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author | Nicolas Pennequin <nicolas.pennequin@free.fr> | 2008-07-11 16:51:25 +0000 |
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committer | Nicolas Pennequin <nicolas.pennequin@free.fr> | 2008-07-11 16:51:25 +0000 |
commit | ca5bb76d2b8f65aa97e50b633f828c1deb241526 (patch) | |
tree | 453a1b2de3a0dc0d0b2f7080d10d033bf8fbcdf1 /utils/zenutils/libraries/zlib123/zlib/FAQ | |
parent | 141774be48940d56e3ad4dbf451d245b61d4f8b2 (diff) | |
download | rockbox-ca5bb76d2b8f65aa97e50b633f828c1deb241526.tar.gz rockbox-ca5bb76d2b8f65aa97e50b633f828c1deb241526.zip |
Delete the svn:executable property and set svn:eol-style to native for all those text files.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@18012 a1c6a512-1295-4272-9138-f99709370657
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1 | 1 | ||
2 | Frequently Asked Questions about zlib | 2 | Frequently Asked Questions about zlib |
3 | 3 | ||
4 | 4 | ||
5 | If your question is not there, please check the zlib home page | 5 | If your question is not there, please check the zlib home page |
6 | http://www.zlib.org which may have more recent information. | 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 | 7 | The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html |
8 | 8 | ||
9 | 9 | ||
10 | 1. Is zlib Y2K-compliant? | 10 | 1. Is zlib Y2K-compliant? |
11 | 11 | ||
12 | Yes. zlib doesn't handle dates. | 12 | Yes. zlib doesn't handle dates. |
13 | 13 | ||
14 | 2. Where can I get a Windows DLL version? | 14 | 2. Where can I get a Windows DLL version? |
15 | 15 | ||
16 | The zlib sources can be compiled without change to produce a DLL. | 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. | 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 | 18 | Pointers to the precompiled DLL are found in the zlib web site at |
19 | http://www.zlib.org. | 19 | http://www.zlib.org. |
20 | 20 | ||
21 | 3. Where can I get a Visual Basic interface to zlib? | 21 | 3. Where can I get a Visual Basic interface to zlib? |
22 | 22 | ||
23 | See | 23 | See |
24 | * http://www.dogma.net/markn/articles/zlibtool/zlibtool.htm | 24 | * http://www.dogma.net/markn/articles/zlibtool/zlibtool.htm |
25 | * contrib/visual-basic.txt in the zlib distribution | 25 | * contrib/visual-basic.txt in the zlib distribution |
26 | * win32/DLL_FAQ.txt in the zlib distribution | 26 | * win32/DLL_FAQ.txt in the zlib distribution |
27 | 27 | ||
28 | 4. compress() returns Z_BUF_ERROR. | 28 | 4. compress() returns Z_BUF_ERROR. |
29 | 29 | ||
30 | Make sure that before the call of compress, the length of the compressed | 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 | 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 | 32 | zero. For Visual Basic, check that this parameter is passed by reference |
33 | ("as any"), not by value ("as long"). | 33 | ("as any"), not by value ("as long"). |
34 | 34 | ||
35 | 5. deflate() or inflate() returns Z_BUF_ERROR. | 35 | 5. deflate() or inflate() returns Z_BUF_ERROR. |
36 | 36 | ||
37 | Before making the call, make sure that avail_in and avail_out are not | 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 | 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. | 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 | 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 | 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 | 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 | 43 | it is not possible to tell whether or not there is more output pending |
44 | when strm.avail_out returns with zero. | 44 | when strm.avail_out returns with zero. |
45 | 45 | ||
46 | 6. Where's the zlib documentation (man pages, etc.)? | 46 | 6. Where's the zlib documentation (man pages, etc.)? |
47 | 47 | ||
48 | It's in zlib.h for the moment, and Francis S. Lin has converted it to a | 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, | 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 | 50 | please contact us (zlib@gzip.org). Examples of zlib usage are in the files |
51 | example.c and minigzip.c. | 51 | example.c and minigzip.c. |
52 | 52 | ||
53 | 7. Why don't you use GNU autoconf or libtool or ...? | 53 | 7. Why don't you use GNU autoconf or libtool or ...? |
54 | 54 | ||
55 | Because we would like to keep zlib as a very small and simple | 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. | 56 | package. zlib is rather portable and doesn't need much configuration. |
57 | 57 | ||
58 | 8. I found a bug in zlib. | 58 | 8. I found a bug in zlib. |
59 | 59 | ||
60 | Most of the time, such problems are due to an incorrect usage of | 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 | 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 | 62 | the corresponding source to us at zlib@gzip.org . Do not send |
63 | multi-megabyte data files without prior agreement. | 63 | multi-megabyte data files without prior agreement. |
64 | 64 | ||
65 | 9. Why do I get "undefined reference to gzputc"? | 65 | 9. Why do I get "undefined reference to gzputc"? |
