How to Create a TCP DNS Mock Server in Python

import socket
import threading


def handle_client(client_socket, address):
    print(f"[+] Connection from {address}")
    try:
        while True:
            data = client_socket.recv(1024)
            if not data:
                break
            print(f"[*] Received {len(data)} bytes (TCP DNS probe)")
            # Mock response: echo a fixed DNS response header (2 bytes ID + 1 byte flags)
            response = data[:2] + b"\x81\x80" + b"\x00\x01\x00\x01\x00\x00\x00\x00"
            client_socket.send(response)
    except Exception as e:
        print(f"[-] Error: {e}")
    finally:
        client_socket.close()
        print(f"[-] Closed connection from {address}")


def start_server(host="127.0.0.1", port=5353):
    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    server.bind((host, port))
    server.listen(5)
    print(f"[*] TCP DNS mock listening on {host}:{port}")
    try:
        while True:
            client, addr = server.accept()
            threading.Thread(target=handle_client, args=(client, addr), daemon=True).start()
    except KeyboardInterrupt:
        print("\n[!] Shutting down")
    finally:
        server.close()


if __name__ == "__main__":
    start_server()