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Diffstat (limited to 'cpan/IO-Compress/lib/IO/Compress/FAQ.pod')
| -rw-r--r-- | cpan/IO-Compress/lib/IO/Compress/FAQ.pod | 183 |
1 files changed, 97 insertions, 86 deletions
diff --git a/cpan/IO-Compress/lib/IO/Compress/FAQ.pod b/cpan/IO-Compress/lib/IO/Compress/FAQ.pod index ee8a2c6569..c1059101c1 100644 --- a/cpan/IO-Compress/lib/IO/Compress/FAQ.pod +++ b/cpan/IO-Compress/lib/IO/Compress/FAQ.pod @@ -1,12 +1,14 @@ =head1 NAME -IO::Compress::FAQ -- Frequently Asked Questions about IO::Compress +IO::Conmpress::FAQ -- Frequently Asked Questions about IO::Compress =head1 DESCRIPTION Common questions answered. +=head1 GENERAL + =head2 Compatibility with Unix compress/uncompress. Although C<Compress::Zlib> has a pair of functions called C<compress> and @@ -83,18 +85,62 @@ write a C<.tar.Z> file $tar->write($fh); $fh->close ; -=head2 Accessing Zip Files +=head2 How do I recompress using a different compression? + +This is easier that you might expect if you realise that all the +C<IO::Compress::*> objects are derived from C<IO::File> and that all the +C<IO::Uncompress::*> modules can read from an C<IO::File> filehandle. + +So, for example, say you have a file compressed with gzip that you want to +recompress with bzip2. Here is all that is needed to carry out the +recompression. + + use IO::Uncompress::Gunzip ':all'; + use IO::Compress::Bzip2 ':all'; + + my $gzipFile = "somefile.gz"; + my $bzipFile = "somefile.bz2"; -This module provides support for reading/writing zip files using the -C<IO::Compress::Zip> and C<IO::Uncompress::Unzip> modules. + my $gunzip = new IO::Uncompress::Gunzip $gzipFile + or die "Cannot gunzip $gzipFile: $GunzipError\n" ; -The primary focus of the C<IO::Compress::Zip> and C<IO::Uncompress::Unzip> -modules is to provide an C<IO::File> compatible streaming read/write -interface to zip files/buffers. They are not fully flegged archivers. If -you are looking for an archiver check out the C<Archive::Zip> module. You -can find it on CPAN at + bzip2 $gunzip => $bzipFile + or die "Cannot bzip2 to $bzipFile: $Bzip2Error\n" ; - http://www.cpan.org/modules/by-module/Archive/Archive-Zip-*.tar.gz +Note, there is a limitation of this technique. Some compression file +formats store extra information along with the compressed data payload. For +example, gzip can optionally store the original filename and Zip stores a +lot of information about the original file. If the original compressed file +contains any of this extra information, it will not be transferred to the +new compressed file usign the technique above. + +=head1 ZIP + +=head2 What Compression Types do IO::Compress::Zip & IO::Uncompress::Unzip support? + +The following compression formats are supported by C<IO::Compress::Zip> and +C<IO::Uncompress::Unzip> + +=over 5 + +=item * Store (method 0) + +No compression at all. + +=item * Deflate (method 8) + +This is the default compression used when creating a zip file with +C<IO::Compress::Zip>. + +=item * Bzip2 (method 12) + +Only supported if the C<IO-Compress-Bzip2> module is installed. + +=item * Lzma (method 14) + +Only supported if the C<IO-Compress-Lzma> module is installed. + +=back =head2 Can I Read/Write Zip files larger the 4 Gig? @@ -134,32 +180,6 @@ In particular, if you are using Info-Zip you need to have zip version 3.x or better to update a Zip64 archive and unzip version 6.x to read a zip64 archive. -=head2 What Compression Types do IO::Compress::Zip & IO::Uncompress::Unzip support? - -The following compression formats are supported by C<IO::Compress::Zip> and -C<IO::Uncompress::Unzip> - -=over 5 - -=item * Store (method 0) - -NO compression at all. - -=item * Deflate (method 8) - -This is the default compression used when creating a zip file with -C<IO::Compress::Zip>. - -=item * Bzip2 (method 12) - -Only supported if the C<IO-Compress-Bzip2> module is available. - -=item * Lzma (method 14) - -Only supported if the C<IO-Compress-Lzma> module is available. - -=back - =head2 Zip Resources The primary reference for zip files is the "appnote" document available at @@ -168,63 +188,23 @@ L<http://www.pkware.com/documents/casestudies/APPNOTE.TXT> An alternatively is the Info-Zip appnote. This is available from L<ftp://ftp.info-zip.org/pub/infozip/doc/> -=head2 Compressed files and Net::FTP +=head1 GZIP -The C<Net::FTP> module provides two low-level methods called C<stor> and -C<retr> that both return filehandles. These filehandles can used with the -C<IO::Compress/Uncompress> modules to compress or uncompress files read -from or written to an FTP Server on the fly, without having to create a -temporary file. - -Firstly, here is code that uses C<retr> to uncompressed a file as it is -read from the FTP Server. - - use Net::FTP; - use IO::Uncompress::Gunzip qw(:all); - - my $ftp = new Net::FTP ... - - my $retr_fh = $ftp->retr($compressed_filename); - gunzip $retr_fh => $outFilename, AutoClose => 1 - or die "Cannot uncompress '$compressed_file': $GunzipError\n"; - -and this to compress a file as it is written to the FTP Server - - use Net::FTP; - use IO::Compress::Gzip qw(:all); +=head2 Gzip Resources - my $stor_fh = $ftp->stor($filename); - gzip "filename" => $stor_fh, AutoClose => 1 - or die "Cannot compress '$filename': $GzipError\n"; +The primary reference for gzip files is RFC 1952 +L<http://www.faqs.org/rfcs/rfc1952.html> -=head2 How do I recompress using a different compression? +The primary site for gzip is F<http://www.gzip.org>. -This is easier that you might expect if you realise that all the -C<IO::Compress::*> objects are derived from C<IO::File> and that all the -C<IO::Uncompress::*> modules can read from an C<IO::File> filehandle. +=head1 ZLIB -So, for example, say you have a file compressed with gzip that you want to -recompress with bzip2. Here is all that is needed to carry out the -recompression. - - use IO::Uncompress::Gunzip ':all'; - use IO::Compress::Bzip2 ':all'; - - my $gzipFile = "somefile.gz"; - my $bzipFile = "somefile.bz2"; - - my $gunzip = new IO::Uncompress::Gunzip $gzipFile - or die "Cannot gunzip $gzipFile: $GunzipError\n" ; +=head2 Zlib Resources - bzip2 $gunzip => $bzipFile - or die "Cannot bzip2 to $bzipFile: $Bzip2Error\n" ; +The primary site for the I<zlib> compression library is +F<http://www.zlib.org>. -Note, there is a limitation of this technique. Some compression file -formats store extra information along with the compressed data payload. For -example, gzip can optionally store the original filename and Zip stores a -lot of information about the original file. If the original compressed file -contains any of this extra information, it will not be transferred to the -new compressed file usign the technique above. +=head1 HTTP & NETWORK =head2 Apache::GZip Revisited @@ -388,6 +368,37 @@ for Content-Encoding you should I<always> use this option. In the example above it will prevent the filename being included in the gzip header and make the size of the gzip data stream a slight bit smaller. +=head2 Compressed files and Net::FTP + +The C<Net::FTP> module provides two low-level methods called C<stor> and +C<retr> that both return filehandles. These filehandles can used with the +C<IO::Compress/Uncompress> modules to compress or uncompress files read +from or written to an FTP Server on the fly, without having to create a +temporary file. + +Firstly, here is code that uses C<retr> to uncompressed a file as it is +read from the FTP Server. + + use Net::FTP; + use IO::Uncompress::Gunzip qw(:all); + + my $ftp = new Net::FTP ... + + my $retr_fh = $ftp->retr($compressed_filename); + gunzip $retr_fh => $outFilename, AutoClose => 1 + or die "Cannot uncompress '$compressed_file': $GunzipError\n"; + +and this to compress a file as it is written to the FTP Server + + use Net::FTP; + use IO::Compress::Gzip qw(:all); + + my $stor_fh = $ftp->stor($filename); + gzip "filename" => $stor_fh, AutoClose => 1 + or die "Cannot compress '$filename': $GzipError\n"; + +=head1 MISC + =head2 Using C<InputLength> to uncompress data embedded in a larger file/buffer. A fairly common use-case is where compressed data is embedded in a larger |