haz-exec 0.1.0

//! Production [`ProcessSpawner`] backend over [`tokio::process::Command`].
//!
//! Pipes are attached to stdout and stderr, stdin is closed, and
//! the child is configured to receive `SIGKILL` on drop so a
//! panicking executor task does not leak processes. On Unix the
//! child is also placed in its own process group at spawn time so
//! the cancellation flow (`EXEC-013`, `EXEC-014`) can signal the
//! whole group with `kill(-pgid, sig)` and reach any subprocesses
//! the task itself spawned. On Windows there is no equivalent
//! process-group primitive: only [`Signal::Kill`] is implemented
//! (via [`tokio::process::Child::start_kill`]), and SIGTERM /
//! SIGINT surface [`std::io::ErrorKind::Unsupported`].

use std::io::{Error as IoError, ErrorKind};
use std::process::Stdio;

use snafu::ResultExt;
use tokio::process::{Child, ChildStderr, ChildStdout, Command};

use crate::process::{
    ExitStatus, Process, ProcessError, ProcessId, ProcessSpawner, Signal, SpawnFailedSnafu,
    SpawnPlan, Spawned, WaitFailedSnafu,
};

/// Production [`ProcessSpawner`] over [`tokio::process::Command`].
///
/// The type holds no state and is freely cloneable; instantiate it
/// with [`Self::new`] (or [`Default::default`]) and pass it as a
/// generic parameter to the executor.
#[derive(Debug, Default, Clone, Copy)]
pub struct StdProcessSpawner;

impl StdProcessSpawner {
    /// Construct a new spawner.
    #[must_use]
    pub fn new() -> Self {
        Self
    }
}

impl ProcessSpawner for StdProcessSpawner {
    type Process = StdProcess;

    async fn spawn(&self, plan: &SpawnPlan) -> Result<Spawned<Self::Process>, ProcessError> {
        if !plan.cwd.is_absolute() {
            return Err(ProcessError::NonAbsoluteCwd {
                cwd: plan.cwd.clone(),
            });
        }

        let mut command = Command::new(&plan.program);
        command.args(&plan.args);
        command.current_dir(&plan.cwd);
        command.env_clear();
        for (key, value) in &plan.env {
            command.env(key, value);
        }
        command.stdin(Stdio::null());
        command.stdout(Stdio::piped());
        command.stderr(Stdio::piped());
        command.kill_on_drop(true);
        #[cfg(unix)]
        {
            // Place the child in its own process group so the
            // cancellation flow can `kill(-pgid, sig)` and reach
            // any subprocesses the task itself spawned
            // (`EXEC-013` step 2, `EXEC-014`).
            command.process_group(0);
        }

        let mut child = command.spawn().with_context(|_| SpawnFailedSnafu {
            program: plan.program.clone(),
        })?;

        let stdout = child
            .stdout
            .take()
            .expect("stdout was configured as a pipe");
        let stderr = child
            .stderr
            .take()
            .expect("stderr was configured as a pipe");

        Ok(Spawned {
            process: StdProcess { child },
            stdout,
            stderr,
        })
    }
}

/// Production [`Process`] wrapping [`tokio::process::Child`].
#[derive(Debug)]
pub struct StdProcess {
    child: Child,
}

impl Process for StdProcess {
    type Stdout = ChildStdout;
    type Stderr = ChildStderr;

    fn id(&self) -> Option<ProcessId> {
        self.child.id().map(ProcessId)
    }

    fn send_signal(&mut self, signal: Signal) -> Result<(), ProcessError> {
        let pid = self.id();
        #[cfg(unix)]
        {
            deliver_unix_signal(&mut self.child, signal, pid)
        }
        #[cfg(not(unix))]
        {
            deliver_non_unix_signal(&mut self.child, signal, pid)
        }
    }

    async fn wait(&mut self) -> Result<ExitStatus, ProcessError> {
        let pid = self.id();
        self.child
            .wait()
            .await
            .with_context(|_| WaitFailedSnafu { pid })
    }
}

