Add commitment format to interactive-tx shared input

And remove the unused sealed trait, the commitment format contains the
information we need so we don't need multiple child classes. We still
use a `discriminated` at the codec level though to allow changing the
format in the future if needed.

Author: t-bast

eclair-core/src/main/scala/fr/acinq/eclair/channel/fsm/Channel.scala

@@ -1111,7 +1111,7 @@ class Channel(val nodeParams: NodeParams, val channelKeys: ChannelKeys, val wall
                   isInitiator = false,
                   localContribution = spliceAck.fundingContribution,
                   remoteContribution = msg.fundingContribution,
-                  sharedInput_opt = Some(Multisig2of2Input(channelKeys, parentCommitment)),
+                  sharedInput_opt = Some(SharedFundingInput(channelKeys, parentCommitment)),
                   remoteFundingPubKey = msg.fundingPubKey,
                   localOutputs = Nil,
                   commitmentFormat = commitmentFormat,
@@ -1159,7 +1159,7 @@ class Channel(val nodeParams: NodeParams, val channelKeys: ChannelKeys, val wall
             isInitiator = true,
             localContribution = spliceInit.fundingContribution,
             remoteContribution = msg.fundingContribution,
-            sharedInput_opt = Some(Multisig2of2Input(channelKeys, parentCommitment)),
+            sharedInput_opt = Some(SharedFundingInput(channelKeys, parentCommitment)),
             remoteFundingPubKey = msg.fundingPubKey,
             localOutputs = cmd.spliceOutputs,
             commitmentFormat = commitmentFormat,
@@ -1238,7 +1238,7 @@ class Channel(val nodeParams: NodeParams, val channelKeys: ChannelKeys, val wall
                     isInitiator = false,
                     localContribution = fundingContribution,
                     remoteContribution = msg.fundingContribution,
-                    sharedInput_opt = Some(Multisig2of2Input(channelKeys, rbf.parentCommitment)),
+                    sharedInput_opt = Some(SharedFundingInput(channelKeys, rbf.parentCommitment)),
                     remoteFundingPubKey = rbf.latestFundingTx.fundingParams.remoteFundingPubKey,
                     localOutputs = rbf.latestFundingTx.fundingParams.localOutputs,
                     commitmentFormat = rbf.latestFundingTx.fundingParams.commitmentFormat,
@@ -1295,7 +1295,7 @@ class Channel(val nodeParams: NodeParams, val channelKeys: ChannelKeys, val wall
                     isInitiator = true,
                     localContribution = txInitRbf.fundingContribution,
                     remoteContribution = msg.fundingContribution,
-                    sharedInput_opt = Some(Multisig2of2Input(channelKeys, rbf.parentCommitment)),
+                    sharedInput_opt = Some(SharedFundingInput(channelKeys, rbf.parentCommitment)),
                     remoteFundingPubKey = rbf.latestFundingTx.fundingParams.remoteFundingPubKey,
                     localOutputs = rbf.latestFundingTx.fundingParams.localOutputs,
                     commitmentFormat = rbf.latestFundingTx.fundingParams.commitmentFormat,
@@ -3368,7 +3368,7 @@ class Channel(val nodeParams: NodeParams, val channelKeys: ChannelKeys, val wall
     val targetFeerate = nodeParams.onChainFeeConf.getFundingFeerate(nodeParams.currentFeeratesForFundingClosing)
     val fundingContribution = InteractiveTxFunder.computeSpliceContribution(
       isInitiator = true,
-      sharedInput = Multisig2of2Input(channelKeys, parentCommitment),
+      sharedInput = SharedFundingInput(channelKeys, parentCommitment),
       spliceInAmount = cmd.additionalLocalFunding,
       spliceOut = cmd.spliceOutputs,
       targetFeerate = targetFeerate)

eclair-core/src/main/scala/fr/acinq/eclair/channel/fund/InteractiveTxBuilder.scala

@@ -101,27 +101,21 @@ object InteractiveTxBuilder {
   case class RequireConfirmedInputs(forLocal: Boolean, forRemote: Boolean)
 
