Call functions from your app


The Cloud Functions for Firebase client SDKs let you call functions directly from a Firebase app. To call a function from your app in this way, write and deploy an HTTP Callable function in Cloud Functions, and then add client logic to call the function from your app.

It's important to keep in mind that HTTP callable functions are similar but not identical to HTTP functions. To use HTTP callable functions you must use the client SDK for your platform together with the backend API (or implement the protocol). Callables have these key difference from HTTP functions:

  • With callables, Firebase Authentication tokens, FCM tokens, and App Check tokens, when available, are automatically included in requests.
  • The trigger automatically deserializes the request body and validates auth tokens.

The Firebase SDK for Cloud Functions 2nd gen and higher interoperates with these Firebase client SDK minimum versions to support HTTPS Callable functions:

  • Firebase SDK for Apple platforms 11.4.0
  • Firebase SDK for Android 21.0.0
  • Firebase Modular Web SDK v. 9.7.0

If you want to add similar functionality to an app built on an unsupported platform, see the Protocol Specification for https.onCall. The rest of this guide provides instructions on how to write, deploy, and call an HTTP callable function for Apple platforms, Android, web, C++, and Unity.

Write and deploy the callable function

Use functions.https.onCall to create an HTTPS callable function. This method takes two parameters: data, and optional context:

  // Saves a message to the Firebase Realtime Database but sanitizes the
  // text by removing swearwords.
  exports.addMessage = functions.https.onCall((data, context) => {
    // ...
  });

For a callable function that saves a text message to the Realtime Database, for example, data could contain the message text, while context parameters represent user auth information:

// Message text passed from the client.
const text = request.data.text;
// Authentication / user information is automatically added to the request.
const uid = request.auth.uid;
const name = request.auth.token.name || null;
const picture = request.auth.token.picture || null;
const email = request.auth.token.email || null;
index.js

Distance between the location of the callable function and the location of the calling client can create network latency. To optimize performance, consider specifying the function location where applicable, and make sure to align the callable's location with the location set when you initialize the SDK on the client side.

Optionally, you can attach an App Check attestation to help protect your backend resources from abuse, such as billing fraud or phishing. See Enable App Check enforcement for Cloud Functions.

Sending back the result

To send data back to the client, return data that can be JSON encoded. For example, to return the result of an addition operation:

// returning result.
return {
  firstNumber: firstNumber,
  secondNumber: secondNumber,
  operator: "+",
  operationResult: firstNumber + secondNumber,
};
index.js

To return data after an asynchronous operation, return a promise. The data returned by the promise is sent back to the client. For example, you could return sanitized text that the callable function wrote to the Realtime Database:

// Saving the new message to the Realtime Database.
const sanitizedMessage = sanitizer.sanitizeText(text); // Sanitize message.

return getDatabase().ref("/messages").push({
  text: sanitizedMessage,
  author: {uid, name, picture, email},
}).then(() => {
  logger.info("New Message written");
  // Returning the sanitized message to the client.
  return {text: sanitizedMessage};
})
index.js

Handle errors

To ensure the client gets useful error details, return errors from a callable by throwing (or returning a Promise rejected with) an instance of functions.https.HttpsError. The error has a code attribute that can be one of the values listed at functions.https.HttpsError. The errors also have a string message, which defaults to an empty string. They can also have an optional details field with an arbitrary value. If an error other than HttpsError is thrown from your functions, your client instead receives an error with the message INTERNAL and the code internal.

For example, a function could throw data validation and authentication errors with error messages to return to the calling client:

// Checking attribute.
if (!(typeof text === "string") || text.length === 0) {
  // Throwing an HttpsError so that the client gets the error details.
  throw new HttpsError("invalid-argument", "The function must be called " +
          "with one arguments \"text\" containing the message text to add.");
}
// Checking that the user is authenticated.
if (!request.auth) {
  // Throwing an HttpsError so that the client gets the error details.
  throw new HttpsError("failed-precondition", "The function must be " +
          "called while authenticated.");
}
index.js

Deploy the callable function

After you save a completed callable function within index.js, it is deployed along with all other functions when you run firebase deploy. To deploy only the callable, use the --only argument as shown to perform partial deploys:

firebase deploy --only functions:addMessage

If you encounter permissions errors when deploying functions, make sure that the appropriate IAM roles are assigned to the user running the deployment commands.

