cpython-lru_cache-weakref: Modules/zlib/FAQ annotate

annotate Modules/zlib/FAQ @ 73807:1efefeda00a7 3.2

#8414: add more tests for "assert". Initial patch by Gregory Nofi.

author	Ezio Melotti <ezio.melotti@gmail.com>
date	Fri, 02 Dec 2011 18:22:52 +0200
parents	467019588fcc
children	224aa49f22f1

rev	line source
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	1
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	2 Frequently Asked Questions about zlib
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	3
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	4
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	5 If your question is not there, please check the zlib home page
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	6 http://zlib.net/ which may have more recent information.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	7 The lastest zlib FAQ is at http://zlib.net/zlib_faq.html
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	8
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	9
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	10 1. Is zlib Y2K-compliant?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	11
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	12 Yes. zlib doesn't handle dates.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	13
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	14 2. Where can I get a Windows DLL version?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	15
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	16 The zlib sources can be compiled without change to produce a DLL. See the
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	17 file win32/DLL_FAQ.txt in the zlib distribution. Pointers to the
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	18 precompiled DLL are found in the zlib web site at http://zlib.net/ .
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	19
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	20 3. Where can I get a Visual Basic interface to zlib?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	21
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	22 See
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	23 * http://marknelson.us/1997/01/01/zlib-engine/
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	24 * win32/DLL_FAQ.txt in the zlib distribution
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	25
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	26 4. compress() returns Z_BUF_ERROR.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	27
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	28 Make sure that before the call of compress(), the length of the compressed
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	29 buffer is equal to the available size of the compressed buffer and not
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	30 zero. For Visual Basic, check that this parameter is passed by reference
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	31 ("as any"), not by value ("as long").
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	32
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	33 5. deflate() or inflate() returns Z_BUF_ERROR.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	34
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	35 Before making the call, make sure that avail_in and avail_out are not zero.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	36 When setting the parameter flush equal to Z_FINISH, also make sure that
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	37 avail_out is big enough to allow processing all pending input. Note that a
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	38 Z_BUF_ERROR is not fatal--another call to deflate() or inflate() can be
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	39 made with more input or output space. A Z_BUF_ERROR may in fact be
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	40 unavoidable depending on how the functions are used, since it is not
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	41 possible to tell whether or not there is more output pending when
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	42 strm.avail_out returns with zero. See http://zlib.net/zlib_how.html for a
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	43 heavily annotated example.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	44
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	45 6. Where's the zlib documentation (man pages, etc.)?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	46
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	47 It's in zlib.h . Examples of zlib usage are in the files example.c and
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	48 minigzip.c, with more in examples/ .
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	49
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	50 7. Why don't you use GNU autoconf or libtool or ...?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	51
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	52 Because we would like to keep zlib as a very small and simple package.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	53 zlib is rather portable and doesn't need much configuration.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	54
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	55 8. I found a bug in zlib.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	56
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	57 Most of the time, such problems are due to an incorrect usage of zlib.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	58 Please try to reproduce the problem with a small program and send the
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	59 corresponding source to us at zlib@gzip.org . Do not send multi-megabyte
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	60 data files without prior agreement.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	61
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	62 9. Why do I get "undefined reference to gzputc"?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	63
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	64 If "make test" produces something like
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	65
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	66 example.o(.text+0x154): undefined reference to `gzputc'
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	67
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	68 check that you don't have old files libz.* in /usr/lib, /usr/local/lib or
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	69 /usr/X11R6/lib. Remove any old versions, then do "make install".
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	70
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	71 10. I need a Delphi interface to zlib.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	72
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	73 See the contrib/delphi directory in the zlib distribution.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	74
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	75 11. Can zlib handle .zip archives?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	76
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	77 Not by itself, no. See the directory contrib/minizip in the zlib
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	78 distribution.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	79
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	80 12. Can zlib handle .Z files?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	81
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	82 No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	83 the code of uncompress on your own.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	84
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	85 13. How can I make a Unix shared library?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	86
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	87 make clean
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	88 ./configure -s
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	89 make
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	90
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	91 14. How do I install a shared zlib library on Unix?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	92
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	93 After the above, then:
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	94
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	95 make install
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	96
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	97 However, many flavors of Unix come with a shared zlib already installed.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	98 Before going to the trouble of compiling a shared version of zlib and
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	99 trying to install it, you may want to check if it's already there! If you
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	100 can #include <zlib.h>, it's there. The -lz option will probably link to
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	101 it. You can check the version at the top of zlib.h or with the
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	102 ZLIB_VERSION symbol defined in zlib.h .
