zlib.pm

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undef.

The C<$buffer> parameter can either be a scalar or a scalar reference.

See L<IO::Compress::Gzip|IO::Compress::Gzip> for an alternative way to
carry out in-memory gzip compression.

=head2 Compress::Zlib::memGunzip

This function is used to uncompress an in-memory gzip file.

    $dest = Compress::Zlib::memGunzip($buffer) ;

If successful, it returns the uncompressed gzip file, otherwise it
returns undef.

The C<$buffer> parameter can either be a scalar or a scalar reference. The
contents of the C<$buffer> parameter are destroyed after calling this function.

See L<IO::Uncompress::Gunzip|IO::Uncompress::Gunzip> for an alternative way
to carry out in-memory gzip uncompression.

=head1 COMPRESS/UNCOMPRESS

Two functions are provided to perform in-memory compression/uncompression of
RFC 1950 data streams. They are called C<compress> and C<uncompress>.

=over 5

=item B<$dest = compress($source [, $level] ) ;>

Compresses C<$source>. If successful it returns the compressed
data. Otherwise it returns I<undef>.

The source buffer, C<$source>, can either be a scalar or a scalar
reference.

The C<$level> parameter defines the compression level. Valid values are
0 through 9, C<Z_NO_COMPRESSION>, C<Z_BEST_SPEED>,
C<Z_BEST_COMPRESSION>, and C<Z_DEFAULT_COMPRESSION>.
If C<$level> is not specified C<Z_DEFAULT_COMPRESSION> will be used.


=item B<$dest = uncompress($source) ;>

Uncompresses C<$source>. If successful it returns the uncompressed
data. Otherwise it returns I<undef>.

The source buffer can either be a scalar or a scalar reference.

=back

Please note: the two functions defined above are I<not> compatible with
the Unix commands of the same name.

See L<IO::Deflate|IO::Deflate> and L<IO::Inflate|IO::Inflate> included with
this distribution for an alternative interface for reading/writing RFC 1950
files/buffers.


=head1 Deflate Interface

This section defines an interface that allows in-memory compression using
the I<deflate> interface provided by zlib.

Here is a definition of the interface available:


=head2 B<($d, $status) = deflateInit( [OPT] )>

Initialises a deflation stream. 

It combines the features of the I<zlib> functions C<deflateInit>,
C<deflateInit2> and C<deflateSetDictionary>.

If successful, it will return the initialised deflation stream, C<$d>
and C<$status> of C<Z_OK> in a list context. In scalar context it
returns the deflation stream, C<$d>, only.

If not successful, the returned deflation stream (C<$d>) will be
I<undef> and C<$status> will hold the exact I<zlib> error code.

The function optionally takes a number of named options specified as
C<< -Name=>value >> pairs. This allows individual options to be
tailored without having to specify them all in the parameter list.

For backward compatibility, it is also possible to pass the parameters
as a reference to a hash containing the name=>value pairs.

The function takes one optional parameter, a reference to a hash.  The
contents of the hash allow the deflation interface to be tailored.

Here is a list of the valid options:

=over 5

=item B<-Level>

Defines the compression level. Valid values are 0 through 9,
C<Z_NO_COMPRESSION>, C<Z_BEST_SPEED>, C<Z_BEST_COMPRESSION>, and
C<Z_DEFAULT_COMPRESSION>.

The default is Z_DEFAULT_COMPRESSION.

=item B<-Method>

Defines the compression method. The only valid value at present (and
the default) is Z_DEFLATED.

=item B<-WindowBits>

To create an RFC 1950 data stream, set C<WindowBits> to a positive number.

To create an RFC 1951 data stream, set C<WindowBits> to C<-MAX_WBITS>.

For a full definition of the meaning and valid values for C<WindowBits> refer
to the I<zlib> documentation for I<deflateInit2>.

Defaults to MAX_WBITS.

=item B<-MemLevel>

For a definition of the meaning and valid values for C<MemLevel>
refer to the I<zlib> documentation for I<deflateInit2>.

Defaults to MAX_MEM_LEVEL.

=item B<-Strategy>

Defines the strategy used to tune the compression. The valid values are
C<Z_DEFAULT_STRATEGY>, C<Z_FILTERED> and C<Z_HUFFMAN_ONLY>. 

The default is Z_DEFAULT_STRATEGY.

=item B<-Dictionary>

When a dictionary is specified I<Compress::Zlib> will automatically
call C<deflateSetDictionary> directly after calling C<deflateInit>. The
Adler32 value for the dictionary can be obtained by calling the method 
C<$d->dict_adler()>.

The default is no dictionary.

=item B<-Bufsize>

Sets the initial size for the deflation buffer. If the buffer has to be
reallocated to increase the size, it will grow in increments of
C<Bufsize>.

The default is 4096.

