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.

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.
@@ -27,6 +36,7 @@ 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)
+- `nodes` allows filtering nodes that offer liquidity ads (#2848)
 
 ### Miscellaneous improvements and bug fixes
 

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

@@ -306,6 +306,38 @@ 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%)
+    //   },
+    //   {
+    //     min-funding-amount-satoshis = 500000
+    //     max-funding-amount-satoshis = 5000000
+    //     funding-weight = 750
+    //     fee-base-satoshis = 1000
+    //     fee-basis-points = 200 // 2%
+    //   }
+    // ]
+    // 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],
                       wakeUpTimeout: FiniteDuration) {
   val privateKey: Crypto.PrivateKey = nodeKeyManager.nodeKey.privateKey
 
@@ -477,6 +478,32 @@ 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")
+        )
+      }.toList
+      if (fundingRates.nonEmpty && paymentTypes.nonEmpty) {
+        Some(LiquidityAds.WillFundRates(fundingRates, paymentTypes))
+      } else {
+        None
+      }
+    }
+
     NodeParams(
       nodeKeyManager = nodeKeyManager,
       channelKeyManager = channelKeyManager,
@@ -613,6 +640,7 @@ 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,
       wakeUpTimeout = 30 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/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 selected rate does not match a rate we offer")
 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}")