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author | Mark Adler <madler@alumni.caltech.edu> | 2011-09-09 23:21:57 -0700 |
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committer | Mark Adler <madler@alumni.caltech.edu> | 2011-09-09 23:21:57 -0700 |
commit | 13a294f044ef0a89b2dcbfbb5d4d4c792673348e (patch) | |
tree | d9b377b4d8c00633c3da4e96659bfba9b08287f2 /FAQ | |
parent | 7c2a874e50b871d04fbd19501f7b42cff55e5abc (diff) | |
download | zlib-13a294f044ef0a89b2dcbfbb5d4d4c792673348e.tar.gz zlib-13a294f044ef0a89b2dcbfbb5d4d4c792673348e.tar.bz2 zlib-13a294f044ef0a89b2dcbfbb5d4d4c792673348e.zip |
zlib 1.2.0.1v1.2.0.1
Diffstat (limited to 'FAQ')
-rw-r--r-- | FAQ | 105 |
1 files changed, 67 insertions, 38 deletions
@@ -1,5 +1,5 @@ | |||
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 |
@@ -90,13 +90,14 @@ The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html | |||
90 | ./configure -s | 90 | ./configure -s |
91 | make | 91 | make |
92 | 92 | ||
93 | 14. Why does "make test" fail on Mac OS X? | 93 | 14. How do I install a shared zlib library on Unix? |
94 | 94 | ||
95 | Mac OS X already includes zlib as a shared library, and so -lz links the | 95 | make install |
96 | shared library instead of the one that the "make" compiled. The two are | 96 | |
97 | incompatible due to different compile-time options. Simply change the -lz | 97 | However, many flavors of Unix come with a shared zlib already installed. |
98 | in the Makefile to libz.a, and it will use the compiled library instead | 98 | Before going to the trouble of compiling a shared version of zlib and |
99 | of the shared one and the "make test" will succeed. | 99 | trying to install it, you may want to check if it's already there! If you |
100 | can #include <zlib.h>, it's there. The -lz option will probably link to it. | ||
100 | 101 | ||
101 | 15. I have a question about OttoPDF | 102 | 15. I have a question about OttoPDF |
102 | 103 | ||
@@ -108,8 +109,8 @@ The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html | |||
108 | The compress and deflate functions produce data in the zlib format, which | 109 | The compress and deflate functions produce data in the zlib format, which |
109 | is different and incompatible with the gzip format. The gz* functions in | 110 | is different and incompatible with the gzip format. The gz* functions in |
110 | zlib on the other hand use the gzip format. Both the zlib and gzip | 111 | zlib on the other hand use the gzip format. Both the zlib and gzip |
111 | formats use the same compressed data format, but have different headers | 112 | formats use the same compressed data format internally, but have different |
112 | and trailers. | 113 | headers and trailers around the compressed data. |
113 | 114 | ||
114 | 17. Ok, so why are there two different formats? | 115 | 17. Ok, so why are there two different formats? |
115 | 116 | ||
@@ -127,12 +128,13 @@ The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html | |||
127 | 19. Is zlib thread-safe? | 128 | 19. Is zlib thread-safe? |
128 | 129 | ||
129 | Yes. However any library routines that zlib uses and any application- | 130 | Yes. However any library routines that zlib uses and any application- |
130 | provided memory allocation routines must also be thread-safe. Of course, | 131 | provided memory allocation routines must also be thread-safe. zlib's gz* |
131 | you should only operate on any given zlib or gzip stream from a single | 132 | functions use stdio library routines, and most of zlib's functions use the |
132 | thread. zlib's gz* functions use stdio library routines, and most of | 133 | library memory allocation routines by default. zlib's Init functions allow |
133 | zlib's functions use the library memory allocation routines by default. | 134 | for the application to provide custom memory allocation routines. |
134 | zlib's Init functions allow for the application to provide custom memory | 135 | |
135 | allocation routines. | 136 | Of course, you should only operate on any given zlib or gzip stream from a |
137 | single thread at a time. | ||
136 | 138 | ||
137 | 20. Can I use zlib in my commercial application? | 139 | 20. Can I use zlib in my commercial application? |
138 | 140 | ||
@@ -142,24 +144,44 @@ The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html | |||
