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| <modulesynopsis metafile="mod_negotiation.xml.meta"> |
| |
| <name>mod_negotiation</name> |
| <description>Provides for <a |
| href="../content-negotiation.html">content negotiation</a></description> |
| <status>Base</status> |
| <sourcefile>mod_negotiation.c</sourcefile> |
| <identifier>negotiation_module</identifier> |
| |
| <summary> |
| <p>Content negotiation, or more accurately content selection, is |
| the selection of the document that best matches the clients |
| capabilities, from one of several available documents. There |
| are two implementations of this.</p> |
| |
| <ul> |
| <li>A type map (a file with the handler |
| <code>type-map</code>) which explicitly lists the files |
| containing the variants.</li> |
| |
| <li>A Multiviews search (enabled by the <code>Multiviews</code> |
| <directive module="core">Options</directive>), where the server does |
| an implicit filename pattern match, and choose from amongst the |
| results.</li> |
| </ul> |
| </summary> |
| <seealso><directive module="core">Options</directive></seealso> |
| <seealso><module>mod_mime</module></seealso> |
| <seealso><a href="../content-negotiation.html">Content |
| Negotiation</a></seealso> |
| <seealso><a href="../env.html">Environment Variables</a></seealso> |
| |
| <section id="typemaps"><title>Type maps</title> |
| <p>A type map has a format similar to RFC822 mail headers. It |
| contains document descriptions separated by blank lines, with |
| lines beginning with a hash character ('#') treated as |
| comments. A document description consists of several header |
| records; records may be continued on multiple lines if the |
| continuation lines start with spaces. The leading space will be |
| deleted and the lines concatenated. A header record consists of |
| a keyword name, which always ends in a colon, followed by a |
| value. Whitespace is allowed between the header name and value, |
| and between the tokens of value. The headers allowed are: </p> |
| |
| <dl> |
| <dt><code>Content-Encoding:</code></dt> |
| <dd>The encoding of the file. Apache only recognizes |
| encodings that are defined by an <directive |
| module="mod_mime">AddEncoding</directive> directive. |
| This normally includes the encodings <code>x-compress</code> |
| for compress'd files, and <code>x-gzip</code> for gzip'd |
| files. The <code>x-</code> prefix is ignored for encoding |
| comparisons.</dd> |
| |
| <dt><code>Content-Language:</code></dt> |
| <dd>The language(s) of the variant, as an Internet standard |
| language tag (<a href="http://www.ietf.org/rfc/rfc1766.txt" |
| >RFC 1766</a>). An example is <code>en</code>, |
| meaning English. If the variant contains more than one |
| language, they are separated by a comma.</dd> |
| |
| <dt><code>Content-Length:</code></dt> |
| <dd>The length of the file, in bytes. If this header is not |
| present, then the actual length of the file is used.</dd> |
| |
| <dt><code>Content-Type:</code></dt> |
| |
| <dd> |
| The <glossary ref="mime-type">MIME media type</glossary> of |
| the document, with optional parameters. Parameters are |
| separated from the media type and from one another by a |
| semi-colon, with a syntax of <code>name=value</code>. Common |
| parameters include: |
| |
| <dl> |
| <dt><code>level</code></dt> |
| <dd>an integer specifying the version of the media type. |
| For <code>text/html</code> this defaults to 2, otherwise |
| 0.</dd> |
| |
| <dt><code>qs</code></dt> |
| <dd>a floating-point number with a value in the range 0[.000] |
| to 1[.000], indicating the relative 'quality' of this variant |
| compared to the other available variants, independent of |
| the client's capabilities. For example, a jpeg file is |
| usually of higher source quality than an ascii file if it |
| is attempting to represent a photograph. However, if the |
| resource being represented is ascii art, then an ascii |
| file would have a higher source quality than a jpeg file. |
| All <code>qs</code> values are therefore specific to a given |
| resource.</dd> |
| </dl> |
| |
| <example><title>Example</title> |
| Content-Type: image/jpeg; qs=0.8 |
| </example> |
| </dd> |
| |
| <dt><code>URI:</code></dt> |
| <dd>uri of the file containing the variant (of the given |
| media type, encoded with the given content encoding). These |
