Fix boot_time on windows

Fixes #345

heim-host/src/sys/windows/boot_time.rs

@@ -18,11 +18,31 @@ pub async fn boot_time() -> Result<Time> {
         filetime.assume_init().into_time()
     };
 
+    let elapsed_since_boot = Time::new::<time::millisecond>(unsafe {
+        // https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-gettickcount64
+        // function returns an ULONGLONG and can't fail, apparently
+        sysinfoapi::GetTickCount64() as f64
+    });
+
     // Seconds amount between the "Windows epoch" (January 1, 1601)
     // and the Unix epoch (January 1, 1970).
     // TODO: It would be nice to make it const,
     // as soon as `uom` will mark `Time::new` as a `const fn`
     let unix_epoch_delta = Time::new::<time::second>(11_644_473_600.0);
 
-    Ok(time - unix_epoch_delta)
+    Ok(time - elapsed_since_boot - unix_epoch_delta)
+}
+
+#[cfg(test)]
+mod test {
+    use crate::boot_time;
+    use std::time::{SystemTime, Duration};
+
+    #[test]
+    fn check_boot_time() {
+        let boot_timestamp = smol::block_on(boot_time()).unwrap().value;
+        std::thread::sleep(Duration::from_secs(1));
+        let current_timestamp = std::time::SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_secs_f64();
+        assert!(boot_timestamp < current_timestamp, "Boot time is greater than current time. Boot timestamp: {}, current timestamp: {}", boot_timestamp, current_timestamp);
+    }
 }