Implement Simple Taproot Channels (#805)

* Implement simple taproot channels

This matches changes done on Eclair, and adds support for taproot channels (including splices) with the same TLV extensions.

- All new channels will use the simple taproot format.
- Existing channels will be upgraded to the simple taproot format during the first splice operation.
- Support for signing commit tx with alternative feerates has been removed.
- Almost all existing tests now use the taproot channel type.

---------

Co-authored-by: Bastien Teinturier <[email protected]>

Author: sstone

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

@@ -217,6 +217,13 @@ sealed class Feature {
         override val scopes: Set<FeatureScope> get() = setOf(FeatureScope.Init, FeatureScope.Node)
     }
 
+    // README: this is not the feature bit specified in the BOLT, this one is specific to Phoenix
+    @Serializable
+    object SimpleTaprootChannels : Feature() {
+        override val rfcName get() = "simple_taproot_channels"
+        override val mandatory get() = 564
+        override val scopes: Set<FeatureScope> get() = setOf(FeatureScope.Init, FeatureScope.Node)
+    }
 }
 
 @Serializable
@@ -294,7 +301,8 @@ data class Features(val activated: Map<Feature, FeatureSupport>, val unknown: Se
             Feature.WakeUpNotificationProvider,
             Feature.ExperimentalSplice,
             Feature.OnTheFlyFunding,
-            Feature.FundingFeeCredit
+            Feature.FundingFeeCredit,
+            Feature.SimpleTaprootChannels
         )
 
         operator fun invoke(bytes: ByteVector): Features = invoke(bytes.toByteArray())

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

@@ -200,6 +200,7 @@ data class NodeParams(
             Feature.Wumbo to FeatureSupport.Optional,
             Feature.StaticRemoteKey to FeatureSupport.Mandatory,
             Feature.AnchorOutputs to FeatureSupport.Optional, // can't set Mandatory because peers prefers AnchorOutputsZeroFeeHtlcTx
+            Feature.SimpleTaprootChannels to FeatureSupport.Optional,
             Feature.RouteBlinding to FeatureSupport.Optional,
             Feature.DualFunding to FeatureSupport.Mandatory,
             Feature.ShutdownAnySegwit to FeatureSupport.Mandatory,

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

@@ -92,4 +92,9 @@ data class PleasePublishYourCommitment             (override val channelId: Byte
 data class CommandUnavailableInThisState           (override val channelId: ByteVector32, val state: String) : ChannelException(channelId, "cannot execute command in state=$state")
 data class ForbiddenDuringSplice                   (override val channelId: ByteVector32, val command: String?) : ChannelException(channelId, "cannot process $command while splicing")
 data class InvalidSpliceRequest                    (override val channelId: ByteVector32) : ChannelException(channelId, "invalid splice request")
+data class MissingCommitNonce                      (override val channelId: ByteVector32, val fundingTxId: TxId, val commitmentNumber: Long) : ChannelException(channelId, "missing commit nonce for funding tx $fundingTxId commitmentNumber $commitmentNumber")
+data class InvalidCommitNonce                      (override val channelId: ByteVector32, val fundingTxId: TxId, val commitmentNumber: Long) : ChannelException(channelId, "invalid commit nonce for funding tx $fundingTxId commitmentNumber $commitmentNumber")
+data class MissingFundingNonce                     (override val channelId: ByteVector32, val fundingTxId: TxId) : ChannelException(channelId, "missing funding nonce for funding tx $fundingTxId")
+data class InvalidFundingNonce                     (override val channelId: ByteVector32, val fundingTxId: TxId) : ChannelException(channelId, "invalid funding nonce for funding tx $fundingTxId")
+data class MissingClosingNonce                     (override val channelId: ByteVector32) : ChannelException(channelId, "missing closing nonce")
 // @formatter:on

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

@@ -32,7 +32,7 @@ data class ChannelFeatures(val features: Set<Feature>) {
          * In addition to channel types features, the following features will be added to the permanent channel features if they
          * are supported by both peers.
          */
-        private val permanentChannelFeatures = setOf(Feature.DualFunding)
+        private val permanentChannelFeatures: Set<Feature> = setOf(Feature.DualFunding)
     }
 
 }
@@ -65,6 +65,12 @@ sealed class ChannelType {
             override val commitmentFormat: Transactions.CommitmentFormat get() = Transactions.CommitmentFormat.AnchorOutputs
         }
 
+        object SimpleTaprootChannels : SupportedChannelType() {
+            override val name: String get() = "simple_taproot_channel"
+            override val features: Set<Feature> get() = setOf(Feature.SimpleTaprootChannels, Feature.ZeroReserveChannels)
+            override val permanentChannelFeatures: Set<Feature> get() = setOf(Feature.ZeroReserveChannels)
+            override val commitmentFormat: Transactions.CommitmentFormat get() = Transactions.CommitmentFormat.SimpleTaprootChannels
+        }
     }
 
     data class UnsupportedChannelType(val featureBits: Features) : ChannelType() {
@@ -79,6 +85,7 @@ sealed class ChannelType {
         // NB: Bolt 2: features must exactly match in order to identify a channel type.
         fun fromFeatures(features: Features): ChannelType = when (features) {
             // @formatter:off
+            Features(Feature.SimpleTaprootChannels to FeatureSupport.Mandatory, Feature.ZeroReserveChannels to FeatureSupport.Mandatory) -> SupportedChannelType.SimpleTaprootChannels
             Features(Feature.StaticRemoteKey to FeatureSupport.Mandatory, Feature.AnchorOutputs to FeatureSupport.Mandatory, Feature.ZeroReserveChannels to FeatureSupport.Mandatory) -> SupportedChannelType.AnchorOutputsZeroReserve
             Features(Feature.StaticRemoteKey to FeatureSupport.Mandatory, Feature.AnchorOutputs to FeatureSupport.Mandatory) -> SupportedChannelType.AnchorOutputs
             else -> UnsupportedChannelType(features)