https://github.com/python/cpython/commit/3740f74b39a3a61fa2b8b63f304d9fb8cfdfa168 commit: 3740f74b39a3a61fa2b8b63f304d9fb8cfdfa168 branch: 3.15 author: Victor Stinner <[email protected]> committer: hugovk <[email protected]> date: 2026-09-30T11:32:16+03:00 summary:
[3.15] gh-156939: Fix two bugs in PyBytesWriter (#158404) (#158409) * gh-156939: Fix two bugs in PyBytesWriter (#158404) Fix PyBytesWriter_Format() error handling: restore the writer to its previous state on error. Add an unit test injecting MemoryError. Fix PyBytesWriter_FinishWithSize() to return an empty bytearray when use_bytearray is set and size is 0, instead of always returning an empty bytes object. Fix test_capi.test_bytes: always check writer finish result type, to make sure that _PyBytesWriter_CreateByteArray() always create bytearray objects. Co-authored-by: Claude Opus 4.6 <[email protected]> (cherry picked from commit 24ea85a4c2998b36cc4c83ff0505678d178b49d1) files: A Misc/NEWS.d/next/C_API/2026-09-29-15-40-41.gh-issue-156939.Y5X3Wm.rst A Misc/NEWS.d/next/C_API/2026-09-29-21-37-08.gh-issue-156939.P_UD2P.rst M Lib/test/test_capi/test_bytes.py M Modules/_testcapi/bytes.c M Objects/bytesobject.c diff --git a/Lib/test/test_capi/test_bytes.py b/Lib/test/test_capi/test_bytes.py index 0f2360c90c82c83..eee201b3a75bbd2 100644 --- a/Lib/test/test_capi/test_bytes.py +++ b/Lib/test/test_capi/test_bytes.py @@ -1,6 +1,7 @@ import sys import unittest from test.support import import_helper +from test import support _testlimitedcapi = import_helper.import_module('_testlimitedcapi') _testcapi = import_helper.import_module('_testcapi') @@ -316,41 +317,47 @@ def test_join(self): class BytesWriterTest(unittest.TestCase): - result_type = bytes + RESULT_TYPE = bytes def create_writer(self, alloc=0, string=b''): return _testcapi.PyBytesWriter(alloc, string, 0) + def bytes_equal(self, result, expected): + # Similar to assertEqual(), but check also that the result type + # is RESULT_TYPE. + self.assertEqual(result, expected) + self.assertEqual(type(result), self.RESULT_TYPE) + def test_create(self): # Test PyBytesWriter_Create() writer = self.create_writer() self.assertEqual(writer.get_size(), 0) - self.assertEqual(writer.finish(), self.result_type(b'')) + self.bytes_equal(writer.finish(), b'') writer = self.create_writer(3, b'abc') self.assertEqual(writer.get_size(), 3) - self.assertEqual(writer.finish(), self.result_type(b'abc')) + self.bytes_equal(writer.finish(), b'abc') def test_finish_with_size(self): # Test PyBytesWriter_FinishWithSize() writer = self.create_writer(10, b'abc') self.assertEqual(writer.get_size(), 10) - self.assertEqual(writer.finish_with_size(3), self.result_type(b'abc')) + self.bytes_equal(writer.finish_with_size(3), b'abc') writer = self.create_writer(3, b'abc') with self.assertRaises(SystemError): writer.finish_with_size(-3) def test_write_bytes(self): - # Test PyBytesWriter_WriteBytes() - writer = self.create_writer() - writer.write_bytes(b'Hello World!', -1) - self.assertEqual(writer.finish(), self.result_type(b'Hello World!')) + # Test PyBytesWriter_WriteBytes() + writer = self.create_writer() + writer.write_bytes(b'Hello World!', -1) + self.bytes_equal(writer.finish(), b'Hello World!') - writer = self.create_writer() - writer.write_bytes(b'Hello ', -1) - writer.write_bytes(b'World! <truncated>', 6) - self.assertEqual(writer.finish(), self.result_type(b'Hello World!')) + writer = self.create_writer() + writer.write_bytes(b'Hello ', -1) + writer.write_bytes(b'World! <truncated>', 6) + self.bytes_equal(writer.finish(), b'Hello World!') def test_resize(self): # Test PyBytesWriter_Resize() @@ -358,41 +365,60 @@ def test_resize(self): writer.resize(len(b'number=123456'), b'number=123456') writer.resize(len(b'number=123456'), b'') self.assertEqual(writer.get_size(), len(b'number=123456')) - self.assertEqual(writer.finish(), self.result_type(b'number=123456')) + self.bytes_equal(writer.finish(), b'number=123456') writer = self.create_writer() writer.resize(0, b'') writer.resize(len(b'number=123456'), b'number=123456') - self.assertEqual(writer.finish(), self.result_type(b'number=123456')) + self.bytes_equal(writer.finish(), b'number=123456') writer = self.create_writer() writer.resize(len(b'number='), b'number=') writer.resize(len(b'number=123456'), b'123456') - self.assertEqual(writer.finish(), self.result_type(b'number=123456')) + self.bytes_equal(writer.finish(), b'number=123456') writer = self.create_writer() writer.resize(len(b'number='), b'number=') writer.resize(len(b'number='), b'') writer.resize(len(b'number=123456'), b'123456') - self.assertEqual(writer.finish(), self.result_type(b'number=123456')) + self.bytes_equal(writer.finish(), b'number=123456') writer = self.create_writer() writer.resize(len(b'number'), b'number') writer.resize(len(b'number='), b'=') writer.resize(len(b'number=123'), b'123') writer.resize(len(b'number=123456'), b'456') - self.assertEqual(writer.finish(), self.result_type(b'number=123456')) + self.bytes_equal(writer.finish(), b'number=123456') def test_format_i(self): # Test PyBytesWriter_Format() writer = self.create_writer() writer.format_i(b'x=%i', 123456) - self.assertEqual(writer.finish(), self.result_type(b'x=123456')) + self.bytes_equal(writer.finish(), b'x=123456') writer = self.create_writer() writer.format_i(b'x=%i, ', 123) writer.format_i(b'y=%i', 456) - self.assertEqual(writer.finish(), self.result_type(b'x=123, y=456')) + self.bytes_equal(writer.finish(), b'x=123, y=456') + + def test_format_s(self): + # Test PyBytesWriter_Format() + writer = self.create_writer() + writer.format_s(b's=%s', b'Hello World') + self.bytes_equal(writer.finish(), b's=Hello World') + + @support.nomemtest + def test_format_s_memory_error(self): + writer = self.create_writer() + s = b'x' * 500 + with self.assertRaises(MemoryError): + try: + _testcapi.set_nomemory(0, 0) + writer.format_s(b's=%s', s) + finally: + _testcapi.remove_mem_hooks() + writer.write_bytes(b'after', -1) + self.bytes_equal(writer.finish(), b'after') def test_example_abc(self): self.assertEqual(_testcapi.byteswriter_abc(), b'abc') @@ -405,7 +431,7 @@ def test_example_highlevel(self): class ByteArrayWriterTest(BytesWriterTest): - result_type = bytearray + RESULT_TYPE = bytearray def create_writer(self, alloc=0, string=b''): return _testcapi.PyBytesWriter(alloc, string, 1) diff --git a/Misc/NEWS.d/next/C_API/2026-09-29-15-40-41.gh-issue-156939.Y5X3Wm.rst b/Misc/NEWS.d/next/C_API/2026-09-29-15-40-41.gh-issue-156939.Y5X3Wm.rst new file mode 100644 index 000000000000000..367360ca9a7d81e --- /dev/null +++ b/Misc/NEWS.d/next/C_API/2026-09-29-15-40-41.gh-issue-156939.Y5X3Wm.rst @@ -0,0 +1,2 @@ +Fix :c:func:`PyBytesWriter_Format` error handling: restore the writer to its +previous state on error. Patch by Victor Stinner. diff --git a/Misc/NEWS.d/next/C_API/2026-09-29-21-37-08.gh-issue-156939.P_UD2P.rst b/Misc/NEWS.d/next/C_API/2026-09-29-21-37-08.gh-issue-156939.P_UD2P.rst new file mode 100644 index 000000000000000..b2bbaa210122fc8 --- /dev/null +++ b/Misc/NEWS.d/next/C_API/2026-09-29-21-37-08.gh-issue-156939.P_UD2P.rst @@ -0,0 +1,3 @@ +Fix :c:func:`PyBytesWriter_FinishWithSize` to return an empty bytearray when +:c:func:`!