lnd.xprv/zpay32/encode.go

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package zpay32
import (
"bytes"
"encoding/binary"
"fmt"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcutil"
"github.com/btcsuite/btcutil/bech32"
"github.com/lightningnetwork/lnd/lnwire"
)
// Encode takes the given MessageSigner and returns a string encoding this
// invoice signed by the node key of the signer.
func (invoice *Invoice) Encode(signer MessageSigner) (string, error) {
// First check that this invoice is valid before starting the encoding.
if err := validateInvoice(invoice); err != nil {
return "", err
}
// The buffer will encoded the invoice data using 5-bit groups (base32).
var bufferBase32 bytes.Buffer
// The timestamp will be encoded using 35 bits, in base32.
timestampBase32 := uint64ToBase32(uint64(invoice.Timestamp.Unix()))
// The timestamp must be exactly 35 bits, which means 7 groups. If it
// can fit into fewer groups we add leading zero groups, if it is too
// big we fail early, as there is not possible to encode it.
if len(timestampBase32) > timestampBase32Len {
return "", fmt.Errorf("timestamp too big: %d",
invoice.Timestamp.Unix())
}
// Add zero bytes to the first timestampBase32Len-len(timestampBase32)
// groups, then add the non-zero groups.
zeroes := make([]byte, timestampBase32Len-len(timestampBase32))
_, err := bufferBase32.Write(zeroes)
if err != nil {
return "", fmt.Errorf("unable to write to buffer: %v", err)
}
_, err = bufferBase32.Write(timestampBase32)
if err != nil {
return "", fmt.Errorf("unable to write to buffer: %v", err)
}
// We now write the tagged fields to the buffer, which will fill the
// rest of the data part before the signature.
if err := writeTaggedFields(&bufferBase32, invoice); err != nil {
return "", err
}
// The human-readable part (hrp) is "ln" + net hrp + optional amount.
hrp := "ln" + invoice.Net.Bech32HRPSegwit
if invoice.MilliSat != nil {
// Encode the amount using the fewest possible characters.
am, err := encodeAmount(*invoice.MilliSat)
if err != nil {
return "", err
}
hrp += am
}
// The signature is over the single SHA-256 hash of the hrp + the
// tagged fields encoded in base256.
taggedFieldsBytes, err := bech32.ConvertBits(bufferBase32.Bytes(), 5, 8, true)
if err != nil {
return "", err
}
toSign := append([]byte(hrp), taggedFieldsBytes...)
hash := chainhash.HashB(toSign)
// We use compact signature format, and also encoded the recovery ID
// such that a reader of the invoice can recover our pubkey from the
// signature.
sign, err := signer.SignCompact(hash)
if err != nil {
return "", err
}
// From the header byte we can extract the recovery ID, and the last 64
// bytes encode the signature.
recoveryID := sign[0] - 27 - 4
var sig lnwire.Sig
copy(sig[:], sign[1:])
// If the pubkey field was explicitly set, it must be set to the pubkey
// used to create the signature.
if invoice.Destination != nil {
signature, err := sig.ToSignature()
if err != nil {
return "", fmt.Errorf("unable to deserialize "+
"signature: %v", err)
}
valid := signature.Verify(hash, invoice.Destination)
if !valid {
return "", fmt.Errorf("signature does not match " +
"provided pubkey")
}
}
// Convert the signature to base32 before writing it to the buffer.
signBase32, err := bech32.ConvertBits(append(sig[:], recoveryID), 8, 5, true)
if err != nil {
return "", err
}
bufferBase32.Write(signBase32)
// Now we can create the bech32 encoded string from the base32 buffer.
b32, err := bech32.Encode(hrp, bufferBase32.Bytes())
if err != nil {
return "", err
}
// Before returning, check that the bech32 encoded string is not greater
// than our largest supported invoice size.
if len(b32) > maxInvoiceLength {
return "", ErrInvoiceTooLarge
}
return b32, nil
}
// writeTaggedFields writes the non-nil tagged fields of the Invoice to the
// base32 buffer.
func writeTaggedFields(bufferBase32 *bytes.Buffer, invoice *Invoice) error {
if invoice.PaymentHash != nil {
err := writeBytes32(bufferBase32, fieldTypeP, *invoice.PaymentHash)
if err != nil {
return err
}
}
if invoice.Description != nil {
base32, err := bech32.ConvertBits([]byte(*invoice.Description),
8, 5, true)
if err != nil {
return err
}
err = writeTaggedField(bufferBase32, fieldTypeD, base32)
if err != nil {
return err
}
}
if invoice.DescriptionHash != nil {
err := writeBytes32(
bufferBase32, fieldTypeH, *invoice.DescriptionHash,
)
if err != nil {
return err
}
}
if invoice.minFinalCLTVExpiry != nil {
finalDelta := uint64ToBase32(*invoice.minFinalCLTVExpiry)
err := writeTaggedField(bufferBase32, fieldTypeC, finalDelta)
if err != nil {
return err
}
}
if invoice.expiry != nil {
seconds := invoice.expiry.Seconds()
expiry := uint64ToBase32(uint64(seconds))
err := writeTaggedField(bufferBase32, fieldTypeX, expiry)
if err != nil {
return err
}
}
if invoice.FallbackAddr != nil {
var version byte
switch addr := invoice.FallbackAddr.(type) {
case *btcutil.AddressPubKeyHash:
version = 17
case *btcutil.AddressScriptHash:
version = 18
case *btcutil.AddressWitnessPubKeyHash:
version = addr.WitnessVersion()
case *btcutil.AddressWitnessScriptHash:
version = addr.WitnessVersion()
default:
return fmt.Errorf("unknown fallback address type")
}
base32Addr, err := bech32.ConvertBits(
invoice.FallbackAddr.ScriptAddress(), 8, 5, true)
if err != nil {
return err
}
err = writeTaggedField(bufferBase32, fieldTypeF,
append([]byte{version}, base32Addr...))
