Implement option_simple_close (#597)

Implement `option_simple_close` as defined in lightning/bolts#1205
This is a pre-requisite for taproot channels that is already supported by `eclair`.

Author: t-bast

modules/core/src/commonMain/kotlin/fr/acinq/lightning/Features.kt

@@ -147,8 +147,6 @@ sealed class Feature {
         override val scopes: Set<FeatureScope> get() = setOf(FeatureScope.Invoice)
     }
 
-    // The following features have not been standardised, hence the high feature bits to avoid conflicts.
-
     // We historically used the following feature bit in our invoices.
     // However, the spec assigned the same feature bit to `option_scid_alias` (https://github.com/lightning/bolts/pull/910).
     // We're moving this feature bit to 148, but we have to keep supporting it until enough wallet users have migrated, then we can remove it.
@@ -160,6 +158,15 @@ sealed class Feature {
         override val scopes: Set<FeatureScope> get() = setOf(FeatureScope.Init, FeatureScope.Node, FeatureScope.Invoice)
     }
 
+    @Serializable
+    object SimpleClose : Feature() {
+        override val rfcName get() = "option_simple_close"
+        override val mandatory get() = 60
+        override val scopes: Set<FeatureScope> get() = setOf(FeatureScope.Init, FeatureScope.Node)
+    }
+
+    // The following features have not been standardised, hence the high feature bits to avoid conflicts.
+
     /** This feature bit should be activated when a node accepts having their channel reserve set to 0. */
     @Serializable
     object ZeroReserveChannels : Feature() {
@@ -340,6 +347,7 @@ data class Features(val activated: Map<Feature, FeatureSupport>, val unknown: Se
             Feature.ChannelType,
             Feature.PaymentMetadata,
             Feature.TrampolinePayment,
+            Feature.SimpleClose,
             Feature.ExperimentalTrampolinePayment,
             Feature.ZeroReserveChannels,
             Feature.ZeroConfChannels,
@@ -384,6 +392,7 @@ data class Features(val activated: Map<Feature, FeatureSupport>, val unknown: Se
             Feature.PaymentSecret to listOf(Feature.VariableLengthOnion),
             Feature.BasicMultiPartPayment to listOf(Feature.PaymentSecret),
             Feature.AnchorOutputs to listOf(Feature.StaticRemoteKey),
+            Feature.SimpleClose to listOf(Feature.ShutdownAnySegwit),
             Feature.TrampolinePayment to listOf(Feature.PaymentSecret),
             Feature.ExperimentalTrampolinePayment to listOf(Feature.PaymentSecret),
             Feature.OnTheFlyFunding to listOf(Feature.ExperimentalSplice),

modules/core/src/commonMain/kotlin/fr/acinq/lightning/NodeParams.kt

@@ -174,6 +174,8 @@ data class NodeParams(
         require(features.hasFeature(Feature.ChannelType, FeatureSupport.Mandatory)) { "${Feature.ChannelType.rfcName} should be mandatory" }
         require(features.hasFeature(Feature.DualFunding, FeatureSupport.Mandatory)) { "${Feature.DualFunding.rfcName} should be mandatory" }
         require(features.hasFeature(Feature.RouteBlinding)) { "${Feature.RouteBlinding.rfcName} should be supported" }
+        require(features.hasFeature(Feature.ShutdownAnySegwit, FeatureSupport.Mandatory)) { "${Feature.ShutdownAnySegwit.rfcName} should be mandatory" }
+        require(features.hasFeature(Feature.SimpleClose, FeatureSupport.Mandatory)) { "${Feature.SimpleClose.rfcName} should be mandatory" }
         require(!features.hasFeature(Feature.ZeroConfChannels)) { "${Feature.ZeroConfChannels.rfcName} has been deprecated: use the zeroConfPeers whitelist instead" }
         require(!features.hasFeature(Feature.TrustedSwapInClient)) { "${Feature.TrustedSwapInClient.rfcName} has been deprecated" }
         require(!features.hasFeature(Feature.TrustedSwapInProvider)) { "${Feature.TrustedSwapInProvider.rfcName} has been deprecated" }
@@ -205,6 +207,7 @@ data class NodeParams(
             Feature.Quiescence to FeatureSupport.Mandatory,
             Feature.ChannelType to FeatureSupport.Mandatory,
             Feature.PaymentMetadata to FeatureSupport.Optional,
+            Feature.SimpleClose to FeatureSupport.Mandatory,
             Feature.ExperimentalTrampolinePayment to FeatureSupport.Optional,
             Feature.ZeroReserveChannels to FeatureSupport.Optional,
             Feature.WakeUpNotificationClient to FeatureSupport.Optional,

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

@@ -6,7 +6,6 @@ import fr.acinq.lightning.MilliSatoshi
 import fr.acinq.lightning.blockchain.WatchTriggered
 import fr.acinq.lightning.blockchain.electrum.WalletState
 import fr.acinq.lightning.blockchain.fee.FeeratePerKw
-import fr.acinq.lightning.channel.states.ClosingFeerates
 import fr.acinq.lightning.channel.states.PersistedChannelState
 import fr.acinq.lightning.crypto.KeyManager
 import fr.acinq.lightning.utils.UUID
@@ -105,7 +104,7 @@ sealed class ChannelCommand {
     }
 
     sealed class Close : ChannelCommand() {
-        data class MutualClose(val scriptPubKey: ByteVector?, val feerates: ClosingFeerates?) : Close(), ForbiddenDuringSplice, ForbiddenDuringQuiescence
+        data class MutualClose(val replyTo: CompletableDeferred<ChannelCloseResponse>, val scriptPubKey: ByteVector?, val feerate: FeeratePerKw) : Close(), ForbiddenDuringSplice, ForbiddenDuringQuiescence
         data object ForceClose : Close()
     }
 
