zlib.pm

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        return Z_DATA_ERROR()
            if length($$string) < GZIP_FEXTRA_HEADER_SIZE ;

        my ($extra_len) = unpack ('v', $$string);
        $extra_len += GZIP_FEXTRA_HEADER_SIZE;
        return Z_DATA_ERROR()
            if length($$string) < $extra_len ;

        substr($$string, 0, $extra_len) = '';
    }

    # skip orig name
    if ($flags & GZIP_FLG_FNAME)
    {
        my $name_end = index ($$string, GZIP_NULL_BYTE);
        return Z_DATA_ERROR()
           if $name_end == -1 ;
        substr($$string, 0, $name_end + 1) =  '';
    }

    # skip comment
    if ($flags & GZIP_FLG_FCOMMENT)
    {
        my $comment_end = index ($$string, GZIP_NULL_BYTE);
        return Z_DATA_ERROR()
            if $comment_end == -1 ;
        substr($$string, 0, $comment_end + 1) = '';
    }

    # skip header crc
    if ($flags & GZIP_FLG_FHCRC)
    {
        return Z_DATA_ERROR()
            if length ($$string) < GZIP_FHCRC_SIZE ;
        substr($$string, 0, GZIP_FHCRC_SIZE) = '';
    }
    
    return Z_OK();
}


sub memGunzip($)
{
    # if the buffer isn't a reference, make it one
    my $string = (ref $_[0] ? $_[0] : \$_[0]);
 
    $] >= 5.008 and (utf8::downgrade($$string, 1) 
        or croak "Wide character in memGunzip");

    _removeGzipHeader($string) == Z_OK() 
        or return undef;
     
    my $bufsize = length $$string > 4096 ? length $$string : 4096 ;
    my $x = new Compress::Raw::Zlib::Inflate({-WindowBits => - MAX_WBITS(),
                         -Bufsize => $bufsize}) 

              or return undef;

    my $output = "" ;
    my $status = $x->inflate($string, $output);
    return undef 
        unless $status == Z_STREAM_END();

    if (length $$string >= 8)
    {
        my ($crc, $len) = unpack ("VV", substr($$string, 0, 8));
        substr($$string, 0, 8) = '';
        return undef 
            unless $len == length($output) and
                   $crc == crc32($output);
    }
    else
    {
        $$string = '';
    }
    return $output;   
}

# Autoload methods go after __END__, and are processed by the autosplit program.

1;
__END__


=head1 NAME

Compress::Zlib - Interface to zlib compression library

=head1 SYNOPSIS

    use Compress::Zlib ;

    ($d, $status) = deflateInit( [OPT] ) ;
    $status = $d->deflate($input, $output) ;
    $status = $d->flush($output [, $flush_type]) ;
    $d->deflateParams(OPTS) ;
    $d->deflateTune(OPTS) ;
    $d->dict_adler() ;
    $d->crc32() ;
    $d->adler32() ;
    $d->total_in() ;
    $d->total_out() ;
    $d->msg() ;
    $d->get_Strategy();
    $d->get_Level();
    $d->get_BufSize();

    ($i, $status) = inflateInit( [OPT] ) ;
    $status = $i->inflate($input, $output [, $eof]) ;
    $status = $i->inflateSync($input) ;
    $i->dict_adler() ;
    $d->crc32() ;
    $d->adler32() ;
    $i->total_in() ;
    $i->total_out() ;
    $i->msg() ;
    $d->get_BufSize();

    $dest = compress($source) ;
    $dest = uncompress($source) ;

    $gz = gzopen($filename or filehandle, $mode) ;
    $bytesread = $gz->gzread($buffer [,$size]) ;
    $bytesread = $gz->gzreadline($line) ;
    $byteswritten = $gz->gzwrite($buffer) ;
    $status = $gz->gzflush($flush) ;
    $offset = $gz->gztell() ;
    $status = $gz->gzseek($offset, $whence) ;
    $status = $gz->gzclose() ;
    $status = $gz->gzeof() ;
    $status = $gz->gzsetparams($level, $strategy) ;
    $errstring = $gz->gzerror() ; 
    $gzerrno

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

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

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

    ZLIB_VERSION
    ZLIB_VERNUM



=head1 DESCRIPTION

The I<Compress::Zlib> module provides a Perl interface to the I<zlib>
compression library (see L</AUTHOR> for details about where to get
I<zlib>). 

The C<Compress::Zlib> module can be split into two general areas of
functionality, namely a simple read/write interface to I<gzip> files
and a low-level in-memory compression/decompression interface.

Each of these areas will be discussed in the following sections.

=head2 Notes for users of Compress::Zlib version 1

The main change in C<Compress::Zlib> version 2.x is that it does not now
interface directly to the zlib library. Instead it uses the
C<IO::Compress::Gzip> and C<IO::Uncompress::Gunzip> modules for
reading/writing gzip files, and the C<Compress::Raw::Zlib> module for some
low-level zlib access. 

