omnyssh-core 1.1.0

//! russh-backed SSH sessions for the multi-session terminal.
//!
//! Each session is a tokio task that owns a russh [`Channel`] with a
//! server-allocated PTY (via `request_pty` + `request_shell`), drives a
//! [`vt100::Parser`], and multiplexes I/O over a control channel. The parsed
//! screen state is exposed via an `Arc<Mutex<vt100::Parser>>` that the render
//! loop can snapshot without blocking. Using russh over a plain TCP socket
//! avoids the local pseudo-console entirely, so the same code path works on
//! every OS (notably fixing the dead Windows terminal).
//!
//! [`PtyManager`] owns all active sessions and provides a simple API for the
//! application layer.

use std::sync::{Arc, Mutex};

use anyhow::{Context, Result};
use russh::client::Handle;
use russh::ChannelMsg;
use tokio::sync::mpsc;

use crate::event::CoreEvent;
use crate::ssh::client::Host;
use crate::ssh::session::{connect_and_auth, KnownHostsHandler};

/// Stable numeric identifier for a PTY session (mirrors [`crate::event::SessionId`]).
pub type SessionId = u64;

// ---------------------------------------------------------------------------
// Control messages — main thread → session task
// ---------------------------------------------------------------------------

/// A command sent to a session's owning task.
enum Ctrl {
    /// Keystrokes or pasted bytes for the remote shell.
    Input(Vec<u8>),
    /// Window resize; forwarded to the server as `window_change`.
    Resize { cols: u16, rows: u16 },
    /// Request the task to end and close the connection.
    Close,
}

// ---------------------------------------------------------------------------
// PtySession — a handle to a running session task
// ---------------------------------------------------------------------------

/// Handle to a session task. Holds the shared parser for rendering and the
/// control sender; dropping the sender (or sending [`Ctrl::Close`]) ends the
/// task, which closes the russh connection.
struct PtySession {
    /// Unique identifier for this session.
    id: SessionId,
    /// Shared VT100 parser. The task writes into it; the render loop takes a
    /// read-side snapshot. Held only for microseconds to avoid blocking.
    parser: Arc<Mutex<vt100::Parser>>,
    /// Control channel to the session task (input / resize / close).
    ctrl_tx: mpsc::UnboundedSender<Ctrl>,
}

/// Feeds bytes to the parser in 256-byte sub-chunks, releasing the lock between
/// chunks so a large burst does not starve the render loop.
fn feed_parser(parser: &Arc<Mutex<vt100::Parser>>, data: &[u8]) {
    const CHUNK: usize = 256;
    let mut off = 0;
    while off < data.len() {
        let end = (off + CHUNK).min(data.len());
        if let Ok(mut p) = parser.lock() {
            p.process(&data[off..end]);
        }
        off = end;
    }
}

/// Whether a locale value names the UTF-8 codeset (`en_US.UTF-8`, `ru_RU.utf8`,
/// `de_DE.UTF-8@euro`, …).
fn is_utf8_locale(value: &str) -> bool {
    match value.rsplit_once('.') {
        Some((_, codeset)) => {
            let codeset = codeset.split('@').next().unwrap_or(codeset);
            codeset.eq_ignore_ascii_case("utf-8") || codeset.eq_ignore_ascii_case("utf8")
        }
        None => false,
    }
}

