From 4640507c5fee41398573a676d64d8ea750291f55 Mon Sep 17 00:00:00 2001
From: Jesse de Wit <witdejesse@hotmail.com>
Date: Tue, 17 Oct 2023 16:55:55 +0200
Subject: [PATCH] add option for new onion format for lnd lsp

---
 config/config.go         |  5 +++++
 interceptor/intercept.go | 34 ++++++++++++++++++--------------
 lnd/interceptor.go       | 42 ++++++++++++++++++++++++----------------
 3 files changed, 49 insertions(+), 32 deletions(-)

diff --git a/config/config.go b/config/config.go
index dd287e5..12c773a 100644
--- a/config/config.go
+++ b/config/config.go
@@ -15,6 +15,11 @@ type NodeConfig struct {
 	// configured node, so it's obvious which node an rpc call is meant for.
 	Tokens []string `json:"tokens"`
 
+	// If the used token is in the LegacyOnionTokens array, the forwarded htlc
+	// will have the legacy onion format. As per the time of writing breezmobile
+	// requires the legacy onion format.
+	LegacyOnionTokens []string `json:"legacyOnionTokens"`
+
 	// The network location of the lightning node, e.g. `12.34.56.78:9012` or
 	// `localhost:10011`
 	Host string `json:"host"`
diff --git a/interceptor/intercept.go b/interceptor/intercept.go
index 9bbb0cd..af3b7da 100644
--- a/interceptor/intercept.go
+++ b/interceptor/intercept.go
@@ -15,6 +15,7 @@ import (
 	"github.com/breez/lspd/lightning"
 	"github.com/breez/lspd/notifications"
 	"github.com/btcsuite/btcd/wire"
+	"golang.org/x/exp/slices"
 	"golang.org/x/sync/singleflight"
 )
 
@@ -35,14 +36,15 @@ var (
 )
 
 type InterceptResult struct {
-	Action          InterceptAction
-	FailureCode     InterceptFailureCode
-	Destination     []byte
-	AmountMsat      uint64
-	TotalAmountMsat uint64
-	ChannelPoint    *wire.OutPoint
-	ChannelId       uint64
-	PaymentSecret   []byte
+	Action             InterceptAction
+	FailureCode        InterceptFailureCode
+	Destination        []byte
+	AmountMsat         uint64
+	TotalAmountMsat    uint64
+	ChannelPoint       *wire.OutPoint
+	ChannelId          uint64
+	PaymentSecret      []byte
+	UseLegacyOnionBlob bool
 }
 
 type Interceptor struct {
@@ -257,14 +259,16 @@ func (i *Interceptor) Intercept(scid *basetypes.ShortChannelID, reqPaymentHash [
 					channelID = uint64(chanResult.InitialChannelID)
 				}
 
+				useLegacyOnionBlob := slices.Contains(i.config.LegacyOnionTokens, token)
 				return InterceptResult{
-					Action:          INTERCEPT_RESUME_WITH_ONION,
-					Destination:     destination,
-					ChannelPoint:    channelPoint,
-					ChannelId:       channelID,
-					PaymentSecret:   paymentSecret,
-					AmountMsat:      uint64(amt),
-					TotalAmountMsat: uint64(outgoingAmountMsat),
+					Action:             INTERCEPT_RESUME_WITH_ONION,
+					Destination:        destination,
+					ChannelPoint:       channelPoint,
+					ChannelId:          channelID,
+					PaymentSecret:      paymentSecret,
+					AmountMsat:         uint64(amt),
+					TotalAmountMsat:    uint64(outgoingAmountMsat),
+					UseLegacyOnionBlob: useLegacyOnionBlob,
 				}, nil
 			}
 
diff --git a/lnd/interceptor.go b/lnd/interceptor.go
index 8d1574f..2d4ecb1 100644
--- a/lnd/interceptor.go
+++ b/lnd/interceptor.go
@@ -139,23 +139,7 @@ func (i *LndHtlcInterceptor) intercept() error {
 				interceptResult := i.interceptor.Intercept(&scid, request.PaymentHash, request.OutgoingAmountMsat, request.OutgoingExpiry, request.IncomingExpiry)
 				switch interceptResult.Action {
 				case interceptor.INTERCEPT_RESUME_WITH_ONION:
-					onion, err := i.constructOnion(interceptResult, request.OutgoingExpiry, request.PaymentHash)
-					if err == nil {
-						interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
-							IncomingCircuitKey:      request.IncomingCircuitKey,
-							Action:                  routerrpc.ResolveHoldForwardAction_RESUME,
-							OutgoingAmountMsat:      interceptResult.AmountMsat,
-							OutgoingRequestedChanId: uint64(interceptResult.ChannelId),
-							OnionBlob:               onion,
-						})
-					} else {
-						interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
-							IncomingCircuitKey: request.IncomingCircuitKey,
-							Action:             routerrpc.ResolveHoldForwardAction_FAIL,
-							FailureCode:        lnrpc.Failure_TEMPORARY_CHANNEL_FAILURE,
-						})
-					}
-
+					interceptorClient.Send(i.createOnionResponse(interceptResult, request))
 				case interceptor.INTERCEPT_FAIL_HTLC_WITH_CODE:
 					interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
 						IncomingCircuitKey: request.IncomingCircuitKey,
@@ -257,3 +241,27 @@ func (i *LndHtlcInterceptor) constructOnion(
 
 	return onionBlob.Bytes(), nil
 }
+
+func (i *LndHtlcInterceptor) createOnionResponse(interceptResult interceptor.InterceptResult, request *routerrpc.ForwardHtlcInterceptRequest) *routerrpc.ForwardHtlcInterceptResponse {
+	onionBlob := request.OnionBlob
+
+	if interceptResult.UseLegacyOnionBlob {
+		var err error
+		onionBlob, err = i.constructOnion(interceptResult, request.OutgoingExpiry, request.PaymentHash)
+		if err != nil {
+			return &routerrpc.ForwardHtlcInterceptResponse{
+				IncomingCircuitKey: request.IncomingCircuitKey,
+				Action:             routerrpc.ResolveHoldForwardAction_FAIL,
+				FailureCode:        lnrpc.Failure_TEMPORARY_CHANNEL_FAILURE,
+			}
+		}
+	}
+
+	return &routerrpc.ForwardHtlcInterceptResponse{
+		IncomingCircuitKey:      request.IncomingCircuitKey,
+		Action:                  routerrpc.ResolveHoldForwardAction_RESUME,
+		OutgoingAmountMsat:      interceptResult.AmountMsat,
+		OutgoingRequestedChanId: uint64(interceptResult.ChannelId),
+		OnionBlob:               onionBlob,
+	}
+}