feat: pay 0-amount invoices (#860)

* feat: pay 0-amount invoices

* chore: update lightning-tools dependency

* feat: pay 0 amount invoices in LND

* chore: typo

* fix: lightning-tools dependency version

---------

Co-authored-by: im-adithya <imadithyavardhan@gmail.com>

api/models.go

@@ -36,7 +36,7 @@ type API interface {
 	RedeemOnchainFunds(ctx context.Context, toAddress string, amount uint64, sendAll bool) (*RedeemOnchainFundsResponse, error)
 	GetBalances(ctx context.Context) (*BalancesResponse, error)
 	ListTransactions(ctx context.Context, appId *uint, limit uint64, offset uint64) (*ListTransactionsResponse, error)
-	SendPayment(ctx context.Context, invoice string) (*SendPaymentResponse, error)
+	SendPayment(ctx context.Context, invoice string, amountMsat *uint64) (*SendPaymentResponse, error)
 	CreateInvoice(ctx context.Context, amount uint64, description string) (*MakeInvoiceResponse, error)
 	LookupInvoice(ctx context.Context, paymentHash string) (*LookupInvoiceResponse, error)
 	RequestMempoolApi(endpoint string) (interface{}, error)
@@ -290,6 +290,10 @@ type SignMessageResponse struct {
 	Signature string `json:"signature"`
 }
 
+type PayInvoiceRequest struct {
+	Amount *uint64 `json:"amount"`
+}
+
 type MakeInvoiceRequest struct {
 	Amount      uint64 `json:"amount"`
 	Description string `json:"description"`

api/transactions.go

@@ -53,11 +53,11 @@ func (api *api) ListTransactions(ctx context.Context, appId *uint, limit uint64,
 	return &apiTransactions, nil
 }
 
-func (api *api) SendPayment(ctx context.Context, invoice string) (*SendPaymentResponse, error) {
+func (api *api) SendPayment(ctx context.Context, invoice string, amountMsat *uint64) (*SendPaymentResponse, error) {
 	if api.svc.GetLNClient() == nil {
 		return nil, errors.New("LNClient not started")
 	}
-	transaction, err := api.svc.GetTransactionsService().SendPaymentSync(ctx, invoice, nil, api.svc.GetLNClient(), nil, nil)
+	transaction, err := api.svc.GetTransactionsService().SendPaymentSync(ctx, invoice, amountMsat, nil, api.svc.GetLNClient(), nil, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -131,7 +131,7 @@ func (api *api) TopupIsolatedApp(ctx context.Context, userApp *db.App, amountMsa
 		return err
 	}
 
-	_, err = api.svc.GetTransactionsService().SendPaymentSync(ctx, transaction.PaymentRequest, nil, api.svc.GetLNClient(), nil, nil)
+	_, err = api.svc.GetTransactionsService().SendPaymentSync(ctx, transaction.PaymentRequest, nil, nil, api.svc.GetLNClient(), nil, nil)
 	return err
 }
 

frontend/package.json

@@ -20,7 +20,7 @@
     "prepare": "cd .. && husky frontend/.husky"
   },
   "dependencies": {
-    "@getalby/lightning-tools": "^5.1.1",
+    "@getalby/lightning-tools": "^5.1.2",
     "@getalby/sdk": "^3.8.2",
     "@radix-ui/react-accordion": "^1.2.0",
     "@radix-ui/react-alert-dialog": "^1.0.5",

frontend/src/routes.tsx

@@ -68,6 +68,7 @@ import ReceiveInvoice from "src/screens/wallet/receive/ReceiveInvoice";
 import ConfirmPayment from "src/screens/wallet/send/ConfirmPayment";
 import LnurlPay from "src/screens/wallet/send/LnurlPay";
 import PaymentSuccess from "src/screens/wallet/send/PaymentSuccess";
+import ZeroAmount from "src/screens/wallet/send/ZeroAmount";
 
 const routes = [
   {
@@ -128,6 +129,10 @@ const routes = [
                 path: "lnurl-pay",
                 element: <LnurlPay />,
               },
+              {
+                path: "0-amount",
+                element: <ZeroAmount />,
+              },
               {
                 path: "confirm-payment",
                 element: <ConfirmPayment />,

frontend/src/screens/wallet/Send.tsx

@@ -42,6 +42,15 @@ export default function Send() {
       }
 
       const invoice = new Invoice({ pr: recipient });
+      if (invoice.satoshi === 0) {
+        navigate(`/wallet/send/0-amount`, {
+          state: {
+            args: { paymentRequest: invoice },
+          },
+        });
+        return;
+      }
+
       navigate(`/wallet/send/confirm-payment`, {
         state: {
           args: { paymentRequest: invoice },

frontend/src/screens/wallet/send/ConfirmPayment.tsx

@@ -16,6 +16,7 @@ export default function ConfirmPayment() {
   const { toast } = useToast();
 
