Javascript-请求的资源上不存在“Access Control Allow Origin”标头

Question

我需要发送数据通过XmlHttpRequest从JavaScript到Python服务器。因为我在使用localhost，所以我需要使用CORS。我正在使用Flask框架及其模块flask_cors。

作为JavaScript，我有以下几点：

    var xmlhttp;
    if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp = new XMLHttpRequest();
    }
    else {// code for IE6, IE5
        xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
    xmlhttp.open("POST", "http://localhost:5000/signin", true);
    var params = "email=" + email + "&password=" + password;


    xmlhttp.onreadystatechange = function() {//Call a function when the state changes.
        if(xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            alert(xmlhttp.responseText);
        }
    }
    xmlhttp.send(params);

和Python代码：

@app.route('/signin', methods=['POST'])
@cross_origin()
def sign_in():
    email = cgi.escape(request.values["email"])
    password = cgi.escape(request.values["password"])

但是当我执行它时，我会得到这样的信息：

XMLHttpRequest无法加载localhost:5000/signin.请求的资源上不存在访问控制允许起源标头。因此，不允许访问源'null'。

我该怎么修？我知道我需要使用一些“accesscontrolalloworigin”头，但我不知道如何在这段代码中实现它。顺便说一下，我需要使用纯JavaScript。

Answer 1

通过使用这个装饰器，我获得了使用Flask的Javascript，并将“选项”添加到我的可接受方法列表中。应该在路线装饰器下面使用装饰器，如下所示：

@app.route('/login', methods=['POST', 'OPTIONS'])
@crossdomain(origin='*')
def login()
    ...

编辑：链接似乎已断开。这是我用过的装饰师。

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):
    """Decorator function that allows crossdomain requests.
      Courtesy of
      https://blog.skyred.fi/articles/better-crossdomain-snippet-for-flask.html
    """
    if methods is not None:
        methods = ', '.join(sorted(x.upper() for x in methods))
    # use str instead of basestring if using Python 3.x
    if headers is not None and not isinstance(headers, basestring):
        headers = ', '.join(x.upper() for x in headers)
    # use str instead of basestring if using Python 3.x
    if not isinstance(origin, basestring):
        origin = ', '.join(origin)
    if isinstance(max_age, timedelta):
        max_age = max_age.total_seconds()

    def get_methods():
        """ Determines which methods are allowed
        """
        if methods is not None:
            return methods

        options_resp = current_app.make_default_options_response()
        return options_resp.headers['allow']

    def decorator(f):
        """The decorator function
        """
        def wrapped_function(*args, **kwargs):
            """Caries out the actual cross domain code
            """
            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)
            h['Access-Control-Allow-Credentials'] = 'true'
            h['Access-Control-Allow-Headers'] = \
                "Origin, X-Requested-With, Content-Type, Accept, Authorization"
            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

Answer 2

老问题，但对于未来的谷歌用户有这个问题，我解决了它（和其他一些下游问题与CORS有关）为我的烧瓶restful应用程序通过添加以下内容到我的app.py文件：

app = Flask(__name__)
api = Api(app)

@app.after_request
def after_request(response):
  response.headers.add('Access-Control-Allow-Origin', '*')
  response.headers.add('Access-Control-Allow-Headers', 'Content-Type,Authorization')
  response.headers.add('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE,OPTIONS')
  return response


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

Answer 3

我已经使用了flask-cors扩展。

使用pip安装烧瓶cors安装

那就简单了

from flask_cors import CORS
app = Flask(__name__)
CORS(app)

这将允许所有域