| are interpreted as URLs relative to the map file; they must |
| be on the same server, and they must refer to files to |
| which the client would be granted access if they were to be |
| requested directly.</dd> |
| |
| <dt><code>Body:</code></dt> |
| <dd>The actual content of the resource may |
| be included in the type-map file using the Body header. This |
| header must contain a string that designates a delimiter for |
| the body content. Then all following lines in the type map |
| file will be considered part of the resource body until the |
| delimiter string is found. |
| |
| <example><title>Example:</title> |
| Body:----xyz----<br /> |
| <html><br /> |
| <body><br /> |
| <p>Content of the page.</p><br /> |
| </body><br /> |
| </html><br /> |
| ----xyz---- |
| </example> |
| </dd> |
| </dl> |
| |
| <p>Consider, for example, a resource called |
| <code>document.html</code> which is available in English, French, |
| and German. The files for each of these are called |
| <code>document.html.en</code>, <code>document.html.fr</code>, and |
| <code>document.html.de</code>, respectively. The type map file will |
| be called <code>document.html.var</code>, and will contain the |
| following:</p> |
| |
| <example> |
| URI: document.html<br /> |
| <br /> |
| Content-language: en<br /> |
| Content-type: text/html<br /> |
| URI: document.html.en<br /> |
| <br /> |
| Content-language: fr<br /> |
| Content-type: text/html<br /> |
| URI: document.html.fr<br /> |
| <br /> |
| Content-language: de<br /> |
| Content-type: text/html<br /> |
| URI: document.html.de<br /> |
| <br /> |
| |
| </example> |
| |
| <p>All four of these files should be placed in the same directory, |
| and the <code>.var</code> file should be associated with the |
| <code>type-map</code> handler with an <directive |
| module="mod_mime">AddHandler</directive> directive:</p> |
| |
| <highlight language="config"> |
| AddHandler type-map .var |
| </highlight> |
| |
| <p>A request for <code>document.html.var</code> in this directory will |
| result in choosing the variant which most closely matches the language preference |
| specified in the user's <code>Accept-Language</code> request |
| header.</p> |
| |
| <p>If <code>Multiviews</code> is enabled, and <directive module="mod_mime" |
| >MultiviewsMatch</directive> is set to "handlers" or "any", a request to |
| <code>document.html</code> will discover <code>document.html.var</code> and |
| continue negotiating with the explicit type map.</p> |
| |
| <p>Other configuration directives, such as <directive module="mod_alias" |
| >Alias</directive> can be used to map <code>document.html</code> to |
| <code>document.html.var</code>.</p> |
| |
| </section> |
| |
| <section id="multiviews"><title>Multiviews</title> |
| <p>A Multiviews search is enabled by the <code>Multiviews</code> |
| <directive module="core">Options</directive>. If the server receives a |
| request for <code>/some/dir/foo</code> and |
| <code>/some/dir/foo</code> does <em>not</em> exist, then the |
| server reads the directory looking for all files named |
| <code>foo.*</code>, and effectively fakes up a type map which |
| names all those files, assigning them the same media types and |
| content-encodings it would have if the client had asked for one |
| of them by name. It then chooses the best match to the client's |
| requirements, and returns that document.</p> |
| |
| <p>The <directive module="mod_mime">MultiviewsMatch</directive> |
| directive configures whether Apache will consider files |
| that do not have content negotiation meta-information assigned |
| to them when choosing files.</p> |
| </section> |
| |
| <directivesynopsis> |
| <name>CacheNegotiatedDocs</name> |
| <description>Allows content-negotiated documents to be |
| cached by proxy servers</description> |
| <syntax>CacheNegotiatedDocs On|Off</syntax> |
| <default>CacheNegotiatedDocs Off</default> |
| <contextlist><context>server config</context><context>virtual host</context> |
| </contextlist> |
| |
| <usage> |
| <p>If set, this directive allows content-negotiated documents |
| to be cached by proxy servers. This could mean that clients |
| behind those proxys could retrieve versions of the documents |
| that are not the best match for their abilities, but it will |
| make caching more efficient.</p> |
| |
