Abort splice attempts when balance is too low

If our balance, combined with our fee credit, doesn't allow us to pay
the liquidity fees with the payment type we chose, we immediately abort
the splice.

Author: t-bast

src/commonMain/kotlin/fr/acinq/lightning/channel/ChannelCommand.kt

@@ -87,7 +87,15 @@ sealed class ChannelCommand {
         data class UpdateFee(val feerate: FeeratePerKw, val commit: Boolean = false) : Commitment(), ForbiddenDuringSplice, ForbiddenDuringQuiescence
         data object CheckHtlcTimeout : Commitment()
         sealed class Splice : Commitment() {
-            data class Request(val replyTo: CompletableDeferred<Response>, val spliceIn: SpliceIn?, val spliceOut: SpliceOut?, val requestRemoteFunding: LiquidityAds.RequestFunding?, val feerate: FeeratePerKw, val origins: List<Origin>) : Splice() {
+            data class Request(
+                val replyTo: CompletableDeferred<Response>,
+                val spliceIn: SpliceIn?,
+                val spliceOut: SpliceOut?,
+                val requestRemoteFunding: LiquidityAds.RequestFunding?,
+                val currentFeeCredit: MilliSatoshi,
+                val feerate: FeeratePerKw,
+                val origins: List<Origin>
+            ) : Splice() {
                 val pushAmount: MilliSatoshi = spliceIn?.pushAmount ?: 0.msat
                 val spliceOutputs: List<TxOut> = spliceOut?.let { listOf(TxOut(it.amount, it.scriptPubKey)) } ?: emptyList()
 
@@ -110,7 +118,7 @@ sealed class ChannelCommand {
                 ) : Response()
 
                 sealed class Failure : Response() {
-                    data object InsufficientFunds : Failure()
+                    data class InsufficientFunds(val balanceAfterFees: MilliSatoshi, val liquidityFees: MilliSatoshi, val currentFeeCredit: MilliSatoshi) : Failure()
                     data object InvalidSpliceOutPubKeyScript : Failure()
                     data object SpliceAlreadyInProgress : Failure()
                     data object ConcurrentRemoteSplice : Failure()

src/commonMain/kotlin/fr/acinq/lightning/channel/states/Normal.kt

@@ -389,22 +389,29 @@ data class Normal(
                                             paysCommitTxFees -> Transactions.commitTxFee(commitments.params.remoteParams.dustLimit, parentCommitment.remoteCommit.spec)
                                             else -> 0.sat
                                         }
-                                        if (parentCommitment.localCommit.spec.toLocal + fundingContribution.toMilliSatoshi() < parentCommitment.localChannelReserve(commitments.params).max(commitTxFees)) {
-                                            logger.warning { "cannot do splice: insufficient funds" }
-                                            spliceStatus.command.replyTo.complete(ChannelCommand.Commitment.Splice.Response.Failure.InsufficientFunds)
-                                            val actions = buildList {
-                                                add(ChannelAction.Message.Send(Warning(channelId, InvalidSpliceRequest(channelId).message)))
-                                                add(ChannelAction.Disconnect)
+                                        val liquidityFees = when (val requestRemoteFunding = spliceStatus.command.requestRemoteFunding) {
+                                            null -> 0.msat
+                                            else -> when (requestRemoteFunding.paymentDetails.paymentType) {
+                                                LiquidityAds.PaymentType.FromChannelBalance -> requestRemoteFunding.fees(spliceStatus.command.feerate, isChannelCreation = false).total.toMilliSatoshi()
+                                                LiquidityAds.PaymentType.FromChannelBalanceForFutureHtlc -> requestRemoteFunding.fees(spliceStatus.command.feerate, isChannelCreation = false).total.toMilliSatoshi()
+                                                // Liquidity fees will be deducted from future HTLCs instead of being paid immediately.
+                                                LiquidityAds.PaymentType.FromFutureHtlc -> 0.msat
+                                                LiquidityAds.PaymentType.FromFutureHtlcWithPreimage -> 0.msat
+                                                is LiquidityAds.PaymentType.Unknown -> 0.msat
                                             }
-                                            Pair(this@Normal.copy(spliceStatus = SpliceStatus.None), actions)
+                                        }
+                                        val liquidityFeesOwed = (liquidityFees - spliceStatus.command.currentFeeCredit).max(0.msat)
+                                        val balanceAfterFees = parentCommitment.localCommit.spec.toLocal + fundingContribution.toMilliSatoshi() - liquidityFeesOwed
+                                        if (balanceAfterFees < parentCommitment.localChannelReserve(commitments.params).max(commitTxFees)) {
+                                            logger.warning { "cannot do splice: insufficient funds (balanceAfterFees=$balanceAfterFees, liquidityFees=$liquidityFees, feeCredit=${spliceStatus.command.currentFeeCredit})" }
+                                            spliceStatus.command.replyTo.complete(ChannelCommand.Commitment.Splice.Response.Failure.InsufficientFunds(balanceAfterFees, liquidityFees, spliceStatus.command.currentFeeCredit))
+                                            val action = listOf(ChannelAction.Message.Send(TxAbort(channelId, InvalidSpliceRequest(channelId).message)))
+                                            Pair(this@Normal.copy(spliceStatus = SpliceStatus.Aborted), action)
                                         } else if (spliceStatus.command.spliceOut?.scriptPubKey?.let { Helpers.Closing.isValidFinalScriptPubkey(it, allowAnySegwit = true) } == false) {
                                             logger.warning { "cannot do splice: invalid splice-out script" }
                                             spliceStatus.command.replyTo.complete(ChannelCommand.Commitment.Splice.Response.Failure.InvalidSpliceOutPubKeyScript)
-                                            val actions = buildList {
-                                                add(ChannelAction.Message.Send(Warning(channelId, InvalidSpliceRequest(channelId).message)))
-                                                add(ChannelAction.Disconnect)
-                                            }
-                                            Pair(this@Normal.copy(spliceStatus = SpliceStatus.None), actions)
+                                            val action = listOf(ChannelAction.Message.Send(TxAbort(channelId, InvalidSpliceRequest(channelId).message)))
+                                            Pair(this@Normal.copy(spliceStatus = SpliceStatus.Aborted), action)
                                         } else {
                                             val spliceInit = SpliceInit(
                                                 channelId,

