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<big>&nbsp;Compress::Zlib - Interface to zlib compression library</big>
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<div name="index">
<a name="__index__"></a>

<ul>

<li><a href="#name">NAME</a></li>
	<li><a href="#synopsis">SYNOPSIS</a></li>
	<li><a href="#description">DESCRIPTION</a></li>
	<ul>

<li><a href="#notes_for_users_of_compress__zlib_version_1">Notes for users of Compress::Zlib version 1</a></li>
	</ul>

<li><a href="#gzip_interface">GZIP INTERFACE</a></li>
	<ul>

<li><a href="#examples">Examples</a></li>
		<li><a href="#compress__zlib__memgzip">Compress::Zlib::memGzip</a></li>
		<li><a href="#compress__zlib__memgunzip">Compress::Zlib::memGunzip</a></li>
	</ul>

<li><a href="#compress_uncompress">COMPRESS/UNCOMPRESS</a></li>
	<li><a href="#deflate_interface">Deflate Interface</a></li>
	<ul>

<li><a href="#__d___status____deflateinit___opt___">($d, $status) = deflateInit( [OPT] )</a></li>
		<li><a href="#__out___status_____d__deflate__buffer_">($out, $status) = $d-&gt;deflate($buffer)</a></li>
		<li><a href="#__out___status_____d__flush__flush_type__">($out, $status) = $d-&gt;flush([flush_type])</a></li>
		<li><a href="#_status____d__deflateparams__opt__">$status = $d-&gt;deflateParams([OPT])</a></li>
		<li><a href="#_d__dict_adler__">$d-&gt;dict_adler()</a></li>
		<li><a href="#_d__msg__">$d-&gt;msg()</a></li>
		<li><a href="#_d__total_in__">$d-&gt;total_in()</a></li>
		<li><a href="#_d__total_out__">$d-&gt;total_out()</a></li>
		<li><a href="#example">Example</a></li>
	</ul>

<li><a href="#inflate_interface">Inflate Interface</a></li>
	<ul>

<li><a href="#__i___status____inflateinit__">($i, $status) = inflateInit()</a></li>
		<li><a href="#__out___status_____i__inflate__buffer_">($out, $status) = $i-&gt;inflate($buffer)</a></li>
		<li><a href="#_status____i__inflatesync__buffer_">$status = $i-&gt;inflateSync($buffer)</a></li>
		<li><a href="#_i__dict_adler__">$i-&gt;dict_adler()</a></li>
		<li><a href="#_i__msg__">$i-&gt;msg()</a></li>
		<li><a href="#_i__total_in__">$i-&gt;total_in()</a></li>
		<li><a href="#_i__total_out__">$i-&gt;total_out()</a></li>
		<li><a href="#example">Example</a></li>
	</ul>

<li><a href="#checksum_functions">CHECKSUM FUNCTIONS</a></li>
	<li><a href="#constants">CONSTANTS</a></li>
	<li><a href="#see_also">SEE ALSO</a></li>
	<li><a href="#author">AUTHOR</a></li>
	<li><a href="#modification_history">MODIFICATION HISTORY</a></li>
	<li><a href="#copyright_and_license">COPYRIGHT AND LICENSE</a></li>
</ul>

<h1><a name="name">NAME</a></h1>
Compress::Zlib - Interface to zlib compression library


<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
 use Compress::Zlib ;</pre>
<pre>
 ($d, $status) = deflateInit( [OPT] ) ;
 $status = $d-&gt;deflate($input, $output) ;
 $status = $d-&gt;flush($output [, $flush_type]) ;
 $d-&gt;deflateParams(OPTS) ;
 $d-&gt;deflateTune(OPTS) ;
 $d-&gt;dict_adler() ;
 $d-&gt;crc32() ;
 $d-&gt;adler32() ;
 $d-&gt;total_in() ;
 $d-&gt;total_out() ;
 $d-&gt;msg() ;
 $d-&gt;get_Strategy();
 $d-&gt;get_Level();
 $d-&gt;get_BufSize();</pre>
<pre>
 ($i, $status) = inflateInit( [OPT] ) ;
 $status = $i-&gt;inflate($input, $output [, $eof]) ;
 $status = $i-&gt;inflateSync($input) ;
 $i-&gt;dict_adler() ;
 $d-&gt;crc32() ;
 $d-&gt;adler32() ;
 $i-&gt;total_in() ;
 $i-&gt;total_out() ;
 $i-&gt;msg() ;
 $d-&gt;get_BufSize();</pre>
<pre>
 $dest = compress($source) ;
 $dest = uncompress($source) ;</pre>
<pre>
 $gz = gzopen($filename or filehandle, $mode) ;
 $bytesread = $gz-&gt;gzread($buffer [,$size]) ;
 $bytesread = $gz-&gt;gzreadline($line) ;
 $byteswritten = $gz-&gt;gzwrite($buffer) ;
 $status = $gz-&gt;gzflush($flush) ;
 $offset = $gz-&gt;gztell() ;
 $status = $gz-&gt;gzseek($offset, $whence) ;
 $status = $gz-&gt;gzclose() ;
 $status = $gz-&gt;gzeof() ;
 $status = $gz-&gt;gzsetparams($level, $strategy) ;
 $errstring = $gz-&gt;gzerror() ; 
 $gzerrno</pre>
<pre>
 $dest = Compress::Zlib::memGzip($buffer) ;
 $dest = Compress::Zlib::memGunzip($buffer) ;</pre>
<pre>
 $crc = adler32($buffer [,$crc]) ;
 $crc = crc32($buffer [,$crc]) ;</pre>
<pre>
 $crc = adler32_combine($crc1, $crc2, $len2)l
 $crc = crc32_combine($adler1, $adler2, $len2)</pre>
<pre>
 ZLIB_VERSION
 ZLIB_VERNUM</pre>


