Timeout value on Socket Connect

[Gareth Crispin]

Good afternoon,

I'm rewriting a piece of perl code in C++ that simply checks
availability of a port.

It's fairly simple, and returns UP, DOWN or NODNS.

This works great, and is just what I need. Except when network issues,
or firewalls drop packets silently. It'll sit and hang around forever,
which grinds the scripts dependant upon it to a halt.

Is there a way of being able to kill the connect() or set a timeout of
say three seconds before assuming a port is DOWN.

I've heard talk of using SIGALARM to break the connect(), but I've no
idea how to implement this. Would anyone mind pointing me in the right
directions?

I'm not concerned with running on anything other than UNIX.

I'm pretty green when it comes to C, so please be gentle.

Thanks in advance, and kind regards
Gareth Crispin
---- CODE ----

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define PORT 13702 // the port client will be connecting to

int main(int argc, char *argv[])
{
int sockfd, numbytes;
struct hostent *he;
struct sockaddr_in their_addr; // connector's
address information

if (argc != 2) {
fprintf(stderr, "usage: client hostname\n");
exit(1);
}

if ((he=gethostbyn ame(argv[1])) == NULL) { // get the host info
//perror("gethost byname");
printf("NODNS") ;
exit(1);
}

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket" );
exit(1);
}

their_addr.sin_ family = AF_INET; // host byte order
their_addr.sin_ port = htons(PORT); // short,
network byte order
their_addr.sin_ addr = *((struct in_addr *)he->h_addr);
memset(&(their_ addr.sin_zero), '\0', 8); // zero the rest
of the struct

if (connect(sockfd , (struct sockaddr *)&their_addr,
sizeof(struct sockaddr)) == -1) {
//perror("connect ");
printf("DOWN");
exit(1);
}

printf("UP");
close(sockfd);
return 0;

---- END CODE ----

[Jack Klein]

On Tue, 28 Jun 2005 13:51:24 +0100, Gareth Crispin
<so***@norealad dresshere.com> wrote in comp.lang.c++:

Good afternoon,

I'm rewriting a piece of perl code in C++ that simply checks
availability of a port.

[snip]

news:comp.unix. programmer

--
Jack Klein
Home: http://JK-Technology.Com
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