fcm.md

Firebase Cloud Messaging Delivery Method

Send Device Notifications using the Google Firebase Cloud Messaging service and the googleauth gem. FCM supports Android, iOS, and web clients.

bundle add "googleauth"

Google Firebase Cloud Messaging Notification Service

To generate your Firebase Cloud Messaging credentials, you'll need to create your project if you have not already. See https://console.firebase.google.com/u/1/ Once you have created your project, visit the project dashboard and click the settings cog in the top of the left sidebar menu, then click project settings.

In the project settings screen click on the Service accounts tab in the top navigation menu, then click the Generate new private key button.

This json file will contain the necessary credentials in order to send notifications via Google Firebase Cloud Messaging. See the below instructions on where to store this information within your application.

Usage

class CommentNotification
  deliver_by :fcm do |config|
    config.credentials = Rails.root.join("config/certs/fcm.json")
    config.device_tokens = -> { recipient.notification_tokens.where(platform: "fcm").pluck(:token) }
    config.json = ->(device_token) {
      {
        message: {
          token: device_token,
          notification: {
            title: "Test Title",
            body: "Test body"
          }
        }
      }
    }
    config.if = -> { recipient.android_notifications? }
  end
end

Options

json

Customize the Firebase Cloud Messaging notification object. This can be a Lambda or Symbol of a method name on the notifier.

The callable object will be given the device token as an argument.

There are lots of options of how to structure a FCM notification message. See https://firebase.google.com/docs/cloud-messaging/concept-options for more details.

credentials

The location of your Firebase Cloud Messaging credentials.

When a String Object

Internally, this string is passed to Rails.root.join() as an argument so there is no need to do this beforehand.

deliver_by :fcm do |config| 
  config.credentials = "config/credentials/fcm.json"
end

When a Pathname object

The Pathname object can point to any location where you are storing your credentials.

deliver_by :fcm do |config| 
  config.credentials = Rails.root.join("config/credentials/fcm.json")
end

When a Hash object

A Hash which contains your credentials

deliver_by :fcm do |config| 
  config.credentials = credentials_hash 
end

credentials_hash = {
  "type": "service_account",
  "project_id": "test-project-1234",
  "private_key_id": ...,
  etc.....
}

When a Symbol

Points to a method which can return a Hash of your credentials, Pathname, or String to your credentials like the examples above.

We pass the notification object as an argument to the method. If you don't need to use it you can use the splat operator (*) to ignore it.

deliver_by :fcm do |config| 
  config.credentials = :fcm_credentials
  config.json = :format_notification
end

def fcm_credentials(*)
  Rails.root.join("config/certs/fcm.json")
end

Otherwise

If the credentials option is left out, it will look for your credentials in: Rails.application.credentials.fcm

Gathering Notification Tokens

A recipient can have multiple tokens (i.e. multiple Android devices), so make sure to return them all.

Here, the recipient has_many :notification_tokens with columns platform and token.

def fcm_device_tokens(recipient)
  recipient.notification_tokens.where(platform: "fcm").pluck(:token)
end

Handling Failures

Firebase Cloud Messaging Notifications may fail delivery if the user has removed the app from their device.

class CommentNotification
  deliver_by :fcm

  # Remove invalid device tokens
  #
  # token - the device token from iOS or FCM
  # platform - "iOS" or "fcm"
  def cleanup_device_token(token:, platform:)
    NotificationToken.where(token: token, platform: platform).destroy_all
  end
end