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1 # Copyright (C) 2007 Joe Gregorio | |
2 # | |
3 # Licensed under the MIT License | |
4 | |
5 """MIME-Type Parser | |
6 | |
7 This module provides basic functions for handling mime-types. It can handle | |
8 matching mime-types against a list of media-ranges. See section 14.1 of the | |
9 HTTP specification [RFC 2616] for a complete explanation. | |
10 | |
11 http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1 | |
12 | |
13 Contents: | |
14 - parse_mime_type(): Parses a mime-type into its component parts. | |
15 - parse_media_range(): Media-ranges are mime-types with wild-cards and a 'q' | |
16 quality parameter. | |
17 - quality(): Determines the quality ('q') of a mime-type when | |
18 compared against a list of media-ranges. | |
19 - quality_parsed(): Just like quality() except the second parameter must be | |
20 pre-parsed. | |
21 - best_match(): Choose the mime-type with the highest quality ('q') | |
22 from a list of candidates. | |
23 """ | |
24 | |
25 __version__ = '0.1.3' | |
26 __author__ = 'Joe Gregorio' | |
27 __email__ = 'joe@bitworking.org' | |
28 __license__ = 'MIT License' | |
29 __credits__ = '' | |
30 | |
31 | |
32 def parse_mime_type(mime_type): | |
33 """Parses a mime-type into its component parts. | |
34 | |
35 Carves up a mime-type and returns a tuple of the (type, subtype, params) | |
36 where 'params' is a dictionary of all the parameters for the media range. | |
37 For example, the media range 'application/xhtml;q=0.5' would get parsed | |
38 into: | |
39 | |
40 ('application', 'xhtml', {'q', '0.5'}) | |
41 """ | |
42 parts = mime_type.split(';') | |
43 params = dict([tuple([s.strip() for s in param.split('=', 1)])\ | |
44 for param in parts[1:] | |
45 ]) | |
46 full_type = parts[0].strip() | |
47 # Java URLConnection class sends an Accept header that includes a | |
48 # single '*'. Turn it into a legal wildcard. | |
49 if full_type == '*': | |
50 full_type = '*/*' | |
51 (type, subtype) = full_type.split('/') | |
52 | |
53 return (type.strip(), subtype.strip(), params) | |
54 | |
55 | |
56 def parse_media_range(range): | |
57 """Parse a media-range into its component parts. | |
58 | |
59 Carves up a media range and returns a tuple of the (type, subtype, | |
60 params) where 'params' is a dictionary of all the parameters for the media | |
61 range. For example, the media range 'application/*;q=0.5' would get parsed | |
62 into: | |
63 | |
64 ('application', '*', {'q', '0.5'}) | |
65 | |
66 In addition this function also guarantees that there is a value for 'q' | |
67 in the params dictionary, filling it in with a proper default if | |
68 necessary. | |
69 """ | |
70 (type, subtype, params) = parse_mime_type(range) | |
71 if not params.has_key('q') or not params['q'] or \ | |
72 not float(params['q']) or float(params['q']) > 1\ | |
73 or float(params['q']) < 0: | |
74 params['q'] = '1' | |
75 | |
76 return (type, subtype, params) | |
77 | |
78 | |
79 def fitness_and_quality_parsed(mime_type, parsed_ranges): | |
80 """Find the best match for a mime-type amongst parsed media-ranges. | |
81 | |
82 Find the best match for a given mime-type against a list of media_ranges | |
83 that have already been parsed by parse_media_range(). Returns a tuple of | |
84 the fitness value and the value of the 'q' quality parameter of the best | |
85 match, or (-1, 0) if no match was found. Just as for quality_parsed(), | |
86 'parsed_ranges' must be a list of parsed media ranges. | |
87 """ | |
88 best_fitness = -1 | |
89 best_fit_q = 0 | |
90 (target_type, target_subtype, target_params) =\ | |
91 parse_media_range(mime_type) | |
92 for (type, subtype, params) in parsed_ranges: | |
93 type_match = (type == target_type or\ | |
94 type == '*' or\ | |
95 target_type == '*') | |
96 subtype_match = (subtype == target_subtype or\ | |
97 subtype == '*' or\ | |
98 target_subtype == '*') | |
99 if type_match and subtype_match: | |
100 param_matches = reduce(lambda x, y: x + y, [1 for (key, value) in \ | |
101 target_params.iteritems() if key != 'q' and \ | |
102 params.has_key(key) and value == params[key]], 0) | |
103 fitness = (type == target_type) and 100 or 0 | |
104 fitness += (subtype == target_subtype) and 10 or 0 | |
105 fitness += param_matches | |
106 if fitness > best_fitness: | |
107 best_fitness = fitness | |
108 best_fit_q = params['q'] | |
109 | |
110 return best_fitness, float(best_fit_q) | |
111 | |
112 | |
113 def quality_parsed(mime_type, parsed_ranges): | |
114 """Find the best match for a mime-type amongst parsed media-ranges. | |
115 | |
116 Find the best match for a given mime-type against a list of media_ranges | |
117 that have already been parsed by parse_media_range(). Returns the 'q' | |
118 quality parameter of the best match, 0 if no match was found. This function | |
119 bahaves the same as quality() except that 'parsed_ranges' must be a list of | |
120 parsed media ranges. | |
121 """ | |
122 | |
123 return fitness_and_quality_parsed(mime_type, parsed_ranges)[1] | |
124 | |
125 | |
126 def quality(mime_type, ranges): | |
127 """Return the quality ('q') of a mime-type against a list of media-ranges. | |
128 | |
129 Returns the quality 'q' of a mime-type when compared against the | |
130 media-ranges in ranges. For example: | |
131 | |
132 >>> quality('text/html','text/*;q=0.3, text/html;q=0.7, | |
133 text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5') | |
134 0.7 | |
135 | |
136 """ | |
137 parsed_ranges = [parse_media_range(r) for r in ranges.split(',')] | |
138 | |
139 return quality_parsed(mime_type, parsed_ranges) | |
140 | |
141 | |
142 def best_match(supported, header): | |
143 """Return mime-type with the highest quality ('q') from list of candidates. | |
144 | |
145 Takes a list of supported mime-types and finds the best match for all the | |
146 media-ranges listed in header. The value of header must be a string that | |
147 conforms to the format of the HTTP Accept: header. The value of 'supported' | |
148 is a list of mime-types. The list of supported mime-types should be sorted | |
149 in order of increasing desirability, in case of a situation where there is | |
150 a tie. | |
151 | |
152 >>> best_match(['application/xbel+xml', 'text/xml'], | |
153 'text/*;q=0.5,*/*; q=0.1') | |
154 'text/xml' | |
155 """ | |
156 split_header = _filter_blank(header.split(',')) | |
157 parsed_header = [parse_media_range(r) for r in split_header] | |
158 weighted_matches = [] | |
159 pos = 0 | |
160 for mime_type in supported: | |
161 weighted_matches.append((fitness_and_quality_parsed(mime_type, | |
162 parsed_header), pos, mime_type)) | |
163 pos += 1 | |
164 weighted_matches.sort() | |
165 | |
166 return weighted_matches[-1][0][1] and weighted_matches[-1][2] or '' | |
167 | |
168 | |
169 def _filter_blank(i): | |
170 for s in i: | |
171 if s.strip(): | |
172 yield s | |
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