SECURITY FIX: do not cancel hodl invoice on payment error

Under some unusual circumstances the `PayInvoice` function can return an error when the payment has been settled.  In these cases it is extremely important not to cancel the hodl invoice since manual recovery is not possible if the hodl invoice is canceled.

Also increases the default `CltvDeltaAlpha` to allow a longer window for manual recovery in the case of an error.

relay.go

@@ -50,13 +50,13 @@ func NewRelay(ln lnc.LN) *Relay {
 			RoutingBudgetBeta:  1_500_000,
 			RoutingFeeBaseMsat: 1000,
 			RoutingFeePPM:      1000,
-			CltvDeltaAlpha:     3,
+			CltvDeltaAlpha:     144,
 			CltvDeltaBeta:      1_500_000,
 			// Should be set to at most the node's `--max-cltv-expiry` setting (default: 2016)
 			MaxCltvDelta: 1800,
 			MinCltvDelta: 120,
 			// Should be set so that CltvDeltaAlpha blocks are very unlikely to be added before timeout
-			PaymentTimeout:        120,
+			PaymentTimeout:        600,
 			PaymentTimePreference: 0.9,
 		},
 		LN: ln,
@@ -194,21 +194,23 @@ func (relay *Relay) OpenCircuit(x ProxyParameters) (string, error) {
 func (relay *Relay) circuitSwitch(hash []byte, invoice string, fee_budget_msat, cltv_limit uint64) {
 	defer relay.WaitGroup.Done()
 	log.Println("opened circuit for:", invoice, hex.EncodeToString(hash))
-	var preimage []byte
 	_, err := relay.LN.WatchInvoice(hash)
 	if err != nil {
 		log.Println("error while watching wrapped invoice:", hex.EncodeToString(hash), err)
-		goto cleanup
+		err = relay.LN.CancelInvoice(hash)
+		if err != nil {
+			log.Println("error while canceling invoice:", hash, err)
+		}
+		return
 	}
-	preimage, err = relay.LN.PayInvoice(lnc.PaymentParameters{
+	preimage, err := relay.LN.PayInvoice(lnc.PaymentParameters{
 		Invoice:        invoice,
 		TimeoutSeconds: relay.PaymentTimeout,
 		FeeLimitMsat:   fee_budget_msat,
 		CltvLimit:      cltv_limit,
 	})
 	if err != nil {
-		log.Println("error paying original invoice:", hex.EncodeToString(hash), err)
-		goto cleanup
+		log.Panicln("error paying original invoice:", hex.EncodeToString(hash), err)
 	}
 	log.Println("preimage:", hex.EncodeToString(preimage), hex.EncodeToString(hash))
 	err = relay.LN.SettleInvoice(preimage)
@@ -217,11 +219,4 @@ func (relay *Relay) circuitSwitch(hash []byte, invoice string, fee_budget_msat,
 	}
 	log.Println("circuit settled")
 	return
-
-cleanup:
-	err = relay.LN.CancelInvoice(hash)
-	if err != nil {
-		log.Println("error while canceling invoice:", hash, err)
-	}
-	return
 }