=back

Here is an example of using the C<deflateInit> optional parameter list
to override the default buffer size and compression level. All other
options will take their default values.

    deflateInit( -Bufsize => 300, 
                 -Level => Z_BEST_SPEED  ) ;


=head2 B<($out, $status) = $d-E<gt>deflate($buffer)>


Deflates the contents of C<$buffer>. The buffer can either be a scalar
or a scalar reference.  When finished, C<$buffer> will be
completely processed (assuming there were no errors). If the deflation
was successful it returns the deflated output, C<$out>, and a status
value, C<$status>, of C<Z_OK>.

On error, C<$out> will be I<undef> and C<$status> will contain the
I<zlib> error code.

In a scalar context C<deflate> will return C<$out> only.

As with the I<deflate> function in I<zlib>, it is not necessarily the
case that any output will be produced by this method. So don't rely on
the fact that C<$out> is empty for an error test.


=head2 B<($out, $status) = $d-E<gt>flush([flush_type])>

Typically used to finish the deflation. Any pending output will be
returned via C<$out>.
C<$status> will have a value C<Z_OK> if successful.

In a scalar context C<flush> will return C<$out> only.

Note that flushing can seriously degrade the compression ratio, so it
should only be used to terminate a decompression (using C<Z_FINISH>) or
when you want to create a I<full flush point> (using C<Z_FULL_FLUSH>).

By default the C<flush_type> used is C<Z_FINISH>. Other valid values
for C<flush_type> are C<Z_NO_FLUSH>, C<Z_PARTIAL_FLUSH>, C<Z_SYNC_FLUSH>
and C<Z_FULL_FLUSH>. It is strongly recommended that you only set the
C<flush_type> parameter if you fully understand the implications of
what it does. See the C<zlib> documentation for details.

=head2 B<$status = $d-E<gt>deflateParams([OPT])>

Change settings for the deflate stream C<$d>.

The list of the valid options is shown below. Options not specified
will remain unchanged.

=over 5

=item B<-Level>

Defines the compression level. Valid values are 0 through 9,
C<Z_NO_COMPRESSION>, C<Z_BEST_SPEED>, C<Z_BEST_COMPRESSION>, and
C<Z_DEFAULT_COMPRESSION>.

=item B<-Strategy>

Defines the strategy used to tune the compression. The valid values are
C<Z_DEFAULT_STRATEGY>, C<Z_FILTERED> and C<Z_HUFFMAN_ONLY>. 

=back

=head2 B<$d-E<gt>dict_adler()>

Returns the adler32 value for the dictionary.

=head2 B<$d-E<gt>msg()>

Returns the last error message generated by zlib.

=head2 B<$d-E<gt>total_in()>

Returns the total number of bytes uncompressed bytes input to deflate.

=head2 B<$d-E<gt>total_out()>

Returns the total number of compressed bytes output from deflate.

=head2 Example


Here is a trivial example of using C<deflate>. It simply reads standard
input, deflates it and writes it to standard output.

    use strict ;
    use warnings ;

    use Compress::Zlib ;

    binmode STDIN;
    binmode STDOUT;
    my $x = deflateInit()
       or die "Cannot create a deflation stream\n" ;

    my ($output, $status) ;
    while (<>)
    {
        ($output, $status) = $x->deflate($_) ;
    
        $status == Z_OK
            or die "deflation failed\n" ;
    
        print $output ;
    }
    
    ($output, $status) = $x->flush() ;
    
    $status == Z_OK
        or die "deflation failed\n" ;
    
    print $output ;

=head1 Inflate Interface

This section defines the interface available that allows in-memory
uncompression using the I<deflate> interface provided by zlib.

Here is a definition of the interface:


=head2 B<($i, $status) = inflateInit()>

Initialises an inflation stream. 

In a list context it returns the inflation stream, C<$i>, and the
I<zlib> status code in C<$status>. In a scalar context it returns the
inflation stream only.

If successful, C<$i> will hold the inflation stream and C<$status> will
be C<Z_OK>.

If not successful, C<$i> will be I<undef> and C<$status> will hold the
I<zlib> error code.

The function optionally takes a number of named options specified as
C<< -Name=>value >> pairs. This allows individual options to be
tailored without having to specify them all in the parameter list.
 
For backward compatibility, it is also possible to pass the parameters
as a reference to a hash containing the name=>value pairs.
 
The function takes one optional parameter, a reference to a hash.  The
contents of the hash allow the deflation interface to be tailored.
 
Here is a list of the valid options:

=over 5

=item B<-WindowBits>

To uncompress an RFC 1950 data stream, set C<WindowBits> to a positive number.

To uncompress an RFC 1951 data stream, set C<WindowBits> to C<-MAX_WBITS>.

For a full definition of the meaning and valid values for C<WindowBits> refer
to the I<zlib> documentation for I<inflateInit2>.

Defaults to MAX_WBITS.

=item B<-Bufsize>

Sets the initial size for the inflation buffer. If the buffer has to be
reallocated to increase the size, it will grow in increments of
C<Bufsize>. 

Default is 4096.

=item B<-Dictionary>

The default is no dictionary.

