package zpay32 import ( "bytes" "encoding/binary" "fmt" "strings" "time" "github.com/lightningnetwork/lnd/lnwire" "github.com/lightningnetwork/lnd/routing" "github.com/roasbeef/btcd/btcec" "github.com/roasbeef/btcd/chaincfg" "github.com/roasbeef/btcd/chaincfg/chainhash" "github.com/roasbeef/btcutil" "github.com/roasbeef/btcutil/bech32" ) const ( // mSatPerBtc is the number of millisatoshis in 1 BTC. mSatPerBtc = 100000000000 // signatureBase32Len is the number of 5-bit groups needed to encode // the 512 bit signature + 8 bit recovery ID. signatureBase32Len = 104 // timestampBase32Len is the number of 5-bit groups needed to encode // the 35-bit timestamp. timestampBase32Len = 7 // hashBase32Len is the number of 5-bit groups needed to encode a // 256-bit hash. Note that the last group will be padded with zeroes. hashBase32Len = 52 // pubKeyBase32Len is the number of 5-bit groups needed to encode a // 33-byte compressed pubkey. Note that the last group will be padded // with zeroes. pubKeyBase32Len = 53 // The following byte values correspond to the supported field types. // The field name is the character representing that 5-bit value in the // bech32 string. // fieldTypeP is the field containing the payment hash. fieldTypeP = 1 // fieldTypeD contains a short description of the payment. fieldTypeD = 13 // fieldTypeN contains the pubkey of the target node. fieldTypeN = 19 // fieldTypeH contains the hash of a description of the payment. fieldTypeH = 23 // fieldTypeX contains the expiry in seconds of the invoice. fieldTypeX = 6 // fieldTypeF contains a fallback on-chain address. fieldTypeF = 9 // fieldTypeR contains extra routing information. fieldTypeR = 3 // fieldTypeC contains an optional requested final CLTV delta. fieldTypeC = 24 ) // MessageSigner is passed to the Encode method to provide a signature // corresponding to the node's pubkey. type MessageSigner struct { // SignCompact signs the passed hash with the node's privkey. The // returned signature should be 65 bytes, where the last 64 are the // compact signature, and the first one is a header byte. This is the // format returned by btcec.SignCompact. SignCompact func(hash []byte) ([]byte, error) } // Invoice represents a decoded invoice, or to-be-encoded invoice. Some of the // fields are optional, and will only be non-nil if the invoice this was parsed // from contains that field. When encoding, only the non-nil fields will be // added to the encoded invoice. type Invoice struct { // Net specifies what network this Lightning invoice is meant for. Net *chaincfg.Params // MilliSat specifies the amount of this invoice in millisatoshi. // Optional. MilliSat *lnwire.MilliSatoshi // Timestamp specifies the time this invoice was created. // Mandatory Timestamp time.Time // PaymentHash is the payment hash to be used for a payment to this // invoice. PaymentHash *[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 // encoding then the destination pubkey won't be added as an 'n' field, // and the pubkey will be extracted from the signature during decoding. Destination *btcec.PublicKey // minFinalCLTVExpiry is the value that the creator of the invoice // expects to be used for the // // NOTE: This value is optional, and should be set to nil if the // invoice creator doesn't have a strong requirement on the CLTV expiry // of the final HTLC extended to it. // // This field is un-exported and can only be read by the // MinFinalCLTVExpiry() method. By forcing callers to read via this // method, we can easily enforce the default if not specified. minFinalCLTVExpiry *uint64 // Description is a short description of the purpose of this invoice. // Optional. Non-nil iff DescriptionHash is nil. Description *string // DescriptionHash is the SHA256 hash of a description of the purpose of // this invoice. // Optional. Non-nil iff Description is nil. DescriptionHash *[32]byte // expiry specifies the timespan this invoice will be valid. // Optional. If not set, a default expiry of 60 min will be implied. // // This field is unexported and can be read by the Expiry() method. This // method makes sure the default expiry time is returned in case the // field is not set. expiry *time.Duration // FallbackAddr is an on-chain address that can be used for payment in // case the Lightning