dart:io | Change File.fullPath to FileSystemEntity.resolveSymbolicLinks.

runtime/bin/file_win.cc

Index: runtime/bin/file_win.cc
diff --git a/runtime/bin/file_win.cc b/runtime/bin/file_win.cc
index 08417ea9ac03220bc7d83a648c42ef3a9b7f8260..bdc4356355a25fcf5dea4a651539b4c24246e646 100644
--- a/runtime/bin/file_win.cc
+++ b/runtime/bin/file_win.cc
@@ -471,20 +471,50 @@ bool File::IsAbsolutePath(const char* pathname) {
 char* File::GetCanonicalPath(const char* pathname) {
   struct _stat st;
   const wchar_t* system_name = StringUtils::Utf8ToWide(pathname);
-  int stat_status = _wstat(system_name, &st);
-  if (stat_status != 0) {
-    SetLastError(ERROR_FILE_NOT_FOUND);
+  HANDLE file_handle = CreateFileW(
+        system_name,
+        0,
+        FILE_SHARE_READ,
+        NULL,
+        OPEN_EXISTING,
+        FILE_FLAG_BACKUP_SEMANTICS,
+        NULL);
+  if (file_handle == INVALID_HANDLE_VALUE) {
     free(const_cast<wchar_t*>(system_name));
     return NULL;
   }
-  int required_size = GetFullPathNameW(system_name, 0, NULL, NULL);
+  wchar_t dummy_buffer[1];
+  int required_size = GetFinalPathNameByHandle(file_handle,
+                                               dummy_buffer,
+                                               0,
+                                               VOLUME_NAME_DOS);
+  if (required_size == 0) {
+    free(const_cast<wchar_t*>(system_name));
+    DWORD error = GetLastError();
+    CloseHandle(file_handle);
+    SetLastError(error);
+    return NULL;
+  }
   wchar_t* path =
       static_cast<wchar_t*>(malloc(required_size * sizeof(wchar_t)));
-  int written = GetFullPathNameW(system_name, required_size, path, NULL);
+  int result_size = GetFinalPathNameByHandle(file_handle,

[Anders Johnsen, 2013/09/09 12:24:48]

From the spec:

"The string that is returned by this function uses the \\?\ syntax."

I read that as we will always get the four character header.

[Bill Hesse, 2013/09/13 06:34:13]

Our current thinking is that we should not add or remove \\?\ from
the user's input, except in the case that \\?\ becomes necessary because the
path is too long.

So this code returns a path beginning with \\?\ only if the input begins with it
or if the path is longer than MAX_PATH.

+                                             path,
+                                             required_size,
+                                             VOLUME_NAME_DOS);
+  ASSERT(result_size == required_size - 1);
+  // Remove leading \\?\ if possible, unless input used it.

[Anders Johnsen, 2013/09/09 12:24:48]

I was under the impression that we:

- Add '\\?\' our-self if needed.
- Remove it if we get it back from the system

Meaning, the user should never see it. Is this assumption wrong?

[Søren Gjesse, 2013/09/11 07:21:01]

In general we should not show '\\?\' to the user however in some cases it's
needed. In addition to the MAX_PATH case there are also the special names 'con',
'prn', etc. See
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
which should have the exhaustive list. I think we should remove \\?\ whenever
it's not needed.

In Uri.toFilePath we need the same checks.

+  char* result;
+  if (result_size < MAX_PATH - 1 + 4 &&

[Anders Johnsen, 2013/09/09 12:24:48]

Why test for < MAX_PATH?

+      result_size > 4 &&
+      wcsncmp(path, L"\\\\?\\", 4) == 0 &&
+      wcsncmp(system_name, L"\\\\?\\", 4) != 0) {
+    result = StringUtils::WideToUtf8(path + 4);
+  } else {
+    result = StringUtils::WideToUtf8(path);
+  }
   free(const_cast<wchar_t*>(system_name));
-  ASSERT(written <= (required_size - 1));
-  char* result = StringUtils::WideToUtf8(path);
   free(path);
+  CloseHandle(file_handle);
   return result;
 }