#include <sys/types.h>   /*******  Demo of One-Shot TCP  *******/
#include <sys/socket.h>  /*******  Client/Server.        *******/
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>

int active;
main()
{
     struct hostent *hptr;
     struct sockaddr_in sin; 
     char s[256];
     int readn(int active, char *buf, int bufsize);
   
     active = socket(AF_INET, SOCK_STREAM, 0);  /**  Test return for -1!  **/
     memset(&sin, 0, sizeof(struct sockaddr_in));
     sin.sin_port = htons(4444); 
     sin.sin_family = AF_INET;
     sin.sin_addr.s_addr = inet_addr("153.18.17.11");

     if (connect(active, (struct sockaddr *)&sin, sizeof(sin)) == -1)
     {
        perror("Bad connection.");
        exit(1);
     }

     printf("Enter string: ");
     memset(s, 0, 256);
     fgets(s, 256, stdin);
     writen(active,s,256); 

     memset(s, 0, 256);
     readn(active,s,256);
     printf("From server: %s\n", s);
     close(active);
}



int readn(int fd, char *buf, int bytes)
{
     int nleft;
     int nread;
     char *mover = buf;

     nleft = bytes;
     while (nleft > 0){
         if ((nread = read(fd,mover,nleft)) < 0)
              return -1;  /**** Error!! ****/
         else if (nread == 0)
              break;      /****  EOF!   ****/
         nleft -= nread;
         mover += nread;
     }
     return (bytes - nleft);
} 
int writen(int fd, char *buf, int bytes)
{
     int nleft;
     int nwritten;
     char *mover = buf;

     nleft = bytes;
     while (nleft > 0){
         if ((nwritten = write(fd,mover,nleft)) < 0)
              return -1;  /**** Error!! ****/
         nleft -= nwritten;
         mover += nwritten;
     }
     return bytes;
}



#define MAXBUF 256    /**********  This is the server.  *********/
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
int active;
main()
{
      struct hostent *hptr;
      int passive, addr_len, n, status;
      char buf[256];
      struct sockaddr_in sin, client; 
      int readn(int active, char *buffer, int buffer_size);
      int writen(int active, char *buffer, int buffer_size);
    
      passive = socket(AF_INET, SOCK_STREAM, 0);
      memset(&sin, 0, sizeof(sin));
      sin.sin_port = htons(4444); 
      sin.sin_family = AF_INET;
      sin.sin_addr.s_addr = htonl(INADDR_ANY);

      if (bind(passive, (struct sockaddr *)&sin, sizeof(sin)) == -1)
      {
        perror("Binding error!");
        exit(1);
      }

      if (listen(passive, 1) < 0)
      {
        perror("Listen error!");
        exit(1);
      }

      addr_len = sizeof(struct sockaddr_in);
      if ((active = accept(passive, (struct sockaddr *)&client, &addr_len)) < 0)
      {
          perror("Accept error!");
          exit(1);
      }

      memset(buf, 0, 256);
      n = readn(active, buf, 256);
      printf("From client: %s\n\n", buf);
      writen(active, buf, 256) ;
}




int readn(int fd, char *buf, int bytes)
{
     int nleft;
     int nread;
     char *mover = buf;

     nleft = bytes;
     while (nleft > 0){
         if ((nread = read(fd,mover,nleft)) < 0)
              return -1;  /**** Error!! ****/
         else if (nread == 0)
              break;      /****  EOF!   ****/
         nleft -= nread;
         mover += nread;
     }
     return (bytes - nleft);
}


int writen(int fd, char *buf, int bytes)
{
     int nleft;
     int nwritten;
     char *mover = buf;

     nleft = bytes;
     while (nleft > 0){
         if ((nwritten = write(fd,mover,nleft)) < 0)
              return -1;  /**** Error!! ****/
         nleft -= nwritten;
         mover += nwritten;
     }
     return bytes;
}
/*******************************  Output Below  ***************************/

$ s&
[1]     21447
$ c
Enter string: hello
From client: hello

From server: hello