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7 Copyright 2002-2005 The Apache Software Foundation or its licensors, as
10 Licensed under the Apache License, Version 2.0 (the "License");
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14 http://www.apache.org/licenses/LICENSE-2.0
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23 <modulesynopsis metafile="mod_negotiation.xml.meta">
25 <name>mod_negotiation</name>
26 <description>Provides for <a
27 href="../content-negotiation.html">content negotiation</a></description>
29 <sourcefile>mod_negotiation.c</sourcefile>
30 <identifier>negotiation_module</identifier>
33 <p>Content negotiation, or more accurately content selection, is
34 the selection of the document that best matches the clients
35 capabilities, from one of several available documents. There
36 are two implementations of this.</p>
39 <li>A type map (a file with the handler
40 <code>type-map</code>) which explicitly lists the files
41 containing the variants.</li>
43 <li>A MultiViews search (enabled by the <code>MultiViews</code>
44 <directive module="core">Options</directive>), where the server does
45 an implicit filename pattern match, and choose from amongst the
49 <seealso><directive module="core">Options</directive></seealso>
50 <seealso><module>mod_mime</module></seealso>
51 <seealso><a href="../content-negotiation.html">Content
52 Negotiation</a></seealso>
53 <seealso><a href="../env.html">Environment Variables</a></seealso>
55 <section id="typemaps"><title>Type maps</title>
56 <p>A type map has a format similar to RFC822 mail headers. It
57 contains document descriptions separated by blank lines, with
58 lines beginning with a hash character ('#') treated as
59 comments. A document description consists of several header
60 records; records may be continued on multiple lines if the
61 continuation lines start with spaces. The leading space will be
62 deleted and the lines concatenated. A header record consists of
63 a keyword name, which always ends in a colon, followed by a
64 value. Whitespace is allowed between the header name and value,
65 and between the tokens of value. The headers allowed are: </p>
68 <dt><code>Content-Encoding:</code></dt>
69 <dd>The encoding of the file. Apache only recognizes
70 encodings that are defined by an <directive
71 module="mod_mime">AddEncoding</directive> directive.
72 This normally includes the encodings <code>x-compress</code>
73 for compress'd files, and <code>x-gzip</code> for gzip'd
74 files. The <code>x-</code> prefix is ignored for encoding
77 <dt><code>Content-Language:</code></dt>
78 <dd>The language(s) of the variant, as an Internet standard
79 language tag (<a href="http://www.ietf.org/rfc/rfc1766.txt"
80 >RFC 1766</a>). An example is <code>en</code>,
81 meaning English. If the variant contains more than one
82 language, they are separated by a comma.</dd>
84 <dt><code>Content-Length:</code></dt>
85 <dd>The length of the file, in bytes. If this header is not
86 present, then the actual length of the file is used.</dd>
88 <dt><code>Content-Type:</code></dt>
91 The MIME media type of the document, with optional
92 parameters. Parameters are separated from the media type
93 and from one another by a semi-colon, with a syntax of
94 <code>name=value</code>. Common parameters include:
97 <dt><code>level</code></dt>
98 <dd>an integer specifying the version of the media type.
99 For <code>text/html</code> this defaults to 2, otherwise
102 <dt><code>qs</code></dt>
103 <dd>a floating-point number with a value in the range 0.0
104 to 1.0, indicating the relative 'quality' of this variant
105 compared to the other available variants, independent of
106 the client's capabilities. For example, a jpeg file is
107 usually of higher source quality than an ascii file if it
108 is attempting to represent a photograph. However, if the
109 resource being represented is ascii art, then an ascii
110 file would have a higher source quality than a jpeg file.
111 All <code>qs</code> values are therefore specific to a given
115 <example><title>Example</title>
116 Content-Type: image/jpeg; qs=0.8
120 <dt><code>URI:</code></dt>
121 <dd>uri of the file containing the variant (of the given
122 media type, encoded with the given content encoding). These
123 are interpreted as URLs relative to the map file; they must
124 be on the same server (!), and they must refer to files to
125 which the client would be granted access if they were to be
126 requested directly.</dd>
128 <dt><code>Body:</code></dt>
129 <dd>New in Apache 2.0, the actual content of the resource may
130 be included in the type-map file using the Body header. This
131 header must contain a string that designates a delimiter for
132 the body content. Then all following lines in the type map
133 file will be considered part of the resource body until the
134 delimiter string is found.
