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gh-155907: Complete PyMarshal C API tests #157452

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a4945b5
gh-155907: Complete PyMarshal C API tests
vstinner Sep 13, 2026
aec3759
Fix PyMarshal_WriteLongToFile() for 32-bit long (Windows)
vstinner Sep 14, 2026
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251 changes: 180 additions & 71 deletions Lib/test/test_capi/test_marshal.py
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Original file line number Diff line number Diff line change
@@ -1,19 +1,54 @@
# Test PyMarshal C API

import marshal
import os.path
import struct
import unittest

from test import support
from test.support import import_helper
from test.support import os_helper
from test.test_marshal import HelperMixin, omit_last_byte


# Skip this test if _testcapi is are not available.
_testcapi = import_helper.import_module('_testcapi')


def noop_func():
pass

NULL = None
SIMPLE_OBJECT = 123
# Only test a few objects: see test_marshal for more exhaustive tests
TEST_OBJECTS = (
'\u20ac',
b'abc',
True,
123,
45.6,
7+8j,
'long line '*1000,
# Check that serializing code object is allowed (allow_code = 1)
noop_func.__code__,
)
UNMARSHALLABLE = object()

# Invalid marshal data
JUNK_BYTES = b'\xff' * 32


def read_file(filename):
with open(filename, 'rb') as fp:
return fp.read()


def write_file(filename, data):
with open(filename, 'wb') as fp:
fp.write(data)


@support.cpython_only
class CAPI_TestCase(unittest.TestCase, HelperMixin):
class CAPI_TestCase(unittest.TestCase):

def test_read_from_file_error(self):
# A read error is reported as OSError, not EOFError.
Expand All @@ -38,89 +73,163 @@ def test_write_to_file_error(self):
_testcapi.pymarshal_write_object_to_file(obj, '/dev/full',
marshal.version)

def test_write_unmarshallable_to_file(self):
self.addCleanup(os_helper.unlink, os_helper.TESTFN)
with self.assertRaisesRegex(ValueError, 'unmarshallable object'):
_testcapi.pymarshal_write_object_to_file(object(), os_helper.TESTFN,
marshal.version)
def check_object(self, obj2, obj):
self.assertEqual(obj2, obj)
self.assertEqual(type(obj2), type(obj))

def test_write_long_to_file(self):
for v in range(marshal.version + 1):
_testcapi.pymarshal_write_long_to_file(0x12345678, os_helper.TESTFN, v)
with open(os_helper.TESTFN, 'rb') as f:
data = f.read()
os_helper.unlink(os_helper.TESTFN)
self.assertEqual(data, b'\x78\x56\x34\x12')
# Test PyMarshal_WriteLongToFile()
write_long_to_file = _testcapi.pymarshal_write_long_to_file
filename = os_helper.TESTFN
self.addCleanup(os_helper.unlink, filename)

def mask32(value):
res = value & (2 ** 32 - 1)
if res >= 2147483648:
return res - 4294967296
else:
return res

limit = 2 ** 31
values = [
_testcapi.LONG_MIN, _testcapi.LONG_MAX,
-limit, -limit + 2, limit - 2, limit - 1,
0, 123, -123,
]
# Test values larger than 32-bit on platforms with 64-bit C long
if _testcapi.LONG_MAX > (2**31-1):
values.extend((-limit - 2, limit, limit + 2))

for version in range(marshal.version + 1):
for value in values:
with self.subTest(value=value, version=version):
write_long_to_file(value, filename, version)
data = read_file(filename)
self.assertEqual(len(data), 4)
value2 = struct.unpack('<i', data)[0]
self.assertEqual(value2, mask32(value))

def test_write_object_to_file(self):
obj = ('\u20ac', b'abc', 123, 45.6, 7+8j, 'long line '*1000)
for v in range(marshal.version + 1):
_testcapi.pymarshal_write_object_to_file(obj, os_helper.TESTFN, v)
with open(os_helper.TESTFN, 'rb') as f:
data = f.read()
os_helper.unlink(os_helper.TESTFN)
self.assertEqual(marshal.loads(data), obj)
# Test PyMarshal_WriteObjectToFile()
write_object_to_file = _testcapi.pymarshal_write_object_to_file
filename = os_helper.TESTFN
self.addCleanup(os_helper.unlink, filename)

for version in range(marshal.version + 1):
for obj in TEST_OBJECTS:
with self.subTest(obj=obj, version=version):
write_object_to_file(obj, filename, version)
data = read_file(filename)
self.assertEqual(marshal.loads(data), obj)

with self.assertRaises(SystemError):
write_object_to_file(NULL, filename, version)

with self.assertRaisesRegex(ValueError, 'unmarshallable object'):
write_object_to_file(UNMARSHALLABLE, filename, version)

def test_read_short_from_file(self):
with open(os_helper.TESTFN, 'wb') as f:
f.write(b'\x34\x12xxxx')
r, p = _testcapi.pymarshal_read_short_from_file(os_helper.TESTFN)
os_helper.unlink(os_helper.TESTFN)
self.assertEqual(r, 0x1234)
self.assertEqual(p, 2)

with open(os_helper.TESTFN, 'wb') as f:
f.write(b'\x12')
# Test PyMarshal_ReadShortFromFile()
read_short_from_file = _testcapi.pymarshal_read_short_from_file
filename = os_helper.TESTFN
self.addCleanup(os_helper.unlink, filename)

for value in (-2**15, 2**15-1, 0, 123, -123):
with self.subTest(value=value):
data = struct.pack('<h', value) + b'xxxx'
write_file(filename, data)
value2 = read_short_from_file(filename)
self.assertEqual(value2, value)

