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| <title>Content Negotiation - Apache HTTP Server</title> |
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| <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> |
| <p class="apache">Apache HTTP Server Version 2.0</p> |
| <img alt="" src="./images/feather.gif" /></div> |
| <div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div> |
| <div id="path"> |
| <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.0</a></div><div id="page-content"><div class="retired"><h4>Please note</h4> |
| <p>This document refers to the <strong>2.0</strong> version of Apache httpd, which <strong>is no longer maintained</strong>. Upgrade, and refer to the current version of httpd instead, documented at:</p> |
| <ul><li><a href="http://httpd.apache.org/docs/current/">Current release version of Apache HTTP Server documentation</a></li></ul><p>You may follow <a href="http://httpd.apache.org/docs/current/content-negotiation.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Content Negotiation</h1> |
| <div class="toplang"> |
| <p><span>Available Languages: </span><a href="./en/content-negotiation.html" title="English"> en </a> | |
| <a href="./fr/content-negotiation.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | |
| <a href="./ja/content-negotiation.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | |
| <a href="./ko/content-negotiation.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | |
| <a href="./tr/content-negotiation.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> |
| </div> |
| |
| |
| <p>Apache supports content negotiation as described in |
| the HTTP/1.1 specification. It can choose the best |
| representation of a resource based on the browser-supplied |
| preferences for media type, languages, character set and |
| encoding. It also implements a couple of features to give |
| more intelligent handling of requests from browsers that send |
| incomplete negotiation information.</p> |
| |
| <p>Content negotiation is provided by the |
| <code class="module"><a href="./mod/mod_negotiation.html">mod_negotiation</a></code> module, which is compiled in |
| by default.</p> |
| </div> |
| <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#about">About Content Negotiation</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#negotiation">Negotiation in Apache</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#methods">The Negotiation Methods</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#better">Fiddling with Quality |
| Values</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#extensions">Extensions to Transparent Content |
| Negotiation</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#naming">Note on hyperlinks and naming conventions</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#caching">Note on Caching</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="about" id="about">About Content Negotiation</a></h2> |
| |
| <p>A resource may be available in several different |
| representations. For example, it might be available in |
| different languages or different media types, or a combination. |
| One way of selecting the most appropriate choice is to give the |
| user an index page, and let them select. However it is often |
| possible for the server to choose automatically. This works |
| because browsers can send, as part of each request, information |
| about what representations they prefer. For example, a browser |
| could indicate that it would like to see information in French, |
| if possible, else English will do. Browsers indicate their |
| preferences by headers in the request. To request only French |
| representations, the browser would send</p> |
| |
| <div class="example"><p><code>Accept-Language: fr</code></p></div> |
| |
| <p>Note that this preference will only be applied when there is |
| a choice of representations and they vary by language.</p> |
| |
| <p>As an example of a more complex request, this browser has |
| been configured to accept French and English, but prefer |
| French, and to accept various media types, preferring HTML over |
| plain text or other text types, and preferring GIF or JPEG over |
| other media types, but also allowing any other media type as a |
