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135 lines
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HTML
135 lines
5.3 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<TITLE>Apache module mod_negotiation</TITLE>
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<H1>Module mod_negotiation</h1>
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This module is contained in the <code>mod_negotiation.c</code> file, and
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is compiled in by default. It provides for
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<A HREF="content-negotiation.html">content negotiation</A>. Any document with
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mime type <code>application/x-type-map</code> will be processed by this module.
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<!--%plaintext <?INDEX {\tt application/x-type-map} mime type> -->
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<h2>Summary</h2>
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Content negotiation, or more accurately content selection, is the
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selection of the document that best matches the clients
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capabilities, from one of several available documents.
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There are two implementations of this.
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<ul>
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<li> A type map (a file with the mime type <code>application/x-type-map</code>)
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which explicitly lists the files containing the variants.
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<li> A MultiViews search (enabled by the MultiViews
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<A HREF="core.html#options">Option</A>, where the server does an implicit
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filename pattern match, and choose from amongst the results.
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</ul>
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<h3>Type maps</h3>
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A type map has the same format as RFC822 mail headers. It contains document
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descriptions separated by blank lines, with lines beginning with a hash
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character ('#') treated as comments. A document description consists of
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several header records; records may be continued on multiple lines if the
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continuation lines start with spaces. The leading space will be deleted
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and the lines concatenated. A header record consists of a keyword
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name, which always ends in a colon, followed by a value. Whitespace is allowed
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between the header name and value, and between the tokens of value.
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The headers
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allowed are:
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<dl>
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<dt>Content-Encoding:
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<dd>The encoding of the file. Currently only two encodings are recognised
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by http; <code>x-compress</code> for compressed files, and <code>x-gzip</code>
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for gzipped files.
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<dt>Content-Language:
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<dd>The language of the variant, as an Internet standard language code, such
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as <code>en</code>.
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<dt>Content-Length:
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<dd>The length of the file, in bytes. If this header is not present, then
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the actual length of the file is used.
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<dt>Content-Type:
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<dd>The MIME media type of the document, with optional parameters.
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parameters are separated from the media type and from one another by
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semi-colons. Parameter syntax is name=value; allowed parameters are:
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<dl>
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<dt>level
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<dd>the value is an integer, which specifies the version of the media type.
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For <code>text/html</code> this defaults to 2, otherwise 0.
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<dt>qs
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<dd>the value is a floating-point number with value between 0. and 1.
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It indications the 'quality' of this variant.
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</dl>
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Example:
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<blockquote><code>Content-Type: image/jpeg; qs=0.8</code></blockquote>
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<dt>URI:
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<dd>The path to the file containing this variant, relative to the map file.
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</dl>
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<h3>MultiViews</h3>
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A MultiViews search is enabled by the MultiViews
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<A HREF="core.html#options">Option</A>.
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If the server receives a request for <code>/some/dir/foo</code> and
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<code>/some/dir/foo</code> does <em>not</em> exist, then the server reads the
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directory looking for all files named <code>foo.*</code>, and effectively
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fakes up a type map which names all those files, assigning them the same media
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types and content-encodings it would have if the client had asked for
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one of them by name. It then chooses the best match to the client's
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requirements, and returns that document.<p>
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<!--%hypertext -->
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<h2>Directives</h2>
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<ul>
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<li><A href="#cachenegotiateddocs">CacheNegotiatedDocs</a>
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<li><A HREF="#languagepriority">LanguagePriority</A>
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</ul>
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<hr>
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<!--/%hypertext -->
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<A name="cachenegotiateddocs"><h2>CacheNegotiatedDocs</h2></A>
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<strong>Syntax:</strong> CacheNegotiatedDocs<br>
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<Strong>Context:</strong> server config<br>
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<strong>Status:</strong> Base<br>
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<strong>Module:</strong> mod_negotiation<br>
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<strong>Compatibility:</strong> CacheNegotiatedDocs is only available
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in Apache 1.1 and later.<p>
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<p>If set, this directive allows content-negotiated documents to be cached
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by
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proxy servers. This could mean that clients behind those proxys could
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retrieve versions of the documents that are not the best match for
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their abilities, but it will make caching more efficient.</p>
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<!--%hypertext -->
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<A name="languagepriority"><h2>LanguagePriority</h2></A>
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<!--%plaintext <?INDEX {\tt LanguagePriority} directive> -->
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<strong>Syntax:</strong> LanguagePriority <em>mime-lang mime-lang...</em><br>
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<Strong>Context:</strong> server config, virtual host, directory, .htaccess<br>
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<Strong>Override:</strong> FileInfo<br>
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<strong>Status:</strong> Base<br>
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<strong>Module:</strong> mod_negotiation<p>
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The LanguagePriority sets the precedence of language variants for the case
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where the client does not express a preference, when handling a
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MultiViews request. The list of <em>mime-lang</em> are in order of decreasing
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preference. Example:
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<blockquote><code>LanguagePriority en fr de</code></blockquote>
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For a request for <code>foo.html</code>, where <code>foo.html.fr</code>
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and <code>foo.html.de</code> both existed, but the browser did not express
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a language preference, then <code>foo.html.fr</code> would be returned.<p>
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