mod_negotiation - Apache HTTP Server Version 2.4









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Apache HTTP Server Version 2.4



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Apache Module mod_negotiation

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Description:Provides for content negotiation
Status:Base
Module Identifier:negotiation_module
Source File:mod_negotiation.c
Summary

    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.

    
      A type map (a file with the handler
      type-map) which explicitly lists the files
      containing the variants.

      A Multiviews search (enabled by the Multiviews
      Options), where the server does
      an implicit filename pattern match, and choose from amongst the
      results.
    

Topics

 Type maps
 Multiviews
Directives

 CacheNegotiatedDocs
 ForceLanguagePriority
 LanguagePriority

Bugfix checklisthttpd changelogKnown issuesReport a bugSee also

Options
mod_mime
Content
Negotiation
Environment Variables
Comments


Type maps
    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:
      The encoding of the file. Apache only recognizes
      encodings that are defined by an 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:
      The language(s) of the variant, as an Internet standard
      language tag (RFC 1766). An example is en,
      meaning English. If the variant contains more than one
      language, they are separated by a comma.

      Content-Length:
      The length of the file, in bytes. If this header is not
      present, then the actual length of the file is used.

      Content-Type:

      
        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 name=value. Common
        parameters include:

        
          level
          an integer specifying the version of the media type.
          For text/html this defaults to 2, otherwise
          0.

          qs
          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 qs values are therefore specific to a given
          resource.
        

        Example
          Content-Type: image/jpeg; qs=0.8
        
      

      URI:
      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.

      Body:
      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:
        Body:----xyz----
        <html>
        <body>
        <p>Content of the page.</p>
        </body>
        </html>
        ----xyz----
      
      
    

    Consider, for example, a resource called
    document.html which is available in English, French,
    and German. The files for each of these are called
    document.html.en, document.html.fr, and
    document.html.de, respectively. The type map file will
    be called document.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 the
    type-map handler with an AddHandler directive:

    AddHandler type-map .var


    A request for document.html.var in this directory will
    result in choosing the variant which most closely matches the language preference
    specified in the user's Accept-Language request
    header.

    If Multiviews is enabled, and MultiviewsMatch is set to "handlers" or "any",  a request to
    document.html will discover document.html.var and
    continue negotiating with the explicit type map.

    Other configuration directives, such as Alias can be used to map document.html to
    document.html.var.



Multiviews
    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.


CacheNegotiatedDocs Directive

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

    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.




ForceLanguagePriority Directive

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

    The ForceLanguagePriority directive uses
    the given LanguagePriority to satisfy
    negotiation 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.

See also

AddLanguage



LanguagePriority Directive

Description:The precedence 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.

See also

AddLanguage




Available Languages:  en  |
 fr  |
 ja 

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