mod_negotiation.html revision bb6a7fc0427d0d197c50de34b94a0d23e5732696
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Apache module mod_negotiation</title>
</head>
<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
<body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
vlink="#000080" alink="#FF0000">
<!--#include virtual="header.html" -->
<h1 align="CENTER">Module mod_negotiation</h1>
<p>This module provides for <a
rel="Help"><strong>Status:</strong></a> Base<br />
<a href="module-dict.html#SourceFile"
rel="Help"><strong>Source File:</strong></a>
mod_negotiation.c<br />
<a href="module-dict.html#ModuleIdentifier"
rel="Help"><strong>Module Identifier:</strong></a>
negotiation_module</p>
<h2>Summary</h2>
Content negotiation, or more accurately content selection, is
the selection of the document that best matches the clients
capabilities, from one of several available documents. There
are two implementations of this.
<ul>
<li>A type map (a file with the handler
<code>type-map</code>) which explicitly lists the files
containing the variants.</li>
<li>A MultiViews search (enabled by the MultiViews <a
href="core.html#options">Option</a>, where the server does an
implicit filename pattern match, and choose from amongst the
results.</li>
</ul>
<h2>Directives</h2>
<ul>
<li><a href="#cachenegotiateddocs">CacheNegotiatedDocs</a></li>
<li><a href="#forcelanguagepriority">ForceLanguagePriority</a></li>
<li><a href="#languagepriority">LanguagePriority</a></li>
</ul>
<strong>See also</strong>: <a
href="core.html#options">Options</a>.
<h2>Type maps</h2>
A type map has the same format as RFC822 mail headers. It
contains document descriptions separated by blank lines, with
lines beginning with a hash character ('#') treated as
comments. A document description consists of several header
records; records may be continued on multiple lines if the
continuation lines start with spaces. The leading space will be
deleted and the lines concatenated. A header record consists of
a keyword name, which always ends in a colon, followed by a
value. Whitespace is allowed between the header name and value,
and between the tokens of value. The headers allowed are:
<dl>
<dt>Content-Encoding:</dt>
<dd>The encoding of the file. Apache only recognizes
encodings that are defined by an <a
href="mod_mime.html#addencoding">AddEncoding</a> directive.
This normally includes the encodings <code>x-compress</code>
for compress'd files, and <code>x-gzip</code> for gzip'd
files. The <code>x-</code> prefix is ignored for encoding
comparisons.</dd>
<dt>Content-Language:</dt>
<dd>The language of the variant, as an Internet standard
language tag (RFC 1766). An example is <code>en</code>,
meaning English.</dd>
<dt>Content-Length:</dt>
<dd>The length of the file, in bytes. If this header is not
present, then the actual length of the file is used.</dd>
<dt>Content-Type:</dt>
<dd>
The MIME media type of the document, with optional
parameters. Parameters are separated from the media type
and from one another by a semi-colon, with a syntax of
<code>name=value</code>. Common parameters include:
<dl>
<dt>level</dt>
<dd>an integer specifying the version of the media type.
0.</dd>
<dt>qs</dt>
<dd>a floating-point number with a value in the range 0.0
to 1.0, indicating 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 ascii art, then an ascii
file would have a higher source quality than a jpeg file.
All qs values are therefore specific to a given
resource.</dd>
</dl>
Example:
<blockquote>
</blockquote>
</dd>
<dt>URI:</dt>
<dd>The path to the file containing this variant, relative to
the map file.</dd>
</dl>
<h2>MultiViews</h2>
A MultiViews search is enabled by the MultiViews <a
href="core.html#options">Option</a>. If the server receives a
server reads the directory looking for all files named
<code>foo.*</code>, 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, and returns that document.
<hr />
<h2><a id="cachenegotiateddocs"
name="cachenegotiateddocs">CacheNegotiatedDocs</a>
directive</h2>
<a href="directive-dict.html#Syntax"
rel="Help"><strong>Syntax:</strong></a> CacheNegotiatedDocs
on|off<br />
<a href="directive-dict.html#Default"
rel="Help"><strong>Default:</strong></a>
<code>CacheNegotiatedDocs off</code><br />
<a href="directive-dict.html#Context"
rel="Help"><strong>Context:</strong></a> server config<br />
<a href="directive-dict.html#Status"
rel="Help"><strong>Status:</strong></a> Base<br />
<a href="directive-dict.html#Module"
rel="Help"><strong>Module:</strong></a> mod_negotiation<br />
<a href="directive-dict.html#Compatibility"
rel="Help"><strong>Compatibility:</strong></a>
CacheNegotiatedDocs is only available in Apache 1.1 and later.
