#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>

#include <arpa/inet.h>
#include <netinet/in.h>

#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define READ_BLOCK_TIME         5       /* unit: sec */

static void
sig_alarm(int sig __unused)
{
#define PANIC_STRING    "read blocks\n"

        write(2, PANIC_STRING, strlen(PANIC_STRING));
        abort();
}

static void
usage(const char *cmd)
{
        fprintf(stderr, "%s -p port\n", cmd);
        exit(1);
}

int
main(int argc, char *argv[])
{
        struct sockaddr_in in;
        struct itimerval it;
        int s, n, error, port, opt;
        char buf;

        port = 0;
        while ((opt = getopt(argc, argv, "p:")) != -1) {
                char *endptr;

                switch (opt) {
                case 'p':
                        port = strtol(optarg, &endptr, 0);
                        if (*endptr != '\0')
                                errx(1, "invalid -p argument");
                        break;

                default:
                        usage(argv[0]);
                }
        }
        if (port <= 0)
                usage(argv[0]);

        s = socket(AF_INET, SOCK_DGRAM | SOCK_NONBLOCK, 0);
        if (s < 0)
                err(1, "socket failed");

        memset(&in, 0, sizeof(in));
        in.sin_family = AF_INET;
        in.sin_port = htons(port);
        if (bind(s, (const struct sockaddr *)&in, sizeof(in)) < 0)
                err(1, "bind %d failed", port);

        memset(&it, 0, sizeof(it));
        it.it_value.tv_sec = READ_BLOCK_TIME;
        if (signal(SIGALRM, sig_alarm) == SIG_ERR)
                err(1, "signal failed");
        if (setitimer(ITIMER_REAL, &it, NULL) < 0)
                err(1, "setitimer failed");

        n = read(s, &buf, 1);
        if (n < 0) {
                error = errno;
                if (error != EAGAIN) {
                        warnx("invalid errno %d", error);
                        abort();
                }
        } else {
                warnx("read works");
                abort();
        }

        fprintf(stderr, "passed\n");
        exit(0);
}