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annotate zlib/FAQ @ 108:7ad14f446135

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add CbC-example/rectypeTest/
author Nobuyasu Oshiro <dimolto@cr.ie.u-ryukyu.ac.jp>
date Thu, 14 Jun 2012 20:30:24 +0900
parents ae3a4bfb450b
children 04ced10e8804
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51
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1
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2 Frequently Asked Questions about zlib
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3
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4
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5 If your question is not there, please check the zlib home page
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6 http://www.zlib.org which may have more recent information.
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7 The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html
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8
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9
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10 1. Is zlib Y2K-compliant?
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11
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12 Yes. zlib doesn't handle dates.
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13
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14 2. Where can I get a Windows DLL version?
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15
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16 The zlib sources can be compiled without change to produce a DLL.
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17 See the file win32/DLL_FAQ.txt in the zlib distribution.
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18 Pointers to the precompiled DLL are found in the zlib web site at
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19 http://www.zlib.org.
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20
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21 3. Where can I get a Visual Basic interface to zlib?
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22
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23 See
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24 * http://www.dogma.net/markn/articles/zlibtool/zlibtool.htm
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25 * contrib/visual-basic.txt in the zlib distribution
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26 * win32/DLL_FAQ.txt in the zlib distribution
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27
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28 4. compress() returns Z_BUF_ERROR.
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29
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30 Make sure that before the call of compress, the length of the compressed
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31 buffer is equal to the total size of the compressed buffer and not
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32 zero. For Visual Basic, check that this parameter is passed by reference
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33 ("as any"), not by value ("as long").
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34
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35 5. deflate() or inflate() returns Z_BUF_ERROR.
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36
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37 Before making the call, make sure that avail_in and avail_out are not
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38 zero. When setting the parameter flush equal to Z_FINISH, also make sure
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39 that avail_out is big enough to allow processing all pending input.
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40 Note that a Z_BUF_ERROR is not fatal--another call to deflate() or
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41 inflate() can be made with more input or output space. A Z_BUF_ERROR
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42 may in fact be unavoidable depending on how the functions are used, since
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43 it is not possible to tell whether or not there is more output pending
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44 when strm.avail_out returns with zero.
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45
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46 6. Where's the zlib documentation (man pages, etc.)?
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47
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48 It's in zlib.h for the moment, and Francis S. Lin has converted it to a
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49 web page zlib.html. Volunteers to transform this to Unix-style man pages,
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50 please contact us (zlib@gzip.org). Examples of zlib usage are in the files
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51 example.c and minigzip.c.
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52
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53 7. Why don't you use GNU autoconf or libtool or ...?
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54
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55 Because we would like to keep zlib as a very small and simple
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56 package. zlib is rather portable and doesn't need much configuration.
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57
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58 8. I found a bug in zlib.
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59
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60 Most of the time, such problems are due to an incorrect usage of
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61 zlib. Please try to reproduce the problem with a small program and send
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62 the corresponding source to us at zlib@gzip.org . Do not send
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63 multi-megabyte data files without prior agreement.
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64
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65 9. Why do I get "undefined reference to gzputc"?
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66
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67 If "make test" produces something like
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68
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69 example.o(.text+0x154): undefined reference to `gzputc'
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70
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71 check that you don't have old files libz.* in /usr/lib, /usr/local/lib or
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72 /usr/X11R6/lib. Remove any old versions, then do "make install".
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73
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74 10. I need a Delphi interface to zlib.
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75
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76 See the contrib/delphi directory in the zlib distribution.
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77
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78 11. Can zlib handle .zip archives?
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79
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80 Not by itself, no. See the directory contrib/minizip in the zlib
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81 distribution.
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82
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83 12. Can zlib handle .Z files?
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84
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85 No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt
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86 the code of uncompress on your own.
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87
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88 13. How can I make a Unix shared library?
