Extensible Liquidity Ads (#2848)

* Add support for extensible liquidity ads

The initiator of `open_channel2`, `tx_init_rbf` and `splice_init` can
request funding from the remote node. The non-initiator node will:

- let the open-channel-interceptor plugin decide whether to provide
  liquidity for new channels or not, and how much
- always honor liquidity requests on existing channels (RBF and splice)
  when funding rates have been configured

Liquidity ads are included in the `node_announcement` message, which
lets buyers compare sellers and connect to sellers that provide rates
they are comfortable with. They are also included in the `init` message
which allows providing different rates to specific peers.

This implements lightning/bolts#1153. We
currently use the temporary tlv tag 1339 while we're waiting for
feedback on the spec proposal.

* Add `channelCreationFee` to liquidity ads

Creating a new channel has an additional cost compared to adding
liquidity to an existing channel: the channel will be closed in the
future, which will require paying on-chain fees. Node operators can
include a `channel-creation-fee-satoshis` in their liquidity ads to
cover some of that future cost.

* Add liquidity purchases to the `AuditDb`

Whenever liquidity is purchased, we store it in the `AuditDb`. This lets
node operators gather useful statistics on their peers, and which ones
are actively using the liquidity that is purchased.

We store minimal information about the liquidity ads itself to be more
easily compatible with potential changes in the spec.

docs/release-notes/eclair-vnext.md

@@ -4,6 +4,15 @@
 
 ## Major changes
 
+### Liquidity Ads
+
+This release includes an early prototype for [liquidity ads](https://github.com/lightning/bolts/pull/1153).
+Liquidity ads allow nodes to sell their liquidity in a trustless and decentralized manner.
+Every node advertizes the rates at which they sell their liquidity, and buyers connect to sellers that offer interesting rates.
+
+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.
+
 ### Update minimal version of Bitcoin Core
 
 With this release, eclair requires using Bitcoin Core 27.1.
@@ -28,6 +37,7 @@ Eclair will not allow remote peers to open new obsolete channels that do not sup
 
 - `channelstats` now takes optional parameters `--count` and `--skip` to control pagination. By default, it will return first 10 entries. (#2890)
 - `createinvoice` now takes an optional `--privateChannelIds` parameter that can be used to add routing hints through private channels. (#2909)
+- `nodes` allows filtering nodes that offer liquidity ads (#2848)
 
 ### Miscellaneous improvements and bug fixes
 

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

@@ -306,6 +306,40 @@ eclair {
     update-fee-min-diff-ratio = 0.1
   }
 
+  // Liquidity Ads allow remote nodes to pay us to provide them with inbound liquidity.
+  liquidity-ads {
+    // Multiple funding rates can be provided, for different funding amounts.
+    funding-rates = []
+    // Sample funding rates:
+    // funding-rates = [
+    //   {
+    //     min-funding-amount-satoshis = 100000 // minimum funding amount at this rate
+    //     max-funding-amount-satoshis = 500000 // maximum funding amount at this rate
+    //     // The seller can ask the buyer to pay for some of the weight of the funding transaction (for the inputs and
+    //     // outputs added by the seller). This field contains the transaction weight (in vbytes) that the seller asks the
+    //     // buyer to pay for. The default value matches the weight of one p2wpkh input with one p2wpkh change output.
+    //     funding-weight = 400
+    //     fee-base-satoshis = 500 // flat fee that we will receive every time we accept a liquidity request
+    //     fee-basis-points = 250 // proportional fee based on the amount requested by our peer (2.5%)
+    //     channel-creation-fee-satoshis = 2500 // flat fee that is added when creating a new channel
+    //   },
+    //   {
+    //     min-funding-amount-satoshis = 500000
+    //     max-funding-amount-satoshis = 5000000
+    //     funding-weight = 750
+    //     fee-base-satoshis = 1000
+    //     fee-basis-points = 200 // 2%
+    //     channel-creation-fee-satoshis = 2000
+    //   }
+    // ]
+    // Multiple ways of paying the liquidity fees can be provided.
+    payment-types = [
+      // Liquidity fees must be paid from the buyer's channel balance during the transaction creation.
+      // This doesn't involve trust from the buyer or the seller.
+      "from_channel_balance"
+    ]
+  }
+
   peer-connection {
     auth-timeout = 15 seconds // will disconnect if connection authentication doesn't happen within that timeframe
     init-timeout = 15 seconds // will disconnect if initialization doesn't happen within that timeframe

