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Cross-site HTTP requests are HTTP requests for resources from a different domain than the domain of the resource making the request. For instance, a resource loaded from Domain A makes a request for a resource on Domain B. The way this is implemented in modern browsers is by using HTTP Access Control headers: Documentation on developer.mozilla.org.
The following view decorator implements this:
from datetime import timedelta from flask import make_response, request, current_app from functools import update_wrapper def crossdomain(origin=None, methods=None, headers=None, max_age=21600, attach_to_all=True, automatic_options=True): if methods is not None: methods = ', '.join(sorted(x.upper() for x in methods)) if headers is not None and not isinstance(headers, basestring): headers = ', '.join(x.upper() for x in headers) if not isinstance(origin, basestring): origin = ', '.join(origin) if isinstance(max_age, timedelta): max_age = max_age.total_seconds() def get_methods(): if methods is not None: return methods options_resp = current_app.make_default_options_response() return options_resp.headers['allow'] def decorator(f): def wrapped_function(*args, **kwargs): if automatic_options and request.method == 'OPTIONS': resp = current_app.make_default_options_response() else: resp = make_response(f(*args, **kwargs)) if not attach_to_all and request.method != 'OPTIONS': return resp h = resp.headers h['Access-Control-Allow-Origin'] = origin h['Access-Control-Allow-Methods'] = get_methods() h['Access-Control-Max-Age'] = str(max_age) if headers is not None: h['Access-Control-Allow-Headers'] = headers return resp f.provide_automatic_options = False return update_wrapper(wrapped_function, f) return decorator
Unmodified this decorator requires Flask 0.8. If you want to use it with earlier versions of Flask you need to make sure to explicitly enable
'OPTIONS' as method when creating the route.
Here a basic overview of what the parameters do:
methods: Optionally a list of methods that are allowed for this view. If not provided it will allow all methods that are implemented.
headers: Optionally a list of headers that are allowed for this request.
'*'to allow all origins, otherwise a string with a URL or a list of URLs that might access the resource.
max_age: The number of seconds as integer or timedelta object for which the preflighted request is valid.
Trueif the decorator should add the access control headers to all HTTP methods or
Falseif it should only add them to
automatic_options: If enabled the decorator will use the default Flask
OPTIONSresponse and attach the headers there, otherwise the view function will be called to generate an appropriate response.
And here is how you can use it:
@app.route('/my_service') @crossdomain(origin='*') def my_service(): return jsonify(foo='cross domain ftw')
Please keep in mind that with Flask 0.7 you need to explicitly provide
@app.route('/my_service', methods=['GET', 'OPTIONS']) @crossdomain(origin='*') def my_service(): return jsonify(foo='cross domain ftw')
This snippet by Armin Ronacher can be used freely for anything you like. Consider it public domain.