142 | 144 | ||
143 | No. Please read the license in zlib.h. | 145 | No. Please read the license in zlib.h. |
144 | 146 | ||
145 | 22. Will zlib work on a big-endian or little-endian architecture, and can I | 147 | 22. The license says that altered source versions must be "plainly marked". So |
148 | what exactly do I need to do to meet that requirement? | ||
149 | |||
150 | You need to append something the ZLIB_VERSION string in zlib.h. For | ||
151 | example, if the version of the base zlib you are altering is "1.2.3", then | ||
152 | you could change the string to "1.2.3-fred-mods-v3". You should not change | ||
153 | it to "1.2.4" or "1.2.3.1" since the zlib authors would like to reserve | ||
154 | those forms of the version for their own use. | ||
155 | |||
156 | For altered source distributions, you should also note the origin and | ||
157 | nature of the changes in zlib.h, as well as in ChangeLog and README, along | ||
158 | with the dates of the alterations. The origin should include at least your | ||
159 | name (or your company's name), and an email address to contact for help or | ||
160 | issues with the library. | ||
161 | |||
162 | Note that distributing a compiled zlib library along with zlib.h and | ||
163 | zconf.h is also a source distribution, and so you should change | ||
164 | ZLIB_VERSION and note the origin and nature of the changes in zlib.h as you | ||
165 | would for a full source distribution. | ||
166 | |||
167 | 23. Will zlib work on a big-endian or little-endian architecture, and can I | ||
146 | exchange compressed data between them? | 168 | exchange compressed data between them? |
147 | 169 | ||
148 | Yes and yes. | 170 | Yes and yes. |
149 | 171 | ||
150 | 23. Will zlib work on a 64-bit machine? | 172 | 24. Will zlib work on a 64-bit machine? |
151 | 173 | ||
152 | It should. It has been tested on 64-bit machines, and has no dependence | 174 | It should. It has been tested on 64-bit machines, and has no dependence |
153 | on any data types being limited to 32-bits in length. If you have any | 175 | on any data types being limited to 32-bits in length. If you have any |
154 | difficulties, please provide a complete problem report to zlib@gzip.org | 176 | difficulties, please provide a complete problem report to zlib@gzip.org |
155 | 177 | ||
156 | 24. Will zlib decompress data from the PKWare Data Compression Library? | 178 | 25. Will zlib decompress data from the PKWare Data Compression Library? |
157 | 179 | ||
158 | No. The PKWare DCL uses a completely different compressed data format | 180 | No. The PKWare DCL uses a completely different compressed data format |
159 | than does PKZIP and zlib. However, you can look in zlib's contrib/blast | 181 | than does PKZIP and zlib. However, you can look in zlib's contrib/blast |
160 | directory for a possible solution to your problem. | 182 | directory for a possible solution to your problem. |
161 | 183 | ||
162 | 25. Can I access data randomly in a compressed stream? | 184 | 26. Can I access data randomly in a compressed stream? |
163 | 185 | ||
164 | No, not without some preparation. If when compressing you periodically | 186 | No, not without some preparation. If when compressing you periodically |
165 | use Z_FULL_FLUSH, carefully write all the pending data at those points, | 187 | use Z_FULL_FLUSH, carefully write all the pending data at those points, |
@@ -167,76 +189,83 @@ The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html | |||
167 | at those points. You have to be careful to not use Z_FULL_FLUSH too | 189 | at those points. You have to be careful to not use Z_FULL_FLUSH too |
168 | often, since it can significantly degrade compression. | 190 | often, since it can significantly degrade compression. |
169 | 191 | ||
170 | 26. Does zlib work on MVS, OS/390, CICS, etc.? | 192 | 27. Does zlib work on MVS, OS/390, CICS, etc.? |
171 | 193 | ||
172 | We don't know for sure. We have heard occasional reports of success on | 194 | We don't know for sure. We have heard occasional reports of success on |
173 | these systems. If you do use it on one of these, please provide us with | 195 | these systems. If you do use it on one of these, please provide us with |
