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<div id="preamble"><h1>Apache Module mod_expires</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_expires.html" title="English"> en </a> |
<a href="../ja/mod/mod_expires.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
<a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Generation of <code>Expires</code> and
<code>Cache-Control</code> HTTP headers according to user-specified
criteria</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module營dentifier:</a></th><td>expires_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source燜ile:</a></th><td>mod_expires.c</td></tr></table>
<h3>Summary</h3>
<p>This module controls the setting of the <code>Expires</code>
HTTP header and the <code>max-age</code> directive of the
<code>Cache-Control</code> HTTP header in server responses. The
expiration date can set to be relative to either the time the
source file was last modified, or to the time of the client
access.</p>
<p>These HTTP headers are an instruction to the client about the
document's validity and persistence. If cached, the document may
be fetched from the cache rather than from the source until this
time has passed. After that, the cache copy is considered
"expired" and invalid, and a new copy must be obtained from the
source.</p>
<p>To modify <code>Cache-Control</code> directives other than
<code>max-age</code> (see <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">RFC
2616 section 14.9</a>), you can use the <code class="directive"><a href="../mod/mod_headers.html#header">Header</a></code> directive.</p>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#expiresactive">ExpiresActive</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#expiresbytype">ExpiresByType</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#expiresdefault">ExpiresDefault</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#AltSyn">Alternate Interval Syntax</a></li>
</ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="AltSyn" id="AltSyn">Alternate Interval Syntax</a></h2>
<p>The <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code> and
<code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directives
can also be defined in a more readable syntax of the form:</p>
<div class="example"><p><code>
ExpiresDefault "<base> [plus] {<num>
<type>}*"<br />
ExpiresByType type/encoding "<base> [plus]
{<num> <type>}*"
</code></p></div>
<p>where <base> is one of:</p>
<ul>
<li><code>access</code></li>
<li><code>now</code> (equivalent to
'<code>access</code>')</li>
<li><code>modification</code></li>
</ul>
<p>The <code>plus</code> keyword is optional. <num>
should be an integer value [acceptable to <code>atoi()</code>],
and <type> is one of:</p>
<ul>
<li><code>years</code></li>
<li><code>months</code></li>
<li><code>weeks</code></li>
<li><code>days</code></li>
<li><code>hours</code></li>
<li><code>minutes</code></li>
<li><code>seconds</code></li>
</ul>
<p>For example, any of the following directives can be used to
make documents expire 1 month after being accessed, by
default:</p>
<div class="example"><p><code>
ExpiresDefault "access plus 1 month"<br />
ExpiresDefault "access plus 4 weeks"<br />
ExpiresDefault "access plus 30 days"
</code></p></div>
<p>The expiry time can be fine-tuned by adding several
'<num> <type>' clauses:</p>
<div class="example"><p><code>
ExpiresByType text/html "access plus 1 month 15
days 2 hours"<br />
ExpiresByType image/gif "modification plus 5 hours 3
minutes"
</code></p></div>
<p>Note that if you use a modification date based setting, the
Expires header will <strong>not</strong> be added to content
that does not come from a file on disk. This is due to the fact
that there is no modification time for such content.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ExpiresActive" id="ExpiresActive">ExpiresActive</a> <a name="expiresactive" id="expiresactive">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enables generation of <code>Expires</code>
headers</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresActive On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
</table>
<p>This directive enables or disables the generation of the
<code>Expires</code> and <code>Cache-Control</code> headers for
the document realm in question. (That is, if found in an
<code>.htaccess</code> file, for instance, it applies only to
documents generated from that directory.) If set to
<code>Off</code>, the headers will not be generated for any
document in the realm (unless overridden at a lower level, such as
an <code>.htaccess</code> file overriding a server config
file). If set to <code>On</code>, the headers will be added to
served documents according to the criteria defined by the
<code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> and
<code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
directives (<em>q.v.</em>).</p>
<p>Note that this directive does not guarantee that an
<code>Expires</code> or <code>Cache-Control</code> header will be
generated. If the criteria aren't met, no header will be sent, and
the effect will be as though this directive wasn't even
specified.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ExpiresByType" id="ExpiresByType">ExpiresByType</a> <a name="expiresbytype" id="expiresbytype">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Value of the <code>Expires</code> header configured
by MIME type</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresByType <var>MIME-type</var>
<var><code>seconds</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
</table>
<p>This directive defines the value of the <code>Expires</code>
header and the <code>max-age</code> directive of the
<code>Cache-Control</code> header generated for documents of the
specified type (<em>e.g.</em>, <code>text/html</code>). The second
argument sets the number of seconds that will be added to a base
time to construct the expiration date. The <code>Cache-Control:
max-age</code> is calculated by subtracting the request time from
the expiration date and expressing the result in seconds.</p>
<p>The base time is either the last modification time of the
file, or the time of the client's access to the document. Which
should be used is specified by the
<code><var><code></var></code> field; <code>M</code>
means that the file's last modification time should be used as
the base time, and <code>A</code> means the client's access
time should be used.</p>
<p>The difference in effect is subtle. If <code>M</code> is used,
all current copies of the document in all caches will expire at
the same time, which can be good for something like a weekly
notice that's always found at the same URL. If <code>A</code> is
used, the date of expiration is different for each client; this
can be good for image files that don't change very often,
particularly for a set of related documents that all refer to
the same images (<em>i.e.</em>, the images will be accessed
repeatedly within a relatively short timespan).</p>
<div class="example"><h3>Example:</h3><p><code>
# enable expirations<br />
ExpiresActive On<br />
# expire GIF images after a month in the client's cache<br />
ExpiresByType image/gif A2592000<br />
# HTML documents are good for a week from the<br />
# time they were changed<br />
ExpiresByType text/html M604800
</code></p></div>
<p>Note that this directive only has effect if
<code>ExpiresActive On</code> has been specified. It overrides,
for the specified MIME type <em>only</em>, any expiration date
set by the <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
directive.</p>
<p>You can also specify the expiration time calculation using
an <a href="#AltSyn">alternate syntax</a>, described earlier in
this document.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ExpiresDefault" id="ExpiresDefault">ExpiresDefault</a> <a name="expiresdefault" id="expiresdefault">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Default algorithm for calculating expiration time</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresDefault <var><code>seconds</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
</table>
<p>This directive sets the default algorithm for calculating the
expiration time for all documents in the affected realm. It can be
overridden on a type-by-type basis by the <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directive. See the
description of that directive for details about the syntax of the
argument, and the <a href="#AltSyn">alternate syntax</a>
description as well.</p>
</div>
</div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/mod/mod_expires.html" title="English"> en </a> |
<a href="../ja/mod/mod_expires.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
<a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
</div><div id="footer">
<p class="apache">Copyright 2006 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
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