// File: prg6_1.c
	#include <stdio.h>          /* These are the usual header files */ 
	#include <strings.h>          /* for bzero() */
	#include <unistd.h>         /* for close() */
	#include <sys/types.h> 
	#include <sys/socket.h> 
	#include <netinet/in.h> 
	#include <arpa/inet.h>

	#define PORT 1234   /* Port that will be opened */ 
	#define BACKLOG 5   /* Number of allowed connections */ 
	#define MAXDATASIZE 1000  

	void process_cli(int connectfd, sockaddr_in client);

	main() 
	{ 
	int listenfd, connectfd; /* socket descriptors */ 
	struct sockaddr_in server; /* server's address information */ 
	struct sockaddr_in client; /* client's address information */ 
	int sin_size; 

	/* Create TCP socket  */
	if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)  {
	   /* handle exception */
	   perror("Creating socket failed.");
	   exit(1);
	   }

	int opt = SO_REUSEADDR;
	setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

	bzero(&server,sizeof(server));
	server.sin_family=AF_INET; 
	server.sin_port=htons(PORT); 
	server.sin_addr.s_addr = htonl (INADDR_ANY); 
	if (bind(listenfd, (struct sockaddr *)&server, sizeof(struct sockaddr)) == -1) { 
	   /* handle exception */
	   perror("Bind error.");
	   exit(1); 
	   }    

	if(listen(listenfd,BACKLOG) == -1){  /* calls listen() */ 
	   perror("listen() error\n"); 
	   exit(1); 
	  } 

	sin_size=sizeof(struct sockaddr_in); 
	while (1) {
	   if ((connectfd = accept(listenfd,(struct sockaddr *)&client,&sin_size))==-1) {
	      perror("accept() error\n"); 
	      exit(1); 
	      }   
	   process_cli(connectfd, client);
	}

	close(listenfd);   /* close listenfd */         
	} 

	void process_cli(int connectfd, sockaddr_in client)
	{
	int num;
	char recvbuf[MAXDATASIZE], sendbuf[MAXDATASIZE];

	printf("You got a connection from %s\n",inet_ntoa(client.sin_addr) ); /* prints client's IP */ 

	while (num = recv(connectfd, recvbuf, MAXDATASIZE,0)) {
	   recvbuf[num] = '\0';
	   printf("Received client message: %s",recvbuf);

	   for (int i = 0; i < num - 1; i++) {
	      sendbuf[i] = recvbuf[num - i -2];
	      }
	   sendbuf[num - 1] = '\0';

	   send(connectfd,sendbuf,strlen(sendbuf),0); /* send to the client welcome message */ 
	   }

	close(connectfd); /*  close connectfd */ 
}