal documents and fax them back to us | ||
337 | so that we can use your software in our product? | ||
338 | |||
339 | No. Go away. Shoo. | ||