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

@@ -220,6 +220,7 @@ class EclairImpl(appKit: Kit) extends Eclair with Logging {
         pushAmount_opt = pushAmount_opt,
         fundingTxFeerate_opt = fundingFeerate_opt.map(FeeratePerKw(_)),
         fundingTxFeeBudget_opt = Some(fundingFeeBudget),
+        requestFunding_opt = None,
         channelFlags_opt = announceChannel_opt.map(announceChannel => ChannelFlags(announceChannel = announceChannel)),
         timeout_opt = Some(openTimeout))
       res <- (appKit.switchboard ? open).mapTo[OpenChannelResponse]
@@ -228,14 +229,15 @@ 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)))
+      cmdBuilder = CMD_BUMP_FUNDING_FEE(_, targetFeerate, fundingFeeBudget, lockTime_opt.getOrElse(appKit.nodeParams.currentBlockHeight.toLong), requestFunding_opt = None))
   }
 
   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
+        spliceOut_opt = None,
+        requestFunding_opt = None,
       ))
   }
 
@@ -250,7 +252,8 @@ class EclairImpl(appKit: Kit) extends Eclair with Logging {
     sendToChannelTyped(channel = Left(channelId),
       cmdBuilder = CMD_SPLICE(_,
         spliceIn_opt = None,
-        spliceOut_opt = Some(SpliceOut(amount = amountOut, scriptPubKey = script))
+        spliceOut_opt = Some(SpliceOut(amount = amountOut, scriptPubKey = script)),
+        requestFunding_opt = None,
       ))
   }
 

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

@@ -18,7 +18,7 @@ package fr.acinq.eclair
 
 import com.typesafe.config.{Config, ConfigFactory, ConfigValueType}
 import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
-import fr.acinq.bitcoin.scalacompat.{Block, BlockHash, Crypto, Satoshi}
+import fr.acinq.bitcoin.scalacompat.{Block, BlockHash, Crypto, Satoshi, SatoshiLong}
 import fr.acinq.eclair.Setup.Seeds
 import fr.acinq.eclair.blockchain.fee._
 import fr.acinq.eclair.channel.ChannelFlags
@@ -88,6 +88,7 @@ case class NodeParams(nodeKeyManager: NodeKeyManager,
                       onionMessageConfig: OnionMessageConfig,
                       purgeInvoicesInterval: Option[FiniteDuration],
                       revokedHtlcInfoCleanerConfig: RevokedHtlcInfoCleaner.Config,
+                      willFundRates_opt: Option[LiquidityAds.WillFundRates],
                       peerWakeUpConfig: PeerReadyNotifier.WakeUpConfig) {
   val privateKey: Crypto.PrivateKey = nodeKeyManager.nodeKey.privateKey
 
@@ -479,6 +480,33 @@ 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 willFundRates_opt = {
+      val supportedPaymentTypes = Map(
+        LiquidityAds.PaymentType.FromChannelBalance.rfcName -> LiquidityAds.PaymentType.FromChannelBalance
+      )
+      val paymentTypes: Set[LiquidityAds.PaymentType] = config.getStringList("liquidity-ads.payment-types").asScala.map(s => {
+        supportedPaymentTypes.get(s) match {
+          case Some(paymentType) => paymentType
+          case None => throw new IllegalArgumentException(s"unknown liquidity ads payment type: $s")
+        }
+      }).toSet
+      val fundingRates: List[LiquidityAds.FundingRate] = config.getConfigList("liquidity-ads.funding-rates").asScala.map { r =>
+        LiquidityAds.FundingRate(
+          minAmount = r.getLong("min-funding-amount-satoshis").sat,
+          maxAmount = r.getLong("max-funding-amount-satoshis").sat,
+          fundingWeight = r.getInt("funding-weight"),
+          feeBase = r.getLong("fee-base-satoshis").sat,
+          feeProportional = r.getInt("fee-basis-points"),
+          channelCreationFee = r.getLong("channel-creation-fee-satoshis").sat,
+        )
+      }.toList
+      if (fundingRates.nonEmpty && paymentTypes.nonEmpty) {
+        Some(LiquidityAds.WillFundRates(fundingRates, paymentTypes))
+      } else {
+        None
+      }
+    }
+
     NodeParams(
       nodeKeyManager = nodeKeyManager,
       channelKeyManager = channelKeyManager,
@@ -615,6 +643,7 @@ object NodeParams extends Logging {
         batchSize = config.getInt("db.revoked-htlc-info-cleaner.batch-size"),
         interval = FiniteDuration(config.getDuration("db.revoked-htlc-info-cleaner.interval").getSeconds, TimeUnit.SECONDS)
       ),
+      willFundRates_opt = willFundRates_opt,
       peerWakeUpConfig = PeerReadyNotifier.WakeUpConfig(
         enabled = config.getBoolean("peer-wake-up.enabled"),
         timeout = FiniteDuration(config.getDuration("peer-wake-up.timeout").getSeconds, TimeUnit.SECONDS)

