Update to select funding inputs before sending open_channel2 and splice_init

docs/release-notes/eclair-vnext.md

@@ -4,6 +4,39 @@
 
 ## Major changes
 
+### Channel Splicing
+
+With this release, we add support for the final version of [splicing](https://github.com/lightning/bolts/pull/1160) that was recently added to the BOLTs.
+Splicing allows node operators to change the size of their existing channels, which makes it easier and more efficient to allocate liquidity where it is most needed.
+Most node operators can now have a single channel with each of their peer, which costs less on-chain fees and resources, and makes path-finding easier.
+
+The size of an existing channel can be increased with the `splicein` API:
+
+```sh
+eclair-cli splicein --channelId=<channel_id> --amountIn=<amount_satoshis>
+```
+
+Once that transaction confirms, the additional liquidity can be used to send outgoing payments.
+If the transaction doesn't confirm, the node operator can speed up confirmation with the `rbfsplice` API:
+
+```sh
+eclair-cli rbfsplice --channelId=<channel_id> --targetFeerateSatByte=<feerate_satoshis_per_byte> --fundingFeeBudgetSatoshis=<maximum_on_chain_fee_satoshis>
+```
+
+If the node operator wants to reduce the size of a channel, or send some of the channel funds to an on-chain address, they can use the `spliceout` API:
+
+```sh
+eclair-cli spliceout --channelId=<channel_id> --amountOut=<amount_satoshis> --scriptPubKey=<on_chain_address>
+```
+
+That operation can also be RBF-ed with the `rbfsplice` API to speed up confirmation if necessary.
+
+Note that when 0-conf is used for the channel, it is not possible to RBF splice transactions.
+Node operators should instead create a new splice transaction (with `splicein` or `spliceout`) to CPFP the previous transaction.
+
+Note that eclair had already introduced support for a splicing prototype in v0.9.0, which helped improve the BOLT proposal.
+We're removing support for the previous splicing prototype feature: users that depended on this protocol must upgrade to create official splice transactions.
+
 ### Update minimal version of Bitcoin Core
 
 With this release, eclair requires using Bitcoin Core 27.1.
@@ -26,7 +59,8 @@ Eclair will not allow remote peers to open new obsolete channels that do not sup
 
 ### API changes
 
-- `channelstats` now takes optional parameters `--count` and `--skip` to control pagination. By default, it will return first 10 entries. (#2890)
+- `channelstats` now accept `--count` and `--skip` parameters to limit the number of retrieved items (#2890)
+- `rbfsplice` lets any channel participant RBF the current unconfirmed splice transaction (#2887)
 
 ### Miscellaneous improvements and bug fixes
 

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_splice = optional
     trampoline_payment_prototype = disabled
     async_payment_prototype = disabled
   }
@@ -196,6 +197,10 @@ eclair {
 
       min-time-between-updates = 1 hour // minimum time between channel updates because the balance changed
     }
+
+    // if > 0, excess channel funding up to this amount will be added to the amount contributed when funding
+    // dual-funded channels or splices. This is useful to avoid paying fees to add a small change output.
+    max-excess = 0
   }
 
   balance-check-interval = 1 hour

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

@@ -86,14 +86,16 @@ trait Eclair {
 
   def disconnect(nodeId: PublicKey)(implicit timeout: Timeout): Future[String]
 
-  def open(nodeId: PublicKey, fundingAmount: Satoshi, pushAmount_opt: Option[MilliSatoshi], channelType_opt: Option[SupportedChannelType], fundingFeerate_opt: Option[FeeratePerByte], fundingFeeBudget_opt: Option[Satoshi], announceChannel_opt: Option[Boolean], openTimeout_opt: Option[Timeout])(implicit timeout: Timeout): Future[OpenChannelResponse]
+  def open(nodeId: PublicKey, fundingAmount: Satoshi, maxExcess_opt: Option[Satoshi], pushAmount_opt: Option[MilliSatoshi], channelType_opt: Option[SupportedChannelType], fundingFeerate_opt: Option[FeeratePerByte], fundingFeeBudget_opt: Option[Satoshi], announceChannel_opt: Option[Boolean], openTimeout_opt: Option[Timeout])(implicit timeout: Timeout): Future[OpenChannelResponse]
 
   def rbfOpen(channelId: ByteVector32, targetFeerate: FeeratePerKw, fundingFeeBudget: Satoshi, lockTime_opt: Option[Long])(implicit timeout: Timeout): Future[CommandResponse[CMD_BUMP_FUNDING_FEE]]
 
   def spliceIn(channelId: ByteVector32, amountIn: Satoshi, pushAmount_opt: Option[MilliSatoshi])(implicit timeout: Timeout): Future[CommandResponse[CMD_SPLICE]]
 
   def spliceOut(channelId: ByteVector32, amountOut: Satoshi, scriptOrAddress: Either[ByteVector, String])(implicit timeout: Timeout): Future[CommandResponse[CMD_SPLICE]]
 
