//-------------------------------------------------------------------
//	msgserver.cpp
//
//	This example uses the 'recvmsg()' and 'sendmsg()' functions
//	to accept a message from a client and then to echo it back. 
//	The user may terminate this program by hitting <CONTROL>-C.
//
//		to compile:  $ g++ msgserver.cpp -o msgserver
//		to execute:  $ ./msgserver
//
//	programmer: ALLAN CRUSE
//	written on: 24 JAN 2009
//	revised on: 15 FEB 2009 -- to return same length as received
//-------------------------------------------------------------------

#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;
	socklen_t		salen = sizeof( saddr );
	bzero( &saddr, salen );
	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); }

	//------------------------------------------
	// main loop to receive connection-requests
	//------------------------------------------ 
	int	count = 0;
	do	{
		// setup structures needed in our 'struct msghdr' object
		struct sockaddr_in	from;
		socklen_t		flen = sizeof( from );
		bzero( &from, flen );
		char	buf[ 1500 ] = {0};
		int	blen = sizeof( buf );
		struct iovec	myiov[ 1 ] = { { buf, blen } };

		// allocate and initialize the 'struct msghdr' object	
		struct msghdr	mymsg;
		size_t		msglen = sizeof( mymsg );
		bzero( &mymsg, msglen );
		mymsg.msg_name 		= &from;
		mymsg.msg_namelen 	= flen; 
		mymsg.msg_iov		= myiov;
		mymsg.msg_iovlen	= 1;
		mymsg.msg_control 	= NULL;
		mymsg.msg_controllen 	= 0;
		mymsg.msg_flags		= 0;
	
		// show the 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); }
		printf( "\n #%d received %d bytes ", ++count, rx );
		printf( "from \'%s\' \n\n", inet_ntoa( from.sin_addr ) );
		puts( buf );

		// send the received message back to its client
		myiov[0].iov_len = rx;
		int	tx = sendmsg( sock, &mymsg, 0 );
		if ( tx < 0 ) { perror( "sendmsg" ); exit(1); }
		printf( "\n returned %d bytes ", tx );
		printf( "to \'%s\' \n\n", inet_ntoa( from.sin_addr ) );
		}
	while ( 1 );
}