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178 lines
6.0 KiB
HTML
178 lines
6.0 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<TITLE>Apache module mod_negotiation</TITLE>
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</HEAD>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<BODY
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<!--#include virtual="header.html" -->
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<H1 ALIGN="CENTER">Module mod_negotiation</H1>
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This module is contained in the <CODE>mod_negotiation.c</CODE> file,
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and is compiled in by default. It provides for <A
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HREF="../content-negotiation.html">content negotiation</A>.
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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 handler <CODE>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 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 recognized
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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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<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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<H2><A NAME="cachenegotiateddocs">CacheNegotiatedDocs</A></H2>
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<A
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HREF="directive-dict.html#Syntax"
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REL="Help"
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><STRONG>Syntax:</STRONG></A> CacheNegotiatedDocs<BR>
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<A
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HREF="directive-dict.html#Context"
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REL="Help"
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><STRONG>Context:</STRONG></A> server config<BR>
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<A
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HREF="directive-dict.html#Status"
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REL="Help"
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><STRONG>Status:</STRONG></A> Base<BR>
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<A
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HREF="directive-dict.html#Module"
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REL="Help"
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><STRONG>Module:</STRONG></A> mod_negotiation<BR>
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<A
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HREF="directive-dict.html#Compatibility"
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REL="Help"
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><STRONG>Compatibility:</STRONG></A> 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
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cached by proxy servers. This could mean that clients behind those
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proxys could retrieve versions of the documents that are not the best
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match for their abilities, but it will make caching more
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efficient.
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<P>
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This directive only applies to requests which come from HTTP/1.0 browsers.
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HTTP/1.1 provides much better control over the caching of negotiated
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documents, and this directive has no effect in responses to
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HTTP/1.1 requests.
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<H2><A NAME="languagepriority">LanguagePriority</A></H2>
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<!--%plaintext <?INDEX {\tt LanguagePriority} directive> -->
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<A
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HREF="directive-dict.html#Syntax"
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REL="Help"
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><STRONG>Syntax:</STRONG></A> LanguagePriority <EM>mime-lang mime-lang...</EM><BR>
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<A
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HREF="directive-dict.html#Context"
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REL="Help"
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><STRONG>Context:</STRONG></A> server config, virtual host, directory, .htaccess<BR>
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<A
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HREF="directive-dict.html#Override"
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REL="Help"
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><STRONG>Override:</STRONG></A> FileInfo<BR>
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<A
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HREF="directive-dict.html#Status"
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REL="Help"
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><STRONG>Status:</STRONG></A> Base<BR>
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<A
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HREF="directive-dict.html#Module"
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REL="Help"
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><STRONG>Module:</STRONG></A> 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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<P>
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Note that this directive only has an effect if a 'best' language
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cannot be determined by other any other means. Correctly implemented
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HTTP/1.1 requests will mean this directive has no effect.
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<!--#include virtual="footer.html" -->
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</BODY>
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</HTML>
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