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	103
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	104 15. I have a question about OttoPDF.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	105
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	106 We are not the authors of OttoPDF. The real author is on the OttoPDF web
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	107 site: Joel Hainley, jhainley@myndkryme.com.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	108
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	109 16. Can zlib decode Flate data in an Adobe PDF file?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	110
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	111 Yes. See http://www.pdflib.com/ . To modify PDF forms, see
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	112 http://sourceforge.net/projects/acroformtool/ .
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	113
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	114 17. Why am I getting this "register_frame_info not found" error on Solaris?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	115
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	116 After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	117 generates an error such as:
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	118
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	119 ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so:
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	120 symbol __register_frame_info: referenced symbol not found
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	121
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	122 The symbol __register_frame_info is not part of zlib, it is generated by
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	123 the C compiler (cc or gcc). You must recompile applications using zlib
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	124 which have this problem. This problem is specific to Solaris. See
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	125 http://www.sunfreeware.com for Solaris versions of zlib and applications
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	126 using zlib.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	127
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	128 18. Why does gzip give an error on a file I make with compress/deflate?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	129
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	130 The compress and deflate functions produce data in the zlib format, which
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	131 is different and incompatible with the gzip format. The gz* functions in
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	132 zlib on the other hand use the gzip format. Both the zlib and gzip formats
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	133 use the same compressed data format internally, but have different headers
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	134 and trailers around the compressed data.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	135
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	136 19. Ok, so why are there two different formats?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	137
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	138 The gzip format was designed to retain the directory information about a
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	139 single file, such as the name and last modification date. The zlib format
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	140 on the other hand was designed for in-memory and communication channel
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	141 applications, and has a much more compact header and trailer and uses a
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	142 faster integrity check than gzip.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	143
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	144 20. Well that's nice, but how do I make a gzip file in memory?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	145
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	146 You can request that deflate write the gzip format instead of the zlib
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	147 format using deflateInit2(). You can also request that inflate decode the
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	148 gzip format using inflateInit2(). Read zlib.h for more details.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	149
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	150 21. Is zlib thread-safe?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	151
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	152 Yes. However any library routines that zlib uses and any application-
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	153 provided memory allocation routines must also be thread-safe. zlib's gz*
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	154 functions use stdio library routines, and most of zlib's functions use the
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	155 library memory allocation routines by default. zlib's Init functions
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	156 allow for the application to provide custom memory allocation routines.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	157
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	158 Of course, you should only operate on any given zlib or gzip stream from a
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	159 single thread at a time.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	160
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	161 22. Can I use zlib in my commercial application?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	162
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	163 Yes. Please read the license in zlib.h.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	164
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	165 23. Is zlib under the GNU license?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	166
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	167 No. Please read the license in zlib.h.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	168
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	169 24. The license says that altered source versions must be "plainly marked". So
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	170 what exactly do I need to do to meet that requirement?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	171
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	172 You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	173 particular, the final version number needs to be changed to "f", and an
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	174 identification string should be appended to ZLIB_VERSION. Version numbers
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	175 x.x.x.f are reserved for modifications to zlib by others than the zlib
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	176 maintainers. For example, if the version of the base zlib you are altering
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	177 is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	178 ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3". You can also
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	179 update the version strings in deflate.c and inftrees.c.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	180
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	181 For altered source distributions, you should also note the origin and
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	182 nature of the changes in zlib.h, as well as in ChangeLog and README, along
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	183 with the dates of the alterations. The origin should include at least your
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	184 name (or your company's name), and an email address to contact for help or
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	185 issues with the library.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	186
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	187 Note that distributing a compiled zlib library along with zlib.h and
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	188 zconf.h is also a source distribution, and so you should change
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	189 ZLIB_VERSION and ZLIB_VERNUM and note the origin and nature of the changes
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	190 in zlib.h as you would for a full source distribution.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	191
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	192 25. Will zlib work on a big-endian or little-endian architecture, and can I
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	193 exchange compressed data between them?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	194
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	195 Yes and yes.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	196
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	197 26. Will zlib work on a 64-bit machine?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	198
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	199 Yes. It has been tested on 64-bit machines, and has no dependence on any
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	200 data types being limited to 32-bits in length. If you have any
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	201 difficulties, please provide a complete problem report to zlib@gzip.org
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	202
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	203 27. Will zlib decompress data from the PKWare Data Compression Library?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	204
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	205 No. The PKWare DCL uses a completely different compressed data format than
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	206 does PKZIP and zlib. However, you can look in zlib's contrib/blast
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	207 directory for a possible solution to your problem.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	208
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	209 28. Can I access data randomly in a compressed stream?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	210
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	211 No, not without some preparation. If when compressing you periodically use
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	212 Z_FULL_FLUSH, carefully write all the pending data at those points, and
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	213 keep an index of those locations, then you can start decompression at those
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	214 points. You have to be careful to not use Z_FULL_FLUSH too often, since it
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	215 can significantly degrade compression. Alternatively, you can scan a
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	216 deflate stream once to generate an index, and then use that index for
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	217 random access. See examples/zran.c .
