Merge pull request #654 from wilmerpaulino/invoice-without-amount

Support invoices without amount specified

cmd/lncli/commands.go

@@ -1014,6 +1014,7 @@ func sendPayment(ctx *cli.Context) error {
 	if ctx.IsSet("pay_req") {
 		req = &lnrpc.SendRequest{
 			PaymentRequest: ctx.String("pay_req"),
+			Amt:            ctx.Int64("amt"),
 		}
 	} else {
 		args := ctx.Args()
@@ -1138,6 +1139,11 @@ var payInvoiceCommand = cli.Command{
 			Name:  "pay_req",
 			Usage: "a zpay32 encoded payment request to fulfill",
 		},
+		cli.Int64Flag{
+			Name: "amt",
+			Usage: "(optional) number of satoshis to fulfill the " +
+				"invoice",
+		},
 	},
 	Action: actionDecorator(payInvoice),
 }
@@ -1158,6 +1164,7 @@ func payInvoice(ctx *cli.Context) error {
 
 	req := &lnrpc.SendRequest{
 		PaymentRequest: payReq,
+		Amt:            ctx.Int64("amt"),
 	}
 
 	return sendPaymentRequest(ctx, req)
@@ -1168,9 +1175,10 @@ var addInvoiceCommand = cli.Command{
 	Usage: "add a new invoice.",
 	Description: `
 	Add a new invoice, expressing intent for a future payment.
-	
+
-	The number of satoshis in this invoice is necessary for the creation, 
+	Invoices without an amount can be created by not supplying any
-	the remaining parameters are optional.`,
+	parameters or providing an amount of 0. These invoices allow the payee
+	to specify the amount of satoshis they wish to send.`,
 	ArgsUsage: "value preimage",
 	Flags: []cli.Flag{
 		cli.StringFlag{
@@ -1239,8 +1247,6 @@ func addInvoice(ctx *cli.Context) error {
 		if err != nil {
 			return fmt.Errorf("unable to decode amt argument: %v", err)
 		}
-	default:
-		return fmt.Errorf("amt argument missing")
 	}
 
 	switch {

htlcswitch/link.go

@@ -1469,7 +1469,15 @@ func (l *channelLink) processLockedInHtlcs(
 				// Otherwise, we settle this htlc within our
 				// local state update log, then send the update
 				// entry to the remote party.
-				if !l.cfg.DebugHTLC && pd.Amount < invoice.Terms.Value {
+				//
+				// NOTE: We make an exception when the value
+				// requested by the invoice is zero. This means
+				// the invoice allows the payee to specify the
+				// amount of satoshis they wish to send.
+				// So since we expect the htlc to have a
+				// different amount, we should not fail.
+				if !l.cfg.DebugHTLC && invoice.Terms.Value > 0 &&
+					pd.Amount < invoice.Terms.Value {
 					log.Errorf("rejecting htlc due to incorrect "+
 						"amount: expected %v, received %v",
 						invoice.Terms.Value, pd.Amount)
@@ -1484,7 +1492,14 @@ func (l *channelLink) processLockedInHtlcs(
 				// ensure that it was crafted correctly by the
 				// sender and matches the HTLC we were
 				// extended.
-				if !l.cfg.DebugHTLC &&
+				//
+				// NOTE: We make an exception when the value
+				// requested by the invoice is zero. This means
+				// the invoice allows the payee to specify the
+				// amount of satoshis they wish to send.
+				// So since we expect the htlc to have a
+				// different amount, we should not fail.
+				if !l.cfg.DebugHTLC && invoice.Terms.Value > 0 &&
 					fwdInfo.AmountToForward != invoice.Terms.Value {
 
 					log.Errorf("Onion payload of incoming "+

rpcserver.go

@@ -1623,18 +1623,20 @@ func (r *rpcServer) SendPayment(paymentStream lnrpc.Lightning_SendPaymentServer)
 					}
 					p.dest = payReq.Destination.SerializeCompressed()
 
+					// If the amount was not included in the
+					// invoice, then we let the payee
+					// specify the amount of satoshis they
+					// wish to send. We override the amount
+					// to pay with the amount provided from
+					// the payment request.
 					if payReq.MilliSat == nil {
-						err := fmt.Errorf("only payment" +
+						p.msat = lnwire.NewMSatFromSatoshis(
-							" requests specifying" +
+							btcutil.Amount(nextPayment.Amt),
-							" the amount are" +
+						)
-							" currently supported")
+					} else {
-						select {
+						p.msat = *payReq.MilliSat
-						case errChan <- err:
-						case <-reqQuit:
-						}
-						return
 					}
-					p.msat = *payReq.MilliSat
+
 					p.pHash = payReq.PaymentHash[:]
 					p.cltvDelta = uint16(payReq.MinFinalCLTVExpiry())
 				} else {
@@ -1806,11 +1808,18 @@ func (r *rpcServer) SendPaymentSync(ctx context.Context,
 
 		destPub = payReq.Destination
 
+		// If the amount was not included in the invoice, then we let
+		// the payee specify the amount of satoshis they wish to send.
+		// We override the amount to pay with the amount provided from
+		// the payment request.
 		if payReq.MilliSat == nil {
-			return nil, fmt.Errorf("payment requests with no " +
+			amtMSat = lnwire.NewMSatFromSatoshis(
-				"amount specified not currently supported")
+				btcutil.Amount(nextPayment.Amt),
+			)
+		} else {
+			amtMSat = *payReq.MilliSat
 		}
-		amtMSat = *payReq.MilliSat
+
 		rHash = *payReq.PaymentHash
 		cltvDelta = uint16(payReq.MinFinalCLTVExpiry())
 
