feat: add debug-level per-op, session and link metrics

src/session.rs

@@ -44,6 +44,19 @@ impl From<rusqlite::Error> for HandlerError {
 
 type OpResult = Result<(u8, Vec<u8>), HandlerError>;
 
+/// Wire op byte to log name; unknown bytes are logged as dispatched too.
+fn op_name(op: u8) -> &'static str {
+    match op {
+        OP_AUTH => "AUTH",
+        OP_RESOLVE => "RESOLVE",
+        OP_SEND => "SEND",
+        OP_FETCH => "FETCH",
+        OP_DELETE => "DELETE",
+        OP_REGISTER => "REGISTER",
+        _ => "UNKNOWN",
+    }
+}
+
 pub struct Session<'a> {
     config: &'a ServerConfig,
     store: Store,
@@ -72,7 +85,25 @@ impl<'a> Session<'a> {
     /// panicking or propagating errors to the caller: a bad frame or a
     /// storage error both become a response, and the caller decides
     /// separately whether to keep the connection open.
+    ///
+    /// Timing lives in this wrapper because both carriers dispatch through
+    /// it, so the metrics flag covers TCP and RNS from one place.
     pub fn dispatch(&mut self, op: u8, body: &[u8]) -> (u8, Vec<u8>) {
+        let started = std::time::Instant::now();
+        let (status, payload) = self.dispatch_op(op, body);
+        log::debug!(
+            "op {} from {} in {:?}: status {}, {}B request, {}B response",
+            op_name(op),
+            self.peer_ip,
+            started.elapsed(),
+            status,
+            body.len(),
+            payload.len()
+        );
+        (status, payload)
+    }
+
+    fn dispatch_op(&mut self, op: u8, body: &[u8]) -> (u8, Vec<u8>) {
         if matches!(op, OP_FETCH | OP_DELETE) && self.username.is_none() {
             return (AUTH_REQUIRED, Vec::new());
         }