Changeset 0dca067 in rtems for cpukit/zlib


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Timestamp:
Mar 14, 2010, 6:08:12 PM (10 years ago)
Author:
Ralf Corsepius <ralf.corsepius@…>
Branches:
4.10, 4.11, master
Children:
138cc2f
Parents:
00d17034 (diff), 12ff5e9 (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.
Message:

This commit was generated by cvs2svn to compensate for changes in r22743,
which included commits to RCS files with non-trunk default branches.

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1 edited

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  • cpukit/zlib/FAQ

    r00d17034 r0dca067  
    44
    55If your question is not there, please check the zlib home page
    6 http://www.zlib.org which may have more recent information.
    7 The lastest zlib FAQ is at http://www.gzip.org/zlib/zlib_faq.html
     6http://zlib.net/ which may have more recent information.
     7The lastest zlib FAQ is at http://zlib.net/zlib_faq.html
    88
    99
     
    1414 2. Where can I get a Windows DLL version?
    1515
    16     The zlib sources can be compiled without change to produce a DLL.
    17     See the file win32/DLL_FAQ.txt in the zlib distribution.
    18     Pointers to the precompiled DLL are found in the zlib web site at
    19     http://www.zlib.org.
     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/ .
    2019
    2120 3. Where can I get a Visual Basic interface to zlib?
    2221
    2322    See
    24         * http://www.dogma.net/markn/articles/zlibtool/zlibtool.htm
    25         * contrib/visual-basic.txt in the zlib distribution
     23        * http://marknelson.us/1997/01/01/zlib-engine/
    2624        * win32/DLL_FAQ.txt in the zlib distribution
    2725
    2826 4. compress() returns Z_BUF_ERROR.
    2927
    30     Make sure that before the call of compress, the length of the compressed
    31     buffer is equal to the total size of the compressed buffer and not
    32     zero. For Visual Basic, check that this parameter is passed by reference
     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
    3331    ("as any"), not by value ("as long").
    3432
    3533 5. deflate() or inflate() returns Z_BUF_ERROR.
    3634
    37     Before making the call, make sure that avail_in and avail_out are not
    38     zero. When setting the parameter flush equal to Z_FINISH, also make sure
    39     that avail_out is big enough to allow processing all pending input.
    40     Note that a Z_BUF_ERROR is not fatal--another call to deflate() or
    41     inflate() can be made with more input or output space. A Z_BUF_ERROR
    42     may in fact be unavoidable depending on how the functions are used, since
    43     it is not possible to tell whether or not there is more output pending
    44     when strm.avail_out returns with zero.
     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.
    4544
    4645 6. Where's the zlib documentation (man pages, etc.)?
    4746
    48     It's in zlib.h for the moment, and Francis S. Lin has converted it to a
    49     web page zlib.html. Volunteers to transform this to Unix-style man pages,
    50     please contact us (zlib@gzip.org). Examples of zlib usage are in the files
    51     example.c and minigzip.c.
     47    It's in zlib.h .  Examples of zlib usage are in the files example.c and
     48    minigzip.c, with more in examples/ .
    5249
    5350 7. Why don't you use GNU autoconf or libtool or ...?
    5451
    55     Because we would like to keep zlib as a very small and simple
    56     package. zlib is rather portable and doesn't need much configuration.
     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.
    5754
    5855 8. I found a bug in zlib.
    5956
    60     Most of the time, such problems are due to an incorrect usage of
    61     zlib. Please try to reproduce the problem with a small program and send
    62     the corresponding source to us at zlib@gzip.org . Do not send
    63     multi-megabyte data files without prior agreement.
     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.
    6461
    6562 9. Why do I get "undefined reference to gzputc"?
     
    838012. Can zlib handle .Z files?
    8481
    85     No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt
     82    No, sorry.  You have to spawn an uncompress or gunzip subprocess, or adapt
    8683    the code of uncompress on your own.
    8784
     
    10097    However, many flavors of Unix come with a shared zlib already installed.
    10198    Before going to the trouble of compiling a shared version of zlib and
    102     trying to install it, you may want to check if it's already there! If you
    103     can #include <zlib.h>, it's there. The -lz option will probably link to it.
     99    trying to install it, you may want to check if it's already there!  If you
     100    can #include <zlib.h>, it's there.  The -lz option will probably link to
     101    it.  You can check the version at the top of zlib.h or with the
     102    ZLIB_VERSION symbol defined in zlib.h .
    104103
    10510415. I have a question about OttoPDF.
     