/// The locale environment to forward to a remote shell: every `LANG`/`LC_*`
/// variable from `vars`, plus an `LC_CTYPE=C.UTF-8` fallback *only* when the
/// forwarded set doesn't already resolve the character type to UTF-8. Mirrors an
/// ssh client's `SendEnv LANG LC_*` while guaranteeing a UTF-8 character type for
/// a process with no locale env (a GUI launched from Finder) — without clobbering
/// an already-UTF-8 `LANG` with a `C.UTF-8` the server may not have. Pure, so it
/// can be unit-tested; [`forward_locale`] just relays the result.
fn locale_env<I>(vars: I) -> Vec<(String, String)>
where
    I: IntoIterator<Item = (String, String)>,
{
    let mut out = Vec::new();
    let (mut lc_all, mut lc_ctype, mut lang) = (None, None, None);
    for (name, value) in vars {
        if name == "LANG" || name.starts_with("LC_") {
            match name.as_str() {
                "LC_ALL" => lc_all = Some(value.clone()),
                "LC_CTYPE" => lc_ctype = Some(value.clone()),
                "LANG" => lang = Some(value.clone()),
                _ => {}
            }
            out.push((name, value));
        }
    }
    // `LC_ALL` overrides every category, so respect the user's explicit choice
    // verbatim. Otherwise the character type resolves from `LC_CTYPE` then `LANG`;
    // force UTF-8 only when neither already provides it, replacing a non-UTF-8
    // `LC_CTYPE` rather than sending a duplicate.
    let force_utf8 = match lc_all {
        Some(_) => false,
        None => !lc_ctype
            .as_deref()
            .or(lang.as_deref())
            .is_some_and(is_utf8_locale),
    };
    if force_utf8 {
        out.retain(|(name, _)| name != "LC_CTYPE");
        out.push(("LC_CTYPE".to_string(), "C.UTF-8".to_string()));
    }
    out
}

/// Forwards a UTF-8 locale to the remote shell, mirroring an ssh client's
/// default `SendEnv LANG LC_*`. Best-effort: servers without `AcceptEnv` ignore
/// it, so behaviour is unchanged there.
async fn forward_locale(channel: &russh::Channel<russh::client::Msg>) {
    // `vars_os` (not `vars`) so a non-UTF-8 variable elsewhere in the environment
    // can't panic this session task; locale values are ASCII, so dropping any
    // undecodable entry is safe.
    let vars = std::env::vars_os()
        .filter_map(|(k, v)| Some((k.into_string().ok()?, v.into_string().ok()?)));
    for (name, value) in locale_env(vars) {
        let _ = channel.set_env(false, name, value).await;
    }
}

/// Opens a channel and requests a remote PTY + shell (the `ssh -t` equivalent).
async fn open_shell(
    handle: &Handle<KnownHostsHandler>,
    cols: u16,
    rows: u16,
) -> Result<russh::Channel<russh::client::Msg>> {
    let channel = handle
        .channel_open_session()
        .await
        .context("open terminal channel")?;
    // Sent before the shell starts so it inherits the locale.
    forward_locale(&channel).await;
    // IUTF8 tells the server's line discipline that input is UTF-8, so multibyte
    // (e.g. Cyrillic) editing works in canonical mode. Unknown modes are ignored.
    channel
        .request_pty(
            false,
            "xterm-256color",
            cols as u32,
            rows as u32,
            0,
            0,
            &[(russh::Pty::IUTF8, 1)],
        )
        .await
        .context("request remote pty")?;
    channel
        .request_shell(false)
        .await
        .context("request remote shell")?;
    Ok(channel)
}

/// Owns the russh channel for one session and multiplexes I/O until close/EOF.
#[allow(clippy::too_many_arguments)] // additive raw-output sink (§3.6) is the 8th
async fn session_task(
    id: SessionId,
    host: Host,
    cols: u16,
    rows: u16,
    parser: Arc<Mutex<vt100::Parser>>,
    mut ctrl_rx: mpsc::UnboundedReceiver<Ctrl>,
    tx: mpsc::Sender<CoreEvent>,
    raw_output: Option<mpsc::Sender<(SessionId, Vec<u8>)>>,
) {
    // Phase A/B: connect, authenticate, and open the remote shell. Failures are
    // reported in the status bar and tear the tab down via PtyExited.
    let result = async {
        let handle = connect_and_auth(&host).await?;
        open_shell(&handle, cols, rows).await.map(|ch| (handle, ch))
    }
    .await;
    let (_handle, mut channel) = match result {
        Ok(pair) => pair,
        Err(e) => {
            let _ = tx.send(CoreEvent::Error(format!("Terminal: {e}"))).await;
            let _ = tx.send(CoreEvent::PtyExited(id)).await;
            return;
        }
    };

