对于以下ajax发布请求Flask（如何使用从 ajax 在flask 中发布的数据？）：

$.ajax({
    url: "http://127.0.0.1:5000/foo", 
    type: "POST",
    contentType: "application/json",
    data: JSON.stringify({'inputVar': 1}),
    success: function( data ) { 
        alert( "success" + data );
    }   
});

我收到一个Cross Origin Resource Sharing (CORS)错误：

No 'Access-Control-Allow-Origin' header is present on the requested resource. 
Origin 'null' is therefore not allowed access. 
The response had HTTP status code 500.

我尝试通过以下两种方式解决它，但似乎都不起作用。

1. 使用 Flask-CORS

这是一个Flask处理扩展CORS，应该使跨域 AJAX 成为可能。

• http://flask-cors.readthedocs.org/en/latest/
• 如何在flask和heroku中启用CORS
• 应用 jwt auth 包装器时，Flask-cors 包装器不起作用。
• Javascript - 请求的资源上不存在“Access-Control-Allow-Origin”标头

我的pythonServer.py使用这个解决方案：

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

app = Flask(__name__)
cors = CORS(app, resources={r"/foo": {"origins": "*"}})
app.config['CORS_HEADERS'] = 'Content-Type'

@app.route('/foo', methods=['POST','OPTIONS'])
@cross_origin(origin='*',headers=['Content-Type','Authorization'])
def foo():
    return request.json['inputVar']

if __name__ == '__main__':
    app.run()

2. 使用特定的 Flask 装饰器

这是一个官方的Flask 代码片段，定义了一个装饰器，它应该允许CORS它装饰的函数。

• http://flask.pocoo.org/snippets/56/
• Python Flask 跨站点 HTTP POST - 不适用于特定的允许来源
• http://chopapp.com/#351l7gc3

我的pythonServer.py使用这个解决方案：

from flask import Flask, make_response, request, current_app
from datetime import timedelta
from functools import update_wrapper

app = Flask(__name__)

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

@app.route('/foo', methods=['GET','POST','OPTIONS'])
@crossdomain(origin="*")
def foo():
    return request.json['inputVar']

if __name__ == '__main__':
    app.run()

你能给出一些说明为什么会这样吗？