/// Deliver `signal` to the spawned child's process group on Unix.
///
/// All three [`Signal`] variants route through
/// `nix::sys::signal::kill` against `-pgid` so any subprocesses the
/// task itself forked also receive the signal (`EXEC-013` step 2,
/// `EXEC-014`). The child was placed in its own process group at
/// spawn time, so the group id equals the child's pid.
#[cfg(unix)]
fn deliver_unix_signal(
    child: &mut Child,
    signal: Signal,
    pid: Option<ProcessId>,
) -> Result<(), ProcessError> {
    use nix::sys::signal::{Signal as NixSignal, kill as nix_kill};
    use nix::unistd::Pid;

    let Some(ProcessId(raw_pid)) = pid else {
        return Err(ProcessError::SignalFailed {
            signal,
            pid: None,
            source: IoError::new(ErrorKind::NotFound, "child has already been reaped"),
        });
    };

    let signed_pid = i32::try_from(raw_pid).map_err(|_| ProcessError::SignalFailed {
        signal,
        pid,
        source: IoError::other("pid exceeds i32 range"),
    })?;
    let group_target = Pid::from_raw(-signed_pid);

    let nix_sig = match signal {
        Signal::Terminate => NixSignal::SIGTERM,
        Signal::Interrupt => NixSignal::SIGINT,
        Signal::Kill => NixSignal::SIGKILL,
    };

    let send_result = nix_kill(group_target, nix_sig).map_err(|errno| ProcessError::SignalFailed {
        signal,
        pid,
        source: IoError::from_raw_os_error(errno as i32),
    });

    // SIGKILL also needs the kill_on_drop bookkeeping in
    // tokio so a later drop does not race against the kernel
    // having already reaped the child.
    if signal == Signal::Kill && send_result.is_ok() {
        let _ = child.start_kill();
    }

    send_result
}

/// Deliver `signal` to the spawned child on non-Unix hosts.
///
/// Only [`Signal::Kill`] is supported; SIGTERM / SIGINT surface
/// [`std::io::ErrorKind::Unsupported`]. The per-future grace
/// dance in `run_fresh` swallows the SIGTERM error and proceeds
/// straight to the grace timer (then SIGKILL), so Windows hosts
/// still terminate cancelled children, just without any clean-up
/// signal.
#[cfg(not(unix))]
fn deliver_non_unix_signal(
    child: &mut Child,
    signal: Signal,
    pid: Option<ProcessId>,
) -> Result<(), ProcessError> {
    match signal {
        Signal::Kill => child
            .start_kill()
            .map_err(|source| ProcessError::SignalFailed {
                signal,
                pid,
                source,
            }),
        Signal::Interrupt | Signal::Terminate => Err(ProcessError::SignalFailed {
            signal,
            pid,
            source: IoError::new(
                ErrorKind::Unsupported,
                "SIGTERM and SIGINT are Unix-only in haz",
            ),
        }),
    }
}

#[cfg(all(test, unix))]
mod unix_tests {
    use std::ffi::OsString;
    use std::os::unix::process::ExitStatusExt;

    use tokio::io::AsyncReadExt;

    use super::{StdProcessSpawner, *};

    fn temp_cwd() -> std::path::PathBuf {
        std::env::temp_dir()
    }

    fn plan(program: &str, args: &[&str]) -> SpawnPlan {
        SpawnPlan {
            program: OsString::from(program),
            args: args.iter().map(OsString::from).collect(),
            env: Vec::new(),
            cwd: temp_cwd(),
        }
    }

