Keep one long-lived yt-dlp worker process instead of spawning per call

server/package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "start": "bun server.js",
     "dev": "bun --hot server.js",
-    "test": "bun test --timeout 60000 ./media-cache.test.js && bun test ./notes.test.js && bun test ./remote.test.js && bun test ./party.test.js && bun test ./uploads.test.js && bun test ./innertube.test.js"
+    "test": "bun test --timeout 60000 ./media-cache.test.js && bun test ./notes.test.js && bun test ./remote.test.js && bun test ./party.test.js && bun test ./uploads.test.js && bun test ./innertube.test.js && bun test ./ytdlp-pool.test.js"
   },
   "dependencies": {
     "@hono/node-server": "^1.14.0",

server/server.js

@@ -50,6 +50,7 @@ import { createPartyHub } from './party.js';
 import { registerUploadRoutes } from './uploads.js';
 import * as innertube from './innertube.js';
 import QRCode from 'qrcode';
+import { createYtdlpPool } from './ytdlp-pool.js';
 import { dirname, join as pathJoin } from 'node:path';
 
 // A media proxy must not die because one client's stream hit an edge case
@@ -142,7 +143,7 @@ const CHANNEL_LIMIT = 60;
 // concurrent request — including in-flight /api/download proxy streams, which
 // Bun then kills at its idle timeout ("fetch failed" mid-download on clients).
 // Rejects on non-zero exit.
-function runYtdlp(args, { signal } = {}) {
+function runYtdlpSpawn(args, { signal } = {}) {
   return new Promise((resolve, reject) => {
     const child = spawn(YTDLP, args, { stdio: ['ignore', 'pipe', 'pipe'] });
     const t0 = Date.now();
@@ -170,6 +171,29 @@ function runYtdlp(args, { signal } = {}) {
   });
 }
 
+// Read-only calls (-J, --dump-json) go to long-lived workers that import
+// yt_dlp once (~1 s saved per call). Downloads keep spawning. Pool trouble
+// (not a yt-dlp error) falls back to a spawn. YTDLP_WORKER=0 disables it.
+const ytdlpPool = process.env.YTDLP_WORKER === '0' ? null : createYtdlpPool({
+  ytdlpPath: Bun.which(YTDLP) || YTDLP,
+  size: Math.max(1, Number(process.env.YTDLP_WORKERS) || 2),
+});
+function runYtdlp(args, opts = {}) {
+  if (!opts.pooled || !ytdlpPool || opts.signal) return runYtdlpSpawn(args, opts);
+  const t0 = Date.now();
+  return ytdlpPool.run(args).then(
+    (out) => { console.log(`[ytdlp] pooled ${Date.now() - t0}ms ok`); return out; },
+    (err) => {
+      if (err.poolInfra) return runYtdlpSpawn(args, opts);
+      // A bot check can stick to a long-lived process: replace the workers and
+      // answer this call the old way, from a fresh process.
+      if (BOT_CHECK_RE.test(err.message)) { ytdlpPool.recycle(); return runYtdlpSpawn(args, opts); }
+      console.log(`[ytdlp] pooled ${Date.now() - t0}ms fail`);
+      throw err;
+    },
+  );
+}
+
 // YouTube intermittently answers the default (web) innertube client with
 // "Sign in to confirm you're not a bot" — a per-IP rate signal, not a
 // per-video one, so the SAME video that just saved fine fails minutes later
@@ -396,7 +420,7 @@ app.get('/api/search', async (c) => {
         `ytsearch${SEARCH_LIMIT}:${q}`,
         '--dump-json', '--flat-playlist',
         '--no-warnings', '--ignore-errors',
-      ]);
+      ], { pooled: true });
       yt = parseCards(out);
     }
     const results = [...mine, ...yt];
@@ -421,7 +445,7 @@ app.get('/api/channel', async (c) => {
       '--dump-json', '--flat-playlist',
       '--no-warnings', '--ignore-errors',
       '--playlist-end', String(CHANNEL_LIMIT),
-    ]);
+    ], { pooled: true });
     const results = parseCards(out);
     // Extract channel name + URL from the first record
     const first = results[0];
@@ -476,7 +500,7 @@ async function resolveStreamsUncached(videoId) {
   const cached = streamCache.get(videoId);
   if (cached && now < cached.expiresAt) return cached;
 
-  const out = await runYtdlpResilient(['-J', '--no-warnings', `https://www.youtube.com/watch?v=${videoId}`]);
+  const out = await runYtdlpResilient(['-J', '--no-warnings', `https://www.youtube.com/watch?v=${videoId}`], { pooled: true });
   const info = JSON.parse(out);
   const raw = Array.isArray(info.formats) ? info.formats : [];
   const formats = [];
@@ -1760,7 +1784,7 @@ app.get('/api/playlist/expand', async (c) => {
       '--dump-json', '--flat-playlist',
       '--no-warnings', '--ignore-errors',
       '--playlist-end', '201',
-    ]);
+    ], { pooled: true });
     const parsed = parseCards(out);
     let title = '';
     for (const line of out.split('\n')) {

