173 lines
6.3 KiB
Python
173 lines
6.3 KiB
Python
# Copyright (C) 2007 Joe Gregorio
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#
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# Licensed under the MIT License
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"""MIME-Type Parser
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This module provides basic functions for handling mime-types. It can handle
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matching mime-types against a list of media-ranges. See section 14.1 of the
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HTTP specification [RFC 2616] for a complete explanation.
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http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
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Contents:
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- parse_mime_type(): Parses a mime-type into its component parts.
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- parse_media_range(): Media-ranges are mime-types with wild-cards and a 'q'
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quality parameter.
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- quality(): Determines the quality ('q') of a mime-type when
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compared against a list of media-ranges.
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- quality_parsed(): Just like quality() except the second parameter must be
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pre-parsed.
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- best_match(): Choose the mime-type with the highest quality ('q')
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from a list of candidates.
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"""
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__version__ = '0.1.3'
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__author__ = 'Joe Gregorio'
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__email__ = 'joe@bitworking.org'
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__license__ = 'MIT License'
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__credits__ = ''
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def parse_mime_type(mime_type):
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"""Parses a mime-type into its component parts.
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Carves up a mime-type and returns a tuple of the (type, subtype, params)
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where 'params' is a dictionary of all the parameters for the media range.
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For example, the media range 'application/xhtml;q=0.5' would get parsed
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into:
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('application', 'xhtml', {'q', '0.5'})
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"""
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parts = mime_type.split(';')
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params = dict([tuple([s.strip() for s in param.split('=', 1)])\
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for param in parts[1:]
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])
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full_type = parts[0].strip()
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# Java URLConnection class sends an Accept header that includes a
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# single '*'. Turn it into a legal wildcard.
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if full_type == '*':
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full_type = '*/*'
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(type, subtype) = full_type.split('/')
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return (type.strip(), subtype.strip(), params)
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def parse_media_range(range):
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"""Parse a media-range into its component parts.
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Carves up a media range and returns a tuple of the (type, subtype,
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params) where 'params' is a dictionary of all the parameters for the media
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range. For example, the media range 'application/*;q=0.5' would get parsed
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into:
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('application', '*', {'q', '0.5'})
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In addition this function also guarantees that there is a value for 'q'
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in the params dictionary, filling it in with a proper default if
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necessary.
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"""
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(type, subtype, params) = parse_mime_type(range)
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if not params.has_key('q') or not params['q'] or \
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not float(params['q']) or float(params['q']) > 1\
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or float(params['q']) < 0:
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params['q'] = '1'
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return (type, subtype, params)
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def fitness_and_quality_parsed(mime_type, parsed_ranges):
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"""Find the best match for a mime-type amongst parsed media-ranges.
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Find the best match for a given mime-type against a list of media_ranges
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that have already been parsed by parse_media_range(). Returns a tuple of
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the fitness value and the value of the 'q' quality parameter of the best
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match, or (-1, 0) if no match was found. Just as for quality_parsed(),
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'parsed_ranges' must be a list of parsed media ranges.
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"""
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best_fitness = -1
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best_fit_q = 0
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(target_type, target_subtype, target_params) =\
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parse_media_range(mime_type)
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for (type, subtype, params) in parsed_ranges:
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type_match = (type == target_type or\
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type == '*' or\
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target_type == '*')
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subtype_match = (subtype == target_subtype or\
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subtype == '*' or\
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target_subtype == '*')
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if type_match and subtype_match:
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param_matches = reduce(lambda x, y: x + y, [1 for (key, value) in \
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target_params.iteritems() if key != 'q' and \
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params.has_key(key) and value == params[key]], 0)
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fitness = (type == target_type) and 100 or 0
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fitness += (subtype == target_subtype) and 10 or 0
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fitness += param_matches
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if fitness > best_fitness:
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best_fitness = fitness
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best_fit_q = params['q']
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return best_fitness, float(best_fit_q)
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def quality_parsed(mime_type, parsed_ranges):
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"""Find the best match for a mime-type amongst parsed media-ranges.
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Find the best match for a given mime-type against a list of media_ranges
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that have already been parsed by parse_media_range(). Returns the 'q'
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quality parameter of the best match, 0 if no match was found. This function
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bahaves the same as quality() except that 'parsed_ranges' must be a list of
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parsed media ranges.
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"""
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return fitness_and_quality_parsed(mime_type, parsed_ranges)[1]
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def quality(mime_type, ranges):
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"""Return the quality ('q') of a mime-type against a list of media-ranges.
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Returns the quality 'q' of a mime-type when compared against the
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media-ranges in ranges. For example:
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>>> quality('text/html','text/*;q=0.3, text/html;q=0.7,
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text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5')
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0.7
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"""
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parsed_ranges = [parse_media_range(r) for r in ranges.split(',')]
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return quality_parsed(mime_type, parsed_ranges)
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def best_match(supported, header):
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"""Return mime-type with the highest quality ('q') from list of candidates.
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Takes a list of supported mime-types and finds the best match for all the
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media-ranges listed in header. The value of header must be a string that
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conforms to the format of the HTTP Accept: header. The value of 'supported'
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is a list of mime-types. The list of supported mime-types should be sorted
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in order of increasing desirability, in case of a situation where there is
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a tie.
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>>> best_match(['application/xbel+xml', 'text/xml'],
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'text/*;q=0.5,*/*; q=0.1')
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'text/xml'
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"""
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split_header = _filter_blank(header.split(','))
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parsed_header = [parse_media_range(r) for r in split_header]
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weighted_matches = []
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pos = 0
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for mime_type in supported:
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weighted_matches.append((fitness_and_quality_parsed(mime_type,
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parsed_header), pos, mime_type))
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pos += 1
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weighted_matches.sort()
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return weighted_matches[-1][0][1] and weighted_matches[-1][2] or ''
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def _filter_blank(i):
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for s in i:
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if s.strip():
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yield s
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