   const invoice = state?.args?.paymentRequest as Invoice;
+  const amount = state?.args?.amount as number | undefined;
   const [isLoading, setLoading] = React.useState(false);
 
   const onSubmit = async (event: React.FormEvent<HTMLFormElement>) => {
@@ -26,6 +27,9 @@ export default function ConfirmPayment() {
         `/api/payments/${invoice.paymentRequest}`,
         {
           method: "POST",
+          body: JSON.stringify({
+            amount: amount ? amount * 1000 : undefined,
+          }),
           headers: {
             "Content-Type": "application/json",
           },
@@ -71,7 +75,7 @@ export default function ConfirmPayment() {
         <div>
           <Label>Amount</Label>
           <p className="font-bold slashed-zero">
-            {new Intl.NumberFormat().format(invoice.satoshi)} sats
+            {new Intl.NumberFormat().format(amount || invoice.satoshi)} sats
           </p>
         </div>
         {invoice.description && (

frontend/src/screens/wallet/send/ZeroAmount.tsx

@@ -0,0 +1,93 @@
+import React from "react";
+import { Button } from "src/components/ui/button";
+import { Input } from "src/components/ui/input";
+import { Label } from "src/components/ui/label";
+import { LoadingButton } from "src/components/ui/loading-button";
+import { useToast } from "src/components/ui/use-toast";
+
+import { Invoice } from "@getalby/lightning-tools";
+import { Link, useLocation, useNavigate } from "react-router-dom";
+import Loading from "src/components/Loading";
+
+export default function ZeroAmount() {
+  const { state } = useLocation();
+  const navigate = useNavigate();
+  const { toast } = useToast();
+
+  const paymentRequest = state?.args?.paymentRequest as Invoice;
+  const [amount, setAmount] = React.useState("");
+  const [isLoading, setLoading] = React.useState(false);
+
+  const onSubmit = async (event: React.FormEvent<HTMLFormElement>) => {
+    event.preventDefault();
+    try {
+      if (!paymentRequest) {
+        throw new Error("no invoice set");
+      }
+      setLoading(true);
+
+      navigate(`/wallet/send/confirm-payment`, {
+        state: {
+          args: { paymentRequest, amount: parseInt(amount) },
+        },
+      });
+    } catch (e) {
+      toast({
+        variant: "destructive",
+        title: "Failed to send payment",
+        description: "" + e,
+      });
+      console.error(e);
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  React.useEffect(() => {
+    if (!paymentRequest) {
+      navigate("/wallet/send");
+    }
+  }, [navigate, paymentRequest]);
+
+  if (!paymentRequest) {
+    return <Loading />;
+  }
+
+  return (
+    <form onSubmit={onSubmit} className="grid gap-4">
+      <div>
+        {paymentRequest.description && (
+          <div className="mt-2">
+            <Label>Description</Label>
+            <p className="text-muted-foreground">
+              {paymentRequest.description}
+            </p>
+          </div>
+        )}
+        <div className="mb-2">
+          <Label htmlFor="amount">Amount</Label>
+          <Input
+            id="amount"
+            type="number"
+            value={amount}
+            placeholder="Amount in Satoshi..."
+            onChange={(e) => {
+              setAmount(e.target.value.trim());
+            }}
+            min={1}
+            required
+            autoFocus
+          />
+        </div>
+      </div>
+      <div className="flex gap-4">
+        <LoadingButton loading={isLoading} type="submit">
+          Continue
+        </LoadingButton>
+        <Link to="/wallet/send">
+          <Button variant="secondary">Back</Button>
+        </Link>
+      </div>
+    </form>
+  );
+}

frontend/yarn.lock

@@ -1337,10 +1337,10 @@
   resolved "https://registry.yarnpkg.com/@floating-ui/utils/-/utils-0.2.1.tgz#16308cea045f0fc777b6ff20a9f25474dd8293d2"
   integrity sha512-9TANp6GPoMtYzQdt54kfAyMmz1+osLlXdg2ENroU7zzrtflTLrrC/lgrIfaSe+Wu0b89GKccT7vxXA0MoAIO+Q==
 
-"@getalby/lightning-tools@^5.1.1":
-  version "5.1.1"
-  resolved "https://registry.yarnpkg.com/@getalby/lightning-tools/-/lightning-tools-5.1.1.tgz#51125b2c58ef9372ae9efa93d0808d2205914b91"
-  integrity sha512-qiGWY7AMnQXywNlpEUTm/2u7Qx0C0qV0i3vlAV5ip8xV2quo4hkesHuAh6dBg/p3VC7t1fa9YUe9677hvQ3fVA==
+"@getalby/lightning-tools@^5.1.2":
+  version "5.1.2"
+  resolved "https://registry.yarnpkg.com/@getalby/lightning-tools/-/lightning-tools-5.1.2.tgz#8a018e98d5c13097dd98d93192cf5e4e455f4c20"
+  integrity sha512-BwGm8eGbPh59BVa1gI5yJMantBl/Fdps6X4p1ZACnmxz9vDINX8/3aFoOnDlF7yyA2boXWCsReVQSr26Q2yjiQ==
 
