Socket Blocking and Timeout on Select

Question

I am currently creating an echo server that disconnects clients after a maxWaitTime of being in idle.

I was hoping the program would block the socket until the clien

Answer 1

As others have commented, you have some logic holes in your code. By your own admission:

I know retval = 0 whenever it goes through the select and that the fd_set sock goes to [256, (31 zeroes)] and after the select, sock goes to [32 zeroes].

That should have been an indication to you that something was going wrong. The socket was not in the fd_set after select() exited, which meant the socket was not readible yet. retval=0 means select() timed out.

You have to reset not only the fd_set every time select() is called, but also the timeval as well. Try this instead:

int opt = 3; 
setsockopt(sockfd, SOL_SOCKET, SO_RCVLOWAT,&opt,sizeof(opt)); 

for ( ; ; )
{ 
    timeout.tv_sec = maxWaitTime; 
    timeout.tv_usec = 0; 

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

    int retval = select(sockfd+1, &sock, NULL, NULL, &timeout); 
    if (retval <= 0) 
    { 
        quitProgram(number); /* error or connection timed out */
    } 
    else 
    { 
        if ( (n = Readline(sockfd, line, MAXLINE)) <= 0) 
        { 
            return; /* error or connection closed by other end */ 
        } 

        Writen(sockfd, line, n); 
    } 
}