lhns--steam-frame-nix/modules/steam-ui-patches/injector.mjs

// injector.mjs: keeps runtime patches injected into Steam's UI (CEF) through
// Chrome DevTools, and reverts them when stopped.
// usage: node injector.mjs <config.json>
//
// config.json (generated by steam-ui-patches.nix):
//   { "pollMs": 5000,        // target discovery / reconnect interval
//     "reinjectMs": 15000,   // periodic re-injection
//     "debounceMs": 3000,    // delay after a burst of new JS contexts
//     "unpatchTimeoutMs": 2000,
//     "patches": [ { "name": "launcher-menu-order",
//                    "endpoint": "http://127.0.0.1:8080",
//                    "target": { "title": "SharedJSContext" }, // or titleRegex / urlRegex
//                    "patch": "/nix/store/...-patch.js",
//                    "unpatch": "/nix/store/...-unpatch.js",   // optional
//                    "state": true } ] }                        // optional, see below
//
// Every target (page of an endpoint's /json/list) matched by at least one
// patch gets one DevTools session, which evaluates all of its patches: right
// away, after new execution contexts (debounced) and every reinjectMs.
// Patches must be idempotent expressions; their (awaited) result value is
// logged when it changes, e.g. "patched" once, then "unchanged" silently.
// On SIGTERM/SIGINT every live session evaluates its patches' unpatch
// expressions (if any) (each with a timeout), then the process exits.
//
// Persistent state ("state": true): one JSON value per patch, kept in
// $XDG_STATE_HOME/steam-frame-nix/ui-patches/<name>.json (default
// ~/.local/state/...), so it survives SteamVR restarts (steamvr.service wipes
// ~/.cache/SteamVR, the pages' localStorage, on every start) and reboots.
// Before each evaluation of such a patch a prelude defines, in the page,
//   window.__sfuiStore.get(name)         the stored value (undefined: none)
//   window.__sfuiStore.set(name, value)  store it (JSON; true if sent)
// and seeds get(name) from the file only when the page has no value yet (a
// fresh page after a SteamVR restart or reload): the page's value is
// authoritative from then on. set() goes through the CDP binding
// window.__sfuiStoreSave('{"name","value"}'), which this process writes to the
// file (atomically, only on change, only for "state" patches of that target,
// at most 64 KiB). The file is user data: nothing deletes it.
import { mkdirSync, readFileSync, renameSync, writeFileSync } from 'node:fs';
import { join } from 'node:path';

const cfg = JSON.parse(readFileSync(process.argv[2], 'utf8'));
const POLL = cfg.pollMs ?? 5000;
const REINJECT = cfg.reinjectMs ?? 15000;
const DEBOUNCE = cfg.debounceMs ?? 3000;
const UNPATCH_TIMEOUT = cfg.unpatchTimeoutMs ?? 2000;
const sleep = (ms) => new Promise((r) => setTimeout(r, ms));
const STATE_DIR = cfg.stateDir ?? join(process.env.XDG_STATE_HOME || join(process.env.HOME ?? '.', '.local/state'), 'steam-frame-nix/ui-patches');
const STATE_MAX = 64 * 1024;
const BINDING = '__sfuiStoreSave';

// name -> JSON text of the stored value (absent: none), read once at start.
const stored = new Map();
const stateFile = (name) => join(STATE_DIR, `${name}.json`);
function loadState(name) {
  let text;
  try { text = readFileSync(stateFile(name), 'utf8'); } catch { return; }   // none yet
  try { stored.set(name, JSON.stringify(JSON.parse(text))); } catch (e) { console.error(`${name}: ignoring ${stateFile(name)}: ${e.message}`); }
}
function saveState(name, json) {
  if (stored.get(name) === json) return false;
  mkdirSync(STATE_DIR, { recursive: true });
  const tmp = `${stateFile(name)}.tmp`;
  writeFileSync(tmp, `${json}\n`);
  renameSync(tmp, stateFile(name));
  stored.set(name, json);
  return true;
}
// Page side of the store (idempotent), seeding `name` if the page has no value.
const prelude = (name) => `(() => {
  const s = window.__sfuiStore ??= {
    data: {},
    get(n) { return this.data[n]; },
    set(n, v) {
      this.data[n] = v;
      try { if (typeof window.${BINDING} !== 'function') return false; window.${BINDING}(JSON.stringify({ name: n, value: v })); return true; } catch { return false; }
    },
  };
  const n = ${JSON.stringify(name)};
  if (!(n in s.data) && ${stored.has(name)}) s.data[n] = ${stored.get(name) ?? 'undefined'};
  return 'ok';
})()`;

const patches = cfg.patches.map((p) => {
  const t = p.target ?? {};
  const title = t.title, titleRe = t.titleRegex && new RegExp(t.titleRegex), urlRe = t.urlRegex && new RegExp(t.urlRegex);
  return {
    name: p.name,
    endpoint: (p.endpoint ?? 'http://127.0.0.1:8080').replace(/\/+$/, ''),
    matches: (x) => (title === undefined || x.title === title) &&
      (!titleRe || titleRe.test(x.title)) && (!urlRe || urlRe.test(x.url)),
    patch: readFileSync(p.patch, 'utf8'),
    unpatch: p.unpatch ? readFileSync(p.unpatch, 'utf8') : null,
    state: !!p.state,
  };
});
for (const p of patches) if (p.state) loadState(p.name);

const sessions = new Map();                       // "<endpoint> <target id>" -> session
let stopping = false;

