gh-152190: Fix memory checking failure in test_zipfile64.py (GH-152203)

* gh-152190: Fix memory checking failure in `test_strip_removed_large_file_with_dd_no_sig`

Remove the overly restrictive `allowed_memory` override (200 KiB) in
`test_strip_removed_large_file_with_dd_no_sig` to prevent a memory
checking failure.

* gh-152190: Revise comment about the empirical memory threshold

* gh-152190: Improve memory checking accuracy for `test_zipfile64`

Introduce the `assert_memory_usage` context manager to narrow the scope
of tracemalloc tracking down exclusively to the file-repacking phase.

This prevents previous file-writing side effects from interfering with
the baseline, improves tracing accuracy, and eliminates redundant inner
sub-function wrappers.

* gh-152190: Improve coding style and docstrings

* gh-152190: Remove unneeded comments and checks

Remove redundant "TESTFN2" disk space warnings from TestRepack, as
these tests exclusively use TemporaryFile().

Additionally, remove the repetitive `self.assertFalse(f.closed)` checks
from `TestRepack` methods since it's already verified in
`TestsWithSourceFile`.

* gh-152190: Further optimize tests and tidy code

Rename `TestRepack` to `TestRepacker` to better reflect its coverage of
`zipfile._Repacker`.

Move heavy text chunk generation and common constants from `setUp`
to `setUpClass` to ensure single initialization across tests.

Clean up repetitive local definitions of filenames and lorem text by
promoting them to class properties.

Reduce the test file size from 8 GiB to 4.1 GiB, which is large enough
to trigger ZIP64 extension and sufficient for the testing purpose.

---------

Co-authored-by: Zachary Ware <zach@python.org>

Author: danny0838

Lib/test/test_zipfile64.py

@@ -17,6 +17,7 @@
 import sys
 import unittest.mock as mock
 
+from contextlib import contextmanager
 from tempfile import TemporaryFile
 
 from test.support import os_helper
@@ -91,176 +92,133 @@ def tearDown(self):
         os_helper.unlink(TESTFN2)
 
 
-class TestRepack(unittest.TestCase):
-    def setUp(self):
-        # Create test data.
-        line_gen = ("Test of zipfile line %d." % i for i in range(1000000))
-        self.data = '\n'.join(line_gen).encode('ascii')
-
-        # It will contain enough copies of self.data to reach about 8 GiB.
-        self.datacount = 8*1024**3 // len(self.data)
+class TestRepacker(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.largefilename = 'largefile.txt'
 
-        # memory usage should not exceed 10 MiB
-        self.allowed_memory = 10*1024**2
+        line_gen = ("Test of zipfile line %d." % i for i in range(1000000))
+        cls.chunk = '\n'.join(line_gen).encode('ascii')
+
+        # It will contain enough copies of cls.chunk to reach about 4.1 GiB.
+        cls.chunkcount = int(4.1*1024**3 / len(cls.chunk))
+
+        cls.filename = 'file.txt'
+        cls.lorem = b'Sed ut perspiciatis unde omnis iste natus error sit voluptatem'
+
+        # Memory usage should not exceed 10 MiB during repacking.
+        # This empirical threshold ensures that the internal processing
+        # like signature scanning, compressed block end tracing, and
+        # data copying are properly buffered without loading the entire
+        # large file into memory.
+        cls.allowed_memory = 10*1024**2
+
+    @contextmanager
+    def assert_memory_usage(self, threshold):
+        tracemalloc.start()
+        try:
+            yield
+        finally:
+            current, peak = tracemalloc.get_traced_memory()
+            tracemalloc.stop()
+        self.assertLess(peak, threshold)
 
     def _write_large_file(self, fh):
         next_time = time.monotonic() + _PRINT_WORKING_MSG_INTERVAL
-        for num in range(self.datacount):
-            fh.write(self.data)
+        for num in range(self.chunkcount):
+            fh.write(self.chunk)
             # Print still working message since this test can be really slow
             if next_time <= time.monotonic():
                 next_time = time.monotonic() + _PRINT_WORKING_MSG_INTERVAL
                 print((
                 '  writing %d of %d, be patient...' %
-                (num, self.datacount)), file=sys.__stdout__)
+                (num, self.chunkcount)), file=sys.__stdout__)
                 sys.__stdout__.flush()
 
