<!--#include virtual="header.html" -->
<h1 ALIGN="CENTER">Content Negotiation</h1>
+<p>
Apache's support for content negotiation has been updated to meet the
HTTP/1.1 specification. It can choose the best representation of a
resource based on the browser-supplied preferences for media type,
<h2>About Content Negotiation</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
Accept-Language: fr
</pre>
+<p>
Note that this preference will only be applied when there is a choice
of representations and they vary by language.
<p>
<h2>Negotiation in Apache</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:
<h3>Using a type-map file</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
<h3>Multiviews</h3>
+<p>
This is a per-directory option, meaning it can be set with an
<code>Options</code> directive within a <code><Directory></code>,
<code><Location></code> or <code><Files></code>
<h3>Apache Negotiation Algorithm</h3>
+<p>
Apache uses an algorithm to select the 'best' variant (if any) to
return to the browser. This algorithm is not configurable. It operates
like this:
-<p>
<ol>
<li>
dimensions of variance.
</ol>
+
<h2><a name="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 algorithm above. This is to
get a better result from the algorithm for browsers which do not send
<h3>Media Types and Wildcards</h3>
+<p>
The Accept: 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:
<h3>Variants with no Language</h3>
+<p>
If some of the variants for a particular resource have a language
attribute, and some do not, those variants with no language
are given a very low language quality factor of 0.001.<p>
<li>foo.html, no language
</ul>
+<p>
The meaning of a variant with no language is that it is
always acceptable to the browser. If the request Accept-Language
header includes either en or fr (or both) one of foo.en.html
or foo.fr.html will be returned. If the browser does not list
either en or fr as acceptable, foo.html will be returned instead.
+<h2>Note on hyperlinks and naming conventions</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 <a href="mod/mod_mime.html">mod_mime</a> documentation for details).
+<p>
+A typical file has a mime-type extension (e.g. <samp>html</samp>),
+maybe an encoding extension (e.g. <samp>gz</samp> and of course a
+language extension (e.g. <samp>en</samp>) when we have different
+language variants of this file.
+
+<p>
+Examples:
+<ul>
+<li>foo.en.html
+<li>foo.html.en
+<li>foo.en.html.gz
+</ul>
+
+<p>
+Here some more examples of filenames together with valid and invalid hyperlinks:
+</p>
+
+<table border=1 cellpadding=8 cellspacing=0>
+<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 an hyperlink (e.g. <samp>foo</samp>).
+The advantage is that you can hide the actual type of a
+document rsp. file and can change it later, e.g. from <samp>html</samp>
+to <samp>shtml</samp> or <samp>cgi</samp> without changing any
+hyperlink references.
+
+<p>
+If you want to continue to use a mime-type in your hyperlinks (e.g.
+<samp>foo.html</samp>) the language extension (including an encoding extension
+if there is one) must be on the right hand side of the mime-type extension
+(e.g. <samp>foo.html.en</samp>).
+
+
<h2>Note on Caching</h2>
+<p>
When a cache stores a document, it associates it with the request URL.
The next time that URL is requested, the cache can use the stored
document, provided it is still within date. But if the resource is
<!--#include virtual="header.html" -->
<h1 ALIGN="CENTER">Content Negotiation</h1>
+<p>
Apache's support for content negotiation has been updated to meet the
HTTP/1.1 specification. It can choose the best representation of a
resource based on the browser-supplied preferences for media type,
<h2>About Content Negotiation</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
Accept-Language: fr
</pre>
+<p>
Note that this preference will only be applied when there is a choice
of representations and they vary by language.
<p>
<h2>Negotiation in Apache</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:
<h3>Using a type-map file</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
<h3>Multiviews</h3>
+<p>
This is a per-directory option, meaning it can be set with an
<code>Options</code> directive within a <code><Directory></code>,
<code><Location></code> or <code><Files></code>
<h3>Apache Negotiation Algorithm</h3>
+<p>
Apache uses an algorithm to select the 'best' variant (if any) to
return to the browser. This algorithm is not configurable. It operates
like this:
-<p>
<ol>
<li>
dimensions of variance.
</ol>
+
<h2><a name="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 algorithm above. This is to
get a better result from the algorithm for browsers which do not send
<h3>Media Types and Wildcards</h3>
+<p>
The Accept: 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:
<h3>Variants with no Language</h3>
+<p>
If some of the variants for a particular resource have a language
attribute, and some do not, those variants with no language
are given a very low language quality factor of 0.001.<p>
<li>foo.html, no language
</ul>
+<p>
The meaning of a variant with no language is that it is
always acceptable to the browser. If the request Accept-Language
header includes either en or fr (or both) one of foo.en.html
or foo.fr.html will be returned. If the browser does not list
either en or fr as acceptable, foo.html will be returned instead.
+<h2>Note on hyperlinks and naming conventions</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 <a href="mod/mod_mime.html">mod_mime</a> documentation for details).
+<p>
+A typical file has a mime-type extension (e.g. <samp>html</samp>),
+maybe an encoding extension (e.g. <samp>gz</samp> and of course a
+language extension (e.g. <samp>en</samp>) when we have different
+language variants of this file.
+
+<p>
+Examples:
+<ul>
+<li>foo.en.html
+<li>foo.html.en
+<li>foo.en.html.gz
+</ul>
+
+<p>
+Here some more examples of filenames together with valid and invalid hyperlinks:
+</p>
+
+<table border=1 cellpadding=8 cellspacing=0>
+<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 an hyperlink (e.g. <samp>foo</samp>).
+The advantage is that you can hide the actual type of a
+document rsp. file and can change it later, e.g. from <samp>html</samp>
+to <samp>shtml</samp> or <samp>cgi</samp> without changing any
+hyperlink references.
+
+<p>
+If you want to continue to use a mime-type in your hyperlinks (e.g.
+<samp>foo.html</samp>) the language extension (including an encoding extension
+if there is one) must be on the right hand side of the mime-type extension
+(e.g. <samp>foo.html.en</samp>).
+
+
<h2>Note on Caching</h2>
+<p>
When a cache stores a document, it associates it with the request URL.
The next time that URL is requested, the cache can use the stored
document, provided it is still within date. But if the resource is
projects / thirdparty / apache / httpd.git / commitdiff