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89
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90 make clean
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91 ./configure -s
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92 make
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93
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94 14. How do I install a shared zlib library on Unix?
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95
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96 After the above, then:
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97
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98 make install
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99
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100 However, many flavors of Unix come with a shared zlib already installed.
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101 Before going to the trouble of compiling a shared version of zlib and
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102 trying to install it, you may want to check if it's already there! If you
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103 can #include <zlib.h>, it's there. The -lz option will probably link to it.
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104
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105 15. I have a question about OttoPDF.
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106
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107 We are not the authors of OttoPDF. The real author is on the OttoPDF web
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108 site: Joel Hainley, jhainley@myndkryme.com.
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109
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110 16. Can zlib decode Flate data in an Adobe PDF file?
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111
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112 Yes. See http://www.fastio.com/ (ClibPDF), or http://www.pdflib.com/ .
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113 To modify PDF forms, see http://sourceforge.net/projects/acroformtool/ .
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114
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115 17. Why am I getting this "register_frame_info not found" error on Solaris?
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116
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117 After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
118 generates an error such as:
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
119
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
120 ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so:
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
121 symbol __register_frame_info: referenced symbol not found
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
122
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
123 The symbol __register_frame_info is not part of zlib, it is generated by
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
124 the C compiler (cc or gcc). You must recompile applications using zlib
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
125 which have this problem. This problem is specific to Solaris. See
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
126 http://www.sunfreeware.com for Solaris versions of zlib and applications
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
127 using zlib.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
128
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
129 18. Why does gzip give an error on a file I make with compress/deflate?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
130
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
131 The compress and deflate functions produce data in the zlib format, which
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
132 is different and incompatible with the gzip format. The gz* functions in
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
133 zlib on the other hand use the gzip format. Both the zlib and gzip
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
134 formats use the same compressed data format internally, but have different
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
135 headers and trailers around the compressed data.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
136
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
137 19. Ok, so why are there two different formats?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
138
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
139 The gzip format was designed to retain the directory information about
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
140 a single file, such as the name and last modification date. The zlib
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
141 format on the other hand was designed for in-memory and communication
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
142 channel applications, and has a much more compact header and trailer and
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
143 uses a faster integrity check than gzip.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
144
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
145 20. Well that's nice, but how do I make a gzip file in memory?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
146
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
147 You can request that deflate write the gzip format instead of the zlib
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
148 format using deflateInit2(). You can also request that inflate decode
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
149 the gzip format using inflateInit2(). Read zlib.h for more details.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
150
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
151 21. Is zlib thread-safe?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
152
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
153 Yes. However any library routines that zlib uses and any application-
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
154 provided memory allocation routines must also be thread-safe. zlib's gz*
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
155 functions use stdio library routines, and most of zlib's functions use the
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
156 library memory allocation routines by default. zlib's Init functions allow
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
157 for the application to provide custom memory allocation routines.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
158
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
159 Of course, you should only operate on any given zlib or gzip stream from a
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
160 single thread at a time.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
161
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
162 22. Can I use zlib in my commercial application?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
163
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
164 Yes. Please read the license in zlib.h.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
165
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
166 23. Is zlib under the GNU license?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
167
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
168 No. Please read the license in zlib.h.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
169
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
170 24. The license says that altered source versions must be "plainly marked". So
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
171 what exactly do I need to do to meet that requirement?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
172
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
173 You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
174 particular, the final version number needs to be changed to "f", and an
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
175 identification string should be appended to ZLIB_VERSION. Version numbers
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
176 x.x.x.f are reserved for modifications to zlib by others than the zlib
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
177 maintainers. For example, if the version of the base zlib you are altering
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
178 is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
179 ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3". You can also
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
180 update the version strings in deflate.c and inftrees.c.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
181
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
182 For altered source distributions, you should also note the origin and
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
183 nature of the changes in zlib.h, as well as in ChangeLog and README, along
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
