Cache FCM acces_token until expiration

Retrieving the Auth tokens is the slowest part of the notification process.
Caching tokens will give a huge performance boost.

Author: intrip

lib/action_push_native/service/fcm.rb

@@ -13,7 +13,7 @@ def initialize(config)
       end
 
       def push(notification)
-        response = httpx_session.post("v1/projects/#{config.fetch(:project_id)}/messages:send", json: payload_from(notification), headers: { authorization: "Bearer #{access_token}" })
+        response = httpx_session.post("v1/projects/#{config.fetch(:project_id)}/messages:send", json: payload_from(notification))
         handle_error(response) if response.error
       end
 
@@ -22,20 +22,7 @@ def push(notification)
 
         def httpx_session
           self.class.httpx_sessions ||= {}
-          self.class.httpx_sessions[config] ||= build_httpx_session
-        end
-
-        # FCM suggests at least a 10s timeout for requests, we set 15 to add some buffer.
-        # https://firebase.google.com/docs/cloud-messaging/scale-fcm#timeouts
-        DEFAULT_REQUEST_TIMEOUT = 15.seconds
-        DEFAULT_POOL_SIZE       = 5
-
-        def build_httpx_session
-          HTTPX.
-            plugin(:persistent, close_on_fork: true).
-            with(timeout: { request_timeout: config[:request_timeout] || DEFAULT_REQUEST_TIMEOUT }).
-            with(pool_options: { max_connections: config[:connection_pool_size] || DEFAULT_POOL_SIZE }).
-            with(origin: "https://fcm.googleapis.com")
+          self.class.httpx_sessions[config] ||= HttpxSession.new(config)
         end
 
         def payload_from(notification)
@@ -75,13 +62,6 @@ def stringify(hash)
           hash.compact.transform_values(&:to_s)
         end
 
-        def access_token
-          authorizer = Google::Auth::ServiceAccountCredentials.make_creds \
-            json_key_io: StringIO.new(config.fetch(:encryption_key)),
-            scope: "https://www.googleapis.com/auth/firebase.messaging"
-          authorizer.fetch_access_token!["access_token"]
-        end
-
         def handle_error(response)
           if response.is_a?(HTTPX::ErrorResponse)
             handle_network_error(response.error)

lib/action_push_native/service/fcm/httpx_session.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class ActionPushNative::Service::Fcm::HttpxSession
+  # FCM suggests at least a 10s timeout for requests, we set 15 to add some buffer.
+  # https://firebase.google.com/docs/cloud-messaging/scale-fcm#timeouts
+  DEFAULT_REQUEST_TIMEOUT = 15.seconds
+  DEFAULT_POOL_SIZE       = 5
+
+  def initialize(config)
+    @session = \
+      HTTPX.
+      plugin(:persistent, close_on_fork: true).
+      with(timeout: { request_timeout: config[:request_timeout] || DEFAULT_REQUEST_TIMEOUT }).
+      with(pool_options: { max_connections: config[:connection_pool_size] || DEFAULT_POOL_SIZE }).
+      with(origin: "https://fcm.googleapis.com")
+    @token_provider = ActionPushNative::Service::Fcm::TokenProvider.new(config)
+  end
+
+  def post(*uri, **options)
+    options[:headers] ||= {}
+    options[:headers][:authorization] = "Bearer #{token_provider.fresh_access_token}"
+    session.post(*uri, **options)
+  end
+
+  private
+    attr_reader :token_provider, :session
+end

lib/action_push_native/service/fcm/token_provider.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+class ActionPushNative::Service::Fcm::TokenProvider
+  EXPIRED = -1
+
+  def initialize(config)
+    @config = config
+    @expires_at = EXPIRED
+  end
+
+  def fresh_access_token
+    regenerate_if_expired
+    token
+  end
+
+  private
+    attr_reader :config, :token, :expires_at
+
+    def regenerate_if_expired
+      regenerate if Time.now.utc >= expires_at
+    end
+
+    REFRESH_BUFFER = 1.minutes
+
+    def regenerate
+      authorizer = Google::Auth::ServiceAccountCredentials.make_creds \
+        json_key_io: StringIO.new(config.fetch(:encryption_key)),
+        scope: "https://www.googleapis.com/auth/firebase.messaging"
+      oauth2 = authorizer.fetch_access_token!
+      @token = oauth2["access_token"]
+      @expires_at = oauth2["expires_in"].seconds.from_now.utc - REFRESH_BUFFER
+    end
+end

test/jobs/action_push_native/notification_job_test.rb

@@ -38,7 +38,9 @@ class NotificationJobTest < ActiveSupport::TestCase
       device = action_push_native_devices(:pixel9)
       stub_request(:post, "https://fcm.googleapis.com/v1/projects/your_project_id/messages:send").
         to_raise(SocketError.new)
-      ActionPushNative::Service::Fcm.any_instance.stubs(:access_token).returns("fake_access_token")
+      authorizer = stub("authorizer")
+      authorizer.stubs(:fetch_access_token!).returns({ "access_token" => "fake_access_token", "expires_in" => 3599 })
+      Google::Auth::ServiceAccountCredentials.stubs(:make_creds).returns(authorizer)
 
       assert_enqueued_jobs 1, only: ActionPushNative::NotificationJob do
         ActionPushNative::NotificationJob.perform_later("ApplicationPushNotification", @notification_attributes, device)

test/lib/action_push_native/service/fcm_test.rb

@@ -74,6 +74,22 @@ class FcmTest < ActiveSupport::TestCase
         end
       end
 
+      test "access tokens are refreshed" do
+        @fcm.httpx_sessions = {}
+        stub_request(:post, "https://fcm.googleapis.com/v1/projects/your_project_id/messages:send")
+
+        authorizer = stub("authorizer")
+        authorizer.stubs(:fetch_access_token!).once.returns({ "access_token" => "fake_access_token", "expires_in" => 3599 })
+        Google::Auth::ServiceAccountCredentials.stubs(:make_creds).returns(authorizer)
+        @fcm.push(@notification)
+        @fcm.push(@notification)
+
+        authorizer.stubs(:fetch_access_token!).once.returns({ "access_token" => "fake_access_token", "expires_in" => 3599 })
+        travel 3600 do
+          @fcm.push(@notification)
+        end
+      end
+
       private
         def build_notification
           ActionPushNative::Notification.
@@ -93,7 +109,7 @@ def build_notification
 
         def stub_authorizer
           authorizer = stub("authorizer")
-          authorizer.stubs(:fetch_access_token!).returns({ "access_token" => "fake_access_token" })
+          authorizer.stubs(:fetch_access_token!).returns({ "access_token" => "fake_access_token", "expires_in" => 3599 })
           Google::Auth::ServiceAccountCredentials.stubs(:make_creds).returns(authorizer)
         end
     end