From e60f40b8459f1f3697340713b9323c62a133b132 Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Mon, 16 Jan 2017 20:28:30 -0800
Subject: [PATCH] lnwallet: fix bug with funding channels with 50/50 balances
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This commit fixes a prior bug in the wallet triggered by the creation
of a channel using the single funder workflow, but pushing exactly
*half* of the channel over to the other side. The prior logic to
determine who the initiator would result in a disagreement over who
created the channel initially. This wouldn’t manifest until the channel
was attempted to be closed cooperatively. As both side disagreed about
who created the channel they would apply the closing fee to different
outputs, thereby creating mismatched closing transaction. The signature
would fail to validate as the closer will create a different
transaction from that of the responder.

This commit fixes the issue by properly detecting who initially created
the channel.
---
 lnwallet/reservation.go | 37 +++++++++++++------------------------
 1 file changed, 13 insertions(+), 24 deletions(-)

diff --git a/lnwallet/reservation.go b/lnwallet/reservation.go
index d7c59ecb..8e897abf 100644
--- a/lnwallet/reservation.go
+++ b/lnwallet/reservation.go
@@ -146,6 +146,7 @@ func NewChannelReservation(capacity, fundingAmt btcutil.Amount, minFeeRate btcut
 	var (
 		ourBalance   btcutil.Amount
 		theirBalance btcutil.Amount
+		initiator    bool
 	)
 
 	// If we're the responder to a single-funder reservation, then we have
@@ -154,6 +155,7 @@ func NewChannelReservation(capacity, fundingAmt btcutil.Amount, minFeeRate btcut
 	if fundingAmt == 0 {
 		ourBalance = pushSat
 		theirBalance = capacity - commitFee - pushSat
+		initiator = false
 	} else {
 		// TODO(roasbeef): need to rework fee structure in general and
 		// also when we "unlock" dual funder within the daemon
@@ -172,34 +174,21 @@ func NewChannelReservation(capacity, fundingAmt btcutil.Amount, minFeeRate btcut
 		}
 
 		theirBalance = capacity - fundingAmt - commitFee + pushSat
+		initiator = true
 	}
 
-	var (
-		initiator bool
-		chanType  channeldb.ChannelType
-	)
-	switch {
-	// If our balance is zero, or we're being pushed our entire balance in
-	// the first state,  then we're the responder to a single funder
-	// channel workflow.
-	case pushSat != 0 && ourBalance-pushSat == 0:
-		fallthrough
-	case ourBalance == 0:
-		initiator = false
-		chanType = channeldb.SingleFunder
+	// Next we'll set the channel type based on what we can ascertain about
+	// the balances/push amount within the channel.
+	var chanType channeldb.ChannelType
 
-	// If their balance is zero, or being pushed entirely to them, then
-	// we're the initiator to a single funder channel workflow.
-	case pushSat != 0 && theirBalance-pushSat == 0:
-		fallthrough
-	case theirBalance == 0:
-		initiator = true
+	// If either of the balances are zero at this point, or we have a
+	// non-zero push amt (there's no pushing for dual funder), then this is
+	// a single-funder channel.
+	if ourBalance == 0 || theirBalance == 0 || pushSat != 0 {
 		chanType = channeldb.SingleFunder
-
-	// Otherwise, if both sides are starting out with a non-zero balance,
-	// then neither of us is technically the "initiator" and this is a dual
-	// funder channel.
-	default:
+	} else {
+		// Otherwise, this is a dual funder channel, and no side is
+		// technically the "initiator"
 		initiator = false
 		chanType = channeldb.DualFunder
 	}