zpay32: add payment metadata field

zpay32/decode.go

@@ -229,6 +229,15 @@ func parseTaggedFields(invoice *Invoice, fields []byte, net *chaincfg.Params) er
 			}
 
 			invoice.Description, err = parseDescription(base32Data)
+		case fieldTypeM:
+			if invoice.Metadata != nil {
+				// We skip the field if we have already seen a
+				// supported one.
+				continue
+			}
+
+			invoice.Metadata, err = parseMetadata(base32Data)
+
 		case fieldTypeN:
 			if invoice.Destination != nil {
 				// We skip the field if we have already seen a
@@ -345,6 +354,12 @@ func parseDescription(data []byte) (*string, error) {
 	return &description, nil
 }
 
+// parseMetadata converts the data (encoded in base32) into a byte slice to use
+// as the metadata.
+func parseMetadata(data []byte) ([]byte, error) {
+	return bech32.ConvertBits(data, 5, 8, false)
+}
+
 // parseDestination converts the data (encoded in base32) into a 33-byte public
 // key of the payee node.
 func parseDestination(data []byte) (*btcec.PublicKey, error) {

zpay32/encode.go

@@ -164,6 +164,17 @@ func writeTaggedFields(bufferBase32 *bytes.Buffer, invoice *Invoice) error {
 		}
 	}
 
+	if invoice.Metadata != nil {
+		base32, err := bech32.ConvertBits(invoice.Metadata, 8, 5, true)
+		if err != nil {
+			return err
+		}
+		err = writeTaggedField(bufferBase32, fieldTypeM, base32)
+		if err != nil {
+			return err
+		}
+	}
+
 	if invoice.minFinalCLTVExpiry != nil {
 		finalDelta := uint64ToBase32(*invoice.minFinalCLTVExpiry)
 		err := writeTaggedField(bufferBase32, fieldTypeC, finalDelta)

zpay32/invoice.go

@@ -46,6 +46,9 @@ const (
 	// fieldTypeD contains a short description of the payment.
 	fieldTypeD = 13
 
+	// fieldTypeM contains the payment metadata.
+	fieldTypeM = 27
+
 	// fieldTypeN contains the pubkey of the target node.
 	fieldTypeN = 19
 
@@ -183,6 +186,10 @@ type Invoice struct {
 	// Features represents an optional field used to signal optional or
 	// required support for features by the receiver.
 	Features *lnwire.FeatureVector
+
+	// Metadata is additional data that is sent along with the payment to
+	// the payee.
+	Metadata []byte
 }
 
 // Amount is a functional option that allows callers of NewInvoice to set the
@@ -273,6 +280,14 @@ func PaymentAddr(addr [32]byte) func(*Invoice) {
 	}
 }
 
+// Metadata is a functional option that allows callers of NewInvoice to set
+// the desired payment Metadata tht is advertised on the invoice.
+func Metadata(metadata []byte) func(*Invoice) {
+	return func(i *Invoice) {
+		i.Metadata = metadata
+	}
+}
+
 // NewInvoice creates a new Invoice object. The last parameter is a set of
 // variadic arguments for setting optional fields of the invoice.
 //

zpay32/invoice_test.go

@@ -27,6 +27,7 @@ var (
 	testMillisat2500uBTC = lnwire.MilliSatoshi(250000000)
 	testMillisat25mBTC   = lnwire.MilliSatoshi(2500000000)
 	testMillisat20mBTC   = lnwire.MilliSatoshi(2000000000)
+	testMillisat10mBTC   = lnwire.MilliSatoshi(1000000000)
 
 	testPaymentHash = [32]byte{
 		0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
@@ -54,6 +55,7 @@ var (
 	testCoffeeBeans     = "coffee beans"
 	testCupOfNonsense   = "ナンセンス 1杯"
 	testPleaseConsider  = "Please consider supporting this project"
+	testPaymentMetadata = "payment metadata inside"
 
 	testPrivKeyBytes, _     = hex.DecodeString("e126f68f7eafcc8b74f54d269fe206be715000f94dac067d1c04a8ca3b2db734")
 	testPrivKey, testPubKey = btcec.PrivKeyFromBytes(testPrivKeyBytes)
@@ -692,6 +694,33 @@ func TestDecodeEncode(t *testing.T) {
 				}
 			},
 		},
+		{
+			// Please send 0.01 BTC with payment metadata 0x01fafaf0.
+			encodedInvoice: "lnbc10m1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdp9wpshjmt9de6zqmt9w3skgct5vysxjmnnd9jx2mq8q8a04uqsp5zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zygs9q2gqqqqqqsgq7hf8he7ecf7n4ffphs6awl9t6676rrclv9ckg3d3ncn7fct63p6s365duk5wrk202cfy3aj5xnnp5gs3vrdvruverwwq7yzhkf5a3xqpd05wjc",
+			valid:          true,
+			decodedInvoice: func() *Invoice {
+				return &Invoice{
+					Net:         &chaincfg.MainNetParams,
+					MilliSat:    &testMillisat10mBTC,
+					Timestamp:   time.Unix(1496314658, 0),
+					PaymentHash: &testPaymentHash,
+					Description: &testPaymentMetadata,
+					Destination: testPubKey,
+					PaymentAddr: &specPaymentAddr,
+					Features: lnwire.NewFeatureVector(
+						lnwire.NewRawFeatureVector(8, 14, 48),
+						lnwire.Features,
+					),
+					Metadata: []byte{0x01, 0xfa, 0xfa, 0xf0},
+				}
+			},
+			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
+			},
+		},
 	}
 
 	for i, test := range tests {