    #[tokio::test]
    async fn spawn_echo_yields_stdout_and_zero_exit() {
        let spawner = StdProcessSpawner::new();
        let mut child = spawner
            .spawn(&plan("/bin/echo", &["hello"]))
            .await
            .expect("echo should spawn");

        let mut stdout_bytes = Vec::new();
        child
            .stdout
            .read_to_end(&mut stdout_bytes)
            .await
            .expect("stdout drain should succeed");
        let mut stderr_bytes = Vec::new();
        child
            .stderr
            .read_to_end(&mut stderr_bytes)
            .await
            .expect("stderr drain should succeed");

        let status = child.process.wait().await.expect("wait should succeed");

        assert_eq!(stdout_bytes, b"hello\n");
        assert!(stderr_bytes.is_empty());
        assert!(status.success());
        assert_eq!(status.code(), Some(0));
    }

    #[tokio::test]
    async fn spawn_false_yields_nonzero_exit() {
        let spawner = StdProcessSpawner::new();
        let mut child = spawner
            .spawn(&plan("/bin/sh", &["-c", "exit 7"]))
            .await
            .expect("sh should spawn");

        let status = child.process.wait().await.expect("wait should succeed");

        assert!(!status.success());
        assert_eq!(status.code(), Some(7));
    }

    #[tokio::test]
    async fn spawn_propagates_environment() {
        let spawner = StdProcessSpawner::new();
        let mut p = SpawnPlan {
            program: OsString::from("/bin/sh"),
            args: vec![
                OsString::from("-c"),
                OsString::from("printf '%s' \"$HAZ_TEST_VAR\""),
            ],
            env: vec![(OsString::from("HAZ_TEST_VAR"), OsString::from("propagated"))],
            cwd: temp_cwd(),
        };
        // Mutate to ensure the vector is what gets propagated.
        p.env.push((OsString::from("UNUSED"), OsString::from("ok")));

        let mut child = spawner.spawn(&p).await.expect("sh should spawn");
        let mut stdout = Vec::new();
        child
            .stdout
            .read_to_end(&mut stdout)
            .await
            .expect("stdout drain should succeed");
        let status = child.process.wait().await.expect("wait should succeed");

        assert!(status.success());
        assert_eq!(stdout, b"propagated");
    }

    #[tokio::test]
    async fn spawn_runs_in_supplied_cwd() {
        let temp = std::env::temp_dir();
        let spawner = StdProcessSpawner::new();
        let mut child = spawner
            .spawn(&SpawnPlan {
                program: OsString::from("/bin/sh"),
                args: vec![OsString::from("-c"), OsString::from("pwd")],
                env: Vec::new(),
                cwd: temp.clone(),
            })
            .await
            .expect("sh should spawn");
        let mut stdout = Vec::new();
        child
            .stdout
            .read_to_end(&mut stdout)
            .await
            .expect("stdout drain should succeed");
        let status = child.process.wait().await.expect("wait should succeed");

        assert!(status.success());
        // /tmp may itself be a symlink (e.g. macOS), so we accept any
        // cwd whose canonical form matches the supplied one.
        let observed = std::path::PathBuf::from(
            String::from_utf8(stdout)
                .expect("pwd output should be UTF-8")
                .trim_end()
                .to_owned(),
        );
        let expected_canonical = std::fs::canonicalize(&temp).expect("temp should canonicalise");
        let observed_canonical =
            std::fs::canonicalize(&observed).expect("observed cwd should canonicalise");
        assert_eq!(observed_canonical, expected_canonical);
    }

    #[tokio::test]
    async fn spawn_rejects_relative_cwd() {
        let spawner = StdProcessSpawner::new();
        let p = SpawnPlan {
            program: OsString::from("/bin/echo"),
            args: vec![OsString::from("hi")],
            env: Vec::new(),
            cwd: std::path::PathBuf::from("relative/path"),
        };
        match spawner.spawn(&p).await {
            Err(ProcessError::NonAbsoluteCwd { cwd }) => {
                assert_eq!(cwd, std::path::PathBuf::from("relative/path"));
            }
            Err(other) => panic!("expected NonAbsoluteCwd, got {other:?}"),
            Ok(_) => panic!("expected NonAbsoluteCwd, got success"),
        }
    }

