// SPDX-License-Identifier: GPL-2.0

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>

#include <arpa/inet.h>
#include <sys/socket.h>

#define PORT 12345
#define RUNTIME 10

static struct {
        unsigned int timeout;
        unsigned int port;
} opts = {
        .timeout = RUNTIME,
        .port = PORT,
};

static void handler(int sig)
{
        _exit(sig == SIGALRM ? 0 : 1);
}

static void set_timeout(void)
{
        struct sigaction action = {
                .sa_handler = handler,
        };

        sigaction(SIGALRM, &action, NULL);

        alarm(opts.timeout);
}

static void do_connect(const struct sockaddr_in *dst)
{
        int s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

        if (s >= 0)
                fcntl(s, F_SETFL, O_NONBLOCK);

        connect(s, (struct sockaddr *)dst, sizeof(*dst));
        close(s);
}

static void do_accept(const struct sockaddr_in *src)
{
        int c, one = 1, s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

        if (s < 0)
                return;

        setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
        setsockopt(s, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(one));

        bind(s, (struct sockaddr *)src, sizeof(*src));

        listen(s, 16);

        c = accept(s, NULL, NULL);
        if (c >= 0)
                close(c);

        close(s);
}

static int accept_loop(void)
{
        struct sockaddr_in src = {
                .sin_family = AF_INET,
                .sin_port = htons(opts.port),
        };

        inet_pton(AF_INET, "127.0.0.1", &src.sin_addr);

        set_timeout();

        for (;;)
                do_accept(&src);

        return 1;
}

static int connect_loop(void)
{
        struct sockaddr_in dst = {
                .sin_family = AF_INET,
                .sin_port = htons(opts.port),
        };

        inet_pton(AF_INET, "127.0.0.1", &dst.sin_addr);

        set_timeout();

        for (;;)
                do_connect(&dst);

        return 1;
}

static void parse_opts(int argc, char **argv)
{
        int c;

        while ((c = getopt(argc, argv, "t:p:")) != -1) {
                switch (c) {
                case 't':
                        opts.timeout = atoi(optarg);
                        break;
                case 'p':
                        opts.port = atoi(optarg);
                        break;
                }
        }
}

int main(int argc, char *argv[])
{
        pid_t p;

        parse_opts(argc, argv);

        p = fork();
        if (p < 0)
                return 111;

        if (p > 0)
                return accept_loop();

        return connect_loop();
}