Add API methods to spend funds sent to taproot channel addresses (#3220)

diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/Eclair.scala b/eclair-core/src/main/scala/fr/acinq/eclair/Eclair.scala
index 1c7ec9a..ceb96c1 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/Eclair.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/Eclair.scala
@@ -23,6 +23,7 @@ import akka.actor.{ActorRef, typed}
 import akka.pattern._
 import akka.util.Timeout
 import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
+import fr.acinq.bitcoin.scalacompat.Musig2.IndividualNonce
 import fr.acinq.bitcoin.scalacompat.{BlockHash, ByteVector32, ByteVector64, Crypto, DeterministicWallet, OutPoint, Satoshi, Script, Transaction, TxId, addressToPublicKeyScript}
 import fr.acinq.eclair.ApiTypes.ChannelNotFound
 import fr.acinq.eclair.balance.CheckBalance.GlobalBalance
@@ -32,6 +33,7 @@ import fr.acinq.eclair.blockchain.bitcoind.ZmqWatcher.WatchFundingSpentTriggered
 import fr.acinq.eclair.blockchain.bitcoind.rpc.BitcoinCoreClient
 import fr.acinq.eclair.blockchain.bitcoind.rpc.BitcoinCoreClient.{AddressType, Descriptors, WalletTx}
 import fr.acinq.eclair.blockchain.fee.{ConfirmationTarget, FeeratePerByte, FeeratePerKw}
+import fr.acinq.eclair.channel.ChannelSpendSignature.PartialSignatureWithNonce
 import fr.acinq.eclair.channel._
 import fr.acinq.eclair.crypto.Sphinx
 import fr.acinq.eclair.db.AuditDb.{NetworkFee, Stats}
@@ -69,7 +71,7 @@ case class VerifiedMessage(valid: Boolean, publicKey: PublicKey)
 case class SendOnionMessageResponsePayload(tlvs: TlvStream[OnionMessagePayloadTlv])
 case class SendOnionMessageResponse(sent: Boolean, failureMessage: Option[String], response: Option[SendOnionMessageResponsePayload])
 
-case class SpendFromChannelPrep(fundingTxIndex: Long, localFundingPubkey: PublicKey, inputAmount: Satoshi, unsignedTx: Transaction)
+case class SpendFromChannelPrep(fundingTxIndex: Long, localFundingPubkey: PublicKey, localNonce_opt: Option[IndividualNonce], inputAmount: Satoshi, unsignedTx: Transaction)
 case class SpendFromChannelResult(signedTx: Transaction)
 // @formatter:on
 
@@ -212,7 +214,7 @@ trait Eclair {
 
   def spendFromChannelAddressPrep(outPoint: OutPoint, fundingKeyPath: DeterministicWallet.KeyPath, fundingTxIndex: Long, address: String, feerate: FeeratePerKw): Future[SpendFromChannelPrep]
 
-  def spendFromChannelAddress(fundingKeyPath: DeterministicWallet.KeyPath, fundingTxIndex: Long, remoteFundingPubkey: PublicKey, remoteSig: ByteVector64, unsignedTx: Transaction): Future[SpendFromChannelResult]
+  def spendFromChannelAddress(fundingKeyPath: DeterministicWallet.KeyPath, fundingTxIndex: Long, remoteFundingPubkey: PublicKey, localNonce_opt: Option[IndividualNonce], remoteSig: ChannelSpendSignature, unsignedTx: Transaction): Future[SpendFromChannelResult]
 }
 
 class EclairImpl(val appKit: Kit) extends Eclair with Logging with SpendFromChannelAddress {
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/SpendFromChannelAddress.scala b/eclair-core/src/main/scala/fr/acinq/eclair/SpendFromChannelAddress.scala
index 5196498..8d7cff2 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/SpendFromChannelAddress.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/SpendFromChannelAddress.scala
@@ -1,7 +1,8 @@
 package fr.acinq.eclair
 