payment fails. // Optional. FallbackAddr btcutil.Address // RoutingInfo is one or more entries containing extra routing // information for a private route to the target node. // Optional. RoutingInfo []ExtraRoutingInfo } // ExtraRoutingInfo holds the information needed to route a payment along one // private channel. type ExtraRoutingInfo struct { // PubKey is the public key of the node at the start of this channel. PubKey *btcec.PublicKey // ShortChanID is the channel ID of the channel. ShortChanID uint64 // Fee is the fee required for routing along this channel. Fee uint64 // CltvExpDelta is this channel's cltv expiry delta. CltvExpDelta uint16 } // Amount is a functional option that allows callers of NewInvoice to set the // amount in millisatoshis that the Invoice should encode. func Amount(milliSat lnwire.MilliSatoshi) func(*Invoice) { return func(i *Invoice) { i.MilliSat = &milliSat } } // Destination is a functional option that allows callers of NewInvoice to // explicitly set the pubkey of the Invoice's destination node. func Destination(destination *btcec.PublicKey) func(*Invoice) { return func(i *Invoice) { i.Destination = destination } } // Description is a functional option that allows callers of NewInvoice to set // the payment description of the created Invoice. // // NOTE: Must be used if and only if DescriptionHash is not used. func Description(description string) func(*Invoice) { return func(i *Invoice) { i.Description = &description } } // CLTVExpiry is an optional value which allows the receiver of the payment to // specify the delta between the current height and the HTLC extended to the // receiver. func CLTVExpiry(delta uint64) func(*Invoice) { return func(i *Invoice) { i.minFinalCLTVExpiry = &delta } } // DescriptionHash is a functional option that allows callers of NewInvoice to // set the payment description hash of the created Invoice. // // NOTE: Must be used if and only if Description is not used. func DescriptionHash(descriptionHash [32]byte) func(*Invoice) { return func(i *Invoice) { i.DescriptionHash = &descriptionHash } } // Expiry is a functional option that allows callers of NewInvoice to set the // expiry of the created Invoice. If not set, a default expiry of 60 min will // be implied. func Expiry(expiry time.Duration) func(*Invoice) { return func(i *Invoice) { i.expiry = &expiry } } // FallbackAddr is a functional option that allows callers of NewInvoice to set // the Invoice's fallback on-chain address that can be used for payment in case // the Lightning payment fails func FallbackAddr(fallbackAddr btcutil.Address) func(*Invoice) { return func(i *Invoice) { i.FallbackAddr = fallbackAddr } } // RoutingInfo is a functional option that allows callers of NewInvoice to set // one or more entries containing extra routing information for a private route // to the target node. func RoutingInfo(routingInfo []ExtraRoutingInfo) func(*Invoice) { return func(i *Invoice) { i.RoutingInfo = routingInfo } } // NewInvoice creates a new Invoice object. The last parameter is a set of // variadic argumements for setting optional fields of the invoice. // // NOTE: Either Description or DescriptionHash must be provided for the Invoice // to be considered valid. func NewInvoice(net *chaincfg.Params, paymentHash [32]byte, timestamp time.Time, options ...func(*Invoice)) (*Invoice, error) { invoice := &Invoice{ Net: net, PaymentHash: &paymentHash, Timestamp: timestamp, } for _, option := range options { option(invoice) } if err := validateInvoice(invoice); err != nil { return nil, err } return invoice, nil } // Decode parses the provided encoded invoice, and returns a decoded Invoice in // case it is valid by BOLT-0011. func Decode(invoice string) (*Invoice, error) { decodedInvoice := Invoice{} // Decode the invoice using the modified bech32 decoder. hrp, data, err := decodeBech32(invoice) if err != nil { return nil, err } // We expect the human-readable part to at least have ln + two chars // encoding the network. if len(hrp) < 4 { return nil, fmt.Errorf("hrp too short") } // First two characters of HRP should be "ln". if hrp[:2] != "ln" { return nil, fmt.Errorf("prefix should be \"ln\"") } // The next characters should be a valid prefix for a segwit BIP173 // address. This will also determine