+++ /dev/null
-
- Frequently Asked Questions about zlib
-
-
-If your question is not there, please check the zlib home page
-http://www.zlib.org which may have more recent information.
-The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html
-
-
- 1. Is zlib Y2K-compliant?
-
- Yes. zlib doesn't handle dates.
-
- 2. Where can I get a Windows DLL version?
-
- The zlib sources can be compiled without change to produce a DLL.
- See the file win32/DLL_FAQ.txt in the zlib distribution.
- Pointers to the precompiled DLL are found in the zlib web site at
- http://www.zlib.org.
-
- 3. Where can I get a Visual Basic interface to zlib?
-
- See
- * http://www.winimage.com/zLibDll/
- * http://www.dogma.net/markn/articles/zlibtool/zlibtool.htm
- * contrib/visual-basic.txt in the zlib distribution
-
- 4. compress() returns Z_BUF_ERROR
-
- Make sure that before the call of compress, the length of the compressed
- buffer is equal to the total size of the compressed buffer and not
- zero. For Visual Basic, check that this parameter is passed by reference
- ("as any"), not by value ("as long").
-
- 5. deflate() or inflate() returns Z_BUF_ERROR
-
- Before making the call, make sure that avail_in and avail_out are not
- zero. When setting the parameter flush equal to Z_FINISH, also make sure
- that avail_out is big enough to allow processing all pending input.
- Note that a Z_BUF_ERROR is not fatal--another call to deflate() or
- inflate() can be made with more input or output space. A Z_BUF_ERROR
- may in fact be unavoidable depending on how the functions are used, since
- it is not possible to tell whether or not there is more output pending
- when strm.avail_out returns with zero.
-
- 6. Where's the zlib documentation (man pages, etc.)?
-
- It's in zlib.h for the moment, and Francis S. Lin has converted it to a
- web page zlib.html. Volunteers to transform this to Unix-style man pages,
- please contact Jean-loup Gailly (jloup@gzip.org). Examples of zlib usage
- are in the files example.c and minigzip.c.
-
- 7. Why don't you use GNU autoconf or libtool or ...?
-
- Because we would like to keep zlib as a very small and simple
- package. zlib is rather portable and doesn't need much configuration.
-
- 8. I found a bug in zlib.
-
- Most of the time, such problems are due to an incorrect usage of
- zlib. Please try to reproduce the problem with a small program and send
- the corresponding source to us at zlib@gzip.org . Do not send
- multi-megabyte data files without prior agreement.
-
- 9. Why do I get "undefined reference to gzputc"?
-
- If "make test" produces something like
-
- example.o(.text+0x154): undefined reference to `gzputc'
-
- check that you don't have old files libz.* in /usr/lib, /usr/local/lib or
- /usr/X11R6/lib. Remove any old versions, then do "make install".
-
-10. I need a Delphi interface to zlib.
-
- See the contrib/delphi directory in the zlib distribution.
-
-11. Can zlib handle .zip archives?
-
- See the directory contrib/minizip in the zlib distribution.
-
-12. Can zlib handle .Z files?
-
- No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt
- the code of uncompress on your own.
-
-13. How can I make a Unix shared library?
-
- make clean
- ./configure -s
- make
-
-14. How do I install a shared zlib library on Unix?
-
- make install
-
- However, many flavors of Unix come with a shared zlib already installed.
- Before going to the trouble of compiling a shared version of zlib and
- trying to install it, you may want to check if it's already there! If you
- can #include <zlib.h>, it's there. The -lz option will probably link to it.
-
-15. I have a question about OttoPDF
-
- We are not the authors of OttoPDF. The real author is on the OttoPDF web
- site Joel Hainley jhainley@myndkryme.com.
-
-16. Why does gzip give an error on a file I make with compress/deflate?
-
- The compress and deflate functions produce data in the zlib format, which
- is different and incompatible with the gzip format. The gz* functions in
- zlib on the other hand use the gzip format. Both the zlib and gzip
- formats use the same compressed data format internally, but have different
- headers and trailers around the compressed data.
-
-17. Ok, so why are there two different formats?
