[ILUG-Social] tcp programming q

[Stephen Shirley]

Mornin',
	I'm writing a program at the moment that needs to know if another
host is up before sending data. The approach I'm using currently is to try
and open a tcp socket on the remote machine that I know isn't been
listened on. Here is the sample code:

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <setjmp.h>

sigjmp_buf jmp_env;

void alarm_handler(int num)
{
    printf("caught alarm\n");
    siglongjmp(jmp_env,1);
}

int main(int argc, char *argv[])
{
    struct sockaddr_in peer;
    int out_tcp_sock_id=socket(AF_INET,SOCK_STREAM,0);
    int ret_val;

    memset(&peer,0,sizeof(peer));
    peer.sin_family=AF_INET;
    inet_aton(argv[1],&peer.sin_addr);
    peer.sin_port=htons(1);

    printf("connecting to %s:%d\n",inet_ntoa(peer.sin_addr),ntohs(peer.sin_port));

    signal(SIGALRM,alarm_handler);
    alarm(1);

    if(sigsetjmp(jmp_env,1) == 0)
    {
        ret_val=connect(out_tcp_sock_id,&peer,sizeof(peer));

        printf("returned from connect with ret_val %d\n",ret_val);

        if(errno==ECONNREFUSED)
            return 0;

        if(ret_val==0)
        {
            close(out_tcp_sock_id);
            return 0;
        }
    }
    return 1;
}



Now - network programming isn't my strong point, so I was wondering if any
of ye lot have any idea if this can be made better (i.e. lower latency or
bandwidth). As it stands, there are only two packets sent, one in each
direction - to me that seems pretty much optimal. BTW the other machine is
a sun box which I have no control over if that makes any difference.

TIA,
Steve
-- 
"My mom had Windows at work and it hurt her eyes real bad"