contractcourt: add onchain interception

intercepted_forward.go

@@ -0,0 +1,80 @@
+package lnd
+
+import (
+	"errors"
+
+	"github.com/lightningnetwork/lnd/htlcswitch"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+var (
+	// ErrCannotResume is returned when an intercepted forward cannot be
+	// resumed. This is the case in the on-chain resolution flow.
+	ErrCannotResume = errors.New("cannot resume in the on-chain flow")
+
+	// ErrCannotFail is returned when an intercepted forward cannot be failed.
+	// This is the case in the on-chain resolution flow.
+	ErrCannotFail = errors.New("cannot fail in the on-chain flow")
+
+	// ErrPreimageMismatch is returned when the preimage that is specified to
+	// settle an htlc doesn't match the htlc hash.
+	ErrPreimageMismatch = errors.New("preimage does not match hash")
+)
+
+// interceptedForward implements the on-chain behavior for the resolution of
+// a forwarded htlc.
+type interceptedForward struct {
+	packet *htlcswitch.InterceptedPacket
+	beacon *preimageBeacon
+}
+
+func newInterceptedForward(
+	packet *htlcswitch.InterceptedPacket,
+	beacon *preimageBeacon) *interceptedForward {
+
+	return &interceptedForward{
+		beacon: beacon,
+		packet: packet,
+	}
+}
+
+// Packet returns the intercepted htlc packet.
+func (f *interceptedForward) Packet() htlcswitch.InterceptedPacket {
+	return *f.packet
+}
+
+// Resume notifies the intention to resume an existing hold forward. This
+// basically means the caller wants to resume with the default behavior for this
+// htlc which usually means forward it.
+func (f *interceptedForward) Resume() error {
+	return ErrCannotResume
+}
+
+// Fail notifies the intention to fail an existing hold forward with an
+// encrypted failure reason.
+func (f *interceptedForward) Fail(_ []byte) error {
+	// We can't actively fail an htlc. The best we could do is abandon the
+	// resolver, but this wouldn't be a safe operation. There may be a race
+	// with the preimage beacon supplying a preimage. Therefore we don't
+	// attempt to fail and just return an error here.
+	return ErrCannotFail
+}
+
+// FailWithCode notifies the intention to fail an existing hold forward with the
+// specified failure code.
+func (f *interceptedForward) FailWithCode(_ lnwire.FailCode) error {
+	return ErrCannotFail
+}
+
+// Settle notifies the intention to settle an existing hold forward with a given
+// preimage.
+func (f *interceptedForward) Settle(preimage lntypes.Preimage) error {
+	if !preimage.Matches(f.packet.Hash) {
+		return ErrPreimageMismatch
+	}
+
+	// Add preimage to the preimage beacon. The onchain resolver will pick
+	// up the preimage from the beacon.
+	return f.beacon.AddPreimages(preimage)
+}