Add middleware to all firebase functions in one line / function

Question

In express you can add middleware such as app.use(cors()) which adds it to all of the endpoints, however I can't find something similar in firebase examples. Here is the example (see below) of how to apply it in every function. However I want to apply the middleware (cors or other) globally, as I have many functions.

import * as cors from 'cors';
const corsHandler = cors({origin: true});

export const exampleFunction= functions.https.onRequest(async (request, response) => {
       corsHandler(request, response, () => { return handler(req, res) });
});

What is the equivalent of app.use() in firebase? Is adding and express server the only option?

Here is an official firebase functions sample that shows using express to handle the middleware. Export the express app and the function is public. https://github.com/firebase/functions-samples/blob/main/authorized-https-endpoint/functions/index.js — IcyIcicle, May 31 '22 at 22:37

Kevin Danikowski · Accepted Answer · 2021-11-10T14:26:57.677

Use currying to create a handler, you have to repeat it across all the functions, but it's easier than writing the middleware each time:

const applyMiddleware = handler => (req, res) => {
  return cors(req, res, () => {
    return handler(req, res)
  })
}
exports.handler = functions.https.onRequest(applyMiddleware(handler))

Edit, an example of a more complex middleware:

const applyMiddleware =
  (handler, { authenticatedRoute = false } = {}) =>
  (req, res) => {
    if (authenticatedRoute) {
      const isAuthorized = isAuthenticated(req)
      if (!isAuthorized) {
        return res.status(401).send('Unauthorized')
      }
    }
    return cors(req, res, () => {
      return handler(req, res)
    })
  }
exports.handler = functions.https.onRequest(
   applyMiddleware(handler, { authenticatedRoute: true })
)

Add middleware to all firebase functions in one line / function

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