183 lines
6.4 KiB
Python
183 lines
6.4 KiB
Python
# Copyright 2014 Joe Gregorio
|
|
#
|
|
# Licensed under the MIT License
|
|
|
|
"""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 __future__ import absolute_import
|
|
from functools import reduce
|
|
import six
|
|
|
|
__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 = reduce(
|
|
lambda x, y: x + y,
|
|
[
|
|
1
|
|
for (key, value) in six.iteritems(target_params)
|
|
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
|