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Add channelCreationFee to liquidity ads
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Creating a new channel has an additional cost compared to adding
liquidity to an existing channel: the channel will be closed in the
future, which will require paying on-chain fees. Node operators can
include a `channel-creation-fee-satoshis` in their liquidity ads to
cover some of that future cost.
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@t-bast
t-bast committed Sep 3, 2024
1 parent 7f95eb4 commit 87a1d54
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Showing 11 changed files with 70 additions and 59 deletions.
7 changes: 4 additions & 3 deletions src/commonMain/kotlin/fr/acinq/lightning/channel/states/Normal.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -406,7 +406,7 @@ data class Normal(
}
Pair(this@Normal.copy(spliceStatus = SpliceStatus.None), actions)
} else if (!canAffordSpliceLiquidityFees(spliceStatus.command, parentCommitment)) {
val missing = spliceStatus.command.requestRemoteFunding?.let { r -> r.fees(spliceStatus.command.feerate).total - parentCommitment.localCommit.spec.toLocal.truncateToSatoshi() }
val missing = spliceStatus.command.requestRemoteFunding?.let { r -> r.fees(spliceStatus.command.feerate, isChannelCreation = false).total - parentCommitment.localCommit.spec.toLocal.truncateToSatoshi() }
logger.warning { "cannot do splice: balance is too low to pay for inbound liquidity (missing=$missing)" }
spliceStatus.command.replyTo.complete(ChannelCommand.Commitment.Splice.Response.Failure.InsufficientFunds)
val actions = buildList {
Expand Down Expand Up @@ -521,6 +521,7 @@ data class Normal(
Helpers.Funding.makeFundingPubKeyScript(spliceStatus.spliceInit.fundingPubkey, cmd.message.fundingPubkey),
cmd.message.fundingContribution,
spliceStatus.spliceInit.feerate,
isChannelCreation = false,
cmd.message.willFund,
)) {
is Either.Left<ChannelException> -> {
Expand Down Expand Up @@ -858,8 +859,8 @@ data class Normal(
return when (val request = splice.requestRemoteFunding) {
null -> true
else -> when (request.paymentDetails) {
is LiquidityAds.PaymentDetails.FromChannelBalance -> request.fees(splice.feerate).total <= parentCommitment.localCommit.spec.toLocal.truncateToSatoshi()
is LiquidityAds.PaymentDetails.FromChannelBalanceForFutureHtlc -> request.fees(splice.feerate).total <= parentCommitment.localCommit.spec.toLocal.truncateToSatoshi()
is LiquidityAds.PaymentDetails.FromChannelBalance -> request.fees(splice.feerate, isChannelCreation = false).total <= parentCommitment.localCommit.spec.toLocal.truncateToSatoshi()
is LiquidityAds.PaymentDetails.FromChannelBalanceForFutureHtlc -> request.fees(splice.feerate, isChannelCreation = false).total <= parentCommitment.localCommit.spec.toLocal.truncateToSatoshi()
// Fees don't need to be paid during the splice, they will be deducted from relayed HTLCs.
is LiquidityAds.PaymentDetails.FromFutureHtlc -> true
is LiquidityAds.PaymentDetails.FromFutureHtlcWithPreimage -> true
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1 change: 1 addition & 0 deletions src/commonMain/kotlin/fr/acinq/lightning/channel/states/WaitForAcceptChannel.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,7 @@ data class WaitForAcceptChannel(
fundingParams.fundingPubkeyScript(channelKeys),
accept.fundingAmount,
lastSent.fundingFeerate,
isChannelCreation = true,
accept.willFund
)) {
is Either.Left -> {
Expand Down
2 changes: 1 addition & 1 deletion src/commonMain/kotlin/fr/acinq/lightning/channel/states/WaitForOpenChannel.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ data class WaitForOpenChannel(
fundingRates == null -> null
requestFunding == null -> null
requestFunding.requestedAmount > fundingAmount -> null
else -> fundingRates.validateRequest(staticParams.nodeParams.nodePrivateKey, fundingScript, open.fundingFeerate, requestFunding)
else -> fundingRates.validateRequest(staticParams.nodeParams.nodePrivateKey, fundingScript, open.fundingFeerate, requestFunding, isChannelCreation = true)
}
val accept = AcceptDualFundedChannel(
temporaryChannelId = open.temporaryChannelId,
Expand Down
12 changes: 6 additions & 6 deletions src/commonMain/kotlin/fr/acinq/lightning/io/Peer.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,7 @@ data class AddWalletInputsToChannel(val walletInputs: List<WalletState.Utxo>) :
data class AddLiquidityForIncomingPayment(val paymentAmount: MilliSatoshi, val requestedAmount: Satoshi, val fundingRate: LiquidityAds.FundingRate, val preimage: ByteVector32, val willAddHtlcs: List<WillAddHtlc>) : PeerCommand() {
val paymentHash: ByteVector32 = Crypto.sha256(preimage.toByteArray()).byteVector32()

