gh-149578: Fix tarfile.open failing on PAX archives with only global headers

Lib/tarfile.py

@@ -1565,6 +1565,14 @@ def _proc_pax(self, tarfile):
         # Fetch the next header.
         try:
             next = self._fromtarfile(tarfile, dircheck=False)
+        except EOFHeaderError:
+            if self.type == XGLTYPE:
+                # If this is a global header at the end of the archive
+                # (no regular members follow), let the EOFHeaderError
+                # propagate so the caller handles end-of-archive normally.
+                tarfile.offset = tarfile.fileobj.tell() - BLOCKSIZE
+                raise
+            raise SubsequentHeaderError("end of file header") from None
         except HeaderError as e:
             raise SubsequentHeaderError(str(e)) from None
 

Lib/test/test_tarfile.py

@@ -2297,6 +2297,35 @@ def test_pax_global_header(self):
         finally:
             tar.close()
 
+    def test_pax_global_header_empty_archive(self):
+        # An archive that contains only a global header and no regular
+        # members should be opened successfully (gh-149578).
+        pax_headers = {"foo": "bar"}
+
+        # Create a PAX archive with global headers but no file entries.
+        with tarfile.open(tmpname, "w", format=tarfile.PAX_FORMAT,
+                          pax_headers=pax_headers):
+            pass
+
+        # Reading the archive should work and preserve global headers.
+        with tarfile.open(tmpname) as tar:
+            self.assertEqual(tar.pax_headers, pax_headers)
+            self.assertEqual(tar.getmembers(), [])
+
+        # Appending to the archive should work.
+        with tarfile.open(tmpname, "a") as tar:
+            self.assertEqual(tar.pax_headers, pax_headers)
+            self.assertEqual(tar.getmembers(), [])
+            tar.addfile(tarfile.TarInfo("test"))
+
+        # Verify the appended member is present and global headers
+        # are preserved.
+        with tarfile.open(tmpname) as tar:
+            self.assertEqual(tar.pax_headers, pax_headers)
+            members = tar.getmembers()
+            self.assertEqual(len(members), 1)
+            self.assertEqual(members[0].name, "test")
+
     def test_pax_extended_header(self):
         # The fields from the pax header have priority over the
         # TarInfo.

Misc/NEWS.d/next/Library/2026-05-10-12-00-00.gh-issue-149578.5cgq7iV.rst

@@ -0,0 +1,3 @@
+Fix :func:`tarfile.open` failing with :exc:`~tarfile.ReadError` when
+opening a PAX format tar archive that contains only global headers and
+no regular members.