connect system call with blocking timeout.

gistfile1.c

// connect system call with blocking timeout.

#include <sys/socket.h>
#include <sys/select.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

int
connect_with_timeout(int addr_v4, unsigned int port, int timeout)
{
    int sock = -1;
    struct sockaddr_in server = {0};
    struct timeval tv;
    int flags, n, error;
    fd_set rset, wset;
    socklen_t len;
   
    sock = socket(PF_INET, SOCK_STREAM, 0);
    if (sock == -1) {
        goto error;
    }

    // set the socket to nonblocking mode.
    flags = fcntl(sock, F_GETFL, 0);
    if (flags != -1) {
        if (fcntl(sock, F_SETFL, flags | O_NONBLOCK) == -1) {
            goto error;
        }
    } else {
        goto error;
    }

    // connect
    server.sin_family = PF_INET;
    server.sin_addr.s_addr = htonl(addr_v4);
    server.sin_port = htons(port);
    n = connect(sock, (struct sockaddr*)&server, sizeof(server));
    if (n == -1) {
        if (errno == EINPROGRESS) {
            FD_ZERO(&rset);
            FD_SET(sock, &rset);
            wset = rset;
            tv.tv_sec = timeout / 1000;
            tv.tv_usec = (timeout % 1000) * 1000;
            n = select(sock + 1, &rset, &wset, NULL, timeout ? &tv : NULL);
            if (n == -1) {
                goto error;
            } else if (n == 0) {
                // timeout
                goto error;
            }

            if (FD_ISSET(sock, &rset) || FD_ISSET(sock, &wset)) {
                error = 0;
                len = sizeof(error);
                if (getsockopt(sock, SOL_SOCKET, SO_ERROR, &error, &len) == -1) {
                    goto error;
                }

                if (error) {
                    goto error;
                }
            } else {
                goto error;
            }
        } else {
            goto error;
        }
    }

    // recover the socket state.
    if (fcntl(sock, F_SETFL, flags) == -1) {
        goto error;
    }

    return 0;

error:

    if (sock != -1) {
        close(sock);
    }

    return -1;
}