watchtower/wtserver: add DisableReward config option

watchtower/wtserver/create_session.go

@@ -54,6 +54,17 @@ func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
 		)
 	}
 
+	// If the request asks for a reward session and the tower has them
+	// disabled, we will reject the request.
+	if s.cfg.DisableReward && req.BlobType.Has(blob.FlagReward) {
+		log.Debugf("Rejecting CreateSession from %s, reward "+
+			"sessions disabled", id)
+		return s.replyCreateSession(
+			peer, id, wtwire.CreateSessionCodeRejectBlobType, 0,
+			nil,
+		)
+	}
+
 	// Now that we've established that this session does not exist in the
 	// database, retrieve the sweep address that will be given to the
 	// client. This address is to be included by the client when signing

watchtower/wtserver/server.go

@@ -63,6 +63,10 @@ type Config struct {
 	// NoAckUpdates causes the server to not acknowledge state updates, this
 	// should only be used for testing.
 	NoAckUpdates bool
+
+	// DisableReward causes the server to reject any session creation
+	// attempts that request rewards.
+	DisableReward bool
 }
 
 // Server houses the state required to handle watchtower peers. It's primary job