184 with the dates of the alterations. The origin should include at least your
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
185 name (or your company's name), and an email address to contact for help or
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
186 issues with the library.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
187
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
188 Note that distributing a compiled zlib library along with zlib.h and
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
189 zconf.h is also a source distribution, and so you should change
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
190 ZLIB_VERSION and ZLIB_VERNUM and note the origin and nature of the changes
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
191 in zlib.h as you would for a full source distribution.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
192
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
193 25. Will zlib work on a big-endian or little-endian architecture, and can I
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
194 exchange compressed data between them?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
195
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
196 Yes and yes.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
197
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
198 26. Will zlib work on a 64-bit machine?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
199
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
200 It should. It has been tested on 64-bit machines, and has no dependence
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
201 on any data types being limited to 32-bits in length. If you have any
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
202 difficulties, please provide a complete problem report to zlib@gzip.org
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
203
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
204 27. Will zlib decompress data from the PKWare Data Compression Library?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
205
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
206 No. The PKWare DCL uses a completely different compressed data format
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
207 than does PKZIP and zlib. However, you can look in zlib's contrib/blast
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
208 directory for a possible solution to your problem.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
209
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
210 28. Can I access data randomly in a compressed stream?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
211
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
212 No, not without some preparation. If when compressing you periodically
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
213 use Z_FULL_FLUSH, carefully write all the pending data at those points,
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
214 and keep an index of those locations, then you can start decompression
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
215 at those points. You have to be careful to not use Z_FULL_FLUSH too
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
216 often, since it can significantly degrade compression.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
217
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
218 29. Does zlib work on MVS, OS/390, CICS, etc.?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
219
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
220 We don't know for sure. We have heard occasional reports of success on
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
221 these systems. If you do use it on one of these, please provide us with
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
222 a report, instructions, and patches that we can reference when we get
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
223 these questions. Thanks.
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
224
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
225 30. Is there some simpler, easier to read version of inflate I can look at
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
226 to understand the deflate format?
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
227
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
228 First off, you should read RFC 1951. Second, yes. Look in zlib's
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
229 contrib/puff directory.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
230
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
231 31. Does zlib infringe on any patents?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
232
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
233 As far as we know, no. In fact, that was originally the whole point behind
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
234 zlib. Look here for some more information:
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
235
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
236 http://www.gzip.org/#faq11
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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237
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
238 32. Can zlib work with greater than 4 GB of data?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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239
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
240 Yes. inflate() and deflate() will process any amount of data correctly.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
241 Each call of inflate() or deflate() is limited to input and output chunks
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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242 of the maximum value that can be stored in the compiler's "unsigned int"
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
243 type, but there is no limit to the number of chunks. Note however that the
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
244 strm.total_in and strm_total_out counters may be limited to 4 GB. These
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
245 counters are provided as a convenience and are not used internally by
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
246 inflate() or deflate(). The application can easily set up its own counters
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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247 updated after each call of inflate() or deflate() to count beyond 4 GB.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
248 compress() and uncompress() may be limited to 4 GB, since they operate in a
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
249 single call. gzseek() and gztell() may be limited to 4 GB depending on how
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
250 zlib is compiled. See the zlibCompileFlags() function in zlib.h.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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251
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
252 The word "may" appears several times above since there is a 4 GB limit
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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253 only if the compiler's "long" type is 32 bits. If the compiler's "long"
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
254 type is 64 bits, then the limit is 16 exabytes.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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255
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
256 33. Does zlib have any security vulnerabilities?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
257
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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258 The only one that we are aware of is potentially in gzprintf(). If zlib
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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259 is compiled to use sprintf() or vsprintf(), then there is no protection
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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260 against a buffer overflow of a 4K string space, other than the caller of
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
261 gzprintf() assuring that the output will not exceed 4K. On the other
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
262 hand, if zlib is compiled to use snprintf() or vsnprintf(), which should
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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263 normally be the case, then there is no vulnerability. The ./configure
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
264 script will display warnings if an insecure variation of sprintf() will
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
265 be used by gzprintf(). Also the zlibCompileFlags() function will return
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
266 information on what variant of sprintf() is used by gzprintf().
