htlcswitch: add blinding point to sphinx iterator for decoding

contractcourt/htlc_incoming_contest_resolver.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/lightningnetwork/lnd/channeldb"
@@ -18,7 +17,6 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/queue"
-	"github.com/lightningnetwork/lnd/tlv"
 )
 
 // htlcIncomingContestResolver is a ContractResolver that's able to resolve an
@@ -522,18 +520,15 @@ func (h *htlcIncomingContestResolver) Supplement(htlc channeldb.HTLC) {
 func (h *htlcIncomingContestResolver) decodePayload() (*hop.Payload,
 	[]byte, error) {
 
-	var blindingPoint *btcec.PublicKey
-	h.htlc.BlindingPoint.WhenSome(
-		func(b tlv.RecordT[lnwire.BlindingPointTlvType,
-			*btcec.PublicKey]) {
-
-			blindingPoint = b.Val
-		},
-	)
+	blindingInfo := hop.ReconstructBlindingInfo{
+		IncomingAmt:    h.htlc.Amt,
+		IncomingExpiry: h.htlc.RefundTimeout,
+		BlindingKey:    h.htlc.BlindingPoint,
+	}
 
 	onionReader := bytes.NewReader(h.htlc.OnionBlob[:])
 	iterator, err := h.OnionProcessor.ReconstructHopIterator(
-		onionReader, h.htlc.RHash[:], blindingPoint,
+		onionReader, h.htlc.RHash[:], blindingInfo,
 	)
 	if err != nil {
 		return nil, nil, err

contractcourt/htlc_incoming_contest_resolver_test.go

@@ -6,7 +6,6 @@ import (
 	"io/ioutil"
 	"testing"
 
-	"github.com/btcsuite/btcd/btcec/v2"
 	sphinx "github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
@@ -290,7 +289,7 @@ type mockOnionProcessor struct {
 }
 
 func (o *mockOnionProcessor) ReconstructHopIterator(r io.Reader, rHash []byte,
-	blindingPoint *btcec.PublicKey) (hop.Iterator, error) {
+	_ hop.ReconstructBlindingInfo) (hop.Iterator, error) {
 
 	data, err := ioutil.ReadAll(r)
 	if err != nil {

contractcourt/interfaces.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"io"
 
-	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/channeldb/models"
@@ -42,7 +41,7 @@ type OnionProcessor interface {
 	// ReconstructHopIterator attempts to decode a valid sphinx packet from
 	// the passed io.Reader instance.
 	ReconstructHopIterator(r io.Reader, rHash []byte,
-		blindingKey *btcec.PublicKey) (hop.Iterator, error)
+		blindingInfo hop.ReconstructBlindingInfo) (hop.Iterator, error)
 }
 
 // UtxoSweeper defines the sweep functions that contract court requires.

htlcswitch/hop/iterator.go

@@ -55,16 +55,24 @@ type sphinxHopIterator struct {
 	// includes the information required to properly forward the packet to
 	// the next hop.
 	processedPacket *sphinx.ProcessedPacket
+
+	// blindingKit contains the elements required to process hops that are
+	// part of a blinded route.
+	blindingKit BlindingKit
 }
 
 // makeSphinxHopIterator converts a processed packet returned from a sphinx
-// router and converts it into an hop iterator for usage in the link.
+// router and converts it into an hop iterator for usage in the link. A
+// blinding kit is passed through for the link to obtain forwarding information
+// for blinded routes.
 func makeSphinxHopIterator(ogPacket *sphinx.OnionPacket,
-	packet *sphinx.ProcessedPacket) *sphinxHopIterator {
+	packet *sphinx.ProcessedPacket,
+	blindingKit BlindingKit) *sphinxHopIterator {
 
 	return &sphinxHopIterator{
 		ogPacket:        ogPacket,
 		processedPacket: packet,
+		blindingKit:     blindingKit,
 	}
 }
 
@@ -370,11 +378,24 @@ func (p *OnionProcessor) Stop() error {
 	return nil
 }
 
-// ReconstructHopIterator 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.
+// ReconstructBlindingInfo contains the information required to reconstruct a
+// blinded onion.
+type ReconstructBlindingInfo struct {
+	// BlindingKey is the blinding point set in UpdateAddHTLC.
+	BlindingKey lnwire.BlindingPointRecord
+
+	// IncomingAmt is the amount for the incoming HTLC.
+	IncomingAmt lnwire.MilliSatoshi
+
+	// IncomingExpiry is the expiry height of the incoming HTLC.
+	IncomingExpiry uint32
+}
+
+// ReconstructHopIterator 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 *OnionProcessor) ReconstructHopIterator(r io.Reader, rHash []byte,
-	blindingPoint *btcec.PublicKey) (Iterator, error) {
+	blindingInfo ReconstructBlindingInfo) (Iterator, error) {
 
 	onionPkt := &sphinx.OnionPacket{}
 	if err := onionPkt.Decode(r); err != nil {
@@ -382,9 +403,11 @@ func (p *OnionProcessor) ReconstructHopIterator(r io.Reader, rHash []byte,
 	}
 
 	var opts []sphinx.ProcessOnionOpt
-	if blindingPoint != nil {
-		opts = append(opts, sphinx.WithBlindingPoint(blindingPoint))
-	}
+	blindingInfo.BlindingKey.WhenSome(func(
+		r tlv.RecordT[lnwire.BlindingPointTlvType, *btcec.PublicKey]) {
+
+		opts = append(opts, sphinx.WithBlindingPoint(r.Val))
+	})
 
 	// Attempt to process the Sphinx packet. We include the payment hash of
 	// the HTLC as it's authenticated within the Sphinx packet itself as
@@ -398,7 +421,12 @@ func (p *OnionProcessor) ReconstructHopIterator(r io.Reader, rHash []byte,
 		return nil, err
 	}
 
-	return makeSphinxHopIterator(onionPkt, sphinxPacket), nil
+	return makeSphinxHopIterator(onionPkt, sphinxPacket, BlindingKit{
+		Processor:         p.router,
+		UpdateAddBlinding: blindingInfo.BlindingKey,
+		IncomingAmount:    blindingInfo.IncomingAmt,
+		IncomingCltv:      blindingInfo.IncomingExpiry,
+	}), nil
 }
 
 // DecodeHopIteratorRequest encapsulates all date necessary to process an onion
@@ -575,7 +603,14 @@ func (p *OnionProcessor) DecodeHopIterators(id []byte,
 
 		// Finally, construct a hop iterator from our processed sphinx
 		// packet, simultaneously caching the original onion packet.
-		resp.HopIterator = makeSphinxHopIterator(&onionPkts[i], &packets[i])
+		resp.HopIterator = makeSphinxHopIterator(
+			&onionPkts[i], &packets[i], BlindingKit{
+				Processor:         p.router,
+				UpdateAddBlinding: reqs[i].BlindingPoint,
+				IncomingAmount:    reqs[i].IncomingAmount,
+				IncomingCltv:      reqs[i].IncomingCltv,
+			},
+		)
 	}
 
 	return resps, nil