diff -r 000000000000 -r 6474c204b198 xpcom/tests/windows/TestNtPathToDosPath.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/tests/windows/TestNtPathToDosPath.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,222 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "TestHarness.h"
+
+#include <windows.h>
+#include <winnetwk.h>
+
+#include "mozilla/FileUtilsWin.h"
+#include "mozilla/DebugOnly.h"
+#include "nsCRTGlue.h"
+
+class DriveMapping
+{
+public:
+  DriveMapping(const nsAString& aRemoteUNCPath);
+  ~DriveMapping();
+
+  bool
+  Init();
+  bool
+  ChangeDriveLetter();
+  wchar_t
+  GetDriveLetter() { return mDriveLetter; }
+
+private:
+  bool
+  DoMapping();
+  void
+  Disconnect(wchar_t aDriveLetter);
+
+  wchar_t   mDriveLetter;
+  nsString  mRemoteUNCPath;
+};
+
+DriveMapping::DriveMapping(const nsAString& aRemoteUNCPath)
+  : mDriveLetter(0)
+  , mRemoteUNCPath(aRemoteUNCPath)
+{
+}
+
+bool
+DriveMapping::Init()
+{
+  if (mDriveLetter) {
+    return false;
+  }
+  return DoMapping();
+}
+
+bool
+DriveMapping::DoMapping()
+{
+  wchar_t drvTemplate[] = L" :";
+  NETRESOURCEW netRes = {0};
+  netRes.dwType = RESOURCETYPE_DISK;
+  netRes.lpLocalName = drvTemplate;
+  netRes.lpRemoteName = reinterpret_cast<wchar_t*>(mRemoteUNCPath.BeginWriting());
+  wchar_t driveLetter = L'D';
+  DWORD result = NO_ERROR;
+  do {
+    drvTemplate[0] = driveLetter;
+    result = WNetAddConnection2W(&netRes, nullptr, nullptr, CONNECT_TEMPORARY);
+  } while (result == ERROR_ALREADY_ASSIGNED && ++driveLetter <= L'Z');
+  if (result != NO_ERROR) {
+    return false;
+  }
+  mDriveLetter = driveLetter;
+  return true;
+}
+
+bool
+DriveMapping::ChangeDriveLetter()
+{
+  wchar_t prevDriveLetter = mDriveLetter;
+  bool result = DoMapping();
+  MOZ_ASSERT(mDriveLetter != prevDriveLetter);
+  if (result && prevDriveLetter) {
+    Disconnect(prevDriveLetter);
+  }
+  return result;
+}
+
+void
+DriveMapping::Disconnect(wchar_t aDriveLetter)
+{
+  wchar_t drvTemplate[] = {aDriveLetter, L':', L'\0'};
+  mozilla::DebugOnly<DWORD> result = WNetCancelConnection2W(drvTemplate, 0, TRUE);
+  MOZ_ASSERT(result == NO_ERROR);
+}
+
+DriveMapping::~DriveMapping()
+{
+  if (mDriveLetter) {
+    Disconnect(mDriveLetter);
+  }
+}
+
+bool
+DriveToNtPath(const wchar_t aDriveLetter, nsAString& aNtPath)
+{
+  const wchar_t drvTpl[] = {aDriveLetter, L':', L'\0'};
+  aNtPath.SetLength(MAX_PATH);
+  DWORD pathLen;
+  while (true) {
+    pathLen = QueryDosDeviceW(drvTpl, reinterpret_cast<wchar_t*>(aNtPath.BeginWriting()), aNtPath.Length());
+    if (pathLen || GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
+      break;
+    }
+    aNtPath.SetLength(aNtPath.Length() * 2);
+  }
+  if (!pathLen) {
+    return false;
+  }
+  // aNtPath contains embedded NULLs, so we need to figure out the real length
+  // via wcslen.
+  aNtPath.SetLength(NS_strlen(aNtPath.BeginReading()));
+  return true;
+}
+
+bool
+TestNtPathToDosPath(const wchar_t* aNtPath,
+                    const wchar_t* aExpectedDosPath)
+{
+  nsAutoString output;
+  bool result = mozilla::NtPathToDosPath(nsDependentString(aNtPath), output);
+  return result && output == aExpectedDosPath;
+}
+
+int main(int argc, char* argv[])
+{
+  ScopedXPCOM xpcom("NtPathToDosPath");
+  if (xpcom.failed()) {
+    fail("XPCOM Startup");
+    return 1;
+  }
+  nsAutoString cDrive;
+  if (!DriveToNtPath(L'C', cDrive)) {
+    fail("Querying for this machine's C:");
+    return 1;
+  }
+
+  int result = 0;
+
+  // empty string
+  if (!TestNtPathToDosPath(L"", L"")) {
+    fail("Empty string");
+    result = 1;
+  }
+  // non-existent device, must fail
+  if (TestNtPathToDosPath(L"\\Device\\ThisDeviceDoesNotExist\\Foo", nullptr)) {
+    fail("Non-existent device");
+    result = 1;
+  }
+  // base case
+  nsAutoString testPath(cDrive);
+  testPath.Append(L"\\Foo");
+  if (!TestNtPathToDosPath(testPath.get(), L"C:\\Foo")) {
+    fail("Base case");
+    result = 1;
+  }
+  // drive letters as symbolic links (NtCreateFile uses these)
+  if (!TestNtPathToDosPath(L"\\??\\C:\\Foo", L"C:\\Foo")) {
+    fail("Path specified as symbolic link");
+    result = 1;
+  }
+  // other symbolic links (should fail)
+  if (TestNtPathToDosPath(L"\\??\\MountPointManager", nullptr)) {
+    fail("Other symbolic link");
+    result = 1;
+  }
+  // socket (should fail)
+  if (TestNtPathToDosPath(L"\\Device\\Afd\\Endpoint", nullptr)) {
+    fail("Socket");
+    result = 1;
+  }
+  // currently UNC paths that are not mapped to drive letters are unsupported,
+  // so this should fail
+  if (TestNtPathToDosPath(L"\\Device\\Mup\\127.0.0.1\\C$", nullptr)) {
+    fail("Unmapped UNC path");
+    result = 1;
+  }
+  DriveMapping drvMapping(NS_LITERAL_STRING("\\\\127.0.0.1\\C$"));
+  // Only run these tests if we were able to map; some machines don't have perms
+  if (drvMapping.Init()) {
+    wchar_t expected[] = L" :\\";
+    expected[0] = drvMapping.GetDriveLetter();
+    nsAutoString networkPath;
+    if (!DriveToNtPath(drvMapping.GetDriveLetter(), networkPath)) {
+      fail("Querying network drive");
+      return 1;
+    }
+    networkPath += MOZ_UTF16("\\");
+    if (!TestNtPathToDosPath(networkPath.get(), expected)) {
+      fail("Mapped UNC path");
+      result = 1;
+    }
+    // NtPathToDosPath must correctly handle paths whose drive letter mapping has
+    // changed. We need to test this because the APIs called by NtPathToDosPath
+    // return different info if this has happened.
+    if (!drvMapping.ChangeDriveLetter()) {
+      fail("Change drive letter");
+      return 1;
+    }
+    expected[0] = drvMapping.GetDriveLetter();
+    if (!DriveToNtPath(drvMapping.GetDriveLetter(), networkPath)) {
+      fail("Querying second network drive");
+      return 1;
+    }
+    networkPath += MOZ_UTF16("\\");
+    if (!TestNtPathToDosPath(networkPath.get(), expected)) {
+      fail("Re-mapped UNC path");
+      result = 1;
+    }
+  }
+
+  return result;
+}
+