Archive::Zip::FAQ - phpMan

NAME
    Archive::Zip::FAQ - Answers to a few frequently asked questions about
    Archive::Zip

DESCRIPTION
    It seems that I keep answering the same questions over and over again. I
    assume that this is because my documentation is deficient, rather than
    that people don't read the documentation.

    So this FAQ is an attempt to cut down on the number of personal answers
    I have to give. At least I can now say "You *did* read the FAQ, right?".

    The questions are not in any particular order. The answers assume the
    current version of Archive::Zip; some of the answers depend on newly
    added/fixed functionality.

Install problems on RedHat 8 or 9 with Perl 5.8.0
    Q: Archive::Zip won't install on my RedHat 9 system! It's broke!

    A: This has become something of a FAQ. Basically, RedHat broke some
    versions of Perl by setting LANG to UTF8. They apparently have a fixed
    version out as an update.

    You might try running CPAN or creating your Makefile after exporting the
    LANG environment variable as

    "LANG=C"

    <https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=87682>

Why is my zip file so big?
    Q: My zip file is actually bigger than what I stored in it! Why?

    A: Some things to make sure of:

    Make sure that you are requesting COMPRESSION_DEFLATED if you are
    storing strings.
        $member->desiredCompressionMethod( COMPRESSION_DEFLATED );

    Don't make lots of little files if you can help it.
        Since zip computes the compression tables for each member, small
        members without much entropy won't compress well. Instead, if you've
        got lots of repeated strings in your data, try to combine them into
        one big member.

    Make sure that you are requesting COMPRESSION_STORED if you are storing
    things that are already compressed.
        If you're storing a .zip, .jpg, .mp3, or other compressed file in a
        zip, then don't compress them again. They'll get bigger.

Sample code?
    Q: Can you send me code to do (whatever)?

    A: Have you looked in the "examples/" directory yet? It contains:

    examples/calcSizes.pl -- How to find out how big a Zip file will be
    before writing it
    examples/copy.pl -- Copies one Zip file to another
    examples/extract.pl -- extract file(s) from a Zip
    examples/mailZip.pl -- make and mail a zip file
    examples/mfh.pl -- demo for use of MockFileHandle
    examples/readScalar.pl -- shows how to use IO::Scalar as the source of a
    Zip read
    examples/selfex.pl -- a brief example of a self-extracting Zip
    examples/unzipAll.pl -- uses Archive::Zip::Tree to unzip an entire Zip
    examples/updateZip.pl -- shows how to read/modify/write a Zip
    examples/updateTree.pl -- shows how to update a Zip in place
    examples/writeScalar.pl -- shows how to use IO::Scalar as the
    destination of a Zip write
    examples/writeScalar2.pl -- shows how to use IO::String as the
    destination of a Zip write
    examples/zip.pl -- Constructs a Zip file
    examples/zipcheck.pl -- One way to check a Zip file for validity
    examples/zipinfo.pl -- Prints out information about a Zip archive file
    examples/zipGrep.pl -- Searches for text in Zip files
    examples/ziptest.pl -- Lists a Zip file and checks member CRCs
    examples/ziprecent.pl -- Puts recent files into a zipfile
    examples/ziptest.pl -- Another way to check a Zip file for validity

Can't Read/modify/write same Zip file
    Q: Why can't I open a Zip file, add a member, and write it back? I get
    an error message when I try.

    A: 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.

    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).

    Archive::Zip v1.02 added the archive methods "overwrite()" and
    "overwriteAs()" to do this simply and carefully.

    See "examples/updateZip.pl" for an example of this technique.

File creation time not set
    Q: 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?

    A: Mostly because Perl doesn't give cross-platform access to *creation
    time*. 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 "lastModTime()".

Can't use Archive::Zip on gzip files
    Q: Can I use Archive::Zip to extract Unix gzip files?

    A: No.

    There is a distinction between Unix gzip files, and Zip archives that
    also can use the gzip compression.

    Depending on the format of the gzip file, you can use
    Compress::Raw::Zlib, or Archive::Tar to decompress it (and de-archive it
    in the case of Tar files).

    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.

Add a directory/tree to a Zip
    Q: How can I add a directory (or tree) full of files to a Zip?

    A: You can use the Archive::Zip::addTree*() methods:

       use Archive::Zip;
       my $zip = Archive::Zip->new();
       # add all readable files and directories below . as xyz/*
       $zip->addTree( '.', 'xyz' );
       # add all readable plain files below /abc as def/*
       $zip->addTree( '/abc', 'def', sub { -f && -r } );
       # add all .c files below /tmp as stuff/*
       $zip->addTreeMatching( '/tmp', 'stuff', '\.c$' );
       # add all .o files below /tmp as stuff/* if they aren't writable
       $zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { ! -w } );
       # add all .so files below /tmp that are smaller than 200 bytes as stuff/*
       $zip->addTreeMatching( '/tmp', 'stuff', '\.o$', sub { -s < 200 } );
       # and write them into a file
       $zip->writeToFileNamed('xxx.zip');

Extract a directory/tree
    Q: How can I extract some (or all) files from a Zip into a different
    directory?

