ms$1 = function (val, options) {
  options = options || {};
  var type = typeof val;
  if (type === 'string' && val.length > 0) {
    return parse$a(val);
  } else if (type === 'number' && isFinite(val)) {
    return options.long ? fmtLong(val) : fmtShort(val);
  }
  throw new Error(
    'val is not a non-empty string or a valid number. val=' +
      JSON.stringify(val)
  );
}
Transfer the file at the given `path` as an attachment.

Optionally providing an alternate attachment `filename`,
and optional callback `callback(err)`. The callback is invoked
when the data transfer is complete, or when an error has
occurred. Be sure to check `res.headersSent` if you plan to respond.

Optionally providing an `options` object to use with `res.sendFile()`.
This function will set the `Content-Disposition` header, overriding
any `Content-Disposition` header passed as header options in order
to set the attachment and filename.

This method uses `res.sendFile()`.

@public