Set up your client development environment

Make sure you meet any prerequisites, then add the required dependencies and client libraries to your app.

iOS+

Follow the instructions to add Firebase to your Apple app.

Use Swift Package Manager to install and manage Firebase dependencies.

  1. In Xcode, with your app project open, navigate to File > Add Packages.
  2. When prompted, add the Firebase Apple platforms SDK repository:
    3.   https://github.com/firebase/firebase-ios-sdk.git
  3. Choose the Cloud Functions library.
  4. Add the -ObjC flag to the Other Linker Flags section of your target's build settings.
  5. When finished, Xcode will automatically begin resolving and downloading your dependencies in the background.

Web

  1. Follow the instructions to add Firebase to your Web app. Make sure to run the following command from your terminal: 
    npm install firebase@11.0.1 --save

  2. Manually require both Firebase core and Cloud Functions:

     import { initializeApp } from 'firebase/app';
 import { getFunctions } from 'firebase/functions';

 const app = initializeApp({
     projectId: '### CLOUD FUNCTIONS PROJECT ID ###',
     apiKey: '### FIREBASE API KEY ###',
     authDomain: '### FIREBASE AUTH DOMAIN ###',
   });
 const functions = getFunctions(app);

Web

  1. Follow the instructions to add Firebase to your Web app.
  2. Add the Firebase core and Cloud Functions client libraries to your app: 
    <script src="https://www.gstatic.com/firebasejs/8.10.1/firebase.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.10.1/firebase-functions.js"></script>

The Cloud Functions SDK is also available as an npm package.

  1. Run the following command from your terminal: 
    npm install firebase@8.10.1 --save
  2. Manually require both Firebase core and Cloud Functions: 
    const firebase = require("firebase");
// Required for side-effects
require("firebase/functions");

Kotlin+KTX

  1. Follow the instructions to add Firebase to your Android app.

  2. In your module (app-level) Gradle file (usually <project>/<app-module>/build.gradle.kts or <project>/<app-module>/build.gradle), add the dependency for the Cloud Functions library for Android. We recommend using the Firebase Android BoM to control library versioning. 

    dependencies {
    // Import the BoM for the Firebase platform
    implementation(platform("com.google.firebase:firebase-bom:33.5.1"))

    // Add the dependency for the Cloud Functions library
    // When using the BoM, you don't specify versions in Firebase library dependencies
    implementation("com.google.firebase:firebase-functions")
}

    By using the Firebase Android BoM, your app will always use compatible versions of Firebase Android libraries.

    (Alternative)  Add Firebase library dependencies without using the BoM

    If you choose not to use the Firebase BoM, you must specify each Firebase library version in its dependency line.

    Note that if you use multiple Firebase libraries in your app, we strongly recommend using the BoM to manage library versions, which ensures that all versions are compatible. 

    dependencies {
    // Add the dependency for the Cloud Functions library
    // When NOT using the BoM, you must specify versions in Firebase library dependencies
    implementation("com.google.firebase:firebase-functions:21.0.0")
}
         Looking for a Kotlin-specific library module? Starting in October 2023 (Firebase BoM 32.5.0), both Kotlin and Java developers can depend on the main library module (for details, see the FAQ about this initiative).