   /** An input that is already shared between participants (e.g. the current funding output when doing a splice). */
-  sealed trait SharedFundingInput {
-    // @formatter:off
-    def info: InputInfo
-    def weight: Int
-    // @formatter:on
-  }
-
-  case class Multisig2of2Input(info: InputInfo, fundingTxIndex: Long, remoteFundingPubkey: PublicKey) extends SharedFundingInput {
-    override val weight: Int = 388
+  case class SharedFundingInput(info: InputInfo, fundingTxIndex: Long, remoteFundingPubkey: PublicKey, commitmentFormat: CommitmentFormat) {
+    val weight: Int = commitmentFormat.fundingInputWeight
 
     def sign(channelKeys: ChannelKeys, tx: Transaction, spentUtxos: Map[OutPoint, TxOut]): ChannelSpendSignature.IndividualSignature = {
       val localFundingKey = channelKeys.fundingKey(fundingTxIndex)
       Transactions.SpliceTx(info, tx).sign(localFundingKey, remoteFundingPubkey, spentUtxos)
     }
   }
 
-  object Multisig2of2Input {
-    def apply(channelKeys: ChannelKeys, commitment: Commitment): Multisig2of2Input = Multisig2of2Input(
+  object SharedFundingInput {
+    def apply(channelKeys: ChannelKeys, commitment: Commitment): SharedFundingInput = SharedFundingInput(
       info = commitment.commitInput(channelKeys),
       fundingTxIndex = commitment.fundingTxIndex,
-      remoteFundingPubkey = commitment.remoteFundingPubKey
+      remoteFundingPubkey = commitment.remoteFundingPubKey,
+      commitmentFormat = commitment.commitmentFormat,
     )
   }
 
@@ -928,9 +922,10 @@ private class InteractiveTxBuilder(replyTo: ActorRef[InteractiveTxBuilder.Respon
     import fr.acinq.bitcoin.scalacompat.KotlinUtils._
 
     val tx = unsignedTx.buildUnsignedTx()
-    val sharedSig_opt = fundingParams.sharedInput_opt.collect {
-      case i: Multisig2of2Input => i.sign(channelKeys, tx, unsignedTx.inputDetails).sig
-    }
+    val sharedSig_opt = fundingParams.sharedInput_opt.map(i => i.commitmentFormat match {
+      case _: SegwitV0CommitmentFormat => i.sign(channelKeys, tx, unsignedTx.inputDetails).sig
+      case _: SimpleTaprootChannelCommitmentFormat => ???
+    })
     if (unsignedTx.localInputs.isEmpty) {
       context.self ! SignTransactionResult(PartiallySignedSharedTransaction(unsignedTx, TxSignatures(fundingParams.channelId, tx, Nil, sharedSig_opt)))
     } else {
@@ -1054,18 +1049,19 @@ object InteractiveTxSigningSession {
       log.info("invalid tx_signatures: witness count mismatch (expected={}, got={})", partiallySignedTx.tx.remoteInputs.length, remoteSigs.witnesses.length)
       return Left(InvalidFundingSignature(fundingParams.channelId, Some(partiallySignedTx.txId)))
     }
-    val sharedSigs_opt = fundingParams.sharedInput_opt match {
-      case Some(sharedInput: Multisig2of2Input) =>
-        (partiallySignedTx.localSigs.previousFundingTxSig_opt, remoteSigs.previousFundingTxSig_opt) match {
+    val sharedSigs_opt = fundingParams.sharedInput_opt.map(sharedInput => {
+      sharedInput.commitmentFormat match {
+        case _: SegwitV0CommitmentFormat => (partiallySignedTx.localSigs.previousFundingTxSig_opt, remoteSigs.previousFundingTxSig_opt) match {
           case (Some(localSig), Some(remoteSig)) =>
             val localFundingPubkey = channelKeys.fundingKey(sharedInput.fundingTxIndex).publicKey
-            Some(Scripts.witness2of2(localSig, remoteSig, localFundingPubkey, sharedInput.remoteFundingPubkey))
+            Scripts.witness2of2(localSig, remoteSig, localFundingPubkey, sharedInput.remoteFundingPubkey)
           case _ =>
             log.info("invalid tx_signatures: missing shared input signatures")
             return Left(InvalidFundingSignature(fundingParams.channelId, Some(partiallySignedTx.txId)))
         }
-      case None => None
-    }
+        case _: SimpleTaprootChannelCommitmentFormat => ???
+      }
+    })
     val txWithSigs = FullySignedSharedTransaction(partiallySignedTx.tx, partiallySignedTx.localSigs, remoteSigs, sharedSigs_opt)
     if (remoteSigs.txId != txWithSigs.signedTx.txid) {
       log.info("invalid tx_signatures: txId mismatch (expected={}, got={})", txWithSigs.signedTx.txid, remoteSigs.txId)

