archive::zip::faq.3

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.IX Header "Can't Read/modify/write same Zip file"
\&\fBQ:\fR Why can't I open a Zip file, add a member, and write it back? I get an
error message when I try.
.PP
\&\fBA:\fR Because Archive::Zip doesn't (and can't, generally) read file contents into memory,
the original Zip file is required to stay around until the writing of the new
file is completed.
.PP
The best way to do this is to write the Zip to a temporary file and then
rename the temporary file to have the old name (possibly after deleting the
old one).
.PP
Archive::Zip v1.02 added the archive methods \f(CW\*(C`overwrite()\*(C'\fR and
\&\f(CW\*(C`overwriteAs()\*(C'\fR to do this simply and carefully.
.PP
See \f(CW\*(C`examples/updateZip.pl\*(C'\fR for an example of this technique.
.SH "File creation time not set"
.IX Header "File creation time not set"
\&\fBQ:\fR Upon extracting files, I see that their modification (and access) times are
set to the time in the Zip archive. However, their creation time is not set to
the same time. Why?
.PP
\&\fBA:\fR Mostly because Perl doesn't give cross-platform access to \fIcreation time\fR.
Indeed, many systems (like Unix) don't support such a concept.
However, if yours does, you can easily set it. Get the modification time from
the member using \f(CW\*(C`lastModTime()\*(C'\fR.
.SH "Can't use Archive::Zip on gzip files"
.IX Header "Can't use Archive::Zip on gzip files"
\&\fBQ:\fR Can I use Archive::Zip to extract Unix gzip files?
.PP
\&\fBA:\fR No.
.PP
There is a distinction between Unix gzip files, and Zip archives that 
also can use the gzip compression.
.PP
Depending on the format of the gzip file, you can use Compress::Zlib, or
Archive::Tar to decompress it (and de-archive it in the case of Tar files).
.PP
You can unzip PKZIP/WinZip/etc/ archives using Archive::Zip (that's what 
it's for) as long as any compressed members are compressed using 
Deflate compression.
.SH "Add a directory/tree to a Zip"
.IX Header "Add a directory/tree to a Zip"
\&\fBQ:\fR How can I add a directory (or tree) full of files to a Zip?
.PP
\&\fBA:\fR You can use the Archive::Zip::addTree*() methods:
.PP
.Vb 10
\&   use Archive::Zip;
\&   my $zip = Archive::Zip\->new();
\&   # add all readable files and directories below . as xyz/*
\&   $zip\->addTree( \*(Aq.\*(Aq, \*(Aqxyz\*(Aq ); 
\&   # add all readable plain files below /abc as def/*
\&   $zip\->addTree( \*(Aq/abc\*(Aq, \*(Aqdef\*(Aq, sub { \-f && \-r } );    
\&   # add all .c files below /tmp as stuff/*
\&   $zip\->addTreeMatching( \*(Aq/tmp\*(Aq, \*(Aqstuff\*(Aq, \*(Aq\e.c$\*(Aq );
\&   # add all .o files below /tmp as stuff/* if they aren\*(Aqt writable
\&   $zip\->addTreeMatching( \*(Aq/tmp\*(Aq, \*(Aqstuff\*(Aq, \*(Aq\e.o$\*(Aq, sub { ! \-w } );
\&   # add all .so files below /tmp that are smaller than 200 bytes as stuff/*
\&   $zip\->addTreeMatching( \*(Aq/tmp\*(Aq, \*(Aqstuff\*(Aq, \*(Aq\e.o$\*(Aq, sub { \-s < 200 } );
\&   # and write them into a file
\&   $zip\->writeToFileNamed(\*(Aqxxx.zip\*(Aq);
.Ve
.SH "Extract a directory/tree"
.IX Header "Extract a directory/tree"
\&\fBQ:\fR How can I extract some (or all) files from a Zip into a different
directory?
