steam-backlog-enforcer/steam_backlog_enforcer/_web_server.py

"""Minimal read-only localhost HTTP server for the interactive web UI.

Serves the projected dataset at ``GET /api/dataset`` and the built React
bundle (``web/dist``) as static files.  Binds to localhost only and never
exposes secrets: the payload comes from :func:`build_web_dataset`, which reads
the data caches but never ``config.json``.

In development the Vite dev server proxies ``/api`` here; in production the
``serve`` command serves the built bundle and the API from one process.
"""

from __future__ import annotations

from http import HTTPStatus
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
import json
import logging
import mimetypes
from pathlib import Path
import threading
import time
from urllib.parse import urlsplit

from steam_backlog_enforcer._budget_view import build_budget_snapshot
from steam_backlog_enforcer._serve_stale import outdated_source
from steam_backlog_enforcer._web_dataset import build_web_dataset, dataset_to_payload
from steam_backlog_enforcer.config import State
from steam_backlog_enforcer.game_install import _echo

logger = logging.getLogger(__name__)

# Built frontend lives at <repo>/web/dist (sibling of the package directory).
WEB_DIST = (Path(__file__).resolve().parent.parent / "web" / "dist").resolve()

DEFAULT_HOST = "127.0.0.1"
DEFAULT_PORT = 8000
_API_DATASET = "/api/dataset"
_API_BUDGET = "/api/budget"

# Content types that are text but not under the ``text/`` prefix.
_EXTRA_TEXT_TYPES = frozenset(
    {"application/javascript", "application/json", "image/svg+xml"}
)
_NOT_BUILT_MSG = b"Frontend not built. Run: cd web && npm install && npm run build"

# Epoch seconds this process began, captured at import. Anything in the
# package newer than this is code we did not load.
_STARTED_AT = time.time()

# Set once a stale server has begun standing down, so concurrent requests
# do not each spawn a shutdown thread.
_RETIRING = threading.Event()

_STALE_MSG = (
    b"This server is running outdated code and has stopped answering rather "
    b"than report numbers the enforcer is not applying. Restart it: "
    b"./run.sh serve"
)


class _Handler(BaseHTTPRequestHandler):
    """Serve the dataset JSON and the static frontend bundle (read-only)."""

    def log_message(self, fmt: str, *args: object) -> None:
        """Route the default request log to ``logging`` at debug level."""
        logger.debug("%s - %s", self.address_string(), fmt % args)

    def do_GET(self) -> None:
        """Dispatch a GET to one of the APIs or to a static file."""
        stale = outdated_source(_STARTED_AT)
        if stale is not None:
            # Fail closed on every route, static included: a page served from a
            # fresh bundle that then fetches numbers from stale code is the
            # same lie with extra steps.
            self._send(HTTPStatus.SERVICE_UNAVAILABLE, _STALE_MSG, "text/plain")
            self._retire()
            return
        split = urlsplit(self.path)
        if split.path == _API_DATASET:
            self._serve_dataset()
        elif split.path == _API_BUDGET:
            # ``?demo=1`` reads the demo run's state and log, which is how the
            # 60-second demo can be watched hitting its cutoff in the browser
            # without spending a real day's budget to see it.
            self._serve_budget(demo="demo=1" in split.query)
        else:
            self._serve_static(split.path)

    def _retire(self) -> None:
        """Answer this request, then stop the server so it can be replaced.

        Refusing to serve is only half a fix: a process that 503s forever is
        honest and useless. Exiting hands the problem to the supervisor, and
        ``steam-backlog-enforcer-web.service`` has ``Restart=always``, so the
        server comes back on current code with nobody having to remember to
        restart it. Started outside systemd it simply exits, which is still
        better than serving numbers the enforcer is not applying.

        ``shutdown`` blocks until ``serve_forever`` returns and cannot be
        called from the thread handling a request, so it goes to its own.
        """
        if _RETIRING.is_set():
            return
        _RETIRING.set()
        threading.Thread(target=self.server.shutdown, daemon=True).start()

    def _serve_budget(self, *, demo: bool) -> None:
        """Build and send the gaming-budget snapshot as JSON."""
        try:
            body = json.dumps(build_budget_snapshot(demo=demo)).encode("utf-8")
        except OSError, ValueError, KeyError:
            logger.exception("Failed to build budget snapshot")
            self._send(HTTPStatus.INTERNAL_SERVER_ERROR, b"budget error", "text/plain")
            return
        self._send(HTTPStatus.OK, body, "application/json")

    def _serve_dataset(self) -> None:
        """Build and send the projected dataset as JSON."""
        try:
            payload = dataset_to_payload(build_web_dataset(State.load()))
            body = json.dumps(payload).encode("utf-8")
        except OSError, ValueError, KeyError:
            logger.exception("Failed to build web dataset")
            self._send(HTTPStatus.INTERNAL_SERVER_ERROR, b"dataset error", "text/plain")
            return
        self._send(HTTPStatus.OK, body, "application/json")

    def _serve_static(self, path: str) -> None:
        """Serve a file from ``WEB_DIST`` with SPA fallback and traversal guard."""
        rel = path.lstrip("/") or "index.html"
        candidate = (WEB_DIST / rel).resolve()
        # Reject path traversal, then fall back to index.html for SPA routes.
        if not candidate.is_relative_to(WEB_DIST) or not candidate.is_file():
            candidate = WEB_DIST / "index.html"
        if not candidate.is_file():
            self._send(HTTPStatus.NOT_FOUND, _NOT_BUILT_MSG, "text/plain")
            return
        ctype, _ = mimetypes.guess_type(candidate.name)
        self._send(HTTPStatus.OK, candidate.read_bytes(), ctype or "text/plain")

    def _send(self, status: HTTPStatus, body: bytes, ctype: str) -> None:
        """Write a complete response with the given status, body, and type."""
        if ctype.startswith("text/") or ctype in _EXTRA_TEXT_TYPES:
            ctype = f"{ctype}; charset=utf-8"
        self.send_response(status)
        self.send_header("Content-Type", ctype)
        self.send_header("Content-Length", str(len(body)))
        self.end_headers()
        self.wfile.write(body)


def create_server(
    host: str = DEFAULT_HOST, port: int = DEFAULT_PORT
) -> ThreadingHTTPServer:
    """Create (but do not start) the threading HTTP server."""
    return ThreadingHTTPServer((host, port), _Handler)


def serve(host: str = DEFAULT_HOST, port: int = DEFAULT_PORT) -> None:
    """Run the web server until interrupted with Ctrl-C."""
    server = create_server(host, port)
    _echo(f"Steam Backlog Enforcer web UI: http://{host}:{port}")
    _echo("Press Ctrl-C to stop.")
    try:
        server.serve_forever()
    except KeyboardInterrupt:
        _echo("\nShutting down.")
    finally:
        server.server_close()