Java

  1. Follow the instructions to add Firebase to your Android app.

  2. In your module (app-level) Gradle file (usually <project>/<app-module>/build.gradle.kts or <project>/<app-module>/build.gradle), add the dependency for the Cloud Functions library for Android. We recommend using the Firebase Android BoM to control library versioning. 

    dependencies {
    // Import the BoM for the Firebase platform
    implementation(platform("com.google.firebase:firebase-bom:33.5.1"))

    // Add the dependency for the Cloud Functions library
    // When using the BoM, you don't specify versions in Firebase library dependencies
    implementation("com.google.firebase:firebase-functions")
}

    By using the Firebase Android BoM, your app will always use compatible versions of Firebase Android libraries.

    (Alternative)  Add Firebase library dependencies without using the BoM

    If you choose not to use the Firebase BoM, you must specify each Firebase library version in its dependency line.

    Note that if you use multiple Firebase libraries in your app, we strongly recommend using the BoM to manage library versions, which ensures that all versions are compatible. 

    dependencies {
    // Add the dependency for the Cloud Functions library
    // When NOT using the BoM, you must specify versions in Firebase library dependencies
    implementation("com.google.firebase:firebase-functions:21.0.0")
}
         Looking for a Kotlin-specific library module? Starting in October 2023 (Firebase BoM 32.5.0), both Kotlin and Java developers can depend on the main library module (for details, see the FAQ about this initiative).

Dart

  1. Follow the instructions to add Firebase to your Flutter app.

  2. From the root of your Flutter project, run the following command to install the plugin:

    flutter pub add cloud_functions

  3. Once complete, rebuild your Flutter application:

    flutter run

  4. Once installed, you can access the cloud_functions plugin by importing it in your Dart code:

    import 'package:cloud_functions/cloud_functions.dart';

C++

For C++ with Android:

  1. Follow the instructions to add Firebase to your C++ project.
  2. Add the firebase_functions library to your CMakeLists.txt file.

For C++ with Apple platforms:

  1. Follow the instructions to add Firebase to your C++ project.
  2. Add the Cloud Functions pod to your Podfile: 
    pod 'Firebase/Functions'
  3. Save the file, then run: 
    pod install
  4. Add the Firebase core and Cloud Functions frameworks from the Firebase C++ SDK to your Xcode project.
    • firebase.framework
    • firebase_functions.framework

Unity

  1. Follow the instructions to add Firebase to your Unity project.
  2. Add the FirebaseFunctions.unitypackage from the Firebase Unity SDK to your Unity project.

Initialize the client SDK

Initialize an instance of Cloud Functions:

Swift

lazy var functions = Functions.functions()
CloudAddCell.swift

Objective-C

@property(strong, nonatomic) FIRFunctions *functions;
// ...
self.functions = [FIRFunctions functions];
CloudAddCell.m

Web 

firebase.initializeApp({
  apiKey: '### FIREBASE API KEY ###',
  authDomain: '### FIREBASE AUTH DOMAIN ###',
  projectId: '### CLOUD FUNCTIONS PROJECT ID ###'
  databaseURL: 'https://### YOUR DATABASE NAME ###.firebaseio.com',
});

// Initialize Cloud Functions through Firebase
var functions = firebase.functions();

Web 

const app = initializeApp({
  projectId: '### CLOUD FUNCTIONS PROJECT ID ###',
  apiKey: '### FIREBASE API KEY ###',
  authDomain: '### FIREBASE AUTH DOMAIN ###',
});
const functions = getFunctions(app);

Kotlin+KTX 

private lateinit var functions: FirebaseFunctions
// ...
functions = Firebase.functions
MainActivity.kt

Java 

private FirebaseFunctions mFunctions;
// ...
mFunctions = FirebaseFunctions.getInstance();
MainActivity.java

Dart 

final functions = FirebaseFunctions.instance;

C++

firebase::functions::Functions* functions;
// ...
functions = firebase::functions::Functions::GetInstance(app);

Unity

functions = Firebase.Functions.DefaultInstance;