66 | 66 | ||
67 | If "make test" produces something like | 67 | If "make test" produces something like |
68 | 68 | ||
69 | example.o(.text+0x154): undefined reference to `gzputc' | 69 | example.o(.text+0x154): undefined reference to `gzputc' |
70 | 70 | ||
71 | check that you don't have old files libz.* in /usr/lib, /usr/local/lib or | 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". | 72 | /usr/X11R6/lib. Remove any old versions, then do "make install". |
73 | 73 | ||
74 | 10. I need a Delphi interface to zlib. | 74 | 10. I need a Delphi interface to zlib. |
75 | 75 | ||
76 | See the contrib/delphi directory in the zlib distribution. | 76 | See the contrib/delphi directory in the zlib distribution. |
77 | 77 | ||
78 | 11. Can zlib handle .zip archives? | 78 | 11. Can zlib handle .zip archives? |
79 | 79 | ||
80 | Not by itself, no. See the directory contrib/minizip in the zlib | 80 | Not by itself, no. See the directory contrib/minizip in the zlib |
81 | distribution. | 81 | distribution. |
82 | 82 | ||
83 | 12. Can zlib handle .Z files? | 83 | 12. Can zlib handle .Z files? |
84 | 84 | ||
85 | No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt | 85 | No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt |
86 | the code of uncompress on your own. | 86 | the code of uncompress on your own. |
87 | 87 | ||
88 | 13. How can I make a Unix shared library? | 88 | 13. How can I make a Unix shared library? |
89 | 89 | ||
90 | make clean | 90 | make clean |
91 | ./configure -s | 91 | ./configure -s |
92 | make | 92 | make |
93 | 93 | ||
94 | 14. How do I install a shared zlib library on Unix? | 94 | 14. How do I install a shared zlib library on Unix? |
95 | 95 | ||
96 | After the above, then: | 96 | After the above, then: |
97 | 97 | ||
98 | make install | 98 | make install |
99 | 99 | ||
100 | However, many flavors of Unix come with a shared zlib already installed. | 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 | 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 | 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. | 103 | can #include <zlib.h>, it's there. The -lz option will probably link to it. |
104 | 104 | ||
105 | 15. I have a question about OttoPDF. | 105 | 15. I have a question about OttoPDF. |
106 | 106 | ||
107 | We are not the authors of OttoPDF. The real author is on the OttoPDF web | 107 | We are not the authors of OttoPDF. The real author is on the OttoPDF web |
108 | site: Joel Hainley, jhainley@myndkryme.com. | 108 | site: Joel Hainley, jhainley@myndkryme.com. |
109 | 109 | ||
110 | 16. Can zlib decode Flate data in an Adobe PDF file? | 110 | 16. Can zlib decode Flate data in an Adobe PDF file? |
111 | 111 | ||
112 | Yes. See http://www.fastio.com/ (ClibPDF), or http://www.pdflib.com/ . | 112 | Yes. See http://www.fastio.com/ (ClibPDF), or http://www.pdflib.com/ . |
113 | To modify PDF forms, see http://sourceforge.net/projects/acroformtool/ . | 113 | To modify PDF forms, see http://sourceforge.net/projects/acroformtool/ . |
114 | 114 | ||
115 | 17. Why am I getting this "register_frame_info not found" error on Solaris? | 115 | 17. Why am I getting this "register_frame_info not found" error on Solaris? |
116 | 116 | ||
117 | After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib | 117 | After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib |
118 | generates an error such as: | 118 | generates an error such as: |
119 | 119 | ||
120 | ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so: | 120 | ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so: |
121 | symbol __register_frame_info: referenced symbol not found | 121 | symbol __register_frame_info: referenced symbol not found |
122 | 122 | ||
123 | The symbol __register_frame_info is not part of zlib, it is generated by | 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 | 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 | 125 | which have this problem. This problem is specific to Solaris. See |
126 | http://www.sunfreeware.com for Solaris versions of zlib and applications | 126 | http://www.sunfreeware.com for Solaris versions of zlib and applications |
127 | using zlib. | 127 | using zlib. |
128 | 128 | ||
129 | 18. Why does gzip give an error on a file I make with compress/deflate? | 129 | 18. Why does gzip give an error on a file I make with compress/deflate? |
130 | 130 | ||
131 | The compress and deflate functions produce data in the zlib format, which | 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 | 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 | 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 | 134 | formats use the same compressed data format internally, but have different |
135 | headers and trailers around the compressed data. | 135 | headers and trailers around the compressed data. |
136 | 136 | ||
137 | 19. Ok, so why are there two different formats? | 137 | 19. Ok, so why are there two different formats? |
