//-------------------------------------------------------------------
//	pingpipe.cpp
//
//	This program shows how the 'pipe()' system-call can be used 
//	to transfer information from a child-process to its parent.
//	Here the hostname for some computer on the local network is
//	typed as a command-line argument, and this application then
//	will respond by displaying that computer's IP-address.  
//
//	      compile using:  $ g++ pingpipe.cpp -o pingpipe
//	      execute using:  $ ./pingpipe <hostname>
//
//	programmer: ALLAN CRUSE
//	written on: 12 MAR 2008
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write(), close() 
#include <string.h>	// for strchr()
#include <wait.h>	// for waitpid()

char *args[4] = { "/bin/ping", "-c1", };   

int main( int argc, char **argv, char **envp )
{
	if ( argc == 1 )	// command-line argument is needed 
		{
		fprintf( stderr, "usage: pingpipe <hostname> \n" );
		exit(1);
		}
	else	args[ 2 ] = argv[1];	// finish the args[] setup 

	// create a 'pipe' for child-to-parent communication
	int	fd[ 2 ];
	pipe( fd );
	if ( fork() == 0 )
		{
		close( fd[0] );	// child closes the pipe's 'read' end	
		close( STDOUT_FILENO );		// standard output is
		dup2( fd[1], STDOUT_FILENO );	// written to the pipe
		execve( args[0], args, envp );	// child executes 'ping' 
		perror( "execve" );		
		exit(1);
		}

	close( fd[1] );		// parent closes the pipe's 'write' end	
	waitpid( 0, NULL, 0 );	// then parent waits until child quits

	char	info[ 80 ] = {0};	// buffer for data read from pipe
	int	nbytes = read( fd[0], info, 79 );	// read from pipe
	if ( nbytes < 0 ) { perror( "read" ); exit(1); }

	// extract the IP-address for the specified host
	char 	*p = strchr( info, '(' );	// where IP-address starts
	char	*q = strchr( info, ')' );	// where IP-address ends
	printf( "\nIP-address for \'%s\' is ", argv[1] );
	for (int i = 1; i < q-p; i++) printf( "%c", p[i] ); 
	printf( "\n\n" );
}