@@ -1939,14 +1948,10 @@ func (r *rpcServer) AddInvoice(ctx context.Context,
 
 	amt := btcutil.Amount(invoice.Value)
 	amtMSat := lnwire.NewMSatFromSatoshis(amt)
-	switch {
-	// The value of an invoice MUST NOT be zero.
-	case invoice.Value == 0:
-		return nil, fmt.Errorf("zero value invoices are disallowed")
 
 	// The value of the invoice must also not exceed the current soft-limit
 	// on the largest payment within the network.
-	case amtMSat > maxPaymentMSat:
+	if amtMSat > maxPaymentMSat {
 		return nil, fmt.Errorf("payment of %v is too large, max "+
 			"payment allowed is %v", amt, maxPaymentMSat.ToSatoshis())
 	}
@@ -1962,9 +1967,12 @@ func (r *rpcServer) AddInvoice(ctx context.Context,
 	// expiry, fallback address, and the amount field.
 	var options []func(*zpay32.Invoice)
 
-	// Add the amount. This field is optional by the BOLT-11 format, but
+	// We only include the amount in the invoice if it is greater than 0.
-	// we require it for now.
+	// By not including the amount, we enable the creation of invoices that
-	options = append(options, zpay32.Amount(amtMSat))
+	// allow the payee to specify the amount of satoshis they wish to send.
+	if amtMSat > 0 {
+		options = append(options, zpay32.Amount(amtMSat))
+	}
 
 	// If specified, add a fallback address to the payment request.
 	if len(invoice.FallbackAddr) > 0 {

zpay32/invoice_test.go

@@ -233,6 +233,26 @@ func TestDecodeEncode(t *testing.T) {
 			},
 			skipEncoding: true, // Skip encoding since we don't have the unknown fields to encode.
 		},
+		{
+			// Invoice with no amount.
+			encodedInvoice: "lnbc1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5xysxxatsyp3k7enxv4jshwlglv23cytkzvq8ld39drs8sq656yh2zn0aevrwu6uqctaklelhtpjnmgjdzmvwsh0kuxuwqf69fjeap9m5mev2qzpp27xfswhs5vgqmn9xzq",
+			valid:          true,
+			decodedInvoice: func() *Invoice {
+				return &Invoice{
+					Net:         &chaincfg.MainNetParams,
+					Timestamp:   time.Unix(1496314658, 0),
+					PaymentHash: &testPaymentHash,
+					Description: &testCupOfCoffee,
+					Destination: testPubKey,
+				}
+			},
+			beforeEncoding: func(i *Invoice) {
+				// Since this destination pubkey was recovered
+				// from the signature, we must set it nil before
+				// encoding to get back the same invoice string.
+				i.Destination = nil
+			},
+		},
 		{
 			// Please make a donation of any amount using rhash 0001020304050607080900010203040506070809000102030405060708090102 to me @03e7156ae33b0a208d0744199163177e909e80176e55d97a2f221ede0f934dd9ad
 			encodedInvoice: "lnbc1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdpl2pkx2ctnv5sxxmmwwd5kgetjypeh2ursdae8g6twvus8g6rfwvs8qun0dfjkxaq8rkx3yf5tcsyz3d73gafnh3cax9rn449d9p5uxz9ezhhypd0elx87sjle52x86fux2ypatgddc6k63n7erqz25le42c4u4ecky03ylcqca784w",
@@ -531,6 +551,19 @@ func TestNewInvoice(t *testing.T) {
 			},
 			valid: false, // Both Description and DescriptionHash set.
 		},
+		{
+			// Invoice with no amount.
+			newInvoice: func() (*Invoice, error) {
+				return NewInvoice(
+					&chaincfg.MainNetParams,
+					testPaymentHash,
+					time.Unix(1496314658, 0),
+					Description(testCupOfCoffee),
+				)
+			},
+			valid:          true,
+			encodedInvoice: "lnbc1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5xysxxatsyp3k7enxv4jshwlglv23cytkzvq8ld39drs8sq656yh2zn0aevrwu6uqctaklelhtpjnmgjdzmvwsh0kuxuwqf69fjeap9m5mev2qzpp27xfswhs5vgqmn9xzq",
+		},
 		{
 			// 'n' field set.
 			newInvoice: func() (*Invoice, error) {