_PyBytes_Resize

_PyBytes_Resize.c

/* The following function breaks the notion that bytes are immutable:
   it changes the size of a bytes object.  We get away with this only if there
   is only one module referencing the object.  You can also think of it
   as creating a new bytes object and destroying the old one, only
   more efficiently.  In any case, don't use this if the bytes object may
   already be known to some other part of the code...
   Note that if there's not enough memory to resize the bytes object, the
   original bytes object at *pv is deallocated, *pv is set to NULL, an "out of
   memory" exception is set, and -1 is returned.  Else (on success) 0 is
   returned, and the value in *pv may or may not be the same as on input.
   As always, an extra byte is allocated for a trailing \0 byte (newsize
   does *not* include that), and a trailing \0 byte is stored.
*/

int
_PyBytes_Resize(PyObject **pv, Py_ssize_t newsize)
{
    PyObject *v;
    PyBytesObject *sv;
    v = *pv;
    if (!PyBytes_Check(v) || newsize < 0) {
        goto error;
    }
    if (Py_SIZE(v) == newsize) {
        /* return early if newsize equals to v->ob_size */
        return 0;
    }
    if (Py_REFCNT(v) != 1) {
        goto error;
    }
    /* XXX UNREF/NEWREF interface should be more symmetrical */
    _Py_DEC_REFTOTAL;
    _Py_ForgetReference(v);
    *pv = (PyObject *)
        PyObject_REALLOC(v, PyBytesObject_SIZE + newsize);
    if (*pv == NULL) {
        PyObject_Del(v);
        PyErr_NoMemory();
        return -1;
    }
    _Py_NewReference(*pv);
    sv = (PyBytesObject *) *pv;
    Py_SIZE(sv) = newsize;
    sv->ob_sval[newsize] = '\0';
    sv->ob_shash = -1;          /* invalidate cached hash value */
    return 0;
error:
    *pv = 0;
    Py_DECREF(v);
    PyErr_BadInternalCall();
    return -1;
}