2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
3 <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
4 <modulesynopsis metafile="mod_negotiation.xml.meta">
6 <name>mod_negotiation</name>
7 <description>Provides for <a
8 href="../content-negotiation.html">content negotiation</a></description>
10 <sourcefile>mod_negotiation.c</sourcefile>
11 <identifier>negotiation_module</identifier>
14 <p>Content negotiation, or more accurately content selection, is
15 the selection of the document that best matches the clients
16 capabilities, from one of several available documents. There
17 are two implementations of this.</p>
20 <li>A type map (a file with the handler
21 <code>type-map</code>) which explicitly lists the files
22 containing the variants.</li>
24 <li>A MultiViews search (enabled by the <code>MultiViews</code>
25 <directive module="core">Options</directive>), where the server does
26 an implicit filename pattern match, and choose from amongst the
30 <seealso><directive module="core">Options</directive></seealso>
31 <seealso><module>mod_mime</module></seealso>
32 <seealso><a href="../content-negotiation.html">Content
33 Negotiation</a></seealso>
34 <seealso><a href="../env.html">Environment Variables</a></seealso>
36 <section id="typemaps"><title>Type maps</title>
37 <p>A type map has a format similar to RFC822 mail headers. It
38 contains document descriptions separated by blank lines, with
39 lines beginning with a hash character ('#') treated as
40 comments. A document description consists of several header
41 records; records may be continued on multiple lines if the
42 continuation lines start with spaces. The leading space will be
43 deleted and the lines concatenated. A header record consists of
44 a keyword name, which always ends in a colon, followed by a
45 value. Whitespace is allowed between the header name and value,
46 and between the tokens of value. The headers allowed are: </p>
49 <dt><code>Content-Encoding:</code></dt>
50 <dd>The encoding of the file. Apache only recognizes
51 encodings that are defined by an <directive
52 module="mod_mime">AddEncoding</directive> directive.
53 This normally includes the encodings <code>x-compress</code>
54 for compress'd files, and <code>x-gzip</code> for gzip'd
55 files. The <code>x-</code> prefix is ignored for encoding
58 <dt><code>Content-Language:</code></dt>
59 <dd>The language(s) of the variant, as an Internet standard
60 language tag (<a href="http://www.ietf.org/rfc/rfc1766.txt"
61 >RFC 1766</a>). An example is <code>en</code>,
62 meaning English. If the variant contains more than one
63 language, they are separated by a comma.</dd>
65 <dt><code>Content-Length:</code></dt>
66 <dd>The length of the file, in bytes. If this header is not
67 present, then the actual length of the file is used.</dd>
69 <dt><code>Content-Type:</code></dt>
72 The MIME media type of the document, with optional
73 parameters. Parameters are separated from the media type
74 and from one another by a semi-colon, with a syntax of
75 <code>name=value</code>. Common parameters include:
78 <dt><code>level</code></dt>
79 <dd>an integer specifying the version of the media type.
80 For <code>text/html</code> this defaults to 2, otherwise
83 <dt><code>qs</code></dt>
84 <dd>a floating-point number with a value in the range 0.0
85 to 1.0, indicating the relative 'quality' of this variant
86 compared to the other available variants, independent of
87 the client's capabilities. For example, a jpeg file is
88 usually of higher source quality than an ascii file if it
89 is attempting to represent a photograph. However, if the
90 resource being represented is ascii art, then an ascii
91 file would have a higher source quality than a jpeg file.
92 All <code>qs</code> values are therefore specific to a given
96 <example><title>Example</title>
97 Content-Type: image/jpeg; qs=0.8
101 <dt><code>URI:</code></dt>
102 <dd>uri of the file containing the variant (of the given
103 media type, encoded with the given content encoding). These
104 are interpreted as URLs relative to the map file; they must
105 be on the same server (!), and they must refer to files to
106 which the client would be granted access if they were to be
107 requested directly.</dd>
109 <dt><code>Body:</code></dt>
110 <dd>New in Apache 2.0, the actual content of the resource may
111 be included in the type-map file using the Body header. This
112 header must contain a string that designates a delimiter for
113 the body content. Then all following lines in the type map
114 file will be considered part of the resource body until the
115 delimiter string is found.
