Your job is to modify both the client and server applications as such:

Server. The server should function as an echo server, which means it simply returns to the client exactly the message it receives from the client. In the server code, a call to read$()$ on the socket descriptor copies the received message into a buffer. This modification requires that message be transmitted back to the client with a call to write$()$ on the same socket descriptor. In the server code, include a printf$()$ statement to standard output indicating the message is being transmitted to the client.

Client. After transmitting the message to the server, the client process should then await the reply. To do this, in the client code add a call to read$()$ on the same socket descriptor used to send the message. By default, read$()$ is a blocking system call, so the client process will wait for a response from the server before it continues execution. Once the reply is received, output a statement to standard output indicating the message was received $($and be sure include the message in the output$).$ Add code to ADD YOUR CODE HERE

$------------$server.c$--------------------$

#include

#include

#include

#include

#include

#include

#include

#include

#define DEFAULT$\_$PORT $4433$

#define BUFFER$\_$SIZE $256$

int create$\_$socket$($unsigned int port$)\{$

int s;

struct sockaddr$\_$in addr;

addr.sin$\_$family $=$ AF$\_$INET;

addr.sin$\_$port $=$ htons$($port$)$;

addr.sin$\_$addr.s$\_$addr $=$ htonl$($INADDR$\_$ANY$)$;

s $=$ socket$($AF$\_$INET, SOCK$\_$STREAM, $0)$;

if $($s $<0)\{$

fprintf$($stderr$,$ "Server: Unable to create socket: $\%$s$",$ strerror$($errno$))$;

exit$($EXIT$\_$FAILURE$)$;

$\}$

if $($setsockopt$($s$,$ SOL$\_$SOCKET, SO$\_$REUSEADDR, &$($int$)\{1\},$ sizeof$($int$))<0)$

fprintf$($stderr$,$ "Server: setsockopt$($SO$\_$REUSEADDR$)$ failed: $\%$s$",$ strerror$($errno$))$;

if $($bind$($s$,($struct sockaddr$*)$&addr, sizeof$($addr$))<0)\{$

fprintf$($stderr$,$ "Server: Unable to bind to socket: $\%$s$",$ strerror$($errno$))$;

exit$($EXIT$\_$FAILURE$)$;

$\}$

if $($listen$($s$,1)<0)\{$

fprintf$($stderr$,$ "Server: Unable to listen: $\%$s$",$ strerror$($errno$))$;

exit$($EXIT$\_$FAILURE$)$;

$\}$

printf$("$Server: Listening on TCP port $\%$u

$",$ port$)$;

return s;

$\}$

int main$($int argc, char $*$argv$[])\{$

struct sockaddr$\_$in client$\_$addr;

int listensockfd, clientfd;

unsigned int port;

unsigned int len $=$ sizeof$($client$\_$addr$)$;

char client$\_$addr$\_$str$[$INET$\_$ADDRSTRLEN$]$;

char buffer$[$BUFFER$\_$SIZE$]$;

int nbytes$\_$read;

int nbytes$\_$written;

switch$($argc$)\{$

case $1$:

port $=$ DEFAULT$\_$PORT;

break;

case $2$:

port $=$ atoi$($argv$[1])$;

break;

default:

fprintf$($stderr$,$ "Usage: server $($optional$)$

$")$;

exit$($EXIT$\_$FAILURE$)$;

$\}$

listensockfd $=$ create$\_$socket$($port$)$;

while$($true$)\{$

clientfd $=$ accept$($listensockfd$,($struct sockaddr $*)$ &client$\_$addr, &len$)$;

if $($clientfd $<0)\{$

fprintf$($stderr$,$ "Server: Error accepting TCP connection: $\%$s

$",$

strerror$($errno$))$;

continue;

$\}$ else $\{$

inet$\_$ntop$($AF$\_$INET, $($struct in$\_$addr$*)$ &client$\_$addr.sin$\_$addr,

client$\_$addr$\_$str$,$ INET$\_$ADDRSTRLEN$)$;

printf$("$Server: Established TCP connection with client $(\%$s$)$ on port $\%$u

$",$

client$\_$addr$\_$str$,$ port$)$;

$\}$

bzero$($buffer$,$ BUFFER$\_$SIZE$)$;

nbytes$\_$read $=$ read$($clientfd$,$ buffer, BUFFER$\_$SIZE$)$;

if $($nbytes$\_$read $<0)$

fprintf$($stderr$,$ "Server: Error reading from socket: $\%$s

$",$ strerror$($errno$))$;

else

printf$("$Server: Message received from client: $\backslash "\%$s$\backslash "$

$",$ buffer$)$;

$//*************************************************************$

$//$ ADD YOUR CODE HERE

$//*************************************************************$

printf$("$Server: Terminating TCP connection with client $(\%$s$)$

$",$ client$\_$addr$\_$str$)$;

close$($clientfd$)$;

$\}$

return EXIT$\_$SUCCESS;

$\}$

$------------$client.c$----------------$

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

#define DEFAULT$\_$PORT $4433$

#define MAX$\_$HOSTNAME$\_$LENGTH $256$

#define BUFFER$\_$SIZE $256$

int create$\_$socket$($char$*$ hostname, unsigned int port$)\{$

int sockfd;

struct hostent$*$ host;

struct sockaddr$\_$in dest$\_$addr;

host $=$ gethostbyname$($hostname$)$;

if $($host $==$ NULL$)\{$

fprintf$($stderr$,$ "Client: Cannot resolve hostname $\%$s

$",$ hostname$)$;

exit$($EXIT$\_$FAILURE$)$;

$\}$

sockfd $=$ socket$($AF$\_$INET, SOCK$\_$STREAM, $0)$;

if $($sockfd $<0)\{$

fprintf$($stderr$,$ "Client: Unable to create socket: $\%$s$",$ strerror$($errno$))$;

exit$($EXIT$\_$FAILURE$)$;

$\}$

dest$\_$addr.sin$\_$family$=$AF$\_$INET;

dest$\_$addr.sin$\_$port$=$htons$($port$)$;

dest$\_$addr.sin$\_$addr.s$\_$addr $=*($long$*)($host$->$h$\_$addr$)$;

if $($connect$($sockfd$,($struct sockaddr $*)$ &dest$\_$addr,

sizeof$($struct sockaddr$))<0)\{$

fprintf$($stderr$,$ "Client: Cannot connect to host $\%$s $[\%$s$]$ on port $\%$d: $\%$s

$",$

hostname, inet$\_$