    A: You can use the Archive::Zip::extractTree() method: ??? ||

       # now extract the same files into /tmpx
       $zip->extractTree( 'stuff', '/tmpx' );

Update a directory/tree
    Q: How can I update a Zip from a directory tree, adding or replacing
    only the newer files?

    A: You can use the Archive::Zip::updateTree() method that was added in
    version 1.09.

Zip times might be off by 1 second
    Q: 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?

    A: Get over it. This is a result of the Zip format storing times in DOS
    format, which has a resolution of only two seconds.

Zip times don't include time zone information
    Q: My file times don't respect time zones. What gives?

    A: 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 DOS Date/Time, which doesn't have a time zone.

How do I make a self-extracting Zip
    Q: I want to make a self-extracting Zip file. Can I do this?

    A: Yes. You can write a self-extracting archive stub (that is, a version
    of unzip) to the output filehandle that you pass to writeToFileHandle().
    See examples/selfex.pl for how to write a self-extracting archive.

    However, you should understand that this will only work on one kind of
    platform (the one for which the stub was compiled).

How can I deal with Zips with prepended garbage (i.e. from Sircam)
    Q: How can I tell if a Zip has been damaged by adding garbage to the
    beginning or inside the file?

    A: I added code for this for the Amavis virus scanner. You can query
    archives for their 'eocdOffset' property, which should be 0:

      if ($zip->eocdOffset > 0)
        { warn($zip->eocdOffset . " bytes of garbage at beginning or within Zip") }

    When members are extracted, this offset will be used to adjust the start
    of the member if necessary.

Can't extract Shrunk files
    Q: I'm trying to extract a file out of a Zip produced by PKZIP, and keep
    getting this error message:

      error: Unsupported compression combination: read 6, write 0

    A: 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::Raw::Zlib. That means only
    Deflated and Stored members.

    Your file is compressed using the Shrink format, which is not supported
    by Compress::Raw::Zlib.

    You could, perhaps, use a command-line UnZip program (like the Info-Zip
    one) to extract this.

Can't do decryption
    Q: How do I decrypt encrypted Zip members?

    A: With some other program or library. Archive::Zip doesn't support
    decryption, and probably never will (unless *you* write it).

How to test file integrity?
    Q: How can Archive::Zip can test the validity of a Zip file?

    A: If you try to decompress the file, the gzip streams will report
    errors if you have garbage. Most of the time.

    If you try to open the file and a central directory structure can't be
    found, an error will be reported.

    When a file is being read, if we can't find a proper PK.. signature in
    the right places we report a format error.

    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.

    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:

    examples/zipcheck.pl shows how to use an attempted extraction to test a
    file.
    examples/ziptest.pl shows how to test CRCs in a file.

Duplicate files in Zip?
    Q: Archive::Zip let me put the same file in my Zip twice! Why don't you
    prevent this?

    A: 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:

      $zip->addFile($someFile, $someName) unless $zip->memberNamed($someName);

    I can even imagine cases where this might be useful (for instance,
    multiple versions of files).

File ownership/permissions/ACLS/etc
    Q: Why doesn't Archive::Zip deal with file ownership, ACLs, etc.?

    A: 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.

I can't compile but ActiveState only has an old version of Archive::Zip
    Q: I've only installed modules using ActiveState's PPM program and
    repository. But they have a much older version of Archive::Zip than is
    in CPAN. Will you send me a newer PPM?

    A: Probably not, unless I get lots of extra time. But there's no reason
    you can't install the version from CPAN. Archive::Zip is pure Perl, so
    all you need is NMAKE, which you can get for free from Microsoft (see
    the FAQ in the ActiveState documentation for details on how to install
    CPAN modules).

My JPEGs (or MP3's) don't compress when I put them into Zips!
    Q: How come my JPEGs and MP3's don't compress much when I put them into
    Zips?

    A: Because they're already compressed.

Under Windows, things lock up/get damaged
    Q: 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?

    A: First, try the newest version of Compress::Raw::Zlib. I know of
    Windows-related problems prior to v1.14 of that library.

Zip contents in a scalar
    Q: I want to read a Zip file from (or write one to) a scalar variable
    instead of a file. How can I do this?

    A: Use "IO::String" and the "readFromFileHandle()" and
    "writeToFileHandle()" methods. See "examples/readScalar.pl" and
    "examples/writeScalar.pl".

Reading from streams
    Q: How do I read from a stream (like for the Info-Zip "funzip" program)?

    A: This is not currently supported, though writing to a stream is.