.PP
\&\fBA:\fR You can use the \fIArchive::Zip::extractTree()\fR method:
??? ||
.PP
.Vb 2
\&   # now extract the same files into /tmpx
\&   $zip\->extractTree( \*(Aqstuff\*(Aq, \*(Aq/tmpx\*(Aq );
.Ve
.SH "Update a directory/tree"
.IX Header "Update a directory/tree"
\&\fBQ:\fR How can I update a Zip from a directory tree, adding or replacing only
the newer files?
.PP
\&\fBA:\fR You can use the \fIArchive::Zip::updateTree()\fR method that was added in version 1.09.
.SH "Zip times might be off by 1 second"
.IX Header "Zip times might be off by 1 second"
\&\fBQ:\fR It bothers me greatly that my file times are wrong by one second about half
the time. Why don't you do something about it?
.PP
\&\fBA:\fR Get over it. This is a result of the Zip format storing times in \s-1DOS\s0
format, which has a resolution of only two seconds.
.SH "Zip times don't include time zone information"
.IX Header "Zip times don't include time zone information"
\&\fBQ:\fR My file times don't respect time zones. What gives?
.PP
\&\fBA:\fR If this is important to you, please submit patches to read the various
Extra Fields that encode times with time zones. I'm just using the \s-1DOS\s0
Date/Time, which doesn't have a time zone.
.SH "How do I make a self-extracting Zip"
.IX Header "How do I make a self-extracting Zip"
\&\fBQ:\fR I want to make a self-extracting Zip file. Can I do this?
.PP
\&\fBA:\fR Yes. You can write a self-extracting archive stub (that is, a version of
unzip) to the output filehandle that you pass to \fIwriteToFileHandle()\fR. See
examples/selfex.pl for how to write a self-extracting archive.
.PP
However, you should understand that this will only work on one kind of
platform (the one for which the stub was compiled).
.SH "How can I deal with Zips with prepended garbage (i.e. from Sircam)"
.IX Header "How can I deal with Zips with prepended garbage (i.e. from Sircam)"
\&\fBQ:\fR How can I tell if a Zip has been damaged by adding garbage to the
beginning or inside the file?
.PP
\&\fBA:\fR I added code for this for the Amavis virus scanner. You can query archives
for their 'eocdOffset' property, which should be 0:
.PP
.Vb 2
\&  if ($zip\->eocdOffset > 0)
\&    { warn($zip\->eocdOffset . " bytes of garbage at beginning or within Zip") }
.Ve
.PP
When members are extracted, this offset will be used to adjust the start of
the member if necessary.
.SH "Can't extract Shrunk files"
.IX Header "Can't extract Shrunk files"
\&\fBQ:\fR I'm trying to extract a file out of a Zip produced by \s-1PKZIP\s0, and keep
getting this error message:
.PP
.Vb 1
\&  error: Unsupported compression combination: read 6, write 0
.Ve
.PP
\&\fBA:\fR You can't uncompress this archive member. Archive::Zip only supports uncompressed
members, and compressed members that are compressed using the compression
supported by Compress::Zlib. That means only Deflated and Stored members.
.PP
Your file is compressed using the Shrink format, which isn't supported by
Compress::Zlib.
.PP
You could, perhaps, use a command-line UnZip program (like the Info-Zip
one) to extract this.
.SH "Can't do decryption"
.IX Header "Can't do decryption"
\&\fBQ:\fR How do I decrypt encrypted Zip members?
.PP
\&\fBA:\fR With some other program or library. Archive::Zip doesn't support decryption,
and probably never will (unless \fIyou\fR write it).
.SH "How to test file integrity?"
.IX Header "How to test file integrity?"
\&\fBQ:\fR How can Archive::Zip can test the validity of a Zip file?
.PP
\&\fBA:\fR If you try to decompress the file, the gzip streams will report errors 
if you have garbage. Most of the time.
.PP
If you try to open the file and a central directory structure can't be 
found, an error will be reported.
.PP
When a file is being read, if we can't find a proper \s-1PK\s0.. signature in 
the right places we report a format error.
.PP
If there is added garbage at the beginning of a Zip file (as inserted 
by some viruses), you can find out about it, but Archive::Zip will ignore it, 
and you can still use the archive. When it gets written back out the 
added stuff will be gone.
