Javascript - 请求的资源上没有"Access-Control-Allow-Origin"标头

Question

我需要通过XavascriptHttpRequest从javascript向python服务器发送数据.因为我使用的是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我有这个:

    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"])

但当我执行它时,我收到此消息:

XMLHttpRequest无法加载localhost:5000/signin.请求的资源上不存在"Access-Control-Allow-Origin"标头.因此不允许原点'null'访问.

我该如何解决？我知道我需要使用一些"Access-Control-Allow-Origin"标头,但我不知道如何在此代码中实现它.顺便说一句,我需要使用纯JavaScript.

Answer 1

我使用了烧瓶扩展.

安装使用 pip install flask-cors

那就简单了

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

这将允许所有域

Answer 2

老问题,但是对于有这个问题的未来googlers,我通过将以下内容添加到我的app.py文件中来解决它(以及与CORS有关的一些其他下游问题)我的烧瓶休息应用程序:

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

我使用这个装饰器让Javascript与Flask一起工作,并在我可接受的方法列表中添加"OPTIONS".应该在路径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: 链接似乎已损坏.这是我用的装饰器.

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 4

使用python 2.7时

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()

在python3或者前面运行时,使用命令安装flask-cors pip install flask-cors 添加以下内容:

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

Answer 5

Flask网站上实际上有一个很棒的片段来修改Access-Control-Allow-Origin标题服务器端.http://flask.pocoo.org/snippets/56/

您可以轻松地从那里开始,即允许每个*域访问您的URL,或指定您在标头内选择的URL.

来自MDN关于CORS的文章:

在这种情况下,服务器以a响应,Access-Control-Allow-Origin: *这意味着任何域都可以跨站点方式访问资源.如果http://bar.other的资源所有者 希望将资源的访问限制为仅来自 http://foo.example,则他们将发回: Access-Control-Allow-Origin: http://foo.example.