ChatApplicationSystemSocket

client.py

import socket
import select
import errno
import sys

HEADER_LENGTH = 10
IP = '127.0.0.1'
PORT = 3000


username = input('Username: ').encode('utf-8')
username_header = f'{len(username):<{HEADER_LENGTH}}'.encode('utf-8')

client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect((IP, PORT))
client_socket.setblocking(False)  # Receive won't be blocking..
client_socket.send(username_header + username)

while True:
    message = input(f'{username} > ')
    message
    if message:
        message = message.encode('utf-8')
        message_header = f'{len(message):<{HEADER_LENGTH}}'.encode('utf-8')
        client_socket.send(message_header + message)

    try:
        while True:
            username_header = client_socket.recv(HEADER_LENGTH)
            if not len(username_header):
                print('Connection closed by the server')
                sys.exit()

            username_length = int(username_header.decode('utf-8'))
            username = client_socket.recv(username_length).decode('utf-8')

            message_header = client_socket.recv(HEADER_LENGTH)
            message_length = int(message_header.decode('utf-8'))
            message = client_socket.recv(message_length).decode('utf-8')

            print(f'{username} > {message}')

    except IOError as e:
        if e.errno != errno.EAGAIN and e.errno != errno.EWOULDBLOCK:
            print('Reading error:', str(e))
            sys.exit()
        continue

    except Exception as e:
        print('Normal error: ', str(e))
        sys.exit()

server.py

import socket
import select

HEADER_LENGTH = 10
IP = '127.0.0.1'
PORT = 3000

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.setsockopt(
    socket.SOL_SOCKET,  # Thing you want to set
    socket.SO_REUSEADDR,  # What you want to set
    1  # Set the thing
)
server_socket.bind((IP, PORT))

server_socket.listen()

sockets_list = [server_socket]

clients = {}


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'))
        return {
            'header': message_header,
            'data': client_socket.recv(message_length)
        }
    except:
        return False


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

            sockets_list.append(client_socket)

            clients[client_socket] = user

            print(f'Accepted new connection from {client_address[0]}:{client_address[1]} username:{user["data"].decode("utf-8")}')
        else:
            message = receive_message(notified_socket)

            if message is False:
                print(f'Closed connection from {clients[notified_socket]["data"].decode("utf-8")}')
                sockets_list.remove(notified_socket)
                del client_socket[notified_socket]
                continue

            user = clients[notified_socket]
            print(f'Received message from {user["data"].decode("utf-8")}: {message["data"].decode("utf-8")}')

            for client_socket in clients:
                if client_socket != notified_socket:
                    client_socket.send(user["header"] + user["data"] + message["header"] + message["data"])

    for notified_socket in exception_sockets:
        sockets_list.remove(notified_socket)
        del client_socket[notified_socket]