Add feature bits for custom wallet features

Wallets should explicitly advertise support for pay-to-open, trusted swaps
and wake-up notifications  in their `init` message, to allow the LSPs they
connect to to know what they're allowed to do.

This lets LSPs know for example whether they can open a channel on-the-fly
when liquidity is missing to receive a payment.

lightning-kmp-test-fixtures/src/commonMain/kotlin/fr/acinq/lightning/tests/TestConstants.kt

@@ -53,7 +53,11 @@ object TestConstants {
                 Feature.Wumbo to FeatureSupport.Optional,
                 Feature.StaticRemoteKey to FeatureSupport.Mandatory,
                 Feature.AnchorOutputs to FeatureSupport.Mandatory,
-                Feature.TrampolinePayment to FeatureSupport.Optional
+                Feature.TrampolinePayment to FeatureSupport.Optional,
+                Feature.ZeroConfChannels to FeatureSupport.Optional,
+                Feature.WakeUpNotificationClient to FeatureSupport.Optional,
+                Feature.PayToOpenClient to FeatureSupport.Optional,
+                Feature.TrustedSwapInClient to FeatureSupport.Optional,
             ),
             dustLimit = 1_100.sat,
             maxRemoteDustLimit = 1_500.sat,
@@ -123,7 +127,11 @@ object TestConstants {
                 Feature.Wumbo to FeatureSupport.Optional,
                 Feature.StaticRemoteKey to FeatureSupport.Mandatory,
                 Feature.AnchorOutputs to FeatureSupport.Mandatory,
-                Feature.TrampolinePayment to FeatureSupport.Optional
+                Feature.TrampolinePayment to FeatureSupport.Optional,
+                Feature.ZeroConfChannels to FeatureSupport.Optional,
+                Feature.WakeUpNotificationClient to FeatureSupport.Optional,
+                Feature.PayToOpenClient to FeatureSupport.Optional,
+                Feature.TrustedSwapInClient to FeatureSupport.Optional,
             ),
             dustLimit = 1_000.sat,
             maxRemoteDustLimit = 1_500.sat,

src/commonMain/kotlin/fr/acinq/lightning/Features.kt

@@ -91,14 +91,55 @@ sealed class Feature {
         override val mandatory get() = 20
     }
 
-    // TODO: @t-bast: update feature bits once spec-ed (currently reserved here: https://github.com/lightningnetwork/lightning-rfc/issues/605)
-    // We're not advertising these bits yet in our announcements, clients have to assume support.
-    // This is why we haven't added them yet to `areSupported`.
+    // The following features have not been standardised, hence the high feature bits to avoid conflicts.
+
     @Serializable
     object TrampolinePayment : Feature() {
         override val rfcName get() = "trampoline_payment"
         override val mandatory get() = 50
     }
+
+    @Serializable
+    object ZeroConfChannels : Feature() {
+        override val rfcName get() = "zero_conf_channels"
+        override val mandatory get() = 130
+    }
+
+    @Serializable
+    object WakeUpNotificationClient : Feature() {
+        override val rfcName get() = "wake_up_notification_client"
+        override val mandatory get() = 132
+    }
+
+    @Serializable
+    object WakeUpNotificationProvider : Feature() {
+        override val rfcName get() = "wake_up_notification_provider"
+        override val mandatory get() = 134
+    }
+
+    @Serializable
+    object PayToOpenClient : Feature() {
+        override val rfcName get() = "pay_to_open_client"
+        override val mandatory get() = 136
+    }
+
+    @Serializable
+    object PayToOpenProvider : Feature() {
+        override val rfcName get() = "pay_to_open_provider"
+        override val mandatory get() = 138
+    }
+
+    @Serializable
+    object TrustedSwapInClient : Feature() {
+        override val rfcName get() = "trusted_swap_in_client"
+        override val mandatory get() = 140
+    }
+
+    @Serializable
+    object TrustedSwapInProvider : Feature() {
+        override val rfcName get() = "trusted_swap_in_provider"
+        override val mandatory get() = 142
+    }
 }
 
 @Serializable
@@ -153,7 +194,14 @@ data class Features(val activated: Map<Feature, FeatureSupport>, val unknown: Se
             Feature.BasicMultiPartPayment,
             Feature.Wumbo,
             Feature.AnchorOutputs,
-            Feature.TrampolinePayment
+            Feature.TrampolinePayment,
+            Feature.ZeroConfChannels,
+            Feature.WakeUpNotificationClient,
+            Feature.WakeUpNotificationProvider,
+            Feature.PayToOpenClient,
+            Feature.PayToOpenProvider,
+            Feature.TrustedSwapInClient,
+            Feature.TrustedSwapInProvider,
         )
 
         operator fun invoke(bytes: ByteVector): Features = invoke(bytes.toByteArray())

src/jvmTest/kotlin/fr/acinq/lightning/Node.kt

@@ -148,6 +148,10 @@ object Node {
                 Feature.StaticRemoteKey to FeatureSupport.Optional,
                 Feature.AnchorOutputs to FeatureSupport.Optional,
                 Feature.TrampolinePayment to FeatureSupport.Optional,
+                Feature.ZeroConfChannels to FeatureSupport.Optional,
+                Feature.WakeUpNotificationClient to FeatureSupport.Optional,
+                Feature.PayToOpenClient to FeatureSupport.Optional,
+                Feature.TrustedSwapInClient to FeatureSupport.Optional,
             ),
             dustLimit = 546.sat,
             maxRemoteDustLimit = 600.sat,