node: Don't penalize peer for protocol mismatch

Instead of returning a non-transient disconnect reason, return
a transient one, since protocol mismatches can happen.

radicle-node/src/service/session.rs

@@ -119,10 +119,18 @@ pub enum FetchResult {
 
 #[derive(thiserror::Error, Debug)]
 pub enum Error {
+    /// The remote peer sent an invalid announcement timestamp,
+    /// for eg. a timestamp far in the future.
     #[error("invalid announcement timestamp: {0}")]
     InvalidTimestamp(u64),
+    /// The remote peer sent git protocol messages while we were expecting
+    /// gossip messages. Or vice-versa.
+    #[error("protocol mismatch")]
+    ProtocolMismatch,
+    /// The remote peer did something that violates the protocol rules.
     #[error("peer misbehaved")]
     Misbehavior,
+    /// The remote peer timed out.
     #[error("peer timed out")]
     Timeout,
 }
@@ -132,6 +140,7 @@ impl Error {
     pub fn is_transient(&self) -> bool {
         match self {
             Self::InvalidTimestamp(_) => false,
+            Self::ProtocolMismatch => true,
             Self::Misbehavior => false,
             Self::Timeout => true,
         }

radicle-node/src/wire/protocol.rs

@@ -521,9 +521,11 @@ where
                             Err(e) => {
                                 log::error!(target: "wire", "Invalid gossip message from {id}: {e}");
 
+                                let mut reason =
+                                    DisconnectReason::Session(session::Error::Misbehavior);
                                 if let Error::UnknownMessageType(t) = e {
-                                    let mut leftover = t.to_be_bytes().to_vec();
+                                    let leftover =
-                                    leftover.extend(inbox.unparsed());
+                                        inbox.unparsed().chain(t.to_be_bytes()).collect::<Vec<_>>();
 
                                     if let Ok(header) =
                                         str::from_utf8(&leftover[..worker::pktline::HEADER_LEN])
@@ -534,6 +536,10 @@ where
                                                 "Received possible Git packet-line header `{}` from {id} (protocol mismatch)",
                                                 header
                                             );
+                                            // In case of protocol mismatch, don't penalize the peer.
+                                            reason = DisconnectReason::Session(
+                                                session::Error::ProtocolMismatch,
+                                            );
                                         }
                                     }
                                 }
@@ -542,9 +548,8 @@ where
                                     log::debug!(target: "wire", "Dropping read buffer for {id} with {} bytes", inbox.unparsed().count());
                                 }
                                 self.disconnect(
-                                    fd,
+                                    fd, // TODO(cloudhead): Include error in reason.
-                                    // TODO(cloudhead): Include error in reason.
+                                    reason,
-                                    DisconnectReason::Session(session::Error::Misbehavior),
                                 );
                                 break;
                             }