Add comprehensive Unix signal handling for daemon mode

Enhance signal handling to support proper daemon operation:

- SIGTERM: Graceful shutdown (same behavior as SIGINT)
- SIGQUIT: Graceful shutdown with full statistics dump
- SIGUSR1: Log rotation acknowledgment for external tools
- SIGUSR2: Dump runtime status to log without stopping

Statistics dump includes connection counts, ME keepalive metrics,
and relay adaptive tuning counters. SIGHUP config reload unchanged
(handled in hot_reload.rs).

Signals are handled via tokio::signal::unix with async select!
to avoid blocking the runtime. Non-shutdown signals (USR1/USR2)
run in a background task spawned at startup.

Signed-off-by: Vladimir Krivopalov <argenet@yandex.ru>

src/maestro/mod.rs

@@ -638,6 +638,9 @@ async fn run_inner(
 
     runtime_tasks::mark_runtime_ready(&startup_tracker).await;
 
+    // Spawn signal handlers for SIGUSR1/SIGUSR2 (non-shutdown signals)
+    shutdown::spawn_signal_handlers(stats.clone(), process_started_at);
+
     listeners::spawn_tcp_accept_loops(
         listeners,
         config_rx.clone(),
@@ -655,7 +658,7 @@ async fn run_inner(
         max_connections.clone(),
     );
 
-    shutdown::wait_for_shutdown(process_started_at, me_pool).await;
+    shutdown::wait_for_shutdown(process_started_at, me_pool, stats).await;
 
     Ok(())
 }

src/maestro/shutdown.rs

@@ -1,42 +1,211 @@
+//! Shutdown and signal handling for telemt.
+//!
+//! Handles graceful shutdown on various signals:
+//! - SIGINT (Ctrl+C) / SIGTERM: Graceful shutdown
+//! - SIGQUIT: Graceful shutdown with stats dump
+//! - SIGUSR1: Reserved for log rotation (logs acknowledgment)
+//! - SIGUSR2: Dump runtime status to log
+//!
+//! SIGHUP is handled separately in config/hot_reload.rs for config reload.
+
 use std::sync::Arc;
 use std::time::{Duration, Instant};
 
+#[cfg(unix)]
+use tokio::signal::unix::{SignalKind, signal};
+#[cfg(not(unix))]
 use tokio::signal;
-use tracing::{error, info, warn};
+use tracing::{info, warn};
 
+use crate::stats::Stats;
 use crate::transport::middle_proxy::MePool;
 
 use super::helpers::{format_uptime, unit_label};
 
