phpman > perldoc > HTTP::Negotiate(3pm)

NAME
    HTTP::Negotiate - choose a variant to serve

SYNOPSIS
     use HTTP::Negotiate qw(choose);

     #  ID       QS     Content-Type   Encoding Char-Set        Lang   Size
     $variants =
      [['var1',  1.000, 'text/html',   undef,   'iso-8859-1',   'en',   3000],
       ['var2',  0.950, 'text/plain',  'gzip',  'us-ascii',     'no',    400],
       ['var3',  0.3,   'image/gif',   undef,   undef,          undef, 43555],
      ];

     @preferred = choose($variants, $request_headers);
     $the_one   = choose($variants);

DESCRIPTION
    This module provides a complete implementation of the HTTP content negotiation algorithm
    specified in draft-ietf-http-v11-spec-00.ps chapter 12. Content negotiation allows for the
    selection of a preferred content representation based upon attributes of the negotiable variants
    and the value of the various Accept* header fields in the request.

    The variants are ordered by preference by calling the function choose().

    The first parameter is reference to an array of the variants to choose among. Each element in
    this array is an array with the values [$id, $qs, $content_type, $content_encoding, $charset,
    $content_language, $content_length] whose meanings are described below. The $content_encoding
    and $content_language can be either a single scalar value or an array reference if there are
    several values.

    The second optional parameter is either a HTTP::Headers or a HTTP::Request object which is
    searched for "Accept*" headers. If this parameter is missing, then the accept specification is
    initialized from the CGI environment variables HTTP_ACCEPT, HTTP_ACCEPT_CHARSET,
    HTTP_ACCEPT_ENCODING and HTTP_ACCEPT_LANGUAGE.

    In an array context, choose() returns a list of [variant identifier, calculated quality, size]
    tuples. The values are sorted by quality, highest quality first. If the calculated quality is
    the same for two variants, then they are sorted by size (smallest first). *E.g.*:

      (['var1', 1, 2000], ['var2', 0.3, 512], ['var3', 0.3, 1024]);

    Note that also zero quality variants are included in the return list even if these should never
    be served to the client.

    In a scalar context, it returns the identifier of the variant with the highest score or "undef"
    if none have non-zero quality.

    If the $HTTP::Negotiate::DEBUG variable is set to TRUE, then a lot of noise is generated on
    STDOUT during evaluation of choose().

VARIANTS
    A variant is described by a list of the following values. If the attribute does not make sense
    or is unknown for a variant, then use "undef" instead.

    identifier
       This is a string that you use as the name for the variant. This identifier for the preferred
       variants returned by choose().

    qs This is a number between 0.000 and 1.000 that describes the "source quality". This is what
       draft-ietf-http-v11-spec-00.ps says about this value:

       Source quality is measured by the content provider as representing the amount of degradation
       from the original source. For example, a picture in JPEG form would have a lower qs when
       translated to the XBM format, and much lower qs when translated to an ASCII-art
       representation. Note, however, that this is a function of the source - an original piece of
       ASCII-art may degrade in quality if it is captured in JPEG form. The qs values should be
       assigned to each variant by the content provider; if no qs value has been assigned, the
       default is generally "qs=1".

    content-type
       This is the media type of the variant. The media type does not include a charset attribute,
       but might contain other parameters. Examples are:

         text/html
         text/html;version=2.0
         text/plain
         image/gif
         image/jpg

    content-encoding
       This is one or more content encodings that has been applied to the variant. The content
       encoding is generally used as a modifier to the content media type. The most common content
       encodings are:

         gzip
         compress

    content-charset
       This is the character set used when the variant contains text. The charset value should
       generally be "undef" or one of these:

         us-ascii
         iso-8859-1 ... iso-8859-9
         iso-2022-jp
         iso-2022-jp-2
         iso-2022-kr
         unicode-1-1
         unicode-1-1-utf-7
         unicode-1-1-utf-8

    content-language
       This describes one or more languages that are used in the variant. Language is described like
       this in draft-ietf-http-v11-spec-00.ps: A language is in this context a natural language
       spoken, written, or otherwise conveyed by human beings for communication of information to
       other human beings. Computer languages are explicitly excluded.

       The language tags are defined by RFC 3066. Examples are:

         no               Norwegian
         en               International English
         en-US            US English
         en-cockney

    content-length
       This is the number of bytes used to represent the content.

ACCEPT HEADERS
    The following Accept* headers can be used for describing content preferences in a request (This
    description is an edited extract from draft-ietf-http-v11-spec-00.ps):

    Accept
       This header can be used to indicate a list of media ranges which are acceptable as a response
       to the request. The "*" character is used to group media types into ranges, with "*/*"
       indicating all media types and "type/*" indicating all subtypes of that type.

       The parameter q is used to indicate the quality factor, which represents the user's
       preference for that range of media types. The parameter mbx gives the maximum acceptable size
       of the response content. The default values are: q=1 and mbx=infinity. If no Accept header is
       present, then the client accepts all media types with q=1.

       For example:

         Accept: audio/*;q=0.2;mbx=200000, audio/basic

       would mean: "I prefer audio/basic (of any size), but send me any audio type if it is the best
       available after an 80% mark-down in quality and its size is less than 200000 bytes"

    Accept-Charset
       Used to indicate what character sets are acceptable for the response. The "us-ascii"
       character set is assumed to be acceptable for all user agents. If no Accept-Charset field is
       given, the default is that any charset is acceptable. Example:

         Accept-Charset: iso-8859-1, unicode-1-1

    Accept-Encoding
       Restricts the Content-Encoding values which are acceptable in the response. If no
       Accept-Encoding field is present, the server may assume that the client will accept any
       content encoding. An empty Accept-Encoding means that no content encoding is acceptable.
       Example:

         Accept-Encoding: compress, gzip

    Accept-Language
       This field is similar to Accept, but restricts the set of natural languages that are
       preferred in a response. Each language may be given an associated quality value which
       represents an estimate of the user's comprehension of that language. For example:

         Accept-Language: no, en-gb;q=0.8, de;q=0.55

       would mean: "I prefer Norwegian, but will accept British English (with 80% comprehension) or
       German (with 55% comprehension).

COPYRIGHT
    Copyright 1996,2001 Gisle Aas.

    This library is free software; you can redistribute it and/or modify it under the same terms as
    Perl itself.

AUTHOR
    Gisle Aas <gisle AT aas.no>