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=head1 NAME
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Archive::Zip::FAQ - Answers to a few frequently asked questions about Archive::Zip
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=head1 DESCRIPTION
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It seems that I keep answering the same questions over and over again. I
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assume that this is because my documentation is deficient, rather than that
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people don't read the documentation.
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So this FAQ is an attempt to cut down on the number of personal answers I have
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to give. At least I can now say "You I<did> read the FAQ, right?".
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The questions are not in any particular order. The answers assume the current
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version of Archive::Zip; some of the answers depend on newly added/fixed
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functionality.
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=head1 Install problems on RedHat 8 or 9 with Perl 5.8.0
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B<Q:> Archive::Zip won't install on my RedHat 9 system! It's broke!
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B<A:> This has become something of a FAQ.
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Basically, RedHat broke some versions of Perl by setting LANG to UTF8.
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They apparently have a fixed version out as an update.
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You might try running CPAN or creating your Makefile after exporting the LANG
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environment variable as
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C<LANG=C>
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L<https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=87682>
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=head1 Why is my zip file so big?
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B<Q:> My zip file is actually bigger than what I stored in it! Why?
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B<A:> Some things to make sure of:
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=over 4
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=item Make sure that you are requesting COMPRESSION_DEFLATED if you are storing strings.
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$member->desiredCompressionMethod( COMPRESSION_DEFLATED );
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=item Don't make lots of little files if you can help it.
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Since zip computes the compression tables for each member, small
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members without much entropy won't compress well. Instead, if you've
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got lots of repeated strings in your data, try to combine them into
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one big member.
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=item Make sure that you are requesting COMPRESSION_STORED if you are storing things that are already compressed.
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If you're storing a .zip, .jpg, .mp3, or other compressed file in a zip,
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then don't compress them again. They'll get bigger.
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=back
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=head1 Sample code?
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B<Q:> Can you send me code to do (whatever)?
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B<A:> Have you looked in the C<examples/> directory yet? It contains:
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=over 4
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=item examples/calcSizes.pl -- How to find out how big a Zip file will be before writing it
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=item examples/copy.pl -- Copies one Zip file to another
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=item examples/extract.pl -- extract file(s) from a Zip
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=item examples/mailZip.pl -- make and mail a zip file
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=item examples/mfh.pl -- demo for use of MockFileHandle
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=item examples/readScalar.pl -- shows how to use IO::Scalar as the source of a Zip read
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=item examples/selfex.pl -- a brief example of a self-extracting Zip
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=item examples/unzipAll.pl -- uses Archive::Zip::Tree to unzip an entire Zip
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=item examples/updateZip.pl -- shows how to read/modify/write a Zip
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=item examples/updateTree.pl -- shows how to update a Zip in place
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=item examples/writeScalar.pl -- shows how to use IO::Scalar as the destination of a Zip write
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=item examples/writeScalar2.pl -- shows how to use IO::String as the destination of a Zip write
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=item examples/zip.pl -- Constructs a Zip file
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=item examples/zipcheck.pl -- One way to check a Zip file for validity
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=item examples/zipinfo.pl -- Prints out information about a Zip archive file
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=item examples/zipGrep.pl -- Searches for text in Zip files
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=item examples/ziptest.pl -- Lists a Zip file and checks member CRCs
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=item examples/ziprecent.pl -- Puts recent files into a zipfile
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=item examples/ziptest.pl -- Another way to check a Zip file for validity
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=back
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=head1 Can't Read/modify/write same Zip file
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B<Q:> Why can't I open a Zip file, add a member, and write it back? I get an
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error message when I try.
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B<A:> Because Archive::Zip doesn't (and can't, generally) read file contents into memory,
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the original Zip file is required to stay around until the writing of the new
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file is completed.
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The best way to do this is to write the Zip to a temporary file and then
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rename the temporary file to have the old name (possibly after deleting the
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old one).
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Archive::Zip v1.02 added the archive methods C<overwrite()> and
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C<overwriteAs()> to do this simply and carefully.
