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Firebase Cloud Messaging (FCM) for Android and iOS

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The FCM gem lets your ruby backend send notifications to Android and iOS devices via Firebase Cloud Messaging.


$ gem install fcm

or in your Gemfile just include it:

gem 'fcm'


For Android you will need a device running 2.3 (or newer) that also have the Google Play Store app installed, or an emulator running Android 2.3 with Google APIs. iOS devices are also supported.

A version of supported Ruby, currently:
ruby >= 2.4


For your server to send a message to one or more devices, you must first initialise a new FCM class with your Firebase Cloud Messaging server key, and then call the send method on this and give it 1 or more (up to 1000) registration tokens as an array of strings. You can also optionally send further HTTP message parameters like data or time_to_live etc. as a hash via the second optional argument to send.

Example sending notifications:

require 'fcm'

fcm ="my_server_key")

registration_ids= ["12", "13"] # an array of one or more client registration tokens

# See for all available options.
options = { "notification": {
              "title": "Portugal vs. Denmark",
              "body": "5 to 1"
response = fcm.send(registration_ids, options)

Currently response is just a hash containing the response body, headers and status_code. Check here to see how to interpret the responses.

Device Group Messaging

With device group messaging, you can send a single message to multiple instance of an app running on devices belonging to a group. Typically, "group" refers a set of different devices that belong to a single user. However, a group could also represent a set of devices where the app instance functions in a highly correlated manner. To use this feature, you will first need an initialised FCM class.

Generate a Notification Key for device group

Then you will need a notification key which you can create for a particular key_name which needs to be uniquely named per app in case you have multiple apps for the same project_id. This ensures that notifications only go to the intended target app. The create method will do this and return the token notification_key, that represents the device group, in the response:

params = {key_name: "appUser-Chris",
                project_id: "my_project_id",
                registration_ids: ["4", "8", "15", "16", "23", "42"]}
response = fcm.create(*params.values)

Send to Notification Key

Now you can send a message to a particular notification_key via the send_with_notification_key method. This allows the server to send a single data payload or/and notification payload to multiple app instances (typically on multiple devices) owned by a single user (instead of sending to some registration tokens). Note: the maximum number of members allowed for a notification_key is 20.

response = fcm.send_with_notification_key("notification_key",
            data: {score: "3x1"},
            collapse_key: "updated_score")

Add/Remove Registration Tokens

You can also add/remove registration Tokens to/from a particular notification_key of some project_id. For example:

params = { key_name: "appUser-Chris",
                project_id: "my_project_id",
                registration_ids:["7", "3"] }
response = fcm.add(*params.values)

params = { key_name: "appUser-Chris",
                project_id: "my_project_id",
                registration_ids:["8", "15"] }
response = fcm.remove(*params.values)

Send Messages to Topics

FCM topic messaging allows your app server to send a message to multiple devices that have opted in to a particular topic. Based on the publish/subscribe model, topic messaging supports unlimited subscriptions per app. Sending to a topic is very similar to sending to an individual device or to a user group, in the sense that you can use the fcm.send_with_notification_key() method where the notification_key matches the regular expression "/topics/[a-zA-Z0-9-_.~%]+":

response = fcm.send_with_notification_key("/topics/yourTopic",
            notification: {body: "This is a FCM Topic Message!"})

Or you can use the helper:

response = fcm.send_to_topic("yourTopic",
            notification: {body: "This is a FCM Topic Message!"})

Sending to Multiple Topics

To send to combinations of multiple topics, the FCM docs require that you set a condition key (instead of the to: key) to a boolean condition that specifies the target topics. For example, to send messages to devices that subscribed to TopicA and either TopicB or TopicC:

'TopicA' in topics && ('TopicB' in topics || 'TopicC' in topics)

FCM first evaluates any conditions in parentheses, and then evaluates the expression from left to right. In the above expression, a user subscribed to any single topic does not receive the message. Likewise, a user who does not subscribe to TopicA does not receive the message. These combinations do receive it:

  • TopicA and TopicB
  • TopicA and TopicC

You can include up to five topics in your conditional expression, and parentheses are supported. Supported operators: &&, ||, !. Note the usage for !:

!('TopicA' in topics)

With this expression, any app instances that are not subscribed to TopicA, including app instances that are not subscribed to any topic, receive the message.

The send_to_topic_condition method within this library allows you to specicy a condition of multiple topics to which to send to the data payload.

response = fcm.send_to_topic_condition(
  "'TopicA' in topics && ('TopicB' in topics || 'TopicC' in topics)",
  notification: {
    body: "This is an FCM Topic Message sent to a condition!"

Subscribe the client app to a topic

Given a registration token and a topic name, you can add the token to the topic using the Google Instance ID server API.

topic = "YourTopic"
registration_id= "12" # a client registration tokens
response = fcm.topic_subscription(topic, registration_id)

Or you can manage relationship maps for multiple app instances Google Instance ID server API. Manage relationship

topic = "YourTopic"
registration_ids= ["4", "8", "15", "16", "23", "42"] # an array of one or more client registration tokens
response = fcm.batch_topic_subscription(topic, registration_ids)
# or unsubscription
response = fcm.batch_topic_unsubscription(topic, registration_ids)

Mobile Clients

You can find a guide to implement an Android Client app to receive notifications here: Set up a FCM Client App on Android.

The guide to set up an iOS app to get notifications is here: Setting up a FCM Client App on iOS.




  • Bumped supported ruby to >= 2.4
  • Fix deprecation warnings from faraday by changing dependency version to faraday 1.0.0


  • replace httparty with faraday


  • Fixed group messaging url.
  • Added API to recover_notification_key.


  • Initial version.

MIT License

  • Copyright (c) 2016 Kashif Rasul and Shoaib Burq. See LICENSE.txt for details.

Many thanks to all the contributors

Cutting a release

Update version in fcm.gemspec with VERSION and update ## ChangeLog section.

# set the version
# VERSION="1.0.2"
gem build fcm.gemspec
git tag -a v${VERSION} -m "Releasing version v${VERSION}"
git push origin --tags
gem push fcm-${VERSION}.gem