| last resort:</p> |
| |
| <div class="example"><p><code> |
| Accept-Language: fr; q=1.0, en; q=0.5<br /> |
| Accept: text/html; q=1.0, text/*; q=0.8, image/gif; q=0.6, image/jpeg; q=0.6, image/*; q=0.5, */*; q=0.1 |
| </code></p></div> |
| |
| <p>Apache supports 'server driven' content negotiation, as |
| defined in the HTTP/1.1 specification. It fully supports the |
| <code>Accept</code>, <code>Accept-Language</code>, |
| <code>Accept-Charset</code> and<code>Accept-Encoding</code> |
| request headers. Apache also supports 'transparent' |
| content negotiation, which is an experimental negotiation |
| protocol defined in RFC 2295 and RFC 2296. It does not offer |
| support for 'feature negotiation' as defined in these RFCs.</p> |
| |
| <p>A <strong>resource</strong> is a conceptual entity |
| identified by a URI (RFC 2396). An HTTP server like Apache |
| provides access to <strong>representations</strong> of the |
| resource(s) within its namespace, with each representation in |
| the form of a sequence of bytes with a defined media type, |
| character set, encoding, etc. Each resource may be associated |
| with zero, one, or more than one representation at any given |
| time. If multiple representations are available, the resource |
| is referred to as <strong>negotiable</strong> and each of its |
| representations is termed a <strong>variant</strong>. The ways |
| in which the variants for a negotiable resource vary are called |
| the <strong>dimensions</strong> of negotiation.</p> |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="negotiation" id="negotiation">Negotiation in Apache</a></h2> |
| |
| <p>In order to negotiate a resource, the server needs to be |
| given information about each of the variants. This is done in |
| one of two ways:</p> |
| |
| <ul> |
| <li>Using a type map (<em>i.e.</em>, a <code>*.var</code> |
| file) which names the files containing the variants |
| explicitly, or</li> |
| |
| <li>Using a 'MultiViews' search, where the server does an |
| implicit filename pattern match and chooses from among the |
| results.</li> |
| </ul> |
| |
| <h3><a name="type-map" id="type-map">Using a type-map file</a></h3> |
| |
| <p>A type map is a document which is associated with the |
| handler named <code>type-map</code> (or, for |
| backwards-compatibility with older Apache configurations, the |
| MIME type <code>application/x-type-map</code>). Note that to |
| use this feature, you must have a handler set in the |
| configuration that defines a file suffix as |
| <code>type-map</code>; this is best done with</p> |
| |
| <div class="example"><p><code>AddHandler type-map .var</code></p></div> |
| |
| <p>in the server configuration file.</p> |
| |
| <p>Type map files should have the same name as the resource |
| which they are describing, and have an entry for each available |
| variant; these entries consist of contiguous HTTP-format header |
| lines. Entries for different variants are separated by blank |
| lines. Blank lines are illegal within an entry. It is |
| conventional to begin a map file with an entry for the combined |
| entity as a whole (although this is not required, and if |
| present will be ignored). An example map file is shown below. |
| This file would be named <code>foo.var</code>, as it describes |
| a resource named <code>foo</code>.</p> |
| |
| <div class="example"><p><code> |
| URI: foo<br /> |
| <br /> |
| URI: foo.en.html<br /> |
| Content-type: text/html<br /> |
| Content-language: en<br /> |
| <br /> |
| URI: foo.fr.de.html<br /> |
| Content-type: text/html;charset=iso-8859-2<br /> |
| Content-language: fr, de<br /> |
| </code></p></div> |
| <p>Note also that a typemap file will take precedence over the |
| filename's extension, even when Multiviews is on. If the |
| variants have different source qualities, that may be indicated |
| by the "qs" parameter to the media type, as in this picture |
| (available as JPEG, GIF, or ASCII-art): </p> |
| |
| <div class="example"><p><code> |
| URI: foo<br /> |
| <br /> |
| URI: foo.jpeg<br /> |
| Content-type: image/jpeg; qs=0.8<br /> |
| <br /> |
| URI: foo.gif<br /> |
| Content-type: image/gif; qs=0.5<br /> |
| <br /> |
| URI: foo.txt<br /> |