Call the function

Swift

functions.httpsCallable("addMessage").call(["text": inputField.text]) { result, error in
  if let error = error as NSError? {
    if error.domain == FunctionsErrorDomain {
      let code = FunctionsErrorCode(rawValue: error.code)
      let message = error.localizedDescription
      let details = error.userInfo[FunctionsErrorDetailsKey]
    }
    // ...
  }
  if let data = result?.data as? [String: Any], let text = data["text"] as? String {
    self.resultField.text = text
  }
}
CommentCell.swift

Objective-C

[[_functions HTTPSCallableWithName:@"addMessage"] callWithObject:@{@"text": _inputField.text}
                                                      completion:^(FIRHTTPSCallableResult * _Nullable result, NSError * _Nullable error) {
  if (error) {
    if ([error.domain isEqual:@"com.firebase.functions"]) {
      FIRFunctionsErrorCode code = error.code;
      NSString *message = error.localizedDescription;
      NSObject *details = error.userInfo[@"details"];
    }
    // ...
  }
  self->_resultField.text = result.data[@"text"];
}];

Web 

var addMessage = firebase.functions().httpsCallable('addMessage');
addMessage({ text: messageText })
  .then((result) => {
    // Read result of the Cloud Function.
    var sanitizedMessage = result.data.text;
  });
callable.js

Web 

import { getFunctions, httpsCallable } from "firebase/functions";

const functions = getFunctions();
const addMessage = httpsCallable(functions, 'addMessage');
addMessage({ text: messageText })
  .then((result) => {
    // Read result of the Cloud Function.
    /** @type {any} */
    const data = result.data;
    const sanitizedMessage = data.text;
  });
fb_functions_call_add_message.js

Kotlin+KTX 

private fun addMessage(text: String): Task<String> {
    // Create the arguments to the callable function.
    val data = hashMapOf(
        "text" to text,
        "push" to true,
    )

    return functions
        .getHttpsCallable("addMessage")
        .call(data)
        .continueWith { task ->
            // This continuation runs on either success or failure, but if the task
            // has failed then result will throw an Exception which will be
            // propagated down.
            val result = task.result?.data as String
            result
        }
}
MainActivity.kt

Java 

private Task<String> addMessage(String text) {
    // Create the arguments to the callable function.
    Map<String, Object> data = new HashMap<>();
    data.put("text", text);
    data.put("push", true);

    return mFunctions
            .getHttpsCallable("addMessage")
            .call(data)
            .continueWith(new Continuation<HttpsCallableResult, String>() {
                @Override
                public String then(@NonNull Task<HttpsCallableResult> task) throws Exception {
                    // This continuation runs on either success or failure, but if the task
                    // has failed then getResult() will throw an Exception which will be
                    // propagated down.
                    String result = (String) task.getResult().getData();
                    return result;
                }
            });
}
MainActivity.java

Dart 

    final result = await FirebaseFunctions.instance.httpsCallable('addMessage').call(
      {
        "text": text,
        "push": true,
      },
    );
    _response = result.data as String;

C++

firebase::Future<firebase::functions::HttpsCallableResult> AddMessage(
    const std::string& text) {
  // Create the arguments to the callable function.
  firebase::Variant data = firebase::Variant::EmptyMap();
  data.map()["text"] = firebase::Variant(text);
  data.map()["push"] = true;

  // Call the function and add a callback for the result.
  firebase::functions::HttpsCallableReference doSomething =
      functions->GetHttpsCallable("addMessage");
  return doSomething.Call(data);
}

Unity

private Task<string> addMessage(string text) {
  // Create the arguments to the callable function.
  var data = new Dictionary<string, object>();
  data["text"] = text;
  data["push"] = true;

  // Call the function and extract the operation from the result.
  var function = functions.GetHttpsCallable("addMessage");
  return function.CallAsync(data).ContinueWith((task) => {
    return (string) task.Result.Data;
  });
}

Handle errors on the client

The client receives an error if the server threw an error or if the resulting promise was rejected.

If the error returned by the function is of type function.https.HttpsError, then the client receives the error code, message, and details from the server error. Otherwise, the error contains the message INTERNAL and the code INTERNAL. See guidance for how to handle errors in your callable function.

