Section: User Contributed Perl Documentation (3pm)
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);
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,
$content_length] whose meanings are described below. The
$content_languagecan 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::DEBUGvariable is set to TRUE, then a lot of noise is generated on STDOUT during evaluation of choose().
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''.
text/html text/html;version=2.0 text/plain image/gif image/jpg:
"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:
The language tags are defined by RFC 3066. Examples are:
no Norwegian en International English en-US US English en-cockney:
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):
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.
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: iso-8859-1, unicode-1-1:
Accept-Encoding: compress, gzip:
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 1996,2001 Gisle Aas.
Gisle Aas <firstname.lastname@example.org>
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