mirror of
https://github.com/reactos/CMake.git
synced 2024-12-13 06:16:49 +00:00
340 lines
15 KiB
Plaintext
340 lines
15 KiB
Plaintext
|
|
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.dogma.net/markn/articles/zlibtool/zlibtool.htm
|
|
* contrib/visual-basic.txt in the zlib distribution
|
|
* 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 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 us (zlib@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?
|
|
|
|
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?
|
|
|
|
make clean
|
|
./configure -s
|
|
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.
|
|
|
|
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.fastio.com/ (ClibPDF), or 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?
|
|
|
|
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
|
|
|
|
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.
|
|
|
|
29. 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.
|
|
|
|
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 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.
|
|
|
|
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://www.zlib.org/
|
|
|
|
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. 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.
|
|
|
|
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
|
|
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.
|
|
|
|
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. 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.
|