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	218
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	219 29. Does zlib work on MVS, OS/390, CICS, etc.?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	220
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	221 It has in the past, but we have not heard of any recent evidence. There
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	222 were working ports of zlib 1.1.4 to MVS, but those links no longer work.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	223 If you know of recent, successful applications of zlib on these operating
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	224 systems, please let us know. Thanks.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	225
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	226 30. Is there some simpler, easier to read version of inflate I can look at to
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	227 understand the deflate format?
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	228
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	229 First off, you should read RFC 1951. Second, yes. Look in zlib's
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	230 contrib/puff directory.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	231
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	232 31. Does zlib infringe on any patents?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	233
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	234 As far as we know, no. In fact, that was originally the whole point behind
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	235 zlib. Look here for some more information:
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	236
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	237 http://www.gzip.org/#faq11
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	238
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	239 32. Can zlib work with greater than 4 GB of data?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	240
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	241 Yes. inflate() and deflate() will process any amount of data correctly.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	242 Each call of inflate() or deflate() is limited to input and output chunks
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	243 of the maximum value that can be stored in the compiler's "unsigned int"
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	244 type, but there is no limit to the number of chunks. Note however that the
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	245 strm.total_in and strm_total_out counters may be limited to 4 GB. These
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	246 counters are provided as a convenience and are not used internally by
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	247 inflate() or deflate(). The application can easily set up its own counters
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	248 updated after each call of inflate() or deflate() to count beyond 4 GB.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	249 compress() and uncompress() may be limited to 4 GB, since they operate in a
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	250 single call. gzseek() and gztell() may be limited to 4 GB depending on how
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	251 zlib is compiled. See the zlibCompileFlags() function in zlib.h.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	252
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	253 The word "may" appears several times above since there is a 4 GB limit only
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	254 if the compiler's "long" type is 32 bits. If the compiler's "long" type is
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	255 64 bits, then the limit is 16 exabytes.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	256
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	257 33. Does zlib have any security vulnerabilities?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	258
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	259 The only one that we are aware of is potentially in gzprintf(). If zlib is
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	260 compiled to use sprintf() or vsprintf(), then there is no protection
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	261 against a buffer overflow of an 8K string space (or other value as set by
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	262 gzbuffer()), other than the caller of gzprintf() assuring that the output
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	263 will not exceed 8K. On the other hand, if zlib is compiled to use
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	264 snprintf() or vsnprintf(), which should normally be the case, then there is
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	265 no vulnerability. The ./configure script will display warnings if an
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	266 insecure variation of sprintf() will be used by gzprintf(). Also the
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	267 zlibCompileFlags() function will return information on what variant of
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	268 sprintf() is used by gzprintf().
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	269
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	270 If you don't have snprintf() or vsnprintf() and would like one, you can
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	271 find a portable implementation here:
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	272
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	273 http://www.ijs.si/software/snprintf/
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	274
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	275 Note that you should be using the most recent version of zlib. Versions
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	276 1.1.3 and before were subject to a double-free vulnerability, and versions
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	277 1.2.1 and 1.2.2 were subject to an access exception when decompressing
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	278 invalid compressed data.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	279
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	280 34. Is there a Java version of zlib?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	281
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	282 Probably what you want is to use zlib in Java. zlib is already included
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	283 as part of the Java SDK in the java.util.zip package. If you really want
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	284 a version of zlib written in the Java language, look on the zlib home
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	285 page for links: http://zlib.net/ .
