wizwar6e/packages/server/src/keeper.ts

// The keeper's door: a listener of its own on the loopback, apart from the
// port Caddy forwards to, so it answers only on the host itself, and only to
// the key in its key file, so another service on a shared host cannot use
// it. Its one caller is deploy/wizwar-reseat.sh, which sends the key:
//   GET  /keeper/rooms/:id           who sits at the table, and when each person last moved or spoke
//   POST /keeper/rooms/:id/reseat    {seat}   a new token for a player locked out, as a link to send them

import { timingSafeEqual } from "node:crypto";
import { readFileSync } from "node:fs";
import { createServer, type IncomingMessage, type Server, type ServerResponse } from "node:http";
import type { GameEvent, PlayerId } from "@wizwar/engine";
import { getRoom, reseat, seatsForKeeper, type Room } from "./rooms";

function send(res: ServerResponse, status: number, body: unknown): void {
  res.writeHead(status, { "content-type": "application/json" }).end(JSON.stringify(body));
}

/** The key is read on each knock, so a key written after the server started is honoured. Absent, the door stays shut. */
function keyGiven(req: IncomingMessage, keyFile: string): boolean {
  let key: Buffer;
  try {
    key = Buffer.from(readFileSync(keyFile, "utf8").trim());
  } catch {
    return false;
  }
  const given = Buffer.from(String(req.headers["x-keeper-key"] ?? ""));
  return key.length > 0 && given.length === key.length && timingSafeEqual(given, key);
}

async function readSeat(req: IncomingMessage): Promise<string> {
  let raw = "";
  for await (const chunk of req) {
    raw += chunk;
    if (raw.length > 4096) return "";
  }
  try {
    const seat = (JSON.parse(raw) as { seat?: unknown }).seat;
    return typeof seat === "string" ? seat : "";
  } catch {
    return "";
  }
}

export interface KeeperDoor {
  port: number;
  publicUrl: string;
  keyFile: string;
  /** Lets the caller set adrift any socket still seated on the old token,
   * and tell the table when the seat comes back from the clockwork. */
  onReseat: (room: Room, name: PlayerId, returned?: GameEvent) => void;
}

async function handle(req: IncomingMessage, res: ServerResponse, { publicUrl, keyFile, onReseat }: KeeperDoor): Promise<void> {
  const parts = (req.url ?? "/").split("?")[0]!.split("/").filter(Boolean);
  // Nothing proxied belongs here: a forwarded request is turned away even if a proxy is someday pointed at this port.
  if (req.headers["x-forwarded-for"] || !keyGiven(req, keyFile)) return send(res, 404, { error: "not here" });
  if (parts[0] !== "keeper" || parts[1] !== "rooms" || !parts[2]) return send(res, 404, { error: "not here" });
  const room = getRoom(parts[2]);
  if (!room) return send(res, 404, { error: "no such room" });
  if (parts.length === 3 && req.method === "GET") {
    return send(res, 200, { roomId: room.id, started: room.state !== null, finished: room.state?.phase === "finished", seats: seatsForKeeper(room) });
  }
  if (parts.length === 4 && parts[3] === "reseat" && req.method === "POST") {
    const name = await readSeat(req);
    const result = reseat(room, name);
    if ("error" in result) return send(res, 404, result);
    onReseat(room, name, result.returned);
    // The token rides the fragment, which the browser keeps to itself: it reaches neither Caddy's log nor the server.
    return send(res, 200, { name, link: `${publicUrl}/join/${room.id}#seat=${encodeURIComponent(name)}.${result.token}` });
  }
  return send(res, 404, { error: "not here" });
}

/** Open the door on 127.0.0.1, whatever address the game itself listens on. */
export function openKeeperDoor(door: KeeperDoor): Server {
  const server = createServer((req, res) => {
    handle(req, res, door).catch((e) => {
      console.error("keeper door:", e);
      if (!res.headersSent) send(res, 500, { error: "internal error" });
    });
  });
  server.listen(door.port, "127.0.0.1");
  return server;
}