new_contents: """
  tcp_server.py
  """
  import socket
  import json    # for serialize data
  
  s = socket.socket()
  host = socket.gethostname()
  port = 12345   # maximum is 65536, which is max of 16 bits
  s.bind((host, port))
  print("Start listening.")
  print(s)
  s.listen(5)
  while True:
      c, address = s.accept()
      print("Got connection from :", address)
      message = "Thank you for connecting"
      c.send(json.dumps(message).encode("utf-8"))
      lst = json.loads(c.recv(1024).decode("utf-8"))
      print("Sum of the list: " + str(sum(lst)))
      # sustain the chat program
      while True:
          custom_msg = json.loads(c.recv(1024).decode("utf-8"))
          if custom_msg == "q":
              print("Oh no the client leave me!")
              break
          print(custom_msg)
      c.close()
  
subject: add the tcp_server program - one leg of chat program