From 4cd277c8dac689ccf2407b7468fe3e68b399f4db Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Tue, 11 Apr 2017 21:38:55 -0700
Subject: [PATCH] lnwallet: eliminate usage of
 LightningChannel.theirPrevPkScript
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This commit removes the theirPrevPkScript field from the
LightningChannel struct all together. It’s no longer needed as the more
fundamental mutation bug has been fixed within the channel state
machine.
---
 lnwallet/channel.go | 37 +++++++------------------------------
 1 file changed, 7 insertions(+), 30 deletions(-)

diff --git a/lnwallet/channel.go b/lnwallet/channel.go
index a4660197..6ffaf2ff 100644
--- a/lnwallet/channel.go
+++ b/lnwallet/channel.go
@@ -276,7 +276,7 @@ func (c *commitment) toChannelDelta(ourCommit bool) (*channeldb.ChannelDelta, er
 			found bool
 		)
 
-		pkScript := p.theirPrevPkScript
+		pkScript := p.theirPkScript
 		if ourCommit {
 			pkScript = p.ourPkScript
 		}
@@ -294,8 +294,8 @@ func (c *commitment) toChannelDelta(ourCommit bool) (*channeldb.ChannelDelta, er
 			}
 		}
 		if !found {
-			return 0, fmt.Errorf("could not find a matching " +
-				"output for the HTLC in the commitment transaction")
+			return 0, fmt.Errorf("unable to find htlc: script=%x, value=%v",
+				pkScript, p.Amount)
 		}
 
 		return idx, nil
@@ -309,8 +309,8 @@ func (c *commitment) toChannelDelta(ourCommit bool) (*channeldb.ChannelDelta, er
 		if (ourCommit && htlc.isDustLocal) ||
 			(!ourCommit && htlc.isDustRemote) {
 			index = maxUint16
-		} else if index, err = locateOutputIndex(htlc); err != nil {
-			return nil, err
+		} else if index, err = locateOutputIndex(&htlc); err != nil {
+			return nil, fmt.Errorf("unable to find outgoing htlc: %v", err)
 		}
 
 		h := &channeldb.HTLC{
@@ -328,8 +328,8 @@ func (c *commitment) toChannelDelta(ourCommit bool) (*channeldb.ChannelDelta, er
 		if (ourCommit && htlc.isDustLocal) ||
 			(!ourCommit && htlc.isDustRemote) {
 			index = maxUint16
-		} else if index, err = locateOutputIndex(htlc); err != nil {
-			return nil, err
+		} else if index, err = locateOutputIndex(&htlc); err != nil {
+			return nil, fmt.Errorf("unable to find incoming htlc: %v", err)
 		}
 
 		h := &channeldb.HTLC{
@@ -2075,12 +2075,6 @@ func (lc *LightningChannel) SettleHTLC(preimage [32]byte) (uint64, error) {
 
 	lc.localUpdateLog.appendUpdate(pd)
 
-	// Since we will not be adding this HTLC to any commitment transaction
-	// anymore, we should properly set theirPrevPkScript so we can generate
-	// a valid ChannelDelta for a revoked remote commitment.
-	addEntry := lc.remoteUpdateLog.lookup(targetHTLC.Index)
-	addEntry.theirPrevPkScript = addEntry.theirPkScript
-
 	lc.rHashMap[paymentHash][0] = nil
 	lc.rHashMap[paymentHash] = lc.rHashMap[paymentHash][1:]
 	if len(lc.rHashMap[paymentHash]) == 0 {
@@ -2117,12 +2111,6 @@ func (lc *LightningChannel) ReceiveHTLCSettle(preimage [32]byte, logIndex uint64
 	}
 
 	lc.remoteUpdateLog.appendUpdate(pd)
-
-	// Since we will not be adding this HTLC to any commitment transaction
-	// anymore, we should properly set theirPrevPkScript so we can generate
-	// a valid ChannelDelta for a revoked remote commitment.
-	htlc.theirPrevPkScript = htlc.theirPkScript
-
 	return nil
 }
 
@@ -2150,11 +2138,6 @@ func (lc *LightningChannel) FailHTLC(rHash [32]byte) (uint64, error) {
 
 	lc.localUpdateLog.appendUpdate(pd)
 
-	// Since we will not be adding this HTLC to any commitment transaction
-	// anymore, we should properly set theirPrevPkScript so we can generate
-	// a valid ChannelDelta for a revoked remote commitment.
-	addEntry.theirPrevPkScript = addEntry.theirPkScript
-
 	lc.rHashMap[rHash][0] = nil
 	lc.rHashMap[rHash] = lc.rHashMap[rHash][1:]
 	if len(lc.rHashMap[rHash]) == 0 {
@@ -2187,11 +2170,6 @@ func (lc *LightningChannel) ReceiveFailHTLC(logIndex uint64) error {
 
 	lc.remoteUpdateLog.appendUpdate(pd)
 
-	// Since we will not be adding this HTLC to any commitment transaction
-	// anymore, we should properly set theirPrevPkScript so we can generate
-	// a valid ChannelDelta for a revoked remote commitment.
-	htlc.theirPrevPkScript = htlc.theirPkScript
-
 	return nil
 }
 
@@ -2282,7 +2260,6 @@ func (lc *LightningChannel) addHTLC(commitTx *wire.MsgTx, ourCommit bool,
 	if ourCommit {
 		paymentDesc.ourPkScript = htlcP2WSH
 	} else {
-		paymentDesc.theirPrevPkScript = paymentDesc.theirPkScript
 		paymentDesc.theirPkScript = htlcP2WSH
 	}