Add support for watchdog

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "storefd"
-version = "0.1.0"
+version = "0.1.1"
 edition = "2021"
 license = "MIT"
 authors = ["Mathieu Trossevin <mtrossevin@evolix.fr>"]

src/notify/mod.rs

@@ -162,6 +162,40 @@ impl Notifier {
     }
 }
 
+/// Check for watchdog support at runtime
+///
+/// If `unset_env` is true, the environment variables related to watchdog support will be cleared.
+///
+/// # Return
+///
+/// * [`None`] if watchdog support is not enabled.
+/// * The timeout before which the watchdog expects a response from the process otherwise.
+pub fn is_watchdog_enabled(unset_env: bool) -> Option<std::time::Duration> {
+    let timeout = std::env::var("WATCHDOG_USEC").ok();
+    let watchdog_pid = std::env::var("WATCHDOG_PID").ok();
+
+    if unset_env {
+        std::env::remove_var("WATCHDOG_USEC");
+        std::env::remove_var("WATCHDOG_PID");
+    }
+
+    let timeout = timeout
+        .and_then(|timeout| timeout.parse::<u64>().ok())
+        .map(std::time::Duration::from_micros)?;
+
+    let watchdog_pid = if let Some(pid) = watchdog_pid {
+        pid.parse::<u32>().ok()?
+    } else {
+        return Some(timeout);
+    };
+
+    if watchdog_pid == std::process::id() {
+        Some(timeout)
+    } else {
+        None
+    }
+}
+
 /// Status changes, see `sd_notify(3)`.
 #[allow(clippy::module_name_repetitions)]
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]