Implement option_simple_close

docs/release-notes/eclair-vnext.md

@@ -13,6 +13,18 @@ Every node advertizes the rates at which they sell their liquidity, and buyers c
 The liquidity ads specification is still under review and will likely change.
 This feature isn't meant to be used on mainnet yet and is thus disabled by default.
 
+### Simplified mutual close
+
+This release includes support for the latest [mutual close protocol](https://github.com/lightning/bolts/pull/1096).
+This protocol allows both channel participants to decide exactly how much fees they're willing to pay to close the channel.
+Each participant obtains a channel closing transaction where they are paying the fees.
+
+Once closing transactions are broadcast, they can be RBF-ed by calling the `close` RPC again with a higher feerate:
+
+```sh
+./eclair-cli close --channelId=<channel_id> --preferredFeerateSatByte=<rbf_feerate>
+```
+
 ### Update minimal version of Bitcoin Core
 
 With this release, eclair requires using Bitcoin Core 27.1.

eclair-core/src/main/resources/reference.conf

@@ -81,6 +81,7 @@ eclair {
     // node that you trust using override-init-features (see below).
     option_zeroconf = disabled
     keysend = disabled
+    option_simple_close=optional
     trampoline_payment_prototype = disabled
     async_payment_prototype = disabled
     on_the_fly_funding = disabled

eclair-core/src/main/scala/fr/acinq/eclair/Features.scala

@@ -300,6 +300,11 @@ object Features {
     val mandatory = 54
   }
 
+  case object SimpleClose extends Feature with InitFeature with NodeFeature {
+    val rfcName = "option_simple_close"
+    val mandatory = 60
+  }
+
   // TODO: @t-bast: update feature bits once spec-ed (currently reserved here: https://github.com/lightningnetwork/lightning-rfc/issues/605)
   // We're not advertising these bits yet in our announcements, clients have to assume support.
   // This is why we haven't added them yet to `areSupported`.
@@ -363,6 +368,7 @@ object Features {
     PaymentMetadata,
     ZeroConf,
     KeySend,
+    SimpleClose,
     TrampolinePaymentPrototype,
     AsyncPaymentPrototype,
     SplicePrototype,
@@ -380,6 +386,7 @@ object Features {
     RouteBlinding -> (VariableLengthOnion :: Nil),
     TrampolinePaymentPrototype -> (PaymentSecret :: Nil),
     KeySend -> (VariableLengthOnion :: Nil),
+    SimpleClose -> (ShutdownAnySegwit :: Nil),
     AsyncPaymentPrototype -> (TrampolinePaymentPrototype :: Nil),
     OnTheFlyFunding -> (SplicePrototype :: Nil),
     FundingFeeCredit -> (OnTheFlyFunding :: Nil)

eclair-core/src/main/scala/fr/acinq/eclair/balance/CheckBalance.scala

@@ -213,6 +213,7 @@ object CheckBalance {
         case (r, d: DATA_NORMAL) => r.modify(_.normal).using(updateMainAndHtlcBalance(d.commitments, knownPreimages))
         case (r, d: DATA_SHUTDOWN) => r.modify(_.shutdown).using(updateMainAndHtlcBalance(d.commitments, knownPreimages))
         case (r, d: DATA_NEGOTIATING) => r.modify(_.negotiating).using(updateMainBalance(d.commitments.latest.localCommit))
+        case (r, d: DATA_NEGOTIATING_SIMPLE) => r.modify(_.negotiating).using(updateMainBalance(d.commitments.latest.localCommit))
         case (r, d: DATA_CLOSING) =>
           Closing.isClosingTypeAlreadyKnown(d) match {
             case None if d.mutualClosePublished.nonEmpty && d.localCommitPublished.isEmpty && d.remoteCommitPublished.isEmpty && d.nextRemoteCommitPublished.isEmpty && d.revokedCommitPublished.isEmpty =>

