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gh-155742: Use PyBytesWriter in marshal #155748

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de119b3
gh-155742: Use PyBytesWriter in marshal
vstinner Aug 13, 2026
09661e7
Simplify r_object() for TYPE_STRING
vstinner Aug 13, 2026
8ae4563
w_reserve() sets writer to NULL if Resize() fails
vstinner Aug 14, 2026
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59 changes: 36 additions & 23 deletions Python/marshal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -111,7 +111,7 @@ typedef struct {
FILE *fp;
int error; /* see WFERR_* values */
int depth;
PyObject *str;
PyBytesWriter *writer;
char *ptr;
const char *end;
char *buf;
Expand All @@ -136,16 +136,16 @@ w_flush(WFILE *p)
static int
w_reserve(WFILE *p, Py_ssize_t needed)
{
Py_ssize_t pos, size, delta;
if (p->ptr == NULL)
return 0; /* An error already occurred */
if (p->fp != NULL) {
w_flush(p);
return needed <= p->end - p->ptr;
}
assert(p->str != NULL);
pos = p->ptr - p->buf;
size = PyBytes_GET_SIZE(p->str);
assert(p->writer != NULL);
Py_ssize_t pos = p->ptr - p->buf;
Py_ssize_t size = PyBytesWriter_GetSize(p->writer);
Py_ssize_t delta;
if (size > 16*1024*1024)
delta = (size >> 3); /* 12.5% overallocation */
else
Expand All @@ -156,12 +156,14 @@ w_reserve(WFILE *p, Py_ssize_t needed)
return 0;
}
size += delta;
if (_PyBytes_Resize(&p->str, size) != 0) {
if (PyBytesWriter_Resize(p->writer, size) != 0) {
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PyBytesWriter_Discard(p->writer);
p->writer = NULL;
p->end = p->ptr = p->buf = NULL;
return 0;
}
else {
p->buf = PyBytes_AS_STRING(p->str);
p->buf = PyBytesWriter_GetData(p->writer);
p->ptr = p->buf + pos;
p->end = p->buf + size;
return 1;
Expand Down Expand Up @@ -1308,16 +1310,12 @@ r_object(RFILE *p)
}
break;
}
v = PyBytes_FromStringAndSize((char *)NULL, n);
if (v == NULL)
break;
ptr = r_string(n, p);
if (ptr == NULL) {
Py_DECREF(v);
break;
}
memcpy(PyBytes_AS_STRING(v), ptr, n);
retval = v;

retval = PyBytes_FromStringAndSize(ptr, n); // can be NULL
R_REF(retval);
break;
}
Expand Down Expand Up @@ -1908,27 +1906,35 @@ _PyMarshal_WriteObjectToString(PyObject *x, int version, int allow_code)
return NULL;
}
memset(&wf, 0, sizeof(wf));
wf.str = PyBytes_FromStringAndSize((char *)NULL, 50);
if (wf.str == NULL)
wf.writer = PyBytesWriter_Create(50);
if (wf.writer == NULL) {
return NULL;
wf.ptr = wf.buf = PyBytes_AS_STRING(wf.str);
wf.end = wf.ptr + PyBytes_GET_SIZE(wf.str);
}
wf.ptr = wf.buf = PyBytesWriter_GetData(wf.writer);
wf.end = wf.ptr + PyBytesWriter_GetSize(wf.writer);
wf.error = WFERR_OK;
wf.version = version;
wf.allow_code = allow_code;
if (w_init_refs(&wf, version)) {
Py_DECREF(wf.str);
PyBytesWriter_Discard(wf.writer);
return NULL;
}
w_object(x, &wf);
w_clear_refs(&wf);
if (wf.str != NULL) {
const char *base = PyBytes_AS_STRING(wf.str);
if (_PyBytes_Resize(&wf.str, (Py_ssize_t)(wf.ptr - base)) < 0)

if (wf.writer != NULL) {
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assert(wf.ptr != NULL);
const char *base = PyBytesWriter_GetData(wf.writer);
if (PyBytesWriter_Resize(wf.writer, (Py_ssize_t)(wf.ptr - base)) < 0) {
PyBytesWriter_Discard(wf.writer);
// PyBytesWriter_Resize() sets an exception
assert(PyErr_Occurred());
return NULL;
}
}

if (wf.error != WFERR_OK) {
Py_XDECREF(wf.str);
PyBytesWriter_Discard(wf.writer);
switch (wf.error) {
case WFERR_NOMEMORY:
PyErr_NoMemory();
Expand All @@ -1949,7 +1955,14 @@ _PyMarshal_WriteObjectToString(PyObject *x, int version, int allow_code)
}
return NULL;
}
return wf.str;

if (wf.writer == NULL) {
// In w_reserve(), PyBytesWriter_Resize() failed with an exception set
assert(PyErr_Occurred());
return NULL;
}

return PyBytesWriter_Finish(wf.writer);
}

PyObject *
Expand Down
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