    11010916. Can zlib decode Flate data in an Adobe PDF file?
    111110
    112     Yes. See http://www.fastio.com/ (ClibPDF), or http://www.pdflib.com/ .
    113     To modify PDF forms, see http://sourceforge.net/projects/acroformtool/ .
     111    Yes. See http://www.pdflib.com/ . To modify PDF forms, see
     112    http://sourceforge.net/projects/acroformtool/ .
    114113
    11511417. Why am I getting this "register_frame_info not found" error on Solaris?
     
    122121
    123122    The symbol __register_frame_info is not part of zlib, it is generated by
    124     the C compiler (cc or gcc). You must recompile applications using zlib
    125     which have this problem. This problem is specific to Solaris. See
     123    the C compiler (cc or gcc).  You must recompile applications using zlib
     124    which have this problem.  This problem is specific to Solaris. See
    126125    http://www.sunfreeware.com for Solaris versions of zlib and applications
    127126    using zlib.
     
    130129
    131130    The compress and deflate functions produce data in the zlib format, which
    132     is different and incompatible with the gzip format. The gz* functions in
    133     zlib on the other hand use the gzip format. Both the zlib and gzip
    134     formats use the same compressed data format internally, but have different
    135     headers and trailers around the compressed data.
     131    is different and incompatible with the gzip format.  The gz* functions in
     132    zlib on the other hand use the gzip format.  Both the zlib and gzip formats
     133    use the same compressed data format internally, but have different headers
     134    and trailers around the compressed data.
    136135
    13713619. Ok, so why are there two different formats?
    138137
    139     The gzip format was designed to retain the directory information about
    140     a single file, such as the name and last modification date. The zlib
    141     format on the other hand was designed for in-memory and communication
    142     channel applications, and has a much more compact header and trailer and
    143     uses a faster integrity check than gzip.
     138    The gzip format was designed to retain the directory information about a
     139    single file, such as the name and last modification date.  The zlib format
     140    on the other hand was designed for in-memory and communication channel
     141    applications, and has a much more compact header and trailer and uses a
     142    faster integrity check than gzip.
    144143
    14514420. Well that's nice, but how do I make a gzip file in memory?
    146145
    147146    You can request that deflate write the gzip format instead of the zlib
    148     format using deflateInit2(). You can also request that inflate decode
    149     the gzip format using inflateInit2(). Read zlib.h for more details.
     147    format using deflateInit2().  You can also request that inflate decode the
     148    gzip format using inflateInit2(). Read zlib.h for more details.
    150149
    15115021. Is zlib thread-safe?
    152151
    153     Yes. However any library routines that zlib uses and any application-
    154     provided memory allocation routines must also be thread-safe. zlib's gz*
     152    Yes.  However any library routines that zlib uses and any application-
     153    provided memory allocation routines must also be thread-safe.  zlib's gz*
    155154    functions use stdio library routines, and most of zlib's functions use the
    156     library memory allocation routines by default. zlib's Init functions allow
    157     for the application to provide custom memory allocation routines.
     155    library memory allocation routines by default.  zlib's *Init* functions
     156    allow for the application to provide custom memory allocation routines.
    158157
    159158    Of course, you should only operate on any given zlib or gzip stream from a
     
