Add recommended_feerates optional message

We send to our peers an optional message that tells them the feerates
we'd like to use for funding channels. This lets them know which values
are acceptable to us, in case we reject their funding requests.

This is using an odd type and will be automatically ignored by existing
nodes who don't support that feature.

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

@@ -21,9 +21,9 @@ import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
 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
 import fr.acinq.eclair.channel.fsm.Channel
 import fr.acinq.eclair.channel.fsm.Channel.{BalanceThreshold, ChannelConf, UnhandledExceptionStrategy}
+import fr.acinq.eclair.channel.{ChannelFlags, ChannelTypes}
 import fr.acinq.eclair.crypto.Noise.KeyPair
 import fr.acinq.eclair.crypto.keymanager.{ChannelKeyManager, NodeKeyManager, OnChainKeyManager}
 import fr.acinq.eclair.db._
@@ -109,6 +109,15 @@ case class NodeParams(nodeKeyManager: NodeKeyManager,
 
   /** Returns the features that should be used in our init message with the given peer. */
   def initFeaturesFor(nodeId: PublicKey): Features[InitFeature] = overrideInitFeatures.getOrElse(nodeId, features).initFeatures()
+
+  /** Returns the feerates we'd like our peer to use when funding channels. */
+  def recommendedFeerates(remoteNodeId: PublicKey, currentFeerates: FeeratesPerKw, localFeatures: Features[InitFeature], remoteFeatures: Features[InitFeature]): RecommendedFeerates = {
+    val fundingFeerate = onChainFeeConf.getFundingFeerate(currentFeerates)
+    // We use the most likely commitment format, even though there is no guarantee that this is the one that will be used.
+    val commitmentFormat = ChannelTypes.defaultFromFeatures(localFeatures, remoteFeatures, announceChannel = false).commitmentFormat
+    val commitmentFeerate = onChainFeeConf.getCommitmentFeerate(currentFeerates, remoteNodeId, commitmentFormat, channelConf.minFundingPrivateSatoshis)
+    RecommendedFeerates(chainHash, fundingFeerate, commitmentFeerate)
+  }
 }
 
 case class PaymentFinalExpiryConf(min: CltvExpiryDelta, max: CltvExpiryDelta) {

eclair-core/src/main/scala/fr/acinq/eclair/io/Peer.scala

@@ -29,7 +29,7 @@ import fr.acinq.eclair.NotificationsLogger.NotifyNodeOperator
 import fr.acinq.eclair._
 import fr.acinq.eclair.blockchain.bitcoind.ZmqWatcher
 import fr.acinq.eclair.blockchain.fee.FeeratePerKw
-import fr.acinq.eclair.blockchain.{OnChainChannelFunder, OnchainPubkeyCache}
+import fr.acinq.eclair.blockchain.{CurrentFeerates, OnChainChannelFunder, OnchainPubkeyCache}
 import fr.acinq.eclair.channel._
 import fr.acinq.eclair.channel.fsm.Channel
 import fr.acinq.eclair.io.MessageRelay.Status
@@ -63,6 +63,8 @@ class Peer(val nodeParams: NodeParams,
 
   import Peer._
 
+  context.system.eventStream.subscribe(self, classOf[CurrentFeerates])
+
   startWith(INSTANTIATING, Nothing)
 
   when(INSTANTIATING) {
@@ -344,6 +346,13 @@ class Peer(val nodeParams: NodeParams,
       }
       stay()
 
+    case Event(current: CurrentFeerates, d) =>
+      d match {
+        case d: ConnectedData => d.peerConnection ! nodeParams.recommendedFeerates(remoteNodeId, current.feeratesPerKw, d.localFeatures, d.remoteFeatures)
+        case _ => ()
+      }
+      stay()
+
     case Event(_: Peer.OutgoingMessage, _) => stay() // we got disconnected or reconnected and this message was for the previous connection
 
     case Event(RelayOnionMessage(messageId, _, replyTo_opt), _) =>
@@ -388,6 +397,9 @@ class Peer(val nodeParams: NodeParams,
     // let's bring existing/requested channels online
     channels.values.toSet[ActorRef].foreach(_ ! INPUT_RECONNECTED(connectionReady.peerConnection, connectionReady.localInit, connectionReady.remoteInit)) // we deduplicate with toSet because there might be two entries per channel (tmp id and final id)
 
+    // We tell our peer what our current feerates are.
+    connectionReady.peerConnection ! nodeParams.recommendedFeerates(remoteNodeId, nodeParams.currentFeerates, connectionReady.localInit.features, connectionReady.remoteInit.features)
+
     goto(CONNECTED) using ConnectedData(connectionReady.address, connectionReady.peerConnection, connectionReady.localInit, connectionReady.remoteInit, channels)
   }
 

eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecs.scala

@@ -429,6 +429,11 @@ object LightningMessageCodecs {
 
   //
 
+  val recommendedFeeratesCodec: Codec[RecommendedFeerates] = (
+    ("chainHash" | blockHash) ::
+      ("fundingFeerate" | feeratePerKw) ::
+      ("commitmentFeerate" | feeratePerKw)).as[RecommendedFeerates]
+
   val unknownMessageCodec: Codec[UnknownMessage] = (
     ("tag" | uint16) ::
       ("message" | bytes)
@@ -479,6 +484,8 @@ object LightningMessageCodecs {
     .typecase(513, onionMessageCodec)
     // NB: blank lines to minimize merge conflicts
 
