Add support for option_shutdown_anysegwit

Opt-in to allow any future segwit script in shutdown as long as it complies
with BIP 141 (see  lightning/bolts#672).

This is particularly useful to allow wallet users to close channels to a
Taproot address.

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

@@ -91,6 +91,12 @@ sealed class Feature {
         override val mandatory get() = 20
     }
 
+    @Serializable
+    object ShutdownAnySegwit : Feature() {
+        override val rfcName get() = "option_shutdown_anysegwit"
+        override val mandatory get() = 26
+    }
+
     @Serializable
     object ChannelType : Feature() {
         override val rfcName get() = "option_channel_type"
@@ -228,6 +234,7 @@ data class Features(val activated: Map<Feature, FeatureSupport>, val unknown: Se
             Feature.BasicMultiPartPayment,
             Feature.Wumbo,
             Feature.AnchorOutputs,
+            Feature.ShutdownAnySegwit,
             Feature.ChannelType,
             Feature.TrampolinePayment,
             Feature.ZeroReserveChannels,

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

@@ -1887,12 +1887,13 @@ data class Normal(
                         }
                     }
                     is CMD_CLOSE -> {
+                        val allowAnySegwit = Features.canUseFeature(commitments.localParams.features, commitments.remoteParams.features, Feature.ShutdownAnySegwit)
                         val localScriptPubkey = event.command.scriptPubKey ?: commitments.localParams.defaultFinalScriptPubKey
                         when {
                             this.localShutdown != null -> handleCommandError(event.command, ClosingAlreadyInProgress(channelId), channelUpdate)
                             this.commitments.localHasUnsignedOutgoingHtlcs() -> handleCommandError(event.command, CannotCloseWithUnsignedOutgoingHtlcs(channelId), channelUpdate)
                             this.commitments.localHasUnsignedOutgoingUpdateFee() -> handleCommandError(event.command, CannotCloseWithUnsignedOutgoingUpdateFee(channelId), channelUpdate)
-                            !Helpers.Closing.isValidFinalScriptPubkey(localScriptPubkey) -> handleCommandError(event.command, InvalidFinalScript(channelId), channelUpdate)
+                            !Helpers.Closing.isValidFinalScriptPubkey(localScriptPubkey, allowAnySegwit) -> handleCommandError(event.command, InvalidFinalScript(channelId), channelUpdate)
                             else -> {
                                 val shutdown = Shutdown(channelId, localScriptPubkey)
                                 val newState = this.copy(localShutdown = shutdown, closingFeerates = event.command.feerates)
@@ -1995,6 +1996,7 @@ data class Normal(
                         }
                     }
                     is Shutdown -> {
+                        val allowAnySegwit = Features.canUseFeature(commitments.localParams.features, commitments.remoteParams.features, Feature.ShutdownAnySegwit)
                         // they have pending unsigned htlcs         => they violated the spec, close the channel
                         // they don't have pending unsigned htlcs
                         //    we have pending unsigned htlcs
@@ -2010,7 +2012,7 @@ data class Normal(
                         //        there are pending signed changes  => go to SHUTDOWN
                         //        there are no changes              => go to NEGOTIATING
                         when {
-                            !Helpers.Closing.isValidFinalScriptPubkey(event.message.scriptPubKey) -> handleLocalError(event, InvalidFinalScript(channelId))
+                            !Helpers.Closing.isValidFinalScriptPubkey(event.message.scriptPubKey, allowAnySegwit) -> handleLocalError(event, InvalidFinalScript(channelId))
                             commitments.remoteHasUnsignedOutgoingHtlcs() -> handleLocalError(event, CannotCloseWithUnsignedOutgoingHtlcs(channelId))
                             commitments.remoteHasUnsignedOutgoingUpdateFee() -> handleLocalError(event, CannotCloseWithUnsignedOutgoingUpdateFee(channelId))
                             commitments.localHasUnsignedOutgoingHtlcs() -> {

