Add support for RBF-ing splice transactions

If the latest splice transaction doesn't confirm, we allow exchanging
`tx_init_rbf` and `tx_ack_rbf` to create another splice transaction to
replace it. We use the same funding contribution as the previous splice.

We disallow creating another splice transaction using `splice_init` if
we have several RBF attempts for the latest splice: we cannot know which
one of them will confirm and should be spent by the new splice.

TODO: needs tests

docs/release-notes/eclair-vnext.md

@@ -26,7 +26,8 @@ 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/scala/fr/acinq/eclair/Eclair.scala

@@ -94,6 +94,8 @@ trait Eclair {
 
   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]]]]
@@ -227,16 +229,18 @@ 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 +251,18 @@ 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 +569,9 @@ 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 +582,9 @@ 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))
     }
 
   /**