/* http://www.tutorialspoint.com/unix_sockets/socket_server_example.htm


To allow the server to handle multiple simultaneous connections, we make the following
changes in the server.c code:

 - Put the accept statement and the following code in an infinite loop.

 - After a connection is established, call fork() to create a new process.

 - The child process will close sockfd and call doprocessing function, 
   passing the new socket file descriptor as an argument. When the two 
   processes have completed their conversation, as indicated by 
   doprocessing() returning, this process simply exits.

 - The parent process closes newsockfd. Because all of this code is in 
   an infinite loop, it will return to the accept statement to wait for 
   the next connection.
 
*/


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

int main( int argc, char *argv[] )
{
  int sockfd, newsockfd, portno, clilen;
  char buffer[256];
  struct sockaddr_in serv_addr, cli_addr;
  int  n;

  /* First call to socket() function */
  sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (sockfd < 0) 
    {
      perror("ERROR opening socket");
      exit(1);
    }
  /* Initialize socket structure */
  bzero((char *) &serv_addr, sizeof(serv_addr));
  portno = 51001;
  serv_addr.sin_family = AF_INET;
  serv_addr.sin_addr.s_addr = INADDR_ANY;
  serv_addr.sin_port = htons(portno);
 
  /* Now bind the host address using bind() call.*/
  if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
    {
      perror("ERROR on binding");
      exit(1);
    }

  /* Now start listening for the clients, here 
   * process will go in sleep mode and will wait 
   * for the incoming connection
   */

  listen(sockfd,5);
  clilen = sizeof(cli_addr);
  while (1) 
    {
      newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
      if (newsockfd < 0)
        {
	  perror("ERROR on accept");
	  exit(1);
        }
      /* Create child process */
      int pid = fork();
      if (pid < 0)
        {
	  perror("ERROR on fork");
	  exit(1);
        }
      if (pid == 0)  
        {
	  /* This is the client process */
	  close(sockfd);
	  doprocessing(newsockfd);
	  exit(0);
        }
      else
        {
	  close(newsockfd);
        }
    } /* end of while */
}


void doprocessing (int sock)
{
  int n;
  char buffer[256];

  bzero(buffer,256);

  n = read(sock,buffer,255);
  if (n < 0)
    {
      perror("ERROR reading from socket");
      exit(1);
    }
  printf("Here is the message: \n      %20s\n",buffer);
  n = write(sock,"I got your message.\n",21);
  if (n < 0) 
    {
      perror("ERROR writing to socket");
      exit(1);
    }
}