Liquidity Ads (#561)

Implement a prototype for liquidity ads, compatible with ACINQ/eclair#2550
Note that we only implement the buyer side, which limits testing.
The specification is available here: lightning/bolts#878

We currently don't add CLTV locks to the commitment transactions, for simplicity's sake.

src/commonMain/kotlin/fr/acinq/lightning/channel/ChannelAction.kt

@@ -87,6 +87,7 @@ sealed class ChannelAction {
             abstract val txId: TxId
             data class ViaSpliceOut(val amount: Satoshi, override val miningFees: Satoshi, val address: String, override val txId: TxId) : StoreOutgoingPayment()
             data class ViaSpliceCpfp(override val miningFees: Satoshi, override val txId: TxId) : StoreOutgoingPayment()
+            data class ViaInboundLiquidityRequest(override val txId: TxId, override val miningFees: Satoshi, val lease: LiquidityAds.Lease) : StoreOutgoingPayment()
             data class ViaClose(val amount: Satoshi, override val miningFees: Satoshi, val address: String, override val txId: TxId, val isSentToDefaultAddress: Boolean, val closingType: ChannelClosingType) : StoreOutgoingPayment()
         }
         data class SetLocked(val txId: TxId) : Storage()

src/commonMain/kotlin/fr/acinq/lightning/channel/ChannelCommand.kt

@@ -13,6 +13,7 @@ import fr.acinq.lightning.utils.UUID
 import fr.acinq.lightning.utils.msat
 import fr.acinq.lightning.wire.FailureMessage
 import fr.acinq.lightning.wire.LightningMessage
+import fr.acinq.lightning.wire.LiquidityAds
 import fr.acinq.lightning.wire.OnionRoutingPacket
 import kotlinx.coroutines.CompletableDeferred
 import fr.acinq.lightning.wire.Init as InitMessage
@@ -83,14 +84,20 @@ sealed class ChannelCommand {
         data class UpdateFee(val feerate: FeeratePerKw, val commit: Boolean = false) : Commitment(), ForbiddenDuringSplice
         object CheckHtlcTimeout : Commitment()
         sealed class Splice : Commitment() {
-            data class Request(val replyTo: CompletableDeferred<Response>, val spliceIn: SpliceIn?, val spliceOut: SpliceOut?, val feerate: FeeratePerKw, val origins: List<Origin.PayToOpenOrigin> = emptyList()) : Splice() {
+            data class Request(val replyTo: CompletableDeferred<Response>, val spliceIn: SpliceIn?, val spliceOut: SpliceOut?, val requestRemoteFunding: LiquidityAds.RequestRemoteFunding?, val feerate: FeeratePerKw, val origins: List<Origin.PayToOpenOrigin> = emptyList()) : Splice() {
                 val pushAmount: MilliSatoshi = spliceIn?.pushAmount ?: 0.msat
                 val spliceOutputs: List<TxOut> = spliceOut?.let { listOf(TxOut(it.amount, it.scriptPubKey)) } ?: emptyList()
 
                 data class SpliceIn(val walletInputs: List<WalletState.Utxo>, val pushAmount: MilliSatoshi = 0.msat)
                 data class SpliceOut(val amount: Satoshi, val scriptPubKey: ByteVector)
             }
 
+            /**
+             * @param miningFee on-chain fee that will be paid for the splice transaction.
+             * @param serviceFee service-fee that will be paid to the remote node for a service they provide with the splice transaction.
+             */
+            data class Fees(val miningFee: Satoshi, val serviceFee: MilliSatoshi)
+
             sealed class Response {
                 /**
                  * This response doesn't fully guarantee that the splice will confirm, because our peer may potentially double-spend
@@ -101,14 +108,16 @@ sealed class ChannelCommand {
                     val fundingTxIndex: Long,
                     val fundingTxId: TxId,
                     val capacity: Satoshi,
-                    val balance: MilliSatoshi
+                    val balance: MilliSatoshi,
+                    val liquidityLease: LiquidityAds.Lease?,
                 ) : Response()
 