 "@getalby/sdk@^3.8.2":
   version "3.8.2"

http/http_service.go

@@ -459,7 +459,14 @@ func (httpSvc *HttpService) balancesHandler(c echo.Context) error {
 func (httpSvc *HttpService) sendPaymentHandler(c echo.Context) error {
 	ctx := c.Request().Context()
 
-	paymentResponse, err := httpSvc.api.SendPayment(ctx, c.Param("invoice"))
+	var payInvoiceRequest api.PayInvoiceRequest
+	if err := c.Bind(&payInvoiceRequest); err != nil {
+		return c.JSON(http.StatusBadRequest, ErrorResponse{
+			Message: fmt.Sprintf("Bad request: %s", err.Error()),
+		})
+	}
+
+	paymentResponse, err := httpSvc.api.SendPayment(ctx, c.Param("invoice"), payInvoiceRequest.Amount)
 
 	if err != nil {
 		return c.JSON(http.StatusInternalServerError, ErrorResponse{

lnclient/breez/breez.go

@@ -99,7 +99,10 @@ func (bs *BreezService) Shutdown() error {
 	return bs.svc.Disconnect()
 }
 
-func (bs *BreezService) SendPaymentSync(ctx context.Context, payReq string) (*lnclient.PayInvoiceResponse, error) {
+func (bs *BreezService) SendPaymentSync(ctx context.Context, payReq string, amount *uint64) (*lnclient.PayInvoiceResponse, error) {
+	if amount != nil {
+		return nil, errors.New("0-amount invoices not supported")
+	}
 	sendPaymentRequest := breez_sdk.SendPaymentRequest{
 		Bolt11: payReq,
 	}

lnclient/cashu/cashu.go

@@ -76,7 +76,12 @@ func (cs *CashuService) Shutdown() error {
 	return nil
 }
 
-func (cs *CashuService) SendPaymentSync(ctx context.Context, invoice string) (response *lnclient.PayInvoiceResponse, err error) {
+func (cs *CashuService) SendPaymentSync(ctx context.Context, invoice string, amount *uint64) (response *lnclient.PayInvoiceResponse, err error) {
+	// TODO: support 0-amount invoices
+	if amount != nil {
+		return nil, errors.New("0-amount invoices not supported")
+	}
+
 	meltResponse, err := cs.wallet.Melt(invoice, cs.wallet.CurrentMint())
 	if err != nil {
 		logger.Logger.WithError(err).Error("Failed to melt invoice")

lnclient/greenlight/greenlight.go

@@ -117,7 +117,10 @@ func (gs *GreenlightService) Shutdown() error {
 	return nil
 }
 
-func (gs *GreenlightService) SendPaymentSync(ctx context.Context, payReq string) (*lnclient.PayInvoiceResponse, error) {
+func (gs *GreenlightService) SendPaymentSync(ctx context.Context, payReq string, amount *uint64) (*lnclient.PayInvoiceResponse, error) {
+	if amount != nil {
+		return nil, errors.New("0-amount invoices not supported")
+	}
 	response, err := gs.client.Pay(glalby.PayRequest{
 		Bolt11: payReq,
 	})

lnclient/ldk/ldk.go

@@ -472,7 +472,7 @@ func (ls *LDKService) resetRouterInternal() {
 	}
 }
 
-func (ls *LDKService) SendPaymentSync(ctx context.Context, invoice string) (*lnclient.PayInvoiceResponse, error) {
+func (ls *LDKService) SendPaymentSync(ctx context.Context, invoice string, amount *uint64) (*lnclient.PayInvoiceResponse, error) {
 	paymentRequest, err := decodepay.Decodepay(invoice)
 	if err != nil {
 		logger.Logger.WithFields(logrus.Fields{
@@ -482,8 +482,13 @@ func (ls *LDKService) SendPaymentSync(ctx context.Context, invoice string) (*lnc
 		return nil, err
 	}
 
+	paymentAmount := uint64(paymentRequest.MSatoshi)
+	if amount != nil {
+		paymentAmount = *amount
+	}
+
 	maxSpendable := ls.getMaxSpendable()
-	if paymentRequest.MSatoshi > maxSpendable {
+	if paymentAmount > maxSpendable {
 		ls.eventPublisher.Publish(&events.Event{
 			Event: "nwc_outgoing_liquidity_required",
 			Properties: map[string]interface{}{
@@ -499,7 +504,12 @@ func (ls *LDKService) SendPaymentSync(ctx context.Context, invoice string) (*lnc
 	ldkEventSubscription := ls.ldkEventBroadcaster.Subscribe()
 	defer ls.ldkEventBroadcaster.CancelSubscription(ldkEventSubscription)
 
