From 263d6b9c1fbeb67319dda5dee806c47c46534ea5 Mon Sep 17 00:00:00 2001
From: "Johan T. Halseth" <johanth@gmail.com>
Date: Thu, 22 Mar 2018 12:59:11 +0100
Subject: [PATCH] lnwallet/channel: don't accept immediately on empty htlc sigs

This commit fixes an issue where we would blindly accept a commitment
which came without any accompanying HTLC signatures. A test exercising
the scenario is added.
---
 lnwallet/channel.go      |  6 ------
 lnwallet/channel_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/lnwallet/channel.go b/lnwallet/channel.go
index 496425e6..eb0adeaf 100644
--- a/lnwallet/channel.go
+++ b/lnwallet/channel.go
@@ -3465,12 +3465,6 @@ func genHtlcSigValidationJobs(localCommitmentView *commitment,
 	keyRing *CommitmentKeyRing, htlcSigs []lnwire.Sig,
 	localChanCfg, remoteChanCfg *channeldb.ChannelConfig) ([]verifyJob, error) {
 
-	// If this new commitment state doesn't have any HTLC's that are to be
-	// signed, then we'll return a nil slice.
-	if len(htlcSigs) == 0 {
-		return nil, nil
-	}
-
 	txHash := localCommitmentView.txn.TxHash()
 	feePerKw := localCommitmentView.feePerKw
 
diff --git a/lnwallet/channel_test.go b/lnwallet/channel_test.go
index cd56e0e8..01e158d8 100644
--- a/lnwallet/channel_test.go
+++ b/lnwallet/channel_test.go
@@ -1530,6 +1530,30 @@ func TestHTLCSigNumber(t *testing.T) {
 		t.Fatalf("Expected Bob to reject signatures")
 	}
 
+	// ===================================================================
+	// Test that Bob will reject a commitment if Alice doesn't send any
+	// HTLC signatures.
+	// ===================================================================
+	aliceChannel, bobChannel, cleanUp = createChanWithHTLC(aboveDust)
+	defer cleanUp()
+
+	aliceSig, aliceHtlcSigs, err = aliceChannel.SignNextCommitment()
+	if err != nil {
+		t.Fatalf("Error signing next commitment: %v", err)
+	}
+
+	if len(aliceHtlcSigs) != 1 {
+		t.Fatalf("expected 1 htlc sig, instead got %v",
+			len(aliceHtlcSigs))
+	}
+
+	// Now just give Bob an empty htlcSig slice. He should reject the
+	// commitment because of this.
+	err = bobChannel.ReceiveNewCommitment(aliceSig, []lnwire.Sig{})
+	if err == nil {
+		t.Fatalf("Expected Bob to reject signatures")
+	}
+
 }
 
 // TestChannelBalanceDustLimit tests the condition when the remaining balance