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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.stream-filter-prepend" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>stream_filter_prepend</refname>
<refpurpose>Attach a filter to a stream</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>resource</type><methodname>stream_filter_prepend</methodname>
<methodparam><type>resource</type><parameter>stream</parameter></methodparam>
<methodparam><type>string</type><parameter>filtername</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter>read_write</parameter></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>params</parameter></methodparam>
</methodsynopsis>
<para>
Adds <parameter>filtername</parameter> to the list of filters
attached to <parameter>stream</parameter>.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>stream</parameter></term>
<listitem>
<para>
The target stream.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>filtername</parameter></term>
<listitem>
<para>
The filter name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>read_write</parameter></term>
<listitem>
<para>
By default, <function>stream_filter_prepend</function> will
attach the filter to the <literal>read filter chain</literal>
if the file was opened for reading (i.e. File Mode:
<literal>r</literal>, and/or <literal>+</literal>). The filter
will also be attached to the <literal>write filter chain</literal>
if the file was opened for writing (i.e. File Mode:
<literal>w</literal>, <literal>a</literal>, and/or <literal>+</literal>).
<constant>STREAM_FILTER_READ</constant>,
<constant>STREAM_FILTER_WRITE</constant>, and/or
<constant>STREAM_FILTER_ALL</constant> can also be passed to the
<parameter>read_write</parameter> parameter to override this behavior.
See <function>stream_filter_append</function> for an example of
using this parameter.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>params</parameter></term>
<listitem>
<para>
This filter will be added with the specified <parameter>params</parameter>
to the <emphasis>beginning</emphasis> of the list and will therefore be
called first during stream operations. To add a filter to the end of the
list, use <function>stream_filter_append</function>.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
Returns a resource on success or &false; on failure. The resource can be
used to refer to this filter instance during a call to
<function>stream_filter_remove</function>.
</para>
<para>
&false; is returned if <parameter>stream</parameter> is not a resource or
if <parameter>filtername</parameter> cannot be located.
</para>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
<note>
<title>When using custom (user) filters</title>
<simpara>
<function>stream_filter_register</function> must be called first
in order to register the desired user filter to <parameter>filtername</parameter>.
</simpara>
</note>
<note>
<simpara>
Stream data is read from resources (both local and remote) in chunks,
with any unconsumed data kept in internal buffers. When a new
filter is prepended to a stream, data in the internal buffers,
which has already been processed through other filters will
<emphasis>not</emphasis> be reprocessed through the new filter
at that time. This differs from the behavior of
<function>stream_filter_append</function>.
</simpara>
</note>
<note>
<simpara>
When a filter is added for read and write, two instances of the filter
are created. <function>stream_filter_prepend</function> must be called twice
with <constant>STREAM_FILTER_READ</constant> and
<constant>STREAM_FILTER_WRITE</constant> to get both filter resources.
</simpara>
</note>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<simplelist>
<member><function>stream_filter_register</function></member>
<member><function>stream_filter_append</function></member>
</simplelist>
</refsect1>
</refentry>
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