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

@@ -384,14 +384,21 @@ object Helpers {
         // used only to compute tx weights and estimate fees
         private val dummyPublicKey by lazy { PrivateKey(ByteArray(32) { 1.toByte() }).publicKey() }
 
-        private fun isValidFinalScriptPubkey(scriptPubKey: ByteArray): Boolean {
+        private fun isValidFinalScriptPubkey(scriptPubKey: ByteArray, allowAnySegwit: Boolean): Boolean {
             return runTrying {
                 val script = Script.parse(scriptPubKey)
-                Script.isPay2pkh(script) || Script.isPay2sh(script) || Script.isPay2wpkh(script) || Script.isPay2wsh(script)
+                when {
+                    Script.isPay2pkh(script) -> true
+                    Script.isPay2sh(script) -> true
+                    Script.isPay2wpkh(script) -> true
+                    Script.isPay2wsh(script) -> true
+                    Script.isNativeWitnessScript(script) -> allowAnySegwit
+                    else -> false
+                }
             }.getOrElse { false }
         }
 
-        fun isValidFinalScriptPubkey(scriptPubKey: ByteVector): Boolean = isValidFinalScriptPubkey(scriptPubKey.toByteArray())
+        fun isValidFinalScriptPubkey(scriptPubKey: ByteVector, allowAnySegwit: Boolean): Boolean = isValidFinalScriptPubkey(scriptPubKey.toByteArray(), allowAnySegwit)
 
         // To be replaced with corresponding function in bitcoin-kmp
         fun btcAddressFromScriptPubKey(scriptPubKey: ByteVector, chainHash: ByteVector32): String? {
@@ -465,8 +472,9 @@ object Helpers {
             remoteScriptPubkey: ByteArray,
             closingFees: ClosingFees
         ): Pair<ClosingTx, ClosingSigned> {
-            require(isValidFinalScriptPubkey(localScriptPubkey)) { "invalid localScriptPubkey" }
-            require(isValidFinalScriptPubkey(remoteScriptPubkey)) { "invalid remoteScriptPubkey" }
+            val allowAnySegwit = Features.canUseFeature(commitments.localParams.features, commitments.remoteParams.features, Feature.ShutdownAnySegwit)
+            require(isValidFinalScriptPubkey(localScriptPubkey, allowAnySegwit)) { "invalid localScriptPubkey" }
+            require(isValidFinalScriptPubkey(remoteScriptPubkey, allowAnySegwit)) { "invalid remoteScriptPubkey" }
             val dustLimit = commitments.localParams.dustLimit.max(commitments.remoteParams.dustLimit)
             val closingTx = Transactions.makeClosingTx(commitments.commitInput, localScriptPubkey, remoteScriptPubkey, commitments.localParams.isFunder, dustLimit, closingFees.preferred, commitments.localCommit.spec)
             val localClosingSig = keyManager.sign(closingTx, commitments.localParams.channelKeys.fundingPrivateKey)

src/commonTest/kotlin/fr/acinq/lightning/FeaturesTestsCommon.kt

@@ -208,9 +208,10 @@ class FeaturesTestsCommon : LightningTestSuite() {
             byteArrayOf(0x09, 0x00, 0x42, 0x00) to Features(
                 mapOf(
                     VariableLengthOnion to FeatureSupport.Optional,
-                    PaymentSecret to FeatureSupport.Mandatory
+                    PaymentSecret to FeatureSupport.Mandatory,
+                    ShutdownAnySegwit to FeatureSupport.Optional
                 ),
-                setOf(UnknownFeature(24), UnknownFeature(27))
+                setOf(UnknownFeature(24))
             ),
             byteArrayOf(0x52, 0x00, 0x00, 0x00) to Features(
                 mapOf(),

