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HTTP::Negotiate(3)    User Contributed Perl Documentation   HTTP::Negotiate(3)

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@aas.no>

perl v5.12.1                      2008-09-24                HTTP::Negotiate(3)
 

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