#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <signal.h>
#include <linux/sockios.h>

#define PORT   666
#define BACKLOG 10

void sigchld_handler(int s)
{
                while(waitpid(-1, NULL, WNOHANG) > 0);
}

int main(void)

{
                struct sockaddr_in server;
                struct sockaddr_in client;
                struct iphdr *ip_hdr;
                struct tcphdr *tcp_hdr;
                struct sigaction sa;
                socklen_t sin_size;
                char buffer[8192];
                int sockfd, sockfd2;
                int addr_len;
                int opt = 1;

                if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP)) == -1)
                {
                          perror("socket");
                          exit(1);
                }

                if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (char *) &opt, sizeof(opt)) == -1)
                {
                                perror("setsockopt");
                                exit(1);
                }

                server.sin_family = AF_INET;
                server.sin_addr.s_addr = INADDR_ANY;
                server.sin_port = htons(PORT);
                bzero(&(server.sin_zero),8);



                if (bind(sockfd, (struct sockaddr * )&server, sizeof(server)) == -1)
                {
                                perror("bind");
                                exit(1);
                }


               while (read (sockfd, buffer, 8192) > 0)
               printf ("Caught tcp packet: %s\n", buffer + sizeof(struct ip_hdr *) + sizeof(struct tcp_hdr *));



                sa.sa_handler = sigchld_handler;
                sigemptyset(&sa.sa_mask);
                sa.sa_flags = SA_RESTART;

                if (sigaction(SIGCHLD, &sa, NULL) == -1)
                {
                                perror("sigaction");
                                exit(1);
                }

                while(1)
                {
                                sin_size = sizeof(struct sockaddr_in);
                                if ((sockfd2 = accept(sockfd, (struct sockaddr *)&client, &sin_size)) == -1)
                                {
                                                perror("accept");
                                                continue;
                                }

                                printf("Connection from %s\n", inet_ntoa(client.sin_addr));

                                if (!fork())
                                {
                                                close(sockfd);

                                                if (send(sockfd2, "Waiting for your packet:\n", 25, 0) == -1)

                                                        perror("send");
                                                        close(sockfd2);
                                                        exit(0);

                                }

                                close(sockfd2);
                }

                return 0;
}