| Content-type: text/plain; qs=0.01<br /> |
| </code></p></div> |
| |
| <p>qs values can vary in the range 0.000 to 1.000. Note that |
| any variant with a qs value of 0.000 will never be chosen. |
| Variants with no 'qs' parameter value are given a qs factor of |
| 1.0. The qs parameter indicates the relative 'quality' of this |
| variant compared to the other available variants, independent |
| of the client's capabilities. For example, a JPEG file is |
| usually of higher source quality than an ASCII file if it is |
| attempting to represent a photograph. However, if the resource |
| being represented is an original ASCII art, then an ASCII |
| representation would have a higher source quality than a JPEG |
| representation. A qs value is therefore specific to a given |
| variant depending on the nature of the resource it |
| represents.</p> |
| |
| <p>The full list of headers recognized is available in the <a href="mod/mod_negotiation.html#typemaps">mod_negotation |
| typemap</a> documentation.</p> |
| |
| |
| <h3><a name="multiviews" id="multiviews">Multiviews</a></h3> |
| |
| <p><code>MultiViews</code> is a per-directory option, meaning it |
| can be set with an <code class="directive"><a href="./mod/core.html#options">Options</a></code> |
| directive within a <code class="directive"><a href="./mod/core.html#directory"><Directory></a></code>, <code class="directive"><a href="./mod/core.html#location"><Location></a></code> or <code class="directive"><a href="./mod/core.html#files"><Files></a></code> section in |
| <code>httpd.conf</code>, or (if <code class="directive"><a href="./mod/core.html#allowoverride">AllowOverride</a></code> is properly set) in |
| <code>.htaccess</code> files. Note that <code>Options All</code> |
| does not set <code>MultiViews</code>; you have to ask for it by |
| name.</p> |
| |
| <p>The effect of <code>MultiViews</code> is as follows: if the |
| server receives a request for <code>/some/dir/foo</code>, if |
| <code>/some/dir</code> has <code>MultiViews</code> enabled, and |
| <code>/some/dir/foo</code> does <em>not</em> exist, then the |
| server reads the directory looking for files named foo.*, and |
| effectively fakes up a type map which names all those files, |
| assigning them the same media types and content-encodings it |
| would have if the client had asked for one of them by name. It |
| then chooses the best match to the client's requirements.</p> |
| |
| <p><code>MultiViews</code> may also apply to searches for the file |
| named by the <code class="directive"><a href="./mod/mod_dir.html#directoryindex">DirectoryIndex</a></code> directive, if the |
| server is trying to index a directory. If the configuration files |
| specify</p> |
| <div class="example"><p><code>DirectoryIndex index</code></p></div> |
| <p>then the server will arbitrate between <code>index.html</code> |
| and <code>index.html3</code> if both are present. If neither |
| are present, and <code>index.cgi</code> is there, the server |
| will run it.</p> |
| |
| <p>If one of the files found when reading the directory does not |
| have an extension recognized by <code>mod_mime</code> to designate |
| its Charset, Content-Type, Language, or Encoding, then the result |
| depends on the setting of the <code class="directive"><a href="./mod/mod_mime.html#multiviewsmatch">MultiViewsMatch</a></code> directive. This |
| directive determines whether handlers, filters, and other |
| extension types can participate in MultiViews negotiation.</p> |
| |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="methods" id="methods">The Negotiation Methods</a></h2> |
| |
| <p>After Apache has obtained a list of the variants for a given |
| resource, either from a type-map file or from the filenames in |
| the directory, it invokes one of two methods to decide on the |
| 'best' variant to return, if any. It is not necessary to know |
| any of the details of how negotiation actually takes place in |
| order to use Apache's content negotiation features. However the |
| rest of this document explains the methods used for those |
| interested. </p> |
| |
| <p>There are two negotiation methods:</p> |
| |
| <ol> |
| <li><strong>Server driven negotiation with the Apache |
| algorithm</strong> is used in the normal case. The Apache |
