[Python-Dev] [Python-checkins] cpython (2.7): Issue #10276: test_zlib checks that inputs of 2 GB are handled correctly by (original) (raw)

Victor Stinner victor.stinner at haypocalc.com
Thu May 5 11:33:27 CEST 2011

Le mercredi 04 mai 2011 à 15:40 -0700, Ethan Furman a écrit :

Victor Stinner wrote: > Le mardi 03 mai 2011 à 16:22 +0200, Nadeem Vawda a écrit : >> On Tue, May 3, 2011 at 3:19 PM, victor.stinner >> <python-checkins at python.org> wrote: >>> +# Issue #10276 - check that inputs of 2 GB are handled correctly. >>> +# Be aware of issues #1202, #8650, #8651 and #10276 >>> +class ChecksumBigBufferTestCase(unittest.TestCase): >>> + intmax = 0x7FFFFFFF >>> + >>> + @unittest.skipUnless(mmap, "mmap() is not available.") >>> + def testbigbuffer(self): >>> + if sys.platform[:3] == 'win' or sys.platform == 'darwin': >>> + requires('largefile', >>> + 'test requires %s bytes and a long time to run' % >>> + str(self.intmax)) >>> + try: >>> + with open(TESTFN, "wb+") as f: >>> + f.seek(self.intmax-4) >>> + f.write("asdf") >>> + f.flush() >>> + try: >>> + m = mmap.mmap(f.fileno(), 0, access=mmap.ACCESSREAD) >>> + self.assertEqual(zlib.crc32(m), 0x709418e7) >>> + self.assertEqual(zlib.adler32(m), -2072837729) >>> + finally: >>> + m.close() >>> + except (IOError, OverflowError): >>> + raise unittest.SkipTest("filesystem doesn't have largefile support") >>> + finally: >>> + unlink(TESTFN) >>> + >>> + >> 0x7FFFFFFF is (2G-1) bytes. For a 2GB buffer, intmax should be >> 0x80000000. However, if you make this change, crc32() and adler32() >> raise OverflowErrors (see changeset a0681e7a6ded). > > I don't want to check OverflowError: the test is supposed to compute the > checksum of a buffer of 0x7FFFFFFF bytes

The comment says 'check that inputs of 2 GB are handled correctly' but the file created is 1 byte short of 2Gb. Is the test wrong, or just wrongly commented? Or am I not understanding?

If you write a byte after 2 GB of zeros, the file size is 2 GB+the few bytes. This trick is to create quickly a large file: some OSes support sparse files, zeros are not written on disk. But on Mac OS X and Windows, you really write 2 GB+some bytes.

Victor

More information about the Python-Dev mailing list