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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.13 $ -->
<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>
<title>Description</title>
<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>. 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>
<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>
<para>
As of PHP 5.1.0, this function returns a resource which
can be used to refer to this filter instance during a call
to <function>stream_filter_remove</function>.
Prior to PHP 5.1.0, this function returns &true; on success
or &false; on failure.
</para>
<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>
<simpara>
See also
<function>stream_filter_register</function>, and
<function>stream_filter_append</function>.
</simpara>
</refsect1>
</refentry>
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