117 <example><title>Example:</title>
118 Body:----xyz----<br />
121 <p>Content of the page.</p><br />
130 <section id="multiviews"><title>MultiViews</title>
131 <p>A MultiViews search is enabled by the <code>MultiViews</code>
132 <directive module="core">Options</directive>. If the server receives a
133 request for <code>/some/dir/foo</code> and
134 <code>/some/dir/foo</code> does <em>not</em> exist, then the
135 server reads the directory looking for all files named
136 <code>foo.*</code>, and effectively fakes up a type map which
137 names all those files, assigning them the same media types and
138 content-encodings it would have if the client had asked for one
139 of them by name. It then chooses the best match to the client's
140 requirements, and returns that document.</p>
144 <name>CacheNegotiatedDocs</name>
145 <description>Allows content-negotiated documents to be
146 cached by proxy servers</description>
147 <syntax>CacheNegotiatedDocs On|Off</syntax>
148 <default>CacheNegotiatedDocs Off</default>
149 <contextlist><context>server config</context><context>virtual host</context>
151 <compatibility>The syntax changed in version 2.0.</compatibility>
154 <p>If set, this directive allows content-negotiated documents
155 to be cached by proxy servers. This could mean that clients
156 behind those proxys could retrieve versions of the documents
157 that are not the best match for their abilities, but it will
158 make caching more efficient.</p>
160 <p>This directive only applies to requests which come from
161 HTTP/1.0 browsers. HTTP/1.1 provides much better control over
162 the caching of negotiated documents, and this directive has no
163 effect in responses to HTTP/1.1 requests.</p>
165 <p>Prior to version 2.0,
166 <directive>CacheNegotiatedDocs</directive> did not take an
167 argument; it was turned on by the presence of the directive by
173 <name>ForceLanguagePriority</name>
174 <description>Action to take if a single acceptable document is not
176 <syntax>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</syntax>
177 <default>ForceLanguagePriority Prefer</default>
178 <contextlist><context>server config</context><context>virtual host</context>
179 <context>directory</context><context>.htaccess</context></contextlist>
180 <override>FileInfo</override>
181 <compatibility>Available in version 2.0.30 and later</compatibility>
184 <p>The <directive>ForceLanguagePriority</directive> directive uses
186 module="mod_negotiation">LanguagePriority</directive> to satisfy
187 negotation where the server could otherwise not return a single
188 matching document.</p>
190 <p><code>ForceLanguagePriority Prefer</code> uses
191 <code>LanguagePriority</code> to serve a one valid result, rather
192 than returning an HTTP result 300 (MULTIPLE CHOICES) when there
193 are several equally valid choices. If the directives below were
194 given, and the user's <code>Accept-Language</code> header assigned
195 <code>en</code> and <code>de</code> each as quality <code>.500</code>
196 (equally acceptable) then the first matching variant, <code>en</code>,
200 LanguagePriority en fr de<br />
201 ForceLanguagePriority Prefer
204 <p><code>ForceLanguagePriority Fallback</code> uses
205 <directive module="mod_negotiation">LanguagePriority</directive> to
206 serve a valid result, rather than returning an HTTP result 406
207 (NOT ACCEPTABLE). If the directives below were given, and the user's
208 <code>Accept-Language</code> only permitted an <code>es</code>
209 language response, but such a variant isn't found, then the first
210 variant from the <directive module="mod_negotiation"
211 >LanguagePriority</directive> list below will be served.</p>
214 LanguagePriority en fr de<br />
215 ForceLanguagePriority Fallback
218 <p>Both options, <code>Prefer</code> and <code>Fallback</code>, may be
219 specified, so either the first matching variant from <directive
220 module="mod_negotiation">LanguagePriority</directive> will be served if
221 more than one variant is acceptable, or first available document will
222 be served if none of the variants matched the client's acceptable list
225 <seealso><directive module="mod_mime">AddLanguage</directive></seealso>
229 <name>LanguagePriority</name>
230 <description>The precendence of language variants for cases where
231 the client does not express a preference</description>
232 <syntax>LanguagePriority <var>MIME-lang</var> [<var>MIME-lang</var>]
234 <contextlist><context>server config</context><context>virtual host</context>
235 <context>directory</context><context>.htaccess</context></contextlist>
236 <override>FileInfo</override>
239 <p>The <directive>LanguagePriority</directive> sets the precedence
240 of language variants for the case where the client does not
241 express a preference, when handling a MultiViews request. The list
242 of <var>MIME-lang</var> are in order of decreasing preference.</p>
244 <example><title>Example:</title>
245 LanguagePriority en fr de
248 <p>For a request for <code>foo.html</code>, where
249 <code>foo.html.fr</code> and <code>foo.html.de</code> both
250 existed, but the browser did not express a language preference,
251 then <code>foo.html.fr</code> would be returned.</p>
253 <p>Note that this directive only has an effect if a 'best'
254 language cannot be determined by any other means or the <directive
255 module="mod_negotiation">ForceLanguagePriority</directive> directive
256 is not <code>None</code>. Correctly implemented HTTP/1.1 requests
257 will mean this directive has no effect.</p>
259 <seealso><directive module="mod_mime">AddLanguage</directive></seealso>