 import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
-import fr.acinq.bitcoin.scalacompat.{ByteVector64, DeterministicWallet, OutPoint, Satoshi, SatoshiLong, Script, ScriptWitness, Transaction, TxIn, TxOut, addressToPublicKeyScript}
+import fr.acinq.bitcoin.scalacompat.Musig2.{IndividualNonce, LocalNonce}
+import fr.acinq.bitcoin.scalacompat.{DeterministicWallet, Musig2, OutPoint, Satoshi, SatoshiLong, Script, ScriptWitness, Transaction, TxIn, TxOut, addressToPublicKeyScript}
 import fr.acinq.eclair.blockchain.fee.FeeratePerKw
 import fr.acinq.eclair.channel.{ChannelConfig, ChannelSpendSignature}
 import fr.acinq.eclair.transactions.Transactions._
@@ -9,11 +10,15 @@ import fr.acinq.eclair.transactions.{Scripts, Transactions}
 import scodec.bits.ByteVector
 
 import scala.concurrent.Future
+import scala.jdk.CollectionConverters.ConcurrentMapHasAsScala
 
 trait SpendFromChannelAddress {
 
   this: EclairImpl =>
 
+  import java.util.concurrent.ConcurrentHashMap
+  private val nonces = new ConcurrentHashMap[IndividualNonce, LocalNonce]().asScala
+
   private def buildTx(outPoint: OutPoint, outputAmount: Satoshi, pubKeyScript: ByteVector, witness: ScriptWitness) = Transaction(2,
     txIn = Seq(TxIn(outPoint, ByteVector.empty, 0, witness)),
     txOut = Seq(TxOut(outputAmount, pubKeyScript)),
@@ -26,27 +31,41 @@ trait SpendFromChannelAddress {
       Right(pubKeyScript) = addressToPublicKeyScript(appKit.nodeParams.chainHash, address).map(Script.write)
       channelKeys = appKit.nodeParams.channelKeyManager.channelKeys(ChannelConfig.standard, fundingKeyPath)
       localFundingPubkey = channelKeys.fundingKey(fundingTxIndex).publicKey
+      isTaproot = Script.isPay2tr(Script.parse(pubKeyScript))
+      (localNonce_opt, dummyWitness) = if (isTaproot) {
+        val serverNonce = Musig2.generateNonce(randomBytes32(), Right(localFundingPubkey), Seq(localFundingPubkey), None, None)
+        nonces.put(serverNonce.publicNonce, serverNonce)
+        Some(serverNonce.publicNonce) -> Script.witnessKeyPathPay2tr(PlaceHolderSig)
+      } else {
+        None -> Scripts.witness2of2(PlaceHolderSig, PlaceHolderSig, localFundingPubkey, localFundingPubkey)
+      }
       // build the tx a first time with a zero amount to compute the weight
-      dummyWitness = Scripts.witness2of2(PlaceHolderSig, PlaceHolderSig, localFundingPubkey, localFundingPubkey)
       fee = Transactions.weight2fee(feerate, buildTx(outPoint, 0.sat, pubKeyScript, dummyWitness).weight())
       _ = assert(inputAmount - fee > Scripts.dustLimit(pubKeyScript), s"amount insufficient (fee=$fee)")
       unsignedTx = buildTx(outPoint, inputAmount - fee, pubKeyScript, dummyWitness)
-    } yield SpendFromChannelPrep(fundingTxIndex, localFundingPubkey, inputAmount, unsignedTx)
+    } yield SpendFromChannelPrep(fundingTxIndex, localFundingPubkey, localNonce_opt, inputAmount, unsignedTx)
   }
 