138 | 138 | ||
139 | The gzip format was designed to retain the directory information about | 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 | 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 | 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 | 142 | channel applications, and has a much more compact header and trailer and |
143 | uses a faster integrity check than gzip. | 143 | uses a faster integrity check than gzip. |
144 | 144 | ||
145 | 20. Well that's nice, but how do I make a gzip file in memory? | 145 | 20. Well that's nice, but how do I make a gzip file in memory? |
146 | 146 | ||
147 | You can request that deflate write the gzip format instead of the zlib | 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 | 148 | format using deflateInit2(). You can also request that inflate decode |
149 | the gzip format using inflateInit2(). Read zlib.h for more details. | 149 | the gzip format using inflateInit2(). Read zlib.h for more details. |
150 | 150 | ||
151 | 21. Is zlib thread-safe? | 151 | 21. Is zlib thread-safe? |
152 | 152 | ||
153 | Yes. However any library routines that zlib uses and any application- | 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* | 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 | 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 | 156 | library memory allocation routines by default. zlib's Init functions allow |
157 | for the application to provide custom memory allocation routines. | 157 | for the application to provide custom memory allocation routines. |
158 | 158 | ||
159 | Of course, you should only operate on any given zlib or gzip stream from a | 159 | Of course, you should only operate on any given zlib or gzip stream from a |
160 | single thread at a time. | 160 | single thread at a time. |
161 | 161 | ||
162 | 22. Can I use zlib in my commercial application? | 162 | 22. Can I use zlib in my commercial application? |
163 | 163 | ||
164 | Yes. Please read the license in zlib.h. | 164 | Yes. Please read the license in zlib.h. |
165 | 165 | ||
166 | 23. Is zlib under the GNU license? | 166 | 23. Is zlib under the GNU license? |
167 | 167 | ||
168 | No. Please read the license in zlib.h. | 168 | No. Please read the license in zlib.h. |
169 | 169 | ||
170 | 24. The license says that altered source versions must be "plainly marked". So | 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? | 171 | what exactly do I need to do to meet that requirement? |
172 | 172 | ||
173 | You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In | 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 | 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 | 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 | 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 | 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 | 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 | 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. | 180 | update the version strings in deflate.c and inftrees.c. |
181 | 181 | ||
182 | For altered source distributions, you should also note the origin and | 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 | 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 | 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 | 185 | name (or your company's name), and an email address to contact for help or |
186 | issues with the library. | 186 | issues with the library. |
187 | 187 | ||
188 | Note that distributing a compiled zlib library along with zlib.h and | 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 | 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 | 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. | 191 | in zlib.h as you would for a full source distribution. |
192 | 192 | ||
193 | 25. Will zlib work on a big-endian or little-endian architecture, and can I | 193 | 25. Will zlib work on a big-endian or little-endian architecture, and can I |
194 | exchange compressed data between them? | 194 | exchange compressed data between them? |
195 | 195 | ||
196 | Yes and yes. | 196 | Yes and yes. |
197 | 197 | ||
198 | 26. Will zlib work on a 64-bit machine? | 198 | 26. Will zlib work on a 64-bit machine? |
199 | 199 | ||
200 | It should. It has been tested on 64-bit machines, and has no dependence | 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 | 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 | 202 | difficulties, please provide a complete problem report to zlib@gzip.org |
203 | 203 | ||
204 | 27. Will zlib decompress data from the PKWare Data Compression Library? | 204 | 27. Will zlib decompress data from the PKWare Data Compression Library? |
205 | 205 | ||
206 | No. The PKWare DCL uses a completely different compressed data format | 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 | 207 | than does PKZIP and zlib. However, you can look in zlib's contrib/blast |
208 | directory for a possible solution to your problem. | 208 | directory for a possible solution to your problem. |
209 | 209 | ||
