codekingpro/portable-devtools

1# Copyright 2014 Joe Gregorio2#3# Licensed under the MIT License4 5"""MIME-Type Parser6 7This module provides basic functions for handling mime-types. It can handle8matching mime-types against a list of media-ranges. See section 14.1 of the9HTTP specification [RFC 2616] for a complete explanation.10 11   http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.112 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 when18                          compared against a list of media-ranges.19 - quality_parsed():    Just like quality() except the second parameter must be20                          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_import25 26from functools import reduce27 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 parsed41    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 a51    # 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 media64    range.  For example, the media range 'application/*;q=0.5' would get parsed65    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 if71    necessary.72    """73    (type, subtype, params) = parse_mime_type(range)74    if (75        "q" not in params76        or not params["q"]77        or not float(params["q"])78        or float(params["q"]) > 179        or float(params["q"]) < 080    ):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_ranges90    that have already been parsed by parse_media_range(). Returns a tuple of91    the fitness value and the value of the 'q' quality parameter of the best92    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 = -196    best_fit_q = 097    (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                    1108                    for (key, value) in target_params.items()109                    if key != "q" and key in params and value == params[key]110                ],111                0,112            )113            fitness = (type == target_type) and 100 or 0114            fitness += (subtype == target_subtype) and 10 or 0115            fitness += param_matches116            if fitness > best_fitness:117                best_fitness = fitness118                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_ranges127    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 function129    bahaves the same as quality() except that 'parsed_ranges' must be a list of130    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 the140    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    0.7145 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 the156    media-ranges listed in header. The value of header must be a string that157    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 sorted159    in order of increasing desirability, in case of a situation where there is160    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 = 0170    for mime_type in supported:171        weighted_matches.append(172            (fitness_and_quality_parsed(mime_type, parsed_header), pos, mime_type)173        )174        pos += 1175    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 s184