Add a new InitFeatures constructor to capture the types of flags

When `ChannelMessageHandler` implementations wish to return an
`InitFeatures` which contain all the known flags that are relevant
to channel handling, but not gossip handling, they currently need
to do so by manually constructing an InitFeatures with all known
flags and then clearing the ones they dont want.

Instead of spreading this logic out across the codebase, this
consolidates such construction to one place in features.rs.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -6126,7 +6126,7 @@ impl<Signer: Sign, M: Deref , T: Deref , K: Deref , F: Deref , L: Deref >
 	}
 
 	fn provided_init_features(&self, _their_init_features: &PublicKey) -> InitFeatures {
-		InitFeatures::known()
+		InitFeatures::known_channel_features()
 	}
 }
 

lightning/src/ln/features.rs

@@ -163,6 +163,8 @@ mod sealed {
 			,
 		],
 		optional_features: [
+			// Note that if new "non-channel-related" flags are added here they should be
+			// explicitly cleared in InitFeatures::known_channel_features.
 			// Byte 0
 			DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
 			// Byte 1
@@ -545,6 +547,14 @@ impl InitFeatures {
 	pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 		self.to_context_internal()
 	}
+
+	/// Returns the set of known init features that are related to channels. At least some of
+	/// these features are likely required for peers to talk to us.
+	pub fn known_channel_features() -> InitFeatures {
+		let mut features = Self::known().clear_gossip_queries();
+		features.clear_initial_routing_sync();
+		features
+	}
 }
 
 impl InvoiceFeatures {
@@ -763,18 +773,14 @@ impl<T: sealed::UpfrontShutdownScript> Features<T> {
 
 
 impl<T: sealed::GossipQueries> Features<T> {
-	#[cfg(test)]
 	pub(crate) fn clear_gossip_queries(mut self) -> Self {
 		<T as sealed::GossipQueries>::clear_bits(&mut self.flags);
 		self
 	}
 }
 
 impl<T: sealed::InitialRoutingSync> Features<T> {
-	// We are no longer setting initial_routing_sync now that gossip_queries
-	// is enabled. This feature is ignored by a peer when gossip_queries has
-	// been negotiated.
-	#[cfg(test)]
+	// Note that initial_routing_sync is ignored if gossip_queries is set.
 	pub(crate) fn clear_initial_routing_sync(&mut self) {
 		<T as sealed::InitialRoutingSync>::clear_bits(&mut self.flags)
 	}

lightning/src/ln/peer_handler.rs

@@ -206,7 +206,11 @@ impl ChannelMessageHandler for ErroringMessageHandler {
 	fn peer_connected(&self, _their_node_id: &PublicKey, _msg: &msgs::Init) {}
 	fn handle_error(&self, _their_node_id: &PublicKey, _msg: &msgs::ErrorMessage) {}
 	fn provided_node_features(&self) -> NodeFeatures { NodeFeatures::empty() }
-	fn provided_init_features(&self, _their_node_id: &PublicKey) -> InitFeatures { InitFeatures::known() }
+	fn provided_init_features(&self, _their_node_id: &PublicKey) -> InitFeatures {
+		// Use our known channel feature set as peers may otherwise not be willing to talk to us at
+		// all.
+		InitFeatures::known_channel_features()
+	}
 }
 impl Deref for ErroringMessageHandler {
 	type Target = ErroringMessageHandler;

lightning/src/util/test_utils.rs

@@ -361,7 +361,7 @@ impl msgs::ChannelMessageHandler for TestChannelMessageHandler {
 		NodeFeatures::empty()
 	}
 	fn provided_init_features(&self, _their_init_features: &PublicKey) -> InitFeatures {
-		InitFeatures::known()
+		InitFeatures::known_channel_features()
 	}
 }