374 lines
13 KiB
Python
374 lines
13 KiB
Python
# -*- coding: utf-8 -*-
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"""
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flask_cors
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~~~~
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Flask-CORS is a simple extension to Flask allowing you to support cross
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origin resource sharing (CORS) using a simple decorator.
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:copyright: (c) 2014 by Cory Dolphin.
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:license: MIT, see LICENSE for more details.
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"""
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import re
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import logging
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import collections
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from datetime import timedelta
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from six import string_types
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from flask import request, current_app
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try:
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from flask import _app_ctx_stack as stack
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except ImportError:
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from flask import _request_ctx_stack as stack
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# Compatibility with old Pythons!
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if not hasattr(logging, 'NullHandler'):
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class NullHandler(logging.Handler):
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def emit(self, record):
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pass
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logging.NullHandler = NullHandler
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# Response Headers
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ACL_ORIGIN = 'Access-Control-Allow-Origin'
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ACL_METHODS = 'Access-Control-Allow-Methods'
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ACL_ALLOW_HEADERS = 'Access-Control-Allow-Headers'
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ACL_EXPOSE_HEADERS = 'Access-Control-Expose-Headers'
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ACL_CREDENTIALS = 'Access-Control-Allow-Credentials'
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ACL_MAX_AGE = 'Access-Control-Max-Age'
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# Request Header
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ACL_REQUEST_METHOD = 'Access-Control-Request-Method'
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ACL_REQUEST_HEADERS = 'Access-Control-Request-Headers'
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ALL_METHODS = ['GET', 'HEAD', 'POST', 'OPTIONS', 'PUT', 'PATCH', 'DELETE']
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CONFIG_OPTIONS = ['CORS_ORIGINS', 'CORS_METHODS', 'CORS_ALLOW_HEADERS',
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'CORS_EXPOSE_HEADERS', 'CORS_SUPPORTS_CREDENTIALS',
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'CORS_MAX_AGE', 'CORS_SEND_WILDCARD',
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'CORS_AUTOMATIC_OPTIONS', 'CORS_VARY_HEADER',
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'CORS_RESOURCES', 'CORS_INTERCEPT_EXCEPTIONS']
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# Attribute added to request object by decorator to indicate that CORS
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# was evaluated, in case the decorator and extension are both applied
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# to a view.
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FLASK_CORS_EVALUATED = '_FLASK_CORS_EVALUATED'
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# Strange, but this gets the type of a compiled regex, which is otherwise not
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# exposed in a public API.
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RegexObject = type(re.compile(''))
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DEFAULT_OPTIONS = dict(origins='*',
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methods=ALL_METHODS,
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allow_headers='*',
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automatic_options=True,
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send_wildcard=False,
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vary_header=True,
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supports_credentials=False,
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resources=r'/*',
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intercept_exceptions=True)
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def parse_resources(resources):
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if isinstance(resources, dict):
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# To make the API more consistent with the decorator, allow a
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# resource of '*', which is not actually a valid regexp.
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resources = [(re_fix(k), v) for k, v in resources.items()]
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# Sort by regex length to provide consistency of matching and
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# to provide a proxy for specificity of match. E.G. longer
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# regular expressions are tried first.
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def pattern_length(pair):
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maybe_regex, _ = pair
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return len(get_regexp_pattern(maybe_regex))
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return sorted(resources,
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key=pattern_length,
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reverse=True)
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elif isinstance(resources, string_types):
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return [(re_fix(resources), {})]
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elif isinstance(resources, collections.Iterable):
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return [(re_fix(r), {}) for r in resources]
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# Type of compiled regex is not part of the public API. Test for this
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# at runtime.
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elif isinstance(resources, RegexObject):
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return [(re_fix(resources), {})]
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else:
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raise ValueError("Unexpected value for resources argument.")
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def get_regexp_pattern(regexp):
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'''
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Helper that returns regexp pattern from given value.
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:param regexp: regular expression to stringify
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:type regexp: _sre.SRE_Pattern or str
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:returns: string representation of given regexp pattern
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:rtype: str
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'''
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try:
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return regexp.pattern
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except AttributeError:
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return str(regexp)
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def get_cors_origin(options, request_origin):
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origins = options.get('origins')
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wildcard = r'.*' in origins
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# If the Origin header is not present terminate this set of steps.
