Notes

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

#define PORT 12345
#define BUFFER_SIZE 1024

void go_back_n_protocol(int sf, int sn, int ack, int num_frames, int window_size, int *updated_sf, int *updated_sn, int *updated_ack, int *updated_window_range) {
*updated_sn = (sn + num_frames) % (1 << window_size);
*updated_ack = (ack + num_frames) % (1 << window_size);
*updated_sf = (sf + num_frames) % (1 << window_size);

for (int i = 0; i < window_size; i++) {
updated_window_range[i] = (*updated_sf + i) % (1 << window_size);
}
}

int main() {
int server_fd, new_socket;
struct sockaddr_in address;
int opt = 1;
int addrlen = sizeof(address);
char buffer[BUFFER_SIZE] = {0};

// Creating socket file descriptor
if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
perror("socket failed");
exit(EXIT_FAILURE);
}

// Attaching socket to the port
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &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);

// Binding the socket to the 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);
}

printf("Server listening on port %d...n", PORT);

if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
perror("accept");
exit(EXIT_FAILURE);
}

// Read data from the client
read(new_socket, buffer, BUFFER_SIZE);
int sf, sn, ack, num_frames, window_size;
sscanf(buffer, "%d,%d,%d,%d,%d", &sf, &sn, &ack, &num_frames, &window_size);

int updated_sf, updated_sn, updated_ack;
int updated_window_range[window_size];

// Process the data
go_back_n_protocol(sf, sn, ack, num_frames, window_size, &updated_sf, &updated_sn, &updated_ack, updated_window_range);

// Prepare the response
char response[BUFFER_SIZE];
snprintf(response, sizeof(response), "Window Size: %d, Updated SF: %d, Updated SN: %d, Updated Window Range: [", window_size, updated_sf, updated_sn);
for (int i = 0; i < window_size; i++) {
char temp[10];
snprintf(temp, sizeof(temp), "%d", updated_window_range[i]);
strcat(response, temp);
if (i < window_size - 1) {
strcat(response, ", ");
}
}
strcat(response, "]");

// Send response to the client
send(new_socket, response, strlen(response), 0);

// Close sockets
close(new_socket);
close(server_fd);

return 0;
}