if err != nil {
return err
}
}
for _, routeHint := range invoice.RouteHints {
// Each hop hint is encoded using 51 bytes, so we'll make to
// sure to allocate enough space for the whole route hint.
routeHintBase256 := make([]byte, 0, hopHintLen*len(routeHint))
for _, hopHint := range routeHint {
hopHintBase256 := make([]byte, hopHintLen)
copy(hopHintBase256[:33], hopHint.NodeID.SerializeCompressed())
binary.BigEndian.PutUint64(
hopHintBase256[33:41], hopHint.ChannelID,
)
binary.BigEndian.PutUint32(
hopHintBase256[41:45], hopHint.FeeBaseMSat,
)
binary.BigEndian.PutUint32(
hopHintBase256[45:49], hopHint.FeeProportionalMillionths,
)
binary.BigEndian.PutUint16(
hopHintBase256[49:51], hopHint.CLTVExpiryDelta,
)
routeHintBase256 = append(routeHintBase256, hopHintBase256...)
}
routeHintBase32, err := bech32.ConvertBits(
routeHintBase256, 8, 5, true,
)
if err != nil {
return err
}
err = writeTaggedField(bufferBase32, fieldTypeR, routeHintBase32)
if err != nil {
return err
}
}
if invoice.Destination != nil {
// Convert 33 byte pubkey to 53 5-bit groups.
pubKeyBase32, err := bech32.ConvertBits(
invoice.Destination.SerializeCompressed(), 8, 5, true)
if err != nil {
return err
}
if len(pubKeyBase32) != pubKeyBase32Len {
return fmt.Errorf("invalid pubkey length: %d",
len(invoice.Destination.SerializeCompressed()))
}
err = writeTaggedField(bufferBase32, fieldTypeN, pubKeyBase32)
if err != nil {
return err
}
}
if invoice.PaymentAddr != nil {
err := writeBytes32(
bufferBase32, fieldTypeS, *invoice.PaymentAddr,
)
if err != nil {
return err
}
}
if invoice.Features.SerializeSize32() > 0 {
var b bytes.Buffer
err := invoice.Features.RawFeatureVector.EncodeBase32(&b)
if err != nil {
return err
}
err = writeTaggedField(bufferBase32, fieldType9, b.Bytes())
if err != nil {
return err
}
}
return nil
}
// writeBytes32 encodes a 32-byte array as base32 and writes it to bufferBase32
// under the passed fieldType.
func writeBytes32(bufferBase32 *bytes.Buffer, fieldType byte, b [32]byte) error {
// Convert 32 byte hash to 52 5-bit groups.
base32, err := bech32.ConvertBits(b[:], 8, 5, true)
if err != nil {
return err
}
return writeTaggedField(bufferBase32, fieldType, base32)
}
// writeTaggedField takes the type of a tagged data field, and the data of
// the tagged field (encoded in base32), and writes the type, length and data
// to the buffer.
func writeTaggedField(bufferBase32 *bytes.Buffer, dataType byte, data []byte) error {
// Length must be exactly 10 bits, so add leading zero groups if
// needed.
lenBase32 := uint64ToBase32(uint64(len(data)))
for len(lenBase32) < 2 {
lenBase32 = append([]byte{0}, lenBase32...)
}
if len(lenBase32) != 2 {
return fmt.Errorf("data length too big to fit within 10 bits: %d",
len(data))
}
err := bufferBase32.WriteByte(dataType)
if err != nil {
return fmt.Errorf("unable to write to buffer: %v", err)
}
_, err = bufferBase32.Write(lenBase32)
if err != nil {
return fmt.Errorf("unable to write to buffer: %v", err)
}
_, err = bufferBase32.Write(data)
if err != nil {
return fmt.Errorf("unable to write to buffer: %v", err)
}
return nil
}
// uint64ToBase32 converts a uint64 to a base32 encoded integer encoded using
// as few 5-bit groups as possible.
func uint64ToBase32(num uint64) []byte {
// Return at least one group.
if num == 0 {
return []byte{0}
}
// To fit an uint64, we need at most is ceil(64 / 5) = 13 groups.
arr := make([]byte, 13)
i := 13
for num > 0 {
i--
arr[i] = byte(num & uint64(31)) // 0b11111 in binary
num >>= 5
}
// We only return non-zero leading groups.
return arr[i:]
}