Merge pull request #2420 from mrpau/hotfix/add-mimeparse-py

Add `mimeparse.py` from `nalanda-rct3` because `tastypie` needs it.

Author: aronasorman

python-packages/mimeparse.py

@@ -0,0 +1,168 @@
+"""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.
+"""
+from functools import reduce
+
+__version__ = '0.1.4'
+__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 not 'q' 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 = reduce(lambda x, y: x + y, [1 for (key, value) in
+                                   list(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