dto/firebase_message_document library

1. flutter_chat_firebase
2. dto/firebase_message_document.dart

flutter_chat_firebase package

1. Libraries
2. service/firebase_chat_detail_service
3. dto/firebase_chat_document
4. config/firebase_chat_options
5. service/firebase_chat_overview_service
6. service/firebase_chat_service
7. service/firebase_chat_user_service
8. dto/firebase_message_document
9. dto/firebase_user_document
10. flutter_chat_firebase
11. service/service