server/ytdlp-pool.js

@@ -0,0 +1,112 @@
+/* ytdlp-pool.js — a small pool of long-lived yt-dlp workers (ytdlp-worker.py).
+ *
+ * run(args) resolves stdout exactly like a spawned `yt-dlp <args>` would, or
+ * rejects with the captured stderr. Each worker handles one request at a time;
+ * extra requests queue. A worker that exits or exceeds the timeout is killed
+ * and replaced. Errors carrying `poolInfra: true` mean "the pool could not run
+ * this" — the caller falls back to a normal per-call spawn. Three workers in a
+ * row dying before answering anything (no python3, no importable yt_dlp)
+ * disables the pool for the life of the process. Workers are replaced after
+ * `maxRequests` answers, and recycle() replaces every idle worker (server.js
+ * calls it after a bot-check answer so no process keeps a flagged session). */
+import { spawn } from 'node:child_process';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const WORKER = join(dirname(fileURLToPath(import.meta.url)), 'ytdlp-worker.py');
+const infra = (msg) => Object.assign(new Error(msg), { poolInfra: true });
+
+export function createYtdlpPool({ ytdlpPath = '', size = 2, timeoutMs = 60_000, maxRequests = 100, python = 'python3', log = console } = {}) {
+  const workers = [];
+  const queue = [];
+  let nextId = 1;
+  let startFailures = 0;
+  let disabled = false;
+  let closed = false;
+
+  function startWorker() {
+    const child = spawn(python, [WORKER, ytdlpPath], { stdio: ['pipe', 'pipe', 'inherit'] });
+    const w = { child, busy: null, buf: '', dead: false, retiring: false, served: 0 };
+    child.stdout.setEncoding('utf8');
+    child.stdout.on('data', (d) => {
+      w.buf += d;
+      let nl;
+      while ((nl = w.buf.indexOf('\n')) >= 0) {
+        const line = w.buf.slice(0, nl);
+        w.buf = w.buf.slice(nl + 1);
+        let msg;
+        try { msg = JSON.parse(line); } catch { continue; }
+        const job = w.busy;
+        if (!job || msg.id !== job.id) continue;
+        clearTimeout(job.timer);
+        w.busy = null;
+        w.served++;
+        startFailures = 0;
+        if (msg.code === 0) job.resolve(msg.out);
+        else job.reject(new Error((msg.err || '').trim() || 'yt-dlp exited with code ' + msg.code));
+        if (w.served >= maxRequests) retire(w);
+        pump();
+      }
+    });
+    const onDead = (why) => {
+      if (w.dead) return;
+      w.dead = true;
+      const i = workers.indexOf(w);
+      if (i >= 0) workers.splice(i, 1);
+      if (w.busy) { clearTimeout(w.busy.timer); w.busy.reject(infra('yt-dlp worker ' + why)); w.busy = null; }
+      if (closed) return;
+      if (!w.served && ++startFailures >= 3) {
+        disabled = true;
+        log.warn?.(`[ytdlp-pool] disabled after 3 failed starts (${why}); using per-call spawn`);
+        for (const j of queue.splice(0)) j.reject(infra('pool disabled'));
+        return;
+      }
+      if (!w.retiring) log.warn?.(`[ytdlp-pool] worker ${why}; restarting`);
+      const t = setTimeout(() => { if (!closed && !disabled) { workers.push(startWorker()); pump(); } }, 1000);
+      t.unref?.();
+    };
+    child.on('exit', (code) => onDead('exited (' + code + ')'));
+    child.on('error', (e) => onDead('failed to start: ' + e.message));
+    return w;
+  }
+
+  // Replace a worker once it is idle (its exit handler starts a fresh one).
+  function retire(w) {
+    if (w.retiring || w.dead) return;
+    w.retiring = true;
+    try { w.child.kill(); } catch { /* gone */ }
+  }
+
+  for (let i = 0; i < size; i++) workers.push(startWorker());
+
+  function pump() {
+    for (const w of workers) {
+      if (w.dead || w.retiring || w.busy || !queue.length) continue;
+      const job = queue.shift();
+      w.busy = job;
+      job.timer = setTimeout(() => { try { w.child.kill('SIGKILL'); } catch { /* gone */ } }, timeoutMs);
+      try { w.child.stdin.write(JSON.stringify({ id: job.id, args: job.args }) + '\n'); }
+      catch (e) { clearTimeout(job.timer); w.busy = null; job.reject(infra(e.message)); }
+    }
+  }
+
+  function run(args) {
+    if (closed || disabled) return Promise.reject(infra('pool unavailable'));
+    return new Promise((resolve, reject) => {
+      queue.push({ id: nextId++, args: args.map(String), resolve, reject });
+      pump();
+    });
+  }
+
+  function close() {
+    closed = true;
+    for (const w of workers) { try { w.child.kill(); } catch { /* gone */ } }
+    for (const j of queue.splice(0)) j.reject(infra('pool closed'));
+  }
+
+  function recycle() {
+    for (const w of workers) if (!w.busy) retire(w);
+  }
+
+  return { run, close, recycle, get disabled() { return disabled; } };
+}

