Accept incoming liquidity requests

If liquidity ads is active (the node operator has set some funding
rates), we accept selling liquidity to whoever wants to purchase it.
This behavior can be customized by a dedicated liquidity plugin.

This is a work-in-progress: to protect against liquidity griefing, we
must ensure that utxos are never locked when funding transactions.

Author: t-bast

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

@@ -207,14 +207,14 @@ private class OpenChannelInterceptor(peer: ActorRef[Any],
     nodeParams.pluginOpenChannelInterceptor match {
       case Some(plugin) => queryPlugin(plugin, request, localParams, ChannelConfig.standard, channelType)
       case None =>
+        val addFunding_opt = request.open.fold(_ => None, _.requestFunding_opt).map(requestFunding => LiquidityAds.AddFunding(requestFunding.requestedAmount, nodeParams.willFundRates_opt))
         request.open.fold(_ => None, _.requestFunding_opt) match {
           case Some(requestFunding) if Features.canUseFeature(request.localFeatures, request.remoteFeatures, Features.OnTheFlyFunding) && localParams.paysCommitTxFees =>
-            val addFunding = LiquidityAds.AddFunding(requestFunding.requestedAmount, nodeParams.willFundRates_opt)
-            val accept = SpawnChannelNonInitiator(request.open, ChannelConfig.standard, channelType, Some(addFunding), localParams, request.peerConnection.toClassic)
+            val accept = SpawnChannelNonInitiator(request.open, ChannelConfig.standard, channelType, addFunding_opt, localParams, request.peerConnection.toClassic)
             checkNoExistingChannel(request, accept)
           case _ =>
-            // We don't honor liquidity ads for new channels: node operators should use plugin for that.
-            peer ! SpawnChannelNonInitiator(request.open, ChannelConfig.standard, channelType, addFunding_opt = None, localParams, request.peerConnection.toClassic)
+            // TODO: we must change the utxo locking behavior before releasing that change to protect against liquidity griefing.
+            peer ! SpawnChannelNonInitiator(request.open, ChannelConfig.standard, channelType, addFunding_opt, localParams, request.peerConnection.toClassic)
             waitForRequest()
         }
     }