Server Go Back N

#include <netinet/in.h>
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#define PORT 8080
#define window_size 5
void transfer(int sock){
    struct timeval tv;
    tv.tv_sec = 1;
    tv.tv_usec = 0;
    setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, (const char*)&tv, sizeof tv);
    srand(time(NULL));
    int head=0,tail=0,count,red;
      printf("Enter number of frames:");
      scanf("%d",&count);
      for(tail=0;tail<count;tail++){
      red=-1;
      if((tail-head)>window_size||tail==count-1)
      { printf("Timeout resend from %d\n",head);
      tail=head;
      }
      int flag = rand()%2;
      printf("frame %d send\n",tail);
      if(!flag)
      {write(sock,&tail,sizeof(tail));
        }
        read(sock,&red,sizeof(red));
        if(red!=-1){head++;
        printf("\nACK %d\n",red);}

      }


}

int main(int argc, char const* argv[])
{
    int server_fd, new_socket;
    struct sockaddr_in address;
    int opt = 1,n;
    int addrlen = sizeof(address);
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0))
        == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }
    if (setsockopt(server_fd, SOL_SOCKET,
                SO_REUSEADDR | SO_REUSEPORT, &opt,
                sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);
    if (bind(server_fd, (struct sockaddr*)&address,
            sizeof(address))
        < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    if ((new_socket
        = accept(server_fd, (struct sockaddr*)&address,
                (socklen_t*)&addrlen))
        < 0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }

    transfer(new_socket);
    close(new_socket);
    shutdown(server_fd, SHUT_RDWR);
    return 0;
}