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# The request is outside the scope of this specification.-- W3Spec
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if request_origin:
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debugLog("CORS request received with 'Origin' %s", request_origin)
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# If the allowed origins is an asterisk or 'wildcard', always match
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if wildcard and options.get('send_wildcard'):
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debugLog("Allowed origins are set to '*', assuming valid request")
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return '*'
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# If the value of the Origin header is a case-sensitive match
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# for any of the values in list of origins
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elif try_match_any(request_origin, origins):
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debugLog("Given origin matches set of allowed origins")
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# Add a single Access-Control-Allow-Origin header, with either
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# the value of the Origin header or the string "*" as value.
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# -- W3Spec
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return request_origin
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else:
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debugLog("Given origin does not match any of allowed origins: %s",
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map(get_regexp_pattern, origins))
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return None
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# Terminate these steps, return the original request untouched.
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else:
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debugLog("'Origin' header was not set, which means CORS was not requested, skipping")
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return None
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def get_allow_headers(options, acl_request_headers):
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if acl_request_headers:
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request_headers = [h.strip() for h in acl_request_headers.split(',')]
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# any header that matches in the allow_headers
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matching_headers = filter(
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lambda h: try_match_any(h, options.get('allow_headers')),
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request_headers
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)
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return ', '.join(sorted(matching_headers))
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return None
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def get_cors_headers(options, request_headers, request_method, response_headers):
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origin_to_set = get_cors_origin(options, request_headers.get('Origin'))
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headers = {}
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if origin_to_set is None: # CORS is not enabled for this route
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return headers
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infoLog("Request from Origin:%s, setting %s:%s",
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request_headers.get('Origin'), ACL_ORIGIN, origin_to_set)
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headers[ACL_ORIGIN] = origin_to_set
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headers[ACL_EXPOSE_HEADERS] = options.get('expose_headers')
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if options.get('supports_credentials'):
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headers[ACL_CREDENTIALS] = 'true' # case sensative
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# This is a preflight request
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# http://www.w3.org/TR/cors/#resource-preflight-requests
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if request_method == 'OPTIONS':
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acl_request_method = request_headers.get(ACL_REQUEST_METHOD, '').upper()
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# If there is no Access-Control-Request-Method header or if parsing
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# failed, do not set any additional headers
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if acl_request_method and acl_request_method in options.get('methods'):
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# If method is not a case-sensitive match for any of the values in
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# list of methods do not set any additional headers and terminate
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# this set of steps.
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headers[ACL_ALLOW_HEADERS] = get_allow_headers(options, request_headers.get(ACL_REQUEST_HEADERS))
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headers[ACL_MAX_AGE] = options.get('max_age')
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headers[ACL_METHODS] = options.get('methods')
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else:
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infoLog("Access-Control-Request-Method:%s does not match allowed methods %s",
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acl_request_method, options.get('methods'))
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# http://www.w3.org/TR/cors/#resource-implementation
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if options.get('vary_header'):
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# Only set header if the origin returned will vary dynamically,
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# i.e. if we are not returning an asterisk, and there are multiple
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# origins that can be matched.
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if headers[ACL_ORIGIN] != '*' and len(options.get('origins')) > 1:
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vary = ['Origin', response_headers.get('Vary')]
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headers['Vary'] = ', '. join(v for v in vary if v is not None)
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return dict((k, v) for k, v in headers.items() if v)
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def set_cors_headers(resp, options):
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'''
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Performs the actual evaluation of Flas-CORS options and actually
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modifies the response object.
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This function is used both in the decorator and the after_request
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callback
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'''
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# If CORS has already been evaluated via the decorator, skip
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if hasattr(resp, FLASK_CORS_EVALUATED):
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debugLog('CORS have been already evaluated, skipping')
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return resp
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headers_to_set = get_cors_headers(options,
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request.headers,
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request.method,
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resp.headers)
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debugLog('Settings CORS headers: %s', str(headers_to_set))
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for k, v in headers_to_set.items():
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resp.headers[k] = v
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return resp
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def re_fix(reg):
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'''
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Replace the invalid regex r'*' with the valid, wildcard regex r'/.*' to
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enable the CORS app extension to have a more user friendly api.
