Expose SnapshotTime on Session

(cherry picked from commit 1a8932b)

mongo/session.go

@@ -122,6 +122,10 @@ type Session interface {
 	// OperationTime returns the current operation time document associated with the session.
 	OperationTime() *primitive.Timestamp
 
+	// SnapshotTime returns the snapshot timestamp being used for the session.
+	// If the session is not a snapshot session, or no operations have run on the session yet, it will return nil.
+	SnapshotTime() *primitive.Timestamp
+
 	// Client the Client associated with the session.
 	Client() *Client
 
@@ -361,6 +365,11 @@ func (s *sessionImpl) OperationTime() *primitive.Timestamp {
 	return s.clientSession.OperationTime
 }
 
+// SnapshotTime implements the Session interface.
+func (s *sessionImpl) SnapshotTime() *primitive.Timestamp {
+	return s.clientSession.SnapshotTime
+}
+
 // AdvanceOperationTime implements the Session interface.
 func (s *sessionImpl) AdvanceOperationTime(ts *primitive.Timestamp) error {
 	return s.clientSession.AdvanceOperationTime(ts)