rpcserver: refactor invoice parsing for re-use

We'll want to be able to parse the amount and expiry of an invoice in
other places, so we extract that into its own method.

rpcserver.go

@@ -55,6 +55,7 @@ import (
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/invoicesrpc"
+	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/walletrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
@@ -7024,13 +7025,25 @@ func (r *rpcServer) SendPayment(req *tchrpc.SendPaymentRequest,
 		return fmt.Errorf("payment request and keysend custom " +
 			"records cannot be set at the same time")
 
+	// RFQ ID and keysend is set, which isn't a supported combination.
+	case req.RfqId != nil && isKeysend:
+		return fmt.Errorf("RFQ ID and keysend custom records " +
+			"cannot be set at the same time")
+
+	// A payment must either be a keysend payment or pay an invoice.
+	case !isKeysend && pReq.PaymentRequest == "":
+		return fmt.Errorf("payment request or keysend custom records " +
+			"must be set")
+
 	// There are custom records for the first hop set, which means RFQ
 	// negotiation has already happened (or this is a keysend payment and
 	// the correct asset amount is already encoded). So we don't need to do
 	// anything special and can just forward the payment to lnd.
 	case len(firstHopRecords) > 0:
 		// Continue below.
 
+	// The user specified a custom RFQ ID for a quote that should be used
+	// for the payment.
 	case req.RfqId != nil:
 		// Check if the provided RFQ ID matches the expected length.
 		if len(req.RfqId) != 32 {
@@ -7090,14 +7103,6 @@ func (r *rpcServer) SendPayment(req *tchrpc.SendPaymentRequest,
 
 	// The request wants to pay a specific invoice.
 	case pReq.PaymentRequest != "":
-		invoice, err := zpay32.Decode(
-			pReq.PaymentRequest, r.cfg.Lnd.ChainParams,
-		)
-		if err != nil {
-			return fmt.Errorf("error decoding payment request: %w",
-				err)
-		}
-
 		// The peer public key is optional if there is only a single
 		// asset channel.
 		var peerPubKey *route.Vertex
@@ -7128,35 +7133,11 @@ func (r *rpcServer) SendPayment(req *tchrpc.SendPaymentRequest,
 		// paymentMaxAmt is the maximum amount that the counterparty is
 		// expected to pay. This is the amount that the invoice is
 		// asking for plus the fee limit in milli-satoshis.
-		var paymentMaxAmt lnwire.MilliSatoshi
-		if invoice.MilliSat == nil {
-			amt, err := lnrpc.UnmarshallAmt(pReq.Amt, pReq.AmtMsat)
-			if err != nil {
-				return fmt.Errorf("error unmarshalling "+
-					"amount: %w", err)
-			}
-			if amt == 0 {
-				return errors.New("amount must be specified " +
-					"when paying a zero amount invoice")
-			}
-
-			paymentMaxAmt = amt
-		} else {
-			paymentMaxAmt = *invoice.MilliSat
-		}
-
-		// Calculate the fee limit that should be used for this payment.
-		feeLimit, err := lnrpc.UnmarshallAmt(
-			pReq.FeeLimitSat, pReq.FeeLimitMsat,
-		)
+		paymentMaxAmt, expiry, err := r.parseRequest(pReq)
 		if err != nil {
-			return fmt.Errorf("error unmarshalling fee limit: %w",
-				err)
+			return err
 		}
 
-		paymentMaxAmt += feeLimit
-
-		expiryTimestamp := invoice.Timestamp.Add(invoice.Expiry())
 		resp, err := r.AddAssetSellOrder(
 			ctx, &rfqrpc.AddAssetSellOrderRequest{
 				AssetSpecifier: &rfqrpc.AssetSpecifier{
@@ -7165,7 +7146,7 @@ func (r *rpcServer) SendPayment(req *tchrpc.SendPaymentRequest,
 					},
 				},
 				PaymentMaxAmt: uint64(paymentMaxAmt),
-				Expiry:        uint64(expiryTimestamp.Unix()),
+				Expiry:        uint64(expiry.Unix()),
 				PeerPubKey:    peerPubKey[:],
 				TimeoutSeconds: uint32(
 					rfq.DefaultTimeout.Seconds(),
@@ -7295,6 +7276,50 @@ func (r *rpcServer) SendPayment(req *tchrpc.SendPaymentRequest,
 	}
 }
 
+// parseRequest parses the payment request and returns the payment maximum
+// amount and the expiry time.
+func (r *rpcServer) parseRequest(
+	req *routerrpc.SendPaymentRequest) (lnwire.MilliSatoshi, time.Time,
+	error) {
+
+	invoice, err := zpay32.Decode(req.PaymentRequest, r.cfg.Lnd.ChainParams)
+	if err != nil {
+		return 0, time.Time{}, fmt.Errorf("error decoding payment "+
+			"request: %w", err)
+	}
+
+	var paymentMaxAmt lnwire.MilliSatoshi
+	if invoice.MilliSat == nil {
+		amt, err := lnrpc.UnmarshallAmt(req.Amt, req.AmtMsat)
+		if err != nil {
+			return 0, time.Time{}, fmt.Errorf("error "+
+				"unmarshalling amount: %w", err)
+		}
+		if amt == 0 {
+			return 0, time.Time{}, errors.New("amount must be " +
+				"specified when paying a zero amount invoice")
+		}
+
+		paymentMaxAmt = amt
+	} else {
+		paymentMaxAmt = *invoice.MilliSat
+	}
+
+	// Calculate the fee limit that should be used for this payment.
+	feeLimit, err := lnrpc.UnmarshallAmt(
+		req.FeeLimitSat, req.FeeLimitMsat,
+	)
+	if err != nil {
+		return 0, time.Time{}, fmt.Errorf("error unmarshalling fee "+
+			"limit: %w", err)
+	}
+
+	paymentMaxAmt += feeLimit
+
+	expiry := invoice.Timestamp.Add(invoice.Expiry())
+	return paymentMaxAmt, expiry, nil
+}
+
 // AddInvoice is a wrapper around lnd's lnrpc.AddInvoice method with asset
 // specific parameters. It allows RPC users to create invoices that correspond
 // to the specified asset amount.