#include <stdio.h>		/* Basic I/O routines 		*/
#include <sys/types.h>		/* standard system types	*/
#include <netinet/in.h>		/* Internet address structures  */
#include <sys/socket.h>		/* socket interface functions   */
#include <netdb.h>		/* host to IP resolution 	*/

#define	PORT		"5050"	/* port of "hello world" server */
#define	LINE	"hello world"	/* what to say to our clients  */

void main()
{
    int			rc;       /* system calls return value storage  */
    int			s;        /* socket descriptor                  */
    int			cs;       /* new connection's socket descriptor */
    struct sockaddr_in	sa;       /* Internet address struct            */
    struct sockaddr_in	csa;      /* client's address struct            */
    int               	size_csa; /* size of client's address struct    */

    /* initiate machine's Internet address structure */
    /* first clear out the struct, to avoid garbage  */
    memset(&sa, 0, sizeof(sa));
    /* Using Internet address family */
    sa.sin_family = AF_INET;
    /* copy port number in network byte order */
    sa.sin_port = htons(PORT);
    /* we will accept cnnections coming through any IP	*/
    /* address that belongs to our host, using the	*/
    /* INADDR_ANY wild-card.				*/
    sa.sin_addr.s_addr = INADDR_ANY;

    /* allocate a free socket                 */
    /* Internet address family, Stream socket */
    s = socket(AF_INET, SOCK_STREAM, 0);
    if (s < 0) {
	perror("socket: allocation failed");
    }

    /* bind the socket to the newly formed address */
    rc = bind(s, (struct sockaddr *)&sa, sizeof(sa));

    /* check there was no error */
    if (rc) {
	perror("bind");
    }

    /* ask the system to listen for incoming connections	*/
    /* to the address we just bound. specify that up to		*/
    /* 5 pending connection requests will be queued by the	*/
    /* system, if we are not directly awaiting them using	*/
    /* the accept() system cal, when they arrive.		*/
    rc = listen(s, 5);

    /* check there was no error */
    if (rc) {
	perror("listen");
    }

    /* remember size for later usage */
    size_csa = sizeof(csa);
    /* enter an accept-write-close infinite loop */
    while (1) {
       	/* the accept() system call will wait for a	*/
       	/* connection, and when one is established, a	*/
       	/* new socket will be created to form it, and	*/
       	/* the csa variable will hold the address	*/
       	/* of the Client that just connected to us.	*/
       	/* the old socket, s, will still be available	*/
       	/* for future accept() statements.		*/
       	cs = accept(s, (struct sockaddr *)&csa, &size_csa);

       	/* check for errors. if any, enter accept mode again */
       	if (cs < 0)
    	    continue;

	/* ok, we got a new connection. do the job... */
	write(cs, LINE, sizeof(LINE));

	/* now close the connection */
	close(cs);
    }
}