<hr />
<h1><a name="description">DESCRIPTION</a></h1>
The Compress::Zlib module provides a Perl interface to the zlib
compression library (see <a href="#author">AUTHOR</a> for details about where to get
zlib).
The <code>Compress::Zlib</code> module can be split into two general areas of
functionality, namely a simple read/write interface to gzip files
and a low-level in-memory compression/decompression interface.
Each of these areas will be discussed in the following sections.


<h2><a name="notes_for_users_of_compress__zlib_version_1">Notes for users of Compress::Zlib version 1</a></h2>
The main change in <code>Compress::Zlib</code> version 2.x is that it does not now
interface directly to the zlib library. Instead it uses the
<code>IO::Compress::Gzip</code> and <code>IO::Uncompress::Gunzip</code> modules for
reading/writing gzip files, and the <code>Compress::Raw::Zlib</code> 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 <a href="#author">AUTHOR</a>). See <a href="#gzip_interface">GZIP INTERFACE</a>
With the creation of the <code>IO::Compress</code> and <code>IO::Uncompress</code> modules no
new features are planned for <code>Compress::Zlib</code> - the new modules do
everything that <code>Compress::Zlib</code> does and then some. Development on
<code>Compress::Zlib</code> will be limited to bug fixes only.
If you are writing new code, your first port of call should be one of the
new <code>IO::Compress</code> or <code>IO::Uncompress</code> modules.


<hr />
<h1><a name="gzip_interface">GZIP INTERFACE</a></h1>
A number of functions are supplied in zlib for reading and writing
gzip files that conform to <a href="http://www.ietf.org/rfc/rfc1952.txt" class="rfc">RFC 1952</a>. This module provides an interface
to most of them.
If you have previously used <code>Compress::Zlib</code> 1.x, the following
enhancements/changes have been made to the <a href="#gzopen"><code>gzopen</code></a> interface:
<ol>
<li>
If you want to to open either STDIN or STDOUT with <a href="#gzopen"><code>gzopen</code></a>, you can now
optionally use the special filename &quot;<code>-</code>&quot; as a synonym for <code>\*STDIN</code> and
<code>\*STDOUT</code>.
</li>
<li>
In <code>Compress::Zlib</code> version 1.x, <a href="#gzopen"><code>gzopen</code></a> used the zlib library to open
the underlying file. This made things especially tricky when a Perl
filehandle was passed to <a href="#gzopen"><code>gzopen</code></a>. 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 <a href="#gzopen"><code>gzopen</code></a> 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 <code>IO::String</code>.
In <code>Compress::Zlib</code> version 2.x, the <a href="#gzopen"><code>gzopen</code></a> interface has been
completely rewritten to use the <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Compress/Gzip.html">IO::Compress::Gzip</a>
for writing gzip files and <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/Gunzip.html">IO::Uncompress::Gunzip</a>
for reading gzip files. None of the limitations mentioned above apply.
</li>
<li>
Addition of <a href="#gzseek"><code>gzseek</code></a> to provide a restricted <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlfunc.html#seek"><code>seek</code></a> interface.
</li>
<li>
Added <a href="#gztell"><code>gztell</code></a>.
</li>
</ol>
A more complete and flexible interface for reading/writing gzip
files/buffers is included with the module <code>IO-Compress-Zlib</code>. See
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Compress/Gzip.html">IO::Compress::Gzip</a> and
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/Gunzip.html">IO::Uncompress::Gunzip</a> for more details.
<dl>
<dt><a name="gzopen" class="item">$gz = gzopen($filename, $mode)</a>

<dt>$gz = gzopen($filehandle, $mode)