write_file(filename, b'\x12') # less than 2 bytes
with self.assertRaises(EOFError):
_testcapi.pymarshal_read_short_from_file(os_helper.TESTFN)
os_helper.unlink(os_helper.TESTFN)
read_short_from_file(filename)

def test_read_long_from_file(self):
with open(os_helper.TESTFN, 'wb') as f:
f.write(b'\x78\x56\x34\x12xxxx')
r, p = _testcapi.pymarshal_read_long_from_file(os_helper.TESTFN)
os_helper.unlink(os_helper.TESTFN)
self.assertEqual(r, 0x12345678)
self.assertEqual(p, 4)

with open(os_helper.TESTFN, 'wb') as f:
f.write(b'\x56\x34\x12')
# Test PyMarshal_ReadLongFromFile()
read_long_from_file = _testcapi.pymarshal_read_long_from_file
filename = os_helper.TESTFN
self.addCleanup(os_helper.unlink, filename)

for value in (_testcapi.INT_MIN, _testcapi.INT_MAX, 0, 123, -123):
with self.subTest(value=value):
data = struct.pack('<i', value)
write_file(filename, data)
value2 = read_long_from_file(filename)
self.assertEqual(value2, value)

write_file(filename, b'\x56\x34\x12') # less than 4 bytes
with self.assertRaises(EOFError):
read_long_from_file(filename)

def check_read_object(self, read_object_func, check_pos=True):
filename = os_helper.TESTFN
self.addCleanup(os_helper.unlink, filename)

version = marshal.version
for obj in TEST_OBJECTS:
with self.subTest(obj=obj):
data = marshal.dumps(obj, version)
data += b'abc' # following data is ignored
write_file(filename, data)
obj2, pos = read_object_func(filename)
self.check_object(obj2, obj)
if check_pos:
self.assertEqual(pos, len(data))

data = marshal.dumps(SIMPLE_OBJECT, version)
data = data[:-1] # truncate last byte
write_file(filename, data)
with self.assertRaises(EOFError):
_testcapi.pymarshal_read_long_from_file(os_helper.TESTFN)
os_helper.unlink(os_helper.TESTFN)
read_object_func(filename)

write_file(filename, JUNK_BYTES)
with self.assertRaisesRegex(ValueError, 'bad marshal data'):
read_object_func(filename)

def test_read_last_object_from_file(self):
obj = ('\u20ac', b'abc', 123, 45.6, 7+8j)
for v in range(marshal.version + 1):
data = marshal.dumps(obj, v)
with open(os_helper.TESTFN, 'wb') as f:
f.write(data + b'xxxx')
r, p = _testcapi.pymarshal_read_last_object_from_file(os_helper.TESTFN)
os_helper.unlink(os_helper.TESTFN)
self.assertEqual(r, obj)

with open(os_helper.TESTFN, 'wb') as f:
f.write(omit_last_byte(data))
with self.assertRaises(EOFError):
_testcapi.pymarshal_read_last_object_from_file(os_helper.TESTFN)
os_helper.unlink(os_helper.TESTFN)
# Test PyMarshal_ReadLastObjectFromFile()
read_last_object_from_file = _testcapi.pymarshal_read_last_object_from_file
self.check_read_object(read_last_object_from_file)

def test_read_object_from_file(self):
obj = ('\u20ac', b'abc', 123, 45.6, 7+8j)
for v in range(marshal.version + 1):
data = marshal.dumps(obj, v)
with open(os_helper.TESTFN, 'wb') as f:
f.write(data + b'xxxx')
r, p = _testcapi.pymarshal_read_object_from_file(os_helper.TESTFN)
os_helper.unlink(os_helper.TESTFN)
self.assertEqual(r, obj)
self.assertEqual(p, len(data))

with open(os_helper.TESTFN, 'wb') as f:
f.write(omit_last_byte(data))
with self.assertRaises(EOFError):
_testcapi.pymarshal_read_object_from_file(os_helper.TESTFN)
os_helper.unlink(os_helper.TESTFN)
# Test PyMarshal_ReadObjectFromFile()
read_object_from_file = _testcapi.pymarshal_read_object_from_file
self.check_read_object(read_object_from_file, check_pos=False)

def test_pymarshal_readobjectfromstring(self):
# Test PyMarshal_ReadObjectFromString()
readobjectfromstring = _testcapi.pymarshal_readobjectfromstring
for obj in TEST_OBJECTS:
for version in range(marshal.version + 1):
with self.subTest(obj=obj, version=version):
data = marshal.dumps(obj, version)
obj2 = readobjectfromstring(data)
self.check_object(obj2, obj)

data = marshal.dumps(SIMPLE_OBJECT, marshal.version)
data = data[:-1] # truncate last byte
with self.assertRaises(EOFError):
readobjectfromstring(data)

with self.assertRaisesRegex(ValueError, 'bad marshal data'):
readobjectfromstring(JUNK_BYTES)

def test_pymarshal_writeobjecttostring(self):
# Test PyMarshal_WriteObjectToString()
writeobjecttostring = _testcapi.pymarshal_writeobjecttostring
for version in range(marshal.version + 1):
for obj in TEST_OBJECTS:
with self.subTest(obj=obj, version=version):
data = writeobjecttostring(obj, version)
obj2 = marshal.loads(data)
self.check_object(obj2, obj)

with self.assertRaisesRegex(ValueError, 'unmarshallable object'):
writeobjecttostring(UNMARSHALLABLE, version)

with self.assertRaises(SystemError):
writeobjecttostring(NULL, version)


if __name__ == "__main__":
Expand Down
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