The syntax changed in version 2.0.
<p>If set, this directive allows content-negotiated documents
to be cached by proxy servers. This could mean that clients
behind those proxys could retrieve versions of the documents
that are not the best match for their abilities, but it will
make caching more efficient.</p>
<p>This directive only applies to requests which come from
the caching of negotiated documents, and this directive has no
<p>Prior to version 2.0, CacheNegotiatedDocs did not take an
argument; it was turned on by the presence of the directive by
itself.</p>
<hr />
<h2><a id="forcelanguagepriority"
name="forcelanguagepriority">ForceLanguagePriority</a> directive</h2>
<!--%plaintext <?INDEX {\tt ForceLanguagePriority} directive> -->
<a href="directive-dict.html#Syntax"
rel="Help"><strong>Syntax:</strong></a> ForceLanguagePriority
<em>None</em> | [<em>Prefer</em>] [<em>Fallback</em>]</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> FileInfo<br />
<a href="directive-dict.html#Status"
rel="Help"><strong>Status:</strong></a> Base<br />
<a href="directive-dict.html#Module"
rel="Help"><strong>Module:</strong></a> mod_negotiation
<p>The <em>ForceLanguagePriority</em> directive uses the given
<em>LanguagePriority</em> to satisfy two common negotation results.</p>
<p><em>ForceLanguagePriority Prefer</em> uses <em>LanguagePriority</em>
to serve a one valid result, rather than returning an HTTP result 300,
MULTIPLE CHOICES, when there are several equally valid choices.
If the directives below were given, and the user's Accept-Language
header assigned en and de each as quality .500 (equally acceptable)
then then first matching variant, en, will be served;</p>
<blockquote>
<code>LanguagePriority en fr de</code>
<code>ForceLanguagePriority Prefer</code>
</blockquote>
<p><em>ForceLanguagePriority Fallback</em> uses <em>LanguagePriority</em>
to serve a valid result, rather than returning an HTTP result 406,
NOT ACCEPTABLE. If the directives below were given, and the user's
Accept-Language only permitted an es langauge response, but such a
variant isn't found, then the first variant from the LanguagePriority
list below will be served;</p>
<blockquote>
<code>LanguagePriority en fr de</code>
<code>ForceLanguagePriority Fallback</code>
</blockquote>
<p>Both options, Prefer and Fallback, may be specified, so either the
first matching variant from LanguagePriority will be served if more
that one variant is acceptable, or first available document will be
served if none of the variants matched the client's acceptable list of
languages.</p>
<hr />
<h2><a id="languagepriority"
name="languagepriority">LanguagePriority</a> directive</h2>
<!--%plaintext <?INDEX {\tt LanguagePriority} directive> -->
<a href="directive-dict.html#Syntax"
rel="Help"><strong>Syntax:</strong></a> LanguagePriority
<em>MIME-lang</em> [<em>MIME-lang</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> FileInfo<br />
<a href="directive-dict.html#Status"
rel="Help"><strong>Status:</strong></a> Base<br />
<a href="directive-dict.html#Module"
rel="Help"><strong>Module:</strong></a> mod_negotiation
<p>The LanguagePriority sets the precedence of language
variants for the case where the client does not express a
preference, when handling a MultiViews request. The list of
<em>MIME-lang</em> are in order of decreasing preference.
Example:</p>
<blockquote>
<code>LanguagePriority en fr de</code>
</blockquote>
existed, but the browser did not express a language preference,
<p>Note that this directive only has an effect if a 'best'
language cannot be determined by any other means. Correctly
effect.</p>
<p><strong>See also</strong>: <a
href="/mod_mime.html#defaultlanguage">DefaultLanguage</a> and
<!--#include virtual="footer.html" -->
</p>
</body>
</html>