    // Phase C: pump loop (official russh interactive idiom). `wait` is the only
    // &mut method, so a single owning task can select over it and the control
    // receiver without aliasing.
    loop {
        tokio::select! {
            msg = channel.wait() => match msg {
                // stdout and remote stderr both render in a real terminal.
                Some(ChannelMsg::Data { data })
                | Some(ChannelMsg::ExtendedData { data, .. }) => {
                    feed_parser(&parser, &data);
                    let _ = tx.send(CoreEvent::PtyOutput(id)).await;
                    // Additive GUI tap (tech-gui.md §3.6): mirror the raw bytes to
                    // the frontend channel. Absent for the TUI → no behaviour change.
                    if let Some(raw) = &raw_output {
                        let _ = raw.send((id, data.to_vec())).await;
                    }
                }
                Some(ChannelMsg::Eof) | Some(ChannelMsg::Close) | None => break,
                _ => {} // ExitStatus etc.: ignore, wait for Close.
            },
            cmd = ctrl_rx.recv() => match cmd {
                Some(Ctrl::Input(bytes)) => {
                    let _ = channel.data(&bytes[..]).await;
                }
                Some(Ctrl::Resize { cols, rows }) => {
                    let _ = channel.window_change(cols as u32, rows as u32, 0, 0).await;
                }
                Some(Ctrl::Close) | None => break,
            },
        }
    }

    let _ = channel.eof().await;
    let _ = tx.send(CoreEvent::PtyExited(id)).await;
    // _handle drops here → russh closes the TCP connection.
}

// ---------------------------------------------------------------------------
// PtyManager
// ---------------------------------------------------------------------------

/// Manages all active terminal sessions.
///
/// Stored by the frontend outside of its shared state to avoid reference cycles.
/// Dropping `PtyManager` or calling [`PtyManager::shutdown`] closes all
/// sessions gracefully.
pub struct PtyManager {
    sessions: Vec<PtySession>,
    next_id: u64,
    /// Optional raw-output tap (GUI only). When set, each session task ALSO
    /// forwards every data chunk here, tagged by its [`SessionId`], alongside the
    /// existing parser feed + `PtyOutput` nudge. `None` for the TUI, whose path is
    /// byte-for-byte unchanged.
    raw_output: Option<mpsc::Sender<(SessionId, Vec<u8>)>>,
}

impl PtyManager {
    /// Creates an empty manager with no raw-output tap (the TUI path).
    pub fn new() -> Self {
        Self {
            sessions: Vec::new(),
            next_id: 1,
            raw_output: None,
        }
    }

    /// Creates an empty manager that also mirrors every session's raw bytes into
    /// `raw_output`, keyed by [`SessionId`] (the GUI terminal tap). Sessions and
    /// the id space are identical to [`PtyManager::new`]; only the extra sink
    /// differs, so the TUI construction path is unaffected.
    pub fn with_raw_output(raw_output: mpsc::Sender<(SessionId, Vec<u8>)>) -> Self {
        Self {
            sessions: Vec::new(),
            next_id: 1,
            raw_output: Some(raw_output),
        }
    }