eclair-core/src/main/scala/fr/acinq/eclair/transactions/Transactions.scala

@@ -58,6 +58,8 @@ object Transactions {
 
   sealed trait CommitmentFormat {
     // @formatter:off
+    /** Weight of a fully signed channel output, when spent by a [[ChannelSpendTransaction]]. */
+    def fundingInputWeight: Int
     /** Weight of a fully signed [[CommitTx]] transaction without any HTLCs. */
     def commitWeight: Int
     /** Weight of a fully signed [[ClaimLocalAnchorTx]] or [[ClaimRemoteAnchorTx]] input. */
@@ -93,7 +95,9 @@ object Transactions {
     // @formatter:on
   }
 
-  sealed trait SegwitV0CommitmentFormat extends CommitmentFormat
+  sealed trait SegwitV0CommitmentFormat extends CommitmentFormat {
+    override val fundingInputWeight = 384
+  }
 
   /**
    * Commitment format as defined in the v1.0 specification (https://github.com/lightningnetwork/lightning-rfc/tree/v1.0).
@@ -168,6 +172,7 @@ object Transactions {
   sealed trait SimpleTaprootChannelCommitmentFormat extends TaprootCommitmentFormat {
     // weights for taproot transactions are deterministic since signatures are encoded as 64 bytes and
     // not in variable length DER format (around 72 bytes)
+    override val fundingInputWeight = 230
     override val commitWeight = 960
     override val anchorInputWeight = 230
     override val htlcOutputWeight = 172

eclair-core/src/main/scala/fr/acinq/eclair/wire/internal/channel/version4/ChannelCodecs4.scala

@@ -277,12 +277,12 @@ private[channel] object ChannelCodecs4 {
 
     val spentMapCodec: Codec[Map[OutPoint, Transaction]] = mapCodec(outPointCodec, txCodec)
 
-    private val multisig2of2InputCodec: Codec[InteractiveTxBuilder.Multisig2of2Input] = (
+    private val multisig2of2InputCodec: Codec[ChannelTypes4.Multisig2of2Input] = (
       ("info" | inputInfoCodec) ::
         ("fundingTxIndex" | uint32) ::
-        ("remoteFundingPubkey" | publicKey)).as[InteractiveTxBuilder.Multisig2of2Input]
+        ("remoteFundingPubkey" | publicKey)).as[ChannelTypes4.Multisig2of2Input]
 
-    private val sharedFundingInputCodec: Codec[InteractiveTxBuilder.SharedFundingInput] = discriminated[InteractiveTxBuilder.SharedFundingInput].by(uint16)
+    private val sharedFundingInputCodec: Codec[ChannelTypes4.Multisig2of2Input] = discriminated[ChannelTypes4.Multisig2of2Input].by(uint16)
       .typecase(0x01, multisig2of2InputCodec)
 
     private val requireConfirmedInputsCodec: Codec[InteractiveTxBuilder.RequireConfirmedInputs] = (("forLocal" | bool8) :: ("forRemote" | bool8)).as[InteractiveTxBuilder.RequireConfirmedInputs]

eclair-core/src/main/scala/fr/acinq/eclair/wire/internal/channel/version4/ChannelTypes4.scala

@@ -72,12 +72,16 @@ private[channel] object ChannelTypes4 {
     def remoteCommitParams(): channel.CommitParams = channel.CommitParams(remoteParams.dustLimit, remoteParams.htlcMinimum, remoteParams.maxHtlcValueInFlightMsat, remoteParams.maxAcceptedHtlcs, localParams.toSelfDelay)
   }
 
+  case class Multisig2of2Input(info: InputInfo, fundingTxIndex: Long, remoteFundingPubkey: PublicKey) {
+    def migrate(commitmentFormat: CommitmentFormat): InteractiveTxBuilder.SharedFundingInput = InteractiveTxBuilder.SharedFundingInput(info, fundingTxIndex, remoteFundingPubkey, commitmentFormat)
+  }
+
   // We added the commitment format when moving to channel codecs v5.
   case class InteractiveTxParams(channelId: ByteVector32,
                                  isInitiator: Boolean,
                                  localContribution: Satoshi,
                                  remoteContribution: Satoshi,
-                                 sharedInput_opt: Option[InteractiveTxBuilder.SharedFundingInput],
+                                 sharedInput_opt: Option[Multisig2of2Input],
                                  remoteFundingPubKey: PublicKey,
                                  localOutputs: List[TxOut],
                                  lockTime: Long,
@@ -89,7 +93,7 @@ private[channel] object ChannelTypes4 {
       isInitiator = isInitiator,
       localContribution = localContribution,
       remoteContribution = remoteContribution,
-      sharedInput_opt = sharedInput_opt,
+      sharedInput_opt = sharedInput_opt.map(_.migrate(commitmentFormat)),
       remoteFundingPubKey = remoteFundingPubKey,
       localOutputs = localOutputs,
       commitmentFormat = commitmentFormat,

eclair-core/src/main/scala/fr/acinq/eclair/wire/internal/channel/version5/ChannelCodecs5.scala

