CBB_add_u24
int CBB_add_u24(CBB *cbb, size_t value);
int CBB_add_u24(CBB *cbb, size_t value);
if (!CBB_add_u24(&cbb, msg_hdr->msg_len))
if (!CBB_add_u24(&cbb, frag_off))
if (!CBB_add_u24(&cbb, frag_len))
CHECK_GOTO(CBB_add_u24(&cbb, 0x40506));
CHECK_GOTO(CBB_add_u24(&contents, 0x40506));
CHECK_GOTO(CBB_add_u24(&contents, 0xdddddd));
CHECK_GOTO(!CBB_add_u24(&child, 1));