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| <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd"> |
| <?xml-stylesheet type="text/xsl" href="../style/manual.xsl"?> |
| <modulesynopsis> |
| |
| <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 MultiViews <directive |
| module="core.html">Options</directive>, where the server does an |
| implicit filename pattern match, and choose from amongst the |
| results.</li> |
| </ul> |
| </summary> |
| |
| <seealso><directive module="mod_mime">DefaultLangauge</directive></seealso> |
| <seealso><directive module="mod_mime">AddEncoding</directive></seealso> |
| <seealso><directive module="mod_mime">AddLanguage</directive></seealso> |
| <seealso><directive module="mod_mime">AddType</directive></seealso> |
| |
| <section><title>Type maps</title> |
| <p>A type map has the same format as 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>Content-Encoding:</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>Content-Language:</dt> |
| |
| <dd>The language of the variant, as an Internet standard |
| language tag (RFC 1766). An example is <code>en</code>, |
| meaning English.</dd> |
| |
| <dt>Content-Length:</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>Content-Type:</dt> |
| |
| <dd> |
| The MIME media type 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>level</dt> |
| |
| <dd>an integer specifying the version of the media type. |
| For <code>text/html</code> this defaults to 2, otherwise |
| 0.</dd> |
| |
| <dt>qs</dt> |
| |
| <dd>a floating-point number with a value in the range 0.0 |
| to 1.0, 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 qs values are therefore specific to a given |
| resource.</dd> |
| </dl> |
| Example: |
| |
| <blockquote> |
| <code>Content-Type: image/jpeg; qs=0.8</code> |
| </blockquote> |
| </dd> |
| |
| <dt>URI:</dt> |
| |
| <dd>The path to the file containing this variant, relative to |
| the map file.</dd> |
| </dl> |
| </section> |
| |
| <section><title>MultiViews</title> |
| |
| <p>A MultiViews search is enabled by the MultiViews <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> |
| </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></contextlist> |
| <compatibility>The syntax changed in version 2.0.</compatibility> |
| |
| <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> |
| |
| <p>Prior to version 2.0, |
| <directive>CacheNegotiatedDocs</directive> did not take an |
| argument; it was turned on by the presence of the directive by |
| itself.</p> |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>ForceLangaugePriority</name> |
| <description>Action to take if a single acceptable document is not |
| found</description> |
| <syntax>ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback]</syntax> |
| <default>ForceLangaugePriority None</default> |
| <contextlist><context>server config</context> |
| <context>virtual host</context> |
| <context>directory</context> |
| <context>.htaccess</context> |
| </contextlist> |
| <override>FileInfo</override> |
| <compatibility>Available in version 2.0.30 and later</compatibility> |
| |
| <usage> |
| <p>The <directive>ForceLanguagePriority</directive> directive uses |
| the given <directive |
| module="mod_negotiation">LanguagePriority</directive> to satisfy |
| negotation 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 Accept-Language header assigned en and de |
| each as quality .500 (equally acceptable) then then first matching |
| variant, en, will be served.</p> |
| |
| <example> |
| LanguagePriority en fr de<br /> |
| ForceLanguagePriority Prefer |
| </example> |
| |
| <p><code>ForceLanguagePriority Fallback</code> uses |
| <code>LanguagePriority</code> to serve a valid result, rather than |
| returning an HTTP result 406 (NOT ACCEPTABLE). If the directives |
| below were given, and the user's Accept-Language only permitted an |
| es langauge response, but such a variant isn't found, then the |
| first variant from the LanguagePriority list below will be |
| served.</p> |
| |
| <example> |
| LanguagePriority en fr de<br /> |
| ForceLanguagePriority Fallback |
| </example> |
| |
| <p>Both options, Prefer and Fallback, may be specified, so either the |
| first matching variant from LanguagePriority will be served if more |
| that 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> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>LanguagePriority</name> |
| <description>The precendence of language variants for cases where |
| the client does not express a preference</description> |
| <syntax>LanguagePriority <em>MIME-lang</em> [<em>MIME-lang</em>] ...</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 <em>MIME-lang</em> are in order of decreasing preference. |
| Example:</p> |
| |
| <example>LanguagePriority en fr de</example> |
| |
| <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>. Correctly implemented HTTP/1.1 requests |
| will mean this directive has no effect.</p> |
| </usage> |
| </directivesynopsis> |
| |
| </modulesynopsis> |