     def test_strip_removed_large_file(self):
         """Should move the physical data of a file positioned after a large
         removed file without causing a memory issue."""
-        # Try the temp file.  If we do TESTFN2, then it hogs
-        # gigabytes of disk space for the duration of the test.
         with TemporaryFile() as f:
-            tracemalloc.start()
-            self._test_strip_removed_large_file(f)
-            self.assertFalse(f.closed)
-            current, peak = tracemalloc.get_traced_memory()
-            tracemalloc.stop()
-            self.assertLess(peak, self.allowed_memory)
-
-    def _test_strip_removed_large_file(self, f):
-        file = 'file.txt'
-        file1 = 'largefile.txt'
-        data = b'Sed ut perspiciatis unde omnis iste natus error sit voluptatem'
-        with zipfile.ZipFile(f, 'w') as zh:
-            with zh.open(file1, 'w', force_zip64=True) as fh:
-                self._write_large_file(fh)
-            zh.writestr(file, data)
-
-        with zipfile.ZipFile(f, 'a') as zh:
-            zh.remove(file1)
-            zh.repack()
-            self.assertIsNone(zh.testzip())
+            with zipfile.ZipFile(f, 'w') as zh:
+                with zh.open(self.largefilename, 'w', force_zip64=True) as fh:
+                    self._write_large_file(fh)
+                zh.writestr(self.filename, self.lorem)
+
+            with self.assert_memory_usage(self.allowed_memory), \
+                 zipfile.ZipFile(f, 'a') as zh:
+                zh.remove(self.largefilename)
+                zh.repack()
+                self.assertIsNone(zh.testzip())
 
     def test_strip_removed_file_before_large_file(self):
         """Should move the physical data of a large file positioned after a
         removed file without causing a memory issue."""
-        # Try the temp file.  If we do TESTFN2, then it hogs
-        # gigabytes of disk space for the duration of the test.
         with TemporaryFile() as f:
-            tracemalloc.start()
-            self._test_strip_removed_file_before_large_file(f)
-            self.assertFalse(f.closed)
-            current, peak = tracemalloc.get_traced_memory()
-            tracemalloc.stop()
-            self.assertLess(peak, self.allowed_memory)
-
-    def _test_strip_removed_file_before_large_file(self, f):
-        file = 'file.txt'
-        file1 = 'largefile.txt'
-        data = b'Sed ut perspiciatis unde omnis iste natus error sit voluptatem'
-        with zipfile.ZipFile(f, 'w') as zh:
-            zh.writestr(file, data)
-            with zh.open(file1, 'w', force_zip64=True) as fh:
-                self._write_large_file(fh)
-
-        with zipfile.ZipFile(f, 'a') as zh:
-            zh.remove(file)
-            zh.repack()
-            self.assertIsNone(zh.testzip())
+            with zipfile.ZipFile(f, 'w') as zh:
+                zh.writestr(self.filename, self.lorem)
+                with zh.open(self.largefilename, 'w', force_zip64=True) as fh:
+                    self._write_large_file(fh)
+
+            with self.assert_memory_usage(self.allowed_memory), \
+                 zipfile.ZipFile(f, 'a') as zh:
+                zh.remove(self.filename)
+                zh.repack()
+                self.assertIsNone(zh.testzip())
 
     def test_strip_removed_large_file_with_dd(self):
         """Should scan for the data descriptor of a removed large file without
         causing a memory issue."""
-        # Try the temp file.  If we do TESTFN2, then it hogs
-        # gigabytes of disk space for the duration of the test.
         with TemporaryFile() as f:
-            tracemalloc.start()
-            self._test_strip_removed_large_file_with_dd(f)
-            self.assertFalse(f.closed)
-            current, peak = tracemalloc.get_traced_memory()
-            tracemalloc.stop()
-            self.assertLess(peak, self.allowed_memory)
-
-    def _test_strip_removed_large_file_with_dd(self, f):
-        file = 'file.txt'
-        file1 = 'largefile.txt'
-        data = b'Sed ut perspiciatis unde omnis iste natus error sit voluptatem'
-        with zipfile.ZipFile(Unseekable(f), 'w') as zh:
-            with zh.open(file1, 'w', force_zip64=True) as fh:
-                self._write_large_file(fh)
-            zh.writestr(file, data)
-
-        with zipfile.ZipFile(f, 'a') as zh:
-            zh.remove(file1)
-            zh.repack()
-            self.assertIsNone(zh.testzip())
+            with zipfile.ZipFile(Unseekable(f), 'w') as zh:
+                with zh.open(self.largefilename, 'w', force_zip64=True) as fh:
+                    self._write_large_file(fh)
+                zh.writestr(self.filename, self.lorem)
+
+            with self.assert_memory_usage(self.allowed_memory), \
+                 zipfile.ZipFile(f, 'a') as zh:
+                zh.remove(self.largefilename)
+                zh.repack()
+                self.assertIsNone(zh.testzip())
 
     def test_strip_removed_large_file_with_dd_no_sig(self):
-        """Should scan for the data descriptor (without signature) of a removed
-        large file without causing a memory issue."""
+        """Should scan for the unsigned data descriptor of a removed large file
+        without causing a memory issue."""
         # Reduce data scale for this test, as it's especially slow...
-        self.datacount = 30*1024**2 // len(self.data)
-        self.allowed_memory = 200*1024
+        self.chunkcount = int(30*1024**2 / len(self.chunk))
 
