watchtower/wtdb: apply sanity checks to session policy before accepting

watchtower/wtdb/tower_db.go

@@ -193,6 +193,12 @@ func (t *TowerDB) InsertSessionInfo(session *SessionInfo) error {
 			return ErrSessionAlreadyExists
 		}
 
+		// Perform a quick sanity check on the session policy before
+		// accepting.
+		if err := session.Policy.Validate(); err != nil {
+			return err
+		}
+
 		err = putSession(sessions, session)
 		if err != nil {
 			return err

watchtower/wtdb/tower_db_test.go

@@ -150,6 +150,13 @@ func testInsertSession(h *towerDBHarness) {
 		RewardAddress: []byte{0x01, 0x02, 0x03},
 	}
 
+	// Try to insert the session, which should fail since the policy doesn't
+	// meet the current sanity checks.
+	h.insertSession(session, wtpolicy.ErrSweepFeeRateTooLow)
+
+	// Now assign a sane sweep fee rate to the policy, inserting should
+	// succeed.
+	session.Policy.SweepFeeRate = wtpolicy.DefaultSweepFeeRate
 	h.insertSession(session, nil)
 
 	session2 := h.getSession(&id, nil)

watchtower/wtmock/tower_db.go

@@ -81,6 +81,11 @@ func (db *TowerDB) InsertSessionInfo(info *wtdb.SessionInfo) error {
 		return wtdb.ErrSessionAlreadyExists
 	}
 
+	// Perform a quick sanity check on the session policy before accepting.
+	if err := info.Policy.Validate(); err != nil {
+		return err
+	}
+
 	db.sessions[info.ID] = info
 
 	return nil