    16216122. Can I use zlib in my commercial application?
    163162
    164     Yes. Please read the license in zlib.h.
     163    Yes.  Please read the license in zlib.h.
    165164
    16616523. Is zlib under the GNU license?
    167166
    168     No. Please read the license in zlib.h.
     167    No.  Please read the license in zlib.h.
    169168
    17016924. The license says that altered source versions must be "plainly marked". So
    171170    what exactly do I need to do to meet that requirement?
    172171
    173     You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In
     172    You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h.  In
    174173    particular, the final version number needs to be changed to "f", and an
    175     identification string should be appended to ZLIB_VERSION. Version numbers
     174    identification string should be appended to ZLIB_VERSION.  Version numbers
    176175    x.x.x.f are reserved for modifications to zlib by others than the zlib
    177     maintainers. For example, if the version of the base zlib you are altering
     176    maintainers.  For example, if the version of the base zlib you are altering
    178177    is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and
    179     ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3". You can also
     178    ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3".  You can also
    180179    update the version strings in deflate.c and inftrees.c.
    181180
    182181    For altered source distributions, you should also note the origin and
    183182    nature of the changes in zlib.h, as well as in ChangeLog and README, along
    184     with the dates of the alterations. The origin should include at least your
     183    with the dates of the alterations.  The origin should include at least your
    185184    name (or your company's name), and an email address to contact for help or
    186185    issues with the library.
     
    19819726. Will zlib work on a 64-bit machine?
    199198
    200     It should. It has been tested on 64-bit machines, and has no dependence
    201     on any data types being limited to 32-bits in length. If you have any
     199    Yes.  It has been tested on 64-bit machines, and has no dependence on any
     200    data types being limited to 32-bits in length. If you have any
    202201    difficulties, please provide a complete problem report to zlib@gzip.org
    203202
    20420327. Will zlib decompress data from the PKWare Data Compression Library?
    205204
    206     No. The PKWare DCL uses a completely different compressed data format
    207     than does PKZIP and zlib. However, you can look in zlib's contrib/blast
     205    No.  The PKWare DCL uses a completely different compressed data format than
     206    does PKZIP and zlib. However, you can look in zlib's contrib/blast
    208207    directory for a possible solution to your problem.
    209208
    21020928. Can I access data randomly in a compressed stream?
    211210
    212     No, not without some preparation. If when compressing you periodically
    213     use Z_FULL_FLUSH, carefully write all the pending data at those points,
    214     and keep an index of those locations, then you can start decompression
    215     at those points. You have to be careful to not use Z_FULL_FLUSH too
    216     often, since it can significantly degrade compression.
     211    No, not without some preparation.  If when compressing you periodically use
     212    Z_FULL_FLUSH, carefully write all the pending data at those points, and
     213    keep an index of those locations, then you can start decompression at those
     214    points.  You have to be careful to not use Z_FULL_FLUSH too often, since it
     215    can significantly degrade compression.  Alternatively, you can scan a
     216    deflate stream once to generate an index, and then use that index for
     217    random access.  See examples/zran.c .
    217218
    21821929. Does zlib work on MVS, OS/390, CICS, etc.?
    219220
    220     We don't know for sure. We have heard occasional reports of success on
    221     these systems. If you do use it on one of these, please provide us with
    222     a report, instructions, and patches that we can reference when we get
    223     these questions. Thanks.
    224 
    225 30. Is there some simpler, easier to read version of inflate I can look at
    226     to understand the deflate format?
    227 
    228     First off, you should read RFC 1951. Second, yes. Look in zlib's
     221    It has in the past, but we have not heard of any recent evidence.  There
     222    were working ports of zlib 1.1.4 to MVS, but those links no longer work.
     223    If you know of recent, successful applications of zlib on these operating
     224    systems, please let us know. Thanks.
     225
     22630. Is there some simpler, easier to read version of inflate I can look at to
     227    understand the deflate format?
     228
     229    First off, you should read RFC 1951.  Second, yes. Look in zlib's
    229230    contrib/puff directory.
    230231
    23123231. Does zlib infringe on any patents?
    232233
    233     As far as we know, no. In fact, that was originally the whole point behind
    234     zlib. Look here for some more information:
     234    As far as we know, no.  In fact, that was originally the whole point behind
     235    zlib.  Look here for some more information:
    235236
    236237    http://www.gzip.org/#faq11
     
