Question

For Unix in a C/C++ environment

echoServer and echoClient are provided below

In this lab, we will modifiy echoServer.c and echoClient.c programs (for the server's port# not fixed).

(1) Modify echoServer.c program to take one argument (a port number) to be used for its listening port when it starts.

(2) Modify echoClient.c program to take two arguments (server's IP address and Port number) to be used for its connection.

(3) Find a port free for the server using netstat (see Week12 Activity)

    ** For example, to find a port (between 30000 and 30999) which is not available, with netstat command.

    netstat -aont | grep "`hostnname -i`:30[0-9][0-9][0-9] "

      Note: the back-tick (backward single quotation mark to run the command on the run).

(4) Compile and run the server with the port of your choice (from 3).

(5) Compile and run the client with the IP and port# of the server

(6) Show the client sending a text to be echoed back by the server.

(7) After a few successful trials, kill the server and the client.

echoServer.c

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>

#define MAXLINE 4096 /*max text line length*/
#define SERV_PORT 3000 /*port*/
#define LISTENQ 8 /*maximum number of client connections */

int main (int argc, char **argv)
{
int listenfd, connfd, n;
socklen_t clilen;
char buf[MAXLINE];
struct sockaddr_in cliaddr, servaddr;
  
//creation of the socket
listenfd = socket (AF_INET, SOCK_STREAM, 0);
  
//preparation of the socket address
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(SERV_PORT);
  
bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr));
  
listen(listenfd, LISTENQ);
  
printf("%s\n","Server running...waiting for connections.");
  
for ( ; ; ) {
      
clilen = sizeof(cliaddr);
connfd = accept(listenfd, (struct sockaddr *) &cliaddr, &clilen);
printf("%s\n","Received request...");
              
while ( (n = recv(connfd, buf, MAXLINE,0)) > 0) {
printf("%s","String received from and resent to the client:");
puts(buf);
send(connfd, buf, n, 0);
}
          
if (n < 0) {
perror("Read error");
exit(1);
}
close(connfd);
  
}
//close listening socket
close(listenfd);
}

echoClient.c

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <arpa/inet.h>

#define MAXLINE 4096 /*max text line length*/
#define SERV_PORT 3000 /*port*/

int
main(int argc, char **argv)
{
int sockfd;
struct sockaddr_in servaddr;
char sendline[MAXLINE], recvline[MAXLINE];
  
//basic check of the arguments
//additional checks can be inserted
if (argc !=2) {
perror("Usage: TCPClient <IP address of the server");
exit(1);
}
  
//Create a socket for the client
//If sockfd<0 there was an error in the creation of the socket
if ((sockfd = socket (AF_INET, SOCK_STREAM, 0)) <0) {
perror("Problem in creating the socket");
exit(2);
}
  
//Creation of the socket
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr= inet_addr(argv[1]);
servaddr.sin_port = htons(SERV_PORT); //convert to big-endian order
  
//Connection of the client to the socket
if (connect(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr))<0) {
perror("Problem in connecting to the server");
exit(3);
}
  
while (fgets(sendline, MAXLINE, stdin) != NULL) {
  
send(sockfd, sendline, strlen(sendline), 0);
      
if (recv(sockfd, recvline, MAXLINE,0) == 0){
//error: server terminated prematurely
perror("The server terminated prematurely");
exit(4);
}
printf("%s", "String received from the server: ");
fputs(recvline, stdout);
}

exit(0);
}

Answer 1

// TCP Echo Server--tcpechoserver.java import java.net.*; import java.io.*; public class tcpechoserver public static void main(String[] arg)throws IOException ServerSocket sock - null; BufferedReader fromClient null; OutputStreamWriter toclient - null; Socket client - null; try sock = new ServerSocket (4000); System.out.println("Server Ready"); client - sock.accept(); System.out.println("Client Connected") fromClient - new BufferedReader(new InputStreamReader (client.getInputStream())); toclient new OutputStreamwriter (client.getOutputStream()); String 1line; while(true) line - fromClient.readLine(); if((line l) 11 line.equals ("bye")) break; System.out.println ("Client [ " line""); toClient.write("Server [ "+ line"n"); toClient.flush); fromClient.close(); toClient.close(); client.close(); sock.close(); System.out.println("Client Disconnected"); catch (IOException ioe) System.err.print1n(ioe) ;

//TCP Echo Client--tcpechoclient.java import java.net.*; import java.io.*; public class tcpechoclient public static void main(String[] args)throws IOException BufferedReader fromServer - null, fromUser - null; PrintWriter toServer null Socket sock - null; if (args.length -- 8) new Socket (InetAddress. get LocalHost() ,4000); sock else = sock- new Socket (InetAddress.getByName (args[e1),4000); fromServer new BufferedReader (new InputStreamReader(sock.getInputStream())); fromUser - new BufferedReader (new InputstreamReader(System.in)); toServer new Printwriter(sock.getOutputStream(),true); String Usrmsg, Srvmsg; System.out.println("Type \"bye\" to quit"); while (true) System.out.print("Enter msg to server "); Usrmsg -fromUser.readLine(); if (Usrmsgnull|I Usrmsg.equals ("bye")) toServer.println("bye"); break; else toServer.println(Usrmsg); Srvmsg fromServer. readLine(); System.out.println(Srvmsg); fromUser.close(); fromServer.close(); toServer.close(); sock.close();

catch (IOException ioe) System.err.println(ioe); OUTPUT Server $ javac tcpechoserver.java $ java tcpechoserver Server Ready Client Connected Client [ hello] Client [ how are you ] Client [ i am fine ] Client [ ok ] Client Disconnected Client : $ javac tcpechoclient.java $ java tcpechoclient Type "bye" to quit Enter msg to server: hello Server [ hello ] Enter msg to server: how are you Server [ how are you ] Enter msg to server i am fine Server [ i am fine ] Enter msg to server ok Server [ ok ] Enter msg to server: bye