fun fees(fundingFeerate: FeeratePerKw): LiquidityAds.Fees = fundingRate.fees(fundingFeerate, requestedAmount, requestedAmount)
fun fees(fundingFeerate: FeeratePerKw, isChannelCreation: Boolean): LiquidityAds.Fees = fundingRate.fees(fundingFeerate, requestedAmount, requestedAmount, isChannelCreation)
}

data class PeerConnection(val id: Long, val output: Channel<LightningMessage>, val logger: MDCLogger) {
Expand Down Expand Up @@ -600,7 +600,7 @@ class Peer(
// The mining fee below pays for the entirety of the splice transaction, including inputs and outputs from the liquidity provider.
val (actualFeerate, miningFee) = client.computeSpliceCpfpFeerate(channel.commitments, targetFeerate, spliceWeight = weight, logger)
// The mining fee below only covers the remote node's inputs and outputs, which are already included in the mining fee above.
val fundingFees = fundingRate.fees(actualFeerate, amount, amount)
val fundingFees = fundingRate.fees(actualFeerate, amount, amount, isChannelCreation = false)
Pair(actualFeerate, ChannelManagementFees(miningFee, fundingFees.serviceFee))
}
}
Expand Down Expand Up @@ -1291,7 +1291,7 @@ class Peer(
val dummyFundingScript = Script.write(Scripts.multiSig2of2(Transactions.PlaceHolderPubKey, Transactions.PlaceHolderPubKey)).byteVector()
val localMiningFee = Transactions.weight2fee(currentFeerates.fundingFeerate, FundingContributions.computeWeightPaid(isInitiator = true, null, dummyFundingScript, cmd.walletInputs, emptyList()))
val localFundingAmount = cmd.totalAmount - localMiningFee
val fundingFees = requestRemoteFunding.fees(currentFeerates.fundingFeerate)
val fundingFees = requestRemoteFunding.fees(currentFeerates.fundingFeerate, isChannelCreation = true)
// We also refund the liquidity provider for some of the on-chain fees they will pay for their inputs/outputs of the transaction.
// This will be taken from our channel balance during the interactive-tx construction, they shouldn't be deducted from our funding amount.
val totalFees = ChannelManagementFees(miningFee = localMiningFee + fundingFees.miningFee, serviceFee = fundingFees.serviceFee)
Expand Down Expand Up @@ -1347,7 +1347,7 @@ class Peer(
val spliceWeight = FundingContributions.computeWeightPaid(isInitiator = true, commitment = available.channel.commitments.active.first(), walletInputs = listOf(), localOutputs = listOf())
val (fundingFeerate, localMiningFee) = client.computeSpliceCpfpFeerate(available.channel.commitments, currentFeerates.fundingFeerate, spliceWeight, logger)
val (targetFeerate, paymentDetails) = when {
localBalance >= localMiningFee + cmd.fees(fundingFeerate).total -> {
localBalance >= localMiningFee + cmd.fees(fundingFeerate, isChannelCreation = false).total -> {
// We have enough funds to pay the mining fee and the lease fees.
// This the ideal scenario because the fees can be paid immediately with the splice transaction.
Pair(fundingFeerate, LiquidityAds.PaymentDetails.FromChannelBalanceForFutureHtlc(listOf(cmd.paymentHash)))
Expand Down Expand Up @@ -1380,7 +1380,7 @@ class Peer(
logger.warning { "cannot request on-the-fly splice: payment types not supported (${walletParams.remoteFundingRates.paymentTypes.joinToString()})" }
}
else -> {
val leaseFees = cmd.fees(targetFeerate)
val leaseFees = cmd.fees(targetFeerate, isChannelCreation = false)
val totalFees = ChannelManagementFees(miningFee = localMiningFee.min(localBalance.truncateToSatoshi()) + leaseFees.miningFee, serviceFee = leaseFees.serviceFee)