.PP
There are two ready-to-use utilities in the examples directory that can
be used to test file integrity, or that you can use as examples
for your own code:
.IP "examples/zipcheck.pl shows how to use an attempted extraction to test a file." 4
.IX Item "examples/zipcheck.pl shows how to use an attempted extraction to test a file."
.PD 0
.IP "examples/ziptest.pl shows how to test CRCs in a file." 4
.IX Item "examples/ziptest.pl shows how to test CRCs in a file."
.PD
.SH "Duplicate files in Zip?"
.IX Header "Duplicate files in Zip?"
\&\fBQ:\fR Archive::Zip let me put the same file in my Zip twice! Why don't you prevent this?
.PP
\&\fBA:\fR As far as I can tell, this is not disallowed by the Zip spec. If you
think it's a bad idea, check for it yourself:
.PP
.Vb 1
\&  $zip\->addFile($someFile, $someName) unless $zip\->memberNamed($someName);
.Ve
.PP
I can even imagine cases where this might be useful (for instance, multiple
versions of files).
.SH "File ownership/permissions/ACLS/etc"
.IX Header "File ownership/permissions/ACLS/etc"
\&\fBQ:\fR Why doesn't Archive::Zip deal with file ownership, ACLs, etc.?
.PP
\&\fBA:\fR There is no standard way to represent these in the Zip file format. If
you want to send me code to properly handle the various extra fields that
have been used to represent these through the years, I'll look at it.
.SH "I can't compile but ActiveState only has an old version of Archive::Zip"
.IX Header "I can't compile but ActiveState only has an old version of Archive::Zip"
\&\fBQ:\fR I've only installed modules using ActiveState's \s-1PPM\s0 program and
repository. But they have a much older version of Archive::Zip than is in \s-1CPAN\s0. Will
you send me a newer \s-1PPM\s0?
.PP
\&\fBA:\fR Probably not, unless I get lots of extra time. But there's no reason you
can't install the version from \s-1CPAN\s0. Archive::Zip is pure Perl, so all you need is
\&\s-1NMAKE\s0, which you can get for free from Microsoft (see the \s-1FAQ\s0 in the
ActiveState documentation for details on how to install \s-1CPAN\s0 modules).
.SH "My JPEGs (or MP3's) don't compress when I put them into Zips!"
.IX Header "My JPEGs (or MP3's) don't compress when I put them into Zips!"
\&\fBQ:\fR How come my JPEGs and \s-1MP3\s0's don't compress much when I put them into Zips?
.PP
\&\fBA:\fR Because they're already compressed.
.SH "Under Windows, things lock up/get damaged"
.IX Header "Under Windows, things lock up/get damaged"
\&\fBQ:\fR I'm using Windows. When I try to use Archive::Zip, my machine locks up/makes
funny sounds/displays a BSOD/corrupts data. How can I fix this?
.PP
\&\fBA:\fR First, try the newest version of Compress::Zlib. I know of
Windows-related problems prior to v1.14 of that library.
.PP
If that doesn't get rid of the problem, fix your computer or get rid of
Windows.
.SH "Zip contents in a scalar"
.IX Header "Zip contents in a scalar"
\&\fBQ:\fR I want to read a Zip file from (or write one to) a scalar variable instead
of a file. How can I do this?
.PP
\&\fBA:\fR Use \f(CW\*(C`IO::String\*(C'\fR and the \f(CW\*(C`readFromFileHandle()\*(C'\fR and
\&\f(CW\*(C`writeToFileHandle()\*(C'\fR methods.
See \f(CW\*(C`examples/readScalar.pl\*(C'\fR and \f(CW\*(C`examples/writeScalar.pl\*(C'\fR.
.SH "Reading from streams"
.IX Header "Reading from streams"
\&\fBQ:\fR How do I read from a stream (like for the Info-Zip \f(CW\*(C`funzip\*(C'\fR program)?
.PP
\&\fBA:\fR	This isn't currently supported, though writing to a stream is.