@@ -119,13 +119,14 @@ private[channel] object ChannelCodecs5 {
         ("maxAcceptedHtlcs" | uint16) ::
         ("toSelfDelay" | cltvExpiryDelta)).as[CommitParams]
 
-    private val multisig2of2InputCodec: Codec[InteractiveTxBuilder.Multisig2of2Input] = (
+    private val interactiveTxSharedFundingInputCodec: Codec[InteractiveTxBuilder.SharedFundingInput] = (
       ("info" | inputInfoCodec) ::
         ("fundingTxIndex" | uint32) ::
-        ("remoteFundingPubkey" | publicKey)).as[InteractiveTxBuilder.Multisig2of2Input]
+        ("remoteFundingPubkey" | publicKey) ::
+        ("commitmentFormat" | commitmentFormatCodec)).as[InteractiveTxBuilder.SharedFundingInput]
 
     private val sharedFundingInputCodec: Codec[InteractiveTxBuilder.SharedFundingInput] = discriminated[InteractiveTxBuilder.SharedFundingInput].by(uint16)
-      .typecase(0x01, multisig2of2InputCodec)
+      .typecase(0x01, interactiveTxSharedFundingInputCodec)
 
     private val requireConfirmedInputsCodec: Codec[InteractiveTxBuilder.RequireConfirmedInputs] = (("forLocal" | bool8) :: ("forRemote" | bool8)).as[InteractiveTxBuilder.RequireConfirmedInputs]
 

eclair-core/src/test/scala/fr/acinq/eclair/channel/InteractiveTxBuilderSpec.scala

@@ -105,18 +105,18 @@ class InteractiveTxBuilderSpec extends TestKitBaseClass with AnyFunSuiteLike wit
     val fundingPubkeyScript: ByteVector = Script.write(Script.pay2wsh(Scripts.multiSig2of2(fundingParamsB.remoteFundingPubKey, fundingParamsA.remoteFundingPubKey)))
 
     def sharedInputs(commitmentA: Commitment, commitmentB: Commitment): (SharedFundingInput, SharedFundingInput) = {
-      val sharedInputA = Multisig2of2Input(channelKeysA, commitmentA)
-      val sharedInputB = Multisig2of2Input(channelKeysB, commitmentB)
+      val sharedInputA = SharedFundingInput(channelKeysA, commitmentA)
+      val sharedInputB = SharedFundingInput(channelKeysB, commitmentB)
       (sharedInputA, sharedInputB)
     }
 
     def dummySharedInputB(amount: Satoshi): SharedFundingInput = {
       val inputInfo = InputInfo(OutPoint(randomTxId(), 3), TxOut(amount, fundingPubkeyScript))
       val fundingTxIndex = fundingParamsA.sharedInput_opt match {
-        case Some(input: Multisig2of2Input) => input.fundingTxIndex + 1
+        case Some(input) => input.fundingTxIndex + 1
         case _ => 0
       }
-      Multisig2of2Input(inputInfo, fundingTxIndex, fundingParamsA.remoteFundingPubKey)
+      SharedFundingInput(inputInfo, fundingTxIndex, fundingParamsA.remoteFundingPubKey, fundingParamsA.commitmentFormat)
     }
 
