echo-via-server.py

#!/usr/bin/env python3
"""Entry -> queue -> (client request) -> (server response) -> Label"""
import os
import socket
from threading import Thread
from tkinter import BOTH, Tk, ttk
from queue import Queue, Full


def echo_server(host, port):
    # from stdlib docs /library/socket.html#example
    s = None
    for res in socket.getaddrinfo(host, port, socket.AF_UNSPEC,
                                  socket.SOCK_STREAM, 0, socket.AI_PASSIVE):
        af, socktype, proto, canonname, sa = res
        try:
            s = socket.socket(af, socktype, proto)
        except OSError as msg:
            s = None
            continue
        try:
            s.bind(sa)
            s.listen(1)
        except OSError as msg:
            s.close()
            s = None
            continue
        break
    if s is None:
        print('could not open server socket', flush=True)
        os._exit(1)
    print('Serving on {}:{}'.format(*sa))
    while True:
        conn, addr = s.accept()
        with conn:
            print('Connected by {}:{}'.format(*addr))
            while True:  # one client at a time
                data = conn.recv(1024)
                if not data:
                    break
                conn.sendall(data)


def echo_client(input_queue, label, host, port):
    with socket.create_connection((host, port)) as s, \
            s.makefile('r', encoding='utf-8', newline='\n') as file:
        for request in iter(input_queue.get, None):
            # send request (a single line)
            s.sendall(request.encode('utf-8') + b'\n')
            # receive response (a single line)
            label['text'] = file.readline().rstrip('\n')


def on_key(q, value):
    try:
        q.put_nowait(value)
    except Full:
        return 0
    else:
        return 1


def main():
    host, port = 'localhost', int.from_bytes(b'ec', 'big')
    input_queue = Queue()
    root = Tk()
    vcmd = (root.register(lambda P: on_key(input_queue, P)), '%P')
    entry = ttk.Entry(validate="key", validatecommand=vcmd)
    entry.pack(fill=BOTH)
    entry.focus()
    label = ttk.Label(text='nothing yet')
    label.pack()

    Thread(target=echo_server, args=[host, port], daemon=True).start()
    Thread(target=echo_client,
           args=[input_queue, label, host, port], daemon=True).start()

    root.mainloop()


if __name__ == '__main__':
    main()