windows: make fs.realpath(Sync) work with UNC paths

Closes #3542

1 files changed, 61 insertions, 42 deletions

diff --git a/lib/fs.js b/lib/fs.js
index 076ddb50c..4aac1923a 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -966,10 +966,12 @@ if (isWindows) {
   var nextPartRe = /(.*?)(?:[\/]+|$)/g;
 }
 
-// Regex to split a windows path into three parts: [*, device, slash,
-// tail] windows-only
-var splitDeviceRe =
-    /^([a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/][^\\\/]+)?([\\\/])?([\s\S]*?)$/;
+// Regex to find the device root, including trailing slash. E.g. 'c:\\'.
+if (isWindows) {
+  var splitRootRe = /^(?:[a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/][^\\\/]+)?[\\\/]*/;
+} else {
+  var splitRootRe = /^[\/]*/;
+}
 
 fs.realpathSync = function realpathSync(p, cache) {
   // make p is absolute
@@ -984,13 +986,30 @@ fs.realpathSync = function realpathSync(p, cache) {
       knownHard = {};
 
   // current character position in p
-  var pos = 0;
+  var pos;
   // the partial path so far, including a trailing slash if any
-  var current = '';
-  // the partial path without a trailing slash
-  var base = '';
+  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 = '';
+  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
@@ -1004,16 +1023,8 @@ fs.realpathSync = function realpathSync(p, cache) {
     base = previous + result[1];
     pos = nextPartRe.lastIndex;
 
-    // continue if not a symlink, or if root
-    var isRoot = !base;
-    if (isWindows) {
-      // if it doens't have a tail, then it's the root.
-      var split = base.match(splitDeviceRe);
-      if (split) {
-        isRoot = !split[2];
-      }
-    }
-    if (isRoot || knownHard[base] || (cache && cache[base] === base)) {
+    // continue if not a symlink
+    if (knownHard[base] || (cache && cache[base] === base)) {
       continue;
     }
 
@@ -1050,8 +1061,7 @@ fs.realpathSync = function realpathSync(p, cache) {
 
     // resolve the link, then start over
     p = pathModule.resolve(resolvedLink, p.slice(pos));
-    pos = 0;
-    previous = base = current = '';
+    start();
   }
 
   if (cache) cache[original] = p;
@@ -1078,17 +1088,38 @@ fs.realpath = function realpath(p, cache, cb) {
       knownHard = {};
 
   // current character position in p
-  var pos = 0;
+  var pos;
   // the partial path so far, including a trailing slash if any
-  var current = '';
-  // the partial path without a trailing slash
-  var base = '';
+  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 = '';
+  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 cb(err);
+        knownHard[base] = true;
+        LOOP();
+      });
+    } else {
+      process.nextTick(LOOP);
+    }
+  }
 
   // walk down the path, swapping out linked pathparts for their real
   // values
-  return process.nextTick(LOOP);
   function LOOP() {
     // stop if scanned past end of path
     if (pos >= p.length) {
@@ -1104,16 +1135,8 @@ fs.realpath = function realpath(p, cache, cb) {
     base = previous + result[1];
     pos = nextPartRe.lastIndex;
 
-    // continue if not a symlink, or if root
-    var isRoot = !base;
-    if (isWindows) {
-      // if it doens't have a tail, then it's the root.
-      var split = base.match(splitDeviceRe);
-      if (split) {
-        isRoot = !split[2];
-      }
-    }
-    if (isRoot || knownHard[base] || (cache && cache[base] === base)) {
+    // continue if not a symlink
+    if (knownHard[base] || (cache && cache[base] === base)) {
       return process.nextTick(LOOP);
     }
 
@@ -1163,13 +1186,9 @@ fs.realpath = function realpath(p, cache, cb) {
   }
 
   function gotResolvedLink(resolvedLink) {
-
     // resolve the link, then start over
     p = pathModule.resolve(resolvedLink, p.slice(pos));
-    pos = 0;
-    previous = base = current = '';
-
-    return process.nextTick(LOOP);
+    start();
   }
 };