#!/usr/bin/env python3

import struct

import socket

import sys

# --- 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)

try:

# --- 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

# --- 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() # socket, address

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

# --- receive data ---

print('[DEBUG] receive')

# receive length as 4-bytes

length = conn.recv(4)

print('[DEBUG] length as 4 bytes:', length)

# convert length from 4-bytes to int

length = struct.unpack('!i', length)[0] # unpack returns tuple with one element

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

# receive data as bytes using length

data = conn.recv(length)

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

# convert bytes to text

text = data.decode('utf-8')

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

# --- close connection ---

# first close `conn`, later `s`

print('[DEBUG] close conn')

conn.close()

except Exception as ex:

print(ex)

except KeyboardInterrupt as ex:

print(ex)

except:

print(sys.exc_info())

finally:

# --- close socket ---

print('[DEBUG] close socket')

s.close()