<dd>
This function opens either the gzip file <code>$filename</code> for reading or
writing or attaches to the opened filehandle, <code>$filehandle</code>. 
It returns an object on success and <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlfunc.html#undef"><code>undef</code></a> on failure.
</dd>
<dd>
When writing a gzip file this interface will 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 <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Compress/Gzip.html">IO::Compress::Gzip</a> instead. Similarly if
you want to read the contents of the gzip header use
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/Gunzip.html">IO::Uncompress::Gunzip</a>.
</dd>
<dd>
The second parameter, <code>$mode</code>, is used to specify whether the file is
opened for reading or writing and to optionally specify a compression
level and compression strategy when writing. The format of the <code>$mode</code>
parameter is similar to the mode parameter to the 'C' function <code>fopen</code>,
so &quot;rb&quot; is used to open for reading, &quot;wb&quot; for writing and &quot;ab&quot; for
appending (writing at the end of the file).
</dd>
<dd>
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.
</dd>
<dd>
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.
</dd>
<dd>
So, for example, &quot;wb9&quot; means open for writing with the maximum compression
using the default strategy and &quot;wb4R&quot; means open for writing with compression
level 4 and run-length encoding.
</dd>
<dd>
Refer to the zlib documentation for the exact format of the <code>$mode</code>
parameter.
</dd>
</li>
<dt><a name="gzread" class="item">$bytesread = $gz-&gt;gzread($buffer [, $size]) ;</a>

<dd>
Reads <code>$size</code> bytes from the compressed file into <code>$buffer</code>. If
<code>$size</code> is not specified, it will default to 4096. If the scalar
<code>$buffer</code> is not large enough, it will be extended automatically.
</dd>
<dd>
Returns the number of bytes actually read. On EOF it returns 0 and in
the case of an error, -1.
</dd>
</li>
<dt><a name="gzreadline" class="item">$bytesread = $gz-&gt;gzreadline($line) ;</a>

<dd>
Reads the next line from the compressed file into <code>$line</code>.
</dd>
<dd>
Returns the number of bytes actually read. On EOF it returns 0 and in
the case of an error, -1.
</dd>
<dd>
It is legal to intermix calls to <a href="#gzread"><code>gzread</code></a> and <a href="#gzreadline"><code>gzreadline</code></a>.
</dd>
<dd>
To maintain backward compatibility with version 1.x of this module
<a href="#gzreadline"><code>gzreadline</code></a> ignores the <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlvar.html#__"><code>$/</code></a> variable - it always uses the string
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlrun.html#n"><code>&quot;\n&quot;</code></a> as the line delimiter.
</dd>
<dd>
If you want to read a gzip file a line at a time and have it respect the
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlvar.html#__"><code>$/</code></a> variable (or <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlvar.html#_input_record_separator"><code>$INPUT_RECORD_SEPARATOR</code></a>, or <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlvar.html#_rs"><code>$RS</code></a> when <code>English</code> is
in use) see <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/Gunzip.html">IO::Uncompress::Gunzip</a>.
</dd>
</li>
<dt><a name="gzwrite" class="item">$byteswritten = $gz-&gt;gzwrite($buffer) ;</a>

<dd>
Writes the contents of <code>$buffer</code> to the compressed file. Returns the
number of bytes actually written, or 0 on error.
</dd>
</li>
<dt><a name="gzflush" class="item">$status = $gz-&gt;gzflush($flush_type) ;</a>

<dd>
Flushes all pending output into the compressed file.
</dd>
<dd>
This method takes an optional parameter, <code>$flush_type</code>, that controls
how the flushing will be carried out. By default the <code>$flush_type</code>
used is <code>Z_FINISH</code>. Other valid values for <code>$flush_type</code> are
<code>Z_NO_FLUSH</code>, <code>Z_SYNC_FLUSH</code>, <code>Z_FULL_FLUSH</code> and <code>Z_BLOCK</code>. It is
strongly recommended that you only set the <code>flush_type</code> parameter if
you fully understand the implications of what it does - overuse of <code>flush</code>
can seriously degrade the level of compression achieved. See the <code>zlib</code>
documentation for details.
</dd>
<dd>
Returns 0 on success.
</dd>
</li>
<dt><a name="gztell" class="item">$offset = $gz-&gt;gztell() ;</a>

<dd>
Returns the uncompressed file offset.
</dd>
</li>
<dt><a name="gzseek" class="item">$status = $gz-&gt;gzseek($offset, $whence) ;</a>

<dd>
Provides a sub-set of the <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlfunc.html#seek"><code>seek</code></a> 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.
</dd>
<dd>
When opened for writing, empty parts of the file will have NULL (0x00)
bytes written to them.
</dd>
<dd>
The <code>$whence</code> parameter should be one of SEEK_SET, SEEK_CUR or SEEK_END.
</dd>
<dd>
Returns 1 on success, 0 on failure.
</dd>
</li>
<dt><a name="gzclose" class="item">$gz-&gt;gzclose</a>

<dd>
Closes the compressed file. Any pending data is flushed to the file
before it is closed.
</dd>
<dd>
Returns 0 on success.
</dd>
</li>
<dt><a name="gzsetparams" class="item">$gz-&gt;gzsetparams($level, $strategy</a>