+  def rbfSplice(channelId: ByteVector32, targetFeerate: FeeratePerKw, fundingFeeBudget: Satoshi, lockTime_opt: Option[Long])(implicit timeout: Timeout): Future[CommandResponse[CMD_BUMP_FUNDING_FEE]]
+
   def close(channels: List[ApiTypes.ChannelIdentifier], scriptPubKey_opt: Option[ByteVector], closingFeerates_opt: Option[ClosingFeerates])(implicit timeout: Timeout): Future[Map[ApiTypes.ChannelIdentifier, Either[Throwable, CommandResponse[CMD_CLOSE]]]]
 
   def forceClose(channels: List[ApiTypes.ChannelIdentifier])(implicit timeout: Timeout): Future[Map[ApiTypes.ChannelIdentifier, Either[Throwable, CommandResponse[CMD_FORCECLOSE]]]]
@@ -206,7 +208,7 @@ class EclairImpl(appKit: Kit) extends Eclair with Logging {
     (appKit.switchboard ? Peer.Disconnect(nodeId)).mapTo[Peer.DisconnectResponse].map(_.toString)
   }
 
-  override def open(nodeId: PublicKey, fundingAmount: Satoshi, pushAmount_opt: Option[MilliSatoshi], channelType_opt: Option[SupportedChannelType], fundingFeerate_opt: Option[FeeratePerByte], fundingFeeBudget_opt: Option[Satoshi], announceChannel_opt: Option[Boolean], openTimeout_opt: Option[Timeout])(implicit timeout: Timeout): Future[OpenChannelResponse] = {
+  override def open(nodeId: PublicKey, fundingAmount: Satoshi, maxExcess_opt: Option[Satoshi], pushAmount_opt: Option[MilliSatoshi], channelType_opt: Option[SupportedChannelType], fundingFeerate_opt: Option[FeeratePerByte], fundingFeeBudget_opt: Option[Satoshi], announceChannel_opt: Option[Boolean], openTimeout_opt: Option[Timeout])(implicit timeout: Timeout): Future[OpenChannelResponse] = {
     // we want the open timeout to expire *before* the default ask timeout, otherwise user will get a generic response
     val openTimeout = openTimeout_opt.getOrElse(Timeout(20 seconds))
     // if no budget is provided for the mining fee of the funding tx, we use a default of 0.1% of the funding amount as a safety measure
@@ -216,6 +218,7 @@ class EclairImpl(appKit: Kit) extends Eclair with Logging {
       open = Peer.OpenChannel(
         remoteNodeId = nodeId,
         fundingAmount = fundingAmount,
+        maxExcess_opt = maxExcess_opt,
         channelType_opt = channelType_opt,
         pushAmount_opt = pushAmount_opt,
         fundingTxFeerate_opt = fundingFeerate_opt.map(FeeratePerKw(_)),
@@ -227,16 +230,18 @@ class EclairImpl(appKit: Kit) extends Eclair with Logging {
   }
 
   override def rbfOpen(channelId: ByteVector32, targetFeerate: FeeratePerKw, fundingFeeBudget: Satoshi, lockTime_opt: Option[Long])(implicit timeout: Timeout): Future[CommandResponse[CMD_BUMP_FUNDING_FEE]] = {
-    sendToChannelTyped(channel = Left(channelId),
-      cmdBuilder = CMD_BUMP_FUNDING_FEE(_, targetFeerate, fundingFeeBudget, lockTime_opt.getOrElse(appKit.nodeParams.currentBlockHeight.toLong)))
+    sendToChannelTyped(
+      channel = Left(channelId),
+      cmdBuilder = CMD_BUMP_FUNDING_FEE(_, targetFeerate, fundingFeeBudget, lockTime_opt.getOrElse(appKit.nodeParams.currentBlockHeight.toLong))
+    )
   }
 
   override def spliceIn(channelId: ByteVector32, amountIn: Satoshi, pushAmount_opt: Option[MilliSatoshi])(implicit timeout: Timeout): Future[CommandResponse[CMD_SPLICE]] = {
-    sendToChannelTyped(channel = Left(channelId),
-      cmdBuilder = CMD_SPLICE(_,
-        spliceIn_opt = Some(SpliceIn(additionalLocalFunding = amountIn, pushAmount = pushAmount_opt.getOrElse(0.msat))),
-        spliceOut_opt = None
-      ))
+    val spliceIn = SpliceIn(additionalLocalFunding = amountIn, pushAmount = pushAmount_opt.getOrElse(0.msat))
+    sendToChannelTyped(
+      channel = Left(channelId),
+      cmdBuilder = CMD_SPLICE(_, spliceIn_opt = Some(spliceIn), spliceOut_opt = None)
+    )
   }
 
