Cute IG Notes: Fix tarfile.open failing on PAX archives with only global headers (Facebook Post Backgrounds Free)

When a PAX format tar archive contains only global headers and no regular members, tarfile.open() raised ReadError because the EOFHeaderError from reaching end-of-archive after the global header was being caught and converted to SubsequentHeaderError in TarInfo._proc_pax(). This prevented the caller from handling end-of-archive normally. Fix by letting EOFHeaderError propagate when processing a global header (XGLTYPE), while still treating it as a SubsequentHeaderError for extended headers (XHDTYPE) where a following file entry is mandatory. Co-authored-by: Ethan Furman <ethan@stoneleaf.us>

Author: Doe Food Services

Lib/tarfile.py

@@ -1601,6 +1601,14 @@ 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

@@ -2499,6 +2499,35 @@ 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.