logger.info { "requesting on-the-fly splice for paymentHash=${cmd.paymentHash} feerate=$targetFeerate fee=${totalFees.total} paymentType=${paymentDetails.paymentType}" }
val spliceCommand = ChannelCommand.Commitment.Splice.Request(
Expand All @@ -1406,7 +1406,7 @@ class Peer(
// We only need to cover the shared output, which doesn't add too much weight, so we add 25%.
val fundingFeerate = currentFeerates.fundingFeerate * 1.25
// We don't pay any local on-chain fees, our fee is only for the liquidity lease.
val leaseFees = cmd.fees(fundingFeerate)
val leaseFees = cmd.fees(fundingFeerate, isChannelCreation = true)
val totalFees = ChannelManagementFees(miningFee = leaseFees.miningFee, serviceFee = leaseFees.serviceFee)
// We cannot pay the liquidity fees from our channel balance, so we fall back to future HTLCs.
val paymentDetails = when {
Expand Down
4 changes: 3 additions & 1 deletion src/commonMain/kotlin/fr/acinq/lightning/payment/IncomingPaymentHandler.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -305,7 +305,9 @@ class IncomingPaymentHandler(val nodeParams: NodeParams, val db: PaymentsDb, pri
when (val fundingRate = remoteFundingRates.findRate(requestedAmount)) {
null -> Either.Left(LiquidityEvents.Rejected(requestedAmount.toMilliSatoshi(), 0.msat, LiquidityEvents.Source.OffChainPayment, LiquidityEvents.Rejected.Reason.NoMatchingFundingRate))
else -> {
val fees = fundingRate.fees(currentFeerate, requestedAmount, requestedAmount).total
// We don't know at that point if we'll need a channel or if we already have one.
// We must use the worst case fees that applies to channel creation.
val fees = fundingRate.fees(currentFeerate, requestedAmount, requestedAmount, isChannelCreation = true).total
val rejected = when {
// We only initiate on-the-fly funding if the missing amount is greater than the fees paid.
// Otherwise our peer may not be able to claim the funding fees from the relayed HTLCs.
Expand Down
22 changes: 14 additions & 8 deletions src/commonMain/kotlin/fr/acinq/lightning/wire/LiquidityAds.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -43,14 +43,16 @@ object LiquidityAds {
* The buyer refunds those on-chain fees for the given vbytes.
* @param feeProportional proportional fee (expressed in basis points) based on the amount contributed by the seller.
* @param feeBase flat fee that must be paid regardless of the amount contributed by the seller.
* @param channelCreationFee flat fee that must be paid when a new channel is created.
*/
data class FundingRate(val minAmount: Satoshi, val maxAmount: Satoshi, val fundingWeight: Int, val feeProportional: Int, val feeBase: Satoshi) {
data class FundingRate(val minAmount: Satoshi, val maxAmount: Satoshi, val fundingWeight: Int, val feeProportional: Int, val feeBase: Satoshi, val channelCreationFee: Satoshi) {
/** Fees paid by the liquidity buyer. */
fun fees(feerate: FeeratePerKw, requestedAmount: Satoshi, contributedAmount: Satoshi): Fees {
fun fees(feerate: FeeratePerKw, requestedAmount: Satoshi, contributedAmount: Satoshi, isChannelCreation: Boolean): Fees {
val onChainFees = Transactions.weight2fee(feerate, fundingWeight)
// If the seller adds more liquidity than requested, the buyer doesn't pay for that extra liquidity.
val proportionalFee = requestedAmount.min(contributedAmount) * feeProportional / 10_000
return Fees(onChainFees, feeBase + proportionalFee)
val flatFee = if (isChannelCreation) channelCreationFee + feeBase else feeBase
return Fees(onChainFees, flatFee + proportionalFee)
}