   override def spliceOut(channelId: ByteVector32, amountOut: Satoshi, scriptOrAddress: Either[ByteVector, String])(implicit timeout: Timeout): Future[CommandResponse[CMD_SPLICE]] = {
@@ -247,11 +252,18 @@ class EclairImpl(appKit: Kit) extends Eclair with Logging {
         case Right(script) => Script.write(script)
       }
     }
-    sendToChannelTyped(channel = Left(channelId),
-      cmdBuilder = CMD_SPLICE(_,
-        spliceIn_opt = None,
-        spliceOut_opt = Some(SpliceOut(amount = amountOut, scriptPubKey = script))
-      ))
+    val spliceOut = SpliceOut(amount = amountOut, scriptPubKey = script)
+    sendToChannelTyped(
+      channel = Left(channelId),
+      cmdBuilder = CMD_SPLICE(_, spliceIn_opt = None, spliceOut_opt = Some(spliceOut))
+    )
+  }
+
+  override def rbfSplice(channelId: ByteVector32, targetFeerate: FeeratePerKw, fundingFeeBudget: Satoshi, lockTime_opt: Option[Long])(implicit timeout: Timeout): Future[CommandResponse[CMD_BUMP_FUNDING_FEE]] = {
+    sendToChannelTyped(
+      channel = Left(channelId),
+      cmdBuilder = CMD_BUMP_FUNDING_FEE(_, targetFeerate, fundingFeeBudget, lockTime_opt.getOrElse(appKit.nodeParams.currentBlockHeight.toLong))
+    )
   }
 
   override def close(channels: List[ApiTypes.ChannelIdentifier], scriptPubKey_opt: Option[ByteVector], closingFeerates_opt: Option[ClosingFeerates])(implicit timeout: Timeout): Future[Map[ApiTypes.ChannelIdentifier, Either[Throwable, CommandResponse[CMD_CLOSE]]]] = {
@@ -558,9 +570,9 @@ class EclairImpl(appKit: Kit) extends Eclair with Logging {
     case Left(channelId) => appKit.register ? Register.Forward(null, channelId, request)
     case Right(shortChannelId) => appKit.register ? Register.ForwardShortId(null, shortChannelId, request)
   }).map {
-    case t: R@unchecked => t
-    case t: Register.ForwardFailure[C]@unchecked => throw ChannelNotFound(Left(t.fwd.channelId))
-    case t: Register.ForwardShortIdFailure[C]@unchecked => throw ChannelNotFound(Right(t.fwd.shortChannelId))
+    case t: R @unchecked => t
+    case t: Register.ForwardFailure[C] @unchecked => throw ChannelNotFound(Left(t.fwd.channelId))
+    case t: Register.ForwardShortIdFailure[C] @unchecked => throw ChannelNotFound(Right(t.fwd.shortChannelId))
   }
 
   private def sendToChannelTyped[C <: Command, R <: CommandResponse[C]](channel: ApiTypes.ChannelIdentifier, cmdBuilder: akka.actor.typed.ActorRef[Any] => C)(implicit timeout: Timeout): Future[R] =
@@ -571,9 +583,9 @@ class EclairImpl(appKit: Kit) extends Eclair with Logging {
         case Right(shortChannelId) => Register.ForwardShortId(replyTo, shortChannelId, cmd)
       }
     }.map {
-      case t: R@unchecked => t
-      case t: Register.ForwardFailure[C]@unchecked => throw ChannelNotFound(Left(t.fwd.channelId))
-      case t: Register.ForwardShortIdFailure[C]@unchecked => throw ChannelNotFound(Right(t.fwd.shortChannelId))
+      case t: R @unchecked => t
+      case t: Register.ForwardFailure[C] @unchecked => throw ChannelNotFound(Left(t.fwd.channelId))
+      case t: Register.ForwardShortIdFailure[C] @unchecked => throw ChannelNotFound(Right(t.fwd.shortChannelId))
     }
 
   /**

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

@@ -264,8 +264,7 @@ object Features {
     val mandatory = 28
   }
 
-  // TODO: this should also extend NodeFeature once the spec is finalized
-  case object Quiescence extends Feature with InitFeature {
+  case object Quiescence extends Feature with InitFeature with NodeFeature {
     val rfcName = "option_quiesce"
     val mandatory = 34
   }
@@ -300,6 +299,11 @@ object Features {
     val mandatory = 54
   }
 