<dd>
Change settings for the deflate stream <code>$gz</code>.
</dd>
<dd>
The list of the valid options is shown below. Options not specified
will remain unchanged.
</dd>
<dd>
Note: This method is only available if you are running zlib 1.0.6 or better.
</dd>
<dl>
<dt><a name="_level" class="item">$level</a>

<dd>
Defines the compression level. Valid values are 0 through 9,
<code>Z_NO_COMPRESSION</code>, <code>Z_BEST_SPEED</code>, <code>Z_BEST_COMPRESSION</code>, and
<code>Z_DEFAULT_COMPRESSION</code>.
</dd>
</li>
<dt><a name="_strategy" class="item">$strategy</a>

<dd>
Returns the zlib error message or number for the last operation
associated with <code>$gz</code>. The return value will be the zlib error
number when used in a numeric context and the zlib error message
when used in a string context. The zlib error number constants,
shown below, are available for use.
</dd>
<dd>
<pre>
 Z_OK
 Z_STREAM_END
 Z_ERRNO
 Z_STREAM_ERROR
 Z_DATA_ERROR
 Z_MEM_ERROR
 Z_BUF_ERROR</pre>
</dd>
</li>
<dt><a name="_gzerrno" class="item">$gzerrno</a>

<dd>
The <a href="#_gzerrno"><code>$gzerrno</code></a> scalar holds the error code associated with the most
recent gzip routine. Note that unlike <a href="#gzerror"><code>gzerror()</code></a>, the error is
not associated with a particular file.
</dd>
<dd>
As with <a href="#gzerror"><code>gzerror()</code></a> it returns an error number in numeric context and
an error message in string context. Unlike <a href="#gzerror"><code>gzerror()</code></a> though, the
error message will correspond to the zlib message when the error is
associated with zlib itself, or the UNIX error message when it is
not (i.e. zlib returned <code>Z_ERRORNO</code>).
</dd>
<dd>
As there is an overlap between the error numbers used by zlib and
UNIX, <a href="#_gzerrno"><code>$gzerrno</code></a> should only be used to check for the presence of
an error in numeric context. Use <a href="#gzerror"><code>gzerror()</code></a> to check for specific
zlib errors. The gzcat example below shows how the variable can
be used safely.
</dd>
</li>
</dl>


<h2><a name="examples">Examples</a></h2>
Here is an example script which uses the interface. It implements a
gzcat function.
<pre>
 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, &quot;rb&quot;) 
 or die &quot;Cannot open $file: $gzerrno\n&quot; ;
 
 print $buffer while $gz-&gt;gzread($buffer) &gt; 0 ;
 
 die &quot;Error reading from $file: $gzerrno&quot; . ($gzerrno+0) . &quot;\n&quot; 
 if $gzerrno != Z_STREAM_END ;
 
 $gz-&gt;gzclose() ;
 }</pre>
Below is a script which makes use of <a href="#gzreadline"><code>gzreadline</code></a>. It implements a
very simple grep like script.
<pre>
 use strict ;
 use warnings ;
 
 use Compress::Zlib ;
 
 die &quot;Usage: gzgrep pattern [file...]\n&quot;
 unless @ARGV &gt;= 1;
 
 my $pattern = shift ;
 
 # use stdin if no files supplied
 @ARGV = '-' unless @ARGV ;
 
 foreach my $file (@ARGV) {
 my $gz = gzopen($file, &quot;rb&quot;) 
 or die &quot;Cannot open $file: $gzerrno\n&quot; ;
 
 while ($gz-&gt;gzreadline($_) &gt; 0) {
 print if /$pattern/ ;
 }
 
 die &quot;Error reading from $file: $gzerrno\n&quot; 
 if $gzerrno != Z_STREAM_END ;
 
 $gz-&gt;gzclose() ;
 }</pre>
This script, gzstream, does the opposite of the gzcat script
above. It reads from standard input and writes a gzip data stream to
standard output.
<pre>
 use strict ;
 use warnings ;
 
 use Compress::Zlib ;
 
 binmode STDOUT; # gzopen only sets it on the fd
 
 my $gz = gzopen(\*STDOUT, &quot;wb&quot;)
 or die &quot;Cannot open stdout: $gzerrno\n&quot; ;
 
 while (&lt;&gt;) {
 $gz-&gt;gzwrite($_) 
 or die &quot;error writing: $gzerrno\n&quot; ;
 }</pre>
<pre>
 $gz-&gt;gzclose ;</pre>


<h2><a name="compress__zlib__memgzip">Compress::Zlib::memGzip</a></h2>
This function is used to create an in-memory gzip file with the minimum
possible gzip header (exactly 10 bytes).
<pre>
 $dest = Compress::Zlib::memGzip($buffer) ;</pre>
If successful, it returns the in-memory gzip file, otherwise it returns
undef.
The <code>$buffer</code> parameter can either be a scalar or a scalar reference.
See <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Compress/Gzip.html">IO::Compress::Gzip</a> for an alternative way to
carry out in-memory gzip compression.


