//-------------------------------------------------------------------
//	triptime.cpp
//
//	This example demonstrates use of Linux's 'timestamp' socket
//	option to obtain a measurement of the round-trip time taken
//	by a small network packet sent to an echo-server running on 
//	a remote host and then returned to this client application.
//	It shows how to access the 'ancillary data' returned by the
//	'recvmsg()' function in an architecture-independent manner.
//	(You can test this program using our 'msgserver.cpp' demo.)
//
//	     compile using:  $ g++ triptime.cpp -o triptime
//	     execute using:  $ ./triptime <target> <port>
//
//	NOTE: This timestamp socket option provided by Linux should 
//	not be confused with timestamp request/reply ICMP messages.  
//
//	programmer: ALLAN CRUSE
//	written on: 15 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()
#include <sys/time.h>	// for gettimeofday()



int main( int argc, char **argv )
{
	//---------------------------------------------------------
	// check for the required number of command-line arguments 
	//---------------------------------------------------------
	if ( argc < 3 ) 
		{ 
		fprintf( stderr, "usage: ./triptime <target> <port> \n" );
		exit(1);
		} 

	//---------------------------------------------------------------
	// get the target hostname and port-number from the command-line
	//---------------------------------------------------------------
	char	peername[ 64 ] = { 0 };
	int	port = atoi( argv[2] );
	strncpy( peername, argv[1], 63 );
	
	//-------------------------------------------------
	// obtain the internet address for the remote host
	//-------------------------------------------------
	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 a socket-address object for the remote host
	//--------------------------------------------------------
	struct sockaddr_in	paddr = { 0 };
	socklen_t		palen = sizeof( paddr );
	paddr.sin_family	= AF_INET;
	paddr.sin_port		= htons( port );
	paddr.sin_addr.s_addr	= *(uint32_t*)pp->h_addr;

	//----------------------------------
	// open an internet datagram socket
	//----------------------------------
	int	sock = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
	if ( sock < 0 ) { perror( "socket" ); exit(1); }

	//-------------------------------------
	// set a timeout for receiving replies
	//-------------------------------------
	struct timeval	myto = { 5, 0 };
	int		tlen = sizeof( myto );
	if ( setsockopt( sock, SOL_SOCKET, SO_RCVTIMEO, &myto, tlen ) < 0 )
		{ perror( "setsockopt RCVTIMEO" ); exit(1); }

	//---------------------------------------
	// enable the SO_TIMESTAMP socket-option
	//---------------------------------------
	int	oval = 1;
	int	olen = sizeof( oval );
	if ( setsockopt( sock, SOL_SOCKET, SO_TIMESTAMP, &oval, olen ) < 0 )
		{ perror( "setsockopt TIMESTAMP"); exit(1); }

	//-----------------------------------------------------
	// initialize objects for our measage-header structure
	//-----------------------------------------------------
	char	msg[] = " ABCDEFGHIJKLMNOPQRSTUVWXYZ 1234567890 =";
	char	buf[] = "----------------------------------------";
	int	len = strlen( msg );

	struct iovec	myiov[1] = { { msg, len } };

	unsigned char	cbuf[ 40 ] = { 0 };
	int		clen = sizeof( cbuf ); 

	//-----------------------------------------
	// initialize our message-header structure
	//-----------------------------------------
	struct msghdr	mymsghdr = { 0 };
	mymsghdr.msg_name	= &paddr;
	mymsghdr.msg_namelen	= palen;
	mymsghdr.msg_iov	= myiov;
	mymsghdr.msg_iovlen	= 1;
	mymsghdr.msg_control	= NULL;
	mymsghdr.msg_controllen	= 0;
	mymsghdr.msg_flags	= 0;

	//-------------------------------------
	// get this system's current timestamp
	//-------------------------------------
	struct timeval	tvsend, tvrecv;
	if ( gettimeofday( &tvsend, NULL ) < 0 )
		{ perror( "gettimeofday" ); exit(1); }

	//------------------------------------------------------
	// then immediately send our message to the remote host
	//------------------------------------------------------
	int	tx = sendmsg( sock, &mymsghdr, 0 );
	if ( tx < 0 ) { perror( "sendmsg" ); exit(1); }

	//-----------------------------------------------------
	// now adjust some fields in our message-header object 
	//-----------------------------------------------------
	myiov[0].iov_base = buf;
	mymsghdr.msg_control	= cbuf;
	mymsghdr.msg_controllen	= clen;
	
	//--------------------------------------------------------
	// receive a reply from our echo-server (or else timeout)
	//--------------------------------------------------------
	int	rx = recvmsg( sock, &mymsghdr, 0 );
	if ( rx < 0 ) { perror( "recvmsg" ); exit(1); }

	//-------------------------------------------------------
	// Apply system macros for accessing the ancilliary data
	//-------------------------------------------------------
	struct msghdr	*msgp = &mymsghdr;
	struct cmsghdr	*cmsg;
	for (	cmsg = CMSG_FIRSTHDR( msgp );
		cmsg != NULL;
		cmsg = CMSG_NXTHDR( msgp, cmsg ) )
		{
		if (( cmsg->cmsg_level == SOL_SOCKET )
			&&( cmsg->cmsg_type == SO_TIMESTAMP ))
				memcpy( &tvrecv, CMSG_DATA( cmsg ), tlen );
		}			

	//-----------------------------
	// compute the round-trip time
	//-----------------------------
	unsigned long long	stamp0, stamp1;
	stamp0 = tvsend.tv_sec * 1000000LL + tvsend.tv_usec;
	stamp1 = tvrecv.tv_sec * 1000000LL + tvrecv.tv_usec;
	unsigned long long	rtt = stamp1 - stamp0;

	//-------------------------------------
	// report this transaction to the user
	//-------------------------------------
	printf( "\n contacted server on \'%s\' (%s) \n", peername, peeraddr );
	printf( "   %d bytes sent, %d bytes received \n", tx, rx );
	printf( " round-trip time was %llu microseconds \n\n", rtt );
}