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<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_*</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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