Python Flask Cors Issue

Question

I am kind of new to Python, but I have had the same issue working with Node apps. I am making a pretty standard jQuery AJAX request to my local Python sever:

init: function(callback) {
            var token = _config.get_token();

            $.ajax({
                    url: 'http://localhost:5000/api/ia/v1/user_likes',
                    type: 'POST',
                    contentType: 'application/json',
                    datatype: 'json',
                    data: token
                })
                .done(function(data) {
                    callback(data);
                })
                .fail(function(err) {
                    callback(err);
                });

            callback(token);
        }

I can confirm that the variable token is confirming like this:

Object {access_token: "791415154.2c0a5f7.4d707361de394512a29682f9cb2d2846", campaign_id: "102"}

But I am getting this error from my javascript console:

XMLHttpRequest cannot load http://localhost:5000/api/ia/v1/user_likes. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://s3.amazonaws.com' is therefore not allowed access. The response had HTTP status code 500.

I have found that when I am building Node apps that this is a cors error. The page that I am running the jQuery AJAX request from is http. Here are the parts of my Python code that I believe I am configuring incorrectly:

from flask import Flask, request, redirect
from flask.ext.cors import CORS, cross_origin

app = Flask(__name__)
cors = CORS(app)
app.config['CORS_HEADERS'] = 'application/json'

And the route:

@app.route("/api/ia/v1/user_likes", methods=['POST', 'OPTIONS'])
def user_likes():
    validate = validate_request(request.data)

    return 'something'

My Python error is also returning an error because the request is never making it to this line of code:

def validate_request(object_from_user):
    load_object = json.loads(object_from_user)

I can fix that later. Anyway, does anyone have any suggestions for Cors configurations for Python?

Solution 1

After I tried others suggestions and answers. Here's what I use, which works.

Steps:

1. pip install flask flask-cors

2. Copy and paste this in app.py file

Code

from flask import Flask, jsonify
from flask_cors import CORS, cross_origin

app = Flask(__name__)
CORS(app, support_credentials=True)

@app.route("/login")
@cross_origin(supports_credentials=True)
def login():
  return jsonify({'success': 'ok'})

if __name__ == "__main__":
  app.run(host='0.0.0.0', port=8000, debug=True)

3. python app.py

Note: be sure in your client's ajax configuration has the following:

$.ajaxSetup({
    type: "POST",
    data: {},
    dataType: 'json',
    xhrFields: {
       withCredentials: true
    },
    crossDomain: true,
    contentType: 'application/json; charset=utf-8'
});

If one wonders, support_credentials=True just means it sends cookies along the payload back and forth.

Solution 2

Flask has the flask-cors module. Following is the code snippet as well as the procedure.

1. pip install -U flask-cors

2. Add this lines in your flask application:

   from flask import Flask
   from flask_cors import CORS, cross_origin
   
   app = Flask(__name__)
   CORS(app)
   
   @app.route("/")
   def helloWorld():
       return "Hello world"
   

See more by clicking on this link

Solution 3

Here is how to get your hand dirty by handling the CORS detail all by yourself:

handle_result = {'result': True, 'msg': 'success'}

try:
    # origin, where does this request come from, like www.amazon.com
    origin = flask.request.environ['HTTP_ORIGIN']
except KeyError:
    origin = None

# only accept CORS request from amazon.com
if origin and origin.find('.amazon.com') > -1:
    resp = flask.make_response(str(handle_result))
    resp.headers['Content-Type'] = 'application/json'

    h = resp.headers
    # prepare headers for CORS authentication
    h['Access-Control-Allow-Origin'] = origin
    h['Access-Control-Allow-Methods'] = 'GET'
    h['Access-Control-Allow-Headers'] = 'X-Requested-With'

    resp.headers = h
    return resp

return flask.abort(403)

Solution 4

Please use @cross_origin(origin='*') in your python file

from flask import Flask, jsonify
from flask_cors import CORS, cross_origin

app = Flask(__name__)

@app.route("/login", methods = ['GET'])
@cross_origin(origin='*')
def login():
  return jsonify({'success': 'ok'})

if __name__ == "__main__":
  app.run(host='0.0.0.0', port=8000, debug=True)

Solution 5

use the cors decorator after the route decorator.

here's a snippet from the documentation...

@app.route("/")
@cross_origin() # allow all origins all methods.
def helloWorld():
  return "Hello, cross-origin-world!"

now, it appears you are using json, if that's the case, you should likely just read the documentation as it specifically mentions this use case, and what cors_headers to set... it's below the fold, but this documentation is well written and easy to understand.

http://flask-cors.readthedocs.org/en/latest/#using-json-with-cors

View more solutions

Comments

[Max Baldwin]

I took a look at these docs early today and tried several different configurations. Adding @cross_origin did not help with my current configuration.

[Cory Dolphin]

In the case of JSON, previously you needed to specify the allowed headers. This is now relaxed and should work out-of-the box. Please let me know if you have any issues.

[Max Baldwin]

Was this a recent update to Flask? I haven't written Python in a while.

[Addinall]

I am trying to implement that as well. I use the @cors decorator and still get

[Abhilash KK]

In my case, the ajax setup added extra header field like headers: { 'Access-Control-Allow-Origin':'*' },

[JacobIRR]

For me, this works for GET and POST routes, but when I added a DELETE route, it failed for CORS reasons... ?

[Hethcox]

I made the same mistake. It seems axios doesn't assume http(s).

[Edward]

Should this work with blueprints as well?