+  case object Splicing extends Feature with InitFeature with NodeFeature {
+    val rfcName = "option_splice"
+    val mandatory = 62
+  }
+
   // 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`.
@@ -317,12 +321,6 @@ object Features {
     val mandatory = 152
   }
 
-  // TODO: @pm47 custom splices implementation for phoenix, to be replaced once splices is spec-ed (currently reserved here: https://github.com/lightning/bolts/issues/605)
-  case object SplicePrototype extends Feature with InitFeature {
-    val rfcName = "splice_prototype"
-    val mandatory = 154
-  }
-
   val knownFeatures: Set[Feature] = Set(
     DataLossProtect,
     InitialRoutingSync,
@@ -346,9 +344,9 @@ object Features {
     PaymentMetadata,
     ZeroConf,
     KeySend,
+    Splicing,
     TrampolinePaymentPrototype,
     AsyncPaymentPrototype,
-    SplicePrototype,
   )
 
   // Features may depend on other features, as specified in Bolt 9.

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

@@ -476,6 +476,8 @@ object NodeParams extends Logging {
     val maxNoChannels = config.getInt("peer-connection.max-no-channels")
     require(maxNoChannels > 0, "peer-connection.max-no-channels must be > 0")
 
+    val maxExcess_opt = if (config.getInt("channel.max-excess") > 0) Some(Satoshi(config.getInt("channel.max-excess"))) else None
+
     NodeParams(
       nodeKeyManager = nodeKeyManager,
       channelKeyManager = channelKeyManager,
@@ -524,7 +526,8 @@ object NodeParams extends Logging {
         quiescenceTimeout = FiniteDuration(config.getDuration("channel.quiescence-timeout").getSeconds, TimeUnit.SECONDS),
         balanceThresholds = config.getConfigList("channel.channel-update.balance-thresholds").asScala.map(conf => BalanceThreshold(Satoshi(conf.getLong("available-sat")), Satoshi(conf.getLong("max-htlc-sat")))).toSeq,
         minTimeBetweenUpdates = FiniteDuration(config.getDuration("channel.channel-update.min-time-between-updates").getSeconds, TimeUnit.SECONDS),
-        acceptIncomingStaticRemoteKeyChannels = config.getBoolean("channel.accept-incoming-static-remote-key-channels")
+        acceptIncomingStaticRemoteKeyChannels = config.getBoolean("channel.accept-incoming-static-remote-key-channels"),
+        maxExcess_opt = maxExcess_opt,
       ),
       onChainFeeConf = OnChainFeeConf(
         feeTargets = feeTargets,

eclair-core/src/main/scala/fr/acinq/eclair/blockchain/OnChainWallet.scala

@@ -37,7 +37,7 @@ trait OnChainChannelFunder {
    * Fund the provided transaction by adding inputs (and a change output if necessary).
    * Callers must verify that the resulting transaction isn't sending funds to unexpected addresses (malicious bitcoin node).
    */
-  def fundTransaction(tx: Transaction, feeRate: FeeratePerKw, replaceable: Boolean, externalInputsWeight: Map[OutPoint, Long] = Map.empty, feeBudget_opt: Option[Satoshi])(implicit ec: ExecutionContext): Future[FundTransactionResponse]
+  def fundTransaction(tx: Transaction, feeRate: FeeratePerKw, replaceable: Boolean, externalInputsWeight: Map[OutPoint, Long] = Map.empty, feeBudget_opt: Option[Satoshi], addExcessToRecipientPosition_opt: Option[Int], maxExcess_opt: Option[Satoshi])(implicit ec: ExecutionContext): Future[FundTransactionResponse]
 
   /**
    * Sign a PSBT. Result may be partially signed: only inputs known to our bitcoin wallet will be signed. *
@@ -55,7 +55,7 @@ trait OnChainChannelFunder {
   def publishTransaction(tx: Transaction)(implicit ec: ExecutionContext): Future[TxId]
 
   /** Create a fully signed channel funding transaction with the provided pubkeyScript. */
-  def makeFundingTx(pubkeyScript: ByteVector, amount: Satoshi, feeRate: FeeratePerKw, feeBudget_opt: Option[Satoshi])(implicit ec: ExecutionContext): Future[MakeFundingTxResponse]
+  def makeFundingTx(pubkeyScript: ByteVector, amount: Satoshi, feeRate: FeeratePerKw, feeBudget_opt: Option[Satoshi], maxExcess_opt: Option[Satoshi])(implicit ec: ExecutionContext): Future[MakeFundingTxResponse]
 
   /**
    * Committing *must* include publishing the transaction on the network.