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gh-129813, PEP 782: Set invalid bytes in PyBytesWriter #139054

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Merged
vstinner merged 1 commit into from
Sep 17, 2025
Merged

gh-129813, PEP 782: Set invalid bytes in PyBytesWriter #139054

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21 changes: 15 additions & 6 deletions Objects/bytesobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3799,12 +3799,12 @@ byteswriter_resize(PyBytesWriter *writer, Py_ssize_t size, int overallocate)
{
assert(size >= 0);

if (size <= byteswriter_allocated(writer)) {
Py_ssize_t old_allocated = byteswriter_allocated(writer);
if (size <= old_allocated) {
return 0;
}

overallocate &= writer->overallocate;
if (overallocate) {
if (overallocate & writer->overallocate) {
if (size <= (PY_SSIZE_T_MAX - size / OVERALLOCATE_FACTOR)) {
size += size / OVERALLOCATE_FACTOR;
}
Expand Down Expand Up @@ -3843,6 +3843,15 @@ byteswriter_resize(PyBytesWriter *writer, Py_ssize_t size, int overallocate)
writer->small_buffer,
sizeof(writer->small_buffer));
}

#ifdef Py_DEBUG
Py_ssize_t allocated = byteswriter_allocated(writer);
if (overallocate && allocated > old_allocated) {
memset(byteswriter_data(writer) + old_allocated, 0xff,
allocated - old_allocated);
}
#endif

return 0;
}

Expand All @@ -3863,9 +3872,6 @@ byteswriter_create(Py_ssize_t size, int use_bytearray)
return NULL;
}
}
#ifdef Py_DEBUG
memset(writer->small_buffer, 0xff, sizeof(writer->small_buffer));
#endif
writer->obj = NULL;
writer->size = 0;
writer->use_bytearray = use_bytearray;
Expand All @@ -3878,6 +3884,9 @@ byteswriter_create(Py_ssize_t size, int use_bytearray)
}
writer->size = size;
}
#ifdef Py_DEBUG
memset(byteswriter_data(writer), 0xff, byteswriter_allocated(writer));
#endif
return writer;
}

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