firebase_rules.txt

{
  "rules": {
    "rooms": {
      "$room_id": {
        // only members of rooms should be able to see the room info.
        ".read": "data.child('members/'+auth.uid).exists()",
        // only administrators of rooms should be able to edit the room info.
        ".write": "data.child('administrators/'+auth.uid).exists()",
      }
  	},
    "members":{
      "$room_id": {
        ".read": true,
        ".write": true
      }
    },
    "messages": {
			"$room_id": {
        // only members of rooms should be able to see and add to the messages for a room.
        ".read": "root.child('rooms/'+$room_id+'/members/'+auth.uid).exists()",
      	".write": "root.child('rooms/'+$room_id+'/members/'+auth.uid).exists()"
      }
    },
    "users": {
      "$uid": {
        "favorites" : {
          ".read": "$uid === auth.uid"
        },
      ".write": "$uid === auth.uid"
      }
    }

  }

}