which network this invoice is // meant for. var net *chaincfg.Params if strings.HasPrefix(hrp[2:], chaincfg.MainNetParams.Bech32HRPSegwit) { net = &chaincfg.MainNetParams } else if strings.HasPrefix(hrp[2:], chaincfg.TestNet3Params.Bech32HRPSegwit) { net = &chaincfg.TestNet3Params } else if strings.HasPrefix(hrp[2:], chaincfg.SimNetParams.Bech32HRPSegwit) { net = &chaincfg.SimNetParams } else { return nil, fmt.Errorf("unknown network") } decodedInvoice.Net = net // Optionally, if there's anything left of the HRP, it encodes the // payment amount. if len(hrp) > 4 { amount, err := decodeAmount(hrp[4:]) if err != nil { return nil, err } decodedInvoice.MilliSat = &amount } // Everything except the last 520 bits of the data encodes the invoice's // timestamp and tagged fields. invoiceData := data[:len(data)-signatureBase32Len] // Parse the timestamp and tagged fields, and fill the Invoice struct. if err := parseData(&decodedInvoice, invoiceData, net); err != nil { return nil, err } // The last 520 bits (104 groups) make up the signature. sigBase32 := data[len(data)-signatureBase32Len:] sigBase256, err := bech32.ConvertBits(sigBase32, 5, 8, true) if err != nil { return nil, err } var sigBytes [64]byte copy(sigBytes[:], sigBase256[:64]) recoveryID := sigBase256[64] // The signature is over the hrp + the data the invoice, encoded in // base 256. taggedDataBytes, err := bech32.ConvertBits(invoiceData, 5, 8, true) if err != nil { return nil, err } toSign := append([]byte(hrp), taggedDataBytes...) // We expect the signature to be over the single SHA-256 hash of that // data. hash := chainhash.HashB(toSign) // If the destination pubkey was provided as a tagged field, use that // to verify the signature, if not do public key recovery. if decodedInvoice.Destination != nil { var signature *btcec.Signature err := lnwire.DeserializeSigFromWire(&signature, sigBytes) if err != nil { return nil, fmt.Errorf("unable to deserialize "+ "signature: %v", err) } if !signature.Verify(hash, decodedInvoice.Destination) { return nil, fmt.Errorf("invalid invoice signature") } } else { headerByte := recoveryID + 27 + 4 compactSign := append([]byte{headerByte}, sigBytes[:]...) pubkey, _, err := btcec.RecoverCompact(btcec.S256(), compactSign, hash) if err != nil { return nil, err } decodedInvoice.Destination = pubkey } // Now that we have created the invoice, make sure it has the required // fields set. if err := validateInvoice(&decodedInvoice); err != nil { return nil, err } return &decodedInvoice, nil } // 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), 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 sigBytes [64]byte copy(sigBytes[:], 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 { var signature *btcec.Signature err = lnwire.DeserializeSigFromWire(&signature, sigBytes) 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(sigBytes[:], 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 } return b32, nil } // Expiry returns the expiry time for this invoice. If expiry time is not set // explicitly, the default 3600 second expiry will be returned. func (invoice *Invoice) Expiry() time.Duration { if invoice.expiry != nil { return *invoice.expiry } // If no expiry is set for this invoice, default is 3600 seconds. return 3600 * time.Second } // MinFinalCLTVExpiry returns the minimum final CLTV expiry delta as specified // by the creator of the invoice. This value specifies the delta between the // current height and the expiry height of the HTLC extended in the last hop. func (invoice *Invoice) MinFinalCLTVExpiry() uint64 { if invoice.minFinalCLTVExpiry != nil { return *invoice.minFinalCLTVExpiry } return routing.DefaultFinalCLTVDelta } // validateInvoice does a sanity check of the provided Invoice, making sure it // has all the necessary fields set for it to be considered valid by BOLT-0011. func validateInvoice(invoice *Invoice) error { // The net must be set. if invoice.Net == nil { return fmt.Errorf("net params not set") } // The invoice must contain a payment hash. if invoice.PaymentHash == nil { return fmt.Errorf("no payment hash found") } // Either Description or DescriptionHash must be set, not both. if invoice.Description != nil && invoice.DescriptionHash != nil { return fmt.Errorf("both description and description hash