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Diffstat (limited to 'lib/mimeparse/mimeparse.py')
| -rw-r--r-- | lib/mimeparse/mimeparse.py | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/lib/mimeparse/mimeparse.py b/lib/mimeparse/mimeparse.py new file mode 100644 index 0000000000..7fb4e43477 --- /dev/null +++ b/lib/mimeparse/mimeparse.py @@ -0,0 +1,167 @@ +"""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' +__license__ = 'MIT License' +__credits__ = '' + + +def parse_mime_type(mime_type): + """Parses a mime-type into its component parts. + + 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): + """Parse a media-range into its component parts. + + 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 'q' not 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) + + +def fitness_and_quality_parsed(mime_type, parsed_ranges): + """Find the best match for a mime-type amongst parsed media-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: + type_match = (type == target_type or\ + type == '*' or\ + target_type == '*') + subtype_match = (subtype == target_subtype or\ + subtype == '*' or\ + target_subtype == '*') + if type_match and subtype_match: + param_matches = sum([1 for (key, value) in \ + target_params.items() if key != 'q' and \ + key in params 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 mime-type amongst parsed media-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): + """Return the quality ('q') of a mime-type against a list of media-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): + """Return mime-type with the highest quality ('q') from list of candidates. + + 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' + """ + split_header = _filter_blank(header.split(',')) + parsed_header = [parse_media_range(r) for r in split_header] + 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 |