@@ -145,4 +144,19 @@ sealed class ChannelFundingResponse {
         data class UnexpectedMessage(val msg: LightningMessage) : Failure()
         data object Disconnected : Failure()
     }
+}
+
+sealed class ChannelCloseResponse {
+    /** This response doesn't fully guarantee that the closing transaction will confirm: it can be RBF-ed if necessary. */
+    data class Success(val closingTxId: TxId, val closingFee: Satoshi) : ChannelCloseResponse()
+
+    sealed class Failure : ChannelCloseResponse() {
+        data class ChannelNotOpenedYet(val state: String) : Failure()
+        data object ChannelOffline : Failure()
+        data object ClosingAlreadyInProgress : Failure()
+        data class ClosingUpdated(val updatedFeerate: FeeratePerKw, val updatedScript: ByteVector?) : Failure()
+        data class InvalidClosingAddress(val script: ByteVector) : Failure()
+        data class RbfFeerateTooLow(val proposed: FeeratePerKw, val expected: FeeratePerKw) : Failure()
+        data class Unknown(val reason: ChannelException) : Failure()
+    }
 }

modules/core/src/commonMain/kotlin/fr/acinq/lightning/channel/ChannelData.kt

@@ -13,7 +13,6 @@ import fr.acinq.lightning.logging.LoggingContext
 import fr.acinq.lightning.transactions.Scripts
 import fr.acinq.lightning.transactions.Transactions.TransactionWithInputInfo.*
 import fr.acinq.lightning.utils.toMilliSatoshi
-import fr.acinq.lightning.wire.ClosingSigned
 
 /**
  * Details about a force-close where we published our commitment.
@@ -370,10 +369,6 @@ data class LocalParams(
         features = nodeParams.features.initFeatures()
     )
 
-    // The node responsible for the commit tx fees is also the node paying the mutual close fees.
-    // The other node's balance may be empty, which wouldn't allow them to pay the closing fees.
-    val paysClosingFees: Boolean = paysCommitTxFees
-
     fun channelKeys(keyManager: KeyManager) = keyManager.channelKeys(fundingKeyPath)
 }
 
@@ -397,8 +392,6 @@ data class RemoteParams(
  */
 data class ChannelFlags(val announceChannel: Boolean, val nonInitiatorPaysCommitFees: Boolean)
 
-data class ClosingTxProposed(val unsignedTx: ClosingTx, val localClosingSigned: ClosingSigned)
-
 /**
  * @param miningFee fee paid to miners for the underlying on-chain transaction.
  * @param serviceFee fee paid to our peer for any service provided with the on-chain transaction.

modules/core/src/commonMain/kotlin/fr/acinq/lightning/channel/ChannelException.kt

@@ -1,9 +1,6 @@
 package fr.acinq.lightning.channel
 
-import fr.acinq.bitcoin.BlockHash
-import fr.acinq.bitcoin.ByteVector32
-import fr.acinq.bitcoin.Satoshi
-import fr.acinq.bitcoin.TxId
+import fr.acinq.bitcoin.*
 import fr.acinq.lightning.CltvExpiry
 import fr.acinq.lightning.CltvExpiryDelta
 import fr.acinq.lightning.MilliSatoshi
@@ -62,8 +59,10 @@ data class FeerateTooSmall                         (override val channelId: Byte
 data class FeerateTooDifferent                     (override val channelId: ByteVector32, val localFeeratePerKw: FeeratePerKw, val remoteFeeratePerKw: FeeratePerKw) : ChannelException(channelId, "local/remote feerates are too different: remoteFeeratePerKw=${remoteFeeratePerKw.toLong()} localFeeratePerKw=${localFeeratePerKw.toLong()}")
 data class InvalidCommitmentSignature              (override val channelId: ByteVector32, val txId: TxId) : ChannelException(channelId, "invalid commitment signature: txId=$txId")
 data class InvalidHtlcSignature                    (override val channelId: ByteVector32, val txId: TxId) : ChannelException(channelId, "invalid htlc signature: txId=$txId")
+data class CannotGenerateClosingTx                 (override val channelId: ByteVector32) : ChannelException(channelId, "failed to generate closing transaction: all outputs are trimmed")
+data class MissingCloseSignature                   (override val channelId: ByteVector32) : ChannelException(channelId, "closing_complete is missing a signature for a closing transaction including our output")
 data class InvalidCloseSignature                   (override val channelId: ByteVector32, val txId: TxId) : ChannelException(channelId, "invalid close signature: txId=$txId")
-data class InvalidCloseAmountBelowDust             (override val channelId: ByteVector32, val txId: TxId) : ChannelException(channelId, "invalid closing tx: some outputs are below dust: txId=$txId")
+data class InvalidCloseeScript                     (override val channelId: ByteVector32, val received: ByteVector, val expected: ByteVector) : ChannelException(channelId, "invalid closee script used in closing_complete: our latest script is $expected, you're using $received")
 data class CommitSigCountMismatch                  (override val channelId: ByteVector32, val expected: Int, val actual: Int) : ChannelException(channelId, "commit sig count mismatch: expected=$expected actual=$actual")
 data class HtlcSigCountMismatch                    (override val channelId: ByteVector32, val expected: Int, val actual: Int) : ChannelException(channelId, "htlc sig count mismatch: expected=$expected actual: $actual")
 data class ForcedLocalCommit                       (override val channelId: ByteVector32) : ChannelException(channelId, "forced local commit")