Add experimental config option to send to-device messages to AS's

synapse/config/experimental.py

@@ -54,3 +54,11 @@ class ExperimentalConfig(Config):
         self.msc3202_device_masquerading_enabled: bool = experimental.get(
             "msc3202_device_masquerading", False
         )
+
+        # MSC2409 (this setting only relates to optionally sending to-device messages).
+        # Presence, typing and read receipt EDUs are already sent to application services that
+        # have opted in to receive them. This setting, if enabled, adds to-device messages
+        # to that list.
+        self.msc2409_to_device_messages_enabled: bool = experimental.get(
+            "msc2409_to_device_messages_enabled", False
+        )

synapse/handlers/appservice.py

@@ -55,6 +55,9 @@ class ApplicationServicesHandler:
         self.clock = hs.get_clock()
         self.notify_appservices = hs.config.appservice.notify_appservices
         self.event_sources = hs.get_event_sources()
+        self.msc2409_to_device_messages_enabled = (
+            hs.config.experimental.msc2409_to_device_messages_enabled
+        )
 
         self.current_max = 0
         self.is_processing = False