I am trying to make a cross origin request using jquery but it keeps being reject with the message
XMLHttpRequest cannot load http://... No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin ... is therefore not allowed access.
I am using flask, heroku, and jquery
the client code looks like this:
$(document).ready(function() {
$('#submit_contact').click(function(e){
e.preventDefault();
$.ajax({
type: 'POST',
url: 'http://...',
// data: [
// { name: "name", value: $('name').val()},
// { name: "email", value: $('email').val() },
// { name: "phone", value: $('phone').val()},
// { name: "description", value: $('desc').val()}
//
// ],
data:"name=3&email=3&phone=3&description=3",
crossDomain:true,
success: function(msg) {
alert(msg);
}
});
});
});
on the heroku side i am using flask and it is like this
from flask import Flask,request
from flask.ext.mandrill import Mandrill
try:
from flask.ext.cors import CORS # The typical way to import flask-cors
except ImportError:
# Path hack allows examples to be run without installation.
import os
parentdir = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
os.sys.path.insert(0, parentdir)
from flask.ext.cors import CORS
app = Flask(__name__)
app.config['MANDRILL_API_KEY'] = '...'
app.config['MANDRILL_DEFAULT_FROM']= '...'
app.config['QOLD_SUPPORT_EMAIL']='...'
app.config['CORS_HEADERS'] = 'Content-Type'
mandrill = Mandrill(app)
cors = CORS(app)
@app.route('/email/',methods=['POST'])
def hello_world():
name=request.form['name']
email=request.form['email']
phone=request.form['phone']
description=request.form['description']
mandrill.send_email(
from_email=email,
from_name=name,
to=[{'email': app.config['QOLD_SUPPORT_EMAIL']}],
text="Phone="+phone+"\n\n"+description
)
return '200 OK'
if __name__ == '__main__':
app.run()
Try the following decorators:
@app.route('/email/',methods=['POST', 'OPTIONS']) #Added 'Options'
@crossdomain(origin='*') #Added
def hello_world():
name=request.form['name']
email=request.form['email']
phone=request.form['phone']
description=request.form['description']
mandrill.send_email(
from_email=email,
from_name=name,
to=[{'email': app.config['QOLD_SUPPORT_EMAIL']}],
text="Phone="+phone+"\n\n"+description
)
return '200 OK'
if __name__ == '__main__':
app.run()
This decorator would be created as follows:
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
You can also check out this package Flask-CORS
If you want to enable CORS for all routes, then just install flask_cors extension (pip3 install -U flask_cors) and wrap app like this: CORS(app).
That is enough to do it (I tested this with a POST request to upload an image, and it worked for me):
from flask import Flask
from flask_cors import CORS
app = Flask(__name__)
CORS(app) # This will enable CORS for all routes
Important note: if there is an error in your route, let us say you try to print a variable that does not exist, you will get a CORS error related message which, in fact, has nothing to do with CORS.
Here is what worked for me when I deployed to Heroku.
http://flask-cors.readthedocs.org/en/latest/
Install flask-cors by running -
pip install -U flask-cors
from flask import Flask
from flask_cors import CORS, cross_origin
app = Flask(__name__)
cors = CORS(app)
app.config['CORS_HEADERS'] = 'Content-Type'
@app.route("/")
@cross_origin()
def helloWorld():
return "Hello, cross-origin-world!"
If you can't find your problem and you're code should work, it may be that your request is just reaching the maximum of time heroku allows you to make a request. Heroku cancels requests if it takes more than 30 seconds.
Reference: https://devcenter.heroku.com/articles/request-timeout
OK, I don't think the official snippet mentioned by galuszkak should be used everywhere, we should concern the case that some bug may be triggered during the handler such as hello_world function. Whether the response is correct or uncorrect, the Access-Control-Allow-Origin header is what we should concern. So, thing is very simple, just like bellow:
@blueprint.after_request # blueprint can also be app~~
def after_request(response):
header = response.headers
header['Access-Control-Allow-Origin'] = '*'
return response
That is all~~
I've just faced the same issue and I came to believe that the other answers are a bit more complicated than they need to be, so here's my approach for those who don't want to rely on more libraries or decorators:
A CORS request actually consists of two HTTP requests. A preflight request and then an actual request that is only made if the preflight passes successfully.
Before the actual cross domain POST request, the browser will issue an OPTIONS request. This response should not return any body, but only some reassuring headers telling the browser that it's alright to do this cross-domain request and it's not part of some cross site scripting attack.
I wrote a Python function to build this response using the make_response function from the flask module.
def _build_cors_prelight_response():
response = make_response()
response.headers.add("Access-Control-Allow-Origin", "*")
response.headers.add("Access-Control-Allow-Headers", "*")
response.headers.add("Access-Control-Allow-Methods", "*")
return response
This response is a wildcard one that works for all requests. If you want the additional security gained by CORS, you have to provide a whitelist of origins, headers and methods.