<h2><a name="compress__zlib__memgunzip">Compress::Zlib::memGunzip</a></h2>
This function is used to uncompress an in-memory gzip file.
<pre>
 $dest = Compress::Zlib::memGunzip($buffer) ;</pre>
If successful, it returns the uncompressed gzip file, otherwise it
returns undef.
The <code>$buffer</code> parameter can either be a scalar or a scalar reference. The
contents of the <code>$buffer</code> parameter are destroyed after calling this function.
See <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/Gunzip.html">IO::Uncompress::Gunzip</a> for an alternative way
to carry out in-memory gzip uncompression.


<hr />
<h1><a name="compress_uncompress">COMPRESS/UNCOMPRESS</a></h1>
Two functions are provided to perform in-memory compression/uncompression of
<a href="http://www.ietf.org/rfc/rfc1950.txt" class="rfc">RFC 1950</a> data streams. They are called <a href="#compress"><code>compress</code></a> and <a href="#uncompress"><code>uncompress</code></a>.
<dl>
<dt><a name="compress" class="item">$dest = compress($source [, $level] ) ;</a>

<dd>
Compresses <code>$source</code>. If successful it returns the compressed
data. Otherwise it returns undef.
</dd>
<dd>
The source buffer, <code>$source</code>, can either be a scalar or a scalar
reference.
</dd>
<dd>
The <a href="#_level"><code>$level</code></a> parameter defines the compression level. Valid values are
0 through 9, <code>Z_NO_COMPRESSION</code>, <code>Z_BEST_SPEED</code>,
<code>Z_BEST_COMPRESSION</code>, and <code>Z_DEFAULT_COMPRESSION</code>.
If <a href="#_level"><code>$level</code></a> is not specified <code>Z_DEFAULT_COMPRESSION</code> will be used.
</dd>
</li>
<dt><a name="uncompress" class="item">$dest = uncompress($source) ;</a>

<dd>
Uncompresses <code>$source</code>. If successful it returns the uncompressed
data. Otherwise it returns undef.
</dd>
<dd>
The source buffer can either be a scalar or a scalar reference.
</dd>
</li>
</dl>
Please note: the two functions defined above are not compatible with
the Unix commands of the same name.
See <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/IO/Deflate.html">IO::Deflate</a> and <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/IO/Inflate.html">IO::Inflate</a> included with
this distribution for an alternative interface for reading/writing <a href="http://www.ietf.org/rfc/rfc1950.txt" class="rfc">RFC 1950</a>
files/buffers.


<hr />
<h1><a name="deflate_interface">Deflate Interface</a></h1>
This section defines an interface that allows in-memory compression using
the deflate interface provided by zlib.
Here is a definition of the interface available:


<h2><a name="__d___status____deflateinit___opt___">($d, $status) = deflateInit( [OPT] )</a></h2>
Initialises a deflation stream.
It combines the features of the zlib functions <code>deflateInit</code>,
<code>deflateInit2</code> and <code>deflateSetDictionary</code>.
If successful, it will return the initialised deflation stream, <code>$d</code>
and <code>$status</code> of <code>Z_OK</code> in a list context. In scalar context it
returns the deflation stream, <code>$d</code>, only.
If not successful, the returned deflation stream (<code>$d</code>) will be
undef and <code>$status</code> will hold the exact zlib error code.
The function optionally takes a number of named options specified as
<code>-Name=&gt;value</code> 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=&gt;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:
<dl>
<dt><a name="level3" class="item">-Level</a>

<dd>
Defines the compression level. Valid values are 0 through 9,
<code>Z_NO_COMPRESSION</code>, <code>Z_BEST_SPEED</code>, <code>Z_BEST_COMPRESSION</code>, and
<code>Z_DEFAULT_COMPRESSION</code>.
</dd>
<dd>
The default is Z_DEFAULT_COMPRESSION.
</dd>
</li>
<dt><a name="method2" class="item">-Method</a>

<dd>
Defines the compression method. The only valid value at present (and
the default) is Z_DEFLATED.
</dd>
</li>
<dt><a name="windowbits3" class="item">-WindowBits</a>

<dd>
To create an <a href="http://www.ietf.org/rfc/rfc1950.txt" class="rfc">RFC 1950</a> data stream, set <a href="#windowbits"><code>WindowBits</code></a> to a positive number.
</dd>
<dd>
To create an <a href="http://www.ietf.org/rfc/rfc1951.txt" class="rfc">RFC 1951</a> data stream, set <a href="#windowbits"><code>WindowBits</code></a> to <code>-MAX_WBITS</code>.
</dd>
<dd>
For a full definition of the meaning and valid values for <a href="#windowbits"><code>WindowBits</code></a> refer
to the zlib documentation for deflateInit2.
</dd>
<dd>
Defaults to MAX_WBITS.
</dd>
</li>
<dt><a name="memlevel2" class="item">-MemLevel</a>

