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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.deflate-init" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<refnamediv>
<refname>deflate_init</refname>
<refpurpose>Initialize an incremental deflate context</refpurpose>
</refnamediv>
<refsect1 role="description"><!-- {{{ -->
&reftitle.description;
<methodsynopsis>
<type class="union"><type>DeflateContext</type><type>false</type></type><methodname>deflate_init</methodname>
<methodparam><type>int</type><parameter>encoding</parameter></methodparam>
<methodparam choice="opt"><type>array</type><parameter>options</parameter><initializer>[]</initializer></methodparam>
</methodsynopsis>
<para>
Initializes an incremental deflate context using the specified
<parameter>encoding</parameter>.
</para>
<para>
Note that the <literal>window</literal> option here only sets the window size
of the algorithm, differently from the zlib filters where the same parameter
also sets the encoding to use; the encoding must be set with the
<parameter>encoding</parameter> parameter.
</para>
<para>
Limitation: there is currently no way to set the header information on a GZIP
compressed stream, which are set as follows: GZIP signature
(<literal>\x1f\x8B</literal>); compression method (<literal>\x08</literal>
== DEFLATE); 6 zero bytes; the operating system set to the current system
(<literal>\x00</literal> = Windows, <literal>\x03</literal> = Unix, etc.)
</para>
</refsect1><!-- }}} -->
<refsect1 role="parameters"><!-- {{{ -->
&reftitle.parameters;
<variablelist>
<varlistentry>
<term><parameter>encoding</parameter></term>
<listitem>
<para>
One of the <constant>ZLIB_ENCODING_<replaceable>*</replaceable></constant> constants.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>options</parameter></term>
<listitem>
<para>
An associative array which may contain the following elements:
<variablelist>
<varlistentry>
<term><varname>level</varname></term>
<listitem>
<para>
The compression level in range -1..9; defaults to -1.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>memory</varname></term>
<listitem>
<para>
The compression memory level in range 1..9; defaults to 8.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>window</varname></term>
<listitem>
<para>
The zlib window size (logarithmic) in range <literal>8</literal>..<literal>15</literal>;
defaults to <literal>15</literal>.
zlib changes a window size of <literal>8</literal> to <literal>9</literal>,
and as of zlib 1.2.8 fails with a warning, if a window size of <literal>8</literal>
is requested for <constant>ZLIB_ENCODING_RAW</constant> or <constant>ZLIB_ENCODING_GZIP</constant>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>strategy</varname></term>
<listitem>
<para>
One of <constant>ZLIB_FILTERED</constant>,
<constant>ZLIB_HUFFMAN_ONLY</constant>, <constant>ZLIB_RLE</constant>,
<constant>ZLIB_FIXED</constant> or
<constant>ZLIB_DEFAULT_STRATEGY</constant> (the default).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>dictionary</varname></term>
<listitem>
<para>
A <type>string</type> or an <type>array</type> of <type>strings</type>
of the preset dictionary (default: no preset dictionary).
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1><!-- }}} -->
<refsect1 role="returnvalues"><!-- {{{ -->
&reftitle.returnvalues;
<para>
Returns a deflate context resource (<literal>zlib.deflate</literal>) on
success, &return.falseforfailure;.
</para>
</refsect1><!-- }}} -->
<refsect1 role="errors"><!-- {{{ -->
&reftitle.errors;
<para>
If an invalid option is passed to <parameter>options</parameter> or the
context couldn't be created, an error of level <constant>E_WARNING</constant>
is generated.
</para>
</refsect1><!-- }}} -->
<refsect1 role="changelog">
&reftitle.changelog;
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
<row>
<entry>8.0.0</entry>
<entry>
On success, this function returns a <classname>DeflateContext</classname> instance now;
previously, a <type>resource</type> was returned.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 role="seealso"><!-- {{{ -->
&reftitle.seealso;
<simplelist>
<member><function>deflate_add</function></member>
<member><function>inflate_init</function></member>
</simplelist>
</refsect1><!-- }}} -->
</refentry>
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