bpo-43757: make pathlib use os.path.realpath() to resolve all symlinks in a path

Doc/library/os.path.rst

@@ -344,22 +344,34 @@ the :mod:`glob` module.)
  Accepts a :term:`path-like object`.
 
 
-.. function:: realpath(path)
+.. function:: realpath(path, *, strict=False)
 
  Return the canonical path of the specified filename, eliminating any symbolic
  links encountered in the path (if they are supported by the operating
  system).
 
+ If a path doesn't exist or a symlink loop is encountered, and *strict* is
+ ``True``, :exc:`OSError` is raised. If *strict* is ``False``, the path is
+ resolved as far as possible and any remainder is appended without checking
+ whether it exists.
+
  .. note::
- When symbolic link cycles occur, the returned path will be one member of
- the cycle, but no guarantee is made about which member that will be.
+ This function emulates the operating system's procedure for making a path
+ canonical, which differs slightly between Windows and UNIX with respect
+ to how links and subsequent path components interact.
+
+ Operating system APIs make paths canonical as needed, so it's not
+ normally necessary to call this function.
 
  .. versionchanged:: 3.6
  Accepts a :term:`path-like object`.
 
  .. versionchanged:: 3.8
  Symbolic links and junctions are now resolved on Windows.
 
+ .. versionchanged:: 3.10
+ The *strict* parameter was added.
+
 
 .. function:: relpath(path, start=os.curdir)
 

Lib/ntpath.py

@@ -635,7 +635,7 @@ def _getfinalpathname_nonstrict(path):
  tail = join(name, tail) if tail else name
  return tail
 
- def realpath(path):
+ def realpath(path, *, strict=False):
  path = normpath(path)
  if isinstance(path, bytes):
  prefix = b'\\\\?\\'
@@ -660,6 +660,8 @@ def realpath(path):
  path = _getfinalpathname(path)
  initial_winerror = 0
  except OSError as ex:
+ if strict:
+ raise
  initial_winerror = ex.winerror
  path = _getfinalpathname_nonstrict(path)
  # The path returned by _getfinalpathname will always start with \\?\ -

Lib/pathlib.py

@@ -14,12 +14,6 @@
 from urllib.parse import quote_from_bytes as urlquote_from_bytes
 
 
-if os.name == 'nt':
- from nt import _getfinalpathname
-else:
- _getfinalpathname = None
-
-
 __all__ = [
  "PurePath", "PurePosixPath", "PureWindowsPath",
  "Path", "PosixPath", "WindowsPath",
@@ -29,14 +23,17 @@
 # Internals
 #
 
+_WINERROR_NOT_READY = 21 # drive exists but is not accessible
+_WINERROR_INVALID_NAME = 123 # fix for bpo-35306
+_WINERROR_CANT_RESOLVE_FILENAME = 1921 # broken symlink pointing to itself
+
 # EBADF - guard against macOS `stat` throwing EBADF
 _IGNORED_ERROS = (ENOENT, ENOTDIR, EBADF, ELOOP)
 
 _IGNORED_WINERRORS = (
- 21, # ERROR_NOT_READY - drive exists but is not accessible
- 123, # ERROR_INVALID_NAME - fix for bpo-35306
- 1921, # ERROR_CANT_RESOLVE_FILENAME - fix for broken symlink pointing to itself
-)
+ _WINERROR_NOT_READY,
+ _WINERROR_INVALID_NAME,
+ _WINERROR_CANT_RESOLVE_FILENAME)
 
 def _ignore_error(exception):
  return (getattr(exception, 'errno', None) in _IGNORED_ERROS or
@@ -186,30 +183,6 @@ def casefold_parts(self, parts):
  def compile_pattern(self, pattern):
  return re.compile(fnmatch.translate(pattern), re.IGNORECASE).fullmatch
 
- def resolve(self, path, strict=False):
- s = str(path)
- if not s:
- return path._accessor.getcwd()
- previous_s = None
- if _getfinalpathname is not None:
- if strict:
- return self._ext_to_normal(_getfinalpathname(s))
- else:
- tail_parts = [] # End of the path after the first one not found
- while True:
- try:
- s = self._ext_to_normal(_getfinalpathname(s))
- except FileNotFoundError:
- previous_s = s
- s, tail = os.path.split(s)
- tail_parts.append(tail)
- if previous_s == s:
- return path
- else:
- return os.path.join(s, *reversed(tail_parts))
- # Means fallback on absolute
- return None
-
  def _split_extended_path(self, s, ext_prefix=ext_namespace_prefix):
  prefix = ''
  if s.startswith(ext_prefix):
@@ -220,10 +193,6 @@ def _split_extended_path(self, s, ext_prefix=ext_namespace_prefix):
  s = '\\' + s[3:]
  return prefix, s
 
- def _ext_to_normal(self, s):
- # Turn back an extended path into a normal DOS-like path
- return self._split_extended_path(s)[1]
-
  def is_reserved(self, parts):
  # NOTE: the rules for reserved names seem somewhat complicated
  # (e.g. r"..\NUL" is reserved but not r"foo\NUL").
@@ -281,54 +250,6 @@ def casefold_parts(self, parts):
  def compile_pattern(self, pattern):
  return re.compile(fnmatch.translate(pattern)).fullmatch
 
