derp/plugins/webhook.py

"""Webhook listener: receive HTTP POST requests and relay messages to IRC."""

from __future__ import annotations

import asyncio
import hashlib
import hmac
import json
import logging
import time

from derp.plugin import command, event

log = logging.getLogger(__name__)

_MAX_BODY = 65536  # 64 KB


def _ps(bot):
    """Per-bot plugin runtime state."""
    return bot._pstate.setdefault("webhook", {
        "server": None,
        "request_count": 0,
        "started": 0.0,
    })


def _verify_signature(secret: str, body: bytes, signature: str) -> bool:
    """Verify HMAC-SHA256 signature from X-Signature header."""
    if not secret:
        return True  # no secret configured = open access
    if not signature.startswith("sha256="):
        return False
    expected = hmac.new(secret.encode(), body, hashlib.sha256).hexdigest()
    return hmac.compare_digest(expected, signature[7:])


def _http_response(status: int, reason: str, body: str = "") -> bytes:
    """Build a minimal HTTP/1.1 response."""
    body_bytes = body.encode("utf-8") if body else b""
    lines = [
        f"HTTP/1.1 {status} {reason}",
        "Content-Type: text/plain; charset=utf-8",
        f"Content-Length: {len(body_bytes)}",
        "Connection: close",
        "",
        "",
    ]
    return "\r\n".join(lines).encode("utf-8") + body_bytes


async def _handle_request(reader: asyncio.StreamReader,
                          writer: asyncio.StreamWriter,
                          bot, secret: str) -> None:
    """Parse one HTTP request and dispatch to IRC."""
    ps = _ps(bot)

    try:
        # Read request line
        request_line = await asyncio.wait_for(reader.readline(), timeout=10.0)
        if not request_line:
            return
        parts = request_line.decode("utf-8", errors="replace").strip().split()
        if len(parts) < 2:
            writer.write(_http_response(400, "Bad Request", "malformed request"))
            return
        method, _path = parts[0], parts[1]

        # Read headers
        headers: dict[str, str] = {}
        while True:
            line = await asyncio.wait_for(reader.readline(), timeout=10.0)
            if not line or line == b"\r\n" or line == b"\n":
                break
            decoded = line.decode("utf-8", errors="replace").strip()
            if ":" in decoded:
                key, val = decoded.split(":", 1)
                headers[key.strip().lower()] = val.strip()

        # Method check
        if method != "POST":
            writer.write(_http_response(405, "Method Not Allowed", "POST only"))
            return

        # Read body
        content_length = int(headers.get("content-length", "0"))
        if content_length > _MAX_BODY:
            writer.write(_http_response(413, "Payload Too Large",
                                        f"max {_MAX_BODY} bytes"))
            return
        body = await asyncio.wait_for(reader.readexactly(content_length),
                                      timeout=10.0)

        # Verify HMAC signature
        signature = headers.get("x-signature", "")
        if not _verify_signature(secret, body, signature):
            writer.write(_http_response(401, "Unauthorized", "bad signature"))
            return

        # Parse JSON
        try:
            data = json.loads(body)
        except (json.JSONDecodeError, UnicodeDecodeError):
            writer.write(_http_response(400, "Bad Request", "invalid JSON"))
            return

        # Validate fields
        channel = data.get("channel", "")
        text = data.get("text", "")
        is_action = data.get("action", False)

        if not isinstance(channel, str) or not channel.startswith(("#", "&")):
            writer.write(_http_response(400, "Bad Request", "invalid channel"))
            return
        if not isinstance(text, str) or not text.strip():
            writer.write(_http_response(400, "Bad Request", "empty text"))
            return

        # Send to IRC
        text = text.strip()
        if is_action:
            await bot.action(channel, text)
        else:
            await bot.send(channel, text)

        ps["request_count"] += 1
        writer.write(_http_response(200, "OK", "sent"))
        log.info("webhook: relayed to %s (%d bytes)", channel, len(text))

    except (asyncio.TimeoutError, asyncio.IncompleteReadError, ConnectionError):
        log.debug("webhook: client disconnected")
    except Exception:
        log.exception("webhook: error handling request")
        try:
            writer.write(_http_response(500, "Internal Server Error"))
        except Exception:
            pass
    finally:
        try:
            writer.close()
            await writer.wait_closed()
        except Exception:
            pass


@event("001")
async def on_connect(bot, message):
    """Start the webhook HTTP server on connect (if enabled)."""
    ps = _ps(bot)

    if ps["server"] is not None:
        return  # already running

    cfg = bot.config.get("webhook", {})
    if not cfg.get("enabled"):
        return

    host = cfg.get("host", "127.0.0.1")
    port = cfg.get("port", 8080)
    secret = cfg.get("secret", "")

    async def handler(reader, writer):
        await _handle_request(reader, writer, bot, secret)

    try:
        ps["server"] = await asyncio.start_server(handler, host, port)
        ps["started"] = time.monotonic()
        ps["request_count"] = 0
        log.info("webhook: listening on %s:%d", host, port)
    except OSError as exc:
        log.error("webhook: failed to bind %s:%d: %s", host, port, exc)


@command("webhook", help="Show webhook listener status", admin=True)
async def cmd_webhook(bot, message):
    """Display webhook server status."""
    ps = _ps(bot)

    if ps["server"] is None:
        await bot.reply(message, "Webhook: not running")
        return

    socks = ps["server"].sockets
    if socks:
        addr = socks[0].getsockname()
        address = f"{addr[0]}:{addr[1]}"
    else:
        address = "unknown"

    elapsed = int(time.monotonic() - ps["started"])
    hours, rem = divmod(elapsed, 3600)
    minutes, secs = divmod(rem, 60)
    parts = []
    if hours:
        parts.append(f"{hours}h")
    if minutes:
        parts.append(f"{minutes}m")
    parts.append(f"{secs}s")
    uptime = " ".join(parts)

    await bot.reply(
        message,
        f"Webhook: {address} | {ps['request_count']} requests | up {uptime}",
    )