174 | a report, instructions, and patches that we can reference when we get | 196 | a report, instructions, and patches that we can reference when we get |
175 | these questions. Thanks. | 197 | these questions. Thanks. |
176 | 198 | ||
177 | 27. Is there some simpler, easier to read version of inflate I can look at | 199 | 28. Is there some simpler, easier to read version of inflate I can look at |
178 | to understand the deflate format? | 200 | to understand the deflate format? |
179 | 201 | ||
180 | First off, you should read RFC 1951. Second, yes. Look in zlib's | 202 | First off, you should read RFC 1951. Second, yes. Look in zlib's |
181 | contrib/puff directory. | 203 | contrib/puff directory. |
182 | 204 | ||
183 | 28. Does zlib infringe on any patents? | 205 | 29. Does zlib infringe on any patents? |
184 | 206 | ||
185 | As far as we know, no. In fact, that was originally the whole point behind | 207 | As far as we know, no. In fact, that was originally the whole point behind |
186 | zlib. Look here for some more information: | 208 | zlib. Look here for some more information: |
187 | 209 | ||
188 | http://www.gzip.org/#faq11 | 210 | http://www.gzip.org/#faq11 |
189 | 211 | ||
190 | 29. Can zlib work with greater than 4 GB of data? | 212 | 30. Can zlib work with greater than 4 GB of data? |
191 | 213 | ||
192 | Yes. inflate() and deflate() will process any amount of data correctly. | 214 | Yes. inflate() and deflate() will process any amount of data correctly. |
193 | However the strm.total_in and strm_total_out counters may be limited to | 215 | However the strm.total_in and strm_total_out counters may be limited to |
194 | 4 GB. The user can easily set up their own counters updated after each | 216 | 4 GB. The application can easily set up its own counters updated after each |
195 | call of inflate() or deflate() to count beyond 4 GB. compress() and | 217 | call of inflate() or deflate() to count beyond 4 GB. compress() and |
196 | uncompress() may be limited to 4 GB, since they operate in a single | 218 | uncompress() may be limited to 4 GB, since they operate in a single call |
197 | call using unsigned long lengths. gzseek() may be limited to 4 GB | 219 | using unsigned long lengths. gzseek() and gztell() may be limited to 4 GB |
198 | depending on how zlib is compiled. | 220 | depending on how zlib is compiled. |
199 | 221 | ||
200 | 30. Does zlib have any security vulnerabilities? | 222 | 31. Does zlib have any security vulnerabilities? |
201 | 223 | ||
202 | The only one that we are aware of is potentially in gzprintf(). If zlib | 224 | The only one that we are aware of is potentially in gzprintf(). If zlib |
203 | is compiled to use sprintf() or vsprintf(), then there is no protection | 225 | is compiled to use sprintf() or vsprintf(), then there is no protection |
204 | against a buffer overflow of a 4K string space, other than the caller of | 226 | against a buffer overflow of a 4K string space, other than the caller of |
205 | gzprintf() assuring that the output will not exceed 4K. On the other | 227 | gzprintf() assuring that the output will not exceed 4K. On the other |
206 | hand, if zlib is compiled to use snprintf() or vsnprintf(), then there is | 228 | hand, if zlib is compiled to use snprintf() or vsnprintf(), which should |
207 | no vulnerability. | 229 | normally be the case, then there is no vulnerability. The ./configure |
230 | script will display warnings if an insecure variation of sprintf() will | ||
231 | be used by gzprintf(). | ||
232 | |||
233 | If you don't have snprintf() or vsnprintf() and would like one, you can | ||
234 | find a portable implementation here: | ||
235 | |||
236 | http://www.ijs.si/software/snprintf/ | ||
208 | 237 | ||
209 | Note that you should be using the most recent version of zlib. Versions | 238 | Note that you should be using the most recent version of zlib. Versions |
210 | 1.1.3 and before were subject to a double-free vulnerability. | 239 | 1.1.3 and before were subject to a double-free vulnerability. |
211 | 240 | ||
212 | 31. Is there a Java version of zlib? | 241 | 32. Is there a Java version of zlib? |
213 | 242 | ||
214 | Probably what you want is to use zlib in Java. zlib is already included | 243 | Probably what you want is to use zlib in Java. zlib is already included |
