fs: restore JS implementation of realpath

This reverts parts of b488b19eaf
restoring javascript implementation of realpath and realpathSync.

Fixes: https://github.com/nodejs/node/issues/7175
Fixes: https://github.com/nodejs/node/issues/6861
Fixes: https://github.com/nodejs/node/issues/7294
Fixes: https://github.com/nodejs/node/issues/7192
Fixes: https://github.com/nodejs/node/issues/7044
Fixes: https://github.com/nodejs/node/issues/6624
Fixes: https://github.com/nodejs/node/issues/6978
PR-URL: https://github.com/nodejs/node/pull/7899
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/fs.md

@@ -1222,6 +1222,8 @@ added: v0.1.31
 Asynchronous realpath(3). The `callback` gets two arguments `(err,
 resolvedPath)`. May use `process.cwd` to resolve relative paths.
 
+Only paths that can be converted to UTF8 strings are supported. 
+
 The optional `options` argument can be a string specifying an encoding, or an
 object with an `encoding` property specifying the character encoding to use for
 the path passed to the callback. If the `encoding` is set to `'buffer'`,
@@ -1238,10 +1240,12 @@ added: v0.1.31
 
 Synchronous realpath(3). Returns the resolved path.
 
+Only paths that can be converted to UTF8 strings are supported.
+
 The optional `options` argument can be a string specifying an encoding, or an
 object with an `encoding` property specifying the character encoding to use for
-the path passed to the callback. If the `encoding` is set to `'buffer'`,
+the returned value. If the `encoding` is set to `'buffer'`, the path returned
-the path returned will be passed as a `Buffer` object.
+will be passed as a `Buffer` object.
 
 ## fs.rename(oldPath, newPath, callback)
 <!-- YAML

lib/fs.js

@@ -1563,38 +1563,239 @@ fs.unwatchFile = function(filename, listener) {
 };
 
 
-fs.realpathSync = function realpathSync(path, options) {
+// Regexp that finds the next portion of a (partial) path
+// result is [base_with_slash, base], e.g. ['somedir/', 'somedir']
+const nextPartRe = isWindows ?
+  /(.*?)(?:[\/\\]+|$)/g :
+  /(.*?)(?:[\/]+|$)/g;
+
+// Regex to find the device root, including trailing slash. E.g. 'c:\\'.
+const splitRootRe = isWindows ?
+  /^(?:[a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/][^\\\/]+)?[\\\/]*/ :
+  /^[\/]*/;
+
+function encodeRealpathResult(result, options, err) {
+  if (!options || !options.encoding || options.encoding === 'utf8' || err)
+    return result;
+  const asBuffer = Buffer.from(result);
+  if (options.encoding === 'buffer') {
+    return asBuffer;
+  } else {
+    return asBuffer.toString(options.encoding);
+  }
+}
+
+fs.realpathSync = function realpathSync(p, options) {
   if (!options)
     options = {};
   else if (typeof options === 'string')
     options = {encoding: options};
   else if (typeof options !== 'object')
     throw new TypeError('"options" must be a string or an object');
-  nullCheck(path);
+  nullCheck(p);
-  return binding.realpath(pathModule._makeLong(path), options.encoding);
+
+  p = p.toString('utf8');
+  p = pathModule.resolve(p);
+
+  const seenLinks = {};
+  const knownHard = {};
+
+  // current character position in p
+  var pos;
+  // the partial path so far, including a trailing slash if any
+  var current;
+  // the partial path without a trailing slash (except when pointing at a root)
+  var base;
+  // the partial path scanned in the previous round, with slash
+  var previous;
+
+  start();
+
+  function start() {
+    // Skip over roots
+    var m = splitRootRe.exec(p);
+    pos = m[0].length;
+    current = m[0];
+    base = m[0];
+    previous = '';
+
+    // On windows, check that the root exists. On unix there is no need.
+    if (isWindows && !knownHard[base]) {
+      fs.lstatSync(base);
+      knownHard[base] = true;
+    }
+  }
+
+  // walk down the path, swapping out linked pathparts for their real
+  // values
+  // NB: p.length changes.
+  while (pos < p.length) {
+    // find the next part
+    nextPartRe.lastIndex = pos;
+    var result = nextPartRe.exec(p);
+    previous = current;
+    current += result[0];
+    base = previous + result[1];
+    pos = nextPartRe.lastIndex;
+
+    // continue if not a symlink
+    if (knownHard[base]) {
+      continue;
+    }
+
+    var resolvedLink;
+    var stat = fs.lstatSync(base);
+    if (!stat.isSymbolicLink()) {
+      knownHard[base] = true;
+      continue;
+    }
+
+    // read the link if it wasn't read before
+    // dev/ino always return 0 on windows, so skip the check.
+    var linkTarget = null;
+    if (!isWindows) {
+      var id = stat.dev.toString(32) + ':' + stat.ino.toString(32);
+      if (seenLinks.hasOwnProperty(id)) {
+        linkTarget = seenLinks[id];
+      }
+    }
+    if (linkTarget === null) {
+      fs.statSync(base);
+      linkTarget = fs.readlinkSync(base);
+    }
+    resolvedLink = pathModule.resolve(previous, linkTarget);
+
+    if (!isWindows) seenLinks[id] = linkTarget;
+
+    // resolve the link, then start over
+    p = pathModule.resolve(resolvedLink, p.slice(pos));
+    start();
+  }
+
+  return encodeRealpathResult(p, options);
 };
 
