minesweeper/sidecar/prefix.ts

import { existsSync, lstatSync, mkdirSync, readdirSync, rmSync } from 'node:fs';
import { join } from 'node:path';
import { WINEPREFIX } from './paths';
import { run } from './run';

/**
 * Building the wine prefix, once, on first start.
 *
 * ── Why this is code and not an install step ──
 *
 * The plugin system has no install hook, and it should not grow one for this: an install that takes four
 * minutes and downloads from Microsoft is not something to do behind a progress bar the owner cannot
 * cancel. Doing it inside the first `POST /start` means it happens when somebody actually wants to play,
 * it can report what it is doing, and a machine that installs the plugin and never opens it pays nothing.
 *
 * It is also self-healing. Deleting the prefix — which is the standard fix for a wedged wine — is safe,
 * because the next start rebuilds it.
 *
 * ── The two facts that decide the whole setup ──
 *
 * Minesweeper X is a 68 KB i386 PE (machine `0x014c`, verified), so the prefix must be `win32`. A 64-bit
 * prefix cannot load it and the failure is a bare `Bad EXE format`.
 *
 * It was built with Visual Basic 6, so it needs `MSVBVM60.DLL`, which wine does not ship. Without it the
 * process exits immediately having printed one line — `err:module:import_dll Library MSVBVM60.DLL not
 * found` — and nothing else. That is a quiet enough failure that it is worth checking for the DLL directly
 * rather than inferring readiness from the prefix existing.
 */

/** The one file whose presence means this prefix can actually run the game. */
const VB6_RUNTIME = join(WINEPREFIX, 'drive_c', 'windows', 'system32', 'msvbvm60.dll');

export const prefixReady = (): boolean => existsSync(VB6_RUNTIME);

export const WINE_ENV = {
  WINEPREFIX,
  WINEARCH: 'win32',
  // wine narrates every unimplemented call otherwise, and the game triggers thousands.
  WINEDEBUG: '-all',
  // Never prompt to install .NET or an embedded IE. The dialog appears on a display nobody is watching,
  // and the start then hangs until it times out.
  WINEDLLOVERRIDES: 'mscoree,mshtml=',
};

export type PrefixResult = { ok: boolean; detail: string };

/**
 * Create the prefix if it is not there, then install the VB6 runtime into it.
 *
 * `winetricks -q vb6run` fetches Microsoft's own `VB6.0-KB290887-X86.exe` and verifies its checksum before
 * unpacking, which is why this does not carry a redistributable of its own.
 */
export async function ensurePrefix(log: (line: string) => void): Promise<PrefixResult> {
  // Before the early return as well: an existing prefix may predate this, or have had `z:` restored by a
  // wine upgrade. It is a few `unlink` calls, so it is cheaper to re-assert than to detect.
  if (prefixReady()) {
    confinePrefix();
    return { ok: true, detail: 'prefix ready' };
  }

  if (!Bun.which('wine')) {
    return { ok: false, detail: 'wine is not installed. On Debian or Ubuntu this also needs i386 multiarch: `sudo dpkg --add-architecture i386 && sudo apt update && sudo apt install wine wine32:i386`' };
  }
  if (!Bun.which('winetricks')) {
    return { ok: false, detail: 'winetricks is not installed, and it is what fetches the Visual Basic 6 runtime the game needs' };
  }

  if (!existsSync(WINEPREFIX)) {
    log('creating the 32-bit wine prefix (first run only, this takes a minute)');
    // `wineboot -i` rather than letting the first wine call create it implicitly: implicit creation happens
    // inside the game launch, races the window-detection poll, and looks like the game failing to start.
    const boot = await run(['wineboot', '-i'], WINE_ENV, 300_000);
    if (!boot.ok && !existsSync(WINEPREFIX)) {
      return { ok: false, detail: `wineboot failed: ${(boot.stderr || boot.stdout).trim().slice(-400)}` };
    }
  }

  log('installing the Visual Basic 6 runtime into the prefix (downloads from Microsoft)');
  const tricks = await run(['winetricks', '-q', 'vb6run'], WINE_ENV, 600_000);

  // winetricks exits 0 having done nothing often enough that the exit code is not the answer. The file is.
  if (!prefixReady()) {
    return {
      ok: false,
      detail: `the VB6 runtime did not install; msvbvm60.dll is still missing. winetricks said: ${(tricks.stderr || tricks.stdout).trim().slice(-400)}`,
    };
  }

  // Last, not first: `winetricks` runs wine, and wine recreates `z:` on the way past.
  confinePrefix();

  log('prefix ready and confined to drive C');
  return { ok: true, detail: 'prefix built' };
}

/**
 * Cut the prefix off from the rest of the machine.
 *
 * ── Why this exists, and why it is not optional ──
 *
 * A fresh wine prefix is not a sandbox. `wineboot` creates `dosdevices/z: -> /`, which maps the ENTIRE
 * filesystem to a drive letter, and symlinks the profile's Documents, Downloads and Music straight into the
 * owner's real home. Minesweeper X has a replay feature with Open and Save dialogs, so anyone looking at the
 * display gets a file browser over all of that, running as the server owner.
 *
 * That is precisely why the platform's permission registry classified Minesweeper as `execution` — a kind
 * that can never be granted to anyone. But **a plugin permission is always grantable**, by design and with
 * no field to opt out of. So extracting this feature without also fixing the prefix would have converted a
 * structurally ungrantable capability into one an owner could hand to a Member, complete with a file picker
 * over the owner's home. The extraction is what made this urgent; the hole was always there.
 *
 * `docs/affordances.md` has the rule that applies: if it can be fixed instead of documented, fix it. A note
 * saying "do not grant this" outlives everyone's memory of why.
 *
 * ── What is left ──
 *
 * `C:` alone, pointing at the prefix. The game keeps its own directory, its settings and its replays; it can
 * see nothing else. Serial and parallel device nodes go too — a 1997 puzzle game has no business holding an
 * open descriptor on `/dev/ttyS0`.
 *
 * Re-asserted on every start rather than only at creation, because wine recreates `z:` whenever it decides
 * the prefix needs updating — a wine package upgrade is enough, and it would restore the hole silently.
 */
export function confinePrefix(): void {
  const dosdevices = join(WINEPREFIX, 'dosdevices');
  if (existsSync(dosdevices)) {
    for (const entry of readdirSync(dosdevices)) {
      // Keep `c:` and only `c:`. Everything else is a door out of the prefix or a device node.
      if (entry.toLowerCase() === 'c:') continue;
      rmSync(join(dosdevices, entry), { force: true, recursive: true });
    }
  }

  const users = join(WINEPREFIX, 'drive_c', 'users');
  if (!existsSync(users)) return;
  for (const user of readdirSync(users)) {
    const profile = join(users, user);
    for (const folder of readdirSync(profile)) {
      const path = join(profile, folder);
      // A symlink here points into the real home. Replace it with an ordinary directory so the game still
      // has somewhere to save a replay, and that somewhere is inside the prefix.
      if (!lstatSync(path).isSymbolicLink()) continue;
      rmSync(path, { force: true });
      mkdirSync(path, { recursive: true });
    }
  }
}