| algorithm is explained in more detail below. When this |
| algorithm is used, Apache can sometimes 'fiddle' the quality |
| factor of a particular dimension to achieve a better result. |
| The ways Apache can fiddle quality factors is explained in |
| more detail below.</li> |
| |
| <li><strong>Transparent content negotiation</strong> is used |
| when the browser specifically requests this through the |
| mechanism defined in RFC 2295. This negotiation method gives |
| the browser full control over deciding on the 'best' variant, |
| the result is therefore dependent on the specific algorithms |
| used by the browser. As part of the transparent negotiation |
| process, the browser can ask Apache to run the 'remote |
| variant selection algorithm' defined in RFC 2296.</li> |
| </ol> |
| |
| <h3><a name="dimensions" id="dimensions">Dimensions of Negotiation</a></h3> |
| |
| <table> |
| |
| <tr valign="top"> |
| <th>Dimension</th> |
| |
| <th>Notes</th> |
| </tr> |
| |
| <tr valign="top"> |
| <td>Media Type</td> |
| |
| <td>Browser indicates preferences with the <code>Accept</code> |
| header field. Each item can have an associated quality factor. |
| Variant description can also have a quality factor (the "qs" |
| parameter).</td> |
| </tr> |
| |
| <tr valign="top"> |
| <td>Language</td> |
| |
| <td>Browser indicates preferences with the |
| <code>Accept-Language</code> header field. Each item can have |
| a quality factor. Variants can be associated with none, one or |
| more than one language.</td> |
| </tr> |
| |
| <tr valign="top"> |
| <td>Encoding</td> |
| |
| <td>Browser indicates preference with the |
| <code>Accept-Encoding</code> header field. Each item can have |
| a quality factor.</td> |
| </tr> |
| |
| <tr valign="top"> |
| <td>Charset</td> |
| |
| <td>Browser indicates preference with the |
| <code>Accept-Charset</code> header field. Each item can have a |
| quality factor. Variants can indicate a charset as a parameter |
| of the media type.</td> |
| </tr> |
| </table> |
| |
| |
| <h3><a name="algorithm" id="algorithm">Apache Negotiation Algorithm</a></h3> |
| |
| <p>Apache can use the following algorithm to select the 'best' |
| variant (if any) to return to the browser. This algorithm is |
| not further configurable. It operates as follows:</p> |
| |
| <ol> |
| <li>First, for each dimension of the negotiation, check the |
| appropriate <em>Accept*</em> header field and assign a |
| quality to each variant. If the <em>Accept*</em> header for |
| any dimension implies that this variant is not acceptable, |
| eliminate it. If no variants remain, go to step 4.</li> |
| |
| <li> |
| Select the 'best' variant by a process of elimination. Each |
| of the following tests is applied in order. Any variants |
| not selected at each test are eliminated. After each test, |
| if only one variant remains, select it as the best match |
| and proceed to step 3. If more than one variant remains, |
| move on to the next test. |
| |
| <ol> |
| <li>Multiply the quality factor from the <code>Accept</code> |
| header with the quality-of-source factor for this variants |
| media type, and select the variants with the highest |
| value.</li> |
| |
| <li>Select the variants with the highest language quality |
| factor.</li> |
| |
| <li>Select the variants with the best language match, |
| using either the order of languages in the |
| <code>Accept-Language</code> header (if present), or else |
| the order of languages in the <code>LanguagePriority</code> |
| directive (if present).</li> |
| |
| <li>Select the variants with the highest 'level' media |
| parameter (used to give the version of text/html media |
| types).</li> |
| |
| <li>Select variants with the best charset media |
| parameters, as given on the <code>Accept-Charset</code> |
| header line. Charset ISO-8859-1 is acceptable unless |
| explicitly excluded. Variants with a <code>text/*</code> |
| media type but not explicitly associated with a particular |
| charset are assumed to be in ISO-8859-1.</li> |
| |
| <li>Select those variants which have associated charset |
| media parameters that are <em>not</em> ISO-8859-1. If |
| there are no such variants, select all variants |
| instead.</li> |
| |