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

@@ -22,7 +22,7 @@ import fr.acinq.bitcoin.scalacompat.{ByteVector32, Satoshi}
 import fr.acinq.eclair.channel.Origin
 import fr.acinq.eclair.io.OpenChannelInterceptor.{DefaultParams, OpenChannelNonInitiator}
 import fr.acinq.eclair.payment.relay.PostRestartHtlcCleaner.IncomingHtlc
-import fr.acinq.eclair.wire.protocol.Error
+import fr.acinq.eclair.wire.protocol.{Error, LiquidityAds}
 
 /** Custom plugin parameters. */
 trait PluginParams {
@@ -67,7 +67,7 @@ case class InterceptOpenChannelReceived(replyTo: ActorRef[InterceptOpenChannelRe
 }
 
 sealed trait InterceptOpenChannelResponse
-case class AcceptOpenChannel(temporaryChannelId: ByteVector32, defaultParams: DefaultParams, localFundingAmount_opt: Option[Satoshi]) extends InterceptOpenChannelResponse
+case class AcceptOpenChannel(temporaryChannelId: ByteVector32, defaultParams: DefaultParams, addFunding_opt: Option[LiquidityAds.AddFunding]) extends InterceptOpenChannelResponse
 case class RejectOpenChannel(temporaryChannelId: ByteVector32, error: Error) extends InterceptOpenChannelResponse
 // @formatter:on
 

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, OnionRoutingPacket, OpenChannel, OpenDualFundedChannel, Shutdown, SpliceInit, Stfu, TxSignatures, UpdateAddHtlc, UpdateFailHtlc, UpdateFailMalformedHtlc, UpdateFulfillHtlc}
+import fr.acinq.eclair.wire.protocol.{ChannelAnnouncement, ChannelReady, ChannelReestablish, ChannelUpdate, ClosingSigned, CommitSig, FailureMessage, FundingCreated, FundingSigned, Init, LiquidityAds, OnionRoutingPacket, OpenChannel, OpenDualFundedChannel, Shutdown, SpliceInit, Stfu, TxSignatures, UpdateAddHtlc, UpdateFailHtlc, UpdateFailMalformedHtlc, UpdateFulfillHtlc}
 import fr.acinq.eclair.{Alias, BlockHeight, CltvExpiry, CltvExpiryDelta, Features, InitFeature, MilliSatoshi, MilliSatoshiLong, RealShortChannelId, TimestampMilli, UInt64}
 import scodec.bits.ByteVector
 
@@ -98,6 +98,7 @@ case class INPUT_INIT_CHANNEL_INITIATOR(temporaryChannelId: ByteVector32,
                                         fundingTxFeeBudget_opt: Option[Satoshi],
                                         pushAmount_opt: Option[MilliSatoshi],
                                         requireConfirmedInputs: Boolean,
+                                        requestFunding_opt: Option[LiquidityAds.RequestFunding],
                                         localParams: LocalParams,
                                         remote: ActorRef,
                                         remoteInit: Init,
@@ -109,7 +110,7 @@ case class INPUT_INIT_CHANNEL_INITIATOR(temporaryChannelId: ByteVector32,
   require(!(channelType.features.contains(Features.ScidAlias) && channelFlags.announceChannel), "option_scid_alias is not compatible with public channels")
 }
 case class INPUT_INIT_CHANNEL_NON_INITIATOR(temporaryChannelId: ByteVector32,
-                                            fundingContribution_opt: Option[Satoshi],
+                                            fundingContribution_opt: Option[LiquidityAds.AddFunding],
                                             dualFunded: Boolean,
                                             pushAmount_opt: Option[MilliSatoshi],
                                             localParams: LocalParams,
@@ -214,10 +215,10 @@ final case class CMD_CLOSE(replyTo: ActorRef, scriptPubKey: Option[ByteVector],
 final case class CMD_FORCECLOSE(replyTo: ActorRef) extends CloseCommand
 final case class CMD_BUMP_FORCE_CLOSE_FEE(replyTo: akka.actor.typed.ActorRef[CommandResponse[CMD_BUMP_FORCE_CLOSE_FEE]], confirmationTarget: ConfirmationTarget) extends Command
 
