Thread: unix network programming

Beej is your friend.

Quzah.

Well spend a couple more seconds with your favourite search engine and you'll get something like this.

Keywords used: C socket programming "time out"

Not real hard.

Basicly you use select().

After all, that's what that final parameter is there for.

Quzah.

You could also setup a signal handler for SIGALRM using signal(2)

and then use alarm(2) to send an alarm signal at a specified time.

This will cause connect() to return with EINTR (INTERRUPTED)

Originally posted by quagsire
In section 6.2 of BeeJ's Guide to Network Programming you can find info on how to use timeouts with select.

Yeah, but they "already read [all] that".

Quzah.

Timeout's on connect()'s isn't too hard.

This book explains it well, but you have to buy/borrow it. However, the sample source code from it is available here which I suggest you download. The file to look at is connectto1.c which is contained within the zip file.

Basically, it creates a socket, then sets it to non-blocking and calls connect(). If connect() fails, with errno == EINPROGRESS the connect is still happening, so you can use select() to wait a certain amount of time for the connect to finish. I've used this approx on *nix and Cygwin on Windows and it's work just fine.

thanks hammer, but i've gone for the alarm signal approach.

its pretty simple (as i know signals) and seems less of a hack.

Code:

        struct sigaction action;

        void timed_out(){}

        .....
        s = socket(PF_INET,SOCK_STREAM,0); //create socket
        if(s == -1)
                return 

        //initialise server struct
        memset(&adr_srvr,0,sizeof adr_srvr);
        adr_srvr.sin_family = AF_INET;
        adr_srvr.sin_port = htons(atoi(srvr_port));
	adr_srvr.sin_addr.s_addr = inet_addr(srvr_addr);

        //verify staright ip address or resolved ip address
	if(adr_srvr.sin_addr.s_addr == INADDR_NONE)
	{
		hp = gethostbyname(ip);
		if(!hp)
			return "0 - Hostname does not exist.";
		if(hp->h_addrtype == AF_INET)
			adr_srvr.sin_addr.s_addr = inet_addr(inet_ntoa(*(struct in_addr *) hp->h_addr_list[0]));
			if(adr_srvr.sin_addr.s_addr == INADDR_NONE)
				return "0 - Bad IP address";
	}
	
        len_inet = sizeof adr_srvr;

        //initialise signal handler
	bzero(&action, sizeof(action));
	action.sa_handler = timed_out;
	action.sa_flags = 0;

	sigaction(SIGALRM, &action, 0);

	alarm(5); //start alarm count - 5 secs

        z = connect(s,&adr_srvr, len_inet); //attempt to connect
	alarm(0); //turn off alarm
	if(z == -1)
        	return "0 - Cannot connect to host.";