eclair-core/src/main/scala/fr/acinq/eclair/channel/ChannelData.scala

@@ -26,7 +26,7 @@ import fr.acinq.eclair.channel.fund.{InteractiveTxBuilder, InteractiveTxSigningS
 import fr.acinq.eclair.io.Peer
 import fr.acinq.eclair.transactions.CommitmentSpec
 import fr.acinq.eclair.transactions.Transactions._
-import fr.acinq.eclair.wire.protocol.{ChannelAnnouncement, ChannelReady, ChannelReestablish, ChannelUpdate, ClosingSigned, CommitSig, FailureMessage, FundingCreated, FundingSigned, Init, LiquidityAds, OnionRoutingPacket, OpenChannel, OpenDualFundedChannel, Shutdown, SpliceInit, Stfu, TxInitRbf, TxSignatures, UpdateAddHtlc, UpdateFailHtlc, UpdateFailMalformedHtlc, UpdateFulfillHtlc}
+import fr.acinq.eclair.wire.protocol.{ChannelAnnouncement, ChannelReady, ChannelReestablish, ChannelUpdate, ClosingComplete, ClosingSig, ClosingSigned, CommitSig, FailureMessage, FundingCreated, FundingSigned, Init, LiquidityAds, OnionRoutingPacket, OpenChannel, OpenDualFundedChannel, Shutdown, SpliceInit, Stfu, TxInitRbf, TxSignatures, UpdateAddHtlc, UpdateFailHtlc, UpdateFailMalformedHtlc, UpdateFulfillHtlc}
 import fr.acinq.eclair.{Alias, BlockHeight, CltvExpiry, CltvExpiryDelta, Features, InitFeature, MilliSatoshi, MilliSatoshiLong, RealShortChannelId, TimestampMilli, UInt64}
 import scodec.bits.ByteVector
 
@@ -72,6 +72,7 @@ case object WAIT_FOR_DUAL_FUNDING_READY extends ChannelState
 case object NORMAL extends ChannelState
 case object SHUTDOWN extends ChannelState
 case object NEGOTIATING extends ChannelState
+case object NEGOTIATING_SIMPLE extends ChannelState
 case object CLOSING extends ChannelState
 case object CLOSED extends ChannelState
 case object OFFLINE extends ChannelState
@@ -535,6 +536,38 @@ object SpliceStatus {
   case object SpliceAborted extends SpliceStatus
 }
 
