contractcourt: add onchain interception

witness_beacon.go

@@ -3,8 +3,12 @@ package lnd
 import (
 	"sync"
 
+	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/contractcourt"
+	"github.com/lightningnetwork/lnd/htlcswitch"
+	"github.com/lightningnetwork/lnd/htlcswitch/hop"
 	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwire"
 )
 
 // preimageSubscriber reprints an active subscription to be notified once the
@@ -36,18 +40,27 @@ type preimageBeacon struct {
 
 	clientCounter uint64
 	subscribers   map[uint64]*preimageSubscriber
+
+	interceptor func(htlcswitch.InterceptedForward) error
 }
 
-func newPreimageBeacon(wCache witnessCache) *preimageBeacon {
+func newPreimageBeacon(wCache witnessCache,
+	interceptor func(htlcswitch.InterceptedForward) error) *preimageBeacon {
+
 	return &preimageBeacon{
 		wCache:      wCache,
+		interceptor: interceptor,
 		subscribers: make(map[uint64]*preimageSubscriber),
 	}
 }
 
 // SubscribeUpdates returns a channel that will be sent upon *each* time a new
 // preimage is discovered.
-func (p *preimageBeacon) SubscribeUpdates() *contractcourt.WitnessSubscription {
+func (p *preimageBeacon) SubscribeUpdates(
+	chanID lnwire.ShortChannelID, htlc *channeldb.HTLC,
+	payload *hop.Payload,
+	nextHopOnionBlob []byte) (*contractcourt.WitnessSubscription, error) {
+
 	p.Lock()
 	defer p.Unlock()
 
@@ -64,7 +77,7 @@ func (p *preimageBeacon) SubscribeUpdates() *contractcourt.WitnessSubscription {
 	srvrLog.Debugf("Creating new witness beacon subscriber, id=%v",
 		p.clientCounter)
 
-	return &contractcourt.WitnessSubscription{
+	sub := &contractcourt.WitnessSubscription{
 		WitnessUpdates: client.updateChan,
 		CancelSubscription: func() {
 			p.Lock()
@@ -75,6 +88,32 @@ func (p *preimageBeacon) SubscribeUpdates() *contractcourt.WitnessSubscription {
 			close(client.quit)
 		},
 	}
+
+	// Notify the htlc interceptor. There may be a client connected
+	// and willing to supply a preimage.
+	packet := &htlcswitch.InterceptedPacket{
+		Hash:           htlc.RHash,
+		IncomingExpiry: htlc.RefundTimeout,
+		IncomingAmount: htlc.Amt,
+		IncomingCircuit: channeldb.CircuitKey{
+			ChanID: chanID,
+			HtlcID: htlc.HtlcIndex,
+		},
+		OutgoingChanID: payload.FwdInfo.NextHop,
+		OutgoingExpiry: payload.FwdInfo.OutgoingCTLV,
+		OutgoingAmount: payload.FwdInfo.AmountToForward,
+		CustomRecords:  payload.CustomRecords(),
+	}
+	copy(packet.OnionBlob[:], nextHopOnionBlob)
+
+	fwd := newInterceptedForward(packet, p)
+
+	err := p.interceptor(fwd)
+	if err != nil {
+		return nil, err
+	}
+
+	return sub, nil
 }
 
 // LookupPreImage attempts to lookup a preimage in the global cache.  True is