// gcc server.c -o server
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/tcp.h>

int main() {
    int sockfd, connfd;
    struct sockaddr_in servaddr;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    int opt = 1;
    setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &opt, sizeof(opt));
    int idle = 10, intvl = 5, cnt = 4;
    setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPIDLE, &idle, sizeof(idle));
    setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPINTVL, &intvl, sizeof(intvl));
    setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPCNT, &cnt, sizeof(cnt));

    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = INADDR_ANY;
    servaddr.sin_port = htons(9090);

    bind(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr));
    listen(sockfd, 1);

    printf("Server waiting...\n");
    connfd = accept(sockfd, NULL, NULL);
    printf("Client connected!\n");

    char buf[100];
    int n = read(connfd, buf, sizeof(buf)-1);
    buf[n] = '\0';
    printf("Received: %s\n", buf);

    pause(); // keep running to see keepalives in Wireshark
    return 0;
}