denoland/deno · error · TypeError

ERR_SOCKET_BAD_TYPE

ERR_SOCKET_BAD_TYPE

Error message

Bad socket type specified. Valid types are: udp4, udp6

What it means

dgram.createSocket() builds its native handle through newHandle(type): only exact lowercase 'udp4' and 'udp6' are accepted; every other value falls through to ERR_SOCKET_BAD_TYPE. Unlike Node, Deno's polyfill does not implement 'unix_dgram', so that otherwise-valid Node type also throws here.

Source

Thrown at ext/node/polyfills/internal/dgram.ts:117

    const handle = new UDP();

    handle.lookup = FunctionPrototypeBind(lookup4, handle, lookup);

    return handle;
  }

  if (type === "udp6") {
    const handle = new UDP();

    handle.lookup = FunctionPrototypeBind(lookup6, handle, lookup);
    handle.bind = handle.bind6;
    handle.connect = handle.connect6;
    handle.send = handle.send6;

    return handle;
  }

  throw new ERR_SOCKET_BAD_TYPE();
}

function _createSocketHandle(
  address: string,
  port: number,
  addressType: SocketType,
  fd: number,
  flags: number,
) {
  const handle = newHandle(addressType);
  let err;

  if (isInt32(fd) && fd > 0) {
    const type = guessHandleType(fd);

    if (type !== "UDP") {
      err = MapPrototypeGet(codeMap, "EINVAL")!;
    } else {

View on GitHub (pinned to 9ad36f7a2c)

Solutions

Use exactly 'udp4' or 'udp6'.
Replace unix datagram IPC with Deno.connect({ transport: 'unix' }) streams or a loopback UDP socket.
Normalize and whitelist config-driven types before createSocket (lowercase, trim, allowlist).

Example fix

// before
const sock = dgram.createSocket(config.sockType); // 'unix_dgram'

// after
const sock = dgram.createSocket(config.sockType === 'udp6' ? 'udp6' : 'udp4');

Defensive patterns

Strategy: validation

Validate before calling

const SOCKET_TYPES = new Set(['udp4', 'udp6']);
const type = String(config.socketType ?? '').toLowerCase().trim();
if (!SOCKET_TYPES.has(type)) {
  throw new RangeError('socket type must be udp4 or udp6, got ' + config.socketType);
}
const sock = dgram.createSocket(type);

Type guard

const isUdpType = (t) => t === 'udp4' || t === 'udp6';

Try / catch

try {
  sock = dgram.createSocket(type);
} catch (err) {
  if (err?.code === 'ERR_SOCKET_BAD_TYPE') {
    sock = dgram.createSocket('udp4'); // safe default after logging the config error
  } else {
    throw err;
  }
}

Prevention

Whitelist socket types from config; normalize case and trim before createSocket.
Do not port Node unix_dgram code to Deno node:dgram - redesign to unix streams or loopback UDP.
Fail fast on unknown socket types at startup, not mid-request.

When it happens

Trigger: dgram.createSocket('unix_dgram') (unix datagram socket, unsupported); createSocket('UDP4') or 'udp4 ' (case/whitespace mismatch); a type variable that is undefined or came from unvalidated config.

Common situations: Porting Node services that log to a local unix datagram socket (syslog-style) to Deno; config-driven socket types with casing mismatches; feature flags selecting socket families.

Related errors

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/315f7e72d4be7570. Report an issue: GitHub.