//-------------------------------------------------------------------
//	sendback.cpp
//
//	This program receives packets from the network interface and 
//	returns any whose protocol-type it recognizes to the sender. 
//
//	programmer: ALLAN CRUSE
//	written on: 01 MAY 2005
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write() 
#include <string.h>	// for memcpy()
#include <netdb.h>	// for htons()
#include <sys/ioctl.h>	// ioctl()

#define MY_TYPE	0x0635	// our protocol type-identifier

char nicname[] = "/dev/nic";
unsigned char nicaddr[6];

int main( int argc, char **argv )
{
	// open device-file and get hardware-address
	int	nic = open( nicname, O_RDWR );
	if ( nic < 0 ) { perror( nicname ); exit(1); }
	if ( ioctl( nic, 0, &nicaddr ) < 0 ) { perror( "ioctl" ); exit(1); }

	// show the station-name and hardware-address 
	char	hostname[ 64 ] = {0};
	gethostname( hostname, 64 );
	printf( "\n\tstation-hostname: %s ", hostname );
	printf( "\n\thardware-address: " );
	for (int i = 0; i < 6; i++)
		{
		printf( "%02X", nicaddr[i] );
		if ( i < 5 ) printf( ":" ); else printf( " " );	
		}
	printf( "\n\nPress <CONTROL>-C to terminate...\n" );

	unsigned char	packet[4096] = {0};
	for(;;)	{	
		int	nbytes = read( nic, packet, sizeof( packet ) );
		if ( nbytes < 0 ) continue;
		if ( *(short*)(packet+12) == ntohs( MY_TYPE ) )
			{
			memcpy( packet+0, packet+6, 6 );
			memcpy( packet+6, nicaddr, 6 );
			nbytes = write( nic, packet, nbytes );
			}
	    	}
}