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
267
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
268 If you don't have snprintf() or vsnprintf() and would like one, you can
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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269 find a portable implementation here:
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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270
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
271 http://www.ijs.si/software/snprintf/
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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272
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
273 Note that you should be using the most recent version of zlib. Versions
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
274 1.1.3 and before were subject to a double-free vulnerability.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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275
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
276 34. Is there a Java version of zlib?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
277
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
278 Probably what you want is to use zlib in Java. zlib is already included
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
279 as part of the Java SDK in the java.util.zip package. If you really want
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
280 a version of zlib written in the Java language, look on the zlib home
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
281 page for links: http://www.zlib.org/
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
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282
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
283 35. I get this or that compiler or source-code scanner warning when I crank it
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
284 up to maximally-pedantic. Can't you guys write proper code?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
285
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
286 Many years ago, we gave up attempting to avoid warnings on every compiler
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
287 in the universe. It just got to be a waste of time, and some compilers
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
288 were downright silly. So now, we simply make sure that the code always
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
289 works.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
290
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
291 36. Valgrind (or some similar memory access checker) says that deflate is
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
292 performing a conditional jump that depends on an uninitialized value.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
293 Isn't that a bug?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
294
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
295 No. That is intentional for performance reasons, and the output of
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
296 deflate is not affected. This only started showing up recently since
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
297 zlib 1.2.x uses malloc() by default for allocations, whereas earlier
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
298 versions used calloc(), which zeros out the allocated memory.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
299
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
300 37. Will zlib read the (insert any ancient or arcane format here) compressed
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
301 data format?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
302
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
303 Probably not. Look in the comp.compression FAQ for pointers to various
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
304 formats and associated software.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
305
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
306 38. How can I encrypt/decrypt zip files with zlib?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
307
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
308 zlib doesn't support encryption. The original PKZIP encryption is very weak
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
309 and can be broken with freely available programs. To get strong encryption,
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
310 use GnuPG, http://www.gnupg.org/ , which already includes zlib compression.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
311 For PKZIP compatible "encryption", look at http://www.info-zip.org/
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
312
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
313 39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
314
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
315 "gzip" is the gzip format, and "deflate" is the zlib format. They should
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
316 probably have called the second one "zlib" instead to avoid confusion
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
317 with the raw deflate compressed data format. While the HTTP 1.1 RFC 2616
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
318 correctly points to the zlib specification in RFC 1950 for the "deflate"
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
319 transfer encoding, there have been reports of servers and browsers that
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
320 incorrectly produce or expect raw deflate data per the deflate
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
321 specficiation in RFC 1951, most notably Microsoft. So even though the
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
322 "deflate" transfer encoding using the zlib format would be the more
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
323 efficient approach (and in fact exactly what the zlib format was designed
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
324 for), using the "gzip" transfer encoding is probably more reliable due to
ae3a4bfb450b add some files of version 4.4.3 that have been forgotten.
kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
325 an unfortunate choice of name on the part of the HTTP 1.1 authors.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
326
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
327 Bottom line: use the gzip format for HTTP 1.1 encoding.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
328
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
329 40. Does zlib support the new "Deflate64" format introduced by PKWare?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
330
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
331 No. PKWare has apparently decided to keep that format proprietary, since
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
332 they have not documented it as they have previous compression formats.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
333 In any case, the compression improvements are so modest compared to other
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
334 more modern approaches, that it's not worth the effort to implement.
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
335
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
336 41. Can you please sign these lengthy legal documents and fax them back to us
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
337 so that we can use your software in our product?
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
338
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kent <kent@cr.ie.u-ryukyu.ac.jp>
parents:
diff changeset
339 No. Go away. Shoo.