=back

Here is an example of using the C<inflateInit> optional parameter to
override the default buffer size.

    inflateInit( -Bufsize => 300 ) ;

=head2 B<($out, $status) = $i-E<gt>inflate($buffer)>

Inflates the complete contents of C<$buffer>. The buffer can either be
a scalar or a scalar reference.

Returns C<Z_OK> if successful and C<Z_STREAM_END> if the end of the
compressed data has been successfully reached. 
If not successful, C<$out> will be I<undef> and C<$status> will hold
the I<zlib> error code.

The C<$buffer> parameter is modified by C<inflate>. On completion it
will contain what remains of the input buffer after inflation. This
means that C<$buffer> will be an empty string when the return status is
C<Z_OK>. When the return status is C<Z_STREAM_END> the C<$buffer>
parameter will contains what (if anything) was stored in the input
buffer after the deflated data stream.

This feature is useful when processing a file format that encapsulates
a  compressed data stream (e.g. gzip, zip).

=head2 B<$status = $i-E<gt>inflateSync($buffer)>

Scans C<$buffer> until it reaches either a I<full flush point> or the
end of the buffer.

If a I<full flush point> is found, C<Z_OK> is returned and C<$buffer>
will be have all data up to the flush point removed. This can then be
passed to the C<deflate> method.

Any other return code means that a flush point was not found. If more
data is available, C<inflateSync> can be called repeatedly with more
compressed data until the flush point is found.


=head2 B<$i-E<gt>dict_adler()>

Returns the adler32 value for the dictionary.

=head2 B<$i-E<gt>msg()>

Returns the last error message generated by zlib.

=head2 B<$i-E<gt>total_in()>

Returns the total number of bytes compressed bytes input to inflate.

=head2 B<$i-E<gt>total_out()>

Returns the total number of uncompressed bytes output from inflate.

=head2 Example

Here is an example of using C<inflate>.

    use strict ;
    use warnings ;
    
    use Compress::Zlib ;
    
    my $x = inflateInit()
       or die "Cannot create a inflation stream\n" ;
    
    my $input = '' ;
    binmode STDIN;
    binmode STDOUT;
    
    my ($output, $status) ;
    while (read(STDIN, $input, 4096))
    {
        ($output, $status) = $x->inflate(\$input) ;
    
        print $output 
            if $status == Z_OK or $status == Z_STREAM_END ;
    
        last if $status != Z_OK ;
    }
    
    die "inflation failed\n"
        unless $status == Z_STREAM_END ;

=head1 CHECKSUM FUNCTIONS

Two functions are provided by I<zlib> to calculate checksums. For the
Perl interface, the order of the two parameters in both functions has
been reversed. This allows both running checksums and one off
calculations to be done.

    $crc = adler32($buffer [,$crc]) ;
    $crc = crc32($buffer [,$crc]) ;

The buffer parameters can either be a scalar or a scalar reference.

If the $crc parameters is C<undef>, the crc value will be reset.

If you have built this module with zlib 1.2.3 or better, two more
CRC-related functions are available.

    $crc = adler32_combine($crc1, $crc2, $len2)l
    $crc = crc32_combine($adler1, $adler2, $len2)

These functions allow checksums to be merged.

=head1 CONSTANTS

All the I<zlib> constants are automatically imported when you make use
of I<Compress::Zlib>.


=head1 SEE ALSO

L<IO::Compress::Gzip>, L<IO::Uncompress::Gunzip>, L<IO::Compress::Deflate>, L<IO::Uncompress::Inflate>, L<IO::Compress::RawDeflate>, L<IO::Uncompress::RawInflate>, L<IO::Compress::Bzip2>, L<IO::Uncompress::Bunzip2>, L<IO::Compress::Lzop>, L<IO::Uncompress::UnLzop>, L<IO::Compress::Lzf>, L<IO::Uncompress::UnLzf>, L<IO::Uncompress::AnyInflate>, L<IO::Uncompress::AnyUncompress>

L<Compress::Zlib::FAQ|Compress::Zlib::FAQ>

L<File::GlobMapper|File::GlobMapper>, L<Archive::Zip|Archive::Zip>,
L<Archive::Tar|Archive::Tar>,
L<IO::Zlib|IO::Zlib>


For RFC 1950, 1951 and 1952 see 
F<http://www.faqs.org/rfcs/rfc1950.html>,
F<http://www.faqs.org/rfcs/rfc1951.html> and
F<http://www.faqs.org/rfcs/rfc1952.html>

The I<zlib> compression library was written by Jean-loup Gailly
F<[e-mail]> and Mark Adler F<[e-mail]>.

The primary site for the I<zlib> compression library is
F<http://www.zlib.org>.

The primary site for gzip is F<http://www.gzip.org>.




=head1 AUTHOR

This module was written by Paul Marquess, F<[e-mail]>. 



=head1 MODIFICATION HISTORY

See the Changes file.

=head1 COPYRIGHT AND LICENSE

Copyright (c) 1995-2007 Paul Marquess. All rights reserved.

This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.