215 | as part of the Java SDK in the java.util.zip class. If you really want | 244 | as part of the Java SDK in the java.util.zip class. If you really want |
216 | a version of zlib written in the Java language, look on the zlib home | 245 | a version of zlib written in the Java language, look on the zlib home |
217 | page for links: http://www.zlib.org/ | 246 | page for links: http://www.zlib.org/ |
218 | 247 | ||
219 | 32. I get this or that compiler or source-code scanner warning. Can't you guys | 248 | 33. I get this or that compiler or source-code scanner warning when I crank it |
220 | write proper code? | 249 | up to maximally-pendantic. Can't you guys write proper code? |
221 | 250 | ||
222 | Many years ago, we gave up attempting to avoid warnings on every compiler | 251 | Many years ago, we gave up attempting to avoid warnings on every compiler |
223 | in the universe. It just got to be a waste of time, and some compilers | 252 | in the universe. It just got to be a waste of time, and some compilers |
224 | were downright silly. So now, we simply make sure that the code always | 253 | were downright silly. So now, we simply make sure that the code always |
225 | works. | 254 | works. |
226 | 255 | ||
227 | 33. Will zlib read the (insert any ancient or arcane format here) compressed | 256 | 34. Will zlib read the (insert any ancient or arcane format here) compressed |
228 | data format? | 257 | data format? |
229 | 258 | ||
230 | Probably not. Look in the comp.compression FAQ for pointers to various | 259 | Probably not. Look in the comp.compression FAQ for pointers to various |
231 | formats and associated software. | 260 | formats and associated software. |
232 | 261 | ||
233 | 34. How can I encrypt/decrypt zip files with zlib? | 262 | 35. How can I encrypt/decrypt zip files with zlib? |
234 | 263 | ||
235 | zlib doesn't support encryption. PKZIP encryption is very weak and can be | 264 | zlib doesn't support encryption. PKZIP encryption is very weak and can be |
236 | broken with freely available programs. To get strong encryption, use gpg | 265 | broken with freely available programs. To get strong encryption, use gpg |
237 | which already includes zlib compression. | 266 | which already includes zlib compression. |
238 | 267 | ||
239 | 35. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings? | 268 | 36. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings? |
240 | 269 | ||
241 | "gzip" is the gzip format, and "deflate" is the zlib format. They should | 270 | "gzip" is the gzip format, and "deflate" is the zlib format. They should |
242 | probably have called the second one "zlib" instead to avoid confusion | 271 | probably have called the second one "zlib" instead to avoid confusion |
@@ -250,14 +279,14 @@ The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html | |||
250 | for), using the "gzip" transfer encoding is probably more reliable due to | 279 | for), using the "gzip" transfer encoding is probably more reliable due to |
251 | an unfortunate choice of name on the part of the HTTP 1.1 authors. | 280 | an unfortunate choice of name on the part of the HTTP 1.1 authors. |
252 | 281 | ||
253 | 36. Does zlib support the new "Deflate64" format introduced by PKWare? | 282 | 37. Does zlib support the new "Deflate64" format introduced by PKWare? |
254 | 283 | ||
255 | No. PKWare has apparently decided to keep that format proprietary, since | 284 | No. PKWare has apparently decided to keep that format proprietary, since |
256 | they have not documented it as they have previous compression formats. | 285 | they have not documented it as they have previous compression formats. |
257 | In any case, the compression improvements are so modest compared to other | 286 | In any case, the compression improvements are so modest compared to other |
258 | more modern approaches, that it's not worth the effort to implement. | 287 | more modern approaches, that it's not worth the effort to implement. |
259 | 288 | ||
260 | 37. Can you please sign these lengthy legal documents and fax them back to us | 289 | 38. Can you please sign these lengthy legal documents and fax them back to us |
261 | so that we can use your software in our product? | 290 | so that we can use your software in our product? |
262 | 291 | ||
263 | No. | 292 | No. Go away. |