Use fallback feerates on testnets (#3233)

When using testnet3 or testnet4, Bitcoin Core may fail to estimate fees
because there isn't enough block data. We now use the configured default
feerates when that happens to make it easier to run on testnets.

We also update the default feerates to better match current values.

Fixes #3105

Author: t-bast

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

@@ -271,11 +271,11 @@ eclair {
     smoothing-window = 6 // 1 = no smoothing
 
     default-feerates { // the following values are in satoshis per byte
-      minimum = 5
-      slow = 5
-      medium = 10
-      fast = 20
-      fastest = 30
+      minimum = 1
+      slow = 2
+      medium = 5
+      fast = 10
+      fastest = 20
     }
 
     // confirmation priority for each transaction type, can be slow/medium/fast

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

@@ -22,7 +22,6 @@ import akka.actor.typed.scaladsl.adapter.{ClassicActorRefOps, ClassicActorSystem
 import akka.actor.{ActorRef, ActorSystem, Props, SupervisorStrategy, typed}
 import akka.pattern.after
 import akka.util.Timeout
-import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
 import fr.acinq.bitcoin.scalacompat.{Block, BlockHash, BlockId, ByteVector32, Satoshi, Script, ScriptElt, addressToPublicKeyScript}
 import fr.acinq.eclair.NodeParams.hashFromChain
 import fr.acinq.eclair.Setup.Seeds
@@ -250,7 +249,12 @@ class Setup(val datadir: File,
       feeProvider = nodeParams.chainHash match {
         case Block.RegtestGenesisBlock.hash | Block.SignetGenesisBlock.hash =>
           FallbackFeeProvider(ConstantFeeProvider(defaultFeerates) :: Nil, minFeeratePerByte)
+        case Block.Testnet3GenesisBlock.hash | Block.Testnet4GenesisBlock.hash =>
+          // On testnet, we fallback to default feerates when there aren't enough block data to estimate fees.
+          val smoothFeerateWindow = config.getInt("on-chain-fees.smoothing-window")
+          FallbackFeeProvider(SmoothFeeProvider(BitcoinCoreFeeProvider(bitcoin, defaultFeerates), smoothFeerateWindow) :: ConstantFeeProvider(defaultFeerates) :: Nil, minFeeratePerByte)
         case _ =>
+          // On mainnet, we always use blockchain data to estimate fees and ignore configured fallbacks.
           val smoothFeerateWindow = config.getInt("on-chain-fees.smoothing-window")
           FallbackFeeProvider(SmoothFeeProvider(BitcoinCoreFeeProvider(bitcoin, defaultFeerates), smoothFeerateWindow) :: Nil, minFeeratePerByte)
       }