set") } if invoice.Description == nil && invoice.DescriptionHash == nil { return fmt.Errorf("neither description nor description hash set") } // Can have at most 20 extra hops for routing. if len(invoice.RoutingInfo) > 20 { return fmt.Errorf("too many extra hops: %d", len(invoice.RoutingInfo)) } // Check that we support the field lengths. if len(invoice.PaymentHash) != 32 { return fmt.Errorf("unsupported payment hash length: %d", len(invoice.PaymentHash)) } if invoice.DescriptionHash != nil && len(invoice.DescriptionHash) != 32 { return fmt.Errorf("unsupported description hash length: %d", len(invoice.DescriptionHash)) } if invoice.Destination != nil && len(invoice.Destination.SerializeCompressed()) != 33 { return fmt.Errorf("unsupported pubkey length: %d", len(invoice.Destination.SerializeCompressed())) } return nil } // parseData parses the data part of the invoice. It expects base32 data // returned from the bech32.Decode method, except signature. func parseData(invoice *Invoice, data []byte, net *chaincfg.Params) error { // It must contain the timestamp, encoded using 35 bits (7 groups). if len(data) < timestampBase32Len { return fmt.Errorf("data too short: %d", len(data)) } // Timestamp: 35 bits, 7 groups. t, err := base32ToUint64(data[:7]) if err != nil { return err } invoice.Timestamp = time.Unix(int64(t), 0) // The rest are tagged parts. tagData := data[7:] if err := parseTaggedFields(invoice, tagData, net); err != nil { return err } return nil } // parseTimestamp converts a 35-bit timestamp (encoded in base32) to uint64. func parseTimestamp(data []byte) (uint64, error) { if len(data) != 7 { return 0, fmt.Errorf("timestamp must be 35 bits, was %d", len(data)*5) } return base32ToUint64(data) } // parseTaggedFields takes the base32 encoded tagged fields of the invoice, and // fills the Invoice struct accordingly. func parseTaggedFields(invoice *Invoice, fields []byte, net *chaincfg.Params) error { index := 0 for { // If less than 3 groups less, it cannot possibly contain more // interesting information, as we need the type (1 group) and // length (2 groups). if len(fields)-index < 3 { break } typ := fields[index] dataLength := uint16(fields[index+1]<<5) | uint16(fields[index+2]) // If we don't have enough field data left to read this length, // return error. if len(fields) < index+3+int(dataLength) { return fmt.Errorf("invalid field length") } base32Data := fields[index+3 : index+3+int(dataLength)] // Advance the index in preparation for the next iteration. index += 3 + int(dataLength) switch typ { case fieldTypeP: if invoice.PaymentHash != nil { // We skip the field if we have already seen a // supported one. continue } if dataLength != hashBase32Len { // Skipping unknown field length. continue } hash, err := bech32.ConvertBits(base32Data, 5, 8, false) if err != nil { return err } var pHash [32]byte copy(pHash[:], hash[:]) invoice.PaymentHash = &pHash case fieldTypeD: if invoice.Description != nil { // We skip the field if we have already seen a // supported one. continue } base256Data, err := bech32.ConvertBits(base32Data, 5, 8, false) if err != nil { return err } desc := string(base256Data) invoice.Description = &desc case fieldTypeN: if invoice.Destination != nil { // We skip the field if we have already seen a // supported one. continue } if len(base32Data) != pubKeyBase32Len { // Skip unknown length. continue } base256Data, err := bech32.ConvertBits(base32Data, 5, 8, false) if err != nil { return err } invoice.Destination, err = btcec.ParsePubKey(base256Data, btcec.S256()) if err != nil { return err } case fieldTypeH: if invoice.DescriptionHash != nil { // We skip the field if we have already seen a // supported one. continue } if len(base32Data) != hashBase32Len { // Skip unknown length. continue } hash, err := bech32.ConvertBits(base32Data, 5, 8, false) if err != nil { return err } var dHash [32]byte copy(dHash[:], hash[:]) invoice.DescriptionHash = &dHash case fieldTypeX: if invoice.expiry != nil { // We skip the field if we have already seen a // supported one. continue } exp, err := base32ToUint64(base32Data) if err != nil { return err } dur := time.Duration(exp) * time.Second invoice.expiry = &dur case fieldTypeC: if invoice.minFinalCLTVExpiry != nil { // We skip the field if we have already