File size: 5,745 Bytes
ae4627d | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 | """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 explanation.
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
Contents:
- parse_mime_type(): Parses a mime-type into its 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.
"""
__version__ = "0.1.3"
__author__ = 'Joe Gregorio'
__email__ = "joe@bitworking.org"
__credits__ = ""
def parse_mime_type(mime_type):
"""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("=", 1)])\
for param in parts[1:] ])
full_type = parts[0].strip()
# Java URLConnection class sends an Accept header that includes a single "*"
# Turn it into a legal wildcard.
if full_type == '*': full_type = '*/*'
(type, subtype) = full_type.split("/")
return (type.strip(), subtype.strip(), params)
def parse_media_range(range):
"""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 params.has_key('q') 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)
def fitness_and_quality_parsed(mime_type, parsed_ranges):
"""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 a tuple of
the fitness value and the value of the 'q' quality
parameter of the best match, or (-1, 0) if no match
was found. Just as for quality_parsed(), 'parsed_ranges'
must be a list of parsed media ranges. """
best_fitness = -1
best_fit_q = 0
(target_type, target_subtype, target_params) =\
parse_media_range(mime_type)
for (type, subtype, params) in parsed_ranges:
if (type == target_type or type == '*' or target_type == '*') and \
(subtype == target_subtype or subtype == '*' or target_subtype == '*'):
param_matches = reduce(lambda x, y: x+y, [1 for (key, value) in \
target_params.iteritems() if key != 'q' and \
params.has_key(key) and value == params[key]], 0)
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 best_fitness, float(best_fit_q)
def quality_parsed(mime_type, parsed_ranges):
"""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. """
return fitness_and_quality_parsed(mime_type, parsed_ranges)[1]
def quality(mime_type, ranges):
"""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)
def best_match(supported, header):
"""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. The list of supported mime-types should be sorted
in order of increasing desirability, in case of a situation
where there is a tie
>>> 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 _filter_blank(header.split(","))]
weighted_matches = []
pos = 0
for mime_type in supported:
weighted_matches.append((fitness_and_quality_parsed(mime_type,
parsed_header), pos, mime_type))
pos += 1
weighted_matches.sort()
return weighted_matches[-1][0][1] and weighted_matches[-1][2] or ''
def _filter_blank(i):
for s in i:
if s.strip():
yield s
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