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| <title>mod_expires - Apache HTTP Server</title> |
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| <div id="preamble"><h1>Apache Module mod_expires</h1> |
| <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Generation of <code>Expires</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 Identifier:</a></th><td>expires_module</td></tr> |
| <tr><th><a href="module-dict.html#SourceFile">Source File:</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 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>The <code>Expires</code> HTTP header is 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> |
| </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 Expires |
| 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> header 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>, no <code>Expires</code> header |
| will 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 header 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> 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 Expires 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 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.</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> |
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