/************************************************************************/
/*   PROGRAM NAME: server2.c  (works with client.c)                     */
/*                                                                      */
/*   Server creates a socket to listen for the connection from Client   */
/*   When the communication established, Server echoes data from Client */
/*   and writes them back.                                              */
/*                                                                      */
/*   Using socket() to create an endpoint for communication. It         */
/*   returns socket descriptor. Stream socket (SOCK_STREAM) is used here*/
/*   as opposed to a Datagram Socket (SOCK_DGRAM)                       */  
/*   Using bind() to bind/assign a name to an unnamed socket.           */
/*   Using listen() to listen for connections on a socket.              */
/*   Using accept() to accept a connection on a socket. It returns      */
/*   the descriptor for the accepted socket.                            */
/*                                                                      */
/*   To run this program, first compile the server_ex.c and run it      */
/*   on a server machine. Then run the client program on another        */
/*   machine.                                                           */
/*                                                                      */
/*   LINUX:      gcc -o server  server2.c -lnsl                         */
/*                                                                      */
/************************************************************************/


#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>  /* define socket */
#include <netinet/in.h>  /* define internet socket */
#include <netdb.h>       /* define internet socket */

#define SERVER_PORT 9999        /* define a server port number */

int main()
{
    int sd, ns, k, pid;
    struct sockaddr_in server_addr = { AF_INET, htons( SERVER_PORT ) };
    struct sockaddr_in client_addr = { AF_INET };
    int client_len = sizeof( client_addr );
    char buf[512], *host;

    /* create a stream socket */
    if( ( sd = socket( AF_INET, SOCK_STREAM, 0 ) ) == -1 )
    {
	perror( "server: socket failed" );
	exit( 1 );
    }
    
    /* bind the socket to an internet port */
    if( bind(sd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1 )
    {
	perror( "server: bind failed" );
	exit( 1 );
    }

    /* listen for clients */
    if( listen( sd, 1 ) == -1 )
    {
	perror( "server: listen failed" );
	exit( 1 );
    }

    printf("SERVER is listening for clients to establish a connection\n");

   if ( (pid=fork()) == 0 ){  /* child code begins */

    if( ( ns = accept( sd, (struct sockaddr*)&client_addr,
                       &client_len ) ) == -1 )
    {
        perror( "server: accept failed" );
        exit( 1 );
    }

    printf("Child accept() successful.. a client has connected to child ! waiting for a message\n");

    /* data transfer on connected socket ns */
    while( (k = read(ns, buf, sizeof(buf))) != 0)
    {    printf("SERVER(Child) RECEIVED: %s\n", buf);
         write(ns, buf, k);
    }
    close(ns);
    close(sd);
    }
    else {   /* Parent code */
    if( ( ns = accept( sd, (struct sockaddr*)&client_addr,
                       &client_len ) ) == -1 )
    {
        perror( "server: accept failed" );
        exit( 1 );
    }

    printf("Parent accept() successful.. a client has connected to Parent! waiting for a message\n");

    /* data transfer on connected socket ns */
    while( (k = read(ns, buf, sizeof(buf))) != 0)
    {    printf("SERVER(Parent) RECEIVED: %s\n", buf);
         write(ns, buf, k);
    }
    close(ns);
    close(sd);
    }


    unlink(server_addr.sin_addr);

    return(0);
}