-final case class CMD_BUMP_FUNDING_FEE(replyTo: akka.actor.typed.ActorRef[CommandResponse[CMD_BUMP_FUNDING_FEE]], targetFeerate: FeeratePerKw, fundingFeeBudget: Satoshi, lockTime: Long) extends Command
+final case class CMD_BUMP_FUNDING_FEE(replyTo: akka.actor.typed.ActorRef[CommandResponse[CMD_BUMP_FUNDING_FEE]], targetFeerate: FeeratePerKw, fundingFeeBudget: Satoshi, lockTime: Long, requestFunding_opt: Option[LiquidityAds.RequestFunding]) extends Command
 case class SpliceIn(additionalLocalFunding: Satoshi, pushAmount: MilliSatoshi = 0 msat)
 case class SpliceOut(amount: Satoshi, scriptPubKey: ByteVector)
-final case class CMD_SPLICE(replyTo: akka.actor.typed.ActorRef[CommandResponse[CMD_SPLICE]], spliceIn_opt: Option[SpliceIn], spliceOut_opt: Option[SpliceOut]) extends Command {
+final case class CMD_SPLICE(replyTo: akka.actor.typed.ActorRef[CommandResponse[CMD_SPLICE]], spliceIn_opt: Option[SpliceIn], spliceOut_opt: Option[SpliceOut], requestFunding_opt: Option[LiquidityAds.RequestFunding]) extends Command {
   require(spliceIn_opt.isDefined || spliceOut_opt.isDefined, "there must be a splice-in or a splice-out")
   val additionalLocalFunding: Satoshi = spliceIn_opt.map(_.additionalLocalFunding).getOrElse(0 sat)
   val pushAmount: MilliSatoshi = spliceIn_opt.map(_.pushAmount).getOrElse(0 msat)

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

@@ -18,12 +18,11 @@ package fr.acinq.eclair.channel
 
 import akka.actor.ActorRef
 import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
-import fr.acinq.bitcoin.scalacompat.{ByteVector32, Satoshi, Transaction}
+import fr.acinq.bitcoin.scalacompat.{ByteVector32, Satoshi, Transaction, TxId}
 import fr.acinq.eclair.blockchain.fee.FeeratePerKw
 import fr.acinq.eclair.channel.Helpers.Closing.ClosingType
-import fr.acinq.eclair.io.Peer.OpenChannelResponse
-import fr.acinq.eclair.wire.protocol.{ChannelAnnouncement, ChannelUpdate}
-import fr.acinq.eclair.{BlockHeight, Features, ShortChannelId}
+import fr.acinq.eclair.wire.protocol.{ChannelAnnouncement, ChannelUpdate, LiquidityAds}
+import fr.acinq.eclair.{BlockHeight, Features, MilliSatoshi, ShortChannelId}
 
 /**
  * Created by PM on 17/08/2016.
@@ -79,6 +78,14 @@ case class ChannelSignatureSent(channel: ActorRef, commitments: Commitments) ext
 
 case class ChannelSignatureReceived(channel: ActorRef, commitments: Commitments) extends ChannelEvent
 