    /// Opens a new terminal tab for `host` and returns the assigned [`SessionId`].
    ///
    /// Returns immediately; the connection runs in a background task. Connection
    /// or auth errors surface later via `CoreEvent::Error` + `PtyExited`.
    ///
    /// # Errors
    /// Currently infallible, but kept fallible so the caller's error handling
    /// (and the public API) stays unchanged.
    pub fn open(
        &mut self,
        host: &Host,
        cols: u16,
        rows: u16,
        tx: mpsc::Sender<CoreEvent>,
    ) -> Result<SessionId> {
        // ProxyJump is not yet wired into the russh terminal path. Refuse rather
        // than silently connecting direct to the wrong host.
        if host.proxy_jump.is_some() {
            anyhow::bail!("ProxyJump is not yet supported in the terminal");
        }
        let id = self.next_id;
        self.next_id += 1;
        let parser = Arc::new(Mutex::new(vt100::Parser::new(rows, cols, 1000)));
        let (ctrl_tx, ctrl_rx) = mpsc::unbounded_channel();
        tokio::spawn(session_task(
            id,
            host.clone(),
            cols,
            rows,
            Arc::clone(&parser),
            ctrl_rx,
            tx,
            self.raw_output.clone(),
        ));
        self.sessions.push(PtySession {
            id,
            parser,
            ctrl_tx,
        });
        tracing::info!("terminal session {} opened for host '{}'", id, host.name);
        Ok(id)
    }

    /// Sends raw bytes to the session identified by `id`. Unknown id is a no-op.
    ///
    /// # Errors
    /// Infallible in practice; a dropped task is ignored like a closed session.
    pub fn write(&mut self, id: SessionId, data: &[u8]) -> Result<()> {
        if let Some(s) = self.sessions.iter().find(|s| s.id == id) {
            let _ = s.ctrl_tx.send(Ctrl::Input(data.to_vec()));
        }
        Ok(())
    }

    /// Forwards a resize to the session identified by `id`. No-op if not found.
    ///
    /// The vt100 parser is resized by the app layer; the task only relays
    /// `window_change` to the server.
    ///
    /// # Errors
    /// Infallible; kept fallible to preserve the public signature.
    pub fn resize(&mut self, id: SessionId, cols: u16, rows: u16) -> Result<()> {
        if let Some(s) = self.sessions.iter().find(|s| s.id == id) {
            let _ = s.ctrl_tx.send(Ctrl::Resize { cols, rows });
        }
        Ok(())
    }

    /// Closes and removes the session with the given `id`.
    pub fn close(&mut self, id: SessionId) {
        if let Some(pos) = self.sessions.iter().position(|s| s.id == id) {
            let s = self.sessions.remove(pos);
            let _ = s.ctrl_tx.send(Ctrl::Close);
            tracing::info!("terminal session {} closed", id);
        }
    }

    /// Gracefully shuts down all sessions.
    pub fn shutdown(self) {
        for s in self.sessions {
            let _ = s.ctrl_tx.send(Ctrl::Close);
        }
        // Dropping each ctrl_tx also ends its task as a backstop.
    }

    /// Returns the parser `Arc` for the session with the given `id`, if any.
    pub fn parser_for(&self, id: SessionId) -> Option<Arc<Mutex<vt100::Parser>>> {
        self.sessions
            .iter()
            .find(|s| s.id == id)
            .map(|s| Arc::clone(&s.parser))
    }
}

impl Default for PtyManager {
    fn default() -> Self {
        Self::new()
    }
}

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

    fn dummy_tx() -> mpsc::Sender<CoreEvent> {
        mpsc::channel(1).0
    }

    #[test]
    fn default_construction_has_no_raw_tap() {
        // The TUI path must be byte-for-byte unchanged (tech-gui.md §3.6): the
        // additive sink is absent unless a GUI opts in via `with_raw_output`.
        assert!(PtyManager::new().raw_output.is_none());
        assert!(PtyManager::default().raw_output.is_none());
    }

    #[test]
    fn with_raw_output_installs_the_tap() {
        let (raw_tx, _raw_rx) = mpsc::channel::<(SessionId, Vec<u8>)>(1);
        assert!(PtyManager::with_raw_output(raw_tx).raw_output.is_some());
    }

    #[tokio::test]
    async fn open_assigns_incrementing_ids() {
        let mut mgr = PtyManager::new();
        let host = Host::default();
        let a = mgr.open(&host, 80, 24, dummy_tx()).unwrap();
        let b = mgr.open(&host, 80, 24, dummy_tx()).unwrap();
        assert_eq!((a, b), (1, 2));
        assert_eq!(mgr.sessions.len(), 2);
    }

