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26 <div id="page-content">
27 <div id="preamble"><h1>Apache Module mod_negotiation</h1>
29 <p><span>Available Languages: </span><a href="../en/mod/mod_negotiation.html" title="English"> en </a> |
30 <a href="../fr/mod/mod_negotiation.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
31 <a href="../ja/mod/mod_negotiation.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
33 <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>
34 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Base</td></tr>
35 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>negotiation_module</td></tr>
36 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_negotiation.c</td></tr></table>
39 <p>Content negotiation, or more accurately content selection, is
40 the selection of the document that best matches the clients
41 capabilities, from one of several available documents. There
42 are two implementations of this.</p>
45 <li>A type map (a file with the handler
46 <code>type-map</code>) which explicitly lists the files
47 containing the variants.</li>
49 <li>A Multiviews search (enabled by the <code>Multiviews</code>
50 <code class="directive"><a href="../mod/core.html#options">Options</a></code>), where the server does
51 an implicit filename pattern match, and choose from amongst the
55 <div id="quickview"><h3>Topics</h3>
57 <li><img alt="" src="../images/down.gif" /> <a href="#typemaps">Type maps</a></li>
58 <li><img alt="" src="../images/down.gif" /> <a href="#multiviews">Multiviews</a></li>
59 </ul><h3 class="directives">Directives</h3>
61 <li><img alt="" src="../images/down.gif" /> <a href="#cachenegotiateddocs">CacheNegotiatedDocs</a></li>
62 <li><img alt="" src="../images/down.gif" /> <a href="#forcelanguagepriority">ForceLanguagePriority</a></li>
63 <li><img alt="" src="../images/down.gif" /> <a href="#languagepriority">LanguagePriority</a></li>
65 <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__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_negotiation">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_negotiation">Report a bug</a></li></ul><h3>See also</h3>
67 <li><code class="directive"><a href="../mod/core.html#options">Options</a></code></li>
68 <li><code class="module"><a href="../mod/mod_mime.html">mod_mime</a></code></li>
69 <li><a href="../content-negotiation.html">Content
71 <li><a href="../env.html">Environment Variables</a></li>
72 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
73 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
75 <h2><a name="typemaps" id="typemaps">Type maps</a></h2>
76 <p>A type map has a format similar to RFC822 mail headers. It
77 contains document descriptions separated by blank lines, with
78 lines beginning with a hash character ('#') treated as
79 comments. A document description consists of several header
80 records; records may be continued on multiple lines if the
81 continuation lines start with spaces. The leading space will be
82 deleted and the lines concatenated. A header record consists of
83 a keyword name, which always ends in a colon, followed by a
84 value. Whitespace is allowed between the header name and value,
85 and between the tokens of value. The headers allowed are: </p>
88 <dt><code>Content-Encoding:</code></dt>
89 <dd>The encoding of the file. Apache only recognizes
90 encodings that are defined by an <code class="directive"><a href="../mod/mod_mime.html#addencoding">AddEncoding</a></code> directive.
91 This normally includes the encodings <code>x-compress</code>
92 for compress'd files, and <code>x-gzip</code> for gzip'd
93 files. The <code>x-</code> prefix is ignored for encoding
96 <dt><code>Content-Language:</code></dt>
97 <dd>The language(s) of the variant, as an Internet standard
98 language tag (<a href="http://www.ietf.org/rfc/rfc1766.txt">RFC 1766</a>). An example is <code>en</code>,
99 meaning English. If the variant contains more than one
100 language, they are separated by a comma.</dd>
102 <dt><code>Content-Length:</code></dt>
103 <dd>The length of the file, in bytes. If this header is not
104 present, then the actual length of the file is used.</dd>
106 <dt><code>Content-Type:</code></dt>
109 The <a class="glossarylink" href="../glossary.html#mime-type" title="see glossary">MIME media type</a> of
110 the document, with optional parameters. Parameters are
111 separated from the media type and from one another by a
112 semi-colon, with a syntax of <code>name=value</code>. Common
116 <dt><code>level</code></dt>
117 <dd>an integer specifying the version of the media type.