-pub(crate) async fn wait_for_shutdown(process_started_at: Instant, me_pool: Option<Arc<MePool>>) {
-    match signal::ctrl_c().await {
-        Ok(()) => {
-            let shutdown_started_at = Instant::now();
-            info!("Shutting down...");
-            let uptime_secs = process_started_at.elapsed().as_secs();
-            info!("Uptime: {}", format_uptime(uptime_secs));
-            if let Some(pool) = &me_pool {
-                match tokio::time::timeout(Duration::from_secs(2), pool.shutdown_send_close_conn_all())
-                    .await
-                {
-                    Ok(total) => {
-                        info!(
-                            close_conn_sent = total,
-                            "ME shutdown: RPC_CLOSE_CONN broadcast completed"
-                        );
-                    }
-                    Err(_) => {
-                        warn!("ME shutdown: RPC_CLOSE_CONN broadcast timed out");
-                    }
-                }
-            }
-            let shutdown_secs = shutdown_started_at.elapsed().as_secs();
-            info!(
-                "Shutdown completed successfully in {} {}.",
-                shutdown_secs,
-                unit_label(shutdown_secs, "second", "seconds")
-            );
+/// Signal that triggered shutdown.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ShutdownSignal {
+    /// SIGINT (Ctrl+C)
+    Interrupt,
+    /// SIGTERM
+    Terminate,
+    /// SIGQUIT (with stats dump)
+    Quit,
+}
+
+impl std::fmt::Display for ShutdownSignal {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ShutdownSignal::Interrupt => write!(f, "SIGINT"),
+            ShutdownSignal::Terminate => write!(f, "SIGTERM"),
+            ShutdownSignal::Quit => write!(f, "SIGQUIT"),
         }
-        Err(e) => error!("Signal error: {}", e),
     }
 }
+
+/// Waits for a shutdown signal and performs graceful shutdown.
+pub(crate) async fn wait_for_shutdown(
+    process_started_at: Instant,
+    me_pool: Option<Arc<MePool>>,
+    stats: Arc<Stats>,
+) {
+    let signal = wait_for_shutdown_signal().await;
+    perform_shutdown(signal, process_started_at, me_pool, &stats).await;
+}
+
+/// Waits for any shutdown signal (SIGINT, SIGTERM, SIGQUIT).
+#[cfg(unix)]
+async fn wait_for_shutdown_signal() -> ShutdownSignal {
+    let mut sigint = signal(SignalKind::interrupt()).expect("Failed to register SIGINT handler");
+    let mut sigterm = signal(SignalKind::terminate()).expect("Failed to register SIGTERM handler");
+    let mut sigquit = signal(SignalKind::quit()).expect("Failed to register SIGQUIT handler");
+
+    tokio::select! {
+        _ = sigint.recv() => ShutdownSignal::Interrupt,
+        _ = sigterm.recv() => ShutdownSignal::Terminate,
+        _ = sigquit.recv() => ShutdownSignal::Quit,
+    }
+}
+
+#[cfg(not(unix))]
+async fn wait_for_shutdown_signal() -> ShutdownSignal {
+    signal::ctrl_c().await.expect("Failed to listen for Ctrl+C");
+    ShutdownSignal::Interrupt
+}
+
+/// Performs graceful shutdown sequence.
+async fn perform_shutdown(
+    signal: ShutdownSignal,
+    process_started_at: Instant,
+    me_pool: Option<Arc<MePool>>,
+    stats: &Stats,
+) {
+    let shutdown_started_at = Instant::now();
+    info!(signal = %signal, "Received shutdown signal");
+
+    // Dump stats if SIGQUIT
+    if signal == ShutdownSignal::Quit {
+        dump_stats(stats, process_started_at);
+    }
+
+    info!("Shutting down...");
+    let uptime_secs = process_started_at.elapsed().as_secs();
+    info!("Uptime: {}", format_uptime(uptime_secs));
+
+    // Graceful ME pool shutdown
+    if let Some(pool) = &me_pool {
+        match tokio::time::timeout(Duration::from_secs(2), pool.shutdown_send_close_conn_all()).await
+        {
+            Ok(total) => {
+                info!(
+                    close_conn_sent = total,
+                    "ME shutdown: RPC_CLOSE_CONN broadcast completed"
+                );
+            }
+            Err(_) => {
+                warn!("ME shutdown: RPC_CLOSE_CONN broadcast timed out");
+            }
+        }
+    }
+
+    let shutdown_secs = shutdown_started_at.elapsed().as_secs();
+    info!(
+        "Shutdown completed successfully in {} {}.",
+        shutdown_secs,
+        unit_label(shutdown_secs, "second", "seconds")
+    );
+}
+
+/// Dumps runtime statistics to the log.
+fn dump_stats(stats: &Stats, process_started_at: Instant) {
+    let uptime_secs = process_started_at.elapsed().as_secs();
+
+    info!("=== Runtime Statistics Dump ===");
+    info!("Uptime: {}", format_uptime(uptime_secs));
+
+    // Connection stats
+    info!(
+        "Connections: total={}, current={} (direct={}, me={}), bad={}",
+        stats.get_connects_all(),
+        stats.get_current_connections_total(),
+        stats.get_current_connections_direct(),
+        stats.get_current_connections_me(),
+        stats.get_connects_bad(),
+    );
+
+    // ME pool stats
+    info!(
+        "ME keepalive: sent={}, pong={}, failed={}, timeout={}",
+        stats.get_me_keepalive_sent(),
+        stats.get_me_keepalive_pong(),
+        stats.get_me_keepalive_failed(),
+        stats.get_me_keepalive_timeout(),
+    );
+
+    // Relay stats
+    info!(
+        "Relay adaptive: promotions={}, demotions={}, hard_promotions={}",
+        stats.get_relay_adaptive_promotions_total(),
+        stats.get_relay_adaptive_demotions_total(),
+        stats.get_relay_adaptive_hard_promotions_total(),
+    );
+
+    info!("=== End Statistics Dump ===");
+}
+
+/// Spawns a background task to handle operational signals (SIGUSR1, SIGUSR2).
+///
+/// These signals don't trigger shutdown but perform specific actions:
+/// - SIGUSR1: Log rotation acknowledgment (for external log rotation tools)
+/// - SIGUSR2: Dump runtime status to log
+#[cfg(unix)]
+pub(crate) fn spawn_signal_handlers(
+    stats: Arc<Stats>,
+    process_started_at: Instant,
+) {
+    tokio::spawn(async move {
+        let mut sigusr1 = signal(SignalKind::user_defined1())
+            .expect("Failed to register SIGUSR1 handler");
+        let mut sigusr2 = signal(SignalKind::user_defined2())
+            .expect("Failed to register SIGUSR2 handler");
+
+        loop {
+            tokio::select! {
+                _ = sigusr1.recv() => {
+                    handle_sigusr1();
+                }
+                _ = sigusr2.recv() => {
+                    handle_sigusr2(&stats, process_started_at);
+                }
+            }
+        }
+    });
+}
+
+/// No-op on non-Unix platforms.
+#[cfg(not(unix))]
+pub(crate) fn spawn_signal_handlers(
+    _stats: Arc<Stats>,
+    _process_started_at: Instant,
+) {
+    // No SIGUSR1/SIGUSR2 on non-Unix
+}
+
+/// Handles SIGUSR1 - log rotation signal.
+///
+/// This signal is typically sent by logrotate or similar tools after
+/// rotating log files. Since tracing-subscriber doesn't natively support
+/// reopening files, we just acknowledge the signal. If file logging is
+/// added in the future, this would reopen log file handles.
+#[cfg(unix)]
+fn handle_sigusr1() {
+    info!("SIGUSR1 received - log rotation acknowledged");
+    // Future: If using file-based logging, reopen file handles here
+}
+
+/// Handles SIGUSR2 - dump runtime status.
+#[cfg(unix)]
+fn handle_sigusr2(stats: &Stats, process_started_at: Instant) {
+    info!("SIGUSR2 received - dumping runtime status");
+    dump_stats(stats, process_started_at);
+}