dart:io | Add Link.targetSync on all platforms.

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 b23049dce5bfc7241347d89db5fae8060409d6d5..3101e6658f38bf9d28cdbb499e3192f73a2b685f 100644
--- a/runtime/bin/file_win.cc
+++ b/runtime/bin/file_win.cc
@@ -279,6 +279,73 @@ off_t File::LengthFromPath(const char* name) {
 }
 
 
+char* File::LinkTarget(const char* pathname) {
+  const wchar_t* name = StringUtils::Utf8ToWide(pathname);
+  HANDLE dir_handle = CreateFileW(
+      name,
+      GENERIC_READ,
+      FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
+      NULL,
+      OPEN_EXISTING,
+      FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT,
+      NULL);
+  free(const_cast<wchar_t*>(name));
+  if (dir_handle == INVALID_HANDLE_VALUE) {
+    return NULL;
+  }
+
+  int reparse_data_buffer_size =
+      sizeof REPARSE_DATA_BUFFER + 2 * (MAX_PATH + 1) * sizeof WCHAR;
+  REPARSE_DATA_BUFFER* reparse_data_buffer =
+      static_cast<REPARSE_DATA_BUFFER*>(calloc(reparse_data_buffer_size, 1));
+  DWORD received_bytes;
+  int result = DeviceIoControl(
+      dir_handle,
+      FSCTL_GET_REPARSE_POINT,
+      NULL,
+      0,
+      reparse_data_buffer,
+      reparse_data_buffer_size,
+      &received_bytes,
+      NULL);
+  if (CloseHandle(dir_handle) == 0) return NULL;

[Søren Gjesse, 2013/03/18 12:28:03]

Here it seems like we are clearing the last error before returning NULL. Don't
we need a GetLastError/SetLastError here?

[Bill Hesse, 2013/03/18 16:13:27]

Yes.  Fixed.

+  if (result == 0) return NULL;
+  if (reparse_data_buffer->ReparseTag != IO_REPARSE_TAG_MOUNT_POINT) {

[Søren Gjesse, 2013/03/18 12:28:03]

Here GetLastError will return NOERROR, so we get an OSError with an error code
of 0.

[Bill Hesse, 2013/03/18 16:13:27]

Now we are returning Not a Reparse Point.  

+    return NULL;
+  }
+  wchar_t* target = reparse_data_buffer->MountPointReparseBuffer.PathBuffer +
+      reparse_data_buffer->MountPointReparseBuffer.SubstituteNameOffset;
+  size_t target_length =
+      reparse_data_buffer->MountPointReparseBuffer.SubstituteNameLength;
+  // Remove "\??\" from beginning of target.
+  if (target_length <= 4 || wcsncmp(L"\\??\\", target, 4) != 0) return NULL;

[Søren Gjesse, 2013/03/18 12:28:03]

Ditto.

[Bill Hesse, 2013/03/18 16:13:27]

Changed.  Now, we just skip removing \??\ if it isn't there.  This is the right
behavior for symbolic links.

+  int utf8_length = WideCharToMultiByte(CP_UTF8,

[Søren Gjesse, 2013/03/18 12:28:03]

Indentation.

+                                0,
+                                target + 4,
+                                target_length - 4,
+                                NULL,
+                                0,
+                                NULL,
+                                NULL);

[Søren Gjesse, 2013/03/18 12:28:03]

Can this call fail?

[Bill Hesse, 2013/03/18 16:13:27]

If it fails, it returns 0, and the next call to it will fail as well.

+  char* utf8_target = reinterpret_cast<char*>(malloc(utf8_length + 1));
+  if (0 == WideCharToMultiByte(CP_UTF8,
+                               0,
+                               target + 4,
+                               target_length - 4,
+                               utf8_target,
+                               utf8_length,
+                               NULL,
+                               NULL)) {
+    free(reparse_data_buffer);
+    free(utf8_target);

[Søren Gjesse, 2013/03/18 12:28:03]

Set an error code?

[Bill Hesse, 2013/03/18 16:13:27]

Done.

+    return NULL;
+  }
+  utf8_target[utf8_length] = '\0';
+  free(reparse_data_buffer);
+  return utf8_target;
+}
+
+
 time_t File::LastModified(const char* name) {
   struct _stat st;
   const wchar_t* system_name = StringUtils::Utf8ToWide(name);