1 files changed, 159 insertions, 5 deletions

diff --git a/platform_utils_win32.py b/platform_utils_win32.py
index 02fb013a..fe76b3d6 100644
--- a/platform_utils_win32.py
+++ b/platform_utils_win32.py
@@ -15,13 +15,20 @@
 
 import errno
 
-from ctypes import WinDLL, get_last_error, FormatError, WinError
-from ctypes.wintypes import BOOL, LPCWSTR, DWORD
+from ctypes import WinDLL, get_last_error, FormatError, WinError, addressof
+from ctypes import c_buffer
+from ctypes.wintypes import BOOL, LPCWSTR, DWORD, HANDLE, POINTER, c_ubyte
+from ctypes.wintypes import WCHAR, USHORT, LPVOID, Structure, Union, ULONG
+from ctypes.wintypes import byref
 
 kernel32 = WinDLL('kernel32', use_last_error=True)
 
+LPDWORD = POINTER(DWORD)
+UCHAR = c_ubyte
+
 # Win32 error codes
 ERROR_SUCCESS = 0
+ERROR_NOT_SUPPORTED = 50
 ERROR_PRIVILEGE_NOT_HELD = 1314
 
 # Win32 API entry points
@@ -35,6 +42,94 @@ CreateSymbolicLinkW.argtypes = (LPCWSTR,  # lpSymlinkFileName In
 SYMBOLIC_LINK_FLAG_FILE = 0x00
 SYMBOLIC_LINK_FLAG_DIRECTORY = 0x01
 
+GetFileAttributesW = kernel32.GetFileAttributesW
+GetFileAttributesW.restype = DWORD
+GetFileAttributesW.argtypes = (LPCWSTR,)  # lpFileName In
+
+INVALID_FILE_ATTRIBUTES = 0xFFFFFFFF
+FILE_ATTRIBUTE_REPARSE_POINT = 0x00400
+
+CreateFileW = kernel32.CreateFileW
+CreateFileW.restype = HANDLE
+CreateFileW.argtypes = (LPCWSTR,  # lpFileName In
+                        DWORD,    # dwDesiredAccess In
+                        DWORD,    # dwShareMode In
+                        LPVOID,   # lpSecurityAttributes In_opt
+                        DWORD,    # dwCreationDisposition In
+                        DWORD,    # dwFlagsAndAttributes In
+                        HANDLE)   # hTemplateFile In_opt
+
+CloseHandle = kernel32.CloseHandle
+CloseHandle.restype = BOOL
+CloseHandle.argtypes = (HANDLE,)  # hObject In
+
+INVALID_HANDLE_VALUE = HANDLE(-1).value
+OPEN_EXISTING = 3
+FILE_FLAG_BACKUP_SEMANTICS = 0x02000000
+FILE_FLAG_OPEN_REPARSE_POINT = 0x00200000
+
+DeviceIoControl = kernel32.DeviceIoControl
+DeviceIoControl.restype = BOOL
+DeviceIoControl.argtypes = (HANDLE,   # hDevice In
+                            DWORD,    # dwIoControlCode In
+                            LPVOID,   # lpInBuffer In_opt
+                            DWORD,    # nInBufferSize In
+                            LPVOID,   # lpOutBuffer Out_opt
+                            DWORD,    # nOutBufferSize In
+                            LPDWORD,  # lpBytesReturned Out_opt
+                            LPVOID)   # lpOverlapped Inout_opt
+
+# Device I/O control flags and options
+FSCTL_GET_REPARSE_POINT = 0x000900A8
+IO_REPARSE_TAG_MOUNT_POINT = 0xA0000003
+IO_REPARSE_TAG_SYMLINK = 0xA000000C
+MAXIMUM_REPARSE_DATA_BUFFER_SIZE = 0x4000
+
+
+class GENERIC_REPARSE_BUFFER(Structure):
+  _fields_ = (('DataBuffer', UCHAR * 1),)
+
+
+class SYMBOLIC_LINK_REPARSE_BUFFER(Structure):
+  _fields_ = (('SubstituteNameOffset', USHORT),
+              ('SubstituteNameLength', USHORT),
+              ('PrintNameOffset', USHORT),
+              ('PrintNameLength', USHORT),
+              ('Flags', ULONG),
+              ('PathBuffer', WCHAR * 1))
+
+  @property
+  def PrintName(self):
+    arrayt = WCHAR * (self.PrintNameLength // 2)
+    offset = type(self).PathBuffer.offset + self.PrintNameOffset
+    return arrayt.from_address(addressof(self) + offset).value
+
+
+class MOUNT_POINT_REPARSE_BUFFER(Structure):
+  _fields_ = (('SubstituteNameOffset', USHORT),
+              ('SubstituteNameLength', USHORT),
+              ('PrintNameOffset', USHORT),
+              ('PrintNameLength', USHORT),
+              ('PathBuffer', WCHAR * 1))
+
+  @property
+  def PrintName(self):
+    arrayt = WCHAR * (self.PrintNameLength // 2)
+    offset = type(self).PathBuffer.offset + self.PrintNameOffset
+    return arrayt.from_address(addressof(self) + offset).value
+
+
+class REPARSE_DATA_BUFFER(Structure):
+  class REPARSE_BUFFER(Union):
+    _fields_ = (('SymbolicLinkReparseBuffer', SYMBOLIC_LINK_REPARSE_BUFFER),
+                ('MountPointReparseBuffer', MOUNT_POINT_REPARSE_BUFFER),
+                ('GenericReparseBuffer', GENERIC_REPARSE_BUFFER))
+  _fields_ = (('ReparseTag', ULONG),
+              ('ReparseDataLength', USHORT),
+              ('Reserved', USHORT),
+              ('ReparseBuffer', REPARSE_BUFFER))
+  _anonymous_ = ('ReparseBuffer',)
+
 