| <li>Select the variants with the best encoding. If there |
| are variants with an encoding that is acceptable to the |
| user-agent, select only these variants. Otherwise if |
| there is a mix of encoded and non-encoded variants, |
| select only the unencoded variants. If either all |
| variants are encoded or all variants are not encoded, |
| select all variants.</li> |
| |
| <li>Select the variants with the smallest content |
| length.</li> |
| |
| <li>Select the first variant of those remaining. This |
| will be either the first listed in the type-map file, or |
| when variants are read from the directory, the one whose |
| file name comes first when sorted using ASCII code |
| order.</li> |
| </ol> |
| </li> |
| |
| <li>The algorithm has now selected one 'best' variant, so |
| return it as the response. The HTTP response header |
| <code>Vary</code> is set to indicate the dimensions of |
| negotiation (browsers and caches can use this information when |
| caching the resource). End.</li> |
| |
| <li>To get here means no variant was selected (because none |
| are acceptable to the browser). Return a 406 status (meaning |
| "No acceptable representation") with a response body |
| consisting of an HTML document listing the available |
| variants. Also set the HTTP <code>Vary</code> header to |
| indicate the dimensions of variance.</li> |
| </ol> |
| |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="better" id="better">Fiddling with Quality |
| Values</a></h2> |
| |
| <p>Apache sometimes changes the quality values from what would |
| be expected by a strict interpretation of the Apache |
| negotiation algorithm above. This is to get a better result |
| from the algorithm for browsers which do not send full or |
| accurate information. Some of the most popular browsers send |
| <code>Accept</code> header information which would otherwise |
| result in the selection of the wrong variant in many cases. If a |
| browser sends full and correct information these fiddles will not |
| be applied.</p> |
| |
| <h3><a name="wildcards" id="wildcards">Media Types and Wildcards</a></h3> |
| |
| <p>The <code>Accept:</code> request header indicates preferences |
| for media types. It can also include 'wildcard' media types, such |
| as "image/*" or "*/*" where the * matches any string. So a request |
| including:</p> |
| |
| <div class="example"><p><code>Accept: image/*, */*</code></p></div> |
| |
| <p>would indicate that any type starting "image/" is acceptable, |
| as is any other type. |
| Some browsers routinely send wildcards in addition to explicit |
| types they can handle. For example:</p> |
| |
| <div class="example"><p><code> |
| Accept: text/html, text/plain, image/gif, image/jpeg, */* |
| </code></p></div> |
| <p>The intention of this is to indicate that the explicitly listed |
| types are preferred, but if a different representation is |
| available, that is ok too. Using explicit quality values, |
| what the browser really wants is something like:</p> |
| <div class="example"><p><code> |
| Accept: text/html, text/plain, image/gif, image/jpeg, */*; q=0.01 |
| </code></p></div> |
| <p>The explicit types have no quality factor, so they default to a |
| preference of 1.0 (the highest). The wildcard */* is given a |
| low preference of 0.01, so other types will only be returned if |
| no variant matches an explicitly listed type.</p> |
| |
| <p>If the <code>Accept:</code> header contains <em>no</em> q |
| factors at all, Apache sets the q value of "*/*", if present, to |
| 0.01 to emulate the desired behavior. It also sets the q value of |
| wildcards of the format "type/*" to 0.02 (so these are preferred |
| over matches against "*/*". If any media type on the |
| <code>Accept:</code> header contains a q factor, these special |
| values are <em>not</em> applied, so requests from browsers which |
| send the explicit information to start with work as expected.</p> |
| |
| |
| <h3><a name="exceptions" id="exceptions">Language Negotiation Exceptions</a></h3> |
| |
| <p>New in Apache 2.0, some exceptions have been added to the |
| negotiation algorithm to allow graceful fallback when language |
| negotiation fails to find a match.</p> |
| |
| <p>When a client requests a page on your server, but the server |
