Pushing: ActionMailer for Push Notifications

Pushing is a push notification framework that implements interfaces similar to ActionMailer.

• Convention over Configuration: Pushing brings Convention over Configuration to your app for organizing your push notification implementations.
• Extremely Easy to Learn: If you know how to use ActionMailer, you already know how to use Pushing. Send notifications asynchronously with ActiveJob at no learning cost.
• Testability: First-class support for push notification. No more hassle writing custom code or stubs/mocks for your tests.

Getting Started

Add this line to your application’s Gemfile:

gem 'pushing'
gem 'jbuilder' # if you don't have it in your Gemfile

At the time of writing, Pushing only has support for jbuilder (Rails’ default JSON constructor), but there are plans to add support for jb and rabl.

Supported Platforms

Pushing itself doesn’t make HTTP requests. Instead, it uses an adapter to make actual calls. Currently, Pushing has support for the following client gems:

• APNs (iOS):

  • anpotic (recommended)
  • lowdown
  • houston

• FCM (Android):

  • andpush (recommended)
  • fcm

If you are starting from scratch, it is recommended using anpotic for APNs and andpush for FCM due to their reliability and performance:

gem 'apnotic' # APNs
gem 'andpush' # FCM

Walkthrough to Writing a Notifier

Generate a new notifier:

$ rails g pushing:notifier TweetNotifier new_direct_message

# app/notifiers/tweet_notifier.rb
class TweetNotifier < ApplicationNotifier
  def new_direct_message(message_id, token_id)
    @message = DirectMessage.find(message_id)
    @token   = DeviceToken.find(token_id)
    push apn: @token.apn? && @token.device_token, fcm: @token.fcm?
  end
end

Edit the push notification payload:

APNs:

# app/views/tweet_notifier/new_direct_message.json+apn.jbuilder
json.aps do
  json.alert do
    json.title "#{@tweet.user.display_name} tweeted:"
    json.body truncate(@tweet.body, length: 235)
  end
  json.badge 1
  json.sound 'bingbong.aiff'
end

FCM:

# app/views/tweet_notifier/new_direct_message.json+fcm.jbuilder
json.to @token.registration_id
json.notification do
  json.title "#{@tweet.user.display_name} tweeted:"
  json.body truncate(@tweet.body, length: 1024)
  json.icon 1
  json.sound 'default'
end

Deliver the push notifications:

TweetNotifier.new_direct_message(message_id, device_token.id).deliver_now!
# => sends a push notification immediately
TweetNotifier.new_direct_message(message_id, device_token.id).deliver_later!
# => enqueues a job that sends a push notification later

Advanced Usage

Pushing only to one platform

Pushing only sends a notification for the platforms that are given a truthy value. For example, give the following code:

push apn: @token.device_token, fcm: false
# => only sends a push notification to APNs
push apn: @token.device_token
# => same as above but without the `:fcm` key, only sends a push notification to APNs

This will only send a push notification to APNs and skip the call to FCM.

APNs

It is often necessary to switch the environment endpoint or adjust the request headers depending on the notification you want to send. Pushing’s #push method allows for overriding APNs request headers on a delivery-basis:

Overriding the default environment:

push apn: { device_token: @token.device_token, environment: @token.apn_environment }

Overriding the default APN topic:

push apn: { device_token: @token.device_token, headers: { apns_topic: 'your.otherapp.ios' } }

Or all of the above:

push fcm: @token.fcm?,
     apn: {
       device_token: @token.apn? && @token.device_token,
       environment: @token.apn_environment,
       headers: {
         apns_id:          uuid,
         apns_expiration:  7.days.from_now,
         apns_priority:    5,
         apns_topic:       'your.otherapp.ios',
         apns_collapse_id: 'not-so-important-notification'
       }
     }

The :fcm key, on the other hand, doesn’t have any options as everything’s configurable through the request body.

Error Handling

Like ActionMailer, you can use the rescue_from hook to handle exceptions. A common use-case would be to handle a ‘BadDeviceToken’ response from APNs or a response with a ‘Retry-After’ header from FCM.