-	paymentHash, err := ls.node.Bolt11Payment().Send(invoice, nil)
+	var paymentHash string
+	if amount == nil {
+		paymentHash, err = ls.node.Bolt11Payment().Send(invoice, nil)
+	} else {
+		paymentHash, err = ls.node.Bolt11Payment().SendUsingAmount(invoice, *amount, nil)
+	}
 	if err != nil {
 		logger.Logger.WithError(err).Error("SendPayment failed")
 		return nil, err
@@ -649,15 +659,15 @@ func (ls *LDKService) getMaxReceivable() int64 {
 	return int64(receivable)
 }
 
-func (ls *LDKService) getMaxSpendable() int64 {
-	var spendable int64 = 0
+func (ls *LDKService) getMaxSpendable() uint64 {
+	var spendable uint64 = 0
 	channels := ls.node.ListChannels()
 	for _, channel := range channels {
 		if channel.IsUsable {
-			spendable += min(int64(channel.OutboundCapacityMsat), int64(*channel.CounterpartyOutboundHtlcMaximumMsat))
+			spendable += min(channel.OutboundCapacityMsat, *channel.CounterpartyOutboundHtlcMaximumMsat)
 		}
 	}
-	return int64(spendable)
+	return spendable
 }
 
 func (ls *LDKService) MakeInvoice(ctx context.Context, amount int64, description string, descriptionHash string, expiry int64) (transaction *lnclient.Transaction, err error) {

lnclient/lnd/lnd.go

@@ -313,8 +313,14 @@ func (svc *LNDService) LookupInvoice(ctx context.Context, paymentHash string) (t
 	return transaction, nil
 }
 
-func (svc *LNDService) SendPaymentSync(ctx context.Context, payReq string) (*lnclient.PayInvoiceResponse, error) {
-	resp, err := svc.client.SendPaymentSync(ctx, &lnrpc.SendRequest{PaymentRequest: payReq})
+func (svc *LNDService) SendPaymentSync(ctx context.Context, payReq string, amount *uint64) (*lnclient.PayInvoiceResponse, error) {
+	sendRequest := &lnrpc.SendRequest{PaymentRequest: payReq}
+
+	if amount != nil {
+		sendRequest.AmtMsat = int64(*amount)
+	}
+
+	resp, err := svc.client.SendPaymentSync(ctx, sendRequest)
 	if err != nil {
 		return nil, err
 	}

lnclient/models.go

@@ -46,7 +46,7 @@ type NodeConnectionInfo struct {
 }
 
 type LNClient interface {
-	SendPaymentSync(ctx context.Context, payReq string) (*PayInvoiceResponse, error)
+	SendPaymentSync(ctx context.Context, payReq string, amount *uint64) (*PayInvoiceResponse, error)
 	SendKeysend(ctx context.Context, amount uint64, destination string, customRecords []TLVRecord, preimage string) (*PayKeysendResponse, error)
 	GetPubkey() string
 	GetInfo(ctx context.Context) (info *NodeInfo, err error)

lnclient/phoenixd/phoenixd.go

@@ -398,7 +398,11 @@ func (svc *PhoenixService) LookupInvoice(ctx context.Context, paymentHash string
 	return transaction, nil
 }
 
-func (svc *PhoenixService) SendPaymentSync(ctx context.Context, payReq string) (*lnclient.PayInvoiceResponse, error) {
+func (svc *PhoenixService) SendPaymentSync(ctx context.Context, payReq string, amount *uint64) (*lnclient.PayInvoiceResponse, error) {
+	// TODO: support 0-amount invoices
+	if amount != nil {
+		return nil, errors.New("0-amount invoices not supported")
+	}
 	form := url.Values{}
 	form.Add("invoice", payReq)
 	req, err := http.NewRequest(http.MethodPost, svc.Address+"/payinvoice", strings.NewReader(form.Encode()))

nip47/controllers/multi_pay_invoice_controller.go

@@ -69,7 +69,7 @@ func (controller *nip47Controller) HandleMultiPayInvoiceEvent(ctx context.Contex
 			dTag := []string{"d", invoiceDTagValue}
 
 			controller.
-				pay(ctx, bolt11, metadata, &paymentRequest, nip47Request, requestEventId, app, publishResponse, nostr.Tags{dTag})
+				pay(ctx, bolt11, invoiceInfo.Amount, metadata, &paymentRequest, nip47Request, requestEventId, app, publishResponse, nostr.Tags{dTag})
 		}(invoiceInfo)
 	}