Add a keep-alive mechanism (#550)

The goal is to make mobile apps (especially on iOS) more robust wrt to disconnections/app switching/background, etc. by signalling when they need a little bit more uptime to complete some tasks.
ACINQ · Nov 2, 2023 · 0c34d72 · 0c34d72
1 parent 56ade7e
commit 0c34d72
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diff --git a/src/commonMain/kotlin/fr/acinq/lightning/NodeEvents.kt b/src/commonMain/kotlin/fr/acinq/lightning/NodeEvents.kt
@@ -2,6 +2,8 @@ package fr.acinq.lightning
 
 import fr.acinq.bitcoin.ByteVector32
 import fr.acinq.bitcoin.Satoshi
+import fr.acinq.lightning.channel.InteractiveTxParams
+import fr.acinq.lightning.channel.SharedFundingInput
 import fr.acinq.lightning.channel.states.ChannelStateWithCommitments
 import fr.acinq.lightning.channel.states.Normal
 import fr.acinq.lightning.channel.states.WaitForFundingCreated
@@ -41,5 +43,17 @@ sealed interface LiquidityEvents : NodeEvents {
     data class ApprovalRequested(override val amount: MilliSatoshi, override val fee: MilliSatoshi, override val source: Source, val replyTo: CompletableDeferred<Boolean>) : LiquidityEvents
 }
 
+/** This is useful on iOS to ask the OS for time to finish some sensitive tasks. */
+sealed interface SensitiveTaskEvents : NodeEvents {
+    sealed class TaskIdentifier {
+        data class InteractiveTx(val channelId: ByteVector32, val fundingTxIndex: Long) : TaskIdentifier() {
+            constructor(fundingParams: InteractiveTxParams) : this(fundingParams.channelId, (fundingParams.sharedInput as? SharedFundingInput.Multisig2of2)?.fundingTxIndex?.let { it + 1 } ?: 0)
+        }
+    }
+    data class TaskStarted(val id: TaskIdentifier) : SensitiveTaskEvents
+    data class TaskEnded(val id: TaskIdentifier) : SensitiveTaskEvents
+
+}
+
 /** This will be emitted in a corner case where the user restores a wallet on an older version of the app, which is unable to read the channel data. */
 object UpgradeRequired : NodeEvents
diff --git a/src/commonMain/kotlin/fr/acinq/lightning/channel/states/Channel.kt b/src/commonMain/kotlin/fr/acinq/lightning/channel/states/Channel.kt
@@ -78,13 +78,29 @@ sealed class ChannelState {
             is Syncing -> this@ChannelState.state
             else -> this@ChannelState
         }
+        maybeSignalSensitiveTask(oldState, newState)
         return when {
             // we only want to fire the PaymentSent event when we transition to Closing for the first time
             oldState is ChannelStateWithCommitments && oldState !is Closing && newState is Closing -> emitClosingEvents(oldState, newState)
             else -> emptyList()
         }
     }
 
+    /** Some transitions imply that we are in the middle of tasks that may require some time. */
+    private fun ChannelContext.maybeSignalSensitiveTask(oldState: ChannelState, newState: ChannelState) {
+        val spliceStatusBefore = (oldState as? Normal)?.spliceStatus
+        val spliceStatusAfter = (newState as? Normal)?.spliceStatus
+        when {
+            spliceStatusBefore !is SpliceStatus.InProgress && spliceStatusAfter is SpliceStatus.InProgress -> // splice initiated
+                staticParams.nodeParams._nodeEvents.tryEmit(SensitiveTaskEvents.TaskStarted(SensitiveTaskEvents.TaskIdentifier.InteractiveTx(spliceStatusAfter.spliceSession.fundingParams)))
+            spliceStatusBefore is SpliceStatus.InProgress && spliceStatusAfter !is SpliceStatus.WaitingForSigs -> // splice aborted before reaching signing phase
+                staticParams.nodeParams._nodeEvents.tryEmit(SensitiveTaskEvents.TaskEnded(SensitiveTaskEvents.TaskIdentifier.InteractiveTx(spliceStatusBefore.spliceSession.fundingParams)))
+            spliceStatusBefore is SpliceStatus.WaitingForSigs && spliceStatusAfter !is SpliceStatus.WaitingForSigs -> // splice leaving signing phase (successfully or not)
+                staticParams.nodeParams._nodeEvents.tryEmit(SensitiveTaskEvents.TaskEnded(SensitiveTaskEvents.TaskIdentifier.InteractiveTx(spliceStatusBefore.session.fundingParams)))
+            else -> {}
+        }
+    }
+
     private fun ChannelContext.emitClosingEvents(oldState: ChannelStateWithCommitments, newState: Closing): List<ChannelAction> {
         val channelBalance = oldState.commitments.latest.localCommit.spec.toLocal
         return if (channelBalance > 0.msat) {