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'''
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return r'.*' if reg == r'*' else reg
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def try_match_any(inst, patterns):
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return any(try_match(inst, pattern) for pattern in patterns)
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def try_match(request_origin, pattern):
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'''
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Safely attempts to match a pattern or string to a request origin.
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'''
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try:
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if isinstance(pattern, RegexObject):
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return re.match(pattern, request_origin)
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else:
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return re.match(pattern, request_origin, flags=re.IGNORECASE)
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except:
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return request_origin == pattern
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def get_cors_options(appInstance, *dicts):
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'''
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Compute CORS options for an application by combining
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the DEFAULT_OPTIONS, the app's configuration-specified options
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and any dictionaries passed. The last specified option wins.
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'''
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options = DEFAULT_OPTIONS.copy()
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options.update(get_app_kwarg_dict(appInstance))
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if dicts:
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for d in dicts:
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options.update(d)
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return serialize_options(options)
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def get_app_kwarg_dict(appInstance=None):
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'''
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Returns the dictionary of CORS specific app configurations.
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'''
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app = (appInstance or current_app)
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return dict(
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(k.lower().replace('cors_', ''), app.config.get(k))
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for k in CONFIG_OPTIONS
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if app.config.get(k) is not None
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)
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def flexible_str(obj):
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'''
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A more flexible str function which intelligently handles
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stringifying iterables. The results are lexographically
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sorted to ensure generated responses are consistent when
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iterables such as Set are used (whose order is usually platform
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dependent)
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'''
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if(not isinstance(obj, string_types)
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and isinstance(obj, collections.Iterable)):
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return ', '.join(str(item) for item in sorted(obj))
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else:
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return str(obj)
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def serialize_option(options_dict, key, upper=False):
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if key in options_dict:
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value = flexible_str(options_dict[key])
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options_dict[key] = value.upper() if upper else value
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def ensure_iterable(inst):
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'''
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Wraps scalars or string types as a list, or returns the iterable instance.
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'''
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if isinstance(inst, string_types):
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return [inst]
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elif not isinstance(inst, collections.Iterable):
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return [inst]
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else:
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return inst
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def sanitize_regex_param(param):
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return [re_fix(x) for x in ensure_iterable(param)]
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def serialize_options(opts):
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'''
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A helper method to serialize and processes the options dictionary
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where applicable.
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'''
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options = (opts or {}).copy()
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# Ensure origins is a list of allowed origins with at least one entry.
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options['origins'] = sanitize_regex_param(options.get('origins'))
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options['allow_headers'] = sanitize_regex_param(options.get('allow_headers'))
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# This is expressly forbidden by the spec. Raise a value error so people
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# don't get burned in production.
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if r'.*' in options['origins'] and options['supports_credentials'] and options['send_wildcard']:
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raise ValueError("Cannot use supports_credentials in conjunction with"
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"an origin string of '*'. See: "
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"http://www.w3.org/TR/cors/#resource-requests")
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serialize_option(options, 'expose_headers')
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serialize_option(options, 'methods', upper=True)
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if isinstance(options.get('max_age'), timedelta):
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options['max_age'] = str(int(options['max_age'].total_seconds()))
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return options
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def getLogger(app=None):
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'''
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Helper to get Flask-Cor's logger, attached to the current_app's logger
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if it exists.
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'''
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# we are in the context of a request
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if stack.top is not None:
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return logging.getLogger("%s.cors" % current_app.logger_name)
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# For use init method, when an app is known, but there is no context
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elif app is not None:
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return logging.getLogger("%s.cors" % app.logger_name)
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else:
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return logging.getLogger("flask.ext.cors")
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def debugLog(*args, **kwargs):
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'''
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Helper to log a message at the DEBUG level.
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'''
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getLogger().debug(*args, **kwargs)
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def infoLog(*args, **kwargs):
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'''
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Helper to log a message at the INFO level.
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'''
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getLogger().info(*args, **kwargs)
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