ckage scope, or a default `module` scope enabled by the
 * `--experimental-default-type` flag, we check the file contents to disambiguate between ES module JavaScript and Wasm.
 * We do this by taking advantage of the fact that all Wasm files start with the header `0x00 0x61 0x73 0x6d` (`_asm`).
 * @param {URL} url
 */
function getFormatOfExtensionlessFile(url) {
  if (!experimentalWasmModules) { return 'module'; }

  const magic = new Uint8Array(4);
  let fd;
  try {
    // TODO(@anonrig): Optimize the following by having a single C++ call
    fd = openSync(url);
    readSync(fd, magic, 0, 4); // Only read the first four bytes
    if (magic[0] === 0x00 && magic[1] === 0x61 && magic[2] === 0x73 && magic[3] === 0x6d) {
      return 'wasm';
    }
  } finally {
    if (fd !== undefined) { closeSync(fd); }
  }

  return 'module';
}

module.exports = {
  extensionFormatMap,
  getFormatOfExtensionlessFile,
  getLegacyExtensionFormat,
  legacyExtensionFormatMap,
  mimeToFormat,
};
