Generalize with_known_relevant_init_flags

Converting from InitFeatures to other Features is accomplished using
Features::with_known_relevant_init_flags. Define a more general
to_context method which converts from Features of one Context to
another.

Additionally, ensure the source context only has known flags before
selecting flags for the target context.

Author: jkczyz

lightning/src/ln/features.rs

@@ -303,18 +303,19 @@ impl<T: sealed::Context> Features<T> {
 		}
 	}
 
-	/// Takes the flags that we know how to interpret in an init-context features that are also
-	/// relevant in a node-context features and creates a node-context features from them.
-	/// Be sure to blank out features that are unknown to us.
-	pub(crate) fn with_known_relevant_init_flags(init_ctx: &InitFeatures) -> Self {
-		let byte_count = T::KNOWN_FEATURE_MASK.len();
+	/// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
+	/// included in the result.
+	pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
+		let byte_count = C::KNOWN_FEATURE_MASK.len();
 		let mut flags = Vec::new();
-		for (i, feature_byte) in init_ctx.flags.iter().enumerate() {
+		for (i, byte) in self.flags.iter().enumerate() {
 			if i < byte_count {
-				flags.push(feature_byte & T::KNOWN_FEATURE_MASK[i]);
+				let known_source_features = T::KNOWN_FEATURE_MASK[i];
+				let known_target_features = C::KNOWN_FEATURE_MASK[i];
+				flags.push(byte & known_source_features & known_target_features);
 			}
 		}
-		Self { flags, mark: PhantomData, }
+		Features::<C> { flags, mark: PhantomData, }
 	}
 
 	#[cfg(test)]
@@ -399,8 +400,9 @@ impl<T: sealed::UpfrontShutdownScript> Features<T> {
 		<T as sealed::UpfrontShutdownScript>::supports_feature(&self.flags)
 	}
 	#[cfg(test)]
-	pub(crate) fn unset_upfront_shutdown_script(&mut self) {
-		<T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags)
+	pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
+		<T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
+		self
 	}
 }
 
@@ -461,7 +463,7 @@ impl<T: sealed::Context> Readable for Features<T> {
 
 #[cfg(test)]
 mod tests {
-	use super::{ChannelFeatures, InitFeatures, NodeFeatures, Features};
+	use super::{ChannelFeatures, InitFeatures, NodeFeatures};
 
 	#[test]
 	fn sanity_test_our_features() {
@@ -503,26 +505,26 @@ mod tests {
 	}
 
 	#[test]
-	fn test_node_with_known_relevant_init_flags() {
-		// Create an InitFeatures with initial_routing_sync supported.
-		let init_features = InitFeatures::known();
+	fn convert_to_context_with_relevant_flags() {
+		let init_features = InitFeatures::known().clear_upfront_shutdown_script();
 		assert!(init_features.initial_routing_sync());
+		assert!(!init_features.supports_upfront_shutdown_script());
 
-		// Attempt to pull out non-node-context feature flags from these InitFeatures.
-		let res = NodeFeatures::with_known_relevant_init_flags(&init_features);
-
+		let node_features: NodeFeatures = init_features.to_context();
 		{
-			// Check that the flags are as expected: optional_data_loss_protect,
-			// option_upfront_shutdown_script, var_onion_optin, payment_secret, and
-			// basic_mpp.
-			assert_eq!(res.flags.len(), 3);
-			assert_eq!(res.flags[0], 0b00100010);
-			assert_eq!(res.flags[1], 0b10000010);
-			assert_eq!(res.flags[2], 0b00000010);
+			// Check that the flags are as expected:
+			// - option_data_loss_protect
+			// - var_onion_optin | payment_secret
+			// - basic_mpp
+			assert_eq!(node_features.flags.len(), 3);
+			assert_eq!(node_features.flags[0], 0b00000010);
+			assert_eq!(node_features.flags[1], 0b10000010);
+			assert_eq!(node_features.flags[2], 0b00000010);
 		}
 
-		// Check that the initial_routing_sync feature was correctly blanked out.
-		let new_features: InitFeatures = Features::from_le_bytes(res.flags);
-		assert!(!new_features.initial_routing_sync());
+		// Check that cleared flags are kept blank when converting back.
+		let features: InitFeatures = node_features.to_context();
+		assert!(!features.initial_routing_sync());
+		assert!(!features.supports_upfront_shutdown_script());
 	}
 }

lightning/src/ln/functional_tests.rs

@@ -6694,8 +6694,7 @@ fn test_upfront_shutdown_script() {
 	}
 
 	// We test that if case of peer non-signaling we don't enforce committed script at channel opening
-	let mut flags_no = InitFeatures::known();
-	flags_no.unset_upfront_shutdown_script();
+	let flags_no = InitFeatures::known().clear_upfront_shutdown_script();
 	let chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1000000, 1000000, flags_no, flags.clone());
 	nodes[0].node.close_channel(&OutPoint::new(chan.3.txid(), 0).to_channel_id()).unwrap();
 	let mut node_1_shutdown = get_event_msg!(nodes[0], MessageSendEvent::SendShutdown, nodes[1].node.get_our_node_id());

lightning/src/ln/router.rs

@@ -893,9 +893,9 @@ impl Router {
 					return Ok(Route {
 						paths: vec![vec![RouteHop {
 							pubkey: chan.remote_network_id,
-							node_features: NodeFeatures::with_known_relevant_init_flags(&chan.counterparty_features),
+							node_features: chan.counterparty_features.to_context(),
 							short_channel_id,
-							channel_features: ChannelFeatures::with_known_relevant_init_flags(&chan.counterparty_features),
+							channel_features: chan.counterparty_features.to_context(),
 							fee_msat: final_value_msat,
 							cltv_expiry_delta: final_cltv,
 						}]],
@@ -972,7 +972,7 @@ impl Router {
 			( $node: expr, $node_id: expr, $fee_to_target_msat: expr ) => {
 				if first_hops.is_some() {
 					if let Some(&(ref first_hop, ref features)) = first_hop_targets.get(&$node_id) {
-						add_entry!(first_hop, $node_id, dummy_directional_info, ChannelFeatures::with_known_relevant_init_flags(&features), $fee_to_target_msat);
+						add_entry!(first_hop, $node_id, dummy_directional_info, features.to_context(), $fee_to_target_msat);
 					}
 				}
 
@@ -1016,7 +1016,7 @@ impl Router {
 							// bit lazy here. In the future, we should pull them out via our
 							// ChannelManager, but there's no reason to waste the space until we
 							// need them.
-							add_entry!(first_hop, hop.src_node_id, dummy_directional_info, ChannelFeatures::with_known_relevant_init_flags(&features), 0);
+							add_entry!(first_hop, hop.src_node_id, dummy_directional_info, features.to_context(), 0);
 						}
 					}
 					// BOLT 11 doesn't allow inclusion of features for the last hop hints, which
@@ -1031,7 +1031,7 @@ impl Router {
 				let mut res = vec!(dist.remove(&network.our_node_id).unwrap().3);
 				loop {
 					if let Some(&(_, ref features)) = first_hop_targets.get(&res.last().unwrap().pubkey) {
-						res.last_mut().unwrap().node_features = NodeFeatures::with_known_relevant_init_flags(&features);
+						res.last_mut().unwrap().node_features = features.to_context();
 					} else if let Some(node) = network.nodes.get(&res.last().unwrap().pubkey) {
 						res.last_mut().unwrap().node_features = node.features.clone();
 					} else {