Increase channel spent delay to 72 blocks (#3110)

We previously waited for 12 blocks before removing spent channels from
our graph: the spec updates this delay to 72 blocks to allow more time
for splice announcement in lightning/bolts#1270.

We also make this configurable, which can simplify testing and allows
nodes to wait even longer if they wish.

Author: t-bast

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

@@ -415,6 +415,9 @@ eclair {
 
   router {
     watch-spent-window = 60 minutes // at startup watches on public channels will be put back within that window to reduce herd effect; must be > 0s
+    // when we detect that a remote channel has been spent on-chain, we wait for 72 blocks before removing it from the graph
+    // if this was a splice instead of a close, we will be able to simply update the channel in our graph and keep its reputation
+    channel-spent-splice-delay = 72
 
     channel-exclude-duration = 60 seconds // when a temporary channel failure is returned, we exclude the channel from our payment routes for this duration
     broadcast-interval = 60 seconds // see BOLT #7

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

@@ -664,6 +664,7 @@ object NodeParams extends Logging {
       ),
       routerConf = RouterConf(
         watchSpentWindow = watchSpentWindow,
+        channelSpentSpliceDelay = config.getInt("router.channel-spent-splice-delay"),
         channelExcludeDuration = FiniteDuration(config.getDuration("router.channel-exclude-duration").getSeconds, TimeUnit.SECONDS),
         routerBroadcastInterval = FiniteDuration(config.getDuration("router.broadcast-interval").getSeconds, TimeUnit.SECONDS),
         syncConf = Router.SyncConf(

eclair-core/src/main/scala/fr/acinq/eclair/remote/EclairInternalsSerializer.scala

@@ -109,6 +109,7 @@ object EclairInternalsSerializer {
 
   val routerConfCodec: Codec[RouterConf] = (
     ("watchSpentWindow" | finiteDurationCodec) ::
+      ("channelSpentSpliceDelay" | int32) ::
       ("channelExcludeDuration" | finiteDurationCodec) ::
       ("routerBroadcastInterval" | finiteDurationCodec) ::
       ("syncConf" | syncConfCodec) ::

eclair-core/src/main/scala/fr/acinq/eclair/router/Router.scala

@@ -266,7 +266,7 @@ class Router(val nodeParams: NodeParams, watcher: typed.ActorRef[ZmqWatcher.Comm
     case Event(WatchExternalChannelSpentTriggered(shortChannelId, spendingTx), d) if d.channels.contains(shortChannelId) || d.prunedChannels.contains(shortChannelId) =>
       val fundingTxId = d.channels.get(shortChannelId).orElse(d.prunedChannels.get(shortChannelId)).get.fundingTxId
       log.info("funding tx txId={} of channelId={} has been spent by txId={}: waiting for the spending tx to have enough confirmations before removing the channel from the graph", fundingTxId, shortChannelId, spendingTx.txid)
-      watcher ! WatchTxConfirmed(self, spendingTx.txid, ANNOUNCEMENTS_MINCONF * 2)
+      watcher ! WatchTxConfirmed(self, spendingTx.txid, nodeParams.routerConf.channelSpentSpliceDelay)
       stay() using d.copy(spentChannels = d.spentChannels.updated(spendingTx.txid, d.spentChannels.getOrElse(spendingTx.txid, Set.empty) + shortChannelId))
 
     case Event(WatchTxConfirmedTriggered(_, _, spendingTx), d) =>
@@ -345,9 +345,6 @@ class Router(val nodeParams: NodeParams, watcher: typed.ActorRef[ZmqWatcher.Comm
 
 object Router {
 
-  // see https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md#requirements
-  val ANNOUNCEMENTS_MINCONF = 6
-
   def props(nodeParams: NodeParams, watcher: typed.ActorRef[ZmqWatcher.Command], initialized: Option[Promise[Done]] = None) = Props(new Router(nodeParams, watcher, initialized))
 
   case class SearchBoundaries(maxFeeFlat: MilliSatoshi,
@@ -382,6 +379,7 @@ object Router {
   }
 
   case class RouterConf(watchSpentWindow: FiniteDuration,
+                        channelSpentSpliceDelay: Int,
                         channelExcludeDuration: FiniteDuration,
                         routerBroadcastInterval: FiniteDuration,
                         syncConf: SyncConf,

eclair-core/src/test/scala/fr/acinq/eclair/TestConstants.scala

@@ -200,6 +200,7 @@ object TestConstants {
       ),
       routerConf = RouterConf(
         watchSpentWindow = 1 second,
+        channelSpentSpliceDelay = 12,
         channelExcludeDuration = 60 seconds,
         routerBroadcastInterval = 1 day, // "disables" rebroadcast
         syncConf = Router.SyncConf(
@@ -389,6 +390,7 @@ object TestConstants {
       ),
       routerConf = RouterConf(
         watchSpentWindow = 1 second,
+        channelSpentSpliceDelay = 12,
         channelExcludeDuration = 60 seconds,
         routerBroadcastInterval = 1 day, // "disables" rebroadcast
         syncConf = Router.SyncConf(

eclair-core/src/test/scala/fr/acinq/eclair/integration/IntegrationSpec.scala

@@ -85,6 +85,7 @@ abstract class IntegrationSpec extends TestKitBaseClass with BitcoindService wit
     "eclair.channel.max-htlc-value-in-flight-percent" -> 100,
     "eclair.channel.max-block-processing-delay" -> "2 seconds",
     "eclair.channel.to-remote-delay-blocks" -> 24,
+    "eclair.router.channel-spent-splice-delay" -> 12,
     "eclair.router.broadcast-interval" -> "2 seconds",
     "eclair.auto-reconnect" -> false,
     "eclair.multi-part-payment-expiry" -> "20 seconds",