gh-71189: Support all-but-last mode in posixpath.realpath()

Author: serhiy-storchaka

Lib/posixpath.py

@@ -399,17 +399,21 @@ def abspath(path):
 # Return a canonical path (i.e. the absolute location of a file on the
 # filesystem).
 
+# A singleton with true boolean value
+ALL_BUT_LAST = ['ALL_BUT_LAST']
+
 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, strict, {})
+    path = _joinrealpath(filename[:0], filename, {},
+                         strict, strict is ALL_BUT_LAST, False)
     return abspath(path)
 
 # Join two paths, normalizing and eliminating any symbolic links
 # encountered in the second path.
 # Two leading slashes are replaced by a single slash.
-def _joinrealpath(path, rest, strict, seen):
+def _joinrealpath(path, rest, seen, strict, last, isdir):
     if isinstance(path, bytes):
         sep = b'/'
         curdir = b'.'
@@ -424,7 +428,7 @@ def _joinrealpath(path, rest, strict, seen):
         path = sep
 
     while rest:
-        name, _, rest = rest.partition(sep)
+        name, hassep, rest = rest.partition(sep)
         if not name or name == curdir:
             # current dir
             continue
@@ -445,13 +449,18 @@ def _joinrealpath(path, rest, strict, seen):
         newpath = join(path, name)
         try:
             st = os.lstat(newpath)
-        except OSError:
+        except OSError as e:
+            if (last and not rest.strip(sep) and
+                    isinstance(e, FileNotFoundError)):
+                return newpath
             if strict:
                 raise
-            is_link = False
-        else:
-            is_link = stat.S_ISLNK(st.st_mode)
-        if not is_link:
+            path = newpath
+            continue
+        if not stat.S_ISLNK(st.st_mode):
+            if (strict and not stat.S_ISDIR(st.st_mode)
+                    and (isdir or hassep)):
+                os.lstat(newpath + sep)  # raises NotADirectoryError
             path = newpath
             continue
         # Resolve the symbolic link
@@ -465,16 +474,22 @@ def _joinrealpath(path, rest, strict, seen):
             if strict:
                 # Raise OSError(errno.ELOOP)
                 os.stat(newpath)
-            else:
-                # Return already resolved part + rest of the path unchanged.
-                return join(newpath, rest), False
+            path = newpath
+            continue
         seen[newpath] = None # not resolved symlink
-        path, ok = _joinrealpath(path, os.readlink(newpath), strict, seen)
-        if not ok:
-            return join(path, rest), False
+        try:
+            link = os.readlink(newpath)
+        except OSError:
+            if strict:
+                raise
+            path = newpath
+        else:
+            path = _joinrealpath(path, link, seen, strict,
+                                 last and not rest.strip(sep),
+                                 isdir or hassep)
         seen[newpath] = path # resolved symlink
 
-    return path, True
+    return path
 
 
 supports_unicode_filenames = (sys.platform == 'darwin')

Lib/test/test_posixpath.py

@@ -1,8 +1,9 @@
+import errno
 import os
 import posixpath
 import sys
 import unittest
-from posixpath import realpath, abspath, dirname, basename
+from posixpath import realpath, abspath, dirname, basename, ALL_BUT_LAST
 from test import test_genericpath
 from test.support import import_helper
 from test.support import os_helper
@@ -475,7 +476,7 @@ def test_realpath_symlink_loops(self):
             self.assertEqual(realpath(ABSTFN+"1/../x"), dirname(ABSTFN) + "/x")
             os.symlink(ABSTFN+"x", ABSTFN+"y")
             self.assertEqual(realpath(ABSTFN+"1/../" + basename(ABSTFN) + "y"),
-                             ABSTFN + "y")
+                             ABSTFN + "x")
             self.assertEqual(realpath(ABSTFN+"1/../" + basename(ABSTFN) + "1"),
                              ABSTFN + "1")
 
@@ -637,6 +638,129 @@ def test_realpath_resolve_first(self):
             safe_rmdir(ABSTFN + "/k")
             safe_rmdir(ABSTFN)
 
