Learning Python Network Programming

Chapter 8

The rest value is important because we will feed it back to recv_msgs() next time
we call it, and it will be prefixed to the data from the recv() calls. In this way, the
leftover data from the last recv_msgs() call won't be lost.

So, in our preceding example, parsing the messages would take place as shown here:

recv_msgs call data argument recv result Accumulated data msgs rest

1 - 'caerphil' 'caerphil' [] b''

1 - 'ly\0illches' 'caerphilly\0illches' ['caerphilly'] 'illches'

2 'illches' 'ter\0brie\0' 'illchester\0brie\0' ['illchester',

'brie']

b''

Here, we can see that the first recv_msgs() call doesn't return after its first iteration.
It loops again because msgs is still empty. This is why the recv_msgs call numbers
are 1, 1, and 2.

A multithreaded chat server

So let's put this to use and write our chat server. Make a new file called 2.1-chat_
server-multithread.py and put the following code in it:

import threading, queue

import tincanchat

HOST = tincanchat.HOST

PORT = tincanchat.PORT

send_queues = {}

lock = threading.Lock()

def handle_client_recv(sock, addr):

""" Receive messages from client and broadcast them to

other clients until client disconnects """

rest = bytes()

while True:

try:

(msgs, rest) = tincanchat.recv_msgs(sock, rest)

except (EOFError, ConnectionError):

handle_disconnect(sock, addr)

break