Mercurial > hg > CbC > CbC_gcc
annotate zlib/FAQ @ 144:8f4e72ab4e11
fix segmentation fault caused by nothing next cur_op to end
author | Takahiro SHIMIZU <anatofuz@cr.ie.u-ryukyu.ac.jp> |
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date | Sun, 23 Dec 2018 21:23:56 +0900 |
parents | 04ced10e8804 |
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rev | line source |
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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 |
111 | 6 http://zlib.net/ which may have more recent information. |
7 The lastest zlib FAQ is at http://zlib.net/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 |
111 | 16 The zlib sources can be compiled without change to produce a DLL. See the |
17 file win32/DLL_FAQ.txt in the zlib distribution. Pointers to the | |
18 precompiled DLL are found in the zlib web site at http://zlib.net/ . | |
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19 |
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20 3. Where can I get a Visual Basic interface to zlib? |
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21 |
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22 See |
111 | 23 * http://marknelson.us/1997/01/01/zlib-engine/ |
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24 * win32/DLL_FAQ.txt in the zlib distribution |
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25 |
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26 4. compress() returns Z_BUF_ERROR. |
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27 |
111 | 28 Make sure that before the call of compress(), the length of the compressed |
29 buffer is equal to the available size of the compressed buffer and not | |
30 zero. For Visual Basic, check that this parameter is passed by reference | |
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31 ("as any"), not by value ("as long"). |
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32 |
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33 5. deflate() or inflate() returns Z_BUF_ERROR. |
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34 |
111 | 35 Before making the call, make sure that avail_in and avail_out are not zero. |
36 When setting the parameter flush equal to Z_FINISH, also make sure that | |
37 avail_out is big enough to allow processing all pending input. Note that a | |
38 Z_BUF_ERROR is not fatal--another call to deflate() or inflate() can be | |
39 made with more input or output space. A Z_BUF_ERROR may in fact be | |
40 unavoidable depending on how the functions are used, since it is not | |
41 possible to tell whether or not there is more output pending when | |
42 strm.avail_out returns with zero. See http://zlib.net/zlib_how.html for a | |
43 heavily annotated example. | |
51
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44 |
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45 6. Where's the zlib documentation (man pages, etc.)? |
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46 |
111 | 47 It's in zlib.h . Examples of zlib usage are in the files test/example.c |
48 and test/minigzip.c, with more in examples/ . | |
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49 |
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50 7. Why don't you use GNU autoconf or libtool or ...? |
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51 |
111 | 52 Because we would like to keep zlib as a very small and simple package. |
53 zlib is rather portable and doesn't need much configuration. | |
51
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54 |
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55 8. I found a bug in zlib. |
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56 |
111 | 57 Most of the time, such problems are due to an incorrect usage of zlib. |
58 Please try to reproduce the problem with a small program and send the | |
59 corresponding source to us at zlib@gzip.org . Do not send multi-megabyte | |
60 data files without prior agreement. | |
51
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61 |
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62 9. Why do I get "undefined reference to gzputc"? |
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63 |
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64 If "make test" produces something like |
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65 |
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66 example.o(.text+0x154): undefined reference to `gzputc' |
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67 |
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68 check that you don't have old files libz.* in /usr/lib, /usr/local/lib or |
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69 /usr/X11R6/lib. Remove any old versions, then do "make install". |
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70 |
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71 10. I need a Delphi interface to zlib. |
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72 |
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73 See the contrib/delphi directory in the zlib distribution. |
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74 |
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75 11. Can zlib handle .zip archives? |
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76 |
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77 Not by itself, no. See the directory contrib/minizip in the zlib |
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78 distribution. |
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79 |
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80 12. Can zlib handle .Z files? |
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81 |
111 | 82 No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt |
51
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83 the code of uncompress on your own. |
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84 |
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85 13. How can I make a Unix shared library? |
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86 |
111 | 87 By default a shared (and a static) library is built for Unix. So: |
88 | |
89 make distclean | |
90 ./configure | |
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91 make |
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92 |
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93 14. How do I install a shared zlib library on Unix? |
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94 |
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95 After the above, then: |
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96 |
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97 make install |
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98 |
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99 However, many flavors of Unix come with a shared zlib already installed. |
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100 Before going to the trouble of compiling a shared version of zlib and |
111 | 101 trying to install it, you may want to check if it's already there! If you |
102 can #include <zlib.h>, it's there. The -lz option will probably link to | |
103 it. You can check the version at the top of zlib.h or with the | |