_PyBytesWriter_CreateByteArray` is used, instead of returning an +empty bytes string. Patch by Victor Stinner. diff --git a/Modules/_testcapi/bytes.c b/Modules/_testcapi/bytes.c index f12fc7f5f3a2a86..23b065aba869cd4 100644 --- a/Modules/_testcapi/bytes.c +++ b/Modules/_testcapi/bytes.c @@ -183,6 +183,27 @@ writer_format_i(PyObject *self_raw, PyObject *args) } +static PyObject* +writer_format_s(PyObject *self_raw, PyObject *args) +{ + WriterObject *self = (WriterObject *)self_raw; + if (writer_check(self) < 0) { + return NULL; + } + + char *format, *str; + if (!PyArg_ParseTuple(args, "yy", &format, &str)) { + return NULL; + } + + if (PyBytesWriter_Format(self->writer, format, str) < 0) { + return NULL; + } + Py_RETURN_NONE; +} + + +// PyBytesWriter_Resize static PyObject* writer_resize(PyObject *self_raw, PyObject *args) { @@ -262,6 +283,7 @@ writer_finish_with_size(PyObject *self_raw, PyObject *args) static PyMethodDef writer_methods[] = { {"write_bytes", _PyCFunction_CAST(writer_write_bytes), METH_VARARGS}, {"format_i", _PyCFunction_CAST(writer_format_i), METH_VARARGS}, + {"format_s", _PyCFunction_CAST(writer_format_s), METH_VARARGS}, {"resize", _PyCFunction_CAST(writer_resize), METH_VARARGS}, {"get_size", _PyCFunction_CAST(writer_get_size), METH_NOARGS}, {"finish", _PyCFunction_CAST(writer_finish), METH_NOARGS}, diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c index 1f0b03beed43b10..a537f084129eea5 100644 --- a/Objects/bytesobject.c +++ b/Objects/bytesobject.c @@ -218,7 +218,7 @@ bytes_fromformat(PyBytesWriter *writer, Py_ssize_t writer_pos, size_t len = (len_expr); \ s = PyBytesWriter_GrowAndUpdatePointer(writer, len, s); \ if (s == NULL) { \ - goto error; \ + return NULL; \ } \ memcpy(s, (str), len); \ s += len; \ @@ -272,7 +272,7 @@ bytes_fromformat(PyBytesWriter *writer, Py_ssize_t writer_pos, PyErr_SetString(PyExc_OverflowError, "PyBytes_FromFormatV(): %c format " "expects an integer in range [0; 255]"); - goto error; + return NULL; } *s++ = (unsigned char)c; break; @@ -365,9 +365,6 @@ bytes_fromformat(PyBytesWriter *writer, Py_ssize_t writer_pos, #undef WRITE_BYTES_LEN return s; - - error: - return NULL; } @@ -3746,7 +3743,7 @@ PyObject* PyBytesWriter_FinishWithSize(PyBytesWriter *writer, Py_ssize_t size) { PyObject *result; - if (size == 0) { + if (size == 0 && !writer->use_bytearray) { result = bytes_get_empty(); } else if (writer->obj != NULL) { @@ -3910,6 +3907,7 @@ int PyBytesWriter_Format(PyBytesWriter *writer, const char *format, ...) { Py_ssize_t pos = writer->size; + Py_ssize_t old_pos = pos; if (PyBytesWriter_Grow(writer, strlen(format)) < 0) { return -1; } @@ -3919,6 +3917,12 @@ PyBytesWriter_Format(PyBytesWriter *writer, const char *format, ...) char *buf = bytes_fromformat(writer, pos, format, vargs); va_end(vargs); + if (buf == NULL) { + // On error, reset the writer to its previous state (undo any write) + writer->size = old_pos; + return -1; + } + Py_ssize_t size = buf - byteswriter_data(writer); return PyBytesWriter_Resize(writer, size); } _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