Handling a ‘BadDeviceToken’ response from APNs:

class ApplicationNotifier < Pushing::Base
  rescue_from Pushing::ApnDeliveryError do |error|
    response = error.response
    if response.status == 410 || (response.status == 400 && response.json[:reason] == 'BadDeviceToken')
      token = error.notification.device_token
      Rails.logger.info("APN device token #{token} has been expired and will be removed.")
      # delete or expire device token accordingly
    else
      raise # Make sure to raise any other types of error to re-enqueue the job
    end
  end
end

Handling a ‘Retry-After’ header from FCM:

class ApplicationNotifier < Pushing::Base
  rescue_from Pushing::FcmDeliveryError do |error|
    if error.response&.headers['Retry-After']
      # re-enqueue the job honoring the 'Retry-After' header
    else
      raise # Make sure to raise any other types of error to re-enqueue the job
    end
  end
end

Interceptors and Observers

Pushing implements the Interceptor and Observer patterns. A common use-case would be to update registration ids with canonical ids from FCM:

# app/observers/fcm_token_handler.rb
class FcmTokenHandler
  def delivered_notification(payload, response)
    return if response.json[:canonical_ids].to_i.zero?
    response.json[:results].select {|result| result[:registration_id] }.each do |result|
      result[:registration_id] # => returns a canonical id
      # Update registration ids accordingly
    end
  end
end
# app/notifiers/application_notifier.rb
class ApplicationNotifier < Pushing::Base
  register_observer FcmTokenHandler.new
  ...
end

Configuration

TODO: Make this section more helpful

Pushing.configure do |config|
  # Adapter that is used to send push notifications through FCM
  config.fcm.adapter = Rails.env.test? ? :test : :andpush
  # Your FCM servery key that can be found here: https://console.firebase.google.com/project/_/settings/cloudmessaging
  config.fcm.server_key = 'YOUR_FCM_SERVER_KEY'
  # Adapter that is used to send push notifications through APNs
  config.apn.adapter = Rails.env.test? ? :test : :apnotic
  # The environment that is used by default to send push notifications through APNs
  config.apn.environment = Rails.env.production? ? :production : :development
  # The scheme that is used for negotiating connection trust between your provider
  # servers and Apple Push Notification service. As documented in the offitial doc,
  # there are two schemes available:
  #
  #   :token       - Token-based provider connection trust (default)
  #   :certificate - Certificate-based provider connection trust
  #
  # This option is only applied when using an adapter that uses the HTTP/2-based
  # API.
  config.apn.connection_scheme = :token
  # Path to the certificate or auth key for establishing a connection to APNs.
  #
  # This config is always required.
  config.apn.certificate_path = 'path/to/your/certificate'
  # Password for the certificate specified above if there's any.
  # config.apn.certificate_password = 'passphrase'
  # A 10-character key identifier (kid) key, obtained from your developer account.
  # If you haven't created an Auth Key for your app, create a new one at:
  #   https://developer.apple.com/account/ios/authkey/
  #
  # Required if the +connection_scheme+ is set to +:token+.
  config.apn.key_id = 'DEF123GHIJ'
  # The issuer (iss) registered claim key, whose value is your 10-character Team ID,
  # obtained from your developer account. Your team id could be found at:
  #   https://developer.apple.com/account/#/membership
  #
  # Required if the +connection_scheme+ is set to +:token+.
  config.apn.team_id = 'ABC123DEFG'
  # Header values that are added to every request to APNs. documentation for the
  # headers available can be found here:
  #   https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/CommunicatingwithAPNs.html#//apple_ref/doc/uid/TP40008194-CH11-SW13
  config.apn.default_headers = {
    apns_priority:    10,
    apns_topic:       'your.awesomeapp.ios',
    apns_collapse_id: 'wrong.topicname.com'
  }
end

Testing

Pushing provides first-class support for testing. In order to test your notifier, use the :test adapter in the test environment instead of an actual adapter in development/production.

# config/initializers/pushing.rb
Pushing.configure do |config|
  config.apn.adapter = Rails.env.test? ? :test : :apnotic
  config.fcm.adapter = Rails.env.test? ? :test : :andpush
end

Now you can call the #deliveries method on the notifier. Here is an example with ActiveSupport::TestCase:

TweetNotifier.deliveries.clear # => clears the test inbox
assert_changes -> { TweetNotifier.deliveries.apn.size }, from: 0, to: 1 do
  TweetNotifier.new_direct_message(message.id, apn_device_token.id).deliver_now!
end
apn_message = TweetNotifier.deliveries.apn.first
assert_equal 'apn-device-token',  apn_message.device_token
assert_equal "Hey coffee break?", apn_message.payload[:aps][:alert][:body]
assert_changes -> { TweetNotifier.deliveries.fcm.size }, from: 0, to: 1 do
  TweetNotifier.new_direct_message(message.id, fcm_registration_id.id).deliver_now!
end
fcm_payload = TweetNotifier.deliveries.fcm.first.payload
assert_equal 'fcm-registration-id', fcm_payload[:to]
assert_equal "Hey coffee break?",   fcm_payload[:notification][:body]

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/yuki24/pushing. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.