                 sealed class Failure : Response() {
                     object InsufficientFunds : Failure()
                     object InvalidSpliceOutPubKeyScript : Failure()
                     object SpliceAlreadyInProgress : Failure()
                     object ChannelNotIdle : Failure()
+                    data class InvalidLiquidityAds(val reason: ChannelException) : Failure()
                     data class FundingFailure(val reason: FundingContributionFailure) : Failure()
                     object CannotStartSession : Failure()
                     data class InteractiveTxSessionFailed(val reason: InteractiveTxSessionAction.RemoteFailure) : Failure()

src/commonMain/kotlin/fr/acinq/lightning/channel/ChannelException.kt

@@ -25,6 +25,10 @@ data class MissingChannelType                      (override val channelId: Byte
 data class DustLimitTooSmall                       (override val channelId: ByteVector32, val dustLimit: Satoshi, val min: Satoshi) : ChannelException(channelId, "dustLimit=$dustLimit is too small (min=$min)")
 data class DustLimitTooLarge                       (override val channelId: ByteVector32, val dustLimit: Satoshi, val max: Satoshi) : ChannelException(channelId, "dustLimit=$dustLimit is too large (max=$max)")
 data class ToSelfDelayTooHigh                      (override val channelId: ByteVector32, val toSelfDelay: CltvExpiryDelta, val max: CltvExpiryDelta) : ChannelException(channelId, "unreasonable to_self_delay=$toSelfDelay (max=$max)")
+data class MissingLiquidityAds                     (override val channelId: ByteVector32) : ChannelException(channelId, "liquidity ads field is missing")
+data class InvalidLiquidityAdsSig                  (override val channelId: ByteVector32) : ChannelException(channelId, "liquidity ads signature is invalid")
+data class InvalidLiquidityAdsAmount               (override val channelId: ByteVector32, val proposed: Satoshi, val min: Satoshi) : ChannelException(channelId, "liquidity ads funding amount is too low (expected at least $min, got $proposed)")
+data class InvalidLiquidityRates                   (override val channelId: ByteVector32) : ChannelException(channelId, "rejecting liquidity ads proposed rates")
 data class ChannelFundingError                     (override val channelId: ByteVector32) : ChannelException(channelId, "channel funding error")
 data class RbfAttemptAborted                       (override val channelId: ByteVector32) : ChannelException(channelId, "rbf attempt aborted")
 data class SpliceAborted                           (override val channelId: ByteVector32) : ChannelException(channelId, "splice aborted")

src/commonMain/kotlin/fr/acinq/lightning/channel/Helpers.kt

@@ -257,6 +257,10 @@ object Helpers {
             }
         }
 
+        fun makeFundingPubKeyScript(localFundingPubkey: PublicKey, remoteFundingPubkey: PublicKey): ByteVector {
+            return write(pay2wsh(multiSig2of2(localFundingPubkey, remoteFundingPubkey))).toByteVector()
+        }
+
         fun makeFundingInputInfo(
             fundingTxId: TxId,
             fundingTxOutputIndex: Int,

src/commonMain/kotlin/fr/acinq/lightning/channel/InteractiveTx.kt

@@ -86,7 +86,7 @@ data class InteractiveTxParams(
 
     fun fundingPubkeyScript(channelKeys: KeyManager.ChannelKeys): ByteVector {
         val fundingTxIndex = (sharedInput as? SharedFundingInput.Multisig2of2)?.let { it.fundingTxIndex + 1 } ?: 0
-        return Script.write(Script.pay2wsh(Scripts.multiSig2of2(channelKeys.fundingPubKey(fundingTxIndex), remoteFundingPubkey))).toByteVector()
+        return Helpers.Funding.makeFundingPubKeyScript(channelKeys.fundingPubKey(fundingTxIndex), remoteFundingPubkey)
     }
 }
 
@@ -751,8 +751,9 @@ data class InteractiveTxSigningSession(
     val fundingParams: InteractiveTxParams,
     val fundingTxIndex: Long,
     val fundingTx: PartiallySignedSharedTransaction,
+    val liquidityLease: LiquidityAds.Lease?,
     val localCommit: Either<UnsignedLocalCommit, LocalCommit>,
-    val remoteCommit: RemoteCommit
+    val remoteCommit: RemoteCommit,
 ) {
 
