rust-template-foundation 0.1.0

//! Systemd readiness notification and watchdog heartbeats.

use std::time::Duration;
use tracing::{info, warn};

/// Notify systemd that the service is ready to accept connections.  Safe to
/// call when NOTIFY_SOCKET is unset; sd_notify returns Ok(()) silently in
/// that case.
pub fn notify_ready() {
  if let Err(e) = sd_notify::notify(false, &[sd_notify::NotifyState::Ready]) {
    warn!("sd-notify ready signal failed: {}", e);
  }
}

/// Spawn a background task that sends watchdog heartbeats to systemd if
/// WATCHDOG_USEC is set in the environment.  The task runs for the lifetime
/// of the Tokio runtime and is dropped automatically during shutdown.
pub fn spawn_watchdog() {
  let Some(interval) = watchdog_interval() else {
    return;
  };
  info!("Watchdog enabled; sending heartbeats every {:?}", interval);
  tokio::spawn(async move {
    let mut ticker = tokio::time::interval(interval);
    loop {
      ticker.tick().await;
      if let Err(e) =
        sd_notify::notify(false, &[sd_notify::NotifyState::Watchdog])
      {
        warn!("sd-notify watchdog heartbeat failed: {}", e);
      }
    }
  });
}

/// Returns half of the watchdog timeout, or None when the watchdog is not
/// configured.  Uses sd_notify::watchdog_enabled, which validates WATCHDOG_PID
/// in addition to WATCHDOG_USEC so spurious inherited env vars are ignored.
/// Pinging at half the interval provides a safety margin before systemd
/// declares the service dead.
fn watchdog_interval() -> Option<Duration> {
  let mut usec = 0u64;
  sd_notify::watchdog_enabled(false, &mut usec)
    .then(|| Duration::from_micros(usec / 2))
}