server/ytdlp-pool.test.js

@@ -0,0 +1,44 @@
+import { test, expect } from 'bun:test';
+import { existsSync, readFileSync } from 'node:fs';
+import { createYtdlpPool } from './ytdlp-pool.js';
+
+// The worker imports yt_dlp from the release ZIPAPP (a python script, starts with
+// "#!"). `npm run setup` downloads yt-dlp_linux, a compiled ELF Python can't import,
+// so an ELF (or nothing) means these tests skip.
+const isZipapp = (p) => { try { return readFileSync(p).subarray(0, 2).toString() === '#!'; } catch { return false; } };
+const YTDLP = [process.env.YTDLP_PATH, '../bin/yt-dlp', Bun.which('yt-dlp')].find((p) => p && existsSync(p) && isZipapp(p)) || '';
+const quiet = { warn() {}, info() {} };
+
+test.skipIf(!YTDLP)('runs requests and reports yt-dlp errors without dying', async () => {
+  const pool = createYtdlpPool({ ytdlpPath: YTDLP, size: 1, log: quiet });
+  try {
+    const v = await pool.run(['--version']);
+    expect(v.trim()).toMatch(/^\d{4}\.\d{2}\.\d{2}/);
+    const err = await pool.run(['--definitely-not-a-flag']).catch((e) => e);
+    expect(err).toBeInstanceOf(Error);
+    expect(err.poolInfra).toBeFalsy();
+    expect((await pool.run(['--version'])).trim()).toBe(v.trim());
+  } finally { pool.close(); }
+}, 30000);
+
+test('a broken python disables the pool and rejects as infra', async () => {
+  const pool = createYtdlpPool({ python: '/nonexistent/python3', size: 1, log: quiet });
+  const err = await pool.run(['--version']).catch((e) => e);
+  expect(err.poolInfra).toBe(true);
+  await new Promise((r) => setTimeout(r, 3500));
+  expect(pool.disabled).toBe(true);
+  expect((await pool.run(['--version']).catch((e) => e)).poolInfra).toBe(true);
+  pool.close();
+}, 15000);
+
+test.skipIf(!YTDLP)('workers are replaced after maxRequests and by recycle(), without failing requests', async () => {
+  const pool = createYtdlpPool({ ytdlpPath: YTDLP, size: 1, maxRequests: 1, log: quiet });
+  try {
+    const a = await pool.run(['--version']);
+    const b = await pool.run(['--version']); // served by a fresh worker
+    expect(b).toBe(a);
+    pool.recycle();
+    expect(await pool.run(['--version'])).toBe(a);
+    expect(pool.disabled).toBe(false);
+  } finally { pool.close(); }
+}, 30000);

server/ytdlp-worker.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+"""ytdlp-worker.py - one long-lived yt-dlp process answering many requests.
+
+Spawning yt-dlp per call pays Python start-up + extractor import every time.
+This worker imports yt_dlp ONCE and runs each request's argv in-process
+through the CLI's own entry point (yt_dlp._real_main), so config files such
+as /etc/yt-dlp.conf and everything else the command line sets up apply.
+
+Protocol (newline-delimited JSON):
+  stdin : {"id": <int>, "args": [<yt-dlp argv>...]}
+  stdout: {"id": <int>, "code": <int>, "out": "<captured stdout>", "err": "<stderr tail>"}
+Only for calls whose result is printed to stdout (-J, --dump-json, --version).
+Usage: python3 ytdlp-worker.py <path-to-yt-dlp-zipapp-or-empty>
+"""
+import io, json, sys, contextlib
+
+if len(sys.argv) > 1 and sys.argv[1]:
+    sys.path.insert(0, sys.argv[1])   # the yt-dlp release binary is a zipapp
+import yt_dlp  # noqa: E402
+
+proto_out = sys.stdout
+sys.stdout = io.StringIO()            # nothing may leak onto the protocol pipe
+
+def run(args):
+    out, err = io.StringIO(), io.StringIO()
+    code = 0
+    with contextlib.redirect_stdout(out), contextlib.redirect_stderr(err):
+        try:
+            # The CLI's own entry point (not parse_options + YoutubeDL): it also
+            # sets up what the command line does (JS challenge solving, plugins,
+            # post-processing defaults). A bare YoutubeDL got "Sign in to
+            # confirm you're not a bot" where the CLI succeeded.
+            ret = yt_dlp._real_main(args)
+            code = ret[0] if isinstance(ret, tuple) else (ret or 0)
+        except SystemExit as e:
+            code = e.code if isinstance(e.code, int) else 1
+        except Exception as e:  # report, never die
+            err.write(f"ERROR: {e}\n")
+            code = 1
+    return code, out.getvalue(), err.getvalue()[-8000:]
+
+for line in sys.stdin:
+    line = line.strip()
+    if not line:
+        continue
+    try:
+        req = json.loads(line)
+        code, out, err = run([str(a) for a in req.get("args", [])])
+        resp = {"id": req.get("id"), "code": code, "out": out, "err": err}
+    except Exception as e:
+        resp = {"id": None, "code": 1, "out": "", "err": f"worker: {e}"}
+    proto_out.write(json.dumps(resp) + "\n")
+    proto_out.flush()