Function realpath

lib/fs.js:3399–3533

* Asynchronously computes the canonical pathname by * resolving `.`, `..` and symbolic links. * @param {string | Buffer | URL} p * @param {string | { encoding?: string; }} [options] * @param {( * err?: Error, * resolvedPath?: string | Buffer * ) => any} callback * @returns {void}

(p, options, callback)

 * @returns {void}
 */
function realpath(p, options, callback) {
  if (typeof options === 'function') {
    callback = options;
    options = undefined;
  } else {
    validateFunction(callback, 'cb');
  }

  const h = vfsState.handlers;
  if (h !== null && vfsResult(h.realpath(p, options), callback)) return;

  options = getOptions(options);
  p = toPathIfFileURL(p);

  if (typeof p !== 'string') {
    p += '';
  }
  validatePath(p);
  p = pathModule.resolve(p);

  const seenLinks = new SafeMap();
  const knownHard = new SafeSet();

  // Current character position in p
  let pos;
  // The partial path so far, including a trailing slash if any
  let current;
  // The partial path without a trailing slash (except when pointing at a root)
  let base;
  // The partial path scanned in the previous round, with slash
  let previous;

  current = base = splitRoot(p);
  pos = current.length;

  // On windows, check that the root exists. On unix there is no need.
  if (isWindows && !knownHard.has(base)) {
    fs.lstat(base, (err) => {
      if (err) return callback(err);
      knownHard.add(base);
      LOOP();
    });
  } else {
    process.nextTick(LOOP);
  }

  // Walk down the path, swapping out linked path parts for their real
  // values
  function LOOP() {
    // Stop if scanned past end of path
    if (pos >= p.length) {
      return callback(null, encodeRealpathResult(p, options));
    }

    // find the next part
    const result = nextPart(p, pos);
    previous = current;
    if (result === -1) {