-  override def spendFromChannelAddress(fundingKeyPath: DeterministicWallet.KeyPath, fundingTxIndex: Long, remoteFundingPubkey: PublicKey, remoteSig: ByteVector64, unsignedTx: Transaction): Future[SpendFromChannelResult] = {
+  override def spendFromChannelAddress(fundingKeyPath: DeterministicWallet.KeyPath, fundingTxIndex: Long, remoteFundingPubkey: PublicKey, localNonce_opt: Option[IndividualNonce], remoteSig: ChannelSpendSignature, unsignedTx: Transaction): Future[SpendFromChannelResult] = {
     for {
       _ <- Future.successful(())
       outPoint = unsignedTx.txIn.head.outPoint
       inputTx <- appKit.wallet.getTransaction(outPoint.txid)
-      channelKeys = appKit.nodeParams.channelKeyManager.channelKeys(ChannelConfig.standard, fundingKeyPath)
-      localFundingKey = channelKeys.fundingKey(fundingTxIndex)
       inputInfo = InputInfo(outPoint, inputTx.txOut(outPoint.index.toInt))
       // classify as splice, doesn't really matter
       tx = Transactions.SpliceTx(inputInfo, unsignedTx)
-      localSig = tx.sign(localFundingKey, remoteFundingPubkey, extraUtxos = Map.empty)
-      signedTx = tx.aggregateSigs(localFundingKey.publicKey, remoteFundingPubkey, localSig, ChannelSpendSignature.IndividualSignature(remoteSig))
+      channelKeys = appKit.nodeParams.channelKeyManager.channelKeys(ChannelConfig.standard, fundingKeyPath)
+      localFundingKey = channelKeys.fundingKey(fundingTxIndex)
+      signedTx = remoteSig match {
+        case individualRemoteSig: ChannelSpendSignature.IndividualSignature =>
+          val localSig = tx.sign(localFundingKey, remoteFundingPubkey, extraUtxos = Map.empty)
+          tx.aggregateSigs(localFundingKey.publicKey, remoteFundingPubkey, localSig, individualRemoteSig)
+        case remotePartialSig: ChannelSpendSignature.PartialSignatureWithNonce =>
+          val localPrivateNonce = nonces(localNonce_opt.get)
+          val Right(localSig) = tx.partialSign(localFundingKey, remoteFundingPubkey, extraUtxos = Map.empty, localNonce = localPrivateNonce, publicNonces = Seq(localPrivateNonce.publicNonce, remotePartialSig.nonce))
+          val Right(signedTx) = tx.aggregateSigs(localFundingKey.publicKey, remoteFundingPubkey, localSig, remotePartialSig, extraUtxos = Map.empty)
+          signedTx
+      }
     } yield SpendFromChannelResult(signedTx)
   }
-
 }
diff --git a/eclair-node/src/main/scala/fr/acinq/eclair/api/handlers/Control.scala b/eclair-node/src/main/scala/fr/acinq/eclair/api/handlers/Control.scala
index f5892a7..a4806d5 100644
--- a/eclair-node/src/main/scala/fr/acinq/eclair/api/handlers/Control.scala
+++ b/eclair-node/src/main/scala/fr/acinq/eclair/api/handlers/Control.scala
@@ -19,11 +19,14 @@ package fr.acinq.eclair.api.handlers
 import akka.http.scaladsl.server.Route
 import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
 import fr.acinq.bitcoin.scalacompat.DeterministicWallet.KeyPath
+import fr.acinq.bitcoin.scalacompat.Musig2.IndividualNonce
 import fr.acinq.bitcoin.scalacompat.{ByteVector32, ByteVector64, OutPoint, Transaction, TxId}
 import fr.acinq.eclair.api.Service
 import fr.acinq.eclair.api.directives.EclairDirectives
 import fr.acinq.eclair.api.serde.FormParamExtractors._
-import fr.acinq.eclair.blockchain.fee.{FeeratePerByte, FeeratePerKw}
+import fr.acinq.eclair.blockchain.fee.FeeratePerByte
+import fr.acinq.eclair.channel.ChannelSpendSignature
+import fr.acinq.eclair.channel.ChannelSpendSignature.PartialSignatureWithNonce
 
