From 8cc2e4afda3933d0123c04d388222c100c7e4630 Mon Sep 17 00:00:00 2001
From: Richard Myers <remyers@yakshaver.org>
Date: Tue, 27 Aug 2024 14:50:03 +0200
Subject: [PATCH] Add maxExcess_opt to ChannelParams in NodeParams

This will be used by non-initiators when funding dual funded channels and splicing
---
 eclair-core/src/main/resources/reference.conf               | 4 ++++
 eclair-core/src/main/scala/fr/acinq/eclair/NodeParams.scala | 5 ++++-
 .../main/scala/fr/acinq/eclair/channel/fsm/Channel.scala    | 3 ++-
 .../src/test/scala/fr/acinq/eclair/TestConstants.scala      | 6 ++++--
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/eclair-core/src/main/resources/reference.conf b/eclair-core/src/main/resources/reference.conf
index ca283b18b6..be0e6b722b 100644
--- a/eclair-core/src/main/resources/reference.conf
+++ b/eclair-core/src/main/resources/reference.conf
@@ -197,6 +197,10 @@ eclair {
 
       min-time-between-updates = 1 hour // minimum time between channel updates because the balance changed
     }
+
+    // if > 0, excess channel funding up to this amount will be added to the amount contributed when funding
+    // dual-funded channels or splices. This is useful to avoid paying fees to add a small change output.
+    max-excess = 0
   }
 
   balance-check-interval = 1 hour
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/NodeParams.scala b/eclair-core/src/main/scala/fr/acinq/eclair/NodeParams.scala
index 1c66625b53..68ef887768 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/NodeParams.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/NodeParams.scala
@@ -476,6 +476,8 @@ 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 maxExcess_opt = if (config.getInt("channel.max-excess") > 0) Some(Satoshi(config.getInt("channel.max-excess"))) else None
+
     NodeParams(
       nodeKeyManager = nodeKeyManager,
       channelKeyManager = channelKeyManager,
@@ -524,7 +526,8 @@ object NodeParams extends Logging {
         quiescenceTimeout = FiniteDuration(config.getDuration("channel.quiescence-timeout").getSeconds, TimeUnit.SECONDS),
         balanceThresholds = config.getConfigList("channel.channel-update.balance-thresholds").asScala.map(conf => BalanceThreshold(Satoshi(conf.getLong("available-sat")), Satoshi(conf.getLong("max-htlc-sat")))).toSeq,
         minTimeBetweenUpdates = FiniteDuration(config.getDuration("channel.channel-update.min-time-between-updates").getSeconds, TimeUnit.SECONDS),
-        acceptIncomingStaticRemoteKeyChannels = config.getBoolean("channel.accept-incoming-static-remote-key-channels")
+        acceptIncomingStaticRemoteKeyChannels = config.getBoolean("channel.accept-incoming-static-remote-key-channels"),
+        maxExcess_opt = maxExcess_opt,
       ),
       onChainFeeConf = OnChainFeeConf(
         feeTargets = feeTargets,
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/channel/fsm/Channel.scala b/eclair-core/src/main/scala/fr/acinq/eclair/channel/fsm/Channel.scala
index 757c804031..356415856b 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/channel/fsm/Channel.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/channel/fsm/Channel.scala
@@ -104,7 +104,8 @@ object Channel {
                          quiescenceTimeout: FiniteDuration,
                          balanceThresholds: Seq[BalanceThreshold],
                          minTimeBetweenUpdates: FiniteDuration,
-                         acceptIncomingStaticRemoteKeyChannels: Boolean) {
+                         acceptIncomingStaticRemoteKeyChannels: Boolean,
+                         maxExcess_opt: Option[Satoshi]) {
     require(0 <= maxHtlcValueInFlightPercent && maxHtlcValueInFlightPercent <= 100, "max-htlc-value-in-flight-percent must be between 0 and 100")
     require(balanceThresholds.sortBy(_.available) == balanceThresholds, "channel-update.balance-thresholds must be sorted by available-sat")
 
diff --git a/eclair-core/src/test/scala/fr/acinq/eclair/TestConstants.scala b/eclair-core/src/test/scala/fr/acinq/eclair/TestConstants.scala
index 6f520c1fb6..dde428f09c 100644
--- a/eclair-core/src/test/scala/fr/acinq/eclair/TestConstants.scala
+++ b/eclair-core/src/test/scala/fr/acinq/eclair/TestConstants.scala
@@ -144,7 +144,8 @@ object TestConstants {
         quiescenceTimeout = 2 minutes,
         balanceThresholds = Nil,
         minTimeBetweenUpdates = 0 hours,
-        acceptIncomingStaticRemoteKeyChannels = false
+        acceptIncomingStaticRemoteKeyChannels = false,
+        maxExcess_opt = None
       ),
       onChainFeeConf = OnChainFeeConf(
         feeTargets = FeeTargets(funding = ConfirmationPriority.Medium, closing = ConfirmationPriority.Medium),
@@ -316,7 +317,8 @@ object TestConstants {
         quiescenceTimeout = 2 minutes,
         balanceThresholds = Nil,
         minTimeBetweenUpdates = 0 hour,
-        acceptIncomingStaticRemoteKeyChannels = false
+        acceptIncomingStaticRemoteKeyChannels = false,
+        maxExcess_opt = None
       ),
       onChainFeeConf = OnChainFeeConf(
         feeTargets = FeeTargets(funding = ConfirmationPriority.Medium, closing = ConfirmationPriority.Medium),