| <p>This directive only applies to requests which come from |
| HTTP/1.0 browsers. HTTP/1.1 provides much better control over |
| the caching of negotiated documents, and this directive has no |
| effect in responses to HTTP/1.1 requests.</p> |
| |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>ForceLanguagePriority</name> |
| <description>Action to take if a single acceptable document is not |
| found</description> |
| <syntax>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</syntax> |
| <default>ForceLanguagePriority Prefer</default> |
| <contextlist><context>server config</context><context>virtual host</context> |
| <context>directory</context><context>.htaccess</context></contextlist> |
| <override>FileInfo</override> |
| |
| <usage> |
| <p>The <directive>ForceLanguagePriority</directive> directive uses |
| the given <directive |
| module="mod_negotiation">LanguagePriority</directive> to satisfy |
| negotiation where the server could otherwise not return a single |
| matching document.</p> |
| |
| <p><code>ForceLanguagePriority Prefer</code> uses |
| <code>LanguagePriority</code> to serve a one valid result, rather |
| than returning an HTTP result 300 (MULTIPLE CHOICES) when there |
| are several equally valid choices. If the directives below were |
| given, and the user's <code>Accept-Language</code> header assigned |
| <code>en</code> and <code>de</code> each as quality <code>.500</code> |
| (equally acceptable) then the first matching variant, <code>en</code>, |
| will be served.</p> |
| |
| <highlight language="config"> |
| LanguagePriority en fr de |
| ForceLanguagePriority Prefer |
| </highlight> |
| |
| <p><code>ForceLanguagePriority Fallback</code> uses |
| <directive module="mod_negotiation">LanguagePriority</directive> to |
| serve a valid result, rather than returning an HTTP result 406 |
| (NOT ACCEPTABLE). If the directives below were given, and the user's |
| <code>Accept-Language</code> only permitted an <code>es</code> |
| language response, but such a variant isn't found, then the first |
| variant from the <directive module="mod_negotiation" |
| >LanguagePriority</directive> list below will be served.</p> |
| |
| <highlight language="config"> |
| LanguagePriority en fr de |
| ForceLanguagePriority Fallback |
| </highlight> |
| |
| <p>Both options, <code>Prefer</code> and <code>Fallback</code>, may be |
| specified, so either the first matching variant from <directive |
| module="mod_negotiation">LanguagePriority</directive> will be served if |
| more than one variant is acceptable, or first available document will |
| be served if none of the variants matched the client's acceptable list |
| of languages.</p> |
| </usage> |
| <seealso><directive module="mod_mime">AddLanguage</directive></seealso> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>LanguagePriority</name> |
| <description>The precedence of language variants for cases where |
| the client does not express a preference</description> |
| <syntax>LanguagePriority <var>MIME-lang</var> [<var>MIME-lang</var>] |
| ...</syntax> |
| <contextlist><context>server config</context><context>virtual host</context> |
| <context>directory</context><context>.htaccess</context></contextlist> |
| <override>FileInfo</override> |
| |
| <usage> |
| <p>The <directive>LanguagePriority</directive> sets the precedence |
| of language variants for the case where the client does not |
| express a preference, when handling a Multiviews request. The list |
| of <var>MIME-lang</var> are in order of decreasing preference.</p> |
| |
| <highlight language="config"> |
| LanguagePriority en fr de |
| </highlight> |
| |
| <p>For a request for <code>foo.html</code>, where |
| <code>foo.html.fr</code> and <code>foo.html.de</code> both |
| existed, but the browser did not express a language preference, |
| then <code>foo.html.fr</code> would be returned.</p> |
| |
| <p>Note that this directive only has an effect if a 'best' |
| language cannot be determined by any other means or the <directive |
| module="mod_negotiation">ForceLanguagePriority</directive> directive |
| is not <code>None</code>. In general, the client determines the |
| language preference, not the server.</p> |
| </usage> |
| <seealso><directive module="mod_mime">AddLanguage</directive></seealso> |
| </directivesynopsis> |
| |
| </modulesynopsis> |