hermes-webui/api/terminal.py

"""Embedded workspace terminal support for Hermes Web UI.

The terminal is intentionally independent from the agent execution path.  It
starts a shell with an explicit cwd/env per process and never mutates
process-global os.environ, which avoids expanding the session-env race tracked
in the agent execution layer.
"""

from __future__ import annotations

import errno
import atexit
import codecs
import fcntl
import os
import queue
import select
import shutil
import signal
import struct
import subprocess
import termios
import threading
from dataclasses import dataclass, field
from pathlib import Path


def _set_nonblocking(fd: int) -> None:
    flags = fcntl.fcntl(fd, fcntl.F_GETFL)
    fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)


def _winsize(rows: int, cols: int) -> bytes:
    rows = max(8, min(int(rows or 24), 80))
    cols = max(20, min(int(cols or 80), 240))
    return struct.pack("HHHH", rows, cols, 0, 0)


@dataclass
class TerminalSession:
    session_id: str
    workspace: str
    proc: subprocess.Popen
    master_fd: int
    rows: int = 24
    cols: int = 80
    output: queue.Queue = field(default_factory=lambda: queue.Queue(maxsize=2000))
    closed: threading.Event = field(default_factory=threading.Event)
    reader: threading.Thread | None = None

    def is_alive(self) -> bool:
        return not self.closed.is_set() and self.proc.poll() is None

    def put_output(self, event: str, payload: dict) -> None:
        try:
            self.output.put_nowait((event, payload))
        except queue.Full:
            # Keep the terminal responsive by dropping the oldest queued chunk.
            try:
                self.output.get_nowait()
            except queue.Empty:
                pass
            try:
                self.output.put_nowait((event, payload))
            except queue.Full:
                pass


_TERMINALS: dict[str, TerminalSession] = {}
_LOCK = threading.RLock()


# NOTE on parent-death-signal: a previous version of this module set
# PR_SET_PDEATHSIG via a preexec_fn to terminate orphaned PTY shells when the
# WebUI process crashed.  That broke every Linux user (#2853): WebUI runs a
# ThreadingHTTPServer, so the Popen call happens on a short-lived per-request
# thread, and PR_SET_PDEATHSIG is per-thread.  The PTY shell registered the
# spawning thread as its "parent" and was killed with SIGTERM the instant that
# thread joined — within ~10 ms of opening the terminal — surfacing as the
# `[terminal closed]` banner.  The graceful path is covered by
# `atexit.register(close_all_terminals)` and the explicit `close_terminal`
# call sites; hard kills of the WebUI process leak the shell, which is the
# tradeoff for working on Linux at all.


def _decode_terminal_output(decoder, data: bytes) -> str:
    """Decode PTY bytes without stripping terminal control sequences."""
    return decoder.decode(data)


def _shell_path() -> str:
    shell = os.environ.get("SHELL") or ""
    if shell and Path(shell).exists():
        return shell
    return shutil.which("zsh") or shutil.which("bash") or shutil.which("sh") or "/bin/sh"


def _shell_argv(shell: str) -> list[str]:
    name = Path(shell).name
    if name in {"zsh", "bash", "sh"}:
        return [shell, "-i"]
    return [shell]


def _reader_loop(term: TerminalSession) -> None:
    decoder = codecs.getincrementaldecoder("utf-8")("replace")
    try:
        while not term.closed.is_set():
            if term.proc.poll() is not None:
                break
            try:
                ready, _, _ = select.select([term.master_fd], [], [], 0.25)
            except (OSError, ValueError):
                break
            if not ready:
                continue
            try:
                data = os.read(term.master_fd, 8192)
            except OSError as exc:
                if exc.errno in (errno.EIO, errno.EBADF):
                    break
                raise
            if not data:
                break
            text = _decode_terminal_output(decoder, data)
            if text:
                term.put_output("output", {"text": text})
    except Exception as exc:
        term.put_output("terminal_error", {"error": str(exc)})
    finally:
        term.closed.set()
        code = term.proc.poll()
        term.put_output("terminal_closed", {"exit_code": code})


def _set_size(term: TerminalSession, rows: int, cols: int) -> None:
    term.rows = max(8, min(int(rows or term.rows or 24), 80))
    term.cols = max(20, min(int(cols or term.cols or 80), 240))
    try:
        fcntl.ioctl(term.master_fd, termios.TIOCSWINSZ, _winsize(term.rows, term.cols))
    except OSError:
        pass
    try:
        if term.proc.poll() is None:
            os.killpg(term.proc.pid, signal.SIGWINCH)
    except (OSError, ProcessLookupError):
        pass


