def test_extraData(self):
        """
        readfile() should skip over 'extra' data present in the zip metadata.
        """
        fn = self.mktemp()
        with zipfile.ZipFile(fn, 'w') as zf:
            zi = zipfile.ZipInfo("0")
            extra_data = b"hello, extra"
            zi.extra = (
                struct.pack('<hh', 42, len(extra_data))
                + extra_data
            )
            zf.writestr(zi, b"the real data")
        with zipstream.ChunkingZipFile(fn) as czf, czf.readfile("0") as zfe:
            self.assertEqual(zfe.read(), b"the real data")

        readfile() should skip over 'extra' data present in the zip metadata.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_zipstream.py