 def create_filesymlink(source, link_name):
   """Creates a Windows file symbolic link source pointing to link_name."""
@@ -58,6 +153,65 @@ def _create_symlink(source, link_name, dwFlags):
     error_desc = FormatError(code).strip()
     if code == ERROR_PRIVILEGE_NOT_HELD:
       raise OSError(errno.EPERM, error_desc, link_name)
-    error_desc = 'Error creating symbolic link %s: %s'.format(
-        link_name, error_desc)
-    raise WinError(code, error_desc)
+    _raise_winerror(
+        code,
+        'Error creating symbolic link \"%s\"'.format(link_name))
+
+
+def islink(path):
+  result = GetFileAttributesW(path)
+  if result == INVALID_FILE_ATTRIBUTES:
+    return False
+  return bool(result & FILE_ATTRIBUTE_REPARSE_POINT)
+
+
+def readlink(path):
+  reparse_point_handle = CreateFileW(path,
+                                     0,
+                                     0,
+                                     None,
+                                     OPEN_EXISTING,
+                                     FILE_FLAG_OPEN_REPARSE_POINT |
+                                     FILE_FLAG_BACKUP_SEMANTICS,
+                                     None)
+  if reparse_point_handle == INVALID_HANDLE_VALUE:
+    _raise_winerror(
+        get_last_error(),
+        'Error opening symblic link \"%s\"'.format(path))
+  target_buffer = c_buffer(MAXIMUM_REPARSE_DATA_BUFFER_SIZE)
+  n_bytes_returned = DWORD()
+  io_result = DeviceIoControl(reparse_point_handle,
+                              FSCTL_GET_REPARSE_POINT,
+                              None,
+                              0,
+                              target_buffer,
+                              len(target_buffer),
+                              byref(n_bytes_returned),
+                              None)
+  CloseHandle(reparse_point_handle)
+  if not io_result:
+    _raise_winerror(
+        get_last_error(),
+        'Error reading symblic link \"%s\"'.format(path))
+  rdb = REPARSE_DATA_BUFFER.from_buffer(target_buffer)
+  if rdb.ReparseTag == IO_REPARSE_TAG_SYMLINK:
+    return _preserve_encoding(path, rdb.SymbolicLinkReparseBuffer.PrintName)
+  elif rdb.ReparseTag == IO_REPARSE_TAG_MOUNT_POINT:
+    return _preserve_encoding(path, rdb.MountPointReparseBuffer.PrintName)
+  # Unsupported reparse point type
+  _raise_winerror(
+      ERROR_NOT_SUPPORTED,
+      'Error reading symblic link \"%s\"'.format(path))
+
+
+def _preserve_encoding(source, target):
+  """Ensures target is the same string type (i.e. unicode or str) as source."""
+  if isinstance(source, unicode):
+    return unicode(target)
+  return str(target)
+
+
+def _raise_winerror(code, error_desc):
+  win_error_desc = FormatError(code).strip()
+  error_desc = "%s: %s".format(error_desc, win_error_desc)
+  raise WinError(code, error_desc)