* If extend == 0, obtain new n-byte packet; if extend == 1, increase
* packet by another n bytes. The packet will be in the sub-array of
* s->s3->rbuf.buf specified by s->packet and s->packet_length. (If
* If extend == 0, obtain new n-byte packet; if extend == 1, increase
* packet by another n bytes. The packet will be in the sub-array of
* s->s3->rbuf.buf specified by s->packet and s->packet_length. (If