connect( ) timeout

How do you go about setting the timeout for the connect( ) function?

Bunch of ways. The easist (IMO) is something like the following

Code:

---

  FD_ZERO(&set);
  FD_SET(sock, &set);

  fcntl(sock, F_SETFL, O_NONBLOCK);

  if ( (ret = connect (sock, (sockaddr *)&addr, sizeof (sockaddr))) == -1)
  {
    if ( errno != EINPROGRESS )
      return 0;

  }
  ret = select(sock+1, NULL, &set, NULL, &timeout);

  close(sock);

---

Thats a code segment obviously.

What you are doing is setting the socket to be non blocking, as such connect will immediatly fail but should errno should be set to EINPROGRESS from there you use select to see if you can write to it. Select is always blocking but has a timeout parameter.

There are also ways using signal() and alarm().

>>from there you use select to see if you can write to it
The socket can be writable if the connect works or if it fails, so you need another level of testing to see if you're actually connected or not.

The following is based on Jon Snader's code from Effective TCP/IP Programming:

Code:

---

int IsSocketConnected(int fd, fd_set *rd, fd_set *wr)
{
  /*
    * Code taken from Effective TCP/IP Programming, by Jon Snader, p185
    */
  int    err;
  size_t  len = sizeof(int);

  errno = 0;

  if (!FD_ISSET(fd, rd) && !FD_ISSET(fd, wr))
  {
    return(0);
  }

  if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &len) < 0)
  {
    return(0);
  }

  errno = err;
  return(errno == 0);
}

---

You'd call IsSocketConnected() after doing the select().

The Windows version looks like so:

Code:

---

int isconnected(SOCKET s, fd_set *rd, fd_set *wr, fd_set *ex)
{
  WSASetLastError(0);
  if (!FD_ISSET(s, rd) && !FD_ISSET(s, wr))
  {
    return(0);
  }

  if (FD_ISSET(s, ex))
  {
    return(0);
  }

  return(1);
}

---