/* 
 * COSC 6377 Sample Code #4 - How to execute filter - a pipe example
 *
 * This program is an example to demonstrate the use of pipe.
 * There are two processes in this program, the child process
 * calls "execve" to execute an external program; the father 
 * process read input from stdin, copy it to the child process 
 * via a pipe, read output of the child process via another
 * pipe and print out output of the child process to stdout. 
 * Actually, this program does nothing, just an encapsulatiaon
 * of the child process. For more information, refer to pipe (2),
 * "man -s2 pipe".
 *
 * To compile: 	g++ -o pipe_test pipe.cc
 * To test:  	pipe_test /bin/cat
 *
 * -- C. T.
 */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

int main (int argc, char **argv)
{
    int childpid, pipe1[2], pipe2[2];
    char buf[256];

    if (argc != 2) {
	printf ("Usuage: %s command\n", argv[0]);
	exit (1);
    }

    // create 2 pipe, data flow:
    // father process =pipe1=> child process =pipe2=> father process
    if (pipe (pipe1) < 0 || pipe (pipe2) < 0) {
	perror ("pipe error");
	return 1;
    }
    if ((childpid = fork ()) < 0) {
	perror ("fork error");
	return 1;
    }
    else if (childpid > 0)	// father
    {
	close (pipe1[0]);	// father don't need these fds.
	close (pipe2[1]);

	while (!feof (stdin)) {
	    fgets (buf, 255, stdin);			// read from stdin
	    buf[strlen(buf)-1] = 0;
	    strcat (buf, " -- Garbled by father\n");	// garble the string
	    write (pipe1[1], buf, strlen (buf));	// write to child

	    read (pipe2[0], buf, 255);	// read from child - should get garbled string
	    puts (buf);			// write to stdout
	}
	close (pipe1[1]);
	close (pipe2[0]);
    }
    else			// child
    {
	char *chd_argv[2];

	close (pipe1[1]);	// child don't need these fds.
	close (pipe2[0]);

	close (0);
	dup (pipe1[0]);		// redirect child's stdin to pipe1

	close (1);
	dup (pipe2[1]);		// redirect child's stdout to pipe2

	chd_argv[0]=argv[1];
	chd_argv[1]=0;
	// if you use execve, you have to fill in chd_argv to
	// supply the argumets for the command.
	// execve(argv[1], chd_argv, NULL); // exececute argv[1]
	
	// if you use system, argument is parsed by shell
	// automatically.
	system(argv[1]);

	close (pipe1[0]);
	close (pipe2[1]);
    }

    return 0;
}