lnd/htlcswitch/iterator.go

188 lines
6.6 KiB
Go

package htlcswitch
import (
"encoding/binary"
"io"
"github.com/go-errors/errors"
"github.com/lightningnetwork/lightning-onion"
"github.com/lightningnetwork/lnd/lnwire"
"github.com/roasbeef/btcutil"
)
// NetworkHop indicates the blockchain network that is intended to be the next
// hop for a forwarded HTLC. The existnce of this field within the
// ForwardingInfo struct enables the ability for HTLC to cross chain-boundaries
// at will.
type NetworkHop uint8
const (
// BitcoinHop denotes that an HTLC is to be forwarded along the Bitcoin
// link with the specified short channel ID.
BitcoinHop NetworkHop = iota
// LitecoinHop denotes that an HTLC is to be forwarded along the
// Litecoin link with the specified short channel ID.
LitecoinHop
)
// String returns the string representation of the target NetworkHop.
func (c NetworkHop) String() string {
switch c {
case BitcoinHop:
return "Bitcoin"
case LitecoinHop:
return "Litecoin"
default:
return "Kekcoin"
}
}
var (
// exitHop is a special "hop" which denotes that an incoming HTLC is
// meant to pay finally to the receiving node.
exitHop lnwire.ShortChannelID
)
// ForwardingInfo contains all the information that is necessary to forward and
// incoming HTLC to the next hop encoded within a valid HopIterator instance.
// Forwarding links are to use this information to authenticate the information
// received within the incoming HTLC, to ensure that the prior hop didn't
// tamper with the end-to-end routing information at all.
type ForwardingInfo struct {
// Network is the target blockchain network that the HTLC will travel
// over next.
Network NetworkHop
// NextHop is the channel ID of the next hop. The received HTLC should
// be forwarded to this particular channel in order to continue the
// end-to-end route.
NextHop lnwire.ShortChannelID
// AmountToForward is the amount that the receiving node should forward
// to the next hop.
AmountToForward btcutil.Amount
// OutgoingCTLV is the specified value of the CTLV timelock to be used
// in the outgoing HTLC.
OutgoingCTLV uint32
// TODO(roasbeef): modify sphinx logic to not just discard the
// remaining bytes, instead should include the rest as excess
}
// HopIterator is an interface that abstracts away the routing information
// included in HTLC's which includes the entirety of the payment path of an
// HTLC. This interface provides two basic method which carry out: how to
// interpret the forwarding information encoded within the HTLC packet, and hop
// to encode the forwarding information for the _next_ hop.
type HopIterator interface {
// ForwardingInstructions returns the set of fields that detail exactly
// _how_ this hop should forward the HTLC to the next hop.
// Additionally, the information encoded within the returned
// ForwardingInfo is to be used by each hop to authenticate the
// information given to it by the prior hop.
ForwardingInstructions() ForwardingInfo
// EncodeNextHop encodes the onion packet destined for the next hop
// into the passed io.Writer.
EncodeNextHop(w io.Writer) error
}
// sphinxHopIterator is the Sphinx implementation of hop iterator which uses
// onion routing to encode the payment route in such a way so that node might
// see only the next hop in the route..
type sphinxHopIterator struct {
// nextPacket is the decoded onion packet for the _next_ hop.
nextPacket *sphinx.OnionPacket
// processedPacket is the outcome of processing an onion packet. It
// includes the information required to properly forward the packet to
// the next hop.
processedPacket *sphinx.ProcessedPacket
}
// A compile time check to ensure sphinxHopIterator implements the HopIterator
// interface.
var _ HopIterator = (*sphinxHopIterator)(nil)
// Encode encodes iterator and writes it to the writer.
//
// NOTE: Part of the HopIterator interface.
func (r *sphinxHopIterator) EncodeNextHop(w io.Writer) error {
return r.nextPacket.Encode(w)
}
// ForwardingInstructions returns the set of fields that detail exactly _how_
// this hop should forward the HTLC to the next hop. Additionally, the
// information encoded within the returned ForwardingInfo is to be used by each
// hop to authenticate the information given to it by the prior hop.
//
// NOTE: Part of the HopIterator interface.
func (r *sphinxHopIterator) ForwardingInstructions() ForwardingInfo {
fwdInst := r.processedPacket.ForwardingInstructions
var nextHop lnwire.ShortChannelID
switch r.processedPacket.Action {
case sphinx.ExitNode:
nextHop = exitHop
case sphinx.MoreHops:
s := binary.BigEndian.Uint64(fwdInst.NextAddress[:])
nextHop = lnwire.NewShortChanIDFromInt(s)
}
return ForwardingInfo{
Network: BitcoinHop,
NextHop: nextHop,
AmountToForward: btcutil.Amount(fwdInst.ForwardAmount),
OutgoingCTLV: fwdInst.OutgoingCltv,
}
}
// SphinxDecoder is responsible for keeping all sphinx dependent parts inside
// and expose only decoding function. With such approach we give freedom for
// subsystems which wants to decode sphinx path to not be dependable from
// sphinx at all.
//
// NOTE: The reason for keeping decoder separated from hop iterator is too
// maintain the hop iterator abstraction. Without it the structures which using
// the hop iterator should contain sphinx router which makes their creations in
// tests dependent from the sphinx internal parts.
type SphinxDecoder struct {
router *sphinx.Router
}
// NewSphinxDecoder creates new instance of decoder.
func NewSphinxDecoder(router *sphinx.Router) *SphinxDecoder {
return &SphinxDecoder{router}
}
// Decode attempts to decode a valid sphinx packet from the passed io.Reader
// instance using the rHash as the associated data when checking the relevant
// MACs during the decoding process.
func (p *SphinxDecoder) Decode(r io.Reader, rHash []byte) (HopIterator, error) {
// Before adding the new HTLC to the state machine, parse the onion
// object in order to obtain the routing information.
onionPkt := &sphinx.OnionPacket{}
if err := onionPkt.Decode(r); err != nil {
return nil, errors.Errorf("unable to decode onion pkt: %v",
err)
}
// Attempt to process the Sphinx packet. We include the payment hash of
// the HTLC as it's authenticated within the Sphinx packet itself as
// associated data in order to thwart attempts a replay attacks. In the
// case of a replay, an attacker is *forced* to use the same payment
// hash twice, thereby losing their money entirely.
sphinxPacket, err := p.router.ProcessOnionPacket(onionPkt, rHash)
if err != nil {
return nil, errors.Errorf("unable to process onion pkt: "+
"%v", err)
}
return &sphinxHopIterator{
nextPacket: sphinxPacket.NextPacket,
processedPacket: sphinxPacket,
}, nil
}