socket_server.py

import socket
import select

HEADER_LENGTH = 128

IP = socket.gethostbyname(socket.gethostname())
PORT = 8765

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
server_socket.bind((IP, PORT))
server_socket.listen()

sockets_list = [server_socket]
clients = {}
keys = {}

print(f'Listening for connections on {IP}:{PORT}...')

def receive_message(client_socket):
    try:
        message_header = client_socket.recv(HEADER_LENGTH)
        if not len(message_header):
            return False

        message_length = int(message_header.decode('utf-8').strip())
        message = client_socket.recv(message_length).decode('utf-8')
        if ':>>>:' in message:
            message = message.split(':>>>:')
            message = {
                'header': message_header,
                'data': message[0].encode('utf-8'),
                'addressee': message[1]
            }
        else:
            message = {
                'header': message_header,
                'data': message.encode('utf-8')
            }
        return message
    except Exception as e:
        return False

def update_users_status():
    for client_socket in clients:
        others_keys = {}
        for key in keys.keys():
            if clients[client_socket]['data'] != key:
                others_keys[key.decode("utf-8")] = keys[key]
        message = repr(others_keys).encode('utf-8')
        message_header = f"{len(message):<{HEADER_LENGTH}}".encode('utf-8')
        flag = '__flag__'.encode('utf-8')
        flag_header = f"{len(flag):<{HEADER_LENGTH}}".encode('utf-8')
        client_socket.send(flag_header + flag + message_header + message)

while True:
    read_sockets, _, exception_sockets = select.select(sockets_list, [], sockets_list)

    for notified_socket in read_sockets:
        if notified_socket == server_socket:
            client_socket, client_address = server_socket.accept()
            user = receive_message(client_socket)
            if user is False:
                continue

            des_key = receive_message(client_socket)
            if des_key is False:
                continue

            des_key = eval(des_key['data'])
            sockets_list.append(client_socket)
            clients[client_socket] = user
            keys[user['data']] = des_key
            
            username = user['data'].decode('utf-8')
            print(f'\n{username} joined the room')
            update_users_status()

        else:
            message = receive_message(notified_socket)

            if message is False:
                username = clients[notified_socket]['data'].decode('utf-8')
                print(f'\n{username} left the room')
                
                keys.pop(clients[notified_socket]['data'])
                sockets_list.remove(notified_socket)
                del clients[notified_socket]
                update_users_status()
                continue

            user = clients[notified_socket]
            sender = user["data"].decode("utf-8")
            recipient = message['addressee']
            print(f'\n{sender} sent a message to {recipient}')

            for client_socket in clients:
                if clients[client_socket]['data'] == message['addressee'].encode('utf-8'):
                    client_socket.send(user['header'] + user['data'] + message['header'] + message['data'])

    for notified_socket in exception_sockets:
        username = clients[notified_socket]['data'].decode('utf-8')
        print(f'\n{username} left the room')
        sockets_list.remove(notified_socket)
        del clients[notified_socket]
        update_users_status()