UDP Hole punching in python

Question

I am trying to establish a peer to peer communication using UDP hole punching. I am first establishing a connection with the server and then trying to make communication between 2 clients, but I am not able to communicate between 2 computers that are behind 2 different NATs as I am not understanding what IP address and port must I enter for the establishment of communication. Please tell me what changes must I make in the code below so that 2 computers are able to communicate.

P.S : External IP doesn't seem to work and I am not supposed to use any additional tool like ngrok

Server.py

import socket
import struct
import sys

server_listening_port = 12345

sockfd = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sockfd.bind(("", server_listening_port))
print("Listening on the port " + str(server_listening_port))

client_requests = []

while True:
    data, addr = sockfd.recvfrom(32)
    client_requests.append(addr)
    print("Connection from: " + str(addr))

    if len(client_requests) == 2:
        break

client_a_ip = client_requests[0][0]
client_a_port = client_requests[0][1]
client_b_ip = client_requests[1][0]
client_b_port = client_requests[1][1]

message = ": "

sockfd.sendto(str(client_a_ip).encode("utf-8") + message.encode("utf-8") + str(client_a_port).encode("utf-8"), client_requests[1])
sockfd.sendto(str(client_b_ip).encode("utf-8") + message.encode("utf-8") + str(client_b_port).encode("utf-8"), client_requests[0])
sockfd.close()

Above is the rendezvous server

ClientA.py

import socket
import struct
import sys
import time
master = ("Server_IP", Port)

#Create dgram udp socket
try:
    sockfd = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    message = "Hello"
    sockfd.bind(('', 0))
    sockfd.sendto(message.encode("utf-8"), master)

except socket.error:
    print("Failed to create socket")
    sys.exit()

# #Receiving peer info from server
peer_data, addr = sockfd.recvfrom(1024)
print (peer_data)

print("trying to communicate with peer")
peer_ip = peer_data.decode("utf-8").split(":")[0]
peer_port = int(peer_data.decode("utf-8").split(":")[1])

peer = (peer_ip, peer_port)

while 1:
    message1 = input(str("You:>>"))
    message = message.encode("utf-8")
    sockfd.sendto(str(message).encode("utf-8"), peer)
    incoming_msg, sendaddr = sockfd.recvfrom(1024)
    incoming_msg = incoming_msg.decode("utf-8")
    print("ClientB:>>",incoming_msg)

Above code is Client A

ClientB.py

import socket  #For sockets
import struct
import sys    #For exit
import time
master = ("Server_IP", port)
me = ("ClientB_IP", port)

#Create dgram udp socket
try:
    sockfd = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    message = "Hello"
    sockfd.bind(('', 0))
    sockfd.sendto(message.encode("utf-8"), master)

except socket.error:
    print("Failed to create socket")
    sys.exit()

# #Receiving peer info from server
peer_data, addr = sockfd.recvfrom(1024)
print (peer_data)

print("trying to communicate with peer")
peer_ip = peer_data.decode("utf-8").split(":")[0]
peer_port = int(peer_data.decode("utf-8").split(":")[1])
peer = (peer_ip, peer_port)

while 1:
    incoming_msg, sendaddr = sockfd.recvfrom(1024)
    incoming_msg = incoming_msg.decode("utf-8")
    print("ClientA:>>", incoming_msg)
    message = input(str("You :>>"))
    message = message.encode("utf-8")
    sockfd.sendto(str(message).encode("utf-8"), peer)

Above is client B

I am facing problem only in the IP address and port. So , please do help me with it to establish communication between 2 computers behind 2 different NATs

Answer 1

I'm currently on the same problem and I want to program it for myself. With some research I found a really good paper explaining the process in detail. I let you know if I succeed. https://bford.info/pub/net/p2pnat/