From 1f28bd80869ebe7e185659f949ff79a012bc4e6f Mon Sep 17 00:00:00 2001
From: "Johan T. Halseth" <johanth@gmail.com>
Date: Fri, 6 Mar 2020 16:11:46 +0100
Subject: [PATCH] contractcourt/commit_sweep_resolver: set sweep witness type
 based on witness script

We use the fact that we can tell whether the commit is local or remote
by inspecting the witness script. We cannot use the maturity delay
anymore, as we can have delayed to_remote outputs also now.

Co-authored-by: Joost Jager <joost.jager@gmail.com>
---
 contractcourt/commit_sweep_resolver.go      | 36 +++++++++++++++++----
 contractcourt/commit_sweep_resolver_test.go |  2 ++
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/contractcourt/commit_sweep_resolver.go b/contractcourt/commit_sweep_resolver.go
index f2061c0fa..fe09dc09f 100644
--- a/contractcourt/commit_sweep_resolver.go
+++ b/contractcourt/commit_sweep_resolver.go
@@ -6,6 +6,7 @@ import (
 	"io"
 	"sync"
 
+	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/input"
@@ -172,24 +173,45 @@ func (c *commitSweepResolver) Resolve() (ContractResolver, error) {
 		}
 	}
 
-	// We're dealing with our commitment transaction if the delay on the
-	// resolution isn't zero.
-	isLocalCommitTx := c.commitResolution.MaturityDelay != 0
+	// The output is on our local commitment if the script starts with
+	// OP_IF for the revocation clause. On the remote commitment it will
+	// either be a regular P2WKH or a simple sig spend with a CSV delay.
+	isLocalCommitTx := c.commitResolution.SelfOutputSignDesc.WitnessScript[0] == txscript.OP_IF
+	isDelayedOutput := c.commitResolution.MaturityDelay != 0
 
-	// There're two types of commitments, those that have tweaks
-	// for the remote key (us in this case), and those that don't.
-	// We'll rely on the presence of the commitment tweak to to
-	// discern which type of commitment this is.
+	c.log.Debugf("isDelayedOutput=%v, isLocalCommitTx=%v", isDelayedOutput,
+		isLocalCommitTx)
+
+	// There're three types of commitments, those that have tweaks
+	// for the remote key (us in this case), those that don't, and a third
+	// where there is no tweak and the output is delayed. On the local
+	// commitment our output will always be delayed. We'll rely on the
+	// presence of the commitment tweak to to discern which type of
+	// commitment this is.
 	var witnessType input.WitnessType
 	switch {
+
+	// Delayed output to us on our local commitment.
 	case isLocalCommitTx:
 		witnessType = input.CommitmentTimeLock
+
+	// A confirmed output to us on the remote commitment.
+	case isDelayedOutput:
+		witnessType = input.CommitmentToRemoteConfirmed
+
+	// A non-delayed output on the remote commitment where the key is
+	// tweakless.
 	case c.commitResolution.SelfOutputSignDesc.SingleTweak == nil:
 		witnessType = input.CommitSpendNoDelayTweakless
+
+	// A non-delayed output on the remote commitment where the key is
+	// tweaked.
 	default:
 		witnessType = input.CommitmentNoDelay
 	}
 
+	c.log.Infof("Sweeping with witness type: %v", witnessType)
+
 	// We'll craft an input with all the information required for
 	// the sweeper to create a fully valid sweeping transaction to
 	// recover these coins.
diff --git a/contractcourt/commit_sweep_resolver_test.go b/contractcourt/commit_sweep_resolver_test.go
index 4ca018334..c142167e1 100644
--- a/contractcourt/commit_sweep_resolver_test.go
+++ b/contractcourt/commit_sweep_resolver_test.go
@@ -133,6 +133,7 @@ func TestCommitSweepResolverNoDelay(t *testing.T) {
 			Output: &wire.TxOut{
 				Value: 100,
 			},
+			WitnessScript: []byte{0},
 		},
 	}
 
@@ -162,6 +163,7 @@ func TestCommitSweepResolverDelay(t *testing.T) {
 			Output: &wire.TxOut{
 				Value: amt,
 			},
+			WitnessScript: []byte{0},
 		},
 		MaturityDelay: 3,
 		SelfOutPoint:  outpoint,