<dd>
For a definition of the meaning and valid values for <a href="#memlevel"><code>MemLevel</code></a>
refer to the zlib documentation for deflateInit2.
</dd>
<dd>
Defaults to MAX_MEM_LEVEL.
</dd>
</li>
<dt><a name="strategy3" class="item">-Strategy</a>

<dd>
Defines the strategy used to tune the compression. The valid values are
<code>Z_DEFAULT_STRATEGY</code>, <code>Z_FILTERED</code> and <code>Z_HUFFMAN_ONLY</code>.
</dd>
<dd>
The default is Z_DEFAULT_STRATEGY.
</dd>
</li>
<dt><a name="dictionary3" class="item">-Dictionary</a>

<dd>
When a dictionary is specified Compress::Zlib will automatically
call <code>deflateSetDictionary</code> directly after calling <code>deflateInit</code>. The
Adler32 value for the dictionary can be obtained by calling the method 
<code>$d-</code>dict_adler()&gt;.
</dd>
<dd>
The default is no dictionary.
</dd>
</li>
<dt><a name="bufsize3" class="item">-Bufsize</a>

<dd>
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
<a href="#bufsize"><code>Bufsize</code></a>.
</dd>
<dd>
The default is 4096.
</dd>
</li>
</dl>
Here is an example of using the <code>deflateInit</code> optional parameter list
to override the default buffer size and compression level. All other
options will take their default values.
<pre>
 deflateInit( -Bufsize =&gt; 300, 
 -Level =&gt; Z_BEST_SPEED ) ;</pre>


<h2><a name="__out___status_____d__deflate__buffer_">($out, $status) = $d-&gt;deflate($buffer)</a></h2>
Deflates the contents of <code>$buffer</code>. The buffer can either be a scalar
or a scalar reference. When finished, <code>$buffer</code> will be
completely processed (assuming there were no errors). If the deflation
was successful it returns the deflated output, <code>$out</code>, and a status
value, <code>$status</code>, of <code>Z_OK</code>.
On error, <code>$out</code> will be undef and <code>$status</code> will contain the
zlib error code.
In a scalar context <code>deflate</code> will return <code>$out</code> only.
As with the deflate function in zlib, it is not necessarily the
case that any output will be produced by this method. So don't rely on
the fact that <code>$out</code> is empty for an error test.


<h2><a name="__out___status_____d__flush__flush_type__">($out, $status) = $d-&gt;flush([flush_type])</a></h2>
Typically used to finish the deflation. Any pending output will be
returned via <code>$out</code>.
<code>$status</code> will have a value <code>Z_OK</code> if successful.
In a scalar context <code>flush</code> will return <code>$out</code> only.
Note that flushing can seriously degrade the compression ratio, so it
should only be used to terminate a decompression (using <code>Z_FINISH</code>) or
when you want to create a full flush point (using <code>Z_FULL_FLUSH</code>).
By default the <code>flush_type</code> used is <code>Z_FINISH</code>. Other valid values
for <code>flush_type</code> are <code>Z_NO_FLUSH</code>, <code>Z_PARTIAL_FLUSH</code>, <code>Z_SYNC_FLUSH</code>
and <code>Z_FULL_FLUSH</code>. It is strongly recommended that you only set the
<code>flush_type</code> parameter if you fully understand the implications of
what it does. See the <code>zlib</code> documentation for details.


<h2><a name="_status____d__deflateparams__opt__">$status = $d-&gt;deflateParams([OPT])</a></h2>
Change settings for the deflate stream <code>$d</code>.
The list of the valid options is shown below. Options not specified
will remain unchanged.
<dl>
<dt><a name="level4" class="item">-Level</a>

<dd>
Defines the compression level. Valid values are 0 through 9,
<code>Z_NO_COMPRESSION</code>, <code>Z_BEST_SPEED</code>, <code>Z_BEST_COMPRESSION</code>, and
<code>Z_DEFAULT_COMPRESSION</code>.
</dd>
</li>
<dt><a name="strategy4" class="item">-Strategy</a>

<dd>
Defines the strategy used to tune the compression. The valid values are
<code>Z_DEFAULT_STRATEGY</code>, <code>Z_FILTERED</code> and <code>Z_HUFFMAN_ONLY</code>.
</dd>
</li>
</dl>


<h2><a name="_d__dict_adler__">$d-&gt;dict_adler()</a></h2>
Returns the adler32 value for the dictionary.


<h2><a name="_d__msg__">$d-&gt;msg()</a></h2>
Returns the last error message generated by zlib.


<h2><a name="_d__total_in__">$d-&gt;total_in()</a></h2>
Returns the total number of bytes uncompressed bytes input to deflate.


<h2><a name="_d__total_out__">$d-&gt;total_out()</a></h2>
Returns the total number of compressed bytes output from deflate.


