//-------------------------------------------------------------------
//	tweakttl.cpp
//
//	This program utilizes an Internet Protocol socket-option to
//	adjust the 'Time-to-Live' field in an outgoing UDP message.
//
//	    compile using:  $ g++ tweakttl.cpp -o tweakttl
//	    execute using:  $ ./tweakttl <hostname> <port> <ttl>
//
//	programmer: ALLAN CRUSE
//	written on: 10 FEB 2009
//-------------------------------------------------------------------


#include <netdb.h>	// for gethostbyname()
#include <stdio.h>	// for printf(), perror() 
#include <stdlib.h>	// for exit() 
#include <string.h>	// for strncpy()
#include <arpa/inet.h>	// for inet_ntoa()


int main( int argc, char **argv )
{
	//-----------------------------------------------
	// check for the required command-line arguments
	//----------------------------------------------- 
	if ( argc < 4 ) 
		{
		printf( "usage: %s <hostname> <port> <ttl> \n", argv[0] );
		exit(1);
		}

	//----------------------------------------------
	// get the hostname for the destination station
	//---------------------------------------------- 
	char	peername[ 64 ] = {0}; 
	strncpy( peername, argv[ 1 ], 63 );

	//-------------------------------------------
	// get the port-number for the socket to use 
	//-------------------------------------------
	unsigned short	port = atoi( argv[ 2 ] );

	//------------------------------------------
	// get the value for the Time-to-Live field
	//------------------------------------------ 
	unsigned char	ttl = atoi( argv[ 3 ] );
	int		len = sizeof( ttl );

	//-------------------------------------
	// get the peer's IPv4 network address
	//------------------------------------- 
	char	peeraddr[ 16 ] = {0};
	struct hostent	*pp = gethostbyname( peername );
	if ( !pp ) { herror( "gethostbyname" ); exit(1); }
	strcpy( peeraddr, inet_ntoa( *(in_addr*)pp->h_addr ) );
	
	//----------------------------------------------------
	// initialize an internet socket-address for the peer 
	//---------------------------------------------------- 
	struct sockaddr_in	paddr;
	socklen_t		palen = sizeof( paddr );
	bzero( &paddr, palen );
	paddr.sin_family 	= AF_INET;
	paddr.sin_port 		= htons( port );
	paddr.sin_addr.s_addr 	= *(uint32_t*)pp->h_addr;

	//------------------------------------------------------
	// ask the kernel to create an internet datagram socket
	//------------------------------------------------------ 
	int	sock = socket( AF_INET, SOCK_DGRAM, IPPROTO_IP );
	if ( sock < 0 ) { perror( "socket" ); exit(1); }	

	//-----------------------------------------------------
	// set the value of this socket's 'Time-to-Live' field 
	//-----------------------------------------------------
	if ( setsockopt( sock, SOL_IP, IP_TTL, &ttl, len ) < 0 )
		{ perror( "setsockopt TTL" ); exit(1); }

	//---------------------------------------------
	// create the message-string to be transmitted
	//--------------------------------------------- 
	char	msg[] = " ABCDEFGHIJKLMNOPQRSTUVWXYZ 1234567890 *";
	int	mlen = strlen( msg );

	//--------------------------------------------------
	// try to send this message to the destination host 
	//-------------------------------------------------- 
	int	tx = sendto( sock, msg, mlen, 0, (sockaddr*)&paddr, palen ); 
	if ( tx < 0 ) { perror( "sendto" ); exit(1); }

	printf( " sent %d bytes toward port %d", tx, port );
	printf( " on \'%s\' (%s)", peername, peeraddr );
	printf( " with TTL=%u \n", ttl );	
}