Simple peer-to-peer chat using Python sockets.

chat.py

#!/usr/bin/env python3

from sys import argv, stdout, exit
from threading import Thread
import re, socket, random, gnureadline

PORT = 6310

def Bind_UDP():
	global sock2
	try:
		sock2 = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
		sock2.bind(("", PORT))
	except socket.error:
		sock2.close()
		exit(f"Port {PORT} is already in use.")
	while 1:
		_data, addr = sock2.recvfrom(1024)
		data_raw = _data.decode().split("\n")[0]
		prefix, data = data_raw[:4], data_raw[4:]
		# print(f"\n{repr(data_raw)}\n") # DEBUGGING
		if prefix == "HELO":
			sock1.sendto(f"PING{user}".encode(), (addr[0], PORT))
			send("PEER" + addr[0])
			continue
		elif prefix == "PEER":
			sock1.sendto(f"PING{user}".encode(), (data, PORT))
			continue
		elif prefix == "PING":
			sock1.sendto(f"LIVE{user}".encode(), (addr[0], PORT))
			peers[addr[0]] = data
			to_print = f"User [{data}] is online"
		elif prefix == "LIVE":
			peers[addr[0]] = data
			to_print = f"* [{data}] * joined the chat"
		elif prefix == "TEXT":
			to_print = f"[{peers[addr[0]]}] {data}"
		elif prefix == "OLEH":
			to_print = f"* [{peers[addr[0]]}] * left the chat"
			del peers[addr[0]]
		else:
			continue
		temp = gnureadline.get_line_buffer()
		print(f"\n{to_print}\n{prompt}", end="")
		stdout.flush()
		gnureadline.insert_text(temp)
		gnureadline.redisplay()

def send(msg):
	for peer in peers:
		sock1.sendto(msg.encode(), (peer, PORT))

def check(H):
	return re.search(r"^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$", H) and all(int(x) < 256 for x in H.split("."))

def main():
	global sock1, prompt
	listen = Thread(target=Bind_UDP)
	listen.setDaemon(True)
	listen.start()
	sock1 = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
	sock1.sendto(b"HELO", (peer, PORT))
	prompt = f"[\033[9{colors.index(color)};1m{user}\033[0m] "
	while 1:
		ui = input(prompt).strip()
		if ui:
			send("TEXT" + ui)
		# Readline:
		# https://stackoverflow.com/a/28604256
		# https://pymotw.com/3/readline/index.html

try:
	peers = {}
	colors = ["", "red", "green", "yellow", "blue", "pink", "cyan"]
	if not argv[2:] or not check(argv[2]):
		exit(f"Usage: {argv[0]} username peer_ip [prompt_color]")
	user, peer = argv[1:3]
	color = argv[3] if (argv[3:] + [" "])[0] in colors else "red"
	main()
except (KeyboardInterrupt, EOFError):
	send("OLEH")
	sock1.close()
	sock2.close()
	exit("")