2. Project Description UChat is a chat application that allows one single chat s

Question

2. Project Description UChat is a chat application that allows one single chat server (called UChatServer.py) serves multiple chat clients (called UChatClient.py)simultaneously. In particular, connected clients can: list the members already logged in, log in with a username, exchange messages with other logged in users, and log out. The chat server can accept and maintain connections to all the clients and relay chat messages between them. 2.1 The Chat Client The chat client application has to do the following tasks: 1. Connect to a chat server. The client obtains the server IP address and the port it is listening on from commandline arguments. For example: > ./UChatClient.py 128.32.48.187 10000 Then, the client immediately attempts to connect to the server socket using TCP. If it fails, the client application prints an error message to the console and returns. To print the error message, the client must give the name of the socket function that failed in lowercase. If, on the other hand, the connection succeeds, the client continues to step 2. 2. Accept console text commands from the user. The client must be able to handle the following commands. Parameters are enclosed in <>: a. login b. list c. sendto d. logout e. exit Each line must begin with a command. The parameters (if any) are separated by a space. The commands and parameters are described in more detail below. In order to implement these commands correctly, thclient will have to send and receive the following messages to/from the server: a. Send messages to the server. The client must be able to send the following messages to the server. These messages are described in detail in section 4 of the document: i. Login Message ii. List Messageiii. Sendto Message iv. Logout Message b. Accept incoming messages from the server. The client must be able to properly react to the following messages. These messages are shown in section 5 of the document: i. List Message ii. Response Message iii. Sendto Message

Explanation / Answer

Server:

import socket, select

#Function to broadcast chat messages to all connected clients
def broadcast_data (sock, message):
#Do not send the message to master socket and the client who has send us the message
for socket in CONNECTION_LIST:
if socket != server_socket and socket != sock :
try :
socket.send(message)
except :
# broken socket connection may be, chat client pressed ctrl+c for example
socket.close()
CONNECTION_LIST.remove(socket)

if __name__ == "__main__":

# List to keep track of socket descriptors
CONNECTION_LIST = []
RECV_BUFFER = 4096 # Advisable to keep it as an exponent of 2
PORT = 5000

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# this has no effect, why ?
server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
server_socket.bind(("0.0.0.0", PORT))
server_socket.listen(10)

# Add server socket to the list of readable connections
CONNECTION_LIST.append(server_socket)

print "Chat server started on port " + str(PORT)

while 1:
# Get the list sockets which are ready to be read through select
read_sockets,write_sockets,error_sockets = select.select(CONNECTION_LIST,[],[])

for sock in read_sockets:
#New connection
if sock == server_socket:
# Handle the case in which there is a new connection recieved through server_socket
sockfd, addr = server_socket.accept()
CONNECTION_LIST.append(sockfd)
print "Client (%s, %s) connected" % addr

broadcast_data(sockfd, "[%s:%s] entered room " % addr)

#Some incoming message from a client
else:
# Data recieved from client, process it
try:
#In Windows, sometimes when a TCP program closes abruptly,
# a "Connection reset by peer" exception will be thrown
data = sock.recv(RECV_BUFFER)
if data:
broadcast_data(sock, " " + '<' + str(sock.getpeername()) + '> ' + data)

except:
broadcast_data(sock, "Client (%s, %s) is offline" % addr)
print "Client (%s, %s) is offline" % addr
sock.close()
CONNECTION_LIST.remove(sock)
continue

server_socket.close()

Run the server in a console.

Client:

# telnet program example
import socket, select, string, sys

def prompt() :
sys.stdout.write('<You> ')
sys.stdout.flush()

#main function
if __name__ == "__main__":

if(len(sys.argv) < 3) :
print 'Usage : python telnet.py hostname port'
sys.exit()

host = sys.argv[1]
port = int(sys.argv[2])

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(2)

# connect to remote host
try :
s.connect((host, port))
except :
print 'Unable to connect'
sys.exit()

print 'Connected to remote host. Start sending messages'
prompt()

while 1:
socket_list = [sys.stdin, s]

# Get the list sockets which are readable
read_sockets, write_sockets, error_sockets = select.select(socket_list , [], [])

for sock in read_sockets:
#incoming message from remote server
if sock == s:
data = sock.recv(4096)
if not data :
print ' Disconnected from chat server'
sys.exit()
else :
#print data
sys.stdout.write(data)
prompt()

#user entered a message
else :
msg = sys.stdin.readline()
s.send(msg)
prompt()
  

Run the client from multiple consoles.

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