Calling a Cloud Function from Android through Firebase

It isn't possible for now but as mentioned in the other answer, you can trigger functions using an HTTP request from Android. If you do so, it's important that you protect your functions with an authentication mechanism. Here's a basic example:

'use strict';

var functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

exports.helloWorld = functions.https.onRequest((request, response) => {
  console.log('helloWorld called');
  if (!request.headers.authorization) {
      console.error('No Firebase ID token was passed');
      response.status(403).send('Unauthorized');
      return;
  }
  admin.auth().verifyIdToken(request.headers.authorization).then(decodedIdToken => {
    console.log('ID Token correctly decoded', decodedIdToken);
    request.user = decodedIdToken;
    response.send(request.body.name +', Hello from Firebase!');
  }).catch(error => {
    console.error('Error while verifying Firebase ID token:', error);
    response.status(403).send('Unauthorized');
  });
});

To get the token in Android you should use this and then add it to your request like this:

connection = (HttpsURLConnection) url.openConnection();
...
connection.setRequestProperty("Authorization", token);

firebaser here

Update: There is now a client-side SDK that allows you to call Cloud Functions directly from supported devices. See Dima's answer for a sample and the latest updates.

Original answer below...

---

@looptheloop88 is correct. There is no SDK for calling Google Cloud Functions from your Android app. I would definitely file a feature request.

But at the moment that means you should use the regular means of calling HTTP end points from Android:

• Make an HTTP request with android
• Android: AsyncTask to make an HTTP GET Request?
• Http Get using Android HttpURLConnection
• Android's HTTP Triggers documentation

Since version 12.0.0 you can call cloud function in more simple way

Add following line in your build.gradle

implementation 'com.google.firebase:firebase-functions:19.0.2'

And use following code

FirebaseFunctions.getInstance() // Optional region: .getInstance("europe-west1")
    .getHttpsCallable("myCoolFunction")
    .call(optionalObject)
    .addOnFailureListener {
        Log.wtf("FF", it) 
    }
    .addOnSuccessListener {
        toast(it.data.toString())
    }

You can use it on main thread safely. Callbacks is triggered on main thread as well.

You can read more in official docs: https://firebase.google.com/docs/functions/callable