The interface provided by version 2 of this module should be 100% backward
compatible with version 1. If you find a difference in the expected
behaviour please contact the author (See L</AUTHOR>). See L<GZIP INTERFACE> 

With the creation of the C<IO::Compress> and C<IO::Uncompress> modules no
new features are planned for C<Compress::Zlib> - the new modules do
everything that C<Compress::Zlib> does and then some. Development on
C<Compress::Zlib> will be limited to bug fixes only.

If you are writing new code, your first port of call should be one of the
new C<IO::Compress> or C<IO::Uncompress> modules.

=head1 GZIP INTERFACE

A number of functions are supplied in I<zlib> for reading and writing
I<gzip> files that conform to RFC 1952. This module provides an interface
to most of them. 

If you have previously used C<Compress::Zlib> 1.x, the following
enhancements/changes have been made to the C<gzopen> interface:

=over 5

=item 1

If you want to to open either STDIN or STDOUT with C<gzopen>, you can now
optionally use the special filename "C<->" as a synonym for C<\*STDIN> and
C<\*STDOUT>.

=item 2 

In C<Compress::Zlib> version 1.x, C<gzopen> used the zlib library to open
the underlying file. This made things especially tricky when a Perl
filehandle was passed to C<gzopen>. Behind the scenes the numeric C file
descriptor had to be extracted from the Perl filehandle and this passed to
the zlib library.

Apart from being non-portable to some operating systems, this made it
difficult to use C<gzopen> in situations where you wanted to extract/create
a gzip data stream that is embedded in a larger file, without having to
resort to opening and closing the file multiple times. 

It also made it impossible to pass a perl filehandle that wasn't associated
with a real filesystem file, like, say, an C<IO::String>.

In C<Compress::Zlib> version 2.x, the C<gzopen> interface has been
completely rewritten to use the L<IO::Compress::Gzip|IO::Compress::Gzip>
for writing gzip files and L<IO::Uncompress::Gunzip|IO::Uncompress::Gunzip>
for reading gzip files. None of the limitations mentioned above apply.

=item 3

Addition of C<gzseek> to provide a restricted C<seek> interface.

=item 4.

Added C<gztell>.

=back

A more complete and flexible interface for reading/writing gzip
files/buffers is included with the module C<IO-Compress-Zlib>. See
L<IO::Compress::Gzip|IO::Compress::Gzip> and
L<IO::Uncompress::Gunzip|IO::Uncompress::Gunzip> for more details.

=over 5

=item B<$gz = gzopen($filename, $mode)>

=item B<$gz = gzopen($filehandle, $mode)>

This function opens either the I<gzip> file C<$filename> for reading or
writing or attaches to the opened filehandle, C<$filehandle>. 
It returns an object on success and C<undef> on failure.

When writing a gzip file this interface will I<always> create the smallest
possible gzip header (exactly 10 bytes). If you want greater control over
what gets stored in the gzip header (like the original filename or a
comment) use L<IO::Compress::Gzip|IO::Compress::Gzip> instead. Similarly if
you want to read the contents of the gzip header use
L<IO::Uncompress::Gunzip|IO::Uncompress::Gunzip>.

The second parameter, C<$mode>, is used to specify whether the file is
opened for reading or writing and to optionally specify a compression
level and compression strategy when writing. The format of the C<$mode>
parameter is similar to the mode parameter to the 'C' function C<fopen>,
so "rb" is used to open for reading, "wb" for writing and "ab" for
appending (writing at the end of the file).

To specify a compression level when writing, append a digit between 0
and 9 to the mode string -- 0 means no compression and 9 means maximum
compression.
If no compression level is specified Z_DEFAULT_COMPRESSION is used.

To specify the compression strategy when writing, append 'f' for filtered
data, 'h' for Huffman only compression, or 'R' for run-length encoding.
If no strategy is specified Z_DEFAULT_STRATEGY is used.

So, for example, "wb9" means open for writing with the maximum compression
using the default strategy and "wb4R" means open for writing with compression
level 4 and run-length encoding.

Refer to the I<zlib> documentation for the exact format of the C<$mode>
parameter.

=item B<$bytesread = $gz-E<gt>gzread($buffer [, $size]) ;>

Reads C<$size> bytes from the compressed file into C<$buffer>. If
C<$size> is not specified, it will default to 4096. If the scalar
C<$buffer> is not large enough, it will be extended automatically.

Returns the number of bytes actually read. On EOF it returns 0 and in
the case of an error, -1.

=item B<$bytesread = $gz-E<gt>gzreadline($line) ;>

Reads the next line from the compressed file into C<$line>. 

Returns the number of bytes actually read. On EOF it returns 0 and in
the case of an error, -1.

It is legal to intermix calls to C<gzread> and C<gzreadline>.

To maintain backward compatibility with version 1.x of this module
C<gzreadline> ignores the C<$/> variable - it I<always> uses the string
C<"\n"> as the line delimiter.  

If you want to read a gzip file a line at a time and have it respect the
C<$/> variable (or C<$INPUT_RECORD_SEPARATOR>, or C<$RS> when C<English> is
in use) see L<IO::Uncompress::Gunzip|IO::Uncompress::Gunzip>.

=item B<$byteswritten = $gz-E<gt>gzwrite($buffer) ;>

Writes the contents of C<$buffer> to the compressed file. Returns the
number of bytes actually written, or 0 on error.