| cannot find a single page that matches the |
| <code>Accept-language</code> sent by |
| the browser, the server will return either a "No Acceptable |
| Variant" or "Multiple Choices" response to the client. To avoid |
| these error messages, it is possible to configure Apache to ignore |
| the <code>Accept-language</code> in these cases and provide a |
| document that does not explicitly match the client's request. The |
| <code class="directive"><a href="./mod/mod_negotiation.html#forcelanguagepriority">ForceLanguagePriority</a></code> |
| directive can be used to override one or both of these error |
| messages and substitute the servers judgement in the form of the |
| <code class="directive"><a href="./mod/mod_negotiation.html#languagepriority">LanguagePriority</a></code> |
| directive.</p> |
| |
| <p>The server will also attempt to match language-subsets when no |
| other match can be found. For example, if a client requests |
| documents with the language <code>en-GB</code> for British |
| English, the server is not normally allowed by the HTTP/1.1 |
| standard to match that against a document that is marked as simply |
| <code>en</code>. (Note that it is almost surely a configuration |
| error to include <code>en-GB</code> and not <code>en</code> in the |
| <code>Accept-Language</code> header, since it is very unlikely |
| that a reader understands British English, but doesn't understand |
| English in general. Unfortunately, many current clients have |
| default configurations that resemble this.) However, if no other |
| language match is possible and the server is about to return a "No |
| Acceptable Variants" error or fallback to the <code class="directive"><a href="./mod/mod_negotiation.html#languagepriority">LanguagePriority</a></code>, the server |
| will ignore the subset specification and match <code>en-GB</code> |
| against <code>en</code> documents. Implicitly, Apache will add |
| the parent language to the client's acceptable language list with |
| a very low quality value. But note that if the client requests |
| "en-GB; q=0.9, fr; q=0.8", and the server has documents |
| designated "en" and "fr", then the "fr" document will be returned. |
| This is necessary to maintain compliance with the HTTP/1.1 |
| specification and to work effectively with properly configured |
| clients.</p> |
| |
| <p>In order to support advanced techniques (such as cookies or |
| special URL-paths) to determine the user's preferred language, |
| since Apache 2.0.47 <code class="module"><a href="./mod/mod_negotiation.html">mod_negotiation</a></code> recognizes |
| the <a href="env.html">environment variable</a> |
| <code>prefer-language</code>. If it exists and contains an |
| appropriate language tag, <code class="module"><a href="./mod/mod_negotiation.html">mod_negotiation</a></code> will |
| try to select a matching variant. If there's no such variant, |
| the normal negotiation process applies.</p> |
| |
| <div class="example"><h3>Example</h3><p><code> |
| SetEnvIf Cookie "language=en" prefer-language=en<br /> |
| SetEnvIf Cookie "language=fr" prefer-language=fr |
| </code></p></div> |
| |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="extensions" id="extensions">Extensions to Transparent Content |
| Negotiation</a></h2> |
| |
| <p>Apache extends the transparent content negotiation protocol (RFC |
| 2295) as follows. A new <code>{encoding ..}</code> element is used in |
| variant lists to label variants which are available with a specific |
| content-encoding only. The implementation of the RVSA/1.0 algorithm |
| (RFC 2296) is extended to recognize encoded variants in the list, and |
| to use them as candidate variants whenever their encodings are |
| acceptable according to the <code>Accept-Encoding</code> request |
| header. The RVSA/1.0 implementation does not round computed quality |
| factors to 5 decimal places before choosing the best variant.</p> |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="naming" id="naming">Note on hyperlinks and naming conventions</a></h2> |
| |
| <p>If you are using language negotiation you can choose between |
| different naming conventions, because files can have more than |