-        # Try the temp file.  If we do TESTFN2, then it hogs
-        # gigabytes of disk space for the duration of the test.
         with TemporaryFile() as f:
-            tracemalloc.start()
-            self._test_strip_removed_large_file_with_dd_no_sig(f)
-            self.assertFalse(f.closed)
-            current, peak = tracemalloc.get_traced_memory()
-            tracemalloc.stop()
-            self.assertLess(peak, self.allowed_memory)
-
-    def _test_strip_removed_large_file_with_dd_no_sig(self, f):
-        file = 'file.txt'
-        file1 = 'largefile.txt'
-        data = b'Sed ut perspiciatis unde omnis iste natus error sit voluptatem'
-        with mock.patch('zipfile.struct.pack', side_effect=struct_pack_no_dd_sig):
-            with zipfile.ZipFile(Unseekable(f), 'w') as zh:
-                with zh.open(file1, 'w', force_zip64=True) as fh:
+            with mock.patch('zipfile.struct.pack', side_effect=struct_pack_no_dd_sig), \
+                 zipfile.ZipFile(Unseekable(f), 'w') as zh:
+                with zh.open(self.largefilename, 'w', force_zip64=True) as fh:
                     self._write_large_file(fh)
-                zh.writestr(file, data)
+                zh.writestr(self.filename, self.lorem)
 
-        with zipfile.ZipFile(f, 'a') as zh:
-            zh.remove(file1)
-            # strict_descriptor=False to scan the unsigned data descriptor
-            # (scanning is disabled under the strict_descriptor=True default)
-            zh.repack(strict_descriptor=False)
-            self.assertIsNone(zh.testzip())
+            with self.assert_memory_usage(self.allowed_memory), \
+                 zipfile.ZipFile(f, 'a') as zh:
+                zh.remove(self.largefilename)
+                # strict_descriptor=False to scan the unsigned data descriptor
+                # (scanning is disabled under the strict_descriptor=True default)
+                zh.repack(strict_descriptor=False)
+                self.assertIsNone(zh.testzip())
 
     @requires_zlib()
     def test_strip_removed_large_file_with_dd_no_sig_by_decompression(self):
-        """Should scan for the data descriptor (without signature) of a removed
-        large file without causing a memory issue."""
-        # Try the temp file.  If we do TESTFN2, then it hogs
-        # gigabytes of disk space for the duration of the test.
+        """Should scan for the unsigned data descriptor (via tracing compressed
+        block end) of a removed large file without causing a memory issue."""
         with TemporaryFile() as f:
-            tracemalloc.start()
-            self._test_strip_removed_large_file_with_dd_no_sig_by_decompression(
-                f, zipfile.ZIP_DEFLATED)
-            self.assertFalse(f.closed)
-            current, peak = tracemalloc.get_traced_memory()
-            tracemalloc.stop()
-            self.assertLess(peak, self.allowed_memory)
-
-    def _test_strip_removed_large_file_with_dd_no_sig_by_decompression(self, f, method):
-        file = 'file.txt'
-        file1 = 'largefile.txt'
-        data = b'Sed ut perspiciatis unde omnis iste natus error sit voluptatem'
-        with mock.patch('zipfile.struct.pack', side_effect=struct_pack_no_dd_sig):
-            with zipfile.ZipFile(Unseekable(f), 'w', compression=method) as zh:
-                with zh.open(file1, 'w', force_zip64=True) as fh:
+            with mock.patch('zipfile.struct.pack', side_effect=struct_pack_no_dd_sig), \
+                 zipfile.ZipFile(Unseekable(f), 'w', compression=zipfile.ZIP_DEFLATED) as zh:
+                with zh.open(self.largefilename, 'w', force_zip64=True) as fh:
                     self._write_large_file(fh)
-                zh.writestr(file, data)
-
-        with zipfile.ZipFile(f, 'a') as zh:
-            zh.remove(file1)
-            # strict_descriptor=False to detect the unsigned data descriptor
-            # (scanning is disabled under the strict_descriptor=True default)
-            zh.repack(strict_descriptor=False)
-            self.assertIsNone(zh.testzip())
+                zh.writestr(self.filename, self.lorem)
+
+            with self.assert_memory_usage(self.allowed_memory), \
+                 zipfile.ZipFile(f, 'a') as zh:
+                zh.remove(self.largefilename)
+                # strict_descriptor=False to detect the unsigned data descriptor
+                # (scanning is disabled under the strict_descriptor=True default)
+                zh.repack(strict_descriptor=False)
+                self.assertIsNone(zh.testzip())
 
 
 class OtherTests(unittest.TestCase):