104 ZLIB_VERSION symbol defined in zlib.h . | |
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105 |
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106 15. I have a question about OttoPDF. |
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107 |
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108 We are not the authors of OttoPDF. The real author is on the OttoPDF web |
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109 site: Joel Hainley, jhainley@myndkryme.com. |
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110 |
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111 16. Can zlib decode Flate data in an Adobe PDF file? |
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112 |
111 | 113 Yes. See http://www.pdflib.com/ . To modify PDF forms, see |
114 http://sourceforge.net/projects/acroformtool/ . | |
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115 |
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116 17. Why am I getting this "register_frame_info not found" error on Solaris? |
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117 |
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118 After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib |
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119 generates an error such as: |
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120 |
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121 ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so: |
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122 symbol __register_frame_info: referenced symbol not found |
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123 |
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124 The symbol __register_frame_info is not part of zlib, it is generated by |
111 | 125 the C compiler (cc or gcc). You must recompile applications using zlib |
126 which have this problem. This problem is specific to Solaris. See | |
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127 http://www.sunfreeware.com for Solaris versions of zlib and applications |
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128 using zlib. |
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129 |
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130 18. Why does gzip give an error on a file I make with compress/deflate? |
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131 |
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132 The compress and deflate functions produce data in the zlib format, which |
111 | 133 is different and incompatible with the gzip format. The gz* functions in |
134 zlib on the other hand use the gzip format. Both the zlib and gzip formats | |
135 use the same compressed data format internally, but have different headers | |
136 and trailers around the compressed data. | |
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137 |
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138 19. Ok, so why are there two different formats? |
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139 |
111 | 140 The gzip format was designed to retain the directory information about a |
141 single file, such as the name and last modification date. The zlib format | |
142 on the other hand was designed for in-memory and communication channel | |
143 applications, and has a much more compact header and trailer and uses a | |
144 faster integrity check than gzip. | |
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145 |
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146 20. Well that's nice, but how do I make a gzip file in memory? |
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147 |
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148 You can request that deflate write the gzip format instead of the zlib |
111 | 149 format using deflateInit2(). You can also request that inflate decode the |
150 gzip format using inflateInit2(). Read zlib.h for more details. | |
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151 |
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152 21. Is zlib thread-safe? |
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153 |
111 | 154 Yes. However any library routines that zlib uses and any application- |
155 provided memory allocation routines must also be thread-safe. zlib's gz* | |
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156 functions use stdio library routines, and most of zlib's functions use the |
111 | 157 library memory allocation routines by default. zlib's *Init* functions |
158 allow for the application to provide custom memory allocation routines. | |
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159 |
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160 Of course, you should only operate on any given zlib or gzip stream from a |
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161 single thread at a time. |
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162 |
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163 22. Can I use zlib in my commercial application? |
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164 |
111 | 165 Yes. Please read the license in zlib.h. |
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166 |
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167 23. Is zlib under the GNU license? |
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168 |
111 | 169 No. Please read the license in zlib.h. |
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170 |
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171 24. The license says that altered source versions must be "plainly marked". So |
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172 what exactly do I need to do to meet that requirement? |
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173 |
111 | 174 You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In |
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175 particular, the final version number needs to be changed to "f", and an |
111 | 176 identification string should be appended to ZLIB_VERSION. Version numbers |
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177 x.x.x.f are reserved for modifications to zlib by others than the zlib |
111 | 178 maintainers. For example, if the version of the base zlib you are altering |
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179 is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and |
111 | 180 ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3". You can also |
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181 update the version strings in deflate.c and inftrees.c. |
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182 |
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183 For altered source distributions, you should also note the origin and |
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184 nature of the changes in zlib.h, as well as in ChangeLog and README, along |
111 | 185 with the dates of the alterations. The origin should include at least your |
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186 name (or your company's name), and an email address to contact for help or |
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187 issues with the library. |
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188 |