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See C<examples/updateZip.pl> for an example of this technique.
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=head1 File creation time not set
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B<Q:> Upon extracting files, I see that their modification (and access) times are
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set to the time in the Zip archive. However, their creation time is not set to
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the same time. Why?
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B<A:> Mostly because Perl doesn't give cross-platform access to I<creation time>.
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Indeed, many systems (like Unix) don't support such a concept.
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However, if yours does, you can easily set it. Get the modification time from
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the member using C<lastModTime()>.
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=head1 Can't use Archive::Zip on gzip files
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B<Q:> Can I use Archive::Zip to extract Unix gzip files?
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B<A:> No.
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There is a distinction between Unix gzip files, and Zip archives that
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also can use the gzip compression.
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Depending on the format of the gzip file, you can use L<Compress::Raw::Zlib>, or
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L<Archive::Tar> to decompress it (and de-archive it in the case of Tar files).
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You can unzip PKZIP/WinZip/etc/ archives using Archive::Zip (that's what
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it's for) as long as any compressed members are compressed using
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Deflate compression.
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=head1 Add a directory/tree to a Zip
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B<Q:> How can I add a directory (or tree) full of files to a Zip?
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B<A:> You can use the Archive::Zip::addTree*() methods:
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use Archive::Zip;
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my $zip = Archive::Zip->new();
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# add all readable files and directories below . as xyz/*
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$zip->addTree( '.', 'xyz' );
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# add all readable plain files below /abc as def/*
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$zip->addTree( '/abc', 'def', sub { -f && -r } );
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# add all .c files below /tmp as stuff/*
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$zip->addTreeMatching( '/tmp', 'stuff', '\.c$' );
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# add all .o files below /tmp as stuff/* if they aren't writable
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$zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { ! -w } );
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# add all .so files below /tmp that are smaller than 200 bytes as stuff/*
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$zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { -s < 200 } );
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# and write them into a file
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$zip->writeToFileNamed('xxx.zip');
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=head1 Extract a directory/tree
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B<Q:> How can I extract some (or all) files from a Zip into a different
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directory?
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B<A:> You can use the Archive::Zip::extractTree() method:
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??? ||
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# now extract the same files into /tmpx
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$zip->extractTree( 'stuff', '/tmpx' );
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=head1 Update a directory/tree
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B<Q:> How can I update a Zip from a directory tree, adding or replacing only
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the newer files?
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B<A:> You can use the Archive::Zip::updateTree() method that was added in version 1.09.
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=head1 Zip times might be off by 1 second
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B<Q:> It bothers me greatly that my file times are wrong by one second about half
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the time. Why don't you do something about it?
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B<A:> Get over it. This is a result of the Zip format storing times in DOS
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format, which has a resolution of only two seconds.
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=head1 Zip times don't include time zone information
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B<Q:> My file times don't respect time zones. What gives?
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B<A:> If this is important to you, please submit patches to read the various
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Extra Fields that encode times with time zones. I'm just using the DOS
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Date/Time, which doesn't have a time zone.
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=head1 How do I make a self-extracting Zip
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B<Q:> I want to make a self-extracting Zip file. Can I do this?
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B<A:> Yes. You can write a self-extracting archive stub (that is, a version of
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unzip) to the output filehandle that you pass to writeToFileHandle(). See
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examples/selfex.pl for how to write a self-extracting archive.
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However, you should understand that this will only work on one kind of
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platform (the one for which the stub was compiled).
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=head1 How can I deal with Zips with prepended garbage (i.e. from Sircam)
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B<Q:> How can I tell if a Zip has been damaged by adding garbage to the
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beginning or inside the file?
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B<A:> I added code for this for the Amavis virus scanner. You can query archives
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for their 'eocdOffset' property, which should be 0:
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if ($zip->eocdOffset > 0)
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{ warn($zip->eocdOffset . " bytes of garbage at beginning or within Zip") }
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When members are extracted, this offset will be used to adjust the start of
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the member if necessary.
