Firestore: Do I get charged for a read operation when adding a document while listening to snapshots?

I develop an app in Flutter and use Cloud Firestore as Database. To get data in realtime I use following code:

class Database {
  final usersCol = FirebaseFirestore.instance.collection('users');

  Stream<List<DataModel>> getDataModelStream() {
    return usersCol
        .doc('uid')
        .collection('data')
        .orderBy('date', descending: true)
        .limit(30)
        .snapshots()
        .map((list) {
      return list.docs.map((doc) => DataModel.fromFirestore(doc.data()['dataModel'])).toList();
    });
  }
}

To add / update a document in Firestore I use following code:

 Future addDataModel(String date, DataModel dataModel) async {
    await usersCol
        .doc('uid')
        .collection('workouts')
        .doc(date)
        .set({
      'date': date,
      'dataModel': DataModel.toFirestore(dataModel),
    });
  }

Now I add / update a document in Firestore with addDataModel while I am listening to a Stream with getDataModelStream.

I have two Questions:

1. Does the listener gets triggered immediately so that the UI can get updated without any delay for user?

2. Do I get charged for a read operation or not since the updated document is already present and don't need to get fetched from Firestore?

Yes, in your scenario you pay a document read. Despite the information (likely) being the same as what the client already has, the server has to read the document and that is a charged operation.

To answer your more specific question:

1. Your listener indeed immediately gets triggered with the local data for the write operation, before it's even sent to the server. This is not a charged document read.

2. Because you have a listener, the client also gets the data back from the server when the write completes. This is a charged document read. If the document is different then what was raised in step 1, your listener gets called again with the updated data.