136 <example><title>Example:</title>
137 Body:----xyz----<br />
140 <p>Content of the page.</p><br />
149 <section id="multiviews"><title>MultiViews</title>
150 <p>A MultiViews search is enabled by the <code>MultiViews</code>
151 <directive module="core">Options</directive>. If the server receives a
152 request for <code>/some/dir/foo</code> and
153 <code>/some/dir/foo</code> does <em>not</em> exist, then the
154 server reads the directory looking for all files named
155 <code>foo.*</code>, and effectively fakes up a type map which
156 names all those files, assigning them the same media types and
157 content-encodings it would have if the client had asked for one
158 of them by name. It then chooses the best match to the client's
159 requirements, and returns that document.</p>
161 <p>The <directive module="mod_mime">MultiViewsMatch</directive>
162 directive configures whether Apache will consider files
163 that do not have content negotiation meta-information assigned
164 to them when choosing files.</p>
168 <name>CacheNegotiatedDocs</name>
169 <description>Allows content-negotiated documents to be
170 cached by proxy servers</description>
171 <syntax>CacheNegotiatedDocs On|Off</syntax>
172 <default>CacheNegotiatedDocs Off</default>
173 <contextlist><context>server config</context><context>virtual host</context>
175 <compatibility>The syntax changed in version 2.0.</compatibility>
178 <p>If set, this directive allows content-negotiated documents
179 to be cached by proxy servers. This could mean that clients
180 behind those proxys could retrieve versions of the documents
181 that are not the best match for their abilities, but it will
182 make caching more efficient.</p>
184 <p>This directive only applies to requests which come from
185 HTTP/1.0 browsers. HTTP/1.1 provides much better control over
186 the caching of negotiated documents, and this directive has no
187 effect in responses to HTTP/1.1 requests.</p>
189 <p>Prior to version 2.0,
190 <directive>CacheNegotiatedDocs</directive> did not take an
191 argument; it was turned on by the presence of the directive by
197 <name>ForceLanguagePriority</name>
198 <description>Action to take if a single acceptable document is not
200 <syntax>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</syntax>
201 <default>ForceLanguagePriority Prefer</default>
202 <contextlist><context>server config</context><context>virtual host</context>
203 <context>directory</context><context>.htaccess</context></contextlist>
204 <override>FileInfo</override>
205 <compatibility>Available in version 2.0.30 and later</compatibility>
208 <p>The <directive>ForceLanguagePriority</directive> directive uses
210 module="mod_negotiation">LanguagePriority</directive> to satisfy
211 negotation where the server could otherwise not return a single
212 matching document.</p>
214 <p><code>ForceLanguagePriority Prefer</code> uses
215 <code>LanguagePriority</code> to serve a one valid result, rather
216 than returning an HTTP result 300 (MULTIPLE CHOICES) when there
217 are several equally valid choices. If the directives below were
218 given, and the user's <code>Accept-Language</code> header assigned
219 <code>en</code> and <code>de</code> each as quality <code>.500</code>
220 (equally acceptable) then the first matching variant, <code>en</code>,
224 LanguagePriority en fr de<br />
225 ForceLanguagePriority Prefer
228 <p><code>ForceLanguagePriority Fallback</code> uses
229 <directive module="mod_negotiation">LanguagePriority</directive> to
230 serve a valid result, rather than returning an HTTP result 406
231 (NOT ACCEPTABLE). If the directives below were given, and the user's
232 <code>Accept-Language</code> only permitted an <code>es</code>
233 language response, but such a variant isn't found, then the first
234 variant from the <directive module="mod_negotiation"
235 >LanguagePriority</directive> list below will be served.</p>
238 LanguagePriority en fr de<br />
239 ForceLanguagePriority Fallback
242 <p>Both options, <code>Prefer</code> and <code>Fallback</code>, may be
243 specified, so either the first matching variant from <directive
244 module="mod_negotiation">LanguagePriority</directive> will be served if
245 more than one variant is acceptable, or first available document will
246 be served if none of the variants matched the client's acceptable list
249 <seealso><directive module="mod_mime">AddLanguage</directive></seealso>
253 <name>LanguagePriority</name>
254 <description>The precendence of language variants for cases where
255 the client does not express a preference</description>
256 <syntax>LanguagePriority <var>MIME-lang</var> [<var>MIME-lang</var>]
258 <contextlist><context>server config</context><context>virtual host</context>
259 <context>directory</context><context>.htaccess</context></contextlist>
260 <override>FileInfo</override>
263 <p>The <directive>LanguagePriority</directive> sets the precedence
264 of language variants for the case where the client does not
265 express a preference, when handling a MultiViews request. The list
266 of <var>MIME-lang</var> are in order of decreasing preference.</p>
268 <example><title>Example:</title>
269 LanguagePriority en fr de
272 <p>For a request for <code>foo.html</code>, where
273 <code>foo.html.fr</code> and <code>foo.html.de</code> both
274 existed, but the browser did not express a language preference,
275 then <code>foo.html.fr</code> would be returned.</p>
277 <p>Note that this directive only has an effect if a 'best'
278 language cannot be determined by any other means or the <directive
279 module="mod_negotiation">ForceLanguagePriority</directive> directive
280 is not <code>None</code>. In general, the client determines the
281 language preference, not the server.</p>
283 <seealso><directive module="mod_mime">AddLanguage</directive></seealso>