// Result value of a Runtime.evaluate reply, or the exception text.
const value = (r) => r.error?.message ?? r.result?.exceptionDetails?.exception?.description ??
  r.result?.exceptionDetails?.text ?? r.result?.result?.value ?? r.result?.result?.type ?? 'no reply';

function open(endpoint, target, list) {
  const key = `${endpoint} ${target.id}`;
  const tag = `[${target.title}]`;
  const ws = new WebSocket(target.webSocketDebuggerUrl);
  let id = 0, soon = null, timer = null, connected = false;
  const pending = new Map();
  const last = new Map();                         // patch name -> last logged result
  const call = (method, params = {}) => new Promise((res) => {
    if (ws.readyState !== WebSocket.OPEN) return res({ error: { message: 'closed' } });
    const i = ++id; pending.set(i, res); ws.send(JSON.stringify({ id: i, method, params }));
  });
  const evaluate = (expression) => call('Runtime.evaluate', { expression, returnByValue: true, awaitPromise: true });
  const inject = async () => {
    for (const p of list) {
      if (p.state) await evaluate(prelude(p.name));
      const v = String(value(await evaluate(p.patch)));
      if (last.get(p.name) !== v && v !== 'unchanged') console.log(`${tag} ${p.name}: ${v}`);
      last.set(p.name, v);
    }
  };
  const injectSoon = () => { clearTimeout(soon); soon = setTimeout(() => inject().catch(() => {}), DEBOUNCE); };
  const unpatch = () => Promise.all(list.filter((p) => p.unpatch).map(async (p) => {
    const r = await Promise.race([evaluate(p.unpatch), sleep(UNPATCH_TIMEOUT).then(() => ({ error: { message: 'timeout' } }))]);
    console.log(`${tag} ${p.name} unpatch: ${value(r)}`);
  }));
  const session = { unpatch };
  const stateful = new Set(list.filter((p) => p.state).map((p) => p.name));
  const onSave = (payload) => {
    try {
      if (payload.length > STATE_MAX) throw new Error(`${payload.length} bytes, max ${STATE_MAX}`);
      const { name, value: v } = JSON.parse(payload);
      if (!stateful.has(name)) throw new Error(`no state for ${JSON.stringify(name)} here`);
      if (v === undefined) throw new Error('no value');
      if (saveState(name, JSON.stringify(v))) console.log(`${tag} ${name}: state saved`);
    } catch (e) { console.error(`${tag} state save refused: ${e.message}`); }
  };
  sessions.set(key, session);

  ws.onopen = async () => {
    connected = true;
    console.log(`${tag} connected (${endpoint}): ${list.map((p) => p.name).join(', ')}`);
    await call('Runtime.enable');
    if (stateful.size) await call('Runtime.addBinding', { name: BINDING });
    await inject().catch((e) => console.error(`${tag} inject:`, e.message));
    timer = setInterval(() => inject().catch(() => {}), REINJECT);
  };
  ws.onmessage = (e) => {
    const m = JSON.parse(e.data);
    if (m.id && pending.has(m.id)) { pending.get(m.id)(m); pending.delete(m.id); }
    else if (m.method === 'Runtime.executionContextCreated' && !stopping) injectSoon();
    else if (m.method === 'Runtime.bindingCalled' && m.params?.name === BINDING && stateful.size) onSave(String(m.params.payload));
  };
  ws.onerror = () => {};                          // followed by onclose
  ws.onclose = () => {
    if (sessions.get(key) === session) sessions.delete(key);
    clearTimeout(soon); clearInterval(timer);
    for (const r of pending.values()) r({ error: { message: 'closed' } });
    pending.clear();
    if (connected) console.log(`${tag} disconnected`);
  };
}

// Discovery: connect to every matching target that has no session yet.
// Sessions of vanished targets end on their own (socket closes).
const down = new Set();
async function poll(endpoint, list) {
  let targets;
  try {
    targets = await (await fetch(`${endpoint}/json/list`, { signal: AbortSignal.timeout(3000) })).json();
    if (down.delete(endpoint)) console.log(`${endpoint} up`);
  } catch (e) {
    if (!down.has(endpoint)) { down.add(endpoint); console.error(`${endpoint} unreachable: ${e.message}`); }
    return;
  }
  for (const t of targets) {
    if (stopping || !t.webSocketDebuggerUrl || sessions.has(`${endpoint} ${t.id}`)) continue;
    const matching = list.filter((p) => p.matches(t));
    if (matching.length) open(endpoint, t, matching);
  }
}

for (const sig of ['SIGTERM', 'SIGINT']) process.on(sig, async () => {
  if (stopping) return;
  stopping = true;
  await Promise.all([...sessions.values()].map((s) => s.unpatch()));
  setTimeout(() => process.exit(0), 200);
});

const endpoints = [...new Set(patches.map((p) => p.endpoint))];
console.log(`patches: ${patches.map((p) => `${p.name} @ ${p.endpoint}`).join(', ')}`);
while (!stopping) {
  await Promise.all(endpoints.map((ep) => poll(ep, patches.filter((p) => p.endpoint === ep))));
  await sleep(POLL);
}