From 5d6b8e49a3678db0cd694eaf6c54d8b1e63a3b6b Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Sun, 23 Oct 2016 18:42:03 -0700
Subject: [PATCH] lnwallet: disallow creating a funding reservation with zero
 total satoshis

---
 lnwallet/reservation.go | 10 +++++++++-
 lnwallet/wallet.go      | 30 +++++++++++++++++++-----------
 2 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/lnwallet/reservation.go b/lnwallet/reservation.go
index 39ba76e2..e86ee874 100644
--- a/lnwallet/reservation.go
+++ b/lnwallet/reservation.go
@@ -140,17 +140,25 @@ func NewChannelReservation(capacity, fundingAmt btcutil.Amount, minFeeRate btcut
 	var ourBalance btcutil.Amount
 	var theirBalance btcutil.Amount
 
+	// If we're the responder to a single-funder reservation, then we have
+	// no initial balance in the channel.
 	if fundingAmt == 0 {
 		ourBalance = 0
 		theirBalance = capacity - commitFee
 	} else {
 		// TODO(roasbeef): need to rework fee structure in general and
 		// also when we "unlock" dual funder within the daemon
-		if capacity == fundingAmt+commitFee { // Single funder
+
+		// If we're initiating a single funder workflow, then we pay
+		// all the initial fees within the commitment transaction.
+		if capacity == fundingAmt+commitFee {
 			ourBalance = capacity - commitFee
+			// Otherwise, this is a dual funder workflow where both slides
+			// split the amount funded and the commitment fee.
 		} else {
 			ourBalance = fundingAmt - commitFee
 		}
+
 		theirBalance = capacity - fundingAmt - commitFee
 	}
 
diff --git a/lnwallet/wallet.go b/lnwallet/wallet.go
index 862dbcbb..deb997b3 100644
--- a/lnwallet/wallet.go
+++ b/lnwallet/wallet.go
@@ -495,6 +495,14 @@ func (l *LightningWallet) InitChannelReservation(capacity,
 // handleFundingReserveRequest processes a message intending to create, and
 // validate a funding reservation request.
 func (l *LightningWallet) handleFundingReserveRequest(req *initFundingReserveMsg) {
+	// It isn't possible to create a channel with zero funds committed.
+	if req.fundingAmount+req.capacity == 0 {
+		req.err <- fmt.Errorf("cannot have channel with zero " +
+			"satoshis funded")
+		req.resp <- nil
+		return
+	}
+
 	id := atomic.AddUint64(&l.nextFundingID, 1)
 	totalCapacity := req.capacity + commitFee
 	reservation := NewChannelReservation(totalCapacity, req.fundingAmount,
@@ -612,11 +620,11 @@ func (l *LightningWallet) handleFundingCancelRequest(req *fundingReserveCancelMs
 	req.err <- nil
 }
 
-// handleFundingCounterPartyFunds processes the second workflow step for the
-// lifetime of a channel reservation. Upon completion, the reservation will
-// carry a completed funding transaction (minus the counterparty's input
-// signatures), both versions of the commitment transaction, and our signature
-// for their version of the commitment transaction.
+// handleContributionMsg processes the second workflow step for the lifetime of
+// a channel reservation. Upon completion, the reservation will carry a
+// completed funding transaction (minus the counterparty's input signatures),
+// both versions of the commitment transaction, and our signature for their
+// version of the commitment transaction.
 func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
 	l.limboMtx.Lock()
 	pendingReservation, ok := l.fundingLimbo[req.pendingFundingID]
@@ -793,11 +801,11 @@ func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
 	// transaction.
 	signDesc = SignDescriptor{
 		WitnessScript: witnessScript,
-		PubKey:       ourKey,
-		Output:       multiSigOut,
-		HashType:     txscript.SigHashAll,
-		SigHashes:    txscript.NewTxSigHashes(theirCommitTx),
-		InputIndex:   0,
+		PubKey:        ourKey,
+		Output:        multiSigOut,
+		HashType:      txscript.SigHashAll,
+		SigHashes:     txscript.NewTxSigHashes(theirCommitTx),
+		InputIndex:    0,
 	}
 	sigTheirCommit, err := l.Signer.SignOutputRaw(theirCommitTx, &signDesc)
 	if err != nil {
@@ -1101,7 +1109,7 @@ func (l *LightningWallet) handleSingleFunderSigs(req *addSingleFunderSigsMsg) {
 	}
 	signDesc := SignDescriptor{
 		WitnessScript: witnessScript,
-		PubKey:       ourKey,
+		PubKey:        ourKey,
 		Output: &wire.TxOut{
 			PkScript: p2wsh,
 			Value:    channelValue,