210 | 28. Can I access data randomly in a compressed stream? | 210 | 28. Can I access data randomly in a compressed stream? |
211 | 211 | ||
212 | No, not without some preparation. If when compressing you periodically | 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, | 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 | 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 | 215 | at those points. You have to be careful to not use Z_FULL_FLUSH too |
216 | often, since it can significantly degrade compression. | 216 | often, since it can significantly degrade compression. |
217 | 217 | ||
218 | 29. Does zlib work on MVS, OS/390, CICS, etc.? | 218 | 29. Does zlib work on MVS, OS/390, CICS, etc.? |
219 | 219 | ||
220 | We don't know for sure. We have heard occasional reports of success on | 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 | 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 | 222 | a report, instructions, and patches that we can reference when we get |
223 | these questions. Thanks. | 223 | these questions. Thanks. |
224 | 224 | ||
225 | 30. Is there some simpler, easier to read version of inflate I can look at | 225 | 30. Is there some simpler, easier to read version of inflate I can look at |
226 | to understand the deflate format? | 226 | to understand the deflate format? |
227 | 227 | ||
228 | First off, you should read RFC 1951. Second, yes. Look in zlib's | 228 | First off, you should read RFC 1951. Second, yes. Look in zlib's |
229 | contrib/puff directory. | 229 | contrib/puff directory. |
230 | 230 | ||
231 | 31. Does zlib infringe on any patents? | 231 | 31. Does zlib infringe on any patents? |
232 | 232 | ||
233 | As far as we know, no. In fact, that was originally the whole point behind | 233 | As far as we know, no. In fact, that was originally the whole point behind |
234 | zlib. Look here for some more information: | 234 | zlib. Look here for some more information: |
235 | 235 | ||
236 | http://www.gzip.org/#faq11 | 236 | http://www.gzip.org/#faq11 |
237 | 237 | ||
238 | 32. Can zlib work with greater than 4 GB of data? | 238 | 32. Can zlib work with greater than 4 GB of data? |
239 | 239 | ||
240 | Yes. inflate() and deflate() will process any amount of data correctly. | 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 | 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" | 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 | 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 | 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 | 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 | 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. | 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 | 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 | 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. | 250 | zlib is compiled. See the zlibCompileFlags() function in zlib.h. |
251 | 251 | ||
252 | The word "may" appears several times above since there is a 4 GB limit | 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" | 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. | 254 | type is 64 bits, then the limit is 16 exabytes. |
255 | 255 | ||
256 | 33. Does zlib have any security vulnerabilities? | 256 | 33. Does zlib have any security vulnerabilities? |
257 | 257 | ||
258 | The only one that we are aware of is potentially in gzprintf(). If zlib | 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 | 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 | 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 | 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 | 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 | 263 | normally be the case, then there is no vulnerability. The ./configure |
264 | script will display warnings if an insecure variation of sprintf() will | 264 | script will display warnings if an insecure variation of sprintf() will |
265 | be used by gzprintf(). Also the zlibCompileFlags() function will return | 265 | be used by gzprintf(). Also the zlibCompileFlags() function will return |
266 | information on what variant of sprintf() is used by gzprintf(). | 266 | information on what variant of sprintf() is used by gzprintf(). |
267 | 267 | ||
268 | If you don't have snprintf() or vsnprintf() and would like one, you can | 268 | If you don't have snprintf() or vsnprintf() and would like one, you can |
269 | find a portable implementation here: | 269 | find a portable implementation here: |
270 | 270 | ||
271 | http://www.ijs.si/software/snprintf/ | 271 | http://www.ijs.si/software/snprintf/ |
272 | 272 | ||
273 | Note that you should be using the most recent version of zlib. Versions | 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. | 274 | 1.1.3 and before were subject to a double-free vulnerability. |
275 | 275 | ||
276 | 34. Is there a Java version of zlib? | 276 | 34. Is there a Java version of zlib? |
277 | 277 | ||