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189 Note that distributing a compiled zlib library along with zlib.h and |
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190 zconf.h is also a source distribution, and so you should change |
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191 ZLIB_VERSION and ZLIB_VERNUM and note the origin and nature of the changes |
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192 in zlib.h as you would for a full source distribution. |
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193 |
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194 25. Will zlib work on a big-endian or little-endian architecture, and can I |
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195 exchange compressed data between them? |
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196 |
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197 Yes and yes. |
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198 |
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199 26. Will zlib work on a 64-bit machine? |
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200 |
111 | 201 Yes. It has been tested on 64-bit machines, and has no dependence on any |
202 data types being limited to 32-bits in length. If you have any | |
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203 difficulties, please provide a complete problem report to zlib@gzip.org |
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204 |
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205 27. Will zlib decompress data from the PKWare Data Compression Library? |
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206 |
111 | 207 No. The PKWare DCL uses a completely different compressed data format than |
208 does PKZIP and zlib. However, you can look in zlib's contrib/blast | |
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209 directory for a possible solution to your problem. |
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210 |
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211 28. Can I access data randomly in a compressed stream? |
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212 |
111 | 213 No, not without some preparation. If when compressing you periodically use |
214 Z_FULL_FLUSH, carefully write all the pending data at those points, and | |
215 keep an index of those locations, then you can start decompression at those | |
216 points. You have to be careful to not use Z_FULL_FLUSH too often, since it | |
217 can significantly degrade compression. Alternatively, you can scan a | |
218 deflate stream once to generate an index, and then use that index for | |
219 random access. See examples/zran.c . | |
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220 |
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221 29. Does zlib work on MVS, OS/390, CICS, etc.? |
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222 |
111 | 223 It has in the past, but we have not heard of any recent evidence. There |
224 were working ports of zlib 1.1.4 to MVS, but those links no longer work. | |
225 If you know of recent, successful applications of zlib on these operating | |
226 systems, please let us know. Thanks. | |
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227 |
111 | 228 30. Is there some simpler, easier to read version of inflate I can look at to |
229 understand the deflate format? | |
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230 |
111 | 231 First off, you should read RFC 1951. Second, yes. Look in zlib's |
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232 contrib/puff directory. |
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233 |
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234 31. Does zlib infringe on any patents? |
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235 |
111 | 236 As far as we know, no. In fact, that was originally the whole point behind |
237 zlib. Look here for some more information: | |
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238 |
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239 http://www.gzip.org/#faq11 |
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240 |
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241 32. Can zlib work with greater than 4 GB of data? |
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242 |
111 | 243 Yes. inflate() and deflate() will process any amount of data correctly. |
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244 Each call of inflate() or deflate() is limited to input and output chunks |
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245 of the maximum value that can be stored in the compiler's "unsigned int" |
111 | 246 type, but there is no limit to the number of chunks. Note however that the |
247 strm.total_in and strm_total_out counters may be limited to 4 GB. These | |
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248 counters are provided as a convenience and are not used internally by |
111 | 249 inflate() or deflate(). The application can easily set up its own counters |
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250 updated after each call of inflate() or deflate() to count beyond 4 GB. |
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251 compress() and uncompress() may be limited to 4 GB, since they operate in a |
111 | 252 single call. gzseek() and gztell() may be limited to 4 GB depending on how |
253 zlib is compiled. See the zlibCompileFlags() function in zlib.h. | |
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254 |
111 | 255 The word "may" appears several times above since there is a 4 GB limit only |
256 if the compiler's "long" type is 32 bits. If the compiler's "long" type is | |
257 64 bits, then the limit is 16 exabytes. | |
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258 |
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259 33. Does zlib have any security vulnerabilities? |
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260 |
111 | 261 The only one that we are aware of is potentially in gzprintf(). If zlib is |
262 compiled to use sprintf() or vsprintf(), then there is no protection | |
263 against a buffer overflow of an 8K string space (or other value as set by | |
264 gzbuffer()), other than the caller of gzprintf() assuring that the output | |
265 will not exceed 8K. On the other hand, if zlib is compiled to use | |
266 snprintf() or vsnprintf(), which should normally be the case, then there is | |
267 no vulnerability. The ./configure script will display warnings if an | |
268 insecure variation of sprintf() will be used by gzprintf(). Also the | |
269 zlibCompileFlags() function will return information on what variant of | |
270 sprintf() is used by gzprintf(). | |
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271 |
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272 If you don't have snprintf() or vsnprintf() and would like one, you can |
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273 find a portable implementation here: |
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274 |
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275 http://www.ijs.si/software/snprintf/ |
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276 |
