#!/usr/bin/env python3

#

# https://docs.python.org/3.5/library/socket.html

#

import socket

import threading

import time

# --- constants ---

HOST = '' # local address IP (not external address IP)

# '0.0.0.0' or '' - conection on all NICs (Network Interface Card),

# '127.0.0.1' or 'localhost' - local conection only (can't connect from remote computer)

# 'local_IP' - connection only on one NIC which has this IP

PORT = 8000 # local port (not external port)

# --- functions ---

def handle_client(conn, addr):

try:

while True:

# --- receive/send data ---

# if client first `send()` and next `recv()`

# then server have to first `recv`() and next `send()`

# if both will `recv()` at the same time then all will hang

# because both will wait for data and nobody will `send()`

# if you don't use native characters

# then you can use 'ascii' instead of 'utf-8'

now = int(time.time())

# receiving

data = conn.recv(1024)

text = data.decode('utf-8') # decode bytes to string

print('[{}][{}] recv: {}'.format(addr, now, text))

# sending

text = 'Thank you [{}]'.format(now)

data = text.encode('utf-8') # encode string to bytes

conn.send(data)

print('[{}]][{}] send: {}'.format(addr, now, text))

except Exception as e:

print('[DEBUG] exception:', e)

# --- create socket ---

print('[DEBUG] create socket')

#s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

s = socket.socket() # default value is (socket.AF_INET, socket.SOCK_STREAM)

# so you don't have to use it in socket()

# --- options ---

print('[DEBUG] set options')

# solution for "[Error 89] Address already in use". Use before bind()

s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

# --- assign socket to local IP (local NIC) ---

print('[DEBUG] bind:', (HOST, PORT))

s.bind((HOST, PORT)) # one tuple (HOST, PORT), not two arguments

# --- set size of queue ---

print('[DEBUG] listen')

s.listen(1) # number of clients waiting in queue for "accept".

# If queue is full then client can't connect.

while True:

# --- accept client ---

# accept client and create new socket `conn` (with different port) for this client only

# and server will can use `s` to accept other clients (if you will use threading)

print('[DEBUG] accept ... waiting')

conn, addr = s.accept()

print('[DEBUG] addr:', addr)

# --- run thread ---

t = threading.Thread(target=handle_client, args=(conn, addr))

t.start()

# --- close all sockets ---

# alway first close `conn`, next close `s`

print('[DEBUG] close socket(s)')

conn.close()

s.close()