refactor(main): execFileAsync helper — unify the 5 spawn-and-read sites

Replace the hand-rolled `new Promise((resolve) => execFile(…, cb))` wrappers in
probe / ytdlp (×2) / ffmpeg / indexer.probeFlat / download.probeMeta with one
lib/exec.ts execFileAsync returning a normalized
{ok,stdout,stderr,timedOut,error} that never rejects. Each caller keeps its own
error mapping (timedOut -> "Timed out …" vs stderr) and JSON parsing; behaviour
is unchanged. windowsHide defaults on; per-call timeout/maxBuffer preserved.

Foundation for CC4/CC5 — the stdout line-buffer half lands with SIMP5, the
net.request half with SIMP16, at which point those checkboxes close.

Unit-tested (exec.test.ts) against the node binary: ok / stderr+nonzero-exit /
missing-binary / timeout. typecheck + 262 tests + eslint + prettier green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/download.ts

@@ -14,6 +14,7 @@ import {
   YTDLP_MISSING_MSG
 } from './binaries'
 import { getSettings } from './settings'
+import { execFileAsync } from './lib/exec'
 import { getDownloadArchivePath, getDefaultMediaDir } from './paths'
 import { ensureManagedYtdlp } from './ytdlp'
 import { materializeCookies, hasStoredCookies } from './cookies'
@@ -123,32 +124,28 @@ function logFailure(opts: StartDownloadOptions, title: string | undefined, error
 // itself contains a newline, since each --print field is emitted on its own line.
 const META_SEP = '\u001f'
 
-function probeMeta(ytdlp: string, url: string): Promise<DownloadMeta | null> {
-  return new Promise((resolve) => {
-    execFile(
-      ytdlp,
-      [
-        '--no-playlist',
-        '--no-warnings',
-        '--skip-download',
-        '--print',
-        `%(title)s${META_SEP}%(uploader)s${META_SEP}%(duration_string)s`,
-        '--',
-        url
-      ],
-      { windowsHide: true, maxBuffer: META_MAX_BUFFER, timeout: META_PROBE_TIMEOUT_MS },
-      (err, stdout) => {
-        if (err) return resolve(null)
-        const [title, uploader, duration] = stdout.split(META_SEP).map((l) => l.trim())
-        const clean = (v?: string): string | undefined => (v && v !== 'NA' ? v : undefined)
-        resolve({
-          title: clean(title),
-          channel: clean(uploader),
-          durationLabel: clean(duration)
-        })
-      }
-    )
-  })
+async function probeMeta(ytdlp: string, url: string): Promise<DownloadMeta | null> {
+  const r = await execFileAsync(
+    ytdlp,
+    [
+      '--no-playlist',
+      '--no-warnings',
+      '--skip-download',
+      '--print',
+      `%(title)s${META_SEP}%(uploader)s${META_SEP}%(duration_string)s`,
+      '--',
+      url
+    ],
+    { maxBuffer: META_MAX_BUFFER, timeout: META_PROBE_TIMEOUT_MS }
+  )
+  if (!r.ok) return null
+  const [title, uploader, duration] = r.stdout.split(META_SEP).map((l) => l.trim())
+  const clean = (v?: string): string | undefined => (v && v !== 'NA' ? v : undefined)
+  return {
+    title: clean(title),
+    channel: clean(uploader),
+    durationLabel: clean(duration)
+  }
 }
 
 // --- Argv construction (shared by startDownload and the command preview) ---

src/main/ffmpeg.ts

@@ -1,6 +1,6 @@
-import { execFile } from 'child_process'
 import { existsSync } from 'fs'
 import { getFfmpegPath, getFfprobePath } from './binaries'
+import { execFileAsync } from './lib/exec'
 import { VERSION_TIMEOUT_MS } from './constants'
 import type { FfmpegVersionResult } from '@shared/ipc'
 
@@ -12,24 +12,13 @@ import type { FfmpegVersionResult } from '@shared/ipc'
  * out, or the line doesn't parse — Settings then shows "not found" instead of
  * failing. Unlike yt-dlp these are never self-updated, so there's no update path.
  */
-function readToolVersion(path: string): Promise<string | null> {
-  if (!existsSync(path)) return Promise.resolve(null)
-  return new Promise((resolve) => {
-    execFile(
-      path,
-      ['-version'],
-      { windowsHide: true, timeout: VERSION_TIMEOUT_MS },
-      (err, stdout) => {
-        if (err) {
-          resolve(null)
-          return
-        }
-        const firstLine = stdout.split('\n', 1)[0] ?? ''
-        const m = firstLine.match(/version\s+(\S+)/i)
-        resolve(m?.[1] ?? null)
-      }
-    )
-  })
+async function readToolVersion(path: string): Promise<string | null> {
+  if (!existsSync(path)) return null
+  const r = await execFileAsync(path, ['-version'], { timeout: VERSION_TIMEOUT_MS })
+  if (!r.ok) return null
+  const firstLine = r.stdout.split('\n', 1)[0] ?? ''
+  const m = firstLine.match(/version\s+(\S+)/i)
+  return m?.[1] ?? null
 }
 
