// SPDX-License-Identifier: GPL-2.0

#include <arpa/inet.h>
#include <errno.h>
#include <error.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <unistd.h>

static int child_pid;

static unsigned long timediff(struct timeval s, struct timeval e)
{
        unsigned long s_us, e_us;

        s_us = s.tv_sec * 1000000 + s.tv_usec;
        e_us = e.tv_sec * 1000000 + e.tv_usec;
        if (s_us > e_us)
                return 0;
        return e_us - s_us;
}

static void client(int port)
{
        int sock = 0;
        struct sockaddr_in addr, laddr;
        socklen_t len = sizeof(laddr);
        struct linger sl;
        int flag = 1;
        int buffer;
        struct timeval start, end;
        unsigned long lat, sum_lat = 0, nr_lat = 0;

        while (1) {
                gettimeofday(&start, NULL);

                sock = socket(AF_INET, SOCK_STREAM, 0);
                if (sock < 0)
                        error(-1, errno, "socket creation");

                sl.l_onoff = 1;
                sl.l_linger = 0;
                if (setsockopt(sock, SOL_SOCKET, SO_LINGER, &sl, sizeof(sl)))
                        error(-1, errno, "setsockopt(linger)");

                if (setsockopt(sock, IPPROTO_TCP, TCP_NODELAY,
                                        &flag, sizeof(flag)))
                        error(-1, errno, "setsockopt(nodelay)");

                addr.sin_family = AF_INET;
                addr.sin_port = htons(port);

                if (inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr) <= 0)
                        error(-1, errno, "inet_pton");

                if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) < 0)
                        error(-1, errno, "connect");

                send(sock, &buffer, sizeof(buffer), 0);
                if (read(sock, &buffer, sizeof(buffer)) == -1)
                        error(-1, errno, "waiting read");

                gettimeofday(&end, NULL);
                lat = timediff(start, end);
                sum_lat += lat;
                nr_lat++;
                if (lat < 100000)
                        goto close;

                if (getsockname(sock, (struct sockaddr *)&laddr, &len) == -1)
                        error(-1, errno, "getsockname");
                printf("port: %d, lat: %lu, avg: %lu, nr: %lu\n",
                                ntohs(laddr.sin_port), lat,
                                sum_lat / nr_lat, nr_lat);
close:
                fflush(stdout);
                close(sock);
        }
}

static void server(int sock, struct sockaddr_in address)
{
        int accepted;
        int addrlen = sizeof(address);
        int buffer;

        while (1) {
                accepted = accept(sock, (struct sockaddr *)&address,
                                (socklen_t *)&addrlen);
                if (accepted < 0)
                        error(-1, errno, "accept");

                if (read(accepted, &buffer, sizeof(buffer)) == -1)
                        error(-1, errno, "read");
                close(accepted);
        }
}

static void sig_handler(int signum)
{
        kill(SIGTERM, child_pid);
        exit(0);
}

int main(int argc, char const *argv[])
{
        int sock;
        int opt = 1;
        struct sockaddr_in address;
        struct sockaddr_in laddr;
        socklen_t len = sizeof(laddr);

        if (signal(SIGTERM, sig_handler) == SIG_ERR)
                error(-1, errno, "signal");

        sock = socket(AF_INET, SOCK_STREAM, 0);
        if (sock < 0)
                error(-1, errno, "socket");

        if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
                                &opt, sizeof(opt)) == -1)
                error(-1, errno, "setsockopt");

        address.sin_family = AF_INET;
        address.sin_addr.s_addr = INADDR_ANY;
        /* dynamically allocate unused port */
        address.sin_port = 0;

        if (bind(sock, (struct sockaddr *)&address, sizeof(address)) < 0)
                error(-1, errno, "bind");

        if (listen(sock, 3) < 0)
                error(-1, errno, "listen");

        if (getsockname(sock, (struct sockaddr *)&laddr, &len) == -1)
                error(-1, errno, "getsockname");

        fprintf(stderr, "server port: %d\n", ntohs(laddr.sin_port));
        child_pid = fork();
        if (!child_pid)
                client(ntohs(laddr.sin_port));
        else
                server(sock, laddr);

        return 0;
}