-
- The gzip format was designed to retain the directory information about
- a single file, such as the name and last modification date. The zlib
- format on the other hand was designed for in-memory and communication
- channel applications, and has a much more compact header and trailer and
- uses a faster integrity check than gzip.
-
-18. Well that's nice, but how do I make a gzip file in memory?
-
- You can request that deflate write the gzip format instead of the zlib
- format using deflateInit2(). You can also request that inflate decode
- the gzip format using inflateInit2(). Read zlib.h for more details.
-
- Note that you cannot specify special gzip header contents (e.g. a file
- name or modification date), nor will inflate tell you what was in the
- gzip header. If you need to customize the header or see what's in it,
- you can use the raw deflate and inflate operations and the crc32()
- function and roll your own gzip encoding and decoding. Read the gzip
- RFC 1952 for details of the header and trailer format.
-
-19. Is zlib thread-safe?
-
- Yes. However any library routines that zlib uses and any application-
- provided memory allocation routines must also be thread-safe. zlib's gz*
- functions use stdio library routines, and most of zlib's functions use the
- library memory allocation routines by default. zlib's Init functions allow
- for the application to provide custom memory allocation routines.
-
- Of course, you should only operate on any given zlib or gzip stream from a
- single thread at a time.
-
-20. Can I use zlib in my commercial application?
-
- Yes. Please read the license in zlib.h.
-
-21. Is zlib under the GNU license?
-
- No. Please read the license in zlib.h.
-
-22. The license says that altered source versions must be "plainly marked". So
- what exactly do I need to do to meet that requirement?
-
- You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In
- particular, the final version number needs to be changed to "f", and an
- identification string should be appended to ZLIB_VERSION. Version numbers
- x.x.x.f are reserved for modifications to zlib by others than the zlib
- maintainers. For example, if the version of the base zlib you are altering
- is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and
- ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3". You can also
- update the version strings in deflate.c and inftrees.c.
-
- For altered source distributions, you should also note the origin and
- nature of the changes in zlib.h, as well as in ChangeLog and README, along
- with the dates of the alterations. The origin should include at least your
- name (or your company's name), and an email address to contact for help or
- issues with the library.
-
- Note that distributing a compiled zlib library along with zlib.h and
- zconf.h is also a source distribution, and so you should change
- ZLIB_VERSION and ZLIB_VERNUM and note the origin and nature of the changes
- in zlib.h as you would for a full source distribution.
-
-23. Will zlib work on a big-endian or little-endian architecture, and can I
- exchange compressed data between them?
-
- Yes and yes.
-
-24. Will zlib work on a 64-bit machine?
-
- It should. It has been tested on 64-bit machines, and has no dependence
- on any data types being limited to 32-bits in length. If you have any
- difficulties, please provide a complete problem report to zlib@gzip.org
-
-25. Will zlib decompress data from the PKWare Data Compression Library?
-
- No. The PKWare DCL uses a completely different compressed data format
- than does PKZIP and zlib. However, you can look in zlib's contrib/blast
- directory for a possible solution to your problem.
-
-26. Can I access data randomly in a compressed stream?
-
- No, not without some preparation. If when compressing you periodically
- use Z_FULL_FLUSH, carefully write all the pending data at those points,
- and keep an index of those locations, then you can start decompression
- at those points. You have to be careful to not use Z_FULL_FLUSH too
- often, since it can significantly degrade compression.
-
-27. Does zlib work on MVS, OS/390, CICS, etc.?
-
- We don't know for sure. We have heard occasional reports of success on
- these systems. If you do use it on one of these, please provide us with
- a report, instructions, and patches that we can reference when we get
- these questions. Thanks.
-
-28. Is there some simpler, easier to read version of inflate I can look at
- to understand the deflate format?
-
- First off, you should read RFC 1951. Second, yes. Look in zlib's
- contrib/puff directory.
-
-29. Does zlib infringe on any patents?
-
- As far as we know, no. In fact, that was originally the whole point behind
- zlib. Look here for some more information:
-
- http://www.gzip.org/#faq11
-
-30. Can zlib work with greater than 4 GB of data?
-
- Yes. inflate() and deflate() will process any amount of data correctly.