 
-fs.realpath = function realpath(path, options, callback) {
+fs.realpath = function realpath(p, options, callback) {
+  if (typeof callback !== 'function') {
+    callback = maybeCallback(options);
+    options = {};
+  }
+
   if (!options) {
     options = {};
   } else if (typeof options === 'function') {
-    callback = options;
     options = {};
   } else if (typeof options === 'string') {
     options = {encoding: options};
   } else if (typeof options !== 'object') {
     throw new TypeError('"options" must be a string or an object');
   }
-  callback = makeCallback(callback);
+  if (!nullCheck(p, callback))
-  if (!nullCheck(path, callback))
     return;
-  var req = new FSReqWrap();
-  req.oncomplete = callback;
-  binding.realpath(pathModule._makeLong(path), options.encoding, req);
-  return;
-};
 
+  p = p.toString('utf8');
+  p = pathModule.resolve(p);
+
+  const seenLinks = {};
+  const knownHard = {};
+
+  // current character position in p
+  var pos;
+  // the partial path so far, including a trailing slash if any
+  var current;
+  // the partial path without a trailing slash (except when pointing at a root)
+  var base;
+  // the partial path scanned in the previous round, with slash
+  var previous;
+
+  start();
+
+  function start() {
+    // Skip over roots
+    var m = splitRootRe.exec(p);
+    pos = m[0].length;
+    current = m[0];
+    base = m[0];
+    previous = '';
+
+    // On windows, check that the root exists. On unix there is no need.
+    if (isWindows && !knownHard[base]) {
+      fs.lstat(base, function(err) {
+        if (err) return callback(err);
+        knownHard[base] = true;
+        LOOP();
+      });
+    } else {
+      process.nextTick(LOOP);
+    }
+  }
+
+  // walk down the path, swapping out linked pathparts 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
+    nextPartRe.lastIndex = pos;
+    var result = nextPartRe.exec(p);
+    previous = current;
+    current += result[0];
+    base = previous + result[1];
+    pos = nextPartRe.lastIndex;
+
+    // continue if not a symlink
+    if (knownHard[base]) {
+      return process.nextTick(LOOP);
+    }
+
+    return fs.lstat(base, gotStat);
+  }
+
+  function gotStat(err, stat) {
+    if (err) return callback(err);
+
+    // if not a symlink, skip to the next path part
+    if (!stat.isSymbolicLink()) {
+      knownHard[base] = true;
+      return process.nextTick(LOOP);
+    }
+
+    // stat & read the link if not read before
+    // call gotTarget as soon as the link target is known
+    // dev/ino always return 0 on windows, so skip the check.
+    if (!isWindows) {
+      var id = stat.dev.toString(32) + ':' + stat.ino.toString(32);
+      if (seenLinks.hasOwnProperty(id)) {
+        return gotTarget(null, seenLinks[id], base);
+      }
+    }
+    fs.stat(base, function(err) {
+      if (err) return callback(err);
+
+      fs.readlink(base, function(err, target) {
+        if (!isWindows) seenLinks[id] = target;
+        gotTarget(err, target);
+      });
+    });
+  }
+
+  function gotTarget(err, target, base) {
+    if (err) return callback(err);
+
+    var resolvedLink = pathModule.resolve(previous, target);
+    gotResolvedLink(resolvedLink);
+  }
+
+  function gotResolvedLink(resolvedLink) {
+    // resolve the link, then start over
+    p = pathModule.resolve(resolvedLink, p.slice(pos));
+    start();
+  }
+};
 
 fs.mkdtemp = function(prefix, options, callback) {
   if (!prefix || typeof prefix !== 'string')

