From df72097f2dc8879fd2bef8400b0c10f948a10b4a Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@lightning.engineering>
Date: Thu, 5 Dec 2019 07:59:17 -0800
Subject: [PATCH] zpay32/invoice: parse payment address as type s

---
 zpay32/invoice.go      | 33 +++++++++++++++++++++++++++++++++
 zpay32/invoice_test.go | 35 ++++++++++++++++++++++++++++++++---
 2 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/zpay32/invoice.go b/zpay32/invoice.go
index 0df3b1d9..9cfc0a9f 100644
--- a/zpay32/invoice.go
+++ b/zpay32/invoice.go
@@ -73,6 +73,11 @@ const (
 	// supported or required by the receiver.
 	fieldType9 = 5
 
+	// fieldTypeS contains a 32-byte payment address, which is a nonce
+	// included in the final hop's payload to prevent intermediaries from
+	// probing the recipient.
+	fieldTypeS = 16
+
 	// maxInvoiceLength is the maximum total length an invoice can have.
 	// This is chosen to be the maximum number of bytes that can fit into a
 	// single QR code: https://en.wikipedia.org/wiki/QR_code#Storage
@@ -126,6 +131,10 @@ type Invoice struct {
 	// invoice.
 	PaymentHash *[32]byte
 
+	// PaymentAddr is the payment address to be used by payments to prevent
+	// probing of the destination.
+	PaymentAddr *[32]byte
+
 	// Destination is the public key of the target node. This will always
 	// be set after decoding, and can optionally be set before encoding to
 	// include the pubkey as an 'n' field. If this is not set before
@@ -258,6 +267,14 @@ func Features(features *lnwire.FeatureVector) func(*Invoice) {
 	}
 }
 
+// PaymentAddr is a functional option that allows callers of NewInvoice to set
+// the desired payment address tht is advertised on the invoice.
+func PaymentAddr(addr [32]byte) func(*Invoice) {
+	return func(i *Invoice) {
+		i.PaymentAddr = &addr
+	}
+}
+
 // NewInvoice creates a new Invoice object. The last parameter is a set of
 // variadic arguments for setting optional fields of the invoice.
 //
@@ -643,6 +660,14 @@ func parseTaggedFields(invoice *Invoice, fields []byte, net *chaincfg.Params) er
 			}
 
 			invoice.PaymentHash, err = parse32Bytes(base32Data)
+		case fieldTypeS:
+			if invoice.PaymentAddr != nil {
+				// We skip the field if we have already seen a
+				// supported one.
+				continue
+			}
+
+			invoice.PaymentAddr, err = parse32Bytes(base32Data)
 		case fieldTypeD:
 			if invoice.Description != nil {
 				// We skip the field if we have already seen a
@@ -1060,6 +1085,14 @@ func writeTaggedFields(bufferBase32 *bytes.Buffer, invoice *Invoice) error {
 			return err
 		}
 	}
+	if invoice.PaymentAddr != nil {
+		err := writeBytes32(
+			bufferBase32, fieldTypeS, *invoice.PaymentAddr,
+		)
+		if err != nil {
+			return err
+		}
+	}
 
 	return nil
 }
diff --git a/zpay32/invoice_test.go b/zpay32/invoice_test.go
index eec242f7..5feff241 100644
--- a/zpay32/invoice_test.go
+++ b/zpay32/invoice_test.go
@@ -28,7 +28,19 @@ var (
 	testMillisat25mBTC   = lnwire.MilliSatoshi(2500000000)
 	testMillisat20mBTC   = lnwire.MilliSatoshi(2000000000)
 
-	testPaymentHashSlice, _ = hex.DecodeString("0001020304050607080900010203040506070809000102030405060708090102")
+	testPaymentHash = [32]byte{
+		0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+		0x08, 0x09, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05,
+		0x06, 0x07, 0x08, 0x09, 0x00, 0x01, 0x02, 0x03,
+		0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x01, 0x02,
+	}
+
+	testPaymentAddr = [32]byte{
+		0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x01, 0x02,
+		0x06, 0x07, 0x08, 0x09, 0x00, 0x01, 0x02, 0x03,
+		0x08, 0x09, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05,
+		0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+	}
 
 	testEmptyString    = ""
 	testCupOfCoffee    = "1 cup coffee"
@@ -94,7 +106,6 @@ var (
 	}
 
 	// Must be initialized in init().
-	testPaymentHash     [32]byte
 	testDescriptionHash [32]byte
 
 	ltcTestNetParams chaincfg.Params
@@ -102,7 +113,6 @@ var (
 )
 
 func init() {
-	copy(testPaymentHash[:], testPaymentHashSlice[:])
 	copy(testDescriptionHash[:], testDescriptionHashSlice[:])
 
 	// Initialize litecoin testnet and mainnet params by applying key fields
@@ -587,6 +597,25 @@ func TestDecodeEncode(t *testing.T) {
 				return i
 			},
 		},
+		{
+			// Send 2500uBTC for a cup of coffee with a payment
+			// address.
+			encodedInvoice: "lnbc2500u1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5xysxxatsyp3k7enxv4jsnp4q0n326hr8v9zprg8gsvezcch06gfaqqhde2aj730yg0durunfhv66sp5qszsvpcgpyqsyps8pqysqqgzqvyqjqqpqgpsgpgqqypqxpq9qcrsusq8nx2hdt3st3ankwz23xy9w7udvqq3f0mdlpc6ga5ew3y67u4qkx8vu72ejg5x6tqhyclm28r7r0mg6lx9x3vls9g6glp2qy3y34cpry54xp",
+			valid:          true,
+			decodedInvoice: func() *Invoice {
+				i, _ := NewInvoice(
+					&chaincfg.MainNetParams,
+					testPaymentHash,
+					time.Unix(1496314658, 0),
+					Amount(testMillisat2500uBTC),
+					Description(testCupOfCoffee),
+					Destination(testPubKey),
+					PaymentAddr(testPaymentAddr),
+				)
+
+				return i
+			},
+		},
 		{
 			// Decode a mainnet invoice while expecting active net to be testnet
 			encodedInvoice: "lnbc241pveeq09pp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdqqnp4q0n326hr8v9zprg8gsvezcch06gfaqqhde2aj730yg0durunfhv66jd3m5klcwhq68vdsmx2rjgxeay5v0tkt2v5sjaky4eqahe4fx3k9sqavvce3capfuwv8rvjng57jrtfajn5dkpqv8yelsewtljwmmycq62k443",