#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;
socklen_t addr_size;
int socket_fd;

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

void receive_urgent()
{
    double dd;
    if (recvfrom(socket_fd, &dd, sizeof(double), MSG_OOB, (SockAddr *)&addr, &addr_size) == -1)
        handle_error("recvfrom urgent");
    printf("dd: %f\n", dd);

    signal(SIGURG, receive_urgent);
}

int main()
{
    if ((socket_fd = socket(PF_INET, SOCK_DGRAM, 0)) == -1)
        handle_error("socket");

    addr_size = sizeof(SockAddr_in);
    memset(&addr, 0, addr_size);
    addr.sin_port = htons(4040);
    addr.sin_family = PF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    // inet_pton(AF_INET, "127.0.0.1", &(addr.sin_addr.s_addr));

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

    double dd;
    for (;;)
    {
        fcntl(socket_fd, F_SETOWN, getpid());
        signal(SIGURG, receive_urgent);
        int bytes = recvfrom(socket_fd, &dd, sizeof(double), 0, (SockAddr *)&addr, &addr_size);
        if (bytes == -1)
            handle_error("recvfrom");
        if (bytes == 0)
        {
            printf("EOF\n");
        }
        printf("dd: %f\n", dd);
    }

    if (close(socket_fd) == -1)
        handle_error("close");

    return 0;
}