Package apiclient :: Module mimeparse |
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# Source Code for Module apiclient.mimeparse

      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
    173