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

src/server.rs

@@ -103,6 +103,7 @@ fn handle_connection(
 ) -> anyhow::Result<()> {
     stream.set_read_timeout(Some(Duration::from_secs(IDLE_TIMEOUT_SECS)))?;
 
+    let handshake_started = std::time::Instant::now();
     let (transport, handshake_hash) = match handshake(&mut stream, static_key) {
         Ok(v) => v,
         Err(e) => {
@@ -110,6 +111,17 @@ fn handle_connection(
             return Ok(());
         }
     };
+    log::debug!(
+        "handshake from {peer_ip} in {:?}",
+        handshake_started.elapsed()
+    );
+
+    // Drop logs the summary once, whatever return path closes the session.
+    let summary = SessionSummary {
+        peer_ip,
+        started: std::time::Instant::now(),
+        ops: std::cell::Cell::new(0),
+    };
 
     let store = Store::open(db_path)?;
     let server_static = derive_public(static_key);
@@ -129,6 +141,7 @@ fn handle_connection(
                 return Ok(());
             }
         };
+        summary.ops.set(summary.ops.get() + 1);
 
         let (status, payload) = session.dispatch(op, &body);
         let mut response = Vec::with_capacity(1 + payload.len());
@@ -140,6 +153,23 @@ fn handle_connection(
     }
 }
 
+struct SessionSummary<'a> {
+    peer_ip: &'a str,
+    started: std::time::Instant,
+    ops: std::cell::Cell<u64>,
+}
+
+impl Drop for SessionSummary<'_> {
+    fn drop(&mut self) {
+        log::debug!(
+            "session {} closed: {} op(s) in {:?}",
+            self.peer_ip,
+            self.ops.get(),
+            self.started.elapsed()
+        );
+    }
+}
+
 fn is_eof_like(e: &anyhow::Error) -> bool {
     if let Some(io_err) = e.downcast_ref::<std::io::Error>() {
         return matches!(