<h2><a name="example">Example</a></h2>
Here is a trivial example of using <code>deflate</code>. It simply reads standard
input, deflates it and writes it to standard output.
<pre>
 use strict ;
 use warnings ;</pre>
<pre>
 use Compress::Zlib ;</pre>
<pre>
 binmode STDIN;
 binmode STDOUT;
 my $x = deflateInit()
 or die &quot;Cannot create a deflation stream\n&quot; ;</pre>
<pre>
 my ($output, $status) ;
 while (&lt;&gt;)
 {
 ($output, $status) = $x-&gt;deflate($_) ;
 
 $status == Z_OK
 or die &quot;deflation failed\n&quot; ;
 
 print $output ;
 }
 
 ($output, $status) = $x-&gt;flush() ;
 
 $status == Z_OK
 or die &quot;deflation failed\n&quot; ;
 
 print $output ;</pre>


<hr />
<h1><a name="inflate_interface">Inflate Interface</a></h1>
This section defines the interface available that allows in-memory
uncompression using the deflate interface provided by zlib.
Here is a definition of the interface:


<h2><a name="__i___status____inflateinit__">($i, $status) = inflateInit()</a></h2>
Initialises an inflation stream.
In a list context it returns the inflation stream, <code>$i</code>, and the
zlib status code in <code>$status</code>. In a scalar context it returns the
inflation stream only.
If successful, <code>$i</code> will hold the inflation stream and <code>$status</code> will
be <code>Z_OK</code>.
If not successful, <code>$i</code> will be undef and <code>$status</code> will hold the
zlib error code.
The function optionally takes a number of named options specified as
<code>-Name=&gt;value</code> pairs. This allows individual options to be
tailored without having to specify them all in the parameter list.
<pre>

For backward compatibility, it is also possible to pass the parameters
as a reference to a hash containing the name=&gt;value pairs.</pre>
<pre>

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

Here is a list of the valid options:</pre>
<dl>
<dt><a name="windowbits4" class="item">-WindowBits</a>

<dd>
To uncompress an <a href="http://www.ietf.org/rfc/rfc1950.txt" class="rfc">RFC 1950</a> data stream, set <a href="#windowbits"><code>WindowBits</code></a> to a positive number.
</dd>
<dd>
To uncompress an <a href="http://www.ietf.org/rfc/rfc1951.txt" class="rfc">RFC 1951</a> data stream, set <a href="#windowbits"><code>WindowBits</code></a> to <code>-MAX_WBITS</code>.
</dd>
<dd>
For a full definition of the meaning and valid values for <a href="#windowbits"><code>WindowBits</code></a> refer
to the zlib documentation for inflateInit2.
</dd>
<dd>
Defaults to MAX_WBITS.
</dd>
</li>
<dt><a name="bufsize4" class="item">-Bufsize</a>

<dd>
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
<a href="#bufsize"><code>Bufsize</code></a>.
</dd>
<dd>
Default is 4096.
</dd>
</li>
<dt><a name="dictionary4" class="item">-Dictionary</a>

<dd>
The default is no dictionary.
</dd>
</li>
</dl>
Here is an example of using the <code>inflateInit</code> optional parameter to
override the default buffer size.
<pre>
 inflateInit( -Bufsize =&gt; 300 ) ;</pre>


<h2><a name="__out___status_____i__inflate__buffer_">($out, $status) = $i-&gt;inflate($buffer)</a></h2>
Inflates the complete contents of <code>$buffer</code>. The buffer can either be
a scalar or a scalar reference.
Returns <code>Z_OK</code> if successful and <code>Z_STREAM_END</code> if the end of the
compressed data has been successfully reached. 
If not successful, <code>$out</code> will be undef and <code>$status</code> will hold
the zlib error code.
The <code>$buffer</code> parameter is modified by <code>inflate</code>. On completion it
will contain what remains of the input buffer after inflation. This
means that <code>$buffer</code> will be an empty string when the return status is
<code>Z_OK</code>. When the return status is <code>Z_STREAM_END</code> the <code>$buffer</code>
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).


<h2><a name="_status____i__inflatesync__buffer_">$status = $i-&gt;inflateSync($buffer)</a></h2>
Scans <code>$buffer</code> until it reaches either a full flush point or the
end of the buffer.
If a full flush point is found, <code>Z_OK</code> is returned and <code>$buffer</code>
will be have all data up to the flush point removed. This can then be
passed to the <code>deflate</code> method.
Any other return code means that a flush point was not found. If more
data is available, <code>inflateSync</code> can be called repeatedly with more
compressed data until the flush point is found.


<h2><a name="_i__dict_adler__">$i-&gt;dict_adler()</a></h2>
Returns the adler32 value for the dictionary.


<h2><a name="_i__msg__">$i-&gt;msg()</a></h2>
Returns the last error message generated by zlib.


