Source of: /manual/en/filters.php
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<div>
<h1>List of Available Filters</h1>
<h2>Table of Contents</h2><ul class="chunklist chunklist_appendix"><li><a href="filters.string.php">String Filters</a></li><li><a href="filters.convert.php">Conversion Filters</a></li><li><a href="filters.compression.php">Compression Filters</a></li><li><a href="filters.encryption.php">Encryption Filters</a></li></ul>
<p class="para">
The following is a list of a few built-in stream filters for
use with <a href="function.stream-filter-append.php" class="function">stream_filter_append()</a>.
Your version of PHP may have more filters (or fewer) than those
listed here.
</p>
<p class="para">
It is worth noting a slight asymmetry between
<a href="function.stream-filter-append.php" class="function">stream_filter_append()</a>
and <a href="function.stream-filter-prepend.php" class="function">stream_filter_prepend()</a>.
Every PHP stream contains a small <em class="emphasis">read buffer</em>
where it stores blocks of data retrieved from the
filesystem or other resource in order to process data
in the most efficient manner. As soon as data is pulled
from the resource into the stream's internal buffer, it
is immediately processed through any attached filters whether
the PHP application is actually ready for the data or not.
If data is sitting in the read buffer when a filter is
<em class="emphasis">appended</em>, this data will be immediately
processed through that filter making the fact that it was
sitting in the buffer seem transparent. However, if data is
sitting in the read buffer when a filter is
<em class="emphasis">prepended</em>, this data will <em class="emphasis">NOT</em>
be processed through that filter. It will instead wait until
the next block of data is retrieved from the resource.
</p>
<p class="para">
For a list of filters installed in your version of
PHP use <a href="function.stream-get-filters.php" class="function">stream_get_filters()</a>.
</p>
</div>
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