src/commonMain/kotlin/fr/acinq/lightning/io/Peer.kt

@@ -643,6 +643,7 @@ class Peer(
                     spliceIn = null,
                     spliceOut = ChannelCommand.Commitment.Splice.Request.SpliceOut(amount, scriptPubKey),
                     requestRemoteFunding = null,
+                    currentFeeCredit = feeCreditFlow.value,
                     feerate = feerate,
                     origins = listOf(),
                 )
@@ -662,6 +663,7 @@ class Peer(
                     spliceIn = null,
                     spliceOut = null,
                     requestRemoteFunding = null,
+                    currentFeeCredit = feeCreditFlow.value,
                     feerate = feerate,
                     origins = listOf(),
                 )
@@ -680,6 +682,7 @@ class Peer(
                     spliceIn = null,
                     spliceOut = null,
                     requestRemoteFunding = LiquidityAds.RequestFunding(amount, fundingRate, LiquidityAds.PaymentDetails.FromChannelBalance),
+                    currentFeeCredit = feeCreditFlow.value,
                     feerate = feerate,
                     origins = listOf(),
                 )
@@ -1285,6 +1288,7 @@ class Peer(
                                     spliceIn = ChannelCommand.Commitment.Splice.Request.SpliceIn(cmd.walletInputs),
                                     spliceOut = null,
                                     requestRemoteFunding = null,
+                                    currentFeeCredit = feeCreditFlow.value,
                                     feerate = feerate,
                                     origins = listOf(Origin.OnChainWallet(cmd.walletInputs.map { it.outPoint }.toSet(), cmd.totalAmount.toMilliSatoshi(), ChannelManagementFees(fee, 0.sat)))
                                 )
@@ -1425,6 +1429,7 @@ class Peer(
                                     spliceIn = null,
                                     spliceOut = null,
                                     requestRemoteFunding = LiquidityAds.RequestFunding(cmd.requestedAmount, cmd.fundingRate, paymentDetails),
+                                    currentFeeCredit = currentFeeCredit,
                                     feerate = targetFeerate,
                                     origins = listOf(Origin.OffChainPayment(cmd.preimage, cmd.paymentAmount, totalFees))
                                 )

src/commonTest/kotlin/fr/acinq/lightning/channel/states/QuiescenceTestsCommon.kt

@@ -520,6 +520,7 @@ class QuiescenceTestsCommon : LightningTestSuite() {
                 spliceOut = spliceOut?.let { ChannelCommand.Commitment.Splice.Request.SpliceOut(it, Script.write(Script.pay2wpkh(Lightning.randomKey().publicKey())).byteVector()) },
                 feerate = FeeratePerKw(253.sat),
                 requestRemoteFunding = null,
+                currentFeeCredit = 0.msat,
                 origins = listOf(),
             )
         }