[Firebase Messaging] Context information is hidden from messages received in flutter

[bartmentech]

The messages received in Dart are hiding information in the message handlers. The native code for receiving messages only forwards the payload to Flutter. Information from the RemoteMessage is lost, such as the sender of the message.

In use cases where an app will subscribe to more than 1 topic, it becomes hard to figure out where a message originated from. Therefore, the message forwarded to Flutter should also include the context information such as the sender.

The responsible code for the Android implementation is found here

To Reproduce
Steps to reproduce the behavior:

1. Subscribe to a topic using subscribeToTopic("my-topic")
2. Implement the message handler onMessage: (Map<String, dynamic> message) async {}
3. Inspect the format of the message and you will find that only the message payload is included.

Expected behavior
The expected behaviour of receiving a message would be the inclusion of the information present in the RemoteMessage class.