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	286
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	287 35. I get this or that compiler or source-code scanner warning when I crank it
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	288 up to maximally-pedantic. Can't you guys write proper code?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	289
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	290 Many years ago, we gave up attempting to avoid warnings on every compiler
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	291 in the universe. It just got to be a waste of time, and some compilers
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	292 were downright silly as well as contradicted each other. So now, we simply
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	293 make sure that the code always works.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	294
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	295 36. Valgrind (or some similar memory access checker) says that deflate is
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	296 performing a conditional jump that depends on an uninitialized value.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	297 Isn't that a bug?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	298
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	299 No. That is intentional for performance reasons, and the output of deflate
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	300 is not affected. This only started showing up recently since zlib 1.2.x
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	301 uses malloc() by default for allocations, whereas earlier versions used
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	302 calloc(), which zeros out the allocated memory. Even though the code was
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	303 correct, versions 1.2.4 and later was changed to not stimulate these
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	304 checkers.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	305
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	306 37. Will zlib read the (insert any ancient or arcane format here) compressed
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	307 data format?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	308
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	309 Probably not. Look in the comp.compression FAQ for pointers to various
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	310 formats and associated software.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	311
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	312 38. How can I encrypt/decrypt zip files with zlib?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	313
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	314 zlib doesn't support encryption. The original PKZIP encryption is very
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	315 weak and can be broken with freely available programs. To get strong
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	316 encryption, use GnuPG, http://www.gnupg.org/ , which already includes zlib
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	317 compression. For PKZIP compatible "encryption", look at
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	318 http://www.info-zip.org/
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	319
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	320 39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	321
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	322 "gzip" is the gzip format, and "deflate" is the zlib format. They should
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	323 probably have called the second one "zlib" instead to avoid confusion with
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	324 the raw deflate compressed data format. While the HTTP 1.1 RFC 2616
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	325 correctly points to the zlib specification in RFC 1950 for the "deflate"
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	326 transfer encoding, there have been reports of servers and browsers that
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	327 incorrectly produce or expect raw deflate data per the deflate
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	328 specficiation in RFC 1951, most notably Microsoft. So even though the
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	329 "deflate" transfer encoding using the zlib format would be the more
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	330 efficient approach (and in fact exactly what the zlib format was designed
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	331 for), using the "gzip" transfer encoding is probably more reliable due to
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	332 an unfortunate choice of name on the part of the HTTP 1.1 authors.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	333
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	334 Bottom line: use the gzip format for HTTP 1.1 encoding.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	335
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	336 40. Does zlib support the new "Deflate64" format introduced by PKWare?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	337
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	338 No. PKWare has apparently decided to keep that format proprietary, since
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	339 they have not documented it as they have previous compression formats. In
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	340 any case, the compression improvements are so modest compared to other more
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	341 modern approaches, that it's not worth the effort to implement.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	342
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	343 41. I'm having a problem with the zip functions in zlib, can you help?
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	344
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	345 There are no zip functions in zlib. You are probably using minizip by
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	346 Giles Vollant, which is found in the contrib directory of zlib. It is not
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	347 part of zlib. In fact none of the stuff in contrib is part of zlib. The
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	348 files in there are not supported by the zlib authors. You need to contact
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	349 the authors of the respective contribution for help.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	350
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	351 42. The match.asm code in contrib is under the GNU General Public License.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	352 Since it's part of zlib, doesn't that mean that all of zlib falls under the
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	353 GNU GPL?
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	354
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	355 No. The files in contrib are not part of zlib. They were contributed by
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	356 other authors and are provided as a convenience to the user within the zlib
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	357 distribution. Each item in contrib has its own license.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	358
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	359 43. Is zlib subject to export controls? What is its ECCN?
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	360
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	361 zlib is not subject to export controls, and so is classified as EAR99.
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	362
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	363 44. Can you please sign these lengthy legal documents and fax them back to us
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	364 so that we can use your software in our product?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	365
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	366 No. Go away. Shoo.

Mercurial > cpython-lru_cache-weakref

annotate Modules/zlib/FAQ @ 73807:1efefeda00a7 3.2