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<div id="preamble"><h1>Apache Module mod_negotiation</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_negotiation.html" title="English">&nbsp;en&nbsp;</a> |
<a href="../fr/mod/mod_negotiation.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
<a href="../ja/mod/mod_negotiation.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Provides for <a href="../content-negotiation.html">content negotiation</a></td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>negotiation_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_negotiation.c</td></tr></table>
<h3>Summary</h3>
<p>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.</p>
<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 <code>Multiviews</code>
<code class="directive"><a href="../mod/core.html#options">Options</a></code>), where the server does
an implicit filename pattern match, and choose from amongst the
results.</li>
</ul>
</div>
<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#typemaps">Type maps</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#multiviews">Multiviews</a></li>
</ul><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#cachenegotiateddocs">CacheNegotiatedDocs</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#forcelanguagepriority">ForceLanguagePriority</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#languagepriority">LanguagePriority</a></li>
</ul>
<h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&amp;list_id=144532&amp;product=Apache%20httpd-2&amp;query_format=specific&amp;order=changeddate%20DESC%2Cpriority%2Cbug_severity&amp;component=mod_negotiation">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mod_negotiation">Report a bug</a></li></ul><h3>See also</h3>
<ul class="seealso">
<li><code class="directive"><a href="../mod/core.html#options">Options</a></code></li>
<li><code class="module"><a href="../mod/mod_mime.html">mod_mime</a></code></li>
<li><a href="../content-negotiation.html">Content
Negotiation</a></li>
<li><a href="../env.html">Environment Variables</a></li>
<li><a href="#comments_section">Comments</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="typemaps" id="typemaps">Type maps</a></h2>
<p>A type map has a format similar to 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: </p>
<dl>
<dt><code>Content-Encoding:</code></dt>
<dd>The encoding of the file. Apache only recognizes
encodings that are defined by an <code class="directive"><a href="../mod/mod_mime.html#addencoding">AddEncoding</a></code> 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><code>Content-Language:</code></dt>
<dd>The language(s) of the variant, as an Internet standard
language tag (<a href="http://www.ietf.org/rfc/rfc1766.txt">RFC 1766</a>). An example is <code>en</code>,
meaning English. If the variant contains more than one
language, they are separated by a comma.</dd>
<dt><code>Content-Length:</code></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><code>Content-Type:</code></dt>
<dd>
The <a class="glossarylink" href="../glossary.html#mime-type" title="see glossary">MIME media type</a> 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><code>level</code></dt>
<dd>an integer specifying the version of the media type.
For <code>text/html</code> this defaults to 2, otherwise
0.</dd>
<dt><code>qs</code></dt>
<dd>a floating-point number with a value in the range 0[.000]
to 1[.000], 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 <code>qs</code> values are therefore specific to a given
resource.</dd>
</dl>
<div class="example"><h3>Example</h3><p><code>
Content-Type: image/jpeg; qs=0.8
</code></p></div>
</dd>
<dt><code>URI:</code></dt>
<dd>uri of the file containing the variant (of the given
media type, encoded with the given content encoding). These
are interpreted as URLs relative to the map file; they must
be on the same server, and they must refer to files to
which the client would be granted access if they were to be
requested directly.</dd>
<dt><code>Body:</code></dt>
<dd>The actual content of the resource may
be included in the type-map file using the Body header. This
header must contain a string that designates a delimiter for
the body content. Then all following lines in the type map
file will be considered part of the resource body until the
delimiter string is found.