Swift

if let error = error as NSError? {
  if error.domain == FunctionsErrorDomain {
    let code = FunctionsErrorCode(rawValue: error.code)
    let message = error.localizedDescription
    let details = error.userInfo[FunctionsErrorDetailsKey]
  }
  // ...
}
CloudAddCell.swift

Objective-C

if (error) {
  if ([error.domain isEqual:@"com.firebase.functions"]) {
    FIRFunctionsErrorCode code = error.code;
    NSString *message = error.localizedDescription;
    NSObject *details = error.userInfo[@"details"];
  }
  // ...
}
CloudAddCell.m

Web 

var addMessage = firebase.functions().httpsCallable('addMessage');
addMessage({ text: messageText })
  .then((result) => {
    // Read result of the Cloud Function.
    var sanitizedMessage = result.data.text;
  })
  .catch((error) => {
    // Getting the Error details.
    var code = error.code;
    var message = error.message;
    var details = error.details;
    // ...
  });
callable.js

Web 

import { getFunctions, httpsCallable } from "firebase/functions";

const functions = getFunctions();
const addMessage = httpsCallable(functions, 'addMessage');
addMessage({ text: messageText })
  .then((result) => {
    // Read result of the Cloud Function.
    /** @type {any} */
    const data = result.data;
    const sanitizedMessage = data.text;
  })
  .catch((error) => {
    // Getting the Error details.
    const code = error.code;
    const message = error.message;
    const details = error.details;
    // ...
  });
fb_functions_call_add_message_error.js

Kotlin+KTX 

addMessage(inputMessage)
    .addOnCompleteListener { task ->
        if (!task.isSuccessful) {
            val e = task.exception
            if (e is FirebaseFunctionsException) {
                val code = e.code
                val details = e.details
            }
        }
    }
MainActivity.kt

Java 

addMessage(inputMessage)
        .addOnCompleteListener(new OnCompleteListener<String>() {
            @Override
            public void onComplete(@NonNull Task<String> task) {
                if (!task.isSuccessful()) {
                    Exception e = task.getException();
                    if (e instanceof FirebaseFunctionsException) {
                        FirebaseFunctionsException ffe = (FirebaseFunctionsException) e;
                        FirebaseFunctionsException.Code code = ffe.getCode();
                        Object details = ffe.getDetails();
                    }
                }
            }
        });
MainActivity.java

Dart 

try {
  final result =
      await FirebaseFunctions.instance.httpsCallable('addMessage').call();
} on FirebaseFunctionsException catch (error) {
  print(error.code);
  print(error.details);
  print(error.message);
}

C++

void OnAddMessageCallback(
    const firebase::Future<firebase::functions::HttpsCallableResult>& future) {
  if (future.error() != firebase::functions::kErrorNone) {
    // Function error code, will be kErrorInternal if the failure was not
    // handled properly in the function call.
    auto code = static_cast<firebase::functions::Error>(future.error());

    // Display the error in the UI.
    DisplayError(code, future.error_message());
    return;
  }

  const firebase::functions::HttpsCallableResult* result = future.result();
  firebase::Variant data = result->data();
  // This will assert if the result returned from the function wasn't a string.
  std::string message = data.string_value();
  // Display the result in the UI.
  DisplayResult(message);
}

// ...

// ...
  auto future = AddMessage(message);
  future.OnCompletion(OnAddMessageCallback);
  // ...

Unity

 addMessage(text).ContinueWith((task) => {
  if (task.IsFaulted) {
    foreach (var inner in task.Exception.InnerExceptions) {
      if (inner is FunctionsException) {
        var e = (FunctionsException) inner;
        // Function error code, will be INTERNAL if the failure
        // was not handled properly in the function call.
        var code = e.ErrorCode;
        var message = e.ErrorMessage;
      }
    }
  } else {
    string result = task.Result;
  }
});

Before you launch your app, you should enable App Check to help ensure that only your apps can access your callable function endpoints.