firebase hosting blocking script due to CORS issue

I am using firebase hosting to host few scripts and trying to access them from another site. it naturally gets blocked due to CORS issues. based on my research on other forum threads etc i modified the firebase.json as below

{
  "hosting": {
    "public": "public",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**"
    ],
    "headers": [ {
    "source" : "**",
    "headers" : [ {
      "key" : "Access-Control-Allow-Origin",
      "value" : "*"
    } ]
  }]
}
}

which essentially allow any url to access the resources hosted here. however, on trying to run my site i still see below

        Access to XMLHttpRequest at 'https://oracle-bot-sdk.firebaseapp.com//loader.json' 
    from origin 'https://insurance-bot.moblize.it' has been blocked by CORS policy: 
No 'Access-Control-Allow-Origin' header is present on the requested resource.

what else is needed?

In addition to your firebase.json changes for cors, your firebase functions http / https function needs to also include the cors plugin.

Example

const cors = require('cors')({origin: true});
const functions = require('firebase-functions');

const app = functions.https.onRequest((req, res) => {
    cors(req, res, () => {
        // Your app stuff here

        // Send Response
        res.status(200).send(<response data>);
    });
});

Express App Example

import express from "express";
const cors = require('cors')({origin: true});

const app = express();
app.get('**', (req, res) => {
  cors(req, res, () => {
      // Your App Here

      // Send response
      res.status(200).send(<response data>);
    });
});

More documentation Serve Dynamic Content with Cloud Functions - Create an HTTP function to your Hosting site (Cors is not mentioned in the documentation btw)

Make sure you have the Blaze or Flame plan, I think Spark plan blocks external access, maybe for the same reason as it does with cloud functions

Cloud Functions for Firebase - Billing account not configured

Is the site (https://insurance-bot.moblize.it/) that is calling to https://oracle-bot-sdk.firebaseapp.com a Firebase hosted app?

I only ask because with version 4.2+ of Firebase Tools allows you to setup Multisite hosting using the same Firebase Project. I am not sure if that would help your situation out at all. Just wanted to mention it.

In the error message:

insurance-bot.moblize.it/:1 Failed to load https://oracle-bot-sdk.firebaseapp.com//loader.json: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://insurance-bot.moblize.it' is therefore not allowed access.

I noticed an extra '/' in https://oracle-bot-sdk.firebaseapp.com//loader.json. I doubt that is the issue, but wanted to mention it.

There is something that you could try. Similar to the answers above but a little different:

"headers": [
    {
        "source": "*",
        "headers": [
            {
                "key": "Access-Control-Allow-Origin",
                "value": "*"
            }
        ]
    }
]

Also I would read some of the info here: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#Access-Control-Allow-Origin If you have not already.

I hope I was able to help in some way. Let me know.

Ron Royston

Try pasting this as it's directly from the documentation, Customize Hosting Behavior:

"hosting": {
  // Add the "headers" section within "hosting".
  "headers": [ {
    "source" : "**/*.@(eot|otf|ttf|ttc|woff|font.css)",
    "headers" : [ {
      "key" : "Access-Control-Allow-Origin",
      "value" : "*"
    } ]
  }
}

My guess that you've mixed up firebase hosting and firebase cloud functions. Firebase hosting is made for hosting static websites and web apps. As you try to access from your website that is hosted on different domain your configuration for hosting is not applied. You mentioned that you host some scripts and it sounds like cloud functions. And good old CORS headers can help to your cloud functions like:

exports.corsEnabledFunction = (req, res) => {
  res.set("Access-Control-Allow-Origin", "*");
  res.set("Access-Control-Allow-Methods", "GET");
  res.set("Access-Control-Allow-Headers", "Content-Type");
  res.set("Access-Control-Max-Age", "3600");

  // Continue with function code
  ...
}

More info: https://cloud.google.com/functions/docs/writing/http#handling_cors_requests

来源：https://stackoverflow.com/questions/52266714/firebase-hosting-blocking-script-due-to-cors-issue

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