1# Copyright 2014 Joe Gregorio 2# 3# Licensed under the MIT License 4 5"""MIME-Type Parser 6 7This module provides basic functions for handling mime-types. It can handle 8matching mime-types against a list of media-ranges. See section 14.1 of the 9HTTP specification [RFC 2616] for a complete explanation. 10 11 http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1 12 13Contents: 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""" 24from __future__ import absolute_import 25from functools import reduce 26import six 27 28__version__ = "0.1.3" 29__author__ = "Joe Gregorio" 30__email__ = "joe@bitworking.org" 31__license__ = "MIT License" 32__credits__ = "" 33 34 35def parse_mime_type(mime_type): 36 """Parses a mime-type into its component parts. 37 38 Carves up a mime-type and returns a tuple of the (type, subtype, params) 39 where 'params' is a dictionary of all the parameters for the media range. 40 For example, the media range 'application/xhtml;q=0.5' would get parsed 41 into: 42 43 ('application', 'xhtml', {'q', '0.5'}) 44 """ 45 parts = mime_type.split(";") 46 params = dict( 47 [tuple([s.strip() for s in param.split("=", 1)]) for param in parts[1:]] 48 ) 49 full_type = parts[0].strip() 50 # Java URLConnection class sends an Accept header that includes a 51 # single '*'. Turn it into a legal wildcard. 52 if full_type == "*": 53 full_type = "*/*" 54 (type, subtype) = full_type.split("/") 55 56 return (type.strip(), subtype.strip(), params) 57 58 59def parse_media_range(range): 60 """Parse a media-range into its component parts. 61 62 Carves up a media range and returns a tuple of the (type, subtype, 63 params) where 'params' is a dictionary of all the parameters for the media 64 range. For example, the media range 'application/*;q=0.5' would get parsed 65 into: 66 67 ('application', '*', {'q', '0.5'}) 68 69 In addition this function also guarantees that there is a value for 'q' 70 in the params dictionary, filling it in with a proper default if 71 necessary. 72 """ 73 (type, subtype, params) = parse_mime_type(range) 74 if ( 75 "q" not in params 76 or not params["q"] 77 or not float(params["q"]) 78 or float(params["q"]) > 1 79 or float(params["q"]) < 0 80 ): 81 params["q"] = "1" 82 83 return (type, subtype, params) 84 85 86def fitness_and_quality_parsed(mime_type, parsed_ranges): 87 """Find the best match for a mime-type amongst parsed media-ranges. 88 89 Find the best match for a given mime-type against a list of media_ranges 90 that have already been parsed by parse_media_range(). Returns a tuple of 91 the fitness value and the value of the 'q' quality parameter of the best 92 match, or (-1, 0) if no match was found. Just as for quality_parsed(), 93 'parsed_ranges' must be a list of parsed media ranges. 94 """ 95 best_fitness = -1 96 best_fit_q = 0 97 (target_type, target_subtype, target_params) = parse_media_range(mime_type) 98 for (type, subtype, params) in parsed_ranges: 99 type_match = type == target_type or type == "*" or target_type == "*" 100 subtype_match = ( 101 subtype == target_subtype or subtype == "*" or target_subtype == "*" 102 ) 103 if type_match and subtype_match: 104 param_matches = reduce( 105 lambda x, y: x + y, 106 [ 107 1 108 for (key, value) in six.iteritems(target_params) 109 if key != "q" and key in params and value == params[key] 110 ], 111 0, 112 ) 113 fitness = (type == target_type) and 100 or 0 114 fitness += (subtype == target_subtype) and 10 or 0 115 fitness += param_matches 116 if fitness > best_fitness: 117 best_fitness = fitness 118 best_fit_q = params["q"] 119 120 return best_fitness, float(best_fit_q) 121 122 123def quality_parsed(mime_type, parsed_ranges): 124 """Find the best match for a mime-type amongst parsed media-ranges. 125 126 Find the best match for a given mime-type against a list of media_ranges 127 that have already been parsed by parse_media_range(). Returns the 'q' 128 quality parameter of the best match, 0 if no match was found. This function 129 bahaves the same as quality() except that 'parsed_ranges' must be a list of 130 parsed media ranges. 131 """ 132 133 return fitness_and_quality_parsed(mime_type, parsed_ranges)[1] 134 135 136def quality(mime_type, ranges): 137 """Return the quality ('q') of a mime-type against a list of media-ranges. 138 139 Returns the quality 'q' of a mime-type when compared against the 140 media-ranges in ranges. For example: 141 142 >>> quality('text/html','text/*;q=0.3, text/html;q=0.7, 143 text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5') 144 0.7 145 146 """ 147 parsed_ranges = [parse_media_range(r) for r in ranges.split(",")] 148 149 return quality_parsed(mime_type, parsed_ranges) 150 151 152def best_match(supported, header): 153 """Return mime-type with the highest quality ('q') from list of candidates. 154 155 Takes a list of supported mime-types and finds the best match for all the 156 media-ranges listed in header. The value of header must be a string that 157 conforms to the format of the HTTP Accept: header. The value of 'supported' 158 is a list of mime-types. The list of supported mime-types should be sorted 159 in order of increasing desirability, in case of a situation where there is 160 a tie. 161 162 >>> best_match(['application/xbel+xml', 'text/xml'], 163 'text/*;q=0.5,*/*; q=0.1') 164 'text/xml' 165 """ 166 split_header = _filter_blank(header.split(",")) 167 parsed_header = [parse_media_range(r) for r in split_header] 168 weighted_matches = [] 169 pos = 0 170 for mime_type in supported: 171 weighted_matches.append( 172 (fitness_and_quality_parsed(mime_type, parsed_header), pos, mime_type) 173 ) 174 pos += 1 175 weighted_matches.sort() 176 177 return weighted_matches[-1][0][1] and weighted_matches[-1][2] or "" 178 179 180def _filter_blank(i): 181 for s in i: 182 if s.strip(): 183 yield s 184