278 | Probably what you want is to use zlib in Java. zlib is already included | 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 | 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 | 280 | a version of zlib written in the Java language, look on the zlib home |
281 | page for links: http://www.zlib.org/ | 281 | page for links: http://www.zlib.org/ |
282 | 282 | ||
283 | 35. I get this or that compiler or source-code scanner warning when I crank it | 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? | 284 | up to maximally-pedantic. Can't you guys write proper code? |
285 | 285 | ||
286 | Many years ago, we gave up attempting to avoid warnings on every compiler | 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 | 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 | 288 | were downright silly. So now, we simply make sure that the code always |
289 | works. | 289 | works. |
290 | 290 | ||
291 | 36. Valgrind (or some similar memory access checker) says that deflate is | 291 | 36. Valgrind (or some similar memory access checker) says that deflate is |
292 | performing a conditional jump that depends on an uninitialized value. | 292 | performing a conditional jump that depends on an uninitialized value. |
293 | Isn't that a bug? | 293 | Isn't that a bug? |
294 | 294 | ||
295 | No. That is intentional for performance reasons, and the output of | 295 | No. That is intentional for performance reasons, and the output of |
296 | deflate is not affected. This only started showing up recently since | 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 | 297 | zlib 1.2.x uses malloc() by default for allocations, whereas earlier |
298 | versions used calloc(), which zeros out the allocated memory. | 298 | versions used calloc(), which zeros out the allocated memory. |
299 | 299 | ||
300 | 37. Will zlib read the (insert any ancient or arcane format here) compressed | 300 | 37. Will zlib read the (insert any ancient or arcane format here) compressed |
301 | data format? | 301 | data format? |
302 | 302 | ||
303 | Probably not. Look in the comp.compression FAQ for pointers to various | 303 | Probably not. Look in the comp.compression FAQ for pointers to various |
304 | formats and associated software. | 304 | formats and associated software. |
305 | 305 | ||
306 | 38. How can I encrypt/decrypt zip files with zlib? | 306 | 38. How can I encrypt/decrypt zip files with zlib? |
307 | 307 | ||
308 | zlib doesn't support encryption. The original PKZIP encryption is very weak | 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, | 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. | 310 | use GnuPG, http://www.gnupg.org/ , which already includes zlib compression. |
311 | For PKZIP compatible "encryption", look at http://www.info-zip.org/ | 311 | For PKZIP compatible "encryption", look at http://www.info-zip.org/ |
312 | 312 | ||
313 | 39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings? | 313 | 39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings? |
314 | 314 | ||
315 | "gzip" is the gzip format, and "deflate" is the zlib format. They should | 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 | 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 | 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" | 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 | 319 | transfer encoding, there have been reports of servers and browsers that |
320 | incorrectly produce or expect raw deflate data per the deflate | 320 | incorrectly produce or expect raw deflate data per the deflate |
321 | specficiation in RFC 1951, most notably Microsoft. So even though the | 321 | specficiation in RFC 1951, most notably Microsoft. So even though the |
322 | "deflate" transfer encoding using the zlib format would be the more | 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 | 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 | 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. | 325 | an unfortunate choice of name on the part of the HTTP 1.1 authors. |
326 | 326 | ||
327 | Bottom line: use the gzip format for HTTP 1.1 encoding. | 327 | Bottom line: use the gzip format for HTTP 1.1 encoding. |
328 | 328 | ||
329 | 40. Does zlib support the new "Deflate64" format introduced by PKWare? | 329 | 40. Does zlib support the new "Deflate64" format introduced by PKWare? |
330 | 330 | ||
331 | No. PKWare has apparently decided to keep that format proprietary, since | 331 | No. PKWare has apparently decided to keep that format proprietary, since |
332 | they have not documented it as they have previous compression formats. | 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 | 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. | 334 | more modern approaches, that it's not worth the effort to implement. |
335 | 335 | ||
336 | 41. Can you please sign these lengthy legal documents and fax them back to us | 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? | 337 | so that we can use your software in our product? |
338 | 338 | ||
339 | No. Go away. Shoo. | 339 | No. Go away. Shoo. |