    23823932. Can zlib work with greater than 4 GB of data?
    239240
    240     Yes. inflate() and deflate() will process any amount of data correctly.
     241    Yes.  inflate() and deflate() will process any amount of data correctly.
    241242    Each call of inflate() or deflate() is limited to input and output chunks
    242243    of the maximum value that can be stored in the compiler's "unsigned int"
    243     type, but there is no limit to the number of chunks. Note however that the
    244     strm.total_in and strm_total_out counters may be limited to 4 GB. These
     244    type, but there is no limit to the number of chunks.  Note however that the
     245    strm.total_in and strm_total_out counters may be limited to 4 GB.  These
    245246    counters are provided as a convenience and are not used internally by
    246     inflate() or deflate(). The application can easily set up its own counters
     247    inflate() or deflate().  The application can easily set up its own counters
    247248    updated after each call of inflate() or deflate() to count beyond 4 GB.
    248249    compress() and uncompress() may be limited to 4 GB, since they operate in a
    249     single call. gzseek() and gztell() may be limited to 4 GB depending on how
    250     zlib is compiled. See the zlibCompileFlags() function in zlib.h.
    251 
    252     The word "may" appears several times above since there is a 4 GB limit
    253     only if the compiler's "long" type is 32 bits. If the compiler's "long"
    254     type is 64 bits, then the limit is 16 exabytes.
     250    single call.  gzseek() and gztell() may be limited to 4 GB depending on how
     251    zlib is compiled.  See the zlibCompileFlags() function in zlib.h.
     252
     253    The word "may" appears several times above since there is a 4 GB limit only
     254    if the compiler's "long" type is 32 bits.  If the compiler's "long" type is
     255    64 bits, then the limit is 16 exabytes.
    255256
    25625733. Does zlib have any security vulnerabilities?
    257258
    258     The only one that we are aware of is potentially in gzprintf(). If zlib
    259     is compiled to use sprintf() or vsprintf(), then there is no protection
    260     against a buffer overflow of a 4K string space, other than the caller of
    261     gzprintf() assuring that the output will not exceed 4K. On the other
    262     hand, if zlib is compiled to use snprintf() or vsnprintf(), which should
    263     normally be the case, then there is no vulnerability. The ./configure
    264     script will display warnings if an insecure variation of sprintf() will
    265     be used by gzprintf(). Also the zlibCompileFlags() function will return
    266     information on what variant of sprintf() is used by gzprintf().
     259    The only one that we are aware of is potentially in gzprintf().  If zlib is
     260    compiled to use sprintf() or vsprintf(), then there is no protection
     261    against a buffer overflow of an 8K string space (or other value as set by
     262    gzbuffer()), other than the caller of gzprintf() assuring that the output
     263    will not exceed 8K.  On the other hand, if zlib is compiled to use
     264    snprintf() or vsnprintf(), which should normally be the case, then there is
     265    no vulnerability.  The ./configure script will display warnings if an
     266    insecure variation of sprintf() will be used by gzprintf().  Also the
     267    zlibCompileFlags() function will return information on what variant of
     268    sprintf() is used by gzprintf().
    267269
    268270    If you don't have snprintf() or vsnprintf() and would like one, you can
     
    271273        http://www.ijs.si/software/snprintf/
    272274
    273     Note that you should be using the most recent version of zlib. Versions
    274     1.1.3 and before were subject to a double-free vulnerability.
     275    Note that you should be using the most recent version of zlib.  Versions
     276    1.1.3 and before were subject to a double-free vulnerability, and versions
     277    1.2.1 and 1.2.2 were subject to an access exception when decompressing
     278    invalid compressed data.
    275279
    27628034. Is there a Java version of zlib?
     
    279283    as part of the Java SDK in the java.util.zip package. If you really want
    280284    a version of zlib written in the Java language, look on the zlib home
    281     page for links: http://www.zlib.org/
     285    page for links: http://zlib.net/ .
    282286
    28328735. I get this or that compiler or source-code scanner warning when I crank it
     
    285289
    286290    Many years ago, we gave up attempting to avoid warnings on every compiler
    287     in the universe. It just got to be a waste of time, and some compilers
    288     were downright silly. So now, we simply make sure that the code always
    289     works.
     291    in the universe.  It just got to be a waste of time, and some compilers
     292    were downright silly as well as contradicted each other.  So now, we simply
     293    make sure that the code always works.
    290294
    29129536. Valgrind (or some similar memory access checker) says that deflate is
     
