server-manager/core/telnet_client.py

"""
Telnet client — interactive telnet session with the same interface as ShellSession.
"""

import asyncio
import threading
from core.logger import log


class TelnetSession:
    """Interactive telnet session — same interface as ShellSession from ssh_client.py."""

    def __init__(self, server: dict, cols: int = 80, rows: int = 24):
        self.server = server
        self.cols = cols
        self.rows = rows
        self._loop: asyncio.AbstractEventLoop | None = None
        self._thread: threading.Thread | None = None
        self._reader = None
        self._writer = None
        self._running = False

        # Callbacks — set by the owner
        self.on_data = None        # on_data(data: bytes)
        self.on_disconnect = None  # on_disconnect()

    @property
    def connected(self) -> bool:
        return self._running and self._writer is not None

    def connect(self):
        """Start telnet connection in a background thread running an asyncio event loop."""
        self._running = True
        self._thread = threading.Thread(target=self._run_loop, daemon=True)
        self._thread.start()

    def _run_loop(self):
        """Entry point for the background thread — creates event loop and runs connection."""
        self._loop = asyncio.new_event_loop()
        asyncio.set_event_loop(self._loop)
        try:
            self._loop.run_until_complete(self._async_connect())
        except Exception as e:
            log.debug(f"TelnetSession loop error: {e}")
        finally:
            self._running = False
            try:
                self._loop.close()
            except Exception:
                pass
            self._loop = None
            if self.on_disconnect:
                self.on_disconnect()

    async def _async_connect(self):
        """Async telnet connection: open, login, then read loop."""
        try:
            import telnetlib3
        except ImportError:
            log.error("telnetlib3 not installed. Run: pip install telnetlib3")
            raise ImportError("telnetlib3 is required for telnet connections")

        hostname = self.server["ip"]
        port = self.server.get("port", 23)
        user = self.server.get("user", "")
        password = self.server.get("password", "")

        log.info(f"TelnetSession connecting to {self.server.get('alias', '?')} port {port}")

        reader, writer = await telnetlib3.open_connection(
            host=hostname,
            port=port,
            cols=self.cols,
            rows=self.rows,
            connect_minwait=0.5,
        )
        self._reader = reader
        self._writer = writer

        # Login sequence — wait for prompts and send credentials
        await self._login_sequence(reader, writer, user, password)

        # Main read loop
        await self._read_loop(reader)

    async def _login_sequence(self, reader, writer, user: str, password: str):
        """Wait for login/password prompts and send credentials."""
        buf = ""
        timeout = 10.0  # seconds to wait for login prompt

        while self._running:
            try:
                data = await asyncio.wait_for(reader.read(4096), timeout=timeout)
            except asyncio.TimeoutError:
                log.debug("TelnetSession login sequence timed out waiting for prompt")
                break
            except Exception:
                break

            if not data:
                break

            if self.on_data:
                self.on_data(data.encode("utf-8", errors="replace") if isinstance(data, str) else data)

            buf += data if isinstance(data, str) else data.decode("utf-8", errors="replace")
            buf_lower = buf.lower()

            if "login:" in buf_lower or "username:" in buf_lower:
                writer.write(user + "\r\n")
                buf = ""
                continue

            if "password:" in buf_lower:
                writer.write(password + "\r\n")
                buf = ""
                break  # Login done, proceed to read loop

            # If we see a shell prompt, login may not be required
            if buf_lower.rstrip().endswith(("$", "#", ">")):
                break

        log.debug("TelnetSession login sequence complete")

    async def _read_loop(self, reader):
        """Read data from telnet and forward to on_data callback."""
        try:
            while self._running:
                try:
                    data = await asyncio.wait_for(reader.read(65536), timeout=0.5)
                except asyncio.TimeoutError:
                    continue
                except Exception:
                    break

                if not data:
                    break

                raw = data.encode("utf-8", errors="replace") if isinstance(data, str) else data
                if self.on_data:
                    self.on_data(raw)
        except Exception as e:
            log.debug(f"TelnetSession read loop error: {e}")

    def send(self, data: bytes):
        """Send data to the telnet session."""
        if not self._running or self._writer is None or self._loop is None:
            return
        text = data.decode("utf-8", errors="replace")
        try:
            self._loop.call_soon_threadsafe(self._writer.write, text)
        except RuntimeError:
            self._running = False
            if self.on_disconnect:
                self.on_disconnect()

    def resize(self, cols: int, rows: int):
        """Resize terminal — NAWS negotiation if supported, otherwise no-op."""
        self.cols = cols
        self.rows = rows
        # telnetlib3 handles NAWS during initial negotiation;
        # runtime resize requires protocol-level support which
        # is not reliably available, so this is a best-effort no-op.
        log.debug(f"TelnetSession resize requested: {cols}x{rows} (no-op)")

    def disconnect(self):
        """Close telnet session and stop background thread."""
        self._running = False
        if self._writer is not None:
            try:
                self._writer.close()
            except Exception as e:
                log.debug(f"TelnetSession writer close: {e}")
            self._writer = None
        self._reader = None
        if self._loop is not None:
            try:
                self._loop.call_soon_threadsafe(self._loop.stop)
            except RuntimeError:
                pass