118 For <code>text/html</code> this defaults to 2, otherwise
121 <dt><code>qs</code></dt>
122 <dd>a floating-point number with a value in the range 0[.000]
123 to 1[.000], indicating the relative 'quality' of this variant
124 compared to the other available variants, independent of
125 the client's capabilities. For example, a jpeg file is
126 usually of higher source quality than an ascii file if it
127 is attempting to represent a photograph. However, if the
128 resource being represented is ascii art, then an ascii
129 file would have a higher source quality than a jpeg file.
130 All <code>qs</code> values are therefore specific to a given
134 <div class="example"><h3>Example</h3><p><code>
135 Content-Type: image/jpeg; qs=0.8
139 <dt><code>URI:</code></dt>
140 <dd>uri of the file containing the variant (of the given
141 media type, encoded with the given content encoding). These
142 are interpreted as URLs relative to the map file; they must
143 be on the same server, and they must refer to files to
144 which the client would be granted access if they were to be
145 requested directly.</dd>
147 <dt><code>Body:</code></dt>
148 <dd>The actual content of the resource may
149 be included in the type-map file using the Body header. This
150 header must contain a string that designates a delimiter for
151 the body content. Then all following lines in the type map
152 file will be considered part of the resource body until the
153 delimiter string is found.
155 <div class="example"><h3>Example:</h3><p><code>
156 Body:----xyz----<br />
159 <p>Content of the page.</p><br />
167 <p>Consider, for example, a resource called
168 <code>document.html</code> which is available in English, French,
169 and German. The files for each of these are called
170 <code>document.html.en</code>, <code>document.html.fr</code>, and
171 <code>document.html.de</code>, respectively. The type map file will
172 be called <code>document.html.var</code>, and will contain the
175 <div class="example"><p><code>
176 URI: document.html<br />
178 Content-language: en<br />
179 Content-type: text/html<br />
180 URI: document.html.en<br />
182 Content-language: fr<br />
183 Content-type: text/html<br />
184 URI: document.html.fr<br />
186 Content-language: de<br />
187 Content-type: text/html<br />
188 URI: document.html.de<br />
193 <p>All four of these files should be placed in the same directory,
194 and the <code>.var</code> file should be associated with the
195 <code>type-map</code> handler with an <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code> directive:</p>
197 <pre class="prettyprint lang-config">AddHandler type-map .var</pre>
200 <p>A request for <code>document.html.var</code> in this directory will
201 result in choosing the variant which most closely matches the language preference
202 specified in the user's <code>Accept-Language</code> request
205 <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
206 <code>document.html</code> will discover <code>document.html.var</code> and
207 continue negotiating with the explicit type map.</p>
209 <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
210 <code>document.html.var</code>.</p>
212 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
213 <div class="section">
214 <h2><a name="multiviews" id="multiviews">Multiviews</a></h2>
215 <p>A Multiviews search is enabled by the <code>Multiviews</code>
216 <code class="directive"><a href="../mod/core.html#options">Options</a></code>. If the server receives a
217 request for <code>/some/dir/foo</code> and
218 <code>/some/dir/foo</code> does <em>not</em> exist, then the
219 server reads the directory looking for all files named
220 <code>foo.*</code>, and effectively fakes up a type map which
221 names all those files, assigning them the same media types and
222 content-encodings it would have if the client had asked for one
223 of them by name. It then chooses the best match to the client's
224 requirements, and returns that document.</p>
226 <p>The <code class="directive"><a href="../mod/mod_mime.html#multiviewsmatch">MultiviewsMatch</a></code>
227 directive configures whether Apache will consider files
228 that do not have content negotiation meta-information assigned
229 to them when choosing files.</p>
231 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
232 <div class="directive-section"><h2><a name="CacheNegotiatedDocs" id="CacheNegotiatedDocs">CacheNegotiatedDocs</a> <a name="cachenegotiateddocs" id="cachenegotiateddocs">Directive</a></h2>
233 <table class="directive">
234 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Allows content-negotiated documents to be
235 cached by proxy servers</td></tr>
236 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheNegotiatedDocs On|Off</code></td></tr>
237 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheNegotiatedDocs Off</code></td></tr>
238 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
239 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
240 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
242 <p>If set, this directive allows content-negotiated documents
243 to be cached by proxy servers. This could mean that clients
244 behind those proxys could retrieve versions of the documents
245 that are not the best match for their abilities, but it will
