//-------------------------------------------------------------------
//	clonetos.cpp	  (A revision of our ' msgserver.cpp' demo)
//
//	This revision of our 'msgserver.cpp' echo-server will reply
//	to an incoming message with an outgoing message that has an
//	identical value in its IP-header's 'Type-of-Service' field,  
//	thereby providing us with yet another example in which some
//	ancillary data gets delivered via the 'recvmsg()' function.
//
//		to compile:  $ g++ clonetos.cpp -o clonetos
//		to execute:  $ ./clonetos
//
//	programmer: ALLAN CRUSE
//	written on: 18 Feb 2009
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <stdlib.h>	// for exit() 
#include <string.h>	// for bzero()
#include <unistd.h>	// for gethostname()
#include <arpa/inet.h>	// for inet_ntoa()


#define SERVER_PORT	54321


int main( int argc, char **argv )
{
	//-----------------------------------------------
	// get this station's hostname for later display
	//-----------------------------------------------
	char	hostname[ 64 ] = {0};
	gethostname( hostname, 63 ); 

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

	//---------------------------------------------------------
	// set a socket-option allowing this socket to be reusable
	//---------------------------------------------------------
	int	oval = 1;
	int	olen = sizeof( oval );
	if ( setsockopt( sock, SOL_SOCKET, SO_REUSEADDR, &oval, olen ) < 0 )
		{ perror( "setsockopt" ); exit(1); }

	//------------------------------------------------------------------
	// initialize a socket-address structure using a 'wildcard' address
	//------------------------------------------------------------------
	struct sockaddr_in	saddr = { 0 };
	socklen_t		salen = sizeof( saddr );
	saddr.sin_family 	= AF_INET;
	saddr.sin_port 		= htons( SERVER_PORT );
	saddr.sin_addr.s_addr 	= htonl( INADDR_ANY );

	//--------------------------------------------------
	// bind the socket to this socket-address structure
	//--------------------------------------------------
	if ( bind( sock, (sockaddr*)&saddr, salen ) < 0 )
		{ perror( "bind" ); exit(1); }

	//-----------------------------------------------------
	// enable the IP_RECVTOS socket option for this socket 
	//-----------------------------------------------------
	if ( setsockopt( sock, SOL_IP, IP_RECVTOS, &oval, olen ) < 0 )
		{ perror( "setsockopt RECVTOS" ); exit(1); }

	//--------------------------------------------------
	// main loop to receive and echo incomming messages 
	//-------------------------------------------------- 
	int	count = 0;
	do	{
		//-------------------------------------------------------
		// setup structures needed in our 'struct msghdr' object
		//------------------------------------------------------- 
		struct sockaddr_in	from = { 0 };
		socklen_t		flen = sizeof( from );
	
		char	buf[ 1500 ] = {0};
		int	blen = sizeof( buf );
	
		struct iovec	myiov[ 1 ] = { { buf, blen } };
	
		unsigned char	cbuf[ 40 ];

		//----------------------------------------------------
		// allocate and initialize our 'struct msghdr' object
		//---------------------------------------------------- 	
		struct msghdr	mymsg = { 0 };
		size_t		msglen = sizeof( mymsg );
		mymsg.msg_name 		= &from;
		mymsg.msg_namelen 	= flen; 
		mymsg.msg_iov		= myiov;
		mymsg.msg_iovlen	= 1;
		mymsg.msg_control 	= cbuf;
		mymsg.msg_controllen 	= sizeof( cbuf );
		mymsg.msg_flags		= 0;
	
		//---------------------------------------------------------
		// show our socket's port-number and the name of this host 
		//--------------------------------------------------------- 
		printf( "\n ok, server is listening" );
		printf( " to port %u on %s ... ", SERVER_PORT, hostname );
		fflush( stdout );
	
		//-------------------------------------------------------	
		// receive a client's message sent to this server's port 
		//------------------------------------------------------- 
		int	rx = recvmsg( sock, &mymsg, 0 );
		if ( rx < 0 ) { perror( "recvmsg" ); exit(1); }
	
		//-------------------------------------------------------
		// extract this message's TOS-value from ancilliary data
		//-------------------------------------------------------
		int	tos = 0;
		int	tlen = 1;
		struct cmsghdr	*cmsg;
		for ( cmsg = CMSG_FIRSTHDR( &mymsg ); cmsg != NULL;
			cmsg = CMSG_NXTHDR( &mymsg, cmsg ) )
			{
			if (( cmsg->cmsg_level == SOL_IP )
				&&( cmsg->cmsg_type == IP_TOS ))
				{
				memcpy( &tos, CMSG_DATA( cmsg ), tlen );
				}
			}

		//------------------------------------------------------
		// report the incomming message's size, source, and TOS
		//------------------------------------------------------
		printf( "\n #%d received %d bytes ", ++count, rx );
		printf( "from \'%s\' ", inet_ntoa( from.sin_addr ) );
		printf( "with TOS=0x%02X \n\n", tos );
		puts( buf );

		//-----------------------------------------------------
		// modify our socket's default 'Type-of-Service' value
		//----------------------------------------------------- 
		if ( setsockopt( sock, SOL_IP, IP_TOS, &tos, tlen ) < 0 ) 
			{ perror( "setsockopt TOS" ); exit(1); }

		//-------------------------------------------------------
		// send the message back with its same 'Type-of-Service'
		//------------------------------------------------------- 
		myiov[0].iov_len = rx;
		mymsg.msg_control = NULL;
		mymsg.msg_controllen = 0;
		int	tx = sendmsg( sock, &mymsg, 0 );
		if ( tx < 0 ) { perror( "sendmsg" ); exit(1); }
		printf( "\n returned %d bytes ", tx );
		printf( "to \'%s\' ", inet_ntoa( from.sin_addr ) );
		printf( "with TOS=0x%02X \n\n", tos );
		}
	while ( 1 );
}