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=head1 Can't extract Shrunk files
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B<Q:> I'm trying to extract a file out of a Zip produced by PKZIP, and keep
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getting this error message:
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error: Unsupported compression combination: read 6, write 0
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B<A:> You can't uncompress this archive member. Archive::Zip only supports uncompressed
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members, and compressed members that are compressed using the compression
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supported by Compress::Raw::Zlib. That means only Deflated and Stored members.
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Your file is compressed using the Shrink format, which is not supported by
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Compress::Raw::Zlib.
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You could, perhaps, use a command-line UnZip program (like the Info-Zip
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one) to extract this.
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=head1 Can't do decryption
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B<Q:> How do I decrypt encrypted Zip members?
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B<A:> With some other program or library. Archive::Zip doesn't support decryption,
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and probably never will (unless I<you> write it).
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=head1 How to test file integrity?
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B<Q:> How can Archive::Zip can test the validity of a Zip file?
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B<A:> If you try to decompress the file, the gzip streams will report errors
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if you have garbage. Most of the time.
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If you try to open the file and a central directory structure can't be
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found, an error will be reported.
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When a file is being read, if we can't find a proper PK.. signature in
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the right places we report a format error.
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If there is added garbage at the beginning of a Zip file (as inserted
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by some viruses), you can find out about it, but Archive::Zip will ignore it,
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and you can still use the archive. When it gets written back out the
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added stuff will be gone.
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There are two ready-to-use utilities in the examples directory that can
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be used to test file integrity, or that you can use as examples
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for your own code:
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=over 4
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=item examples/zipcheck.pl shows how to use an attempted extraction to test a file.
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=item examples/ziptest.pl shows how to test CRCs in a file.
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=back
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=head1 Duplicate files in Zip?
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B<Q:> Archive::Zip let me put the same file in my Zip twice! Why don't you prevent this?
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B<A:> As far as I can tell, this is not disallowed by the Zip spec. If you
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think it's a bad idea, check for it yourself:
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$zip->addFile($someFile, $someName) unless $zip->memberNamed($someName);
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I can even imagine cases where this might be useful (for instance, multiple
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versions of files).
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=head1 File ownership/permissions/ACLS/etc
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B<Q:> Why doesn't Archive::Zip deal with file ownership, ACLs, etc.?
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B<A:> There is no standard way to represent these in the Zip file format. If
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you want to send me code to properly handle the various extra fields that
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have been used to represent these through the years, I'll look at it.
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=head1 I can't compile but ActiveState only has an old version of Archive::Zip
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B<Q:> I've only installed modules using ActiveState's PPM program and
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repository. But they have a much older version of Archive::Zip than is in CPAN. Will
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you send me a newer PPM?
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B<A:> Probably not, unless I get lots of extra time. But there's no reason you
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can't install the version from CPAN. Archive::Zip is pure Perl, so all you need is
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NMAKE, which you can get for free from Microsoft (see the FAQ in the
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ActiveState documentation for details on how to install CPAN modules).
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=head1 My JPEGs (or MP3's) don't compress when I put them into Zips!
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B<Q:> How come my JPEGs and MP3's don't compress much when I put them into Zips?
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B<A:> Because they're already compressed.
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=head1 Under Windows, things lock up/get damaged
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B<Q:> I'm using Windows. When I try to use Archive::Zip, my machine locks up/makes
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funny sounds/displays a BSOD/corrupts data. How can I fix this?
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B<A:> First, try the newest version of Compress::Raw::Zlib. I know of
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Windows-related problems prior to v1.14 of that library.
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=head1 Zip contents in a scalar
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B<Q:> I want to read a Zip file from (or write one to) a scalar variable instead
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of a file. How can I do this?
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B<A:> Use C<IO::String> and the C<readFromFileHandle()> and
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C<writeToFileHandle()> methods.
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See C<examples/readScalar.pl> and C<examples/writeScalar.pl>.
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=head1 Reading from streams
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B<Q:> How do I read from a stream (like for the Info-Zip C<funzip> program)?
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B<A:> This is not currently supported, though writing to a stream is.
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