test/parallel/test-fs-realpath-buffer-encoding.js

@@ -0,0 +1,88 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+
+const string_dir = fs.realpathSync(common.fixturesDir);
+const buffer_dir = Buffer.from(string_dir);
+
+const encodings = ['ascii', 'utf8', 'utf16le', 'ucs2',
+                   'base64', 'binary', 'hex'];
+var expected = {};
+encodings.forEach((encoding) => {
+  expected[encoding] = buffer_dir.toString(encoding);
+});
+
+
+// test sync version
+for (var encoding in expected) {
+  const expected_value = expected[encoding];
+  let result;
+
+  result = fs.realpathSync(string_dir, {encoding: encoding});
+  assert.strictEqual(result, expected_value);
+
+  result = fs.realpathSync(string_dir, encoding);
+  assert.strictEqual(result, expected_value);
+
+  result = fs.realpathSync(buffer_dir, {encoding: encoding});
+  assert.strictEqual(result, expected_value);
+
+  result = fs.realpathSync(buffer_dir, encoding);
+  assert.strictEqual(result, expected_value);
+}
+
+let buffer_result;
+buffer_result = fs.realpathSync(string_dir, {encoding: 'buffer'});
+assert.deepStrictEqual(buffer_result, buffer_dir);
+
+buffer_result = fs.realpathSync(string_dir, 'buffer');
+assert.deepStrictEqual(buffer_result, buffer_dir);
+
+buffer_result = fs.realpathSync(buffer_dir, {encoding: 'buffer'});
+assert.deepStrictEqual(buffer_result, buffer_dir);
+
+buffer_result = fs.realpathSync(buffer_dir, 'buffer');
+assert.deepStrictEqual(buffer_result, buffer_dir);
+
+// test async version
+for (encoding in expected) {
+  const expected_value = expected[encoding];
+
+  fs.realpath(string_dir, {encoding: encoding}, common.mustCall((err, res) => {
+    assert(!err);
+    assert.strictEqual(res, expected_value);
+  }));
+  fs.realpath(string_dir, encoding, common.mustCall((err, res) => {
+    assert(!err);
+    assert.strictEqual(res, expected_value);
+  }));
+  fs.realpath(buffer_dir, {encoding: encoding}, common.mustCall((err, res) => {
+    assert(!err);
+    assert.strictEqual(res, expected_value);
+  }));
+  fs.realpath(buffer_dir, encoding, common.mustCall((err, res) => {
+    assert(!err);
+    assert.strictEqual(res, expected_value);
+  }));
+}
+
+fs.realpath(string_dir, {encoding: 'buffer'}, common.mustCall((err, res) => {
+  assert(!err);
+  assert.deepStrictEqual(res, buffer_dir);
+}));
+
+fs.realpath(string_dir, 'buffer', common.mustCall((err, res) => {
+  assert(!err);
+  assert.deepStrictEqual(res, buffer_dir);
+}));
+
+fs.realpath(buffer_dir, {encoding: 'buffer'}, common.mustCall((err, res) => {
+  assert(!err);
+  assert.deepStrictEqual(res, buffer_dir);
+}));
+
+fs.realpath(buffer_dir, 'buffer', common.mustCall((err, res) => {
+  assert(!err);
+  assert.deepStrictEqual(res, buffer_dir);
+}));

test/parallel/test-fs-realpath-on-substed-drive.js

@@ -0,0 +1,53 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const spawnSync = require('child_process').spawnSync;
+
+if (!common.isWindows) {
+  common.skip('Test for Windows only');
+  return;
+}
+let result;
+
+// create a subst drive
+const driveLetters = 'ABCDEFGHIJKLMNOPQRSTUWXYZ';
+let drive;
+for (var i = 0; i < driveLetters.length; ++i) {
+  drive = `${driveLetters[i]}:`;
+  result = spawnSync('subst', [drive, common.fixturesDir]);
+  if (result.status === 0)
+    break;
+}
+if (i === driveLetters.length) {
+  common.skip('Cannot create subst drive');
+  return;
+}
+
+// schedule cleanup (and check if all callbacks where called)
+process.on('exit', function() {
+  spawnSync('subst', ['/d', drive]);
+});
+
+// test:
+const filename = `${drive}\\empty.js`;
+const filenameBuffer = Buffer.from(filename);
+
+result = fs.realpathSync(filename);
+assert.strictEqual(result, filename);
+
+result = fs.realpathSync(filename, 'buffer');
+assert(Buffer.isBuffer(result));
+assert(result.equals(filenameBuffer));
+
+fs.realpath(filename, common.mustCall(function(err, result) {
+  assert(!err);
+  assert.strictEqual(result, filename);
+}));
+
+fs.realpath(filename, 'buffer', common.mustCall(function(err, result) {
+  assert(!err);
+  assert(Buffer.isBuffer(result));
+  assert(result.equals(filenameBuffer));
+}));