- def resolve(self, path, strict=False):
- sep = self.sep
- accessor = path._accessor
- seen = {}
- def _resolve(path, rest):
- if rest.startswith(sep):
- path = ''
-
- for name in rest.split(sep):
- if not name or name == '.':
- # current dir
- continue
- if name == '..':
- # parent dir
- path, _, _ = path.rpartition(sep)
- continue
- if path.endswith(sep):
- newpath = path + name
- else:
- newpath = path + sep + name
- if newpath in seen:
- # Already seen this path
- path = seen[newpath]
- if path is not None:
- # use cached value
- continue
- # The symlink is not resolved, so we must have a symlink loop.
- raise RuntimeError("Symlink loop from %r" % newpath)
- # Resolve the symbolic link
- try:
- target = accessor.readlink(newpath)
- except OSError as e:
- if e.errno != EINVAL and strict:
- raise
- # Not a symlink, or non-strict mode. We just leave the path
- # untouched.
- path = newpath
- else:
- seen[newpath] = None # not resolved symlink
- path = _resolve(path, target)
- seen[newpath] = path # resolved symlink
-
- return path
- # NOTE: according to POSIX, getcwd() cannot contain path components
- # which are symlinks.
- base = '' if path.is_absolute() else accessor.getcwd()
- return _resolve(base, str(path)) or sep
-
  def is_reserved(self, parts):
  return False
 
@@ -424,6 +345,8 @@ def group(self, path):
 
  expanduser = staticmethod(os.path.expanduser)
 
+ realpath = staticmethod(os.path.realpath)
+
 
 _normal_accessor = _NormalAccessor()
 
@@ -1132,15 +1055,27 @@ def resolve(self, strict=False):
  normalizing it (for example turning slashes into backslashes under
  Windows).
  """
- s = self._flavour.resolve(self, strict=strict)
- if s is None:
- # No symlink resolution => for consistency, raise an error if
- # the path doesn't exist or is forbidden
- self.stat()
- s = str(self.absolute())
- # Now we have no symlinks in the path, it's safe to normalize it.
- normed = self._flavour.pathmod.normpath(s)
- return self._from_parts((normed,))
+
+ def check_eloop(e):
+ winerror = getattr(e, 'winerror', 0)
+ if e.errno == ELOOP or winerror == _WINERROR_CANT_RESOLVE_FILENAME:
+ raise RuntimeError("Symlink loop from %r" % e.filename)
+
+ try:
+ s = self._accessor.realpath(self, strict=strict)
+ except OSError as e:
+ check_eloop(e)
+ raise
+ p = self._from_parts((s,))
+
+ # In non-strict mode, realpath() doesn't raise on symlink loops.
+ # Ensure we get an exception by calling stat()
+ if not strict:
+ try:
+ p.stat()
+ except OSError as e:
+ check_eloop(e)
+ return p
 
  def stat(self, *, follow_symlinks=True):
  """

Lib/posixpath.py

@@ -387,16 +387,16 @@ def abspath(path):
 # Return a canonical path (i.e. the absolute location of a file on the
 # filesystem).
 
-def realpath(filename):
+def realpath(filename, *, strict=False):
  """Return the canonical path of the specified filename, eliminating any
 symbolic links encountered in the path."""
  filename = os.fspath(filename)
- path, ok = _joinrealpath(filename[:0], filename, {})
+ path, ok = _joinrealpath(filename[:0], filename, strict, {})
  return abspath(path)
 
 # Join two paths, normalizing and eliminating any symbolic links
 # encountered in the second path.
-def _joinrealpath(path, rest, seen):
+def _joinrealpath(path, rest, strict, seen):
  if isinstance(path, bytes):
  sep = b'/'
  curdir = b'.'
@@ -425,7 +425,15 @@ def _joinrealpath(path, rest, seen):
  path = pardir
  continue
  newpath = join(path, name)
- if not islink(newpath):
+ try:
+ st = os.lstat(newpath)
+ except OSError:
+ if strict:
+ raise
+ is_link = False
+ else:
+ is_link = stat.S_ISLNK(st.st_mode)
+ if not is_link:
  path = newpath
  continue
  # Resolve the symbolic link
@@ -436,10 +444,14 @@ def _joinrealpath(path, rest, seen):
  # use cached value
  continue
  # The symlink is not resolved, so we must have a symlink loop.
- # Return already resolved part + rest of the path unchanged.
- return join(newpath, rest), False
+ if strict:
+ # Raise OSError(errno.ELOOP)
+ os.stat(newpath)
+ else:
+ # Return already resolved part + rest of the path unchanged.
+ return join(newpath, rest), False
  seen[newpath] = None # not resolved symlink
- path, ok = _joinrealpath(path, os.readlink(newpath), seen)
+ path, ok = _joinrealpath(path, os.readlink(newpath), strict, seen)
  if not ok:
  return join(path, rest), False
  seen[newpath] = path # resolved symlink