def start_terminal(session_id: str, workspace: Path, rows: int = 24, cols: int = 80, restart: bool = False) -> TerminalSession:
    """Start or return the embedded terminal for a WebUI session."""
    sid = str(session_id or "").strip()
    if not sid:
        raise ValueError("session_id is required")
    cwd = str(Path(workspace).expanduser().resolve())
    if not Path(cwd).is_dir():
        raise ValueError("workspace is not a directory")

    with _LOCK:
        current = _TERMINALS.get(sid)
        if current and current.is_alive() and not restart and current.workspace == cwd:
            _set_size(current, rows, cols)
            return current
        if current:
            close_terminal(sid)

        master_fd, slave_fd = os.openpty()
        # Build a safe env: allowlist common shell vars, strip API keys and secrets.
        # The PTY shell is an interactive UI surface — do not leak server credentials.
        _SAFE_ENV_KEYS = {
            "PATH", "HOME", "USER", "LOGNAME", "SHELL", "LANG", "LC_ALL",
            "LC_CTYPE", "LC_MESSAGES", "LANGUAGE", "TZ", "TMPDIR", "TEMP",
            "XDG_RUNTIME_DIR", "XDG_CONFIG_HOME", "XDG_DATA_HOME",
        }
        env = {k: v for k, v in os.environ.items() if k in _SAFE_ENV_KEYS}
        env.update(
            {
                "TERM": "xterm-256color",
                "COLORTERM": "truecolor",
                "COLUMNS": str(cols),
                "LINES": str(rows),
                "PWD": cwd,
                "HERMES_WEBUI_TERMINAL": "1",
            }
        )
        shell = _shell_path()
        proc = subprocess.Popen(
            _shell_argv(shell),
            cwd=cwd,
            env=env,
            stdin=slave_fd,
            stdout=slave_fd,
            stderr=slave_fd,
            close_fds=True,
            start_new_session=True,
        )
        os.close(slave_fd)
        _set_nonblocking(master_fd)

        term = TerminalSession(
            session_id=sid,
            workspace=cwd,
            proc=proc,
            master_fd=master_fd,
            rows=rows,
            cols=cols,
        )
        _set_size(term, rows, cols)
        term.reader = threading.Thread(target=_reader_loop, args=(term,), daemon=True)
        term.reader.start()
        _TERMINALS[sid] = term
        return term


def get_terminal(session_id: str) -> TerminalSession | None:
    with _LOCK:
        term = _TERMINALS.get(str(session_id or ""))
        if term and term.is_alive():
            return term
        return term


def write_terminal(session_id: str, data: str) -> None:
    term = get_terminal(session_id)
    if not term or not term.is_alive():
        raise KeyError("terminal not running")
    os.write(term.master_fd, str(data or "").encode("utf-8", errors="replace"))


def resize_terminal(session_id: str, rows: int, cols: int) -> None:
    term = get_terminal(session_id)
    if not term:
        raise KeyError("terminal not running")
    _set_size(term, rows, cols)


def close_terminal(session_id: str) -> bool:
    sid = str(session_id or "")
    with _LOCK:
        term = _TERMINALS.pop(sid, None)
    if not term:
        return False
    term.closed.set()
    try:
        if term.proc.poll() is None:
            try:
                os.killpg(term.proc.pid, signal.SIGHUP)
            except ProcessLookupError:
                pass
            try:
                term.proc.wait(timeout=1.5)
            except subprocess.TimeoutExpired:
                try:
                    os.killpg(term.proc.pid, signal.SIGKILL)
                except ProcessLookupError:
                    pass
                try:
                    term.proc.wait(timeout=1.0)
                except (subprocess.TimeoutExpired, ProcessLookupError):
                    pass
    finally:
        try:
            os.close(term.master_fd)
        except OSError:
            pass
    return True


def close_all_terminals() -> None:
    """Best-effort reap of embedded shells during graceful WebUI shutdown."""
    with _LOCK:
        session_ids = list(_TERMINALS)
    for session_id in session_ids:
        close_terminal(session_id)


atexit.register(close_all_terminals)