111 | 277 Note that you should be using the most recent version of zlib. Versions |
278 1.1.3 and before were subject to a double-free vulnerability, and versions | |
279 1.2.1 and 1.2.2 were subject to an access exception when decompressing | |
280 invalid compressed data. | |
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281 |
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282 34. Is there a Java version of zlib? |
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283 |
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284 Probably what you want is to use zlib in Java. zlib is already included |
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285 as part of the Java SDK in the java.util.zip package. If you really want |
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286 a version of zlib written in the Java language, look on the zlib home |
111 | 287 page for links: http://zlib.net/ . |
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288 |
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289 35. I get this or that compiler or source-code scanner warning when I crank it |
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290 up to maximally-pedantic. Can't you guys write proper code? |
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291 |
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292 Many years ago, we gave up attempting to avoid warnings on every compiler |
111 | 293 in the universe. It just got to be a waste of time, and some compilers |
294 were downright silly as well as contradicted each other. So now, we simply | |
295 make sure that the code always works. | |
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296 |
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297 36. Valgrind (or some similar memory access checker) says that deflate is |
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298 performing a conditional jump that depends on an uninitialized value. |
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299 Isn't that a bug? |
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300 |
111 | 301 No. That is intentional for performance reasons, and the output of deflate |
302 is not affected. This only started showing up recently since zlib 1.2.x | |
303 uses malloc() by default for allocations, whereas earlier versions used | |
304 calloc(), which zeros out the allocated memory. Even though the code was | |
305 correct, versions 1.2.4 and later was changed to not stimulate these | |
306 checkers. | |
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307 |
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308 37. Will zlib read the (insert any ancient or arcane format here) compressed |
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309 data format? |
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310 |
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311 Probably not. Look in the comp.compression FAQ for pointers to various |
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312 formats and associated software. |
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313 |
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314 38. How can I encrypt/decrypt zip files with zlib? |
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315 |
111 | 316 zlib doesn't support encryption. The original PKZIP encryption is very |
317 weak and can be broken with freely available programs. To get strong | |
318 encryption, use GnuPG, http://www.gnupg.org/ , which already includes zlib | |
319 compression. For PKZIP compatible "encryption", look at | |
320 http://www.info-zip.org/ | |
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321 |
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322 39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings? |
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323 |
111 | 324 "gzip" is the gzip format, and "deflate" is the zlib format. They should |
325 probably have called the second one "zlib" instead to avoid confusion with | |
326 the raw deflate compressed data format. While the HTTP 1.1 RFC 2616 | |
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327 correctly points to the zlib specification in RFC 1950 for the "deflate" |
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328 transfer encoding, there have been reports of servers and browsers that |
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329 incorrectly produce or expect raw deflate data per the deflate |
111 | 330 specification in RFC 1951, most notably Microsoft. So even though the |
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331 "deflate" transfer encoding using the zlib format would be the more |
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332 efficient approach (and in fact exactly what the zlib format was designed |
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333 for), using the "gzip" transfer encoding is probably more reliable due to |
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334 an unfortunate choice of name on the part of the HTTP 1.1 authors. |
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335 |
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336 Bottom line: use the gzip format for HTTP 1.1 encoding. |
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337 |
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338 40. Does zlib support the new "Deflate64" format introduced by PKWare? |
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339 |
111 | 340 No. PKWare has apparently decided to keep that format proprietary, since |
341 they have not documented it as they have previous compression formats. In | |
342 any case, the compression improvements are so modest compared to other more | |
343 modern approaches, that it's not worth the effort to implement. | |
344 | |
345 41. I'm having a problem with the zip functions in zlib, can you help? | |
346 | |
347 There are no zip functions in zlib. You are probably using minizip by | |
348 Giles Vollant, which is found in the contrib directory of zlib. It is not | |
349 part of zlib. In fact none of the stuff in contrib is part of zlib. The | |
350 files in there are not supported by the zlib authors. You need to contact | |
351 the authors of the respective contribution for help. | |
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352 |
111 | 353 42. The match.asm code in contrib is under the GNU General Public License. |
354 Since it's part of zlib, doesn't that mean that all of zlib falls under the | |
355 GNU GPL? | |
356 | |
357 No. The files in contrib are not part of zlib. They were contributed by | |
358 other authors and are provided as a convenience to the user within the zlib | |
359 distribution. Each item in contrib has its own license. | |
360 | |
361 43. Is zlib subject to export controls? What is its ECCN? | |
362 | |
363 zlib is not subject to export controls, and so is classified as EAR99. | |
364 | |
365 44. Can you please sign these lengthy legal documents and fax them back to us | |
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366 so that we can use your software in our product? |
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367 |
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368 No. Go away. Shoo. |