     //                      Example flow:
@@ -826,6 +827,7 @@ data class InteractiveTxSigningSession(
             sharedTx: SharedTransaction,
             localPushAmount: MilliSatoshi,
             remotePushAmount: MilliSatoshi,
+            liquidityLease: LiquidityAds.Lease?,
             localCommitmentIndex: Long,
             remoteCommitmentIndex: Long,
             commitTxFeerate: FeeratePerKw,
@@ -834,13 +836,14 @@ data class InteractiveTxSigningSession(
             val channelKeys = channelParams.localParams.channelKeys(keyManager)
             val unsignedTx = sharedTx.buildUnsignedTx()
             val sharedOutputIndex = unsignedTx.txOut.indexOfFirst { it.publicKeyScript == fundingParams.fundingPubkeyScript(channelKeys) }
+            val liquidityFees = liquidityLease?.fees?.total?.toMilliSatoshi() ?: 0.msat
             return Helpers.Funding.makeCommitTxsWithoutHtlcs(
                 channelKeys,
                 channelParams.channelId,
                 channelParams.localParams, channelParams.remoteParams,
                 fundingAmount = sharedTx.sharedOutput.amount,
-                toLocal = sharedTx.sharedOutput.localAmount - localPushAmount + remotePushAmount,
-                toRemote = sharedTx.sharedOutput.remoteAmount - remotePushAmount + localPushAmount,
+                toLocal = sharedTx.sharedOutput.localAmount - localPushAmount + remotePushAmount - liquidityFees,
+                toRemote = sharedTx.sharedOutput.remoteAmount - remotePushAmount + localPushAmount + liquidityFees,
                 localCommitmentIndex = localCommitmentIndex,
                 remoteCommitmentIndex = remoteCommitmentIndex,
                 commitTxFeerate,
@@ -869,7 +872,7 @@ data class InteractiveTxSigningSession(
                 val unsignedLocalCommit = UnsignedLocalCommit(localCommitmentIndex, firstCommitTx.localSpec, firstCommitTx.localCommitTx, listOf())
                 val remoteCommit = RemoteCommit(remoteCommitmentIndex, firstCommitTx.remoteSpec, firstCommitTx.remoteCommitTx.tx.txid, remotePerCommitmentPoint)
                 val signedFundingTx = sharedTx.sign(keyManager, fundingParams, channelParams.localParams, channelParams.remoteParams.nodeId)
-                Pair(InteractiveTxSigningSession(fundingParams, fundingTxIndex, signedFundingTx, Either.Left(unsignedLocalCommit), remoteCommit), commitSig)
+                Pair(InteractiveTxSigningSession(fundingParams, fundingTxIndex, signedFundingTx, liquidityLease, Either.Left(unsignedLocalCommit), remoteCommit), commitSig)
             }
         }
 
@@ -900,7 +903,14 @@ sealed class RbfStatus {
 sealed class SpliceStatus {
     object None : SpliceStatus()
     data class Requested(val command: ChannelCommand.Commitment.Splice.Request, val spliceInit: SpliceInit) : SpliceStatus()
-    data class InProgress(val replyTo: CompletableDeferred<ChannelCommand.Commitment.Splice.Response>?, val spliceSession: InteractiveTxSession, val localPushAmount: MilliSatoshi, val remotePushAmount: MilliSatoshi, val origins: List<Origin.PayToOpenOrigin>) : SpliceStatus()
+    data class InProgress(
+        val replyTo: CompletableDeferred<ChannelCommand.Commitment.Splice.Response>?,
+        val spliceSession: InteractiveTxSession,
+        val localPushAmount: MilliSatoshi,
+        val remotePushAmount: MilliSatoshi,
+        val liquidityLease: LiquidityAds.Lease?,
+        val origins: List<Origin.PayToOpenOrigin>
+    ) : SpliceStatus()
     data class WaitingForSigs(val session: InteractiveTxSigningSession, val origins: List<Origin.PayToOpenOrigin>) : SpliceStatus()
     object Aborted : SpliceStatus()
 }

src/commonMain/kotlin/fr/acinq/lightning/channel/states/LegacyWaitForFundingLocked.kt

@@ -47,7 +47,8 @@ data class LegacyWaitForFundingLocked(
                         null,
                         null,
                         null,
-                        SpliceStatus.None
+                        SpliceStatus.None,
+                        listOf(),
                     )
                     val actions = listOf(
                         ChannelAction.Storage.StoreState(nextState),