routing: add cltv limit to payment session

routing/payment_session.go

@@ -138,6 +138,16 @@ func (p *paymentSession) RequestRoute(payment *LightningPayment,
 		"edges, %v vertexes", len(pruneView.edges),
 		len(pruneView.vertexes))
 
+	// If a route cltv limit was specified, we need to subtract the final
+	// delta before passing it into path finding. The optimal path is
+	// independent of the final cltv delta and the path finding algorithm is
+	// unaware of this value.
+	var cltvLimit *uint32
+	if payment.CltvLimit != nil {
+		limit := *payment.CltvLimit - uint32(finalCltvDelta)
+		cltvLimit = &limit
+	}
+
 	// TODO(roasbeef): sync logic amongst dist sys
 
 	// Taking into account this prune view, we'll attempt to locate a path
@@ -154,6 +164,7 @@ func (p *paymentSession) RequestRoute(payment *LightningPayment,
 			IgnoredEdges:      pruneView.edges,
 			FeeLimit:          payment.FeeLimit,
 			OutgoingChannelID: payment.OutgoingChannelID,
+			CltvLimit:         cltvLimit,
 		},
 		p.mc.selfNode.PubKeyBytes, payment.Target,
 		payment.Amount,