246 make caching more efficient.</p>
248 <p>This directive only applies to requests which come from
249 HTTP/1.0 browsers. HTTP/1.1 provides much better control over
250 the caching of negotiated documents, and this directive has no
251 effect in responses to HTTP/1.1 requests.</p>
255 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
256 <div class="directive-section"><h2><a name="ForceLanguagePriority" id="ForceLanguagePriority">ForceLanguagePriority</a> <a name="forcelanguagepriority" id="forcelanguagepriority">Directive</a></h2>
257 <table class="directive">
258 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Action to take if a single acceptable document is not
260 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</code></td></tr>
261 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ForceLanguagePriority Prefer</code></td></tr>
262 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
263 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
264 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
265 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
267 <p>The <code class="directive">ForceLanguagePriority</code> directive uses
268 the given <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> to satisfy
269 negotiation where the server could otherwise not return a single
270 matching document.</p>
272 <p><code>ForceLanguagePriority Prefer</code> uses
273 <code>LanguagePriority</code> to serve a one valid result, rather
274 than returning an HTTP result 300 (MULTIPLE CHOICES) when there
275 are several equally valid choices. If the directives below were
276 given, and the user's <code>Accept-Language</code> header assigned
277 <code>en</code> and <code>de</code> each as quality <code>.500</code>
278 (equally acceptable) then the first matching variant, <code>en</code>,
281 <pre class="prettyprint lang-config">LanguagePriority en fr de
282 ForceLanguagePriority Prefer</pre>
285 <p><code>ForceLanguagePriority Fallback</code> uses
286 <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> to
287 serve a valid result, rather than returning an HTTP result 406
288 (NOT ACCEPTABLE). If the directives below were given, and the user's
289 <code>Accept-Language</code> only permitted an <code>es</code>
290 language response, but such a variant isn't found, then the first
291 variant from the <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> list below will be served.</p>
293 <pre class="prettyprint lang-config">LanguagePriority en fr de
294 ForceLanguagePriority Fallback</pre>
297 <p>Both options, <code>Prefer</code> and <code>Fallback</code>, may be
298 specified, so either the first matching variant from <code class="directive"><a href="#languagepriority">LanguagePriority</a></code> will be served if
299 more than one variant is acceptable, or first available document will
300 be served if none of the variants matched the client's acceptable list
305 <li><code class="directive"><a href="../mod/mod_mime.html#addlanguage">AddLanguage</a></code></li>
308 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
309 <div class="directive-section"><h2><a name="LanguagePriority" id="LanguagePriority">LanguagePriority</a> <a name="languagepriority" id="languagepriority">Directive</a></h2>
310 <table class="directive">
311 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The precendence of language variants for cases where
312 the client does not express a preference</td></tr>
313 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>LanguagePriority <var>MIME-lang</var> [<var>MIME-lang</var>]
315 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
316 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
317 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
318 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_negotiation</td></tr>
320 <p>The <code class="directive">LanguagePriority</code> sets the precedence
321 of language variants for the case where the client does not
322 express a preference, when handling a Multiviews request. The list
323 of <var>MIME-lang</var> are in order of decreasing preference.</p>
325 <pre class="prettyprint lang-config">LanguagePriority en fr de</pre>
328 <p>For a request for <code>foo.html</code>, where
329 <code>foo.html.fr</code> and <code>foo.html.de</code> both
330 existed, but the browser did not express a language preference,
331 then <code>foo.html.fr</code> would be returned.</p>
333 <p>Note that this directive only has an effect if a 'best'
334 language cannot be determined by any other means or the <code class="directive"><a href="#forcelanguagepriority">ForceLanguagePriority</a></code> directive
335 is not <code>None</code>. In general, the client determines the
336 language preference, not the server.</p>
340 <li><code class="directive"><a href="../mod/mod_mime.html#addlanguage">AddLanguage</a></code></li>
344 <div class="bottomlang">
345 <p><span>Available Languages: </span><a href="../en/mod/mod_negotiation.html" title="English"> en </a> |
346 <a href="../fr/mod/mod_negotiation.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
347 <a href="../ja/mod/mod_negotiation.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
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