/** When liquidity is purchased, the seller provides a signature of the funding rate and funding script. */
Expand All @@ -68,6 +70,7 @@ object LiquidityAds {
LightningCodecs.writeU16(fundingWeight, out)
LightningCodecs.writeU16(feeProportional, out)
LightningCodecs.writeU32(feeBase.sat.toInt(), out)
LightningCodecs.writeU32(channelCreationFee.sat.toInt(), out)
}

companion object {
Expand All @@ -77,6 +80,7 @@ object LiquidityAds {
fundingWeight = LightningCodecs.u16(input),
feeProportional = LightningCodecs.u16(input),
feeBase = LightningCodecs.u32(input).sat,
channelCreationFee = LightningCodecs.u32(input).sat,
)
}
}
Expand Down Expand Up @@ -186,14 +190,14 @@ object LiquidityAds {

/** Sellers offer various rates and payment options. */
data class WillFundRates(val fundingRates: List<FundingRate>, val paymentTypes: Set<PaymentType>) {
fun validateRequest(nodeKey: PrivateKey, fundingScript: ByteVector, fundingFeerate: FeeratePerKw, request: RequestFunding): WillFundPurchase? {
fun validateRequest(nodeKey: PrivateKey, fundingScript: ByteVector, fundingFeerate: FeeratePerKw, request: RequestFunding, isChannelCreation: Boolean): WillFundPurchase? {
val paymentTypeOk = paymentTypes.contains(request.paymentDetails.paymentType)
val rateOk = fundingRates.contains(request.fundingRate)
val amountOk = request.fundingRate.minAmount <= request.requestedAmount && request.requestedAmount <= request.fundingRate.maxAmount
return when {
paymentTypeOk && rateOk && amountOk -> {
val sig = Crypto.sign(request.fundingRate.signedData(fundingScript), nodeKey)
val purchase = Purchase.Standard(request.requestedAmount, request.fees(fundingFeerate), request.paymentDetails)
val purchase = Purchase.Standard(request.requestedAmount, request.fees(fundingFeerate, isChannelCreation), request.paymentDetails)
WillFundPurchase(WillFund(request.fundingRate, fundingScript, sig), purchase)
}
else -> null
Expand Down Expand Up @@ -242,14 +246,15 @@ object LiquidityAds {

/** Request inbound liquidity from a remote peer that supports liquidity ads. */
data class RequestFunding(val requestedAmount: Satoshi, val fundingRate: FundingRate, val paymentDetails: PaymentDetails) {
fun fees(feerate: FeeratePerKw): Fees = fundingRate.fees(feerate, requestedAmount, requestedAmount)
fun fees(feerate: FeeratePerKw, isChannelCreation: Boolean): Fees = fundingRate.fees(feerate, requestedAmount, requestedAmount, isChannelCreation)

fun validateRemoteFunding(
remoteNodeId: PublicKey,
channelId: ByteVector32,
fundingScript: ByteVector,
remoteFundingAmount: Satoshi,
fundingFeerate: FeeratePerKw,
isChannelCreation: Boolean,
willFund: WillFund?
): Either<ChannelException, Purchase> {
return when (willFund) {
Expand All @@ -261,7 +266,7 @@ object LiquidityAds {
remoteFundingAmount < requestedAmount -> Either.Left(InvalidLiquidityAdsAmount(channelId, remoteFundingAmount, requestedAmount))
else -> {
val purchasedAmount = requestedAmount.min(remoteFundingAmount)
val fees = fundingRate.fees(fundingFeerate, requestedAmount, remoteFundingAmount)
val fees = fundingRate.fees(fundingFeerate, requestedAmount, remoteFundingAmount, isChannelCreation)
Either.Right(Purchase.Standard(purchasedAmount, fees, paymentDetails))
}
}
Expand Down Expand Up @@ -295,11 +300,12 @@ object LiquidityAds {
fundingScript: ByteVector,
remoteFundingAmount: Satoshi,
fundingFeerate: FeeratePerKw,
isChannelCreation: Boolean,
willFund: WillFund?,
): Either<ChannelException, Purchase?> {
return when (request) {
null -> Either.Right(null)
else -> request.validateRemoteFunding(remoteNodeId, channelId, fundingScript, remoteFundingAmount, fundingFeerate, willFund)
else -> request.validateRemoteFunding(remoteNodeId, channelId, fundingScript, remoteFundingAmount, fundingFeerate, isChannelCreation, willFund)
}
}

Expand Down
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