TCP-over-UDP/client_scenario5.py at main · MahDN/TCP-over-UDP · GitHub

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# client_scenario5.py
# This client tests the server's ability to handle duplicate data packets.
# It sends the same packet twice to simulate a retransmission after a lost ACK.

import socket
import random
import time
from packet import TCPPacket

# --- Settings ---
SERVER_HOST = '127.0.0.1'
SERVER_PORT = 12345
TIMEOUT_SECONDS = 5
MSS = 100

def main():
    client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    # --- Phase 1: Handshake (Unchanged) ---
    print("\n[Client - Handshake]")
    client_seq = random.randint(10001, 20000)
    # ... (Handshake code)
    syn_packet = TCPPacket(src_port=0, dest_port=SERVER_PORT, seq_num=client_seq, ack_num=0, syn=1)
    client_socket.sendto(syn_packet.to_bytes(), (SERVER_HOST, SERVER_PORT))
    client_port = client_socket.getsockname()[1]
    client_socket.settimeout(TIMEOUT_SECONDS)
    syn_ack_data, _ = client_socket.recvfrom(4096)
    syn_ack_packet = TCPPacket.from_bytes(syn_ack_data)
    client_ack = syn_ack_packet.seq_num + 1
    client_seq += 1
    ack_packet = TCPPacket(src_port=client_port, dest_port=SERVER_PORT, seq_num=client_seq, ack_num=client_ack, ack=1)
    client_socket.sendto(ack_packet.to_bytes(), (SERVER_HOST, SERVER_PORT))
    print("Connection Established.")

    # --- Phase 2: Data Transfer - Duplicate Packet Scenario ---
    print("\n[Phase 2: Data Transfer - Duplicate Packet Scenario]")

    message = "This is a test for duplicate packet handling."
    data_to_send = message.encode('utf-8')

    # Create the data packet
    data_packet = TCPPacket(
        src_port=client_port, dest_port=SERVER_PORT,
        seq_num=client_seq, ack_num=client_ack, payload=data_to_send
    )

    # *** Scenario Logic: Send the same packet twice ***

    # 1. Send the packet for the first time
    print(f"\nSending packet for the first time: {data_packet}")
    client_socket.sendto(data_packet.to_bytes(), (SERVER_HOST, SERVER_PORT))

    # Wait for the first ACK from the server
    try:
        client_socket.settimeout(3)
        ack1_bytes, _ = client_socket.recvfrom(4096)
        ack1 = TCPPacket.from_bytes(ack1_bytes)
        print(f"Client received the first ACK: {ack1}")
        print("--> Simulating that this ACK was 'lost' on its way to the client.")
    except socket.timeout:
        print("Did not receive the first ACK from the server.")

    print("\nWaiting 1 second before retransmitting...")
    time.sleep(1)

    # 2. Send the exact same packet again (the duplicate)
    print(f"Retransmitting the same packet (the duplicate): {data_packet}")
    client_socket.sendto(data_packet.to_bytes(), (SERVER_HOST, SERVER_PORT))

    # Wait for the second ACK from the server
    try:
        client_socket.settimeout(3)
        ack2_bytes, _ = client_socket.recvfrom(4096)
        ack2 = TCPPacket.from_bytes(ack2_bytes)
        print(f"Client received the second ACK: {ack2}")

        if ack1.ack_num == ack2.ack_num:
             print("\nSuccess! Server correctly re-sent the same ACK for the duplicate packet.")
        else:
             print("\nFailure! Server sent a different ACK for the duplicate packet.")

    except socket.timeout:
        print("Did not receive the second ACK from server.")

    # --- Phase 3: Termination (Simplified) ---
    print("\nScenario finished. Shutting down.")
    client_socket.close()


if __name__ == "__main__":
    main()