+case class LiquidityPurchase(fundingTxId: TxId, fundingTxIndex: Long, isBuyer: Boolean, amount: Satoshi, fees: LiquidityAds.Fees, capacity: Satoshi, localContribution: Satoshi, remoteContribution: Satoshi, localBalance: MilliSatoshi, remoteBalance: MilliSatoshi, outgoingHtlcCount: Long, incomingHtlcCount: Long) {
+  val previousCapacity: Satoshi = capacity - localContribution - remoteContribution
+  val previousLocalBalance: MilliSatoshi = if (isBuyer) localBalance - localContribution + fees.total else localBalance - localContribution - fees.total
+  val previousRemoteBalance: MilliSatoshi = if (isBuyer) remoteBalance - remoteContribution - fees.total else remoteBalance - remoteContribution + fees.total
+}
+
+case class ChannelLiquidityPurchased(channel: ActorRef, channelId: ByteVector32, remoteNodeId: PublicKey, purchase: LiquidityPurchase) extends ChannelEvent
+
 case class ChannelErrorOccurred(channel: ActorRef, channelId: ByteVector32, remoteNodeId: PublicKey, error: ChannelError, isFatal: Boolean) extends ChannelEvent
 
 // NB: the fee should be set to 0 when we're not paying it.

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

@@ -19,7 +19,7 @@ package fr.acinq.eclair.channel
 import fr.acinq.bitcoin.scalacompat.{BlockHash, ByteVector32, Satoshi, Transaction, TxId}
 import fr.acinq.eclair.blockchain.fee.FeeratePerKw
 import fr.acinq.eclair.wire.protocol
-import fr.acinq.eclair.wire.protocol.{AnnouncementSignatures, InteractiveTxMessage, UpdateAddHtlc}
+import fr.acinq.eclair.wire.protocol.{AnnouncementSignatures, InteractiveTxMessage, LiquidityAds, UpdateAddHtlc}
 import fr.acinq.eclair.{BlockHeight, CltvExpiry, CltvExpiryDelta, MilliSatoshi, UInt64}
 import scodec.bits.ByteVector
 
@@ -51,6 +51,11 @@ case class ToSelfDelayTooHigh                      (override val channelId: Byte
 case class ChannelReserveTooHigh                   (override val channelId: ByteVector32, channelReserve: Satoshi, reserveToFundingRatio: Double, maxReserveToFundingRatio: Double) extends ChannelException(channelId, s"channelReserve too high: reserve=$channelReserve fundingRatio=$reserveToFundingRatio maxFundingRatio=$maxReserveToFundingRatio")
 case class ChannelReserveBelowOurDustLimit         (override val channelId: ByteVector32, channelReserve: Satoshi, dustLimit: Satoshi) extends ChannelException(channelId, s"their channelReserve=$channelReserve is below our dustLimit=$dustLimit")
 case class ChannelReserveNotMet                    (override val channelId: ByteVector32, toLocal: MilliSatoshi, toRemote: MilliSatoshi, reserve: Satoshi) extends ChannelException(channelId, s"channel reserve is not met toLocal=$toLocal toRemote=$toRemote reserve=$reserve")
+case class MissingLiquidityAds                     (override val channelId: ByteVector32) extends ChannelException(channelId, "liquidity ads field is missing")
+case class InvalidLiquidityAdsSig                  (override val channelId: ByteVector32) extends ChannelException(channelId, "liquidity ads signature is invalid")
+case class InvalidLiquidityAdsAmount               (override val channelId: ByteVector32, proposed: Satoshi, min: Satoshi) extends ChannelException(channelId, s"liquidity ads funding amount is too low (expected at least $min, got $proposed)")
+case class InvalidLiquidityAdsPaymentType          (override val channelId: ByteVector32, proposed: LiquidityAds.PaymentType, allowed: Set[LiquidityAds.PaymentType]) extends ChannelException(channelId, s"liquidity ads ${proposed.rfcName} payment type is not supported (allowed=${allowed.map(_.rfcName).mkString(", ")})")
+case class InvalidLiquidityAdsRate                 (override val channelId: ByteVector32) extends ChannelException(channelId, "liquidity ads funding rates don't match")
 case class ChannelFundingError                     (override val channelId: ByteVector32) extends ChannelException(channelId, "channel funding error")
 case class InvalidFundingTx                        (override val channelId: ByteVector32) extends ChannelException(channelId, "invalid funding tx")
 case class InvalidSerialId                         (override val channelId: ByteVector32, serialId: UInt64) extends ChannelException(channelId, s"invalid serial_id=${serialId.toByteVector.toHex}")