Lib/test/test_ntpath.py

@@ -269,6 +269,17 @@ def test_realpath_basic(self):
  self.assertPathEqual(ntpath.realpath(os.fsencode(ABSTFN + "1")),
  os.fsencode(ABSTFN))
 
+ @os_helper.skip_unless_symlink
+ @unittest.skipUnless(HAVE_GETFINALPATHNAME, 'need _getfinalpathname')
+ def test_realpath_strict(self):
+ # Bug #43757: raise FileNotFoundError in strict mode if we encounter
+ # a path that does not exist.
+ ABSTFN = ntpath.abspath(os_helper.TESTFN)
+ os.symlink(ABSTFN + "1", ABSTFN)
+ self.addCleanup(os_helper.unlink, ABSTFN)
+ self.assertRaises(FileNotFoundError, ntpath.realpath, ABSTFN, strict=True)
+ self.assertRaises(FileNotFoundError, ntpath.realpath, ABSTFN + "2", strict=True)
+
  @os_helper.skip_unless_symlink
  @unittest.skipUnless(HAVE_GETFINALPATHNAME, 'need _getfinalpathname')
  def test_realpath_relative(self):
@@ -340,8 +351,9 @@ def test_realpath_broken_symlinks(self):
  @os_helper.skip_unless_symlink
  @unittest.skipUnless(HAVE_GETFINALPATHNAME, 'need _getfinalpathname')
  def test_realpath_symlink_loops(self):
- # Symlink loops are non-deterministic as to which path is returned, but
- # it will always be the fully resolved path of one member of the cycle
+ # Symlink loops in non-strict mode are non-deterministic as to which
+ # path is returned, but it will always be the fully resolved path of
+ # one member of the cycle
  ABSTFN = ntpath.abspath(os_helper.TESTFN)
  self.addCleanup(os_helper.unlink, ABSTFN)
  self.addCleanup(os_helper.unlink, ABSTFN + "1")
@@ -383,6 +395,50 @@ def test_realpath_symlink_loops(self):
  # Test using relative path as well.
  self.assertPathEqual(ntpath.realpath(ntpath.basename(ABSTFN)), ABSTFN)
 
+ @os_helper.skip_unless_symlink
+ @unittest.skipUnless(HAVE_GETFINALPATHNAME, 'need _getfinalpathname')
+ def test_realpath_symlink_loops_strict(self):
+ # Symlink loops raise OSError in strict mode
+ ABSTFN = ntpath.abspath(os_helper.TESTFN)
+ self.addCleanup(os_helper.unlink, ABSTFN)
+ self.addCleanup(os_helper.unlink, ABSTFN + "1")
+ self.addCleanup(os_helper.unlink, ABSTFN + "2")
+ self.addCleanup(os_helper.unlink, ABSTFN + "y")
+ self.addCleanup(os_helper.unlink, ABSTFN + "c")
+ self.addCleanup(os_helper.unlink, ABSTFN + "a")
+
+ os.symlink(ABSTFN, ABSTFN)
+ self.assertRaises(OSError, ntpath.realpath, ABSTFN, strict=True)
+
+ os.symlink(ABSTFN + "1", ABSTFN + "2")
+ os.symlink(ABSTFN + "2", ABSTFN + "1")
+ self.assertRaises(OSError, ntpath.realpath, ABSTFN + "1", strict=True)
+ self.assertRaises(OSError, ntpath.realpath, ABSTFN + "2", strict=True)
+ self.assertRaises(OSError, ntpath.realpath, ABSTFN + "1\\x", strict=True)
+ # Windows eliminates '..' components before resolving links, so the
+ # following call is not expected to raise.
+ self.assertPathEqual(ntpath.realpath(ABSTFN + "1\\..", strict=True),
+ ntpath.dirname(ABSTFN))
+ self.assertRaises(OSError, ntpath.realpath, ABSTFN + "1\\..\\x", strict=True)
+ os.symlink(ABSTFN + "x", ABSTFN + "y")
+ self.assertRaises(OSError, ntpath.realpath, ABSTFN + "1\\..\\"
+ + ntpath.basename(ABSTFN) + "y",
+ strict=True)
+ self.assertRaises(OSError, ntpath.realpath,
+ ABSTFN + "1\\..\\" + ntpath.basename(ABSTFN) + "1",
+ strict=True)
+
+ os.symlink(ntpath.basename(ABSTFN) + "a\\b", ABSTFN + "a")
+ self.assertRaises(OSError, ntpath.realpath, ABSTFN + "a", strict=True)
+
+ os.symlink("..\\" + ntpath.basename(ntpath.dirname(ABSTFN))
+ + "\\" + ntpath.basename(ABSTFN) + "c", ABSTFN + "c")
+ self.assertRaises(OSError, ntpath.realpath, ABSTFN + "c", strict=True)
+
+ # Test using relative path as well.
+ self.assertRaises(OSError, ntpath.realpath, ntpath.basename(ABSTFN),
+ strict=True)
+
  @os_helper.skip_unless_symlink
  @unittest.skipUnless(HAVE_GETFINALPATHNAME, 'need _getfinalpathname')
  def test_realpath_symlink_prefix(self):