can I make a UDP b-socket hold only a single message ?

Question

can I make a UDP berkley socket hold only a UDP single message ? meaning it will override existing message if unread message is present when a new message arrives ?

Answer 1

The only way you could do that would be to handle it on the application side, as far as I know. I assume you have a UDP socket getting some kind of real time data and that you only care about the latest / most recent packet of data to arrive. If that's the case you could do something like the following pseudo code:

struct foo {
   ...
}
int get_most_recent_packet(int sockfd, struct foo *foobuf) {
    ssize_t ret; int gotPacket = 0;
    while ((ret = recvfrom(sockfd, foobuf, sizeof(struct foo), 
                      MSG_DONTWAIT, NULL, NULL)) > 0) {
         gotPacket = 1;
    }
    if (gotPacket) return 1;
    return -1;
}

See the man page for recvfrom.

Answer 2

DNS records have a random transaction ID, so that the application can match the result to the request. You might try using your own transaction ID.