File: gzip.pm

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libperlio-gzip-perl 0.19-1
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package PerlIO::gzip;

use 5.008;
use strict;
use warnings;

use XSLoader ();

our $VERSION = '0.19';

XSLoader::load "PerlIO::gzip", $VERSION;

1;
__END__

=head1 NAME

PerlIO::gzip - Perl extension to provide a PerlIO layer to gzip/gunzip

=head1 SYNOPSIS

  use PerlIO::gzip;
  open FOO, "<:gzip", "file.gz" or die $!;
  print while <FOO>; # And it will be uncompressed...

  binmode FOO, ":gzip(none)" # Starts reading deflate stream from here on

=head1 DESCRIPTION

PerlIO::gzip provides a PerlIO layer that manipulates files in the format used
by the C<gzip> program.  Compression and Decompression are implemented, but
not together.  If you attempt to open a file for reading and writing the open
will fail.

=head1 EXPORT

PerlIO::gzip exports no subroutines or symbols, just a perl layer C<gzip>

=head1 LAYER ARGUMENTS

The C<gzip> layer takes a comma separated list of arguments. 4 exclusive
options choose the header checking mode:

=over 4

=item gzip

The default.  Expects a standard gzip file header for reading, writes a
standard gzip file header.

=item none

Expects or writes no file header; assumes the file handle is immediately a
deflate stream (eg as would be found inside a C<zip> file)

=item auto

Potentially dangerous. If the first two bytes match the C<gzip> header
"\x1f\x8b" then a gzip header is assumed (and checked) else a deflate stream
is assumed.  No different from gzip on writing.

=item autopop

Potentially dangerous. If the first two bytes match the C<gzip> header
"\x1f\x8b" then a gzip header is assumed (and checked) else the layer is
silently popped.  This results in gzip files being transparently
decompressed, other files being treated normally.  Of course, this has sides
effects such as File::Copy becoming gunzip, and File::Compare comparing
the uncompressed contents of files.

In autopop mode Opening a handle for writing (or reading and writing) will
cause the gzip layer to automatically be popped.

=back

Optionally you can add this flag:

=over 4

=item lazy

For reading, defer header checking until the first read.  For writing, don't
write a header until the first buffer empty of compressed data to disk.
(and don't write anything at all if no data was written to the handle)

By default, gzip header checking is done before the C<open> (or C<binmode>)
returns, so if an error is detected in the gzip header the C<open> or
C<binmode> will fail.  However, this will require reading some data, or writing
a header.  With lazy set on a file opened for reading the check is deferred
until the first read so the C<open> should always succeed, but any problems
with the header will cause an error on read.

  open FOO, "<:gzip(lazy)", "file.gz" or die $!; # Dangerous.
  while (<FOO>) {
    print;
  } # Whoa. Bad. You're not distinguishing between errors and EOF.

If you're not careful you won't spot the errors - like the example above
you'll think you got end of file.

lazy is ignored if you are in autopop mode.

=back

=head1 AUTHOR

Nicholas Clark, E<lt>nwc10+perlio-gzip@colon.colondot.netE<gt>

=head1 SEE ALSO

L<perl>, L<gzip>, L<rfc 1952|http://www.ietf.org/rfc/rfc1952.txt> (the gzip
file format specification), L<rfc 1951|http://www.ietf.org/rfc/rfc1951.txt>
(DEFLATE compressed data format specification)

=cut