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"""MIME-Type Parser
This module provides basic functions for handling mime-types. It can handle matching mime-types against a list of media-ranges. See section 14.1 of the HTTP specification [RFC 2616] for a complete explaination.
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
Contents: - parse_mime_type(): Parses a mime-type into it's component parts. - parse_media_range(): Media-ranges are mime-types with wild-cards and a 'q' quality parameter. - quality(): Determines the quality ('q') of a mime-type when compared against a list of media-ranges. - quality_parsed(): Just like quality() except the second parameter must be pre-parsed. - best_match(): Choose the mime-type with the highest quality ('q') from a list of candidates. """
"""Carves up a mime_type and returns a tuple of the (type, subtype, params) where 'params' is a dictionary of all the parameters for the media range. For example, the media range 'application/xhtml;q=0.5' would get parsed into:
('application', 'xhtml', {'q', '0.5'}) """ parts = mime_type.split(";") params = dict([tuple([s.strip() for s in param.split("=")])\ for param in parts[1:]]) (type, subtype) = parts[0].split("/") return (type.strip(), subtype.strip(), params)
"""Carves up a media range and returns a tuple of the (type, subtype, params) where 'params' is a dictionary of all the parameters for the media range. For example, the media range 'application/*;q=0.5' would get parsed into:
('application', '*', {'q', '0.5'})
In addition this function also guarantees that there is a value for 'q' in the params dictionary, filling it in with a proper default if necessary. """ (type, subtype, params) = parse_mime_type(range) if not 'q' in params or not params['q'] or \ not float(params['q']) or float(params['q']) > 1\ or float(params['q']) < 0: params['q'] = '1' return (type, subtype, params)
"""Find the best match for a given mime_type against a list of media_ranges that have already been parsed by parse_media_range(). Returns the 'q' quality parameter of the best match, 0 if no match was found. This function bahaves the same as quality() except that 'parsed_ranges' must be a list of parsed media ranges. """ best_fitness = -1 best_match = "" best_fit_q = 0 (target_type, target_subtype, target_params) =\ parse_media_range(mime_type) for (type, subtype, params) in parsed_ranges: param_matches = reduce(lambda x, y: x + y, [1 for (key, value) in \ target_params.iteritems() if key != 'q' and \ key in params and value == params[key]], 0) if (type == target_type or type == '*' or target_type == '*') and \ (subtype == target_subtype or subtype == '*' or target_subtype == '*'): fitness = (type == target_type) and 100 or 0 fitness += (subtype == target_subtype) and 10 or 0 fitness += param_matches if fitness > best_fitness: best_fitness = fitness best_fit_q = params['q']
return float(best_fit_q)
"""Returns the quality 'q' of a mime_type when compared against the media-ranges in ranges. For example:
>>> quality('text/html','text/*;q=0.3, text/html;q=0.7, text/html;level=1, ' 'text/html;level=2;q=0.4, */*;q=0.5') 0.7
""" parsed_ranges = [parse_media_range(r) for r in ranges.split(",")] return quality_parsed(mime_type, parsed_ranges)
"""Takes a list of supported mime-types and finds the best match for all the media-ranges listed in header. The value of header must be a string that conforms to the format of the HTTP Accept: header. The value of 'supported' is a list of mime-types.
>>> best_match(['application/xbel+xml', 'text/xml'], 'text/*;q=0.5,*/*; q=0.1') 'text/xml' """ parsed_header = [parse_media_range(r) for r in header.split(",")] weighted_matches = [(quality_parsed(mime_type, parsed_header), mime_type)\ for mime_type in supported] weighted_matches.sort() return weighted_matches[-1][0] and weighted_matches[-1][1] or ''
import unittest
class TestMimeParsing(unittest.TestCase):
def test_parse_media_range(self): self.assert_(('application', 'xml', {'q': '1'}) == parse_media_range('application/xml;q=1')) self.assertEqual(('application', 'xml', {'q': '1'}), parse_media_range('application/xml')) self.assertEqual(('application', 'xml', {'q': '1'}), parse_media_range('application/xml;q=')) self.assertEqual(('application', 'xml', {'q': '1'}), parse_media_range('application/xml ; q=')) self.assertEqual(('application', 'xml', {'q': '1', 'b': 'other'}), parse_media_range('application/xml ; q=1;b=other')) self.assertEqual(('application', 'xml', {'q': '1', 'b': 'other'}), parse_media_range('application/xml ; q=2;b=other'))
def test_rfc_2616_example(self): accept = "text/*;q=0.3, text/html;q=0.7, text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5" self.assertEqual(1, quality("text/html;level=1", accept)) self.assertEqual(0.7, quality("text/html", accept)) self.assertEqual(0.3, quality("text/plain", accept)) self.assertEqual(0.5, quality("image/jpeg", accept)) self.assertEqual(0.4, quality("text/html;level=2", accept)) self.assertEqual(0.7, quality("text/html;level=3", accept))
def test_best_match(self): mime_types_supported = ['application/xbel+xml', 'application/xml'] # direct match self.assertEqual(best_match(mime_types_supported, 'application/xbel+xml'), 'application/xbel+xml') # direct match with a q parameter self.assertEqual(best_match(mime_types_supported, 'application/xbel+xml; q=1'), 'application/xbel+xml') # direct match of our second choice with a q parameter self.assertEqual(best_match(mime_types_supported, 'application/xml; q=1'), 'application/xml') # match using a subtype wildcard self.assertEqual(best_match(mime_types_supported, 'application/*; q=1'), 'application/xml') # match using a type wildcard self.assertEqual(best_match(mime_types_supported, '*/*'), 'application/xml')
mime_types_supported = ['application/xbel+xml', 'text/xml'] # match using a type versus a lower weighted subtype self.assertEqual(best_match(mime_types_supported, 'text/*;q=0.5,*/*; q=0.1'), 'text/xml') # fail to match anything self.assertEqual(best_match(mime_types_supported, 'text/html,application/atom+xml; q=0.9'), '')
def test_support_wildcards(self): mime_types_supported = ['image/*', 'application/xml'] # match using a type wildcard self.assertEqual(best_match(mime_types_supported, 'image/png'), 'image/*') # match using a wildcard for both requested and supported self.assertEqual(best_match(mime_types_supported, 'image/*'), 'image/*')
unittest.main() |