<div class="example"><h3>Example:</h3><p><code>
Body:----xyz----<br />
&lt;html&gt;<br />
&lt;body&gt;<br />
&lt;p&gt;Content of the page.&lt;/p&gt;<br />
&lt;/body&gt;<br />
&lt;/html&gt;<br />
----xyz----
</code></p></div>
</dd>
</dl>
<p>Consider, for example, a resource called
<code>document.html</code> which is available in English, French,
and German. The files for each of these are called
<code>document.html.en</code>, <code>document.html.fr</code>, and
<code>document.html.de</code>, respectively. The type map file will
be called <code>document.html.var</code>, and will contain the
following:</p>
<div class="example"><p><code>
URI: document.html<br />
<br />
Content-language: en<br />
Content-type: text/html<br />
URI: document.html.en<br />
<br />
Content-language: fr<br />
Content-type: text/html<br />
URI: document.html.fr<br />
<br />
Content-language: de<br />
Content-type: text/html<br />
URI: document.html.de<br />
<br />
</code></p></div>
<p>All four of these files should be placed in the same directory,
and the <code>.var</code> file should be associated with the
<code>type-map</code> handler with an <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code> directive:</p>
<pre class="prettyprint lang-config">AddHandler type-map .var</pre>
<p>A request for <code>document.html.var</code> in this directory will
result in choosing the variant which most closely matches the language preference
specified in the user's <code>Accept-Language</code> request
header.</p>
<p>If <code>Multiviews</code> is enabled, and <code class="directive"><a href="../mod/mod_mime.html#multiviewsmatch">MultiviewsMatch</a></code> is set to "handlers" or "any", a request to
<code>document.html</code> will discover <code>document.html.var</code> and
continue negotiating with the explicit type map.</p>
<p>Other configuration directives, such as <code class="directive"><a href="../mod/mod_alias.html#alias">Alias</a></code> can be used to map <code>document.html</code> to
<code>document.html.var</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="multiviews" id="multiviews">Multiviews</a></h2>
<p>A Multiviews search is enabled by the <code>Multiviews</code>
<code class="directive"><a href="../mod/core.html#options">Options</a></code>. If the server receives a
request for <code>/some/dir/foo</code> and
<code>/some/dir/foo</code> does <em>not</em> exist, then the
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.</p>
<p>The <code class="directive"><a href="../mod/mod_mime.html#multiviewsmatch">MultiviewsMatch</a></code>
directive configures whether Apache will consider files
that do not have content negotiation meta-information assigned
to them when choosing files.</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="CacheNegotiatedDocs" id="CacheNegotiatedDocs">CacheNegotiatedDocs</a> <a name="cachenegotiateddocs" id="cachenegotiateddocs">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Allows content-negotiated documents to be
cached by proxy servers</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheNegotiatedDocs On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheNegotiatedDocs Off</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
</table>
<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
HTTP/1.0 browsers. HTTP/1.1 provides much better control over
the caching of negotiated documents, and this directive has no
effect in responses to HTTP/1.1 requests.</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="ForceLanguagePriority" id="ForceLanguagePriority">ForceLanguagePriority</a> <a name="forcelanguagepriority" id="forcelanguagepriority">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Action to take if a single acceptable document is not
found</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ForceLanguagePriority Prefer</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>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
</table>
<p>The <code class="directive">ForceLanguagePriority</code> directive uses
the given <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> to satisfy
negotiation where the server could otherwise not return a single
matching document.</p>
<p><code>ForceLanguagePriority Prefer</code> uses
<code>LanguagePriority</code> 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 <code>Accept-Language</code> header assigned
<code>en</code> and <code>de</code> each as quality <code>.500</code>
(equally acceptable) then the first matching variant, <code>en</code>,
will be served.</p>
<pre class="prettyprint lang-config">LanguagePriority en fr de
ForceLanguagePriority Prefer</pre>
<p><code>ForceLanguagePriority Fallback</code> uses
<code class="directive"><a href="#languagepriority">LanguagePriority</a></code> to
serve a valid result, rather than returning an HTTP result 406
(NOT ACCEPTABLE). If the directives below were given, and the user's
<code>Accept-Language</code> only permitted an <code>es</code>
language response, but such a variant isn't found, then the first
variant from the <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> list below will be served.</p>
<pre class="prettyprint lang-config">LanguagePriority en fr de
ForceLanguagePriority Fallback</pre>
<p>Both options, <code>Prefer</code> and <code>Fallback</code>, may be
specified, so either the first matching variant from <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> will be served if
more than 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>
<h3>See also</h3>
<ul>
<li><code class="directive"><a href="../mod/mod_mime.html#addlanguage">AddLanguage</a></code></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="LanguagePriority" id="LanguagePriority">LanguagePriority</a> <a name="languagepriority" id="languagepriority">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The precedence of language variants for cases where
the client does not express a preference</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>LanguagePriority <var>MIME-lang</var> [<var>MIME-lang</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>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
</table>
<p>The <code class="directive">LanguagePriority</code> 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 <var>MIME-lang</var> are in order of decreasing preference.</p>
<pre class="prettyprint lang-config">LanguagePriority en fr de</pre>
<p>For a request for <code>foo.html</code>, where
<code>foo.html.fr</code> and <code>foo.html.de</code> both
existed, but the browser did not express a language preference,
then <code>foo.html.fr</code> would be returned.</p>
<p>Note that this directive only has an effect if a 'best'
language cannot be determined by any other means or the <code class="directive"><a href="#forcelanguagepriority">ForceLanguagePriority</a></code> directive
is not <code>None</code>. In general, the client determines the
language preference, not the server.</p>
<h3>See also</h3>
<ul>
<li><code class="directive"><a href="../mod/mod_mime.html#addlanguage">AddLanguage</a></code></li>
</ul>
</div>
</div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/mod/mod_negotiation.html" title="English">&nbsp;en&nbsp;</a> |
<a href="../fr/mod/mod_negotiation.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
<a href="../ja/mod/mod_negotiation.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a></p>
</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&amp;A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div>
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