     def createSpliceFixtureParams(fundingTxIndex: Long, fundingAmountA: Satoshi, fundingAmountB: Satoshi, targetFeerate: FeeratePerKw, dustLimit: Satoshi, lockTime: Long, sharedInputA: SharedFundingInput, sharedInputB: SharedFundingInput, spliceOutputsA: List[TxOut] = Nil, spliceOutputsB: List[TxOut] = Nil, requireConfirmedInputs: RequireConfirmedInputs = RequireConfirmedInputs(forLocal = false, forRemote = false)): FixtureParams = {
@@ -2606,7 +2606,7 @@ class InteractiveTxBuilderSpec extends TestKitBaseClass with AnyFunSuiteLike wit
     val wallet = new SingleKeyOnChainWallet()
     val params = createFixtureParams(100_000 sat, 0 sat, FeeratePerKw(5000 sat), 330 sat, 0)
     val previousCommitment = CommitmentsSpec.makeCommitments(25_000_000 msat, 50_000_000 msat).active.head
-    val fundingParams = params.fundingParamsB.copy(sharedInput_opt = Some(Multisig2of2Input(previousCommitment.commitInput(params.channelKeysB), 0, randomKey().publicKey)))
+    val fundingParams = params.fundingParamsB.copy(sharedInput_opt = Some(SharedFundingInput(previousCommitment.commitInput(params.channelKeysB), 0, randomKey().publicKey, previousCommitment.commitmentFormat)))
     val bob = params.spawnTxBuilderSpliceBob(fundingParams, previousCommitment, wallet)
     bob ! Start(probe.ref)
     // Alice --- tx_add_input --> Bob
@@ -2622,7 +2622,7 @@ class InteractiveTxBuilderSpec extends TestKitBaseClass with AnyFunSuiteLike wit
     val params = createFixtureParams(100_000 sat, 0 sat, FeeratePerKw(5000 sat), 330 sat, 0)
     val previousCommitment = CommitmentsSpec.makeCommitments(25_000_000 msat, 50_000_000 msat).active.head
     val fundingTx = Transaction(2, Nil, Seq(TxOut(50_000 sat, Script.pay2wpkh(randomKey().publicKey)), TxOut(20_000 sat, Script.pay2wpkh(randomKey().publicKey))), 0)
-    val sharedInput = Multisig2of2Input(InputInfo(OutPoint(fundingTx, 0), fundingTx.txOut.head), 0, randomKey().publicKey)
+    val sharedInput = SharedFundingInput(InputInfo(OutPoint(fundingTx, 0), fundingTx.txOut.head), 0, randomKey().publicKey, previousCommitment.commitmentFormat)
     val bob = params.spawnTxBuilderSpliceBob(params.fundingParamsB.copy(sharedInput_opt = Some(sharedInput)), previousCommitment, wallet)
     bob ! Start(probe.ref)
     // Alice --- tx_add_input --> Bob

eclair-core/src/test/scala/fr/acinq/eclair/transactions/TransactionsSpec.scala

@@ -315,6 +315,9 @@ class TransactionsSpec extends AnyFunSuite with Logging {
           commitTx
       }
       commitTx.correctlySpends(Seq(fundingTx), ScriptFlags.STANDARD_SCRIPT_VERIFY_FLAGS)
+      // We check the expected weight of the commit input:
+      val commitInputWeight = commitTx.copy(txIn = Seq(commitTx.txIn.head, commitTx.txIn.head)).weight() - commitTx.weight()
+      checkExpectedWeight(commitInputWeight, commitmentFormat.fundingInputWeight, commitmentFormat)
       val htlcTxs = makeHtlcTxs(commitTx, outputs, commitmentFormat)
       val expiries = htlcTxs.map(tx => tx.htlcId -> tx.htlcExpiry.toLong).toMap
       val htlcSuccessTxs = htlcTxs.collect { case tx: UnsignedHtlcSuccessTx => tx }

eclair-core/src/test/scala/fr/acinq/eclair/wire/internal/channel/version4/ChannelCodecs4Spec.scala

@@ -101,10 +101,11 @@ class ChannelCodecs4Spec extends AnyFunSuite {
       ),
       createdAt = BlockHeight(1000),
       fundingParams = InteractiveTxParams(channelId = channelId, isInitiator = true, localContribution = 100.sat, remoteContribution = 200.sat,
-        sharedInput_opt = Some(InteractiveTxBuilder.Multisig2of2Input(
+        sharedInput_opt = Some(InteractiveTxBuilder.SharedFundingInput(
           InputInfo(OutPoint(TxId(ByteVector32.Zeroes), 0), TxOut(1000.sat, Script.pay2wsh(script))),
           0,
-          PrivateKey(ByteVector.fromValidHex("02" * 32)).publicKey
+          PrivateKey(ByteVector.fromValidHex("02" * 32)).publicKey,
+          ZeroFeeHtlcTxAnchorOutputsCommitmentFormat,
         )),
         remoteFundingPubKey = PrivateKey(ByteVector.fromValidHex("01" * 32)).publicKey,
         localOutputs = Nil,