#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>

#define DATA1 "In Xanadu, did Kublai Khan . . ."
#define DATA2 "A stately pleasure dome decree . . ."

/*
 * This program creates a pair of connected sockets then forks and
 * communicates over them. This is very similar to communication with pipes,
 * however, socketpairs are two-way communications objects. Therefore I can
 * send messages in both directions.
 */

main() 
{
     int sockets[2], child;
     char buf[1024];

     if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets) < 0) {
          perror("opening stream socket pair");
          exit(1);
     }

     if ((child = fork()) == -1)
          perror("fork");
     else if (child) { /* This is the parent. */
          close(sockets[0]);
          if (read(sockets[1], buf, 1024, 0) < 0)
               perror("reading stream message");
          printf("-->%s\n", buf);
          if (write(sockets[1], DATA2, sizeof(DATA2)) < 0)
               perror("writing stream message");
          close(sockets[1]);
     } else {          /* This is the child. */
          close(sockets[1]);
          if (write(sockets[0], DATA1, sizeof(DATA1)) < 0)
               perror("writing stream message");
          if (read(sockets[0], buf, 1024, 0) < 0)
               perror("reading stream message");
          printf("-->%s\n", buf);
          close(sockets[0]);
     }
}