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Apache HTTP Server Version 2.4
| Description: | Provides forcontent negotiation |
|---|---|
| Status: | Base |
| Module Identifier: | negotiation_module |
| Source File: | mod_negotiation.c |
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.
type-map) which explicitly lists the files containing the variants.MultiviewsOptions), where the server does an implicit filename pattern match, and choose from amongst the results.
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:
Content-Encoding:AddEncoding directive. This normally includes the encodingsx-compress for compress'd files, andx-gzip for gzip'd files. Thex- prefix is ignored for encoding comparisons.Content-Language:en, meaning English. If the variant contains more than one language, they are separated by a comma.Content-Length:Content-Type:name=value. Common parameters include:leveltext/html this defaults to 2, otherwise 0.qsqs values are therefore specific to a given resource. Content-Type: image/jpeg; qs=0.8
URI:Body: Body:----xyz----
<html>
<body>
<p>Content of the page.</p>
</body>
</html>
----xyz----
Consider, for example, a resource calleddocument.html which is available in English, French, and German. The files for each of these are calleddocument.html.en,document.html.fr, anddocument.html.de, respectively. The type map file will be calleddocument.html.var, and will contain the following:
URI: document.html
Content-language: en
Content-type: text/html
URI: document.html.en
Content-language: fr
Content-type: text/html
URI: document.html.fr
Content-language: de
Content-type: text/html
URI: document.html.de
All four of these files should be placed in the same directory, and the.var file should be associated with thetype-map handler with anAddHandler directive:
AddHandler type-map .var
A request fordocument.html.var in this directory will result in choosing the variant which most closely matches the language preference specified in the user'sAccept-Language request header.
IfMultiviews is enabled, andMultiviewsMatch is set to "handlers" or "any", a request todocument.html will discoverdocument.html.var and continue negotiating with the explicit type map.
Other configuration directives, such asAlias can be used to mapdocument.html todocument.html.var.
A Multiviews search is enabled by theMultiviewsOptions. If the server receives a request for/some/dir/foo and/some/dir/foo doesnot exist, then the server reads the directory looking for all files namedfoo.*, 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.
TheMultiviewsMatch directive configures whether Apache will consider files that do not have content negotiation meta-information assigned to them when choosing files.
| Description: | Allows content-negotiated documents to becached by proxy servers |
|---|---|
| Syntax: | CacheNegotiatedDocs On|Off |
| Default: | CacheNegotiatedDocs Off |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_negotiation |
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.
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.
| Description: | Action to take if a single acceptable document is notfound |
|---|---|
| Syntax: | ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback] |
| Default: | ForceLanguagePriority Prefer |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_negotiation |
TheForceLanguagePriority directive uses the givenLanguagePriority to satisfy negotiation where the server could otherwise not return a single matching document.
ForceLanguagePriority Prefer usesLanguagePriority 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'sAccept-Language header assigneden andde each as quality.500 (equally acceptable) then the first matching variant,en, will be served.
LanguagePriority en fr deForceLanguagePriority Prefer
ForceLanguagePriority Fallback usesLanguagePriority to serve a valid result, rather than returning an HTTP result 406 (NOT ACCEPTABLE). If the directives below were given, and the user'sAccept-Language only permitted anes language response, but such a variant isn't found, then the first variant from theLanguagePriority list below will be served.
LanguagePriority en fr deForceLanguagePriority Fallback
Both options,Prefer andFallback, may be specified, so either the first matching variant fromLanguagePriority 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.
| Description: | The precedence of language variants for cases wherethe client does not express a preference |
|---|---|
| Syntax: | LanguagePriorityMIME-lang [MIME-lang]... |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_negotiation |
TheLanguagePriority sets the precedence of language variants for the case where the client does not express a preference, when handling a Multiviews request. The list ofMIME-lang are in order of decreasing preference.
LanguagePriority en fr de
For a request forfoo.html, wherefoo.html.fr andfoo.html.de both existed, but the browser did not express a language preference, thenfoo.html.fr would be returned.
Note that this directive only has an effect if a 'best' language cannot be determined by any other means or theForceLanguagePriority directive is notNone. In general, the client determines the language preference, not the server.
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