greetd-moongreet/src/power.rs

// ABOUTME: Power actions — reboot and shutdown via systemctl.
// ABOUTME: Wrappers around system commands for the greeter UI.

use std::fmt;
use std::io::Read;
use std::process::{Command, Stdio};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::time::Duration;

const POWER_TIMEOUT: Duration = Duration::from_secs(30);

#[derive(Debug)]
pub enum PowerError {
    CommandFailed { action: &'static str, message: String },
    Timeout { action: &'static str },
}

impl fmt::Display for PowerError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            PowerError::CommandFailed { action, message } => {
                write!(f, "{action} failed: {message}")
            }
            PowerError::Timeout { action } => {
                write!(f, "{action} timed out")
            }
        }
    }
}

impl std::error::Error for PowerError {}

/// Run a command with timeout and return a PowerError on failure.
///
/// Uses blocking `child.wait()` with a separate timeout thread that sends
/// SIGKILL after POWER_TIMEOUT. This runs inside `gio::spawn_blocking`,
/// so blocking is expected.
fn run_command(action: &'static str, program: &str, args: &[&str]) -> Result<(), PowerError> {
    log::debug!("Power action: {action} ({program} {args:?})");
    let mut child = Command::new(program)
        .args(args)
        // stdout is never read; piping without draining would deadlock on any
        // command that writes more than one OS pipe buffer before wait() returns.
        .stdout(Stdio::null())
        .stderr(Stdio::piped())
        .spawn()
        .map_err(|e| PowerError::CommandFailed {
            action,
            message: e.to_string(),
        })?;

    let child_pid = nix::unistd::Pid::from_raw(child.id() as i32);
    let done = Arc::new(AtomicBool::new(false));
    let done_clone = done.clone();

    let timeout_thread = std::thread::spawn(move || {
        let interval = Duration::from_millis(100);
        let mut elapsed = Duration::ZERO;
        while elapsed < POWER_TIMEOUT {
            std::thread::sleep(interval);
            if done_clone.load(Ordering::Relaxed) {
                return;
            }
            elapsed += interval;
        }
        // ESRCH if the process already exited — harmless
        let _ = nix::sys::signal::kill(child_pid, nix::sys::signal::Signal::SIGKILL);
    });

    let status = child.wait().map_err(|e| PowerError::CommandFailed {
        action,
        message: e.to_string(),
    })?;

    done.store(true, Ordering::Relaxed);
    let _ = timeout_thread.join();

    if status.success() {
        log::debug!("Power action {action} completed");
        Ok(())
    } else {
        #[cfg(unix)]
        {
            use std::os::unix::process::ExitStatusExt;
            if status.signal() == Some(9) {
                return Err(PowerError::Timeout { action });
            }
        }

        let mut stderr_buf = String::new();
        if let Some(mut stderr) = child.stderr.take() {
            let _ = stderr.read_to_string(&mut stderr_buf);
        }
        Err(PowerError::CommandFailed {
            action,
            message: format!("exit code {}: {}", status, stderr_buf.trim()),
        })
    }
}

/// Reboot the system via systemctl.
///
/// `--no-ask-password` keeps systemctl from spawning an interactive askpass
/// agent — the greeter session has none, so without it a denied authorization
/// would hang instead of failing fast.
pub fn reboot() -> Result<(), PowerError> {
    run_command("reboot", "/usr/bin/systemctl", &["--no-ask-password", "reboot"])
}

/// Shut down the system via systemctl.
///
/// `--no-ask-password` for the same reason as [`reboot`] — the agent-less
/// greeter session has nothing to answer an authorization challenge.
pub fn shutdown() -> Result<(), PowerError> {
    run_command("shutdown", "/usr/bin/systemctl", &["--no-ask-password", "poweroff"])
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn power_error_command_failed_display() {
        let err = PowerError::CommandFailed {
            action: "reboot",
            message: "No such file or directory".to_string(),
        };
        assert_eq!(err.to_string(), "reboot failed: No such file or directory");
    }

    #[test]
    fn power_error_timeout_display() {
        let err = PowerError::Timeout { action: "shutdown" };
        assert_eq!(err.to_string(), "shutdown timed out");
    }

    #[test]
    fn run_command_returns_error_for_missing_binary() {
        let result = run_command("test", "nonexistent-binary-xyz", &[]);
        assert!(result.is_err());
        let err = result.unwrap_err();
        assert!(matches!(err, PowerError::CommandFailed { action: "test", .. }));
    }

    #[test]
    fn run_command_returns_error_on_nonzero_exit() {
        let result = run_command("test", "false", &[]);
        assert!(result.is_err());
        let err = result.unwrap_err();
        assert!(matches!(err, PowerError::CommandFailed { action: "test", .. }));
    }

    #[test]
    fn run_command_succeeds_for_true() {
        let result = run_command("test", "true", &[]);
        assert!(result.is_ok());
    }

    #[test]
    fn run_command_passes_args() {
        let result = run_command("test", "echo", &["hello", "world"]);
        assert!(result.is_ok());
    }
}