Merge pull request lightningdevkit#3346 from TheBlueMatt/2024-10-dns-feature-flag

Add support for parsing the dns_resolver feature bit

Author: TheBlueMatt

lightning-types/src/features.rs

@@ -68,6 +68,8 @@
 //!     (see the [`Keysend` feature assignment proposal](https://github.com/lightning/bolts/issues/605#issuecomment-606679798) for more information).
 //! - `Trampoline` - supports receiving and forwarding Trampoline payments
 //!     (see the [`Trampoline` feature proposal](https://github.com/lightning/bolts/pull/836) for more information).
+//! - `DnsResolver` - supports resolving DNS names to TXT DNSSEC proofs for BIP 353 payments
+//!     (see [bLIP 32](https://github.com/lightning/blips/blob/master/blip-0032.md) for more information).
 //!
 //! LDK knows about the following features, but does not support them:
 //! - `AnchorsNonzeroFeeHtlcTx` - the initial version of anchor outputs, which was later found to be
@@ -174,6 +176,10 @@ mod sealed {
 			ZeroConf | Keysend,
 			// Byte 7
 			Trampoline,
+			// Byte 8 - 31
+			,,,,,,,,,,,,,,,,,,,,,,,,
+			// Byte 32
+			DnsResolver,
 		]
 	);
 	define_context!(ChannelContext, []);
@@ -562,6 +568,17 @@ mod sealed {
 		supports_trampoline_routing,
 		requires_trampoline_routing
 	);
+	define_feature!(
+		259,
+		DnsResolver,
+		[NodeContext],
+		"Feature flags for DNS resolving.",
+		set_dns_resolution_optional,
+		set_dns_resolution_required,
+		supports_dns_resolution,
+		requires_dns_resolution
+	);
+
 	// Note: update the module-level docs when a new feature bit is added!
 
 	#[cfg(any(test, feature = "_test_utils"))]

lightning/src/onion_message/dns_resolution.rs

@@ -34,6 +34,8 @@ use dnssec_prover::validation::verify_rr_stream;
 
 use dnssec_prover::rr::Name;
 
+use lightning_types::features::NodeFeatures;
+
 use crate::blinded_path::message::DNSResolverContext;
 use crate::io;
 #[cfg(feature = "dnssec")]
@@ -67,6 +69,13 @@ pub trait DNSResolverMessageHandler {
 	/// With this, we should be able to validate the DNS record we requested.
 	fn handle_dnssec_proof(&self, message: DNSSECProof, context: DNSResolverContext);
 
+	/// Gets the node feature flags which this handler itself supports. Useful for setting the
+	/// `dns_resolver` flag if this handler supports returning [`DNSSECProof`] messages in response
+	/// to [`DNSSECQuery`] messages.
+	fn provided_node_features(&self) -> NodeFeatures {
+		NodeFeatures::empty()
+	}
+
 	/// Release any [`DNSResolverMessage`]s that need to be sent.
 	fn release_pending_messages(&self) -> Vec<(DNSResolverMessage, MessageSendInstructions)> {
 		vec![]

lightning/src/onion_message/messenger.rs

@@ -1778,7 +1778,7 @@ where
 	fn provided_node_features(&self) -> NodeFeatures {
 		let mut features = NodeFeatures::empty();
 		features.set_onion_messages_optional();
-		features
+		features | self.dns_resolver_handler.provided_node_features()
 	}
 
 	fn provided_init_features(&self, _their_node_id: PublicKey) -> InitFeatures {