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| <h1 align="CENTER">Module mod_expires</h1> |
| |
| <p>This module provides for the generation of |
| <code>Expires</code> HTTP headers according to user-specified |
| criteria.</p> |
| |
| <p><a href="module-dict.html#Status" |
| rel="Help"><strong>Status:</strong></a> Extension<br /> |
| <a href="module-dict.html#SourceFile" |
| rel="Help"><strong>Source File:</strong></a> |
| mod_expires.c<br /> |
| <a href="module-dict.html#ModuleIdentifier" |
| rel="Help"><strong>Module Identifier:</strong></a> |
| expires_module<br /> |
| <a href="module-dict.html#Compatibility" |
| rel="Help"><strong>Compatibility:</strong></a> Available in |
| Apache 1.2 and later.</p> |
| |
| <h2>Summary</h2> |
| |
| <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> |
| |
| <h2>Directives</h2> |
| |
| <ul> |
| <li><a href="#expiresactive">ExpiresActive</a></li> |
| |
| <li><a href="#expiresbytype">ExpiresByType</a></li> |
| |
| <li><a href="#expiresdefault">ExpiresDefault</a></li> |
| </ul> |
| |
| <h2><a id="AltSyn" name="AltSyn">Alternate Interval |
| Syntax</a></h2> |
| |
| <p>The <a |
| href="#expiresdefault"><samp>ExpiresDefault</samp></a> and <a |
| href="#expiresbytype"><samp>ExpiresByType</samp></a> directives |
| can also be defined in a more readable syntax of the form:</p> |
| |
| <dl> |
| <dd><code>ExpiresDefault "<base> [plus] {<num> |
| <type>}*"<br /> |
| ExpiresByType type/encoding "<base> [plus] |
| {<num> <type>}*"</code></dd> |
| </dl> |
| |
| <p>where <base> is one of:</p> |
| |
| <ul> |
| <li><samp>access</samp></li> |
| |
| <li><samp>now</samp> (equivalent to |
| '<samp>access</samp>')</li> |
| |
| <li><samp>modification</samp></li> |
| </ul> |
| |
| <p>The '<samp>plus</samp>' keyword is optional. <num> |
| should be an integer value [acceptable to <samp>atoi()</samp>], |
| and <type> is one of:</p> |
| |
| <ul> |
| <li><samp>years</samp></li> |
| |
| <li><samp>months</samp></li> |
| |
| <li><samp>weeks</samp></li> |
| |
| <li><samp>days</samp></li> |
| |
| <li><samp>hours</samp></li> |
| |
| <li><samp>minutes</samp></li> |
| |
| <li><samp>seconds</samp></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> |
| |
| <dl> |
| <dd><code>ExpiresDefault "access plus 1 month"<br /> |
| ExpiresDefault "access plus 4 weeks"<br /> |
| ExpiresDefault "access plus 30 days"</code></dd> |
| </dl> |
| |
| <p>The expiry time can be fine-tuned by adding several |
| '<num> <type>' clauses:</p> |
| |
| <dl> |
| <dd><code>ExpiresByType text/html "access plus 1 month 15 |
| days 2 hours"<br /> |
| ExpiresByType image/gif "modification plus 5 hours 3 |
| minutes"</code></dd> |
| </dl> |
| |
| <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> |
| <hr /> |
| |
| <h2><a id="expiresactive" name="expiresactive">ExpiresActive |
| directive</a></h2> |
| |
| <p><a href="directive-dict.html#Syntax" |
| rel="Help"><strong>Syntax:</strong></a> ExpiresActive |
| on|off<br /> |
| <a href="directive-dict.html#Context" |
| rel="Help"><strong>Context:</strong></a> server config, virtual |
| host, directory, .htaccess<br /> |
| <a href="directive-dict.html#Override" |
| rel="Help"><strong>Override:</strong></a> Indexes<br /> |
| <a href="directive-dict.html#Status" |
| rel="Help"><strong>Status:</strong></a> Extension<br /> |
| <a href="directive-dict.html#Module" |
| rel="Help"><strong>Module:</strong></a> mod_expires</p> |
| |
| <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 <em><code>Off</code></em>, 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 <em><code>On</code></em>, the header will be added to |
| served documents according to the criteria defined by the <a |
| href="#expiresbytype">ExpiresByType</a> and <a |
| href="#expiresdefault">ExpiresDefault</a> 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> |
| <hr /> |
| |
| <h2><a id="expiresbytype" name="expiresbytype">ExpiresByType |
| directive</a></h2> |
| |
| <p><a href="directive-dict.html#Syntax" |
| rel="Help"><strong>Syntax:</strong></a> ExpiresByType |
| <em>mime-type <code>seconds</em><br /> |
| <a href="directive-dict.html#Context" |
| rel="Help"><strong>Context:</strong></a> server config, virtual |
| host, directory, .htaccess<br /> |
| <a href="directive-dict.html#Override" |
| rel="Help"><strong>Override:</strong></a> Indexes<br /> |
| <a href="directive-dict.html#Status" |
| rel="Help"><strong>Status:</strong></a> Extension<br /> |
| <a href="directive-dict.html#Module" |
| rel="Help"><strong>Module:</strong></a> mod_expires</p> |
| |
| <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><em><code></em></code> field; <strong>M</strong> |
| means that the file's last modification time should be used as |
| the base time, and <strong>A</strong> means the client's access |
| time should be used.</p> |
| |
| <p>The difference in effect is subtle. If <em>M</em> 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 <em>A</em> 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> |
| |
| <p><strong>Example:</strong></p> |
| <pre> |
| ExpiresActive On # enable expirations |
| ExpiresByType image/gif A2592000 # expire GIF images after a month |
| # in the client's cache |
| ExpiresByType text/html M604800 # HTML documents are good for a |
| # week from the time they were |
| # changed, period |
| |
| </pre> |
| |
| <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 <a href="#expiresdefault">ExpiresDefault</a> |
| directive.</p> |
| |
| <p>You can also specify the expiration time calculation using |
| an <a href="#AltSyn">alternate syntax</a>, described later in |
| this document.</p> |
| <hr /> |
| |
| <h2><a id="expiresdefault" name="expiresdefault">ExpiresDefault |
| directive</a></h2> |
| |
| <p><a href="directive-dict.html#Syntax" |
| rel="Help"><strong>Syntax:</strong></a> ExpiresDefault |
| <em><code>seconds</em><br /> |
| <a href="directive-dict.html#Context" |
| rel="Help"><strong>Context:</strong></a> server config, virtual |
| host, directory, .htaccess<br /> |
| <a href="directive-dict.html#Override" |
| rel="Help"><strong>Override:</strong></a> Indexes<br /> |
| <a href="directive-dict.html#Status" |
| rel="Help"><strong>Status:</strong></a> Extension<br /> |
| <a href="directive-dict.html#Module" |
| rel="Help"><strong>Module:</strong></a> mod_expires</p> |
| |
| <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 <a |
| href="#expiresbytype">ExpiresByType</a> 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> |
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