    293297    Isn't that a bug?
    294298
    295     No.  That is intentional for performance reasons, and the output of
    296     deflate is not affected.  This only started showing up recently since
    297     zlib 1.2.x uses malloc() by default for allocations, whereas earlier
    298     versions used calloc(), which zeros out the allocated memory.
     299    No.  That is intentional for performance reasons, and the output of deflate
     300    is not affected.  This only started showing up recently since zlib 1.2.x
     301    uses malloc() by default for allocations, whereas earlier versions used
     302    calloc(), which zeros out the allocated memory.  Even though the code was
     303    correct, versions 1.2.4 and later was changed to not stimulate these
     304    checkers.
    299305
    30030637. Will zlib read the (insert any ancient or arcane format here) compressed
     
    30631238. How can I encrypt/decrypt zip files with zlib?
    307313
    308     zlib doesn't support encryption. The original PKZIP encryption is very weak
    309     and can be broken with freely available programs. To get strong encryption,
    310     use GnuPG, http://www.gnupg.org/ , which already includes zlib compression.
    311     For PKZIP compatible "encryption", look at http://www.info-zip.org/
     314    zlib doesn't support encryption.  The original PKZIP encryption is very
     315    weak and can be broken with freely available programs.  To get strong
     316    encryption, use GnuPG, http://www.gnupg.org/ , which already includes zlib
     317    compression.  For PKZIP compatible "encryption", look at
     318    http://www.info-zip.org/
    312319
    31332039. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?
    314321
    315     "gzip" is the gzip format, and "deflate" is the zlib format. They should
    316     probably have called the second one "zlib" instead to avoid confusion
    317     with the raw deflate compressed data format. While the HTTP 1.1 RFC 2616
     322    "gzip" is the gzip format, and "deflate" is the zlib format.  They should
     323    probably have called the second one "zlib" instead to avoid confusion with
     324    the raw deflate compressed data format. While the HTTP 1.1 RFC 2616
    318325    correctly points to the zlib specification in RFC 1950 for the "deflate"
    319326    transfer encoding, there have been reports of servers and browsers that
    320327    incorrectly produce or expect raw deflate data per the deflate
    321     specficiation in RFC 1951, most notably Microsoft. So even though the
     328    specficiation in RFC 1951, most notably Microsoft.  So even though the
    322329    "deflate" transfer encoding using the zlib format would be the more
    323330    efficient approach (and in fact exactly what the zlib format was designed
     
    32933640. Does zlib support the new "Deflate64" format introduced by PKWare?
    330337
    331     No. PKWare has apparently decided to keep that format proprietary, since
    332     they have not documented it as they have previous compression formats.
    333     In any case, the compression improvements are so modest compared to other
    334     more modern approaches, that it's not worth the effort to implement.
    335 
    336 41. Can you please sign these lengthy legal documents and fax them back to us
     338    No.  PKWare has apparently decided to keep that format proprietary, since
     339    they have not documented it as they have previous compression formats.  In
     340    any case, the compression improvements are so modest compared to other more
     341    modern approaches, that it's not worth the effort to implement.
     342
     34341. I'm having a problem with the zip functions in zlib, can you help?
     344
     345    There are no zip functions in zlib.  You are probably using minizip by
     346    Giles Vollant, which is found in the contrib directory of zlib.  It is not
     347    part of zlib.  In fact none of the stuff in contrib is part of zlib.  The
     348    files in there are not supported by the zlib authors.  You need to contact
     349    the authors of the respective contribution for help.
     350
     35142. The match.asm code in contrib is under the GNU General Public License.
     352    Since it's part of zlib, doesn't that mean that all of zlib falls under the
     353    GNU GPL?
     354
     355    No.  The files in contrib are not part of zlib.  They were contributed by
     356    other authors and are provided as a convenience to the user within the zlib
     357    distribution.  Each item in contrib has its own license.
     358
     35943. Is zlib subject to export controls?  What is its ECCN?
     360
     361    zlib is not subject to export controls, and so is classified as EAR99.
     362
     36344. Can you please sign these lengthy legal documents and fax them back to us
    337364    so that we can use your software in our product?
    338365
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