+    //
+    .typecase(35025, recommendedFeeratesCodec)
     //
     .typecase(37000, spliceInitCodec)
     .typecase(37002, spliceAckCodec)

eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageTypes.scala

@@ -604,4 +604,10 @@ case class OnionMessage(blindingKey: PublicKey, onionRoutingPacket: OnionRouting
 
 //
 
+/**
+ * This message informs our peers of the feerates we recommend using.
+ * We may reject funding attempts that use values that are too far from our recommended feerates.
+ */
+case class RecommendedFeerates(chainHash: BlockHash, fundingFeerate: FeeratePerKw, commitmentFeerate: FeeratePerKw) extends SetupMessage with HasChainHash
+
 case class UnknownMessage(tag: Int, data: ByteVector) extends LightningMessage

eclair-core/src/test/scala/fr/acinq/eclair/io/PeerSpec.scala

@@ -25,8 +25,8 @@ import fr.acinq.eclair.FeatureSupport.{Mandatory, Optional}
 import fr.acinq.eclair.Features._
 import fr.acinq.eclair.TestConstants._
 import fr.acinq.eclair._
-import fr.acinq.eclair.blockchain.DummyOnChainWallet
 import fr.acinq.eclair.blockchain.fee.{FeeratePerKw, FeeratesPerKw}
+import fr.acinq.eclair.blockchain.{CurrentFeerates, DummyOnChainWallet}
 import fr.acinq.eclair.channel._
 import fr.acinq.eclair.channel.states.ChannelStateTestsTags
 import fr.acinq.eclair.io.Peer._
@@ -112,6 +112,7 @@ class PeerSpec extends FixtureSpec {
     switchboard.send(peer, Peer.Init(channels))
     val localInit = protocol.Init(peer.underlyingActor.nodeParams.features.initFeatures())
     switchboard.send(peer, PeerConnection.ConnectionReady(peerConnection.ref, remoteNodeId, fakeIPAddress, outgoing = true, localInit, remoteInit))
+    peerConnection.expectMsgType[RecommendedFeerates]
     val probe = TestProbe()
     probe.send(peer, Peer.GetPeerInfo(Some(probe.ref.toTyped)))
     val peerInfo = probe.expectMsgType[Peer.PeerInfo]
@@ -282,6 +283,7 @@ class PeerSpec extends FixtureSpec {
     }
 
     peerConnection2.send(peer, PeerConnection.ConnectionReady(peerConnection2.ref, remoteNodeId, fakeIPAddress, outgoing = false, localInit, remoteInit))
+    peerConnection2.expectMsgType[RecommendedFeerates]
     // peer should kill previous connection
     peerConnection1.expectMsg(PeerConnection.Kill(PeerConnection.KillReason.ConnectionReplaced))
     channel.expectMsg(INPUT_DISCONNECTED)
@@ -291,6 +293,7 @@ class PeerSpec extends FixtureSpec {
     }
 
     peerConnection3.send(peer, PeerConnection.ConnectionReady(peerConnection3.ref, remoteNodeId, fakeIPAddress, outgoing = false, localInit, remoteInit))
+    peerConnection3.expectMsgType[RecommendedFeerates]
     // peer should kill previous connection
     peerConnection2.expectMsg(PeerConnection.Kill(PeerConnection.KillReason.ConnectionReplaced))
     channel.expectMsg(INPUT_DISCONNECTED)
@@ -325,6 +328,16 @@ class PeerSpec extends FixtureSpec {
     monitor.expectMsg(FSM.Transition(reconnectionTask, ReconnectionTask.CONNECTING, ReconnectionTask.IDLE))
   }
 
+  test("send recommended feerates when feerate changes") { f =>
+    import f._
+
+    connect(remoteNodeId, peer, peerConnection, switchboard, channels = Set(ChannelCodecsSpec.normal))
+
+    // We regularly update our internal feerates.
+    peer ! CurrentFeerates(FeeratesPerKw(FeeratePerKw(253 sat), FeeratePerKw(1000 sat), FeeratePerKw(2500 sat), FeeratePerKw(5000 sat), FeeratePerKw(10_000 sat)))
+    peerConnection.expectMsg(RecommendedFeerates(Block.RegtestGenesisBlock.hash, FeeratePerKw(2500 sat), FeeratePerKw(5000 sat)))
+  }
+
   test("don't spawn a channel with duplicate temporary channel id") { f =>
     import f._
 

eclair-core/src/test/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecsSpec.scala

@@ -488,6 +488,19 @@ class LightningMessageCodecsSpec extends AnyFunSuite {
     }
   }
 
+  test("encode/decode recommended_feerates") {
+    val testCases = Seq(
+      RecommendedFeerates(Block.TestnetGenesisBlock.hash, FeeratePerKw(2500 sat), FeeratePerKw(2500 sat)) -> hex"88d1 43497fd7f826957108f4a30fd9cec3aeba79972084e90ead01ea330900000000 000009c4 000009c4",
+      RecommendedFeerates(Block.TestnetGenesisBlock.hash, FeeratePerKw(5000 sat), FeeratePerKw(253 sat)) -> hex"88d1 43497fd7f826957108f4a30fd9cec3aeba79972084e90ead01ea330900000000 00001388 000000fd",
+    )
+    for ((expected, encoded) <- testCases) {
+      val decoded = lightningMessageCodec.decode(encoded.bits).require.value
+      assert(decoded == expected)
+      val reEncoded = lightningMessageCodec.encode(decoded).require.bytes
+      assert(reEncoded == encoded)
+    }
+  }
+
   test("unknown messages") {
     // Non-standard tag number so this message can only be handled by a codec with a fallback
     val unknown = UnknownMessage(tag = 47282, data = ByteVector32.Zeroes.bytes)