From e9440a24a289c80a1b4cbb93c8cff34d791e9fa4 Mon Sep 17 00:00:00 2001
From: Joost Jager <joost.jager@gmail.com>
Date: Fri, 14 Oct 2022 11:03:31 +0200
Subject: [PATCH] htlcswitch/test: more realistic mock encryption

This mock is used in the switch test TestUpdateFailMalformedHTLCErrorConversion.
But because the mock isn't very realistic, it doesn't detect problems
in the handling of malformed failures in the link.
---
 htlcswitch/mock.go        | 19 +++++++++++++++++--
 htlcswitch/switch_test.go | 15 ++++++++-------
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/htlcswitch/mock.go b/htlcswitch/mock.go
index 9eac221dd..b7bc9b34a 100644
--- a/htlcswitch/mock.go
+++ b/htlcswitch/mock.go
@@ -419,12 +419,16 @@ func (o *mockObfuscator) Reextract(
 	return nil
 }
 
+var fakeHmac = []byte("hmachmachmachmachmachmachmachmac")
+
 func (o *mockObfuscator) EncryptFirstHop(failure lnwire.FailureMessage) (
 	lnwire.OpaqueReason, error) {
 
 	o.failure = failure
 
 	var b bytes.Buffer
+	b.Write(fakeHmac)
+
 	if err := lnwire.EncodeFailure(&b, failure, 0); err != nil {
 		return nil, err
 	}
@@ -436,7 +440,12 @@ func (o *mockObfuscator) IntermediateEncrypt(reason lnwire.OpaqueReason) lnwire.
 }
 
 func (o *mockObfuscator) EncryptMalformedError(reason lnwire.OpaqueReason) lnwire.OpaqueReason {
-	return reason
+	var b bytes.Buffer
+	b.Write(fakeHmac)
+
+	b.Write(reason)
+
+	return b.Bytes()
 }
 
 // mockDeobfuscator mock implementation of the failure deobfuscator which
@@ -447,7 +456,13 @@ func newMockDeobfuscator() ErrorDecrypter {
 	return &mockDeobfuscator{}
 }
 
-func (o *mockDeobfuscator) DecryptError(reason lnwire.OpaqueReason) (*ForwardingError, error) {
+func (o *mockDeobfuscator) DecryptError(reason lnwire.OpaqueReason) (
+	*ForwardingError, error) {
+
+	if !bytes.Equal(reason[:32], fakeHmac) {
+		return nil, errors.New("fake decryption error")
+	}
+	reason = reason[32:]
 
 	r := bytes.NewReader(reason)
 	failure, err := lnwire.DecodeFailure(r, 0)
diff --git a/htlcswitch/switch_test.go b/htlcswitch/switch_test.go
index 461d8875a..4d666b760 100644
--- a/htlcswitch/switch_test.go
+++ b/htlcswitch/switch_test.go
@@ -1,7 +1,6 @@
 package htlcswitch
 
 import (
-	"bytes"
 	"crypto/rand"
 	"crypto/sha256"
 	"fmt"
@@ -23,7 +22,6 @@ import (
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/ticker"
-	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -4088,10 +4086,10 @@ func TestSwitchHoldForward(t *testing.T) {
 	expectedFailure := &lnwire.FailInvalidOnionKey{
 		OnionSHA256: shaOnionBlob,
 	}
-	var b bytes.Buffer
-	require.NoError(t, lnwire.EncodeFailure(&b, expectedFailure, 0))
 
-	assert.Equal(t, lnwire.OpaqueReason(b.Bytes()), failPacket.Reason)
+	fwdErr, err := newMockDeobfuscator().DecryptError(failPacket.Reason)
+	require.NoError(t, err)
+	require.Equal(t, expectedFailure, fwdErr.WireMessage())
 
 	assertNumCircuits(t, c.s, 0, 0)
 
@@ -5515,10 +5513,13 @@ func testSwitchAliasInterceptFail(t *testing.T, zeroConf bool) {
 		failHtlc, ok := failPacket.htlc.(*lnwire.UpdateFailHTLC)
 		require.True(t, ok)
 
-		r := bytes.NewReader(failHtlc.Reason)
-		failure, err := lnwire.DecodeFailure(r, 0)
+		fwdErr, err := newMockDeobfuscator().DecryptError(
+			failHtlc.Reason,
+		)
 		require.NoError(t, err)
 
+		failure := fwdErr.WireMessage()
+
 		failureMsg, ok := failure.(*lnwire.FailTemporaryChannelFailure)
 		require.True(t, ok)