Send a status message on block announce handshake

client/network/src/protocol.rs

@@ -303,6 +303,31 @@ impl Default for ProtocolConfig {
 	}
 }
 
+/// Handshake sent when we open a block announces substream.
+#[derive(Debug, PartialEq, Eq, Clone, Encode, Decode)]
+struct BlockAnnouncesHandshake<B: BlockT> {
+	/// Roles of the node.
+	roles: Roles,
+	/// Best block number.
+	best_number: NumberFor<B>,
+	/// Best block hash.
+	best_hash: B::Hash,
+	/// Genesis block hash.
+	genesis_hash: B::Hash,
+}
+
+impl<B: BlockT> BlockAnnouncesHandshake<B> {
+	fn build(protocol_config: &ProtocolConfig, chain: &Arc<dyn Client<B>>) -> Self {
+		let info = chain.info();
+		BlockAnnouncesHandshake {
+			genesis_hash: info.genesis_hash,
+			roles: protocol_config.roles.into(),
+			best_number: info.best_number,
+			best_hash: info.best_hash,
+		}
+	}
+}
+
 /// Fallback mechanism to use to send a notification if no substream is open.
 #[derive(Debug, Clone, PartialEq, Eq)]
 enum Fallback {
@@ -369,7 +394,10 @@ impl<B: BlockT, H: ExHashT> Protocol<B, H> {
 			proto.extend(b"/block-announces/1");
 			proto
 		});
-		behaviour.register_notif_protocol(block_announces_protocol.clone(), Vec::new());
+		behaviour.register_notif_protocol(
+			block_announces_protocol.clone(),
+			BlockAnnouncesHandshake::build(&config, &chain).encode()
+		);
 		legacy_equiv_by_name.insert(block_announces_protocol.clone(), Fallback::BlockAnnounce);
 
 		let protocol = Protocol {
@@ -1325,6 +1353,10 @@ impl<B: BlockT, H: ExHashT> Protocol<B, H> {
 	pub fn on_block_imported(&mut self, header: &B::Header, is_best: bool) {
 		if is_best {
 			self.sync.update_chain_info(header);
+			self.behaviour.set_notif_protocol_handshake(
+				&self.block_announces_protocol,
+				BlockAnnouncesHandshake::build(&self.config, &self.context_data.chain).encode()
+			);
 		}
 	}
 

client/network/src/protocol/generic_proto/behaviour.rs

@@ -338,6 +338,34 @@ impl GenericProto {
 		self.notif_protocols.push((protocol_name.into(), handshake_msg.into()));
 	}
 
+	/// Modifies the handshake of the given notifications protocol.
+	///
+	/// Has no effect if the protocol is unknown.
+	pub fn set_notif_protocol_handshake(
+		&mut self,
+		protocol_name: &[u8],
+		handshake_message: impl Into<Vec<u8>>
+	) {
+		let handshake_message = handshake_message.into();
+		if let Some(protocol) = self.notif_protocols.iter_mut().find(|(name, _)| name == &protocol_name) {
+			protocol.1 = handshake_message.clone();
+		} else {
+			return;
+		}
+
+		// Send an event to all the peers we're connected to, updating the handshake message.
+		for (peer_id, _) in self.peers.iter().filter(|(_, state)| state.is_open()) {
+			self.events.push(NetworkBehaviourAction::NotifyHandler {
+				peer_id: peer_id.clone(),
+				handler: NotifyHandler::All,
+				event: NotifsHandlerIn::UpdateHandshake {
+					protocol_name: Cow::Owned(protocol_name.to_owned()),
+					handshake_message: handshake_message.clone(),
+				},
+			});
+		}
+	}
+
 	/// Returns the number of discovered nodes that we keep in memory.
 	pub fn num_discovered_peers(&self) -> usize {
 		self.peerset.num_discovered_peers()

client/network/src/protocol/generic_proto/handler/group.rs

@@ -161,6 +161,18 @@ pub enum NotifsHandlerIn {
 		message: Vec<u8>,
 	},
 
+	/// Modifies the handshake message of a notifications protocol.
+	UpdateHandshake {
+		/// Name of the protocol for the message.
+		///
+		/// Must match one of the registered protocols.
+		protocol_name: Cow<'static, [u8]>,
+
+		/// The new handshake message to send if we open a substream or if the remote opens a
+		/// substream towards us.
+		handshake_message: Vec<u8>,
+	},
+
 	/// Sends a notifications message.
 	SendNotification {
 		/// Name of the protocol for the message.
@@ -363,6 +375,18 @@ impl ProtocolsHandler for NotifsHandler {
 			},
 			NotifsHandlerIn::SendLegacy { message } =>
 				self.legacy.inject_event(LegacyProtoHandlerIn::SendCustomMessage { message }),
+			NotifsHandlerIn::UpdateHandshake { protocol_name, handshake_message } => {
+				for (handler, current_handshake) in &mut self.in_handlers {
+					if handler.protocol_name() == &*protocol_name {
+						*current_handshake = handshake_message.clone();
+					}
+				}
+				for (handler, current_handshake) in &mut self.out_handlers {
+					if handler.protocol_name() == &*protocol_name {
+						*current_handshake = handshake_message.clone();
+					}
+				}
+			}
 			NotifsHandlerIn::SendNotification { message, encoded_fallback_message, protocol_name } => {
 				for (handler, _) in &mut self.out_handlers {
 					if handler.protocol_name() != &protocol_name[..] {