- Each call of inflate() or deflate() is limited to input and output chunks
- of the maximum value that can be stored in the compiler's "unsigned int"
- type, but there is no limit to the number of chunks. Note however that the
- strm.total_in and strm_total_out counters may be limited to 4 GB. These
- counters are provided as a convenience and are not used internally by
- inflate() or deflate(). The application can easily set up its own counters
- updated after each call of inflate() or deflate() to count beyond 4 GB.
- compress() and uncompress() may be limited to 4 GB, since they operate in a
- single call. gzseek() and gztell() may be limited to 4 GB depending on how
- zlib is compiled. See the zlibCompileFlags() function in zlib.h.
-
- The word "may" appears several times above since there is a 4 GB limit
- only if the compiler's "long" type is 32 bits. If the compiler's "long"
- type is 64 bits, then the limit is 16 exabytes.
-
-31. Does zlib have any security vulnerabilities?
-
- The only one that we are aware of is potentially in gzprintf(). If zlib
- is compiled to use sprintf() or vsprintf(), then there is no protection
- against a buffer overflow of a 4K string space, other than the caller of
- gzprintf() assuring that the output will not exceed 4K. On the other
- hand, if zlib is compiled to use snprintf() or vsnprintf(), which should
- normally be the case, then there is no vulnerability. The ./configure
- script will display warnings if an insecure variation of sprintf() will
- be used by gzprintf(). Also the zlibCompileFlags() function will return
- information on what variant of sprintf() is used by gzprintf().
-
- If you don't have snprintf() or vsnprintf() and would like one, you can
- find a portable implementation here:
-
- http://www.ijs.si/software/snprintf/
-
- Note that you should be using the most recent version of zlib. Versions
- 1.1.3 and before were subject to a double-free vulnerability.
-
-32. Is there a Java version of zlib?
-
- Probably what you want is to use zlib in Java. zlib is already included
- as part of the Java SDK in the java.util.zip package. If you really want
- a version of zlib written in the Java language, look on the zlib home
- page for links: http://www.zlib.org/
-
-33. I get this or that compiler or source-code scanner warning when I crank it
- up to maximally-pendantic. Can't you guys write proper code?
-
- Many years ago, we gave up attempting to avoid warnings on every compiler
- in the universe. It just got to be a waste of time, and some compilers
- were downright silly. So now, we simply make sure that the code always
- works.
-
-34. Will zlib read the (insert any ancient or arcane format here) compressed
- data format?
-
- Probably not. Look in the comp.compression FAQ for pointers to various
- formats and associated software.
-
-35. How can I encrypt/decrypt zip files with zlib?
-
- zlib doesn't support encryption. The original PKZIP encryption is very weak
- and can be broken with freely available programs. To get strong encryption,
- use gpg ( http://www.gnupg.org/ ) which already includes zlib compression.
- For PKZIP compatible "encryption", look at http://www.info-zip.org/
-
-36. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?
-
- "gzip" is the gzip format, and "deflate" is the zlib format. They should
- probably have called the second one "zlib" instead to avoid confusion
- with the raw deflate compressed data format. While the HTTP 1.1 RFC 2616
- correctly points to the zlib specification in RFC 1950 for the "deflate"
- transfer encoding, there have been reports of servers and browsers that
- incorrectly produce or expect raw deflate data per the deflate
- specficiation in RFC 1951, most notably Microsoft. So even though the
- "deflate" transfer encoding using the zlib format would be the more
- efficient approach (and in fact exactly what the zlib format was designed
- for), using the "gzip" transfer encoding is probably more reliable due to
- an unfortunate choice of name on the part of the HTTP 1.1 authors.
-
- Bottom line: use the gzip format for HTTP 1.1 encoding.
-
-37. Does zlib support the new "Deflate64" format introduced by PKWare?
-
- No. PKWare has apparently decided to keep that format proprietary, since
- they have not documented it as they have previous compression formats.
- In any case, the compression improvements are so modest compared to other
- more modern approaches, that it's not worth the effort to implement.
-
-38. Can you please sign these lengthy legal documents and fax them back to us
- so that we can use your software in our product?
-
- No. Go away. Shoo.
git://git.onelab.eu / bootcd.git / blobdiff