This response will convince your (Chrome) browser to go ahead and do the actual request.
When serving the actual request you have to add one CORS header - otherwise the browser won't return the response to the invoking JavaScript code. Instead the request will fail on the client-side. Example with jsonify
response = jsonify({"order_id": 123, "status": "shipped"}
response.headers.add("Access-Control-Allow-Origin", "*")
return response
I also wrote a function for that.
def _corsify_actual_response(response):
response.headers.add("Access-Control-Allow-Origin", "*")
return response
allowing you to return a one-liner.
from flask import Flask, request, jsonify, make_response
from models import OrderModel
flask_app = Flask(__name__)
@flask_app.route("/api/orders", methods=["POST", "OPTIONS"])
def api_create_order():
if request.method == "OPTIONS": # CORS preflight
return _build_cors_prelight_response()
elif request.method == "POST": # The actual request following the preflight
order = OrderModel.create(...) # Whatever.
return _corsify_actual_response(jsonify(order.to_dict()))
else
raise RuntimeError("Weird - don't know how to handle method {}".format(request.method))
def _build_cors_prelight_response():
response = make_response()
response.headers.add("Access-Control-Allow-Origin", "*")
response.headers.add('Access-Control-Allow-Headers', "*")
response.headers.add('Access-Control-Allow-Methods', "*")
return response
def _corsify_actual_response(response):
response.headers.add("Access-Control-Allow-Origin", "*")
return response
All the responses above work okay, but you'll still probably get a CORS error, if the application throws an error you are not handling, like a key-error, if you aren't doing input validation properly, for example. You could add an error handler to catch all instances of exceptions and add CORS response headers in the server response
So define an error handler - errors.py:
from flask import json, make_response, jsonify
from werkzeug.exceptions import HTTPException
# define an error handling function
def init_handler(app):
# catch every type of exception
@app.errorhandler(Exception)
def handle_exception(e):
#loggit()!
# return json response of error
if isinstance(e, HTTPException):
response = e.get_response()
# replace the body with JSON
response.data = json.dumps({
"code": e.code,
"name": e.name,
"description": e.description,
})
else:
# build response
response = make_response(jsonify({"message": 'Something went wrong'}), 500)
# add the CORS header
response.headers['Access-Control-Allow-Origin'] = '*'
response.content_type = "application/json"
return response
then using Billal's answer:
from flask import Flask
from flask_cors import CORS
# import error handling file from where you have defined it
from . import errors
app = Flask(__name__)
CORS(app) # This will enable CORS for all routes
errors.init_handler(app) # initialise error handling
Improving the solution described here: https://stackoverflow.com/a/52875875/10299604
With after_request we can handle the CORS response headers avoiding to add extra code to our endpoints:
### CORS section
@app.after_request
def after_request_func(response):
origin = request.headers.get('Origin')
if request.method == 'OPTIONS':
response = make_response()
response.headers.add('Access-Control-Allow-Credentials', 'true')
response.headers.add('Access-Control-Allow-Headers', 'Content-Type')
response.headers.add('Access-Control-Allow-Headers', 'x-csrf-token')
response.headers.add('Access-Control-Allow-Methods',
'GET, POST, OPTIONS, PUT, PATCH, DELETE')
if origin:
response.headers.add('Access-Control-Allow-Origin', origin)
else:
response.headers.add('Access-Control-Allow-Credentials', 'true')
if origin:
response.headers.add('Access-Control-Allow-Origin', origin)
return response
### end CORS section
I resolved this same problem in python using flask and with this library. flask_cors
Reference: https://flask-cors.readthedocs.io/en/latest/
My solution is a wrapper around app.route:
def corsapp_route(path, origin=('127.0.0.1',), **options):
"""
Flask app alias with cors
:return:
"""
def inner(func):
def wrapper(*args, **kwargs):
if request.method == 'OPTIONS':
response = make_response()
response.headers.add("Access-Control-Allow-Origin", ', '.join(origin))
response.headers.add('Access-Control-Allow-Headers', ', '.join(origin))
response.headers.add('Access-Control-Allow-Methods', ', '.join(origin))
return response
else:
result = func(*args, **kwargs)
if 'Access-Control-Allow-Origin' not in result.headers:
result.headers.add("Access-Control-Allow-Origin", ', '.join(origin))
return result
wrapper.__name__ = func.__name__
if 'methods' in options:
if 'OPTIONS' in options['methods']:
return app.route(path, **options)(wrapper)
else:
options['methods'].append('OPTIONS')
return app.route(path, **options)(wrapper)
return wrapper
return inner
@corsapp_route('/', methods=['POST'], origin=['*'])
def hello_world():
...
Source: Stackoverflow.com