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

annotate Modules/zlib/FAQ @ 87690:66c1c9f32567 default tip

Add use_weakref option to functools.lru_cache The use_weakref option makes lru_cache create weak references to the function arguments when creating the cache key, which prevents them from staying in the memory forever even after all other references to them are gone. This is a proof of concept for http://bugs.python.org/issue19859

author	Radomir Dopieralski <devel@sheep.art.pl>
date	Tue, 03 Dec 2013 16:02:48 +0100
parents	224aa49f22f1
children

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
86546 224aa49f22f1 Issue #18527: Upgrade internal copy of zlib to 1.2.8 Christian Heimes <christian@cheimes.de> parents: 63336 diff changeset	47 It's in zlib.h . Examples of zlib usage are in the files test/example.c
224aa49f22f1 Issue #18527: Upgrade internal copy of zlib to 1.2.8 Christian Heimes <christian@cheimes.de> parents: 63336 diff changeset	48 and test/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
86546 224aa49f22f1 Issue #18527: Upgrade internal copy of zlib to 1.2.8 Christian Heimes <christian@cheimes.de> parents: 63336 diff changeset	87 By default a shared (and a static) library is built for Unix. So:
224aa49f22f1 Issue #18527: Upgrade internal copy of zlib to 1.2.8 Christian Heimes <christian@cheimes.de> parents: 63336 diff changeset	88
224aa49f22f1 Issue #18527: Upgrade internal copy of zlib to 1.2.8 Christian Heimes <christian@cheimes.de> parents: 63336 diff changeset	89 make distclean
224aa49f22f1 Issue #18527: Upgrade internal copy of zlib to 1.2.8 Christian Heimes <christian@cheimes.de> parents: 63336 diff changeset	90 ./configure
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	91 make
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 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	94
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	95 After the above, then:
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 make install
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	98
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	99 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	100 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	101 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	102 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	103 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	104 ZLIB_VERSION symbol defined in zlib.h .
36186 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 15. I have a question about OttoPDF.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	107
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	108 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	109 site: Joel Hainley, jhainley@myndkryme.com.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	110
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	111 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	112
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	113 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	114 http://sourceforge.net/projects/acroformtool/ .
36186 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 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	117
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	118 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	119 generates an error such as:
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	120
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	121 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	122 symbol __register_frame_info: referenced symbol not found
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	123
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	124 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	125 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	126 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	127 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	128 using zlib.
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 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	131
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	132 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	133 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	134 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	135 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	136 and trailers around the compressed data.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	137
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	138 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	139
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	140 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	141 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	142 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	143 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	144 faster integrity check than gzip.
36186 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 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	147
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	148 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	149 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	150 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	151
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	152 21. Is zlib thread-safe?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	153
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	154 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	155 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	156 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	157 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	158 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	159
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	160 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	161 single thread at a time.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	162
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	163 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	164
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	165 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	166
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	167 23. Is zlib under the GNU license?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	168
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	169 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	170
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	171 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	172 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	173
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	174 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	175 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	176 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	177 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	178 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	179 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	180 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	181 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	182
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	183 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	184 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	185 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	186 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	187 issues with the library.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	188
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	189 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	190 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	191 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	192 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	193
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	194 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	195 exchange compressed data between them?
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 Yes and yes.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	198
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	199 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	200
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	201 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	202 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	203 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	204
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	205 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	206
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	207 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	208 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	209 directory for a possible solution to your problem.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	210
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	211 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	212
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	213 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	214 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	215 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	216 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	217 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	218 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	219 random access. See examples/zran.c .
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	220
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	221 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	222
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	223 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	224 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	225 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	226 systems, please let us know. Thanks.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	227
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	228 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	229 understand the deflate format?
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	230
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	231 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	232 contrib/puff directory.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	233
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	234 31. Does zlib infringe on any patents?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	235
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	236 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	237 zlib. Look here for some more information:
36186 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 http://www.gzip.org/#faq11
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	240
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	241 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	242
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	243 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	244 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	245 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	246 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	247 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	248 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	249 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	250 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	251 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	252 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	253 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	254
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	255 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	256 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	257 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	258
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	259 33. Does zlib have any security vulnerabilities?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	260
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	261 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	262 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	263 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	264 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	265 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	266 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	267 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	268 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	269 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	270 sprintf() is used by gzprintf().
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	271
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	272 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	273 find a portable implementation here:
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	274
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	275 http://www.ijs.si/software/snprintf/
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	276
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	277 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	278 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	279 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	280 invalid compressed data.
36186 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 34. Is there a Java version of zlib?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	283
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	284 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	285 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	286 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	287 page for links: http://zlib.net/ .
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	288
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	289 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	290 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	291
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	292 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	293 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	294 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	295 make sure that the code always works.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	296
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	297 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	298 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	299 Isn't that a bug?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	300
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	301 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	302 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	303 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	304 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	305 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	306 checkers.
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	307
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	308 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	309 data format?
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	310
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	311 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	312 formats and associated software.
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	313
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	314 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	315
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	316 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	317 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	318 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	319 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	320 http://www.info-zip.org/
36186 81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	321
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	322 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	323
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	324 "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	325 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	326 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	327 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	328 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	329 incorrectly produce or expect raw deflate data per the deflate
86546 224aa49f22f1 Issue #18527: Upgrade internal copy of zlib to 1.2.8 Christian Heimes <christian@cheimes.de> parents: 63336 diff changeset	330 specification 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	331 "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	332 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	333 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	334 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	335
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	336 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	337
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	338 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	339
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	340 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	341 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	342 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	343 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	344
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	345 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	346
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	347 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	348 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	349 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	350 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	351 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	352
63336 467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	353 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	354 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	355 GNU GPL?
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	356
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	357 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	358 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	359 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	360
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	361 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	362
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	363 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	364
467019588fcc Import files from zlib 1.2.5. Martin v. Löwis <martin@v.loewis.de> parents: 36186 diff changeset	365 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	366 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	367
81fa47d2d477 Import zlib into Python tree. Martin v. Löwis <martin@v.loewis.de> parents: diff changeset	368 No. Go away. Shoo.

Mercurial > cpython-lru_cache-weakref

annotate Modules/zlib/FAQ @ 87690:66c1c9f32567 default tip