#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

typedef struct sockaddr_in SockAddr_in;
typedef struct sockaddr SockAddr;

SockAddr_in addr;
SockAddr_in addr_client;
socklen_t addr_size;
int socket_fd;
int client_socket;

void handle_error(char *txt)
{
    perror(txt);
    exit(-1);
}

void receive_urgent(int signo)
{
    double dd;
    printf("OOB received\n");
    if (recv(client_socket, &dd, sizeof(double), MSG_OOB) == -1)
        handle_error("recv urgent");
    printf("urgent dd: %f\n", dd);

    signal(SIGURG, receive_urgent);
}

void end_connection()
{
    if (close(socket_fd) == -1)
        handle_error("close");
    exit(0);
}

int main()
{
    signal(SIGINT, end_connection);
    signal(SIGTERM, end_connection);

    if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
        handle_error("socket");
    printf("socket success\n");

    addr_size = sizeof(SockAddr_in);
    memset(&addr, 0, addr_size);
    addr.sin_port = htons(4040);
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);

    if (bind(socket_fd, (SockAddr *)&addr, addr_size) == -1)
        handle_error("bind");
    printf("bind success\n");

    if (listen(socket_fd, 10) == -1)
        handle_error("listen");
    printf("listen success\n");

    double dd;
    for (;;)
    {
        if ((client_socket = accept(socket_fd, (SockAddr *)&addr_client, &addr_size)) == -1)
            handle_error("accept");
        printf("accept success\n");

        int i;
        if ((i = fork()) == -1)
            handle_error("fork");
        printf("fork success\n");
        if (i == 0)
        {
            close(socket_fd);
            signal(SIGURG, receive_urgent);
            fcntl(client_socket, F_SETOWN, getpid());

            for (;;)
            {
                int bytes = read(client_socket, &dd, sizeof(double));
                if (bytes == -1)
                    handle_error("recvfrom");
                if (bytes == 0)
                {
                    printf("EOF\n");
                    break;
                }
                else
                {
                    printf("dd: %f\n", dd);
                }
            }

            close(client_socket);

            return 0;
        }
        else
        {
            sigignore(SIGCHLD);
            close(client_socket);
        }
    }

    return 0;
}