Relax our p2p rules around matching protocol versions (#2764)

p2p/src/handshake.rs

@@ -86,12 +86,7 @@ impl Handshake {
 		// write and read the handshake response
 		write_message(conn, hand, Type::Hand)?;
 		let shake: Shake = read_message(conn, Type::Shake)?;
-		if shake.version != PROTOCOL_VERSION {
-			return Err(Error::ProtocolMismatch {
-				us: PROTOCOL_VERSION,
-				peer: shake.version,
-			});
-		} else if shake.genesis != self.genesis {
+		if shake.genesis != self.genesis {
 			return Err(Error::GenesisMismatch {
 				us: self.genesis,
 				peer: shake.genesis,
@@ -132,12 +127,7 @@ impl Handshake {
 		let hand: Hand = read_message(conn, Type::Hand)?;
 
 		// all the reasons we could refuse this connection for
-		if hand.version != PROTOCOL_VERSION {
-			return Err(Error::ProtocolMismatch {
-				us: PROTOCOL_VERSION,
-				peer: hand.version,
-			});
-		} else if hand.genesis != self.genesis {
+		if hand.genesis != self.genesis {
 			return Err(Error::GenesisMismatch {
 				us: self.genesis,
 				peer: hand.genesis,

p2p/src/msg.rs

@@ -28,7 +28,14 @@ use crate::types::{
 };
 use crate::util::read_write::read_exact;
 
-/// Current latest version of the protocol
+/// Our local node protocol version.
+/// We will increment the protocol version with every change to p2p msg serialization
+/// so we will likely connect with peers with both higher and lower protocol versions.
+/// We need to be aware that some msg formats will be potentially incompatible and handle
+/// this for each individual peer connection.
+/// Note: A peer may disconnect and reconnect with an updated protocol version. Normally
+/// the protocol version will increase but we need to handle decreasing values also
+/// as a peer may rollback to previous version of the code.
 pub const PROTOCOL_VERSION: u32 = 1;
 
 /// Grin's user agent with current version

p2p/src/types.rs

@@ -68,10 +68,6 @@ pub enum Error {
 	Chain(chain::Error),
 	PeerWithSelf,
 	NoDandelionRelay,
-	ProtocolMismatch {
-		us: u32,
-		peer: u32,
-	},
 	GenesisMismatch {
 		us: Hash,
 		peer: Hash,

servers/src/grin/server.rs

@@ -402,6 +402,11 @@ impl Server {
 		self.chain.header_head().map_err(|e| e.into())
 	}
 
+	/// Current p2p layer protocol version.
+	pub fn protocol_version() -> u32 {
+		p2p::msg::PROTOCOL_VERSION
+	}
+
 	/// Returns a set of stats about this server. This and the ServerStats
 	/// structure
 	/// can be updated over time to include any information needed by tests or

src/bin/tui/ui.rs

@@ -88,7 +88,11 @@ impl UI {
 
 		let mut title_string = StyledString::new();
 		title_string.append(StyledString::styled(
-			format!("Grin Version {}", built_info::PKG_VERSION),
+			format!(
+				"Grin Version {} (protocol version: {})",
+				built_info::PKG_VERSION,
+				Server::protocol_version()
+			),
 			Color::Dark(BaseColor::Green),
 		));