seen a // supported one. continue } expiry, err := base32ToUint64(base32Data) if err != nil { return err } invoice.minFinalCLTVExpiry = &expiry case fieldTypeF: if invoice.FallbackAddr != nil { // We skip the field if we have already seen a // supported one. continue } var addr btcutil.Address version := base32Data[0] switch version { case 0: witness, err := bech32.ConvertBits( base32Data[1:], 5, 8, false) if err != nil { return err } switch len(witness) { case 20: addr, err = btcutil.NewAddressWitnessPubKeyHash( witness, net) case 32: addr, err = btcutil.NewAddressWitnessScriptHash( witness, net) default: return fmt.Errorf("unknown witness "+ "program length: %d", len(witness)) } if err != nil { return err } case 17: pkHash, err := bech32.ConvertBits(base32Data[1:], 5, 8, false) if err != nil { return err } addr, err = btcutil.NewAddressPubKeyHash(pkHash, net) if err != nil { return err } case 18: scriptHash, err := bech32.ConvertBits( base32Data[1:], 5, 8, false) if err != nil { return err } addr, err = btcutil.NewAddressScriptHashFromHash( scriptHash, net) if err != nil { return err } default: // Skipping unknown witness version. continue } invoice.FallbackAddr = addr case fieldTypeR: if invoice.RoutingInfo != nil { // We skip the field if we have already seen a // supported one. continue } base256Data, err := bech32.ConvertBits(base32Data, 5, 8, false) if err != nil { return err } for len(base256Data) > 0 { info := ExtraRoutingInfo{} info.PubKey, err = btcec.ParsePubKey( base256Data[:33], btcec.S256()) if err != nil { return err } info.ShortChanID = binary.BigEndian.Uint64( base256Data[33:41]) info.Fee = binary.BigEndian.Uint64( base256Data[41:49]) info.CltvExpDelta = binary.BigEndian.Uint16( base256Data[49:51]) invoice.RoutingInfo = append( invoice.RoutingInfo, info) base256Data = base256Data[51:] } default: // Ignore unknown type. } } return 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 { // Convert 32 byte hash to 52 5-bit groups. base32, err := bech32.ConvertBits(invoice.PaymentHash[:], 8, 5, true) if err != nil { return err } if len(base32) != hashBase32Len { return fmt.Errorf("invalid payment hash length: %d", len(invoice.PaymentHash)) } err = writeTaggedField(bufferBase32, fieldTypeP, base32) 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 { // Convert 32 byte hash to 52 5-bit groups. descBase32, err := bech32.ConvertBits( invoice.DescriptionHash[:], 8, 5, true) if err != nil { return err } if len(descBase32) != hashBase32Len { return fmt.Errorf("invalid description hash length: %d", len(invoice.DescriptionHash)) } err = writeTaggedField(bufferBase32, fieldTypeH, descBase32) if err != nil { return err } } if invoice.minFinalCLTVExpiry != nil { finalDelta := uint64ToBase32(uint64(*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 } } if len(invoice.RoutingInfo) > 0 { // Each extra routing info is encoded using 51 bytes. routingDataBase256 := make([]byte, 0, 51*len(invoice.RoutingInfo)) for _, r := range invoice.RoutingInfo { base256 := make([]byte, 51) copy(base256[:33], r.PubKey.SerializeCompressed()) binary.BigEndian.PutUint64(base256[33:41], r.ShortChanID) binary.BigEndian.PutUint64(base256[41:49], r.Fee) binary.BigEndian.PutUint16(base256[49:51], r.CltvExpDelta) routingDataBase256 = append(routingDataBase256, base256...) } routingDataBase32, err := bech32.ConvertBits(routingDataBase256, 8, 5, true) if err != nil { return err } err = writeTaggedField(bufferBase32, fieldTypeR, routingDataBase32) 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 nil } 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 } } return nil } // 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 } // base32ToUint64 converts a base32 encoded number to uint64. func base32ToUint64(data []byte) (uint64, error) { // Maximum that fits in uint64 is 64 / 5 = 12 groups. if len(data) > 12 { return 0, fmt.Errorf("cannot parse data of length %d as uint64", len(data)) } val := uint64(0) for i := 0; i < len(data); i++ { val = val<<5 | uint64(data[i]) } return val, 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 64 / 5 = 12 groups. arr := make([]byte, 12) i := 12 for num > 0 { i-- arr[i] = byte(num & uint64(31)) // 0b11111 in binary num = num >> 5 } // We only return non-zero leading groups. return arr[i:] }