+    @os_helper.skip_unless_symlink
+    @skip_if_ABSTFN_contains_backslash
+    def test_realpath_mode(self):
+        try:
+            os.mkdir(ABSTFN)
+            os.mkdir(ABSTFN + "/dir")
+            open(ABSTFN + "/file", "wb").close()
+            open(ABSTFN + "/dir/file2", "wb").close()
+            os.symlink("file", ABSTFN + "/link")
+            os.symlink("dir", ABSTFN + "/link2")
+            os.symlink("nonexisting", ABSTFN + "/broken")
+            os.symlink("cycle", ABSTFN + "/cycle")
+            def check(path, mode, expected, errno=None):
+                if isinstance(expected, str):
+                    assert errno is None
+                    self.assertEqual(realpath(path, strict=mode), ABSTFN + expected)
+                else:
+                    with self.assertRaises(expected) as cm:
+                        realpath(path, strict=mode)
+                    if errno is not None:
+                        self.assertEqual(cm.exception.errno, errno)
+
+            with os_helper.change_cwd(ABSTFN):
+                check("file", False, "/file")
+                check("file", ALL_BUT_LAST, "/file")
+                check("file", True, "/file")
+                check("file/", False, "/file")
+                check("file/", ALL_BUT_LAST, NotADirectoryError)
+                check("file/", True, NotADirectoryError)
+                check("file/file2", False, "/file/file2")
+                check("file/file2", ALL_BUT_LAST, NotADirectoryError)
+                check("file/file2", True, NotADirectoryError)
+                check("file/.", False, "/file")
+                check("file/.", ALL_BUT_LAST, NotADirectoryError)
+                check("file/.", True, NotADirectoryError)
+                check("file/../link", False, "/file")
+                check("file/../link", ALL_BUT_LAST, NotADirectoryError)
+                check("file/../link", True, NotADirectoryError)
+
+                check("dir", False, "/dir")
+                check("dir", ALL_BUT_LAST, "/dir")
+                check("dir", True, "/dir")
+                check("dir/", False, "/dir")
+                check("dir/", ALL_BUT_LAST, "/dir")
+                check("dir/", True, "/dir")
+                check("dir/file2", False, "/dir/file2")
+                check("dir/file2", ALL_BUT_LAST, "/dir/file2")
+                check("dir/file2", True, "/dir/file2")
+
+                check("link", False, "/file")
+                check("link", ALL_BUT_LAST, "/file")
+                check("link", True, "/file")
+                check("link/", False, "/file")
+                check("link/", ALL_BUT_LAST, NotADirectoryError)
+                check("link/", True, NotADirectoryError)
+                check("link/file2", False, "/file/file2")
+                check("link/file2", ALL_BUT_LAST, NotADirectoryError)
+                check("link/file2", True, NotADirectoryError)
+                check("link/.", False, "/file")
+                check("link/.", ALL_BUT_LAST, NotADirectoryError)
+                check("link/.", True, NotADirectoryError)
+                check("link/../link", False, "/file")
+                check("link/../link", ALL_BUT_LAST, NotADirectoryError)
+                check("link/../link", True, NotADirectoryError)
+
+                check("link2", False, "/dir")
+                check("link2", ALL_BUT_LAST, "/dir")
+                check("link2", True, "/dir")
+                check("link2/", False, "/dir")
+                check("link2/", ALL_BUT_LAST, "/dir")
+                check("link2/", True, "/dir")
+                check("link2/file2", False, "/dir/file2")
+                check("link2/file2", ALL_BUT_LAST, "/dir/file2")
+                check("link2/file2", True, "/dir/file2")
+
+                check("nonexisting", False, "/nonexisting")
+                check("nonexisting", ALL_BUT_LAST, "/nonexisting")
+                check("nonexisting", True, FileNotFoundError)
+                check("nonexisting/", False, "/nonexisting")
+                check("nonexisting/", ALL_BUT_LAST, "/nonexisting")
+                check("nonexisting/", True, FileNotFoundError)
+                check("nonexisting/file", False, "/nonexisting/file")
+                check("nonexisting/file", ALL_BUT_LAST, FileNotFoundError)
+                check("nonexisting/file", True, FileNotFoundError)
+                check("nonexisting/../link", False, "/file")
+                check("nonexisting/../link", ALL_BUT_LAST, FileNotFoundError)
+                check("nonexisting/../link", True, FileNotFoundError)
+
+                check("broken", False, "/nonexisting")
+                check("broken", ALL_BUT_LAST, "/nonexisting")
+                check("broken", True, FileNotFoundError)
+                check("broken/", False, "/nonexisting")
+                check("broken/", ALL_BUT_LAST, "/nonexisting")
+                check("broken/", True, FileNotFoundError)
+                check("broken/file", False, "/nonexisting/file")
+                check("broken/file", ALL_BUT_LAST, FileNotFoundError)
+                check("broken/file", True, FileNotFoundError)
+                check("broken/../link", False, "/file")
+                check("broken/../link", ALL_BUT_LAST, FileNotFoundError)
+                check("broken/../link", True, FileNotFoundError)
+
+                check("cycle", False, "/cycle")
+                check("cycle", ALL_BUT_LAST, OSError, errno.ELOOP)
+                check("cycle", True, OSError, errno.ELOOP)
+                check("cycle/", False, "/cycle")
+                check("cycle/", ALL_BUT_LAST, OSError, errno.ELOOP)
+                check("cycle/", True, OSError, errno.ELOOP)
+                check("cycle/file", False, "/cycle/file")
+                check("cycle/file", ALL_BUT_LAST, OSError, errno.ELOOP)
+                check("cycle/file", True, OSError, errno.ELOOP)
+                check("cycle/../link", False, "/file")
+                check("cycle/../link", ALL_BUT_LAST, OSError, errno.ELOOP)
+                check("cycle/../link", True, OSError, errno.ELOOP)
+        finally:
+            os_helper.unlink(ABSTFN + "/file")
+            os_helper.unlink(ABSTFN + "/dir/file2")
+            os_helper.unlink(ABSTFN + "/link")
+            os_helper.unlink(ABSTFN + "/link2")
+            os_helper.unlink(ABSTFN + "/broken")
+            os_helper.unlink(ABSTFN + "/cycle")
+            os_helper.rmdir(ABSTFN + "/dir")
+            os_helper.rmdir(ABSTFN)
+
     def test_relpath(self):
         (real_getcwd, os.getcwd) = (os.getcwd, lambda: r"/home/user/bar")
         try: