尝试从前端调用 Google Cloud function 时出现 CORS 错误（网站）

Question

I have a CORS issue with my google cloud function when I try to call it from a Web site (front-end). The problem is that I can succesfully execute the same code in Jupyter notebook without error. I've added so far all what is required to enable CORS access but I'm still getting the same error (Access to XMLHttpRequest at 'https://****' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.. Any help please?

Below is the source code:

import requests
import json
import flask
def myFunction(request):
    request_json = request.get_json()
    # preflight request
    if request.method == 'OPTIONS':
        headers = {
            'Access-Control-Allow-Origin': '*',
            'Access-Control-Allow-Methods': 'OPTIONS,POST,GET',
            'Access-Control-Allow-Headers': 'Content-Type',
            'Access-Control-Max-Age': '3600'
        }

        print ('', 204, headers)

    # main request
    headers = {
        'Access-Control-Allow-Methods': 'OPTIONS,POST,GET',
        'Access-Control-Allow-Origin': '*'
    }
#    Call to get a access token from a refresh token
    response = requests.post(url = "https://accounts.zoho.com/oauth/v2/...",headers = headers)
    accessToken = response.json()['access_token']
    # Call to zoho Api to insert a new lead
    url = 'https://www.zohoapis.com/crm/v2/Leads'
    v_access = 'Zoho-oauthtoken ' + accessToken 
    headers = {
            'Authorization': v_access,
            'Content-Type': 'application/json',
            'Access-Control-Allow-Origin': '*',
            'Access-Control-Allow-Methods': 'OPTIONS,GET, POST'
        }
    json_data = request.get_json(silent=True)
    newdata = json.dumps(json_data)
    v_data = str(json.loads(newdata))
    v_data1 = v_data.encode('utf-8')
    post_response = requests.post(url,headers = headers, data = v_data1)
    post_response.headers['Access-Control-Allow-Origin'] = '*'
    post_response.headers['Access-Control-Allow-Methods'] = 'GET, POST'
    return (post_response.status_code)

Answer 1

You don't normally want to get bogged down handling CORS headers manually, try a middleware such as https://flask-cors.readthedocs.io/en/latest/#route-specific-cors-via-decorator

Specifically around your response though, you never actually return headers, just a status code.

If you see the example on GCP you can see you need ACAO = * header set in the response. https://cloud.google.com/functions/docs/writing/http#preflight_request

# Set CORS headers for the main request
headers = {
    'Access-Control-Allow-Origin': '*'
}

return ('Hello World!', 200, headers) // Need the Headers in the Response