 trait Control {
   this: Service with EclairDirectives =>
@@ -64,10 +67,17 @@ trait Control {
   val spendFromChannelAddress: Route = postRequest("spendfromchanneladdress") { implicit t =>
     formFields("kp", "fi".as[Int], "p".as[PublicKey], "s".as[ByteVector64], "tx") {
       (keyPath, fundingTxIndex, remoteFundingPubkey, remoteSig, unsignedTx) =>
-        complete(eclairApi.spendFromChannelAddress(KeyPath(keyPath), fundingTxIndex, remoteFundingPubkey, remoteSig, Transaction.read(unsignedTx)))
+        complete(eclairApi.spendFromChannelAddress(KeyPath(keyPath), fundingTxIndex, remoteFundingPubkey, localNonce_opt = None, ChannelSpendSignature.IndividualSignature(remoteSig), Transaction.read(unsignedTx)))
     }
   }
 
-  val controlRoutes: Route = enableFromFutureHtlc ~ resetBalance ~ forceCloseResetFundingIndex ~ manualWatchFundingSpent ~ spendFromChannelAddressPrep ~ spendFromChannelAddress
+  val spendFromTaprootChannelAddress: Route = postRequest("spendfromtaprootchanneladdress") { implicit t =>
+    formFields("kp", "fi".as[Int], "p".as[PublicKey], "localNonce".as[IndividualNonce], "remoteNonce".as[IndividualNonce], "remoteSig".as[ByteVector32], "tx".as[String]) {
+      (keyPath, fundingTxIndex, remoteFundingPubkey, localNonce, remoteNonce, remoteSig, unsignedTx) =>
+        complete(eclairApi.spendFromChannelAddress(KeyPath(keyPath), fundingTxIndex, remoteFundingPubkey, localNonce_opt = Some(localNonce), PartialSignatureWithNonce(remoteSig, remoteNonce), Transaction.read(unsignedTx)))
+    }
+  }
+
+  val controlRoutes: Route = enableFromFutureHtlc ~ resetBalance ~ forceCloseResetFundingIndex ~ manualWatchFundingSpent ~ spendFromChannelAddressPrep ~ spendFromChannelAddress ~ spendFromTaprootChannelAddress
 
 }
diff --git a/eclair-node/src/main/scala/fr/acinq/eclair/api/serde/FormParamExtractors.scala b/eclair-node/src/main/scala/fr/acinq/eclair/api/serde/FormParamExtractors.scala
index 688ead9..df97be0 100644
--- a/eclair-node/src/main/scala/fr/acinq/eclair/api/serde/FormParamExtractors.scala
+++ b/eclair-node/src/main/scala/fr/acinq/eclair/api/serde/FormParamExtractors.scala
@@ -19,6 +19,7 @@ package fr.acinq.eclair.api.serde
 import akka.http.scaladsl.unmarshalling.Unmarshaller
 import akka.util.Timeout
 import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
+import fr.acinq.bitcoin.scalacompat.Musig2.IndividualNonce
 import fr.acinq.bitcoin.scalacompat.{ByteVector32, ByteVector64, OutPoint, Satoshi, TxId}
 import fr.acinq.eclair.api.directives.RouteFormat
 import fr.acinq.eclair.api.serde.JsonSupport._
@@ -39,6 +40,8 @@ object FormParamExtractors {
 
   implicit val publicKeyUnmarshaller: Unmarshaller[String, PublicKey] = Unmarshaller.strict { rawPubKey => PublicKey(ByteVector.fromValidHex(rawPubKey)) }
 
+  implicit val individualNonceUnmarshaller: Unmarshaller[String, IndividualNonce] = Unmarshaller.strict { str => IndividualNonce(ByteVector.fromValidHex(str)) }
+
   implicit val bytesUnmarshaller: Unmarshaller[String, ByteVector] = Unmarshaller.strict { str => ByteVector.fromValidHex(str) }
 
   implicit val bytes32Unmarshaller: Unmarshaller[String, ByteVector32] = Unmarshaller.strict { bin => ByteVector32.fromValidHex(bin) }