Convert _hashopenssl function

Author: vstinner

Modules/_hashopenssl.c

@@ -1414,8 +1414,6 @@ _hashlib_scrypt_impl(PyObject *module, Py_buffer *password, Py_buffer *salt,
                      long maxmem, long dklen)
 /*[clinic end generated code: output=14849e2aa2b7b46c input=48a7d63bf3f75c42]*/
 {
-    PyObject *key_obj = NULL;
-    char *key;
     int retval;
     unsigned long n, r, p;
 
@@ -1486,27 +1484,27 @@ _hashlib_scrypt_impl(PyObject *module, Py_buffer *password, Py_buffer *salt,
         return NULL;
    }
 
-    key_obj = PyBytes_FromStringAndSize(NULL, dklen);
-    if (key_obj == NULL) {
+    PyBytesWriter *writer = PyBytesWriter_Create(dklen);
+    if (writer == NULL) {
         return NULL;
     }
-    key = PyBytes_AS_STRING(key_obj);
+    unsigned char *key = PyBytesWriter_GetData(writer);
 
     Py_BEGIN_ALLOW_THREADS
     retval = EVP_PBE_scrypt(
         (const char*)password->buf, (size_t)password->len,
         (const unsigned char *)salt->buf, (size_t)salt->len,
         n, r, p, maxmem,
-        (unsigned char *)key, (size_t)dklen
+        key, (size_t)dklen
     );
     Py_END_ALLOW_THREADS
 
     if (!retval) {
-        Py_CLEAR(key_obj);
+        PyBytesWriter_Discard(writer);
         notify_ssl_error_occurred();
         return NULL;
     }
-    return key_obj;
+    return PyBytesWriter_Finish(writer);
 }
 #endif  /* PY_OPENSSL_HAS_SCRYPT */