//----------------------------------------------------------------
//	udpserver.cpp
//
//	This program creates a network socket which it can use to
//	receive a datagram sent from a remote client to its port.
//	It displays the received message, then transmits it back.   
//
//	     usage:  $ ./udpserver
//
//	NOTE: This code is adapted from an example in the Masters
//	Thesis submitted by Mr. Okki Tranggana on 15 May 1991.
//
//	programmer: ALLAN CRUSE 
//	written on: 19 JAN 2008
//----------------------------------------------------------------

#include <netinet/in.h>	// for socket(), bind()
#include <stdio.h>	// for printf(), perror()
#include <string.h>	// for bzero()
#include <unistd.h>	// for close()
#include <stdlib.h>	// for exit()

#define BUFSZ 1500	// Maximum size for an ethernet datagram

int main( void )
{
	//------------------------------------------------------------
	// create a socket on which to receive and transmit datagrams
	//------------------------------------------------------------
	int	sock = socket( PF_INET, SOCK_DGRAM, IPPROTO_UDP );
	if ( sock < 0 )
		{
		perror( "opening datagram socket" );
		exit( 1 );
		}

	//------------------------------------------------------
	// initialize a socket-address strcture using wildcards 
	//------------------------------------------------------
	struct sockaddr_in	name;
	socklen_t		nlen;
	
	nlen = sizeof( name );
	bzero( &name, nlen );
	name.sin_family = AF_INET;
	name.sin_port = htons( 0 );

	//------------------------------------------------
	// Bind our socket to this generic socket-address   
	//------------------------------------------------
	if ( bind( sock, (sockaddr *)&name, nlen ) )
		{
		perror( "binding datagram socket" );
		exit( 1 );
		}

	//----------------------------------------------------
	// find the system-assigned portnumber and display it
	//----------------------------------------------------
	if ( getsockname( sock, (sockaddr *)&name, &nlen ) )
		{
		perror( "getting socket name" );
		exit( 1 );
		}

	printf( "Socket has port #%d \n", ntohs( name.sin_port ) );
	
	//----------------------------------------------------
	// initialize a socket-address structure for the peer 
	//----------------------------------------------------
	struct sockaddr_in	peer;
	socklen_t		plen = sizeof peer;
	bzero( &peer, plen );

	//---------------------------------------------------
	// read any datagram sent to our socket's portnumber
	//---------------------------------------------------
	char	buf[ BUFSZ ];
	if ( recvfrom( sock, buf, BUFSZ, 0,
			(sockaddr *)&peer, &plen ) < 0 )
		perror( "receiving datagram packet" );

	//-----------------------------------------
	// display the received datagram's message
	//-----------------------------------------
	printf( "-->%s\n", buf );

	//-------------------------------------------------------
	// transmit a message-acknowledgement back to the client
	//-------------------------------------------------------
	int	msbytes = strlen( buf );
	int	txbytes = sendto( sock, buf, msbytes, 0,
				(sockaddr *)&peer, plen );

	//----------------------------------------------------------
	// close the socket, and report on this message-transaction
	//----------------------------------------------------------
	close( sock );

	if ( txbytes < 0 ) perror( "error transmitting reply to client" );
	else	printf( "reply was sent to client (%d bytes)\n", txbytes );	
}