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
+ * win32/DLL_FAQ.txt in the zlib distribution
- 4. compress() returns Z_BUF_ERROR
+ 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
+ 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
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.
+ 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 ...?
11. Can zlib handle .zip archives?
- See the directory contrib/minizip in the zlib distribution.
+ Not by itself, no. See the directory contrib/minizip in the zlib
+ distribution.
12. Can zlib handle .Z files?
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.
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
+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.
+ 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:
-16. Why does gzip give an error on a file I make with compress/deflate?
+ 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
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?
+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
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?
+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.
- 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?
+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*
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?
+22. Can I use zlib in my commercial application?
Yes. Please read the license in zlib.h.
-21. Is zlib under the GNU license?
+23. 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
+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
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
+25. 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?
+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
-25. Will zlib decompress data from the PKWare Data Compression Library?
+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.
-26. Can I access data randomly in a compressed stream?
+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,
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.?
+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.
-28. Is there some simpler, easier to read version of inflate I can look at
+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.
-29. Does zlib infringe on any patents?
+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
-30. Can zlib work with greater than 4 GB of data?
+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
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?
+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
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?
+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/
-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?
+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.
-34. Will zlib read the (insert any ancient or arcane format here) compressed
+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.
-35. How can I encrypt/decrypt zip files with zlib?
+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 gpg ( http://www.gnupg.org/ ) which already includes zlib compression.
+ use GnuPG, 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?
+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
Bottom line: use the gzip format for HTTP 1.1 encoding.
-37. Does zlib support the new "Deflate64" format introduced by PKWare?
+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.
-38. Can you please sign these lengthy legal documents and fax them back to us
+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.
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