+++ /dev/null
-
- Frequently Asked Questions about zlib
-
-
-If your question is not there, please check the zlib home page
-http://zlib.net/ which may have more recent information.
-The lastest zlib FAQ is at http://zlib.net/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://zlib.net/ .
-
- 3. Where can I get a Visual Basic interface to zlib?
-
- See
- * http://marknelson.us/1997/01/01/zlib-engine/
- * win32/DLL_FAQ.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 available 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. See http://zlib.net/zlib_how.html for a
- heavily annotated example.
-
- 6. Where's the zlib documentation (man pages, etc.)?
-
- It's in zlib.h . Examples of zlib usage are in the files test/example.c
- and test/minigzip.c, with more in examples/ .
-
- 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?
-
- Not by itself, no. 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?
-
- By default a shared (and a static) library is built for Unix. So:
-
- make distclean
- ./configure
- make
-
-14. How do I install a shared zlib library on Unix?
-
- After the above, then:
-
- 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. You can check the version at the top of zlib.h or with the
- ZLIB_VERSION symbol defined in zlib.h .
-
-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. Can zlib decode Flate data in an Adobe PDF file?
-
- Yes. See http://www.pdflib.com/ . To modify PDF forms, see
- http://sourceforge.net/projects/acroformtool/ .
-
-17. Why am I getting this "register_frame_info not found" error on Solaris?
-
- After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib
- generates an error such as:
-
- ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so:
- symbol __register_frame_info: referenced symbol not found
-
- The symbol __register_frame_info is not part of zlib, it is generated by
- the C compiler (cc or gcc). You must recompile applications using zlib
- which have this problem. This problem is specific to Solaris. See
- http://www.sunfreeware.com for Solaris versions of zlib and applications
- using zlib.
-
-18. 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.
-
-19. 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.
-
-20. 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.
-
-21. 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.
-
-22. Can I use zlib in my commercial application?
-
- Yes. Please read the license in zlib.h.
-
-23. Is zlib under the GNU license?
-
- No. Please read the license in zlib.h.
-
-24. 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.
-
-25. Will zlib work on a big-endian or little-endian architecture, and can I
- exchange compressed data between them?
-
- Yes and yes.
-
-26. Will zlib work on a 64-bit machine?
-
- Yes. 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
-
-27. 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.
-
-28. 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. Alternatively, you can scan a
- deflate stream once to generate an index, and then use that index for
- random access. See examples/zran.c .
-
-29. Does zlib work on MVS, OS/390, CICS, etc.?
-
- It has in the past, but we have not heard of any recent evidence. There
- were working ports of zlib 1.1.4 to MVS, but those links no longer work.
- If you know of recent, successful applications of zlib on these operating
- systems, please let us know. Thanks.
-
-30. 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.
-
-31. 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
-
-32. 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.
-
-33. 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 an 8K string space (or other value as set by
- gzbuffer()), other than the caller of gzprintf() assuring that the output
- will not exceed 8K. 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, and versions
- 1.2.1 and 1.2.2 were subject to an access exception when decompressing
- invalid compressed data.
-
-34. 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://zlib.net/ .
-
-35. I get this or that compiler or source-code scanner warning when I crank it
- up to maximally-pedantic. 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 as well as contradicted each other. So now, we simply
- make sure that the code always works.
-
-36. Valgrind (or some similar memory access checker) says that deflate is
- performing a conditional jump that depends on an uninitialized value.
- Isn't that a bug?
-
- No. That is intentional for performance reasons, and the output of deflate
- is not affected. This only started showing up recently since zlib 1.2.x
- uses malloc() by default for allocations, whereas earlier versions used
- calloc(), which zeros out the allocated memory. Even though the code was
- correct, versions 1.2.4 and later was changed to not stimulate these
- checkers.
-
-37. 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.
-
-38. 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 GnuPG, http://www.gnupg.org/ , which already includes zlib
- compression. For PKZIP compatible "encryption", look at
- http://www.info-zip.org/
-
-39. 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
- specification 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.
-
-40. 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.
-
-41. I'm having a problem with the zip functions in zlib, can you help?
-
- There are no zip functions in zlib. You are probably using minizip by
- Giles Vollant, which is found in the contrib directory of zlib. It is not
- part of zlib. In fact none of the stuff in contrib is part of zlib. The
- files in there are not supported by the zlib authors. You need to contact
- the authors of the respective contribution for help.
-
-42. The match.asm code in contrib is under the GNU General Public License.
- Since it's part of zlib, doesn't that mean that all of zlib falls under the
- GNU GPL?
-
- No. The files in contrib are not part of zlib. They were contributed by
- other authors and are provided as a convenience to the user within the zlib
- distribution. Each item in contrib has its own license.
-
-43. Is zlib subject to export controls? What is its ECCN?
-
- zlib is not subject to export controls, and so is classified as EAR99.
-
-44. 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.
projects / reactos.git / blobdiff