Write two programs called echo$\_$client.py and echo$\_$server.py$,$ respectively. The

echo$\_$client.py aims to connect and send messages to the echo server. The echo server

can echo back the same message back to the client. Partial code of echo$\_$server.py and

echo$\_$client.py are provided in the course blackboard. You can download them from

$3$

the assessment folder to complete the code.

Run echo server using the following command:

$ python$3$ echo$\_$server.py

Where port$\_$number refers to the port number that the echo server will listen to$.$

Run echo client using the following command:

$ python$3$ echo$\_$client.py

Where port$\_$number refers to the server port number that the client will connect to$.$

The echo server will send back the exact message that it receives.

The client will print the returned message to client$$s stdout:

$ python$3$ echo$\_$client.py # run the echo client

Hello World # client sends a message to the server.

$[$Server$]$ Hello World # response from the server.

ECHO$\_$SERVER

import socket

import sys

class EchoServer:

def $\_\_$init$\_\_($self$)$:

self.addr $=$ None

self.port $=$ None

self.socket $=$ None

self.host $="127\mathrm{.}0\mathrm{.}0\mathrm{.}1"$

self.conn $=$ None

def read$\_$port$\_$number$($self$)$:

$"""$

Read the port number from argument, store it to self.port.

Exit with status $1$ if invalid argument is provided.

$"""$

if len$($sys$.$argv$)!=2$:

print$("$Usage: python echo$\_$server.py $")$

sys$.$exit$(1)$

try:

self.port $=$ int$($sys$.$argv$[1])$

except ValueError:

print$("$Invalid port number"$)$

sys$.$exit$(1)$

def listen$\_$on$\_$port$($self$)$:

$"""$

Create a socket listens on the specified port.

Store the socket object to self.socket.

Store the new accepted connection to self.conn.

$"""$

self.socket $=$ socket.socket$($socket$.$AF$\_$INET, socket.SOCK$\_$STREAM$)$

self.socket.bind$(($self$.$host, self.port$))$

self.socket.listen$(1)$

print$($f$"$Listening on port $\{$self$.$port$\}")$

self.conn, addr $=$ self.socket.accept$()$

print$($f$"$Accepted connection from $\{$addr$\}")$

def receive$\_$message$($self$)$:

$"""$

Receive a TCP packet from the client.

:return: the received message

$"""$

try:

data $=$ self.conn.recv$(1024)$

if not data:

print$("$Connection closed by the client"$)$

sys$.$exit$(0)$

return data.decode$()$

except Exception as e:

print$($f$"$Error receiving message: $\{$e$\}")$

return None

def send$\_$message$($self$,$ msg$)$:

$"""$

Send a message back to the client

:param msg: the message to send to the client

:return: None

$"""$

try:

self.conn.sendall$($msg$.$encode$())$

except Exception as e:

print$($f$"$Error sending message: $\{$e$\}")$

def echo$\_$messages$($self$)$:

$"""$

Use a while loop to echo messages back to client

:return: None

$"""$

while True:

try:

data $=$ self.receive$\_$message$()$

if not data:

print$("$Connection closed by the client"$)$

break

print$($f$"$Received message: $\{$data$\}")$

self.send$\_$message$($data$)$ # Send the received message back to the client

except Exception as e:

print$($f$"$Error receiving message: $\{$e$\}")$

break

def run$\_$echo$\_$server$($self$)$:

$"""$

Run the echo server to receive and echo back messages

:return: None

$"""$

self.read$\_$port$\_$number$()$

self.listen$\_$on$\_$port$()$

self.echo$\_$messages$()$

if $\_\_$name$\_\_=="\_\_$main$\_\_"$:

echo$\_$server $=$ EchoServer$()$

echo$\_$server.run$\_$echo$\_$server$()$

ECHO$\_$CLIENT

import socket

import sys

class EchoClient:

def $\_\_$init$\_\_($self$)$:

self.host $="127\mathrm{.}0\mathrm{.}0\mathrm{.}1"$

self.port $=$ None

self.socket $=$ None

def read$\_$port$\_$number$($self$)$:

$"""$

Read the port number from argument, store it to self.port.

Exit if invalid argument is provided.

:return: None

$"""$

if len$($sys$.$argv$)!=2$:

sys$.$exit$(1)$

try:

self.port $=$ int$($sys$.$argv$[1])$

except ValueError:

print$("$Invalid port number"$)$

sys$.$exit$(1)$

def connect$\_$to$\_$port$($self$)$:

$"""$

Create a socket to try to connect to a specified port,

store the new socket object to self.socket.

:return: None

$"""$

self.socket $=$ socket.socket$($socket$.$AF$\_$INET, socket.SOCK$\_$STREAM$)$

try:

self.socket.connect$(($self$.$host, self.port$))$

except Exception as e:

print$($f$"$Error connecting to server: $\{$e$\}")$

sys$.$exit$(1)$

def receive$\_$and$\_$print$\_$message$($self$)$:

$"""$

Receive a TCP packet from the server and print