+case class ClosingCompleteSent(closingComplete: ClosingComplete, closingFeerate: FeeratePerKw)
+
+sealed trait OnRemoteShutdown
+object OnRemoteShutdown {
+  /** When receiving the remote shutdown, we sign a new version of our closing transaction. */
+  case class SignTransaction(closingFeerate: FeeratePerKw) extends OnRemoteShutdown
+  /** When receiving the remote shutdown, we don't sign a new version of our closing transaction, but our peer may sign theirs. */
+  case object WaitForSigs extends OnRemoteShutdown
+}
+
+sealed trait ClosingNegotiation {
+  def localShutdown: Shutdown
+  // When we disconnect, we discard pending signatures.
+  def disconnect(): ClosingNegotiation.WaitingForRemoteShutdown = this match {
+    case status: ClosingNegotiation.WaitingForRemoteShutdown => status
+    case status: ClosingNegotiation.SigningTransactions => status.closingCompleteSent_opt.map(_.closingFeerate) match {
+      // If we were waiting for their signature, we will send closing_complete again after exchanging shutdown.
+      case Some(closingFeerate) if status.closingSigReceived_opt.isEmpty => ClosingNegotiation.WaitingForRemoteShutdown(status.localShutdown, OnRemoteShutdown.SignTransaction(closingFeerate))
+      case _ => ClosingNegotiation.WaitingForRemoteShutdown(status.localShutdown, OnRemoteShutdown.WaitForSigs)
+    }
+    case status: ClosingNegotiation.WaitingForConfirmation => ClosingNegotiation.WaitingForRemoteShutdown(status.localShutdown, OnRemoteShutdown.WaitForSigs)
+  }
+}
+object ClosingNegotiation {
+  /** We've sent a new shutdown message: we wait for their shutdown message before taking any action. */
+  case class WaitingForRemoteShutdown(localShutdown: Shutdown, onRemoteShutdown: OnRemoteShutdown) extends ClosingNegotiation
+  /** We've exchanged shutdown messages: at least one side will send closing_complete to renew their closing transaction. */
+  case class SigningTransactions(localShutdown: Shutdown, remoteShutdown: Shutdown, closingCompleteSent_opt: Option[ClosingCompleteSent], closingSigSent_opt: Option[ClosingSig], closingSigReceived_opt: Option[ClosingSig]) extends ClosingNegotiation
+  /** We've signed a new closing transaction and are waiting for confirmation or to initiate RBF. */
+  case class WaitingForConfirmation(localShutdown: Shutdown, remoteShutdown: Shutdown) extends ClosingNegotiation
+}
+
 sealed trait ChannelData extends PossiblyHarmful {
   def channelId: ByteVector32
 }
@@ -653,6 +686,16 @@ final case class DATA_NEGOTIATING(commitments: Commitments,
   require(closingTxProposed.nonEmpty, "there must always be a list for the current negotiation")
   require(!commitments.params.localParams.paysClosingFees || closingTxProposed.forall(_.nonEmpty), "initiator must have at least one closing signature for every negotiation attempt because it initiates the closing")
 }
+final case class DATA_NEGOTIATING_SIMPLE(commitments: Commitments,
+                                         status: ClosingNegotiation,
+                                         // Closing transactions we created, where we pay the fees (unsigned).
+                                         proposedClosingTxs: List[ClosingTxs],
+                                         // Closing transactions we published: this contains our local transactions for
+                                         // which they sent a signature, and their closing transactions that we signed.
+                                         publishedClosingTxs: List[ClosingTx]) extends ChannelDataWithCommitments {
+  val localScriptPubKey: ByteVector = status.localShutdown.scriptPubKey
+  def findClosingTx(tx: Transaction): Option[ClosingTx] = publishedClosingTxs.find(_.tx.txid == tx.txid).orElse(proposedClosingTxs.flatMap(_.all).find(_.tx.txid == tx.txid))
+}
 final case class DATA_CLOSING(commitments: Commitments,
                               waitingSince: BlockHeight, // how long since we initiated the closing
                               finalScriptPubKey: ByteVector, // where to send all on-chain funds

eclair-core/src/main/scala/fr/acinq/eclair/channel/ChannelExceptions.scala

@@ -116,7 +116,10 @@ case class FeerateTooDifferent                     (override val channelId: Byte
 case class InvalidAnnouncementSignatures           (override val channelId: ByteVector32, annSigs: AnnouncementSignatures) extends ChannelException(channelId, s"invalid announcement signatures: $annSigs")
 case class InvalidCommitmentSignature              (override val channelId: ByteVector32, fundingTxId: TxId, fundingTxIndex: Long, unsignedCommitTx: Transaction) extends ChannelException(channelId, s"invalid commitment signature: fundingTxId=$fundingTxId fundingTxIndex=$fundingTxIndex commitTxId=${unsignedCommitTx.txid} commitTx=$unsignedCommitTx")
 case class InvalidHtlcSignature                    (override val channelId: ByteVector32, txId: TxId) extends ChannelException(channelId, s"invalid htlc signature: txId=$txId")
+case class CannotGenerateClosingTx                 (override val channelId: ByteVector32) extends ChannelException(channelId, "failed to generate closing transaction: all outputs are trimmed")
+case class MissingCloseSignature                   (override val channelId: ByteVector32) extends ChannelException(channelId, "closing_complete is missing a signature for a closing transaction including our output")
 case class InvalidCloseSignature                   (override val channelId: ByteVector32, txId: TxId) extends ChannelException(channelId, s"invalid close signature: txId=$txId")
+case class UnexpectedClosingComplete               (override val channelId: ByteVector32, fees: Satoshi, lockTime: Long) extends ChannelException(channelId, s"unexpected closing_complete with fees=$fees and lockTime=$lockTime: we already sent closing_sig, you must send shutdown first")
 case class InvalidCloseAmountBelowDust             (override val channelId: ByteVector32, txId: TxId) extends ChannelException(channelId, s"invalid closing tx: some outputs are below dust: txId=$txId")
 case class CommitSigCountMismatch                  (override val channelId: ByteVector32, expected: Int, actual: Int) extends ChannelException(channelId, s"commit sig count mismatch: expected=$expected actual=$actual")
 case class HtlcSigCountMismatch                    (override val channelId: ByteVector32, expected: Int, actual: Int) extends ChannelException(channelId, s"htlc sig count mismatch: expected=$expected actual=$actual")