    #[tokio::test]
    async fn spawn_missing_program_surfaces_spawn_failed() {
        let spawner = StdProcessSpawner::new();
        let p = SpawnPlan {
            program: OsString::from("/nonexistent/haz-exec/spawn-target-please-dont-exist"),
            args: Vec::new(),
            env: Vec::new(),
            cwd: temp_cwd(),
        };
        match spawner.spawn(&p).await {
            Err(ProcessError::SpawnFailed { program, .. }) => {
                assert!(program.to_string_lossy().contains("nonexistent"));
            }
            Err(other) => panic!("expected SpawnFailed, got {other:?}"),
            Ok(_) => panic!("expected SpawnFailed, got success"),
        }
    }

    #[tokio::test]
    async fn send_signal_kill_terminates_long_running_child() {
        let spawner = StdProcessSpawner::new();
        let mut child = spawner
            .spawn(&plan("/bin/sh", &["-c", "sleep 60"]))
            .await
            .expect("sh should spawn");

        assert!(child.process.id().is_some());
        child
            .process
            .send_signal(Signal::Kill)
            .expect("kill should be queued");
        let status = child.process.wait().await.expect("wait should succeed");

        assert!(!status.success());
        // SIGKILL == 9 on every Unix platform haz currently targets.
        assert_eq!(status.signal(), Some(9));
        assert!(
            child.process.id().is_none(),
            "id() should be None after wait"
        );
    }

    #[tokio::test]
    async fn send_signal_terminate_kills_child_that_respects_sigterm() {
        let spawner = StdProcessSpawner::new();
        // `sleep 60` exits on SIGTERM with signal-terminated status.
        let mut child = spawner
            .spawn(&plan("/bin/sh", &["-c", "sleep 60"]))
            .await
            .expect("sh should spawn");

        child
            .process
            .send_signal(Signal::Terminate)
            .expect("SIGTERM should be delivered");
        let status = child.process.wait().await.expect("wait should succeed");

        assert!(!status.success());
        // SIGTERM == 15 on every Unix platform haz targets.
        assert_eq!(status.signal(), Some(15));
    }

    #[tokio::test]
    async fn send_signal_interrupt_kills_child_that_respects_sigint() {
        let spawner = StdProcessSpawner::new();
        let mut child = spawner
            .spawn(&plan("/bin/sh", &["-c", "sleep 60"]))
            .await
            .expect("sh should spawn");

        child
            .process
            .send_signal(Signal::Interrupt)
            .expect("SIGINT should be delivered");
        let status = child.process.wait().await.expect("wait should succeed");

        assert!(!status.success());
        // SIGINT == 2 on every Unix platform haz targets.
        assert_eq!(status.signal(), Some(2));
    }

    #[tokio::test]
    async fn send_signal_terminate_after_reap_errors_not_found() {
        let spawner = StdProcessSpawner::new();
        let mut child = spawner
            .spawn(&plan("/bin/sh", &["-c", "exit 0"]))
            .await
            .expect("sh should spawn");
        // Drain the streams so wait can complete.
        let mut stdout = Vec::new();
        child
            .stdout
            .read_to_end(&mut stdout)
            .await
            .expect("stdout drain should succeed");
        let mut stderr = Vec::new();
        child
            .stderr
            .read_to_end(&mut stderr)
            .await
            .expect("stderr drain should succeed");
        let _ = child.process.wait().await.expect("wait should succeed");

        // The child is reaped; pid is None and the helper rejects.
        match child.process.send_signal(Signal::Terminate) {
            Err(ProcessError::SignalFailed {
                signal,
                pid,
                source,
            }) => {
                assert_eq!(signal, Signal::Terminate);
                assert!(pid.is_none());
                assert_eq!(source.kind(), ErrorKind::NotFound);
            }
            other => panic!("expected SignalFailed, got {other:?}"),
        }
    }
}