| one extension, and the order of the extensions is normally |
| irrelevant (see the <a href="mod/mod_mime.html#multipleext">mod_mime</a> documentation |
| for details).</p> |
| |
| <p>A typical file has a MIME-type extension (<em>e.g.</em>, |
| <code>html</code>), maybe an encoding extension (<em>e.g.</em>, |
| <code>gz</code>), and of course a language extension |
| (<em>e.g.</em>, <code>en</code>) when we have different |
| language variants of this file.</p> |
| |
| <p>Examples:</p> |
| |
| <ul> |
| <li>foo.en.html</li> |
| |
| <li>foo.html.en</li> |
| |
| <li>foo.en.html.gz</li> |
| </ul> |
| |
| <p>Here some more examples of filenames together with valid and |
| invalid hyperlinks:</p> |
| |
| <table class="bordered"> |
| |
| <tr> |
| <th>Filename</th> |
| |
| <th>Valid hyperlink</th> |
| |
| <th>Invalid hyperlink</th> |
| </tr> |
| |
| <tr> |
| <td><em>foo.html.en</em></td> |
| |
| <td>foo<br /> |
| foo.html</td> |
| |
| <td>-</td> |
| </tr> |
| |
| <tr> |
| <td><em>foo.en.html</em></td> |
| |
| <td>foo</td> |
| |
| <td>foo.html</td> |
| </tr> |
| |
| <tr> |
| <td><em>foo.html.en.gz</em></td> |
| |
| <td>foo<br /> |
| foo.html</td> |
| |
| <td>foo.gz<br /> |
| foo.html.gz</td> |
| </tr> |
| |
| <tr> |
| <td><em>foo.en.html.gz</em></td> |
| |
| <td>foo</td> |
| |
| <td>foo.html<br /> |
| foo.html.gz<br /> |
| foo.gz</td> |
| </tr> |
| |
| <tr> |
| <td><em>foo.gz.html.en</em></td> |
| |
| <td>foo<br /> |
| foo.gz<br /> |
| foo.gz.html</td> |
| |
| <td>foo.html</td> |
| </tr> |
| |
| <tr> |
| <td><em>foo.html.gz.en</em></td> |
| |
| <td>foo<br /> |
| foo.html<br /> |
| foo.html.gz</td> |
| |
| <td>foo.gz</td> |
| </tr> |
| </table> |
| |
| <p>Looking at the table above, you will notice that it is always |
| possible to use the name without any extensions in a hyperlink |
| (<em>e.g.</em>, <code>foo</code>). The advantage is that you |
| can hide the actual type of a document rsp. file and can change |
| it later, <em>e.g.</em>, from <code>html</code> to |
| <code>shtml</code> or <code>cgi</code> without changing any |
| hyperlink references.</p> |
| |
| <p>If you want to continue to use a MIME-type in your |
| hyperlinks (<em>e.g.</em> <code>foo.html</code>) the language |
| extension (including an encoding extension if there is one) |
| must be on the right hand side of the MIME-type extension |
| (<em>e.g.</em>, <code>foo.html.en</code>).</p> |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="caching" id="caching">Note on Caching</a></h2> |
| |
| <p>When a cache stores a representation, it associates it with |
| the request URL. The next time that URL is requested, the cache |
| can use the stored representation. But, if the resource is |
| negotiable at the server, this might result in only the first |
| requested variant being cached and subsequent cache hits might |
| return the wrong response. To prevent this, Apache normally |
| marks all responses that are returned after content negotiation |
| as non-cacheable by HTTP/1.0 clients. Apache also supports the |
| HTTP/1.1 protocol features to allow caching of negotiated |
| responses.</p> |
| |
| <p>For requests which come from a HTTP/1.0 compliant client |
| (either a browser or a cache), the directive <code class="directive"><a href="./mod/mod_negotiation.html#cachenegotiateddocs">CacheNegotiatedDocs</a></code> can be |
| used to allow caching of responses which were subject to |
| negotiation. This directive can be given in the server config or |
| virtual host, and takes no arguments. It has no effect on requests |
| from HTTP/1.1 clients.</p> |
| </div></div> |
| <div class="bottomlang"> |
| <p><span>Available Languages: </span><a href="./en/content-negotiation.html" title="English"> en </a> | |
| <a href="./fr/content-negotiation.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | |
| <a href="./ja/content-negotiation.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | |
| <a href="./ko/content-negotiation.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | |
| <a href="./tr/content-negotiation.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> |
| </div><div id="footer"> |
| <p class="apache">Copyright 2013 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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