swap: prevent bad cheques from being sent

swap/peer.go

@@ -204,6 +204,16 @@ func (p *Peer) sendCheque() error {
 		return fmt.Errorf("error while creating cheque: %v", err)
 	}
 
+	availableBalance, err := p.swap.AvailableBalance()
+	if err != nil {
+		return fmt.Errorf("error while getting available balance: %v", err)
+	}
+
+	chequeAmount := uint64(-p.getBalance())
+	if availableBalance < chequeAmount {
+		return fmt.Errorf("cannot send created cheque, amount %d is greater than chequebook available balance %d", chequeAmount, availableBalance)
+	}
+
 	err = p.setPendingCheque(cheque)
 	if err != nil {
 		return fmt.Errorf("error while saving pending cheque: %v", err)

swap/swap_test.go

@@ -1433,5 +1433,4 @@ func TestAvailableBalance(t *testing.T) {
 	if !availableBalance.Equals(expectedBalance) {
 		t.Fatalf("available balance not equal to deposited minus withdraw. available balance: %v, expected balance: %v", availableBalance, expectedBalance)
 	}
-
 }