c - UDP Socket Set Timeout

Question

I am trying to set a 100ms timeout on a UDP Socket. I am using C. I have posted relavent pieces of my code below. I am not sure why this is not timing out, but just hangs when it doesn't receive a segment. Does this only work on sockets that are not bound using the bind() method?

#define TIMEOUT_MS      100     /* Seconds between retransmits */

if ((rcv_sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
    DieWithError("socket() failed");

if ((rcv_sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
    DieWithError("socket() failed");

//set timer for recv_socket
static int timeout = TIMEOUT_MS;
setsockopt(rcv_sock, SOL_SOCKET, SO_RCVTIMEO,(char*)&timeout,sizeof(timeout));

if(recvfrom(rcv_sock, ackBuffer,sizeof(ackBuffer), 0,
       (struct sockaddr *) &servAddr2, &fromSize) < 0){
    //timeout reached
    printf("Timout reached. Resending segment %d
", seq_num);
    num_timeouts++;
}

Answer 1

The SO_RCVTIMEO option expects a struct timeval defined in sys/time.h, not an integer like you're passing to it. The timeval struct has as field for seconds and a field for microseconds. To set the timeout to 100ms, the following should do the trick:

struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 100000;
if (setsockopt(rcv_sock, SOL_SOCKET, SO_RCVTIMEO,&tv,sizeof(tv)) < 0) {
    perror("Error");
}