eclair-core/src/main/scala/fr/acinq/eclair/channel/Commitments.scala

@@ -112,10 +112,11 @@ case class ChannelParams(channelId: ByteVector32,
     // README: if we set our bitcoin node to generate taproot addresses and our peer does not support option_shutdown_anysegwit, we will not be able to mutual-close
     // channels as the isValidFinalScriptPubkey() check would fail.
     val allowAnySegwit = Features.canUseFeature(localParams.initFeatures, remoteParams.initFeatures, Features.ShutdownAnySegwit)
+    val allowOpReturn = Features.canUseFeature(localParams.initFeatures, remoteParams.initFeatures, Features.SimpleClose)
     val mustUseUpfrontShutdownScript = channelFeatures.hasFeature(Features.UpfrontShutdownScript)
     // we only enforce using the pre-generated shutdown script if option_upfront_shutdown_script is set
     if (mustUseUpfrontShutdownScript && localParams.upfrontShutdownScript_opt.exists(_ != localScriptPubKey)) Left(InvalidFinalScript(channelId))
-    else if (!Closing.MutualClose.isValidFinalScriptPubkey(localScriptPubKey, allowAnySegwit)) Left(InvalidFinalScript(channelId))
+    else if (!Closing.MutualClose.isValidFinalScriptPubkey(localScriptPubKey, allowAnySegwit, allowOpReturn)) Left(InvalidFinalScript(channelId))
     else Right(localScriptPubKey)
   }
 
@@ -126,10 +127,11 @@ case class ChannelParams(channelId: ByteVector32,
   def validateRemoteShutdownScript(remoteScriptPubKey: ByteVector): Either[ChannelException, ByteVector] = {
     // to check whether shutdown_any_segwit is active we check features in local and remote parameters, which are negotiated each time we connect to our peer.
     val allowAnySegwit = Features.canUseFeature(localParams.initFeatures, remoteParams.initFeatures, Features.ShutdownAnySegwit)
+    val allowOpReturn = Features.canUseFeature(localParams.initFeatures, remoteParams.initFeatures, Features.SimpleClose)
     val mustUseUpfrontShutdownScript = channelFeatures.hasFeature(Features.UpfrontShutdownScript)
     // we only enforce using the pre-generated shutdown script if option_upfront_shutdown_script is set
     if (mustUseUpfrontShutdownScript && remoteParams.upfrontShutdownScript_opt.exists(_ != remoteScriptPubKey)) Left(InvalidFinalScript(channelId))
-    else if (!Closing.MutualClose.isValidFinalScriptPubkey(remoteScriptPubKey, allowAnySegwit)) Left(InvalidFinalScript(channelId))
+    else if (!Closing.MutualClose.isValidFinalScriptPubkey(remoteScriptPubKey, allowAnySegwit, allowOpReturn)) Left(InvalidFinalScript(channelId))
     else Right(remoteScriptPubKey)
   }