=item B<$status = $gz-E<gt>gzflush($flush_type) ;>

Flushes all pending output into the compressed file.

This method takes an optional parameter, C<$flush_type>, that controls
how the flushing will be carried out. By default the C<$flush_type>
used is C<Z_FINISH>. Other valid values for C<$flush_type> are
C<Z_NO_FLUSH>, C<Z_SYNC_FLUSH>, C<Z_FULL_FLUSH> and C<Z_BLOCK>. It is
strongly recommended that you only set the C<flush_type> parameter if
you fully understand the implications of what it does - overuse of C<flush>
can seriously degrade the level of compression achieved. See the C<zlib>
documentation for details.

Returns 0 on success.


=item B<$offset = $gz-E<gt>gztell() ;>

Returns the uncompressed file offset.

=item B<$status = $gz-E<gt>gzseek($offset, $whence) ;>

Provides a sub-set of the C<seek> functionality, with the restriction
that it is only legal to seek forward in the compressed file.
It is a fatal error to attempt to seek backward.

When opened for writing, empty parts of the file will have NULL (0x00)
bytes written to them.

The C<$whence> parameter should be one of SEEK_SET, SEEK_CUR or SEEK_END.

Returns 1 on success, 0 on failure.

=item B<$gz-E<gt>gzclose>

Closes the compressed file. Any pending data is flushed to the file
before it is closed.

Returns 0 on success.

=item B<$gz-E<gt>gzsetparams($level, $strategy>

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

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

Note: This method is only available if you are running zlib 1.0.6 or better.

=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

=item B<$gz-E<gt>gzerror>

Returns the I<zlib> error message or number for the last operation
associated with C<$gz>. The return value will be the I<zlib> error
number when used in a numeric context and the I<zlib> error message
when used in a string context. The I<zlib> error number constants,
shown below, are available for use.

    Z_OK
    Z_STREAM_END
    Z_ERRNO
    Z_STREAM_ERROR
    Z_DATA_ERROR
    Z_MEM_ERROR
    Z_BUF_ERROR

=item B<$gzerrno>

The C<$gzerrno> scalar holds the error code associated with the most
recent I<gzip> routine. Note that unlike C<gzerror()>, the error is
I<not> associated with a particular file.

As with C<gzerror()> it returns an error number in numeric context and
an error message in string context. Unlike C<gzerror()> though, the
error message will correspond to the I<zlib> message when the error is
associated with I<zlib> itself, or the UNIX error message when it is
not (i.e. I<zlib> returned C<Z_ERRORNO>).

As there is an overlap between the error numbers used by I<zlib> and
UNIX, C<$gzerrno> should only be used to check for the presence of
I<an> error in numeric context. Use C<gzerror()> to check for specific
I<zlib> errors. The I<gzcat> example below shows how the variable can
be used safely.

=back


=head2 Examples

Here is an example script which uses the interface. It implements a
I<gzcat> function.

    use strict ;
    use warnings ;
    
    use Compress::Zlib ;
    
    # use stdin if no files supplied
    @ARGV = '-' unless @ARGV ;
    
    foreach my $file (@ARGV) {
        my $buffer ;
    
        my $gz = gzopen($file, "rb") 
             or die "Cannot open $file: $gzerrno\n" ;
    
        print $buffer while $gz->gzread($buffer) > 0 ;
    
        die "Error reading from $file: $gzerrno" . ($gzerrno+0) . "\n" 
            if $gzerrno != Z_STREAM_END ;
        
        $gz->gzclose() ;
    }

Below is a script which makes use of C<gzreadline>. It implements a
very simple I<grep> like script.

    use strict ;
    use warnings ;
    
    use Compress::Zlib ;
    
    die "Usage: gzgrep pattern [file...]\n"
        unless @ARGV >= 1;
    
    my $pattern = shift ;
    
    # use stdin if no files supplied
    @ARGV = '-' unless @ARGV ;
    
    foreach my $file (@ARGV) {
        my $gz = gzopen($file, "rb") 
             or die "Cannot open $file: $gzerrno\n" ;
    
        while ($gz->gzreadline($_) > 0) {
            print if /$pattern/ ;
        }
    
        die "Error reading from $file: $gzerrno\n" 
            if $gzerrno != Z_STREAM_END ;
        
        $gz->gzclose() ;
    }

This script, I<gzstream>, does the opposite of the I<gzcat> script
above. It reads from standard input and writes a gzip data stream to
standard output.

    use strict ;
    use warnings ;
    
    use Compress::Zlib ;
    
    binmode STDOUT;  # gzopen only sets it on the fd
    
    my $gz = gzopen(\*STDOUT, "wb")
          or die "Cannot open stdout: $gzerrno\n" ;
    
    while (<>) {
        $gz->gzwrite($_) 
          or die "error writing: $gzerrno\n" ;
    }

    $gz->gzclose ;

=head2 Compress::Zlib::memGzip

This function is used to create an in-memory gzip file with the minimum
possible gzip header (exactly 10 bytes).

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

If successful, it returns the in-memory gzip file, otherwise it returns