 /** Versions of the bundled ffmpeg + ffprobe, read in parallel for the Settings panel. */

src/main/indexer.ts

@@ -9,9 +9,9 @@
  * this module is the impure shell that spawns yt-dlp and writes to disk.
  */
 
-import { execFile } from 'child_process'
 import { existsSync } from 'fs'
 import { getYtdlpPath, YTDLP_MISSING_MSG } from './binaries'
+import { execFileAsync } from './lib/exec'
 import { INDEX_MAX_BUFFER, INDEX_TIMEOUT_MS } from './constants'
 import { cleanError } from './log'
 import { assertHttpUrl } from './url'
@@ -46,28 +46,24 @@ interface FlatInfo {
  * flat upload list can be a few MB of JSON; the timeout is generous for the same
  * reason. `--` terminates option parsing so the URL can't be read as a flag.
  */
-function probeFlat(url: string): Promise<FlatInfo> {
-  return new Promise((resolve, reject) => {
-    execFile(
-      getYtdlpPath(),
-      ['-J', '--flat-playlist', '--no-warnings', '--', url],
-      { windowsHide: true, maxBuffer: INDEX_MAX_BUFFER, timeout: INDEX_TIMEOUT_MS },
-      (err, stdout, stderr) => {
-        if (err) {
-          const msg = (err as { killed?: boolean }).killed
-            ? 'Timed out indexing source. Check the link or your connection.'
-            : cleanError(stderr) || err.message
-          reject(new Error(msg))
-          return
-        }
-        try {
-          resolve(JSON.parse(stdout) as FlatInfo)
-        } catch {
-          reject(new Error('Could not parse source info from yt-dlp.'))
-        }
-      }
+async function probeFlat(url: string): Promise<FlatInfo> {
+  const r = await execFileAsync(
+    getYtdlpPath(),
+    ['-J', '--flat-playlist', '--no-warnings', '--', url],
+    { maxBuffer: INDEX_MAX_BUFFER, timeout: INDEX_TIMEOUT_MS }
+  )
+  if (!r.ok) {
+    throw new Error(
+      r.timedOut
+        ? 'Timed out indexing source. Check the link or your connection.'
+        : cleanError(r.stderr) || r.error?.message || ''
     )
-  })
+  }
+  try {
+    return JSON.parse(r.stdout) as FlatInfo
+  } catch {
+    throw new Error('Could not parse source info from yt-dlp.')
+  }
 }
 
 /** Probe a channel tab (e.g. /videos, /playlists); never throws — returns null. */

src/main/lib/exec.ts

@@ -0,0 +1,52 @@
+import { execFile, type ExecFileOptions } from 'child_process'
+
+/**
+ * Normalized result of a one-shot child-process run. `ok` is true on a clean
+ * exit-0; `timedOut` distinguishes a kill-by-timeout (Node sets `err.killed` when
+ * it terminates the process on the `timeout` option) from an ordinary non-zero
+ * exit, so callers can show "Timed out …" versus the captured stderr.
+ */
+export interface ExecResult {
+  ok: boolean
+  stdout: string
+  stderr: string
+  timedOut: boolean
+  /** The raw error on a non-zero exit / spawn failure (undefined when ok). */
+  error?: Error
+}
+
+/**
+ * `execFile` as a promise that never rejects (audit SIMP2/CC4/CC5). Replaces the
+ * six hand-rolled `new Promise((resolve) => execFile(…, cb))` wrappers across
+ * probe / ytdlp (×2) / ffmpeg / indexer / download.probeMeta / schedule — each
+ * caller now maps this normalized result to its own shape instead of repeating the
+ * `err.killed` timeout check and the resolve/reject plumbing.
+ *
+ * `windowsHide` defaults on (every caller wants the console window suppressed);
+ * pass `timeout` / `maxBuffer` per call exactly as before.
+ */
+export function execFileAsync(
+  file: string,
+  args: readonly string[],
+  options: ExecFileOptions = {}
+): Promise<ExecResult> {
+  return new Promise((resolve) => {
+    execFile(file, [...args], { windowsHide: true, ...options }, (err, stdout, stderr) => {
+      // With the default (utf8) encoding stdout/stderr are strings, but ExecFileOptions
+      // permits a Buffer encoding, so normalize defensively.
+      const out = typeof stdout === 'string' ? stdout : stdout.toString()
+      const errOut = typeof stderr === 'string' ? stderr : stderr.toString()
+      if (err) {
+        resolve({
+          ok: false,
+          stdout: out,
+          stderr: errOut,
+          timedOut: (err as { killed?: boolean }).killed === true,
+          error: err
+        })
+      } else {
+        resolve({ ok: true, stdout: out, stderr: errOut, timedOut: false })
+      }
+    })
+  })
+}

src/main/probe.ts

@@ -1,6 +1,6 @@
-import { execFile } from 'child_process'
 import { existsSync } from 'fs'
 import { getYtdlpPath, YTDLP_MISSING_MSG } from './binaries'
+import { execFileAsync } from './lib/exec'
 import { PROBE_MAX_BUFFER, PROBE_TIMEOUT_MS } from './constants'
 import { fmtBytes } from '@shared/format'
 import { cleanError } from './log'
@@ -114,52 +114,40 @@ function buildPlaylist(data: RawInfo): PlaylistInfo {
  * its format list) or, when the URL is a playlist, the flat list of its entries.
  * `--flat-playlist` is a no-op for a lone video, so one call covers both cases.
  */
-export function probeMedia(url: string): Promise<ProbeResult> {
+export async function probeMedia(url: string): Promise<ProbeResult> {
   const ytdlp = getYtdlpPath()
   if (!existsSync(ytdlp)) {
-    return Promise.resolve({
-      ok: false,
-      error: YTDLP_MISSING_MSG
-    })
+    return { ok: false, error: YTDLP_MISSING_MSG }
   }
   let target: string
   try {
     target = assertHttpUrl(url) // normalised form (audit F5)
   } catch (e) {
-    return Promise.resolve({ ok: false, error: (e as Error).message })
+    return { ok: false, error: (e as Error).message }
   }
 
-  return new Promise((resolve) => {
-    execFile(
-      ytdlp,
-      // `--` terminates option parsing so the URL can never be read as a flag.
-      ['-J', '--flat-playlist', '--no-warnings', '--', target],
-      { windowsHide: true, maxBuffer: PROBE_MAX_BUFFER, timeout: PROBE_TIMEOUT_MS },
-      (err, stdout, stderr) => {
-        if (err) {
-          // execFile sets `killed` when it terminated the process on timeout.
-          const msg = (err as { killed?: boolean }).killed
-            ? 'Timed out fetching video info. Check the link or your connection.'
-            : cleanError(stderr) || err.message
-          resolve({ ok: false, error: msg })
-          return
-        }
-        try {
-          const data = JSON.parse(stdout) as RawInfo
-          if (data._type === 'playlist' || Array.isArray(data.entries)) {
-            const playlist = buildPlaylist(data)
-            if (playlist.count === 0) {
-              resolve({ ok: false, error: 'This playlist has no downloadable entries.' })
-              return
-            }
-            resolve({ ok: true, kind: 'playlist', playlist })
-          } else {
-            resolve({ ok: true, kind: 'video', info: buildInfo(data) })
-          }
-        } catch {
-          resolve({ ok: false, error: 'Could not parse video info from yt-dlp.' })
-        }
-      }
-    )
+  // `--` terminates option parsing so the URL can never be read as a flag.
+  const r = await execFileAsync(ytdlp, ['-J', '--flat-playlist', '--no-warnings', '--', target], {
+    maxBuffer: PROBE_MAX_BUFFER,
+    timeout: PROBE_TIMEOUT_MS
   })
+  if (!r.ok) {
+    const msg = r.timedOut
+      ? 'Timed out fetching video info. Check the link or your connection.'
+      : cleanError(r.stderr) || r.error?.message || ''
+    return { ok: false, error: msg }
+  }
+  try {
+    const data = JSON.parse(r.stdout) as RawInfo
+    if (data._type === 'playlist' || Array.isArray(data.entries)) {
+      const playlist = buildPlaylist(data)
+      if (playlist.count === 0) {
+        return { ok: false, error: 'This playlist has no downloadable entries.' }
+      }
+      return { ok: true, kind: 'playlist', playlist }
+    }
+    return { ok: true, kind: 'video', info: buildInfo(data) }
+  } catch {
+    return { ok: false, error: 'Could not parse video info from yt-dlp.' }
+  }
 }

src/main/ytdlp.ts

@@ -1,7 +1,7 @@
-import { execFile } from 'child_process'
 import { existsSync, mkdirSync, copyFileSync } from 'fs'
 import { dirname } from 'path'
 import { getYtdlpPath, getBundledYtdlpPath, YTDLP_MISSING_MSG } from './binaries'
+import { execFileAsync } from './lib/exec'
 import { VERSION_TIMEOUT_MS, YTDLP_UPDATE_TIMEOUT_MS } from './constants'
 import { getSettings, setSettings } from './settings'
 import { shouldAutoCheckYtdlp } from './ytdlpPolicy'
@@ -34,33 +34,21 @@ export function ensureManagedYtdlp(): void {
 }
 
 /** Spawn the bundled yt-dlp and read back its `--version` for the Settings panel. */
-export function getYtdlpVersion(): Promise<YtdlpVersionResult> {
+export async function getYtdlpVersion(): Promise<YtdlpVersionResult> {
   const ytdlpPath = getYtdlpPath()
 
   if (!existsSync(ytdlpPath)) {
-    return Promise.resolve({
-      ok: false,
-      error: YTDLP_MISSING_MSG
-    })
+    return { ok: false, error: YTDLP_MISSING_MSG }
   }
 
-  return new Promise((resolve) => {
-    execFile(
-      ytdlpPath,
-      ['--version'],
-      { windowsHide: true, timeout: VERSION_TIMEOUT_MS },
-      (err, stdout, stderr) => {
-        if (err) {
-          const msg = (err as { killed?: boolean }).killed
-            ? 'Timed out running yt-dlp.'
-            : (stderr || err.message).trim()
-          resolve({ ok: false, error: msg })
-          return
-        }
-        resolve({ ok: true, version: stdout.trim() })
-      }
-    )
-  })
+  const r = await execFileAsync(ytdlpPath, ['--version'], { timeout: VERSION_TIMEOUT_MS })
+  if (!r.ok) {
+    const msg = r.timedOut
+      ? 'Timed out running yt-dlp.'
+      : (r.stderr || r.error?.message || '').trim()
+    return { ok: false, error: msg }
+  }
+  return { ok: true, version: r.stdout.trim() }
 }
 
 /**
@@ -69,13 +57,13 @@ export function getYtdlpVersion(): Promise<YtdlpVersionResult> {
  * yt-dlp.exe lives in, which holds for both the dev resources/bin checkout and
  * a per-user install; it would fail under a locked-down system install.
  */
-export function updateYtdlp(channel: YtdlpUpdateChannel): Promise<YtdlpUpdateResult> {
+export async function updateYtdlp(channel: YtdlpUpdateChannel): Promise<YtdlpUpdateResult> {
   // Validate against the channel allowlist BEFORE the value reaches `--update-to`.
   // That flag also accepts `OWNER/REPO@TAG`, which would download and install an
   // arbitrary binary over yt-dlp.exe — so an unrecognised value (e.g. forged by a
   // compromised renderer over IPC) must never be forwarded. (audit F1)
   if (!isYtdlpUpdateChannel(channel)) {
-    return Promise.resolve({ ok: false, error: 'Unsupported update channel.' })
+    return { ok: false, error: 'Unsupported update channel.' }
   }
 
   // Self-heal: restore the managed copy from the bundled seed before updating, so
@@ -84,29 +72,19 @@ export function updateYtdlp(channel: YtdlpUpdateChannel): Promise<YtdlpUpdateRes
   const ytdlpPath = getYtdlpPath()
 
   if (!existsSync(ytdlpPath)) {
-    return Promise.resolve({
-      ok: false,
-      error: YTDLP_MISSING_MSG
-    })
+    return { ok: false, error: YTDLP_MISSING_MSG }
   }
 
-  return new Promise((resolve) => {
-    execFile(
-      ytdlpPath,
-      ['--update-to', channel],
-      { windowsHide: true, timeout: YTDLP_UPDATE_TIMEOUT_MS },
-      (err, stdout, stderr) => {
-        if (err) {
-          const msg = (err as { killed?: boolean }).killed
-            ? 'Timed out updating yt-dlp.'
-            : (stderr || err.message).trim()
-          resolve({ ok: false, error: msg })
-          return
-        }
-        resolve({ ok: true, output: stdout.trim() })
-      }
-    )
+  const r = await execFileAsync(ytdlpPath, ['--update-to', channel], {
+    timeout: YTDLP_UPDATE_TIMEOUT_MS
   })
+  if (!r.ok) {
+    const msg = r.timedOut
+      ? 'Timed out updating yt-dlp.'
+      : (r.stderr || r.error?.message || '').trim()
+    return { ok: false, error: msg }
+  }
+  return { ok: true, output: r.stdout.trim() }
 }
 
 /**