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

@@ -1,11 +1,8 @@
 package fr.acinq.lightning.channel.states
 
 import fr.acinq.bitcoin.*
-import fr.acinq.lightning.CltvExpiry
-import fr.acinq.lightning.CltvExpiryDelta
-import fr.acinq.lightning.Feature
+import fr.acinq.lightning.*
 import fr.acinq.lightning.Lightning.randomBytes32
-import fr.acinq.lightning.ShortChannelId
 import fr.acinq.lightning.blockchain.*
 import fr.acinq.lightning.blockchain.fee.FeeratePerKw
 import fr.acinq.lightning.channel.*
@@ -1413,6 +1410,28 @@ class NormalTestsCommon : LightningTestSuite() {
         actions1.hasCommandError<InvalidFinalScript>()
     }
 
+    @Test
+    fun `recv CMD_CLOSE (with unsupported native segwit script)`() {
+        val (alice, _) = reachNormal()
+        assertNull(alice.localShutdown)
+        val (alice1, actions1) = alice.processEx(ChannelEvent.ExecuteCommand(CMD_CLOSE(ByteVector("51050102030405"), null)))
+        assertTrue(alice1 is Normal)
+        actions1.hasCommandError<InvalidFinalScript>()
+    }
+
+    @Test
+    fun `recv CMD_CLOSE (with native segwit script)`() {
+        val (alice, _) = reachNormal(
+            aliceFeatures = TestConstants.Alice.nodeParams.features.copy(TestConstants.Alice.nodeParams.features.activated + (Feature.ShutdownAnySegwit to FeatureSupport.Optional)),
+            bobFeatures = TestConstants.Bob.nodeParams.features.copy(TestConstants.Bob.nodeParams.features.activated + (Feature.ShutdownAnySegwit to FeatureSupport.Optional)),
+        )
+        assertNull(alice.localShutdown)
+        val (alice1, actions1) = alice.processEx(ChannelEvent.ExecuteCommand(CMD_CLOSE(ByteVector("51050102030405"), null)))
+        actions1.hasOutgoingMessage<Shutdown>()
+        assertTrue(alice1 is Normal)
+        assertNotNull(alice1.localShutdown)
+    }
+
     @Test
     fun `recv CMD_CLOSE (with signed sent htlcs)`() {
         val (alice, bob) = reachNormal()
@@ -1551,6 +1570,27 @@ class NormalTestsCommon : LightningTestSuite() {
         actions1.hasWatch<WatchConfirmed>()
     }
 
+    @Test
+    fun `recv Shutdown (with unsupported native segwit script)`() {
+        val (_, bob) = reachNormal()
+        val (bob1, actions1) = bob.processEx(ChannelEvent.MessageReceived(Shutdown(bob.channelId, ByteVector("51050102030405"))))
+        assertTrue(bob1 is Closing)
+        actions1.hasOutgoingMessage<Error>()
+        assertEquals(2, actions1.filterIsInstance<ChannelAction.Blockchain.PublishTx>().count())
+        actions1.hasWatch<WatchConfirmed>()
+    }
+
+    @Test
+    fun `recv Shutdown (with native segwit script)`() {
+        val (_, bob) = reachNormal(
+            aliceFeatures = TestConstants.Alice.nodeParams.features.copy(TestConstants.Alice.nodeParams.features.activated + (Feature.ShutdownAnySegwit to FeatureSupport.Optional)),
+            bobFeatures = TestConstants.Bob.nodeParams.features.copy(TestConstants.Bob.nodeParams.features.activated + (Feature.ShutdownAnySegwit to FeatureSupport.Optional)),
+        )
+        val (bob1, actions1) = bob.processEx(ChannelEvent.MessageReceived(Shutdown(bob.channelId, ByteVector("51050102030405"))))
+        assertTrue(bob1 is Negotiating)
+        actions1.hasOutgoingMessage<Shutdown>()
+    }
+
     @Test
     fun `recv Shutdown (with invalid final script and signed htlcs, in response to a Shutdown)`() {
         val (alice, bob) = reachNormal()