denoland/deno · error · NodeTypeError

ERR_INVALID_SYNC_FORK_INPUT

ERR_INVALID_SYNC_FORK_INPUT

Error message

Asynchronous forks do not support Buffer, TypedArray, DataView or string input: ${value}

What it means

While iterating stdio array elements, getValidStdio() recognizes the keywords ('ipc', 'ignore', null, 'pipe', undefined, 'inherit', 'overlapped'), numbers (fds), and objects (fd-holders or Streams). A string element that is not one of those keywords falls into the string branch and throws ERR_INVALID_SYNC_FORK_INPUT, whose message ('Asynchronous forks do not support Buffer, TypedArray, DataView or string input') is inherited verbatim from Node and refers to this class of invalid stdio input values.

Source

Thrown at ext/node/polyfills/internal/child_process.ts:1161

      if (sync) {
        throw new ERR_IPC_SYNC_FORK();
      }
      ipc = i;
      ipcFd = i;
      ArrayPrototypePush(result, { type: "ipc" });
    } else if (value === "ignore" || value === null) {
      ArrayPrototypePush(result, { type: "ignore" });
    } else if (value === "pipe" || value === undefined) {
      ArrayPrototypePush(result, { type: "pipe" });
    } else if (value === "inherit") {
      ArrayPrototypePush(result, { type: "inherit" });
    } else if (value === "overlapped") {
      ArrayPrototypePush(result, { type: "overlapped" });
    } else if (typeof value === "number") {
      ArrayPrototypePush(result, { type: "fd", fd: value });
    } else if (typeof value === "string") {
      // Invalid string value
      throw new ERR_INVALID_SYNC_FORK_INPUT(value);
    } else if (typeof value === "object" && value !== null) {
      // Check if it's a Stream with fd property (like process.stdin/stdout/stderr)
      if (
        value.fd !== undefined && typeof value.fd === "number"
      ) {
        ArrayPrototypePush(result, { type: "fd", fd: value.fd });
      } else if (ObjectPrototypeIsPrototypeOf(Stream.prototype, value)) {
        // Valid Stream object but without fd
        ArrayPrototypePush(result, { type: "pipe" });
      } else {
        // Invalid object
        throw new ERR_INVALID_ARG_VALUE("stdio", value);
      }
    } else {
      throw new ERR_INVALID_ARG_VALUE("stdio", value);
    }
  }

View on GitHub (pinned to 9ad36f7a2c)

Solutions

Map custom vocabulary to real keywords before spawn: silent->'ignore', null->'ignore', inheritAll->'inherit'
Whitelist-check every string element: ['pipe','inherit','ignore','overlapped','ipc']
Trim interpolated values and fall back to 'pipe' for empties

Example fix

// before
const mode = cfg.quiet ? 'silent' : 'pipe';
spawnSync(cmd, args, { stdio: [mode, 'pipe', 'pipe'] });

// after
const mode = cfg.quiet ? 'ignore' : 'pipe';
spawnSync(cmd, args, { stdio: [mode, 'pipe', 'pipe'] });

Defensive patterns

Strategy: type-guard

Validate before calling

const KEYWORDS = new Set(['pipe', 'inherit', 'ignore', 'overlapped', 'ipc']);
const ALIASES = { silent: 'ignore', quiet: 'ignore', null: 'ignore', none: 'ignore', tty: 'inherit' };
function normalizeEntry(e) {
  if (typeof e === 'string') {
    const t = e.trim();
    if (KEYWORDS.has(t)) return t;
    if (t in ALIASES) return ALIASES[t];
    throw new Error(`invalid stdio entry '${e}'`);
  }
  return e;
}

Type guard

const isValidStdioKeyword = (s) =>
  ['pipe', 'inherit', 'ignore', 'overlapped', 'ipc'].includes(s);

Try / catch

try { spawnSync(cmd, { stdio }); } catch (err) {
  if (err?.code === 'ERR_INVALID_SYNC_FORK_INPUT' ||
      (err?.code === 'ERR_INVALID_ARG_VALUE' && /stdio/.test(err.message))) {
    spawnSync(cmd, { stdio: stdio.map((e) => (typeof e === 'string' && isValidStdioKeyword(e)) ? e : 'pipe') });
  }
}

Prevention

Translate library-specific words (silent, null, none) to real keywords before spawning
Trim interpolated strings; empty strings are never valid stdio entries
Centralize a normalizeStdio() helper so every spawn site uses the same vocabulary

When it happens

Trigger: stdio: ['silent', 'pipe', 'pipe']; ['null', 'inherit']; ['ipc2', 'pipe']; strings from config or template literals ('${mode}' resolving to an unknown word).

Common situations: Feature-flag strings ('silent', 'null', 'shared') copied from another library's vocabulary; interpolated stdio values that end up empty ('') or with whitespace; docs examples that use 'inherit-all' pseudo-values.

Related errors

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/0411fc88eddf44a5. Report an issue: GitHub.