gh-112795: Allow `/` folder in a zipfile (#112932)

Allow extraction (no-op) of a "/" folder in a zipfile, they are commonly added by some archive creation tools.

Co-authored-by: Erlend E. Aasland <erlend@python.org>
Co-authored-by: Gregory P. Smith <greg@krypto.org>

Lib/test/test_zipfile/_path/test_path.py

@@ -577,3 +577,15 @@ class TestPath(unittest.TestCase):
         zipfile.Path(alpharep)
         with self.assertRaises(KeyError):
             alpharep.getinfo('does-not-exist')
+
+    def test_root_folder_in_zipfile(self):
+        """
+        gh-112795: Some tools or self constructed codes will add '/' folder to
+        the zip file, this is a strange behavior, but we should support it.
+        """
+        in_memory_file = io.BytesIO()
+        zf = zipfile.ZipFile(in_memory_file, "w")
+        zf.mkdir('/')
+        zf.writestr('./a.txt', 'aaa')
+        tmpdir = pathlib.Path(self.fixtures.enter_context(temp_dir()))
+        zf.extractall(tmpdir)

Lib/zipfile/__init__.py

@@ -1772,7 +1772,7 @@ class ZipFile:
             # filter illegal characters on Windows
             arcname = self._sanitize_windows_name(arcname, os.path.sep)
 
-        if not arcname:
+        if not arcname and not member.is_dir():
             raise ValueError("Empty filename.")
 
         targetpath = os.path.join(targetpath, arcname)

Misc/NEWS.d/next/Library/2024-01-07-00-56-41.gh-issue-112932.OfhUu7.rst

@@ -0,0 +1,3 @@
+Restore the ability for :mod:`zipfile` to ``extractall`` from zip files with
+a "/" directory entry in them as is commonly added to zips by some wiki or
+bug tracker data exporters.