Apache HTTP Server Version 2.0
Apache HTTP Server Version 2.0
| Description: | Provides for content 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.MultiViews Options), 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 encodings x-compress for compress'd files, and x-gzip for gzip'd files. The x- 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----
A MultiViews search is enabled by the MultiViews Options. If the server receives a request for /some/dir/foo and /some/dir/foo does not exist, then the server reads the directory looking for all files named foo.*, 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.
The MultiViewsMatch 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 be cached by proxy servers |
|---|---|
| Syntax: | CacheNegotiatedDocs On|Off |
| Default: | CacheNegotiatedDocs Off |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_negotiation |
| Compatibility: | The syntax changed in version 2.0. |
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.
Prior to version 2.0, CacheNegotiatedDocs did not take an argument; it was turned on by the presence of the directive by itself.
| Description: | Action to take if a single acceptable document is not found |
|---|---|
| Syntax: | ForceLanguagePriority None|Prefer|Fallback [Prefer|Fallback] |
| Default: | ForceLanguagePriority Prefer |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_negotiation |
| Compatibility: | Available in version 2.0.30 and later |
The ForceLanguagePriority directive uses the given LanguagePriority to satisfy negotation where the server could otherwise not return a single matching document.
ForceLanguagePriority Prefer uses LanguagePriority 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 the first matching variant, en, will be served.
LanguagePriority en fr de
ForceLanguagePriority Prefer
ForceLanguagePriority Fallback uses LanguagePriority 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 language response, but such a variant isn't found, then the first variant from the LanguagePriority list below will be served.
LanguagePriority en fr de
ForceLanguagePriority Fallback
Both options, Prefer and Fallback, may be specified, so either the first matching variant from LanguagePriority 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 precendence of language variants for cases where the client does not express a preference |
|---|---|
| Syntax: | LanguagePriority MIME-lang [MIME-lang] ... |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_negotiation |
The LanguagePriority 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 MIME-lang are in order of decreasing preference.
LanguagePriority en fr de
For a request for foo.html, where foo.html.fr and foo.html.de both existed, but the browser did not express a language preference, then foo.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 the ForceLanguagePriority directive is not None. In general, the client determines the language preference, not the server.