windows: fix normalization of UNC paths

1 files changed, 29 insertions, 9 deletions

diff --git a/lib/path.js b/lib/path.js
index 7e521f20de..139d04aae8 100644
--- a/lib/path.js
+++ b/lib/path.js
@@ -59,7 +59,7 @@ if (isWindows) {
   // Regex to split a windows path into three parts: [*, device, slash,
   // tail] windows-only
   var splitDeviceRe =
-      /^([a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/][^\\\/]+)?([\\\/])?([\s\S]*?)$/;
+      /^([a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/]+[^\\\/]+)?([\\\/])?([\s\S]*?)$/;
 
   // Regex to split the tail part of the above into [*, dir, basename, ext]
   var splitTailRe =
@@ -80,6 +80,10 @@ if (isWindows) {
     return [device, dir, basename, ext];
   };
 
+  var normalizeUNCRoot = function(device) {
+    return '\\\\' + device.replace(/^[\\\/]+/, '').replace(/[\\\/]+/g, '\\');
+  }
+
   // path.resolve([from ...], to)
   // windows version
   exports.resolve = function() {
@@ -138,8 +142,11 @@ if (isWindows) {
       }
     }
 
-    // Replace slashes (in UNC share name) by backslashes
-    resolvedDevice = resolvedDevice.replace(/\//g, '\\');
+    // Convert slashes to backslashes when `resolvedDevice` points to an UNC
+    // root. Also squash multiple slashes into a single one where appropriate.
+    if (isUnc) {
+      resolvedDevice = normalizeUNCRoot(resolvedDevice);
+    }
 
     // At this point the path should be resolved to a full absolute path,
     // but handle relative paths to be safe (might happen when process.cwd()
@@ -180,7 +187,10 @@ if (isWindows) {
     }
 
     // Convert slashes to backslashes when `device` points to an UNC root.
-    device = device.replace(/\//g, '\\');
+    // Also squash multiple slashes into a single one where appropriate.
+    if (isUnc) {
+      device = normalizeUNCRoot(device);
+    }
 
     return device + (isAbsolute ? '\\' : '') + tail;
   };
@@ -194,11 +204,21 @@ if (isWindows) {
     var paths = Array.prototype.filter.call(arguments, f);
     var joined = paths.join('\\');
 
-    // Make sure that the joined path doesn't start with two slashes
-    // - it will be mistaken for an unc path by normalize() -
-    // unless the paths[0] also starts with two slashes
-    if (/^[\\\/]{2}/.test(joined) && !/^[\\\/]{2}/.test(paths[0])) {
-      joined = joined.substr(1);
+    // Make sure that the joined path doesn't start with two slashes, because
+    // normalize() will mistake it for an UNC path then.
+    //
+    // This step is skipped when it is very clear that the user actually
+    // intended to point at an UNC path. This is assumed when the first
+    // non-empty string arguments starts with exactly two slashes followed by
+    // at least one more non-slash character.
+    //
+    // Note that for normalize() to treat a path as an UNC path it needs to
+    // have at least 2 components, so we don't filter for that here.
+    // This means that the user can use join to construct UNC paths from
+    // a server name and a share name; for example:
+    //   path.join('//server', 'share') -> '\\\\server\\share\')
+    if (!/^[\\\/]{2}[^\\\/]/.test(paths[0])) {
+      joined = joined.replace(/^[\\\/]{2,}/, '\\');
     }
 
     return exports.normalize(joined);