    #[tokio::test]
    async fn close_removes_only_the_target() {
        let mut mgr = PtyManager::new();
        let host = Host::default();
        let a = mgr.open(&host, 80, 24, dummy_tx()).unwrap();
        let b = mgr.open(&host, 80, 24, dummy_tx()).unwrap();
        mgr.close(a);
        assert_eq!(mgr.sessions.len(), 1);
        assert_eq!(mgr.sessions[0].id, b);
    }

    #[tokio::test]
    async fn write_and_resize_unknown_id_are_noops() {
        let mut mgr = PtyManager::new();
        assert!(mgr.write(999, b"x").is_ok());
        assert!(mgr.resize(999, 80, 24).is_ok());
    }

    #[tokio::test]
    async fn parser_for_returns_open_session_only() {
        let mut mgr = PtyManager::new();
        let id = mgr.open(&Host::default(), 80, 24, dummy_tx()).unwrap();
        assert!(mgr.parser_for(id).is_some());
        assert!(mgr.parser_for(id + 1).is_none());
    }

    fn env(pairs: &[(&str, &str)]) -> Vec<(String, String)> {
        pairs
            .iter()
            .map(|(k, v)| (k.to_string(), v.to_string()))
            .collect()
    }

    #[test]
    fn is_utf8_locale_recognizes_common_forms() {
        assert!(is_utf8_locale("en_US.UTF-8"));
        assert!(is_utf8_locale("ru_RU.utf8"));
        assert!(is_utf8_locale("de_DE.UTF-8@euro"));
        assert!(!is_utf8_locale("C"));
        assert!(!is_utf8_locale("POSIX"));
        assert!(!is_utf8_locale("en_US.ISO8859-1"));
    }

    #[test]
    fn locale_env_defaults_ctype_to_utf8_when_no_locale_env() {
        // A process with no locale env (e.g. a GUI launched from Finder) still
        // gets a UTF-8 character type forwarded.
        let got = locale_env(env(&[("PATH", "/bin"), ("HOME", "/root")]));
        assert_eq!(got, env(&[("LC_CTYPE", "C.UTF-8")]));
    }

    #[test]
    fn locale_env_forces_utf8_when_lang_is_not_utf8() {
        let got = locale_env(env(&[("LANG", "C")]));
        assert!(got.contains(&("LANG".into(), "C".into())));
        assert!(got.contains(&("LC_CTYPE".into(), "C.UTF-8".into())));
    }

    #[test]
    fn locale_env_keeps_a_utf8_lang_and_adds_no_fallback() {
        // Regression guard: a working UTF-8 LANG must not be overridden by a
        // C.UTF-8 the server might not have.
        let got = locale_env(env(&[
            ("LANG", "ru_RU.UTF-8"),
            ("LC_MESSAGES", "ru_RU.UTF-8"),
        ]));
        assert!(got.contains(&("LANG".into(), "ru_RU.UTF-8".into())));
        assert!(got.iter().all(|(k, _)| k != "LC_CTYPE"));
    }

    #[test]
    fn locale_env_replaces_a_non_utf8_ctype_without_duplicating() {
        let got = locale_env(env(&[("LC_CTYPE", "C")]));
        assert_eq!(got, env(&[("LC_CTYPE", "C.UTF-8")]));
    }

    #[test]
    fn locale_env_respects_an_explicit_utf8_ctype() {
        let got = locale_env(env(&[("LC_CTYPE", "ru_RU.UTF-8")]));
        assert_eq!(got, env(&[("LC_CTYPE", "ru_RU.UTF-8")]));
    }

    #[test]
    fn locale_env_respects_lc_all() {
        // LC_ALL overrides every category, so leave the explicit choice untouched.
        let got = locale_env(env(&[("LC_ALL", "C")]));
        assert_eq!(got, env(&[("LC_ALL", "C")]));
    }
}