<h2><a name="_i__total_in__">$i-&gt;total_in()</a></h2>
Returns the total number of bytes compressed bytes input to inflate.


<h2><a name="_i__total_out__">$i-&gt;total_out()</a></h2>
Returns the total number of uncompressed bytes output from inflate.


<h2><a name="example">Example</a></h2>
Here is an example of using <code>inflate</code>.
<pre>
 use strict ;
 use warnings ;
 
 use Compress::Zlib ;
 
 my $x = inflateInit()
 or die &quot;Cannot create a inflation stream\n&quot; ;
 
 my $input = '' ;
 binmode STDIN;
 binmode STDOUT;
 
 my ($output, $status) ;
 while (read(STDIN, $input, 4096))
 {
 ($output, $status) = $x-&gt;inflate(\$input) ;
 
 print $output 
 if $status == Z_OK or $status == Z_STREAM_END ;
 
 last if $status != Z_OK ;
 }
 
 die &quot;inflation failed\n&quot;
 unless $status == Z_STREAM_END ;</pre>


<hr />
<h1><a name="checksum_functions">CHECKSUM FUNCTIONS</a></h1>
Two functions are provided by 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.
<pre>
 $crc = adler32($buffer [,$crc]) ;
 $crc = crc32($buffer [,$crc]) ;</pre>
The buffer parameters can either be a scalar or a scalar reference.
If the $crc parameters is <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/pod/perlfunc.html#undef"><code>undef</code></a>, 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.
<pre>
 $crc = adler32_combine($crc1, $crc2, $len2)l
 $crc = crc32_combine($adler1, $adler2, $len2)</pre>
These functions allow checksums to be merged.


<hr />
<h1><a name="constants">CONSTANTS</a></h1>
All the zlib constants are automatically imported when you make use
of Compress::Zlib.


<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Compress/Gzip.html">the IO::Compress::Gzip manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/Gunzip.html">the IO::Uncompress::Gunzip manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Compress/Deflate.html">the IO::Compress::Deflate manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/Inflate.html">the IO::Uncompress::Inflate manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Compress/RawDeflate.html">the IO::Compress::RawDeflate manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/RawInflate.html">the IO::Uncompress::RawInflate manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/IO/Compress/Bzip2.html">the IO::Compress::Bzip2 manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/IO/Uncompress/Bunzip2.html">the IO::Uncompress::Bunzip2 manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/IO/Compress/Lzop.html">the IO::Compress::Lzop manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/IO/Uncompress/UnLzop.html">the IO::Uncompress::UnLzop manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/IO/Compress/Lzf.html">the IO::Compress::Lzf manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/IO/Uncompress/UnLzf.html">the IO::Uncompress::UnLzf manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/AnyInflate.html">the IO::Uncompress::AnyInflate manpage</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Uncompress/AnyUncompress.html">the IO::Uncompress::AnyUncompress manpage</a>
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/Compress/Zlib/FAQ.html">Compress::Zlib::FAQ</a>
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/File/GlobMapper.html">File::GlobMapper</a>, <a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/Archive/Zip.html">Archive::Zip</a>,
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/Archive/Tar.html">Archive::Tar</a>,
<a href="file://C|\ADE\aime_smenon_perl_090715\perl\html/lib/IO/Zlib.html">IO::Zlib</a>
For <a href="http://www.ietf.org/rfc/rfc1950.txt" class="rfc">RFC 1950</a>, 1951 and 1952 see 
<a href="http://www.faqs.org/rfcs/rfc1950.html">http://www.faqs.org/rfcs/rfc1950.html</a>,
<a href="http://www.faqs.org/rfcs/rfc1951.html">http://www.faqs.org/rfcs/rfc1951.html</a> and
<a href="http://www.faqs.org/rfcs/rfc1952.html">http://www.faqs.org/rfcs/rfc1952.html</a>
The zlib compression library was written by Jean-loup Gailly
<a href="mailto:gzip@prep.ai.mit.edu">gzip@prep.ai.mit.edu</a> and Mark Adler <a href="mailto:madler@alumni.caltech.edu">madler@alumni.caltech.edu</a>.
The primary site for the zlib compression library is
<a href="http://www.zlib.org">http://www.zlib.org</a>.
The primary site for gzip is <a href="http://www.gzip.org">http://www.gzip.org</a>.


<hr />
<h1><a name="author">AUTHOR</a></h1>
This module was written by Paul Marquess, <a href="mailto:pmqs@cpan.org">pmqs@cpan.org</a>.


<hr />
<h1><a name="modification_history">MODIFICATION HISTORY</a></h1>
See the Changes file.


<hr />
<h1><a name="copyright_and_license">COPYRIGHT AND LICENSE</a></h1>
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.
<table border="0" width="100%" cellspacing="0" cellpadding="3">
<tr><td class="block" style="background-color: #cccccc" valign="middle">
<big>&nbsp;Compress::Zlib - Interface to zlib compression library</big>
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