client.py

import socket
import sys
import threading
import errno

HEADER_LENGTH = 10

IP = "127.0.0.1"
PORT = 4747

my_username = input("Username: ")
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

client_socket.connect((IP, PORT))

client_socket.setblocking(False)
username = my_username.encode('utf-8')
username_header = f"{len(username):<{HEADER_LENGTH}}".encode('utf-8')


client_socket.send(username_header + username)

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

def rcv_msg():
    while True:
        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').strip())

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

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

                print(f"\n{username} > {message}\n{my_username}> ", end='')

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

        except Exception as e:
            print('Reading error: '.format(str(e)))
            sys.exit()

if __name__== "__main__":
    t1 = threading.Thread(target=send_msg)
    t2 = threading.Thread(target=rcv_msg)

    t1.start()
    t2.start()