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lnwallet: don't add trimmed HTLC value to initiator commitment fees

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This commit fixes a lingering bug in the way the internal channel state
machine handled fee calculation. Previously, we would count the dust
HTLC’s that were trimmed towards the fee that the initiator paid. This
is invalid as otherwise, the initiator would always benefit from dust
HTLC’s. Instead, we now simply “donate” the dust HTLC’s to the miner in
the commitment transaction. This change puts us in compliance with
BOLT-0003.
This commit is contained in:
Olaoluwa Osuntokun 2017-07-31 20:41:12 -07:00
parent 5ece7fec2d
commit db793991ac
No known key found for this signature in database
GPG Key ID: 9CC5B105D03521A2
1 changed files with 8 additions and 11 deletions
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19
lnwallet/channel.go
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@ -1775,18 +1775,17 @@ func (lc *LightningChannel) fetchCommitmentView(remoteChain bool,
// Determine how many current HTLCs are over the dust limit, and should
// be counted for the purpose of fee calculation.
var dustLimit, dustFees btcutil.Amount
var dustLimit btcutil.Amount
if remoteChain {
dustLimit = lc.remoteChanCfg.DustLimit
} else {
dustLimit = lc.localChanCfg.DustLimit
}
numHTLCs := 0
numHTLCs := int64(0)
for _, htlc := range filteredHTLCView.ourUpdates {
if htlcIsDust(false, ourCommitTx, feePerKw, htlc.Amount,
dustLimit) {
dustFees += htlc.Amount
continue
}
@ -1796,7 +1795,6 @@ func (lc *LightningChannel) fetchCommitmentView(remoteChain bool,
if htlcIsDust(true, ourCommitTx, feePerKw, htlc.Amount,
dustLimit) {
dustFees += htlc.Amount
continue
}
@ -1807,20 +1805,19 @@ func (lc *LightningChannel) fetchCommitmentView(remoteChain bool,
// on its total weight. Once we have the total weight, we'll multiply
// by the current fee-per-kw, then divide by 1000 to get the proper
// fee.
totalCommitWeight := commitWeight + btcutil.Amount(htlcWeight*numHTLCs)
totalCommitWeight := commitWeight + (htlcWeight * numHTLCs)
// With the weight known, we can now calculate the commitment fee,
// ensuring that we account for any dust outputs trimmed above.
commitFee := (feePerKw * totalCommitWeight) / 1000
commitFee -= dustFees
commitFee := btcutil.Amount((int64(feePerKw) * totalCommitWeight) / 1000)
// Currently, within the protocol, the initiator always pays the fees.
// So we'll subtract the fee amount from the balance of the current
// initiator.
if lc.channelState.IsInitiator {
ourBalance = ourBalance - commitFee
ourBalance -= commitFee
} else if !lc.channelState.IsInitiator {
theirBalance = theirBalance - commitFee
theirBalance -= commitFee
}
var (
@ -3686,7 +3683,7 @@ func (lc *LightningChannel) CreateCloseProposal(feeRate uint64,
// Subtract the proposed fee from the appropriate balance, taking care
// not to persist the adjusted balance, as the feeRate may change
// during the channel closing process.
proposedFee := uint64(btcutil.Amount(feeRate) * commitWeight / 1000)
proposedFee := (feeRate * uint64(commitWeight)) / 1000
ourBalance := lc.channelState.LocalBalance
theirBalance := lc.channelState.RemoteBalance
@ -3748,7 +3745,7 @@ func (lc *LightningChannel) CompleteCooperativeClose(localSig, remoteSig,
// Subtract the proposed fee from the appropriate balance, taking care
// not to persist the adjusted balance, as the feeRate may change
// during the channel closing process.
proposedFee := uint64(btcutil.Amount(feeRate) * commitWeight / 1000)
proposedFee := (feeRate * uint64(commitWeight)) / 1000
ourBalance := lc.channelState.LocalBalance
theirBalance := lc.channelState.RemoteBalance