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<title>Attach a filter to a stream</title>
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<h1 class="refname">stream_filter_prepend</h1>
<p class="verinfo">(PHP 4 >= 4.3.0, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">stream_filter_prepend</span> — <span class="dc-title">Attach a filter to a stream</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.stream-filter-prepend-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">resource</span> <span class="methodname"><strong>stream_filter_prepend</strong></span>
( <span class="methodparam"><span class="type">resource</span> <code class="parameter">$stream</code></span>
, <span class="methodparam"><span class="type">string</span> <code class="parameter">$filtername</code></span>
[, <span class="methodparam"><span class="type">int</span> <code class="parameter">$read_write</code></span>
[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$params</code></span>
]] )</div>
<p class="para rdfs-comment">
Adds <code class="parameter">filtername</code> to the list of filters
attached to <code class="parameter">stream</code>.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.stream-filter-prepend-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<code class="parameter">stream</code></dt>
<dd>
<p class="para">
The target stream.
</p>
</dd>
<dt>
<code class="parameter">filtername</code></dt>
<dd>
<p class="para">
The filter name.
</p>
</dd>
<dt>
<code class="parameter">read_write</code></dt>
<dd>
<p class="para">
By default, <span class="function"><strong>stream_filter_prepend()</strong></span> will
attach the filter to the <em>read filter chain</em>
if the file was opened for reading (i.e. File Mode:
<em>r</em>, and/or <em>+</em>). The filter
will also be attached to the <em>write filter chain</em>
if the file was opened for writing (i.e. File Mode:
<em>w</em>, <em>a</em>, and/or <em>+</em>).
<strong><code>STREAM_FILTER_READ</code></strong>,
<strong><code>STREAM_FILTER_WRITE</code></strong>, and/or
<strong><code>STREAM_FILTER_ALL</code></strong> can also be passed to the
<code class="parameter">read_write</code> parameter to override this behavior.
See <span class="function"><a href="function.stream-filter-append.html" class="function">stream_filter_append()</a></span> for an example of
using this parameter.
</p>
</dd>
<dt>
<code class="parameter">params</code></dt>
<dd>
<p class="para">
This filter will be added with the specified <code class="parameter">params</code>
to the <em class="emphasis">beginning</em> of the list and will therefore be
called first during stream operations. To add a filter to the end of the
list, use <span class="function"><a href="function.stream-filter-append.html" class="function">stream_filter_append()</a></span>.
</p>
</dd>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.stream-filter-prepend-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns a resource on success or <strong><code>FALSE</code></strong> on failure. The resource can be
used to refer to this filter instance during a call to
<span class="function"><a href="function.stream-filter-remove.html" class="function">stream_filter_remove()</a></span>.
</p>
<p class="para">
<strong><code>FALSE</code></strong> is returned if <code class="parameter">stream</code> is not a resource or
if <code class="parameter">filtername</code> cannot be located.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.stream-filter-prepend-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>5.1.0</td>
<td>
Prior to PHP 5.1.0, this function returns <strong><code>TRUE</code></strong> on success
or <strong><code>FALSE</code></strong> on failure.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 notes" id="refsect1-function.stream-filter-prepend-notes">
<h3 class="title">Notes</h3>
<blockquote class="note"><p><strong class="note">Note</strong>:
<strong>When using custom (user) filters</strong><br />
<span class="simpara">
<span class="function"><a href="function.stream-filter-register.html" class="function">stream_filter_register()</a></span> must be called first
in order to register the desired user filter to <code class="parameter">filtername</code>.
</span>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="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
<em class="emphasis">not</em> be reprocessed through the new filter
at that time. This differs from the behavior of
<span class="function"><a href="function.stream-filter-append.html" class="function">stream_filter_append()</a></span>.
</span>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
When a filter is added for read and write, two instances of the filter
are created. <span class="function"><strong>stream_filter_prepend()</strong></span> must be called twice
with <strong><code>STREAM_FILTER_READ</code></strong> and
<strong><code>STREAM_FILTER_WRITE</code></strong> to get both filter resources.
</span>
</p></blockquote>
</div>
<div class="refsect1 seealso" id="refsect1-function.stream-filter-prepend-seealso">
<h3 class="title">See Also</h3>
<ul class="simplelist">
<li class="member"><span class="function"><a href="function.stream-filter-register.html" class="function" rel="rdfs-seeAlso">stream_filter_register()</a> - Register a user defined stream filter</span></li>
<li class="member"><span class="function"><a href="function.stream-filter-append.html" class="function" rel="rdfs-seeAlso">stream_filter_append()</a> - Attach a filter to a stream</span></li>
</ul>
</div>
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