/*
 * \brief  User datagram protocol.
 * \author Stefan Kalkowski
 * \date   2010-08-19
 */

/*
 * Copyright (C) 2010-2013 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU General Public License version 2.
 */

#ifndef _UDP_H_
#define _UDP_H_

/* Genode */
#include <base/exception.h>
#include <base/stdint.h>

#include <util/endian.h>
#include <net/ethernet.h>
#include <net/ipv4.h>

namespace Net { class Udp_packet; }


/**
 * Data layout of this class conforms to an UDP packet (RFC 768)
 *
 * UDP-header-format:
 *
 *  -----------------------------------------------------------------------
 * |   source-port   | destination-port |     length      |    checksum    |
 * |     2 bytes     |     2 bytes      |     2 bytes     |    2 bytes     |
 *  -----------------------------------------------------------------------
 */
class Net::Udp_packet
{
	private:

		/***********************
		 ** UDP header fields **
		 ***********************/

		Genode::uint16_t _src_port;
		Genode::uint16_t _dst_port;
		Genode::uint16_t _length;
		Genode::uint16_t _checksum;
		unsigned         _data[0];

	public:

		enum Protocol_id { IP_ID = 0x11 };


		/**
		 * Exception used to indicate protocol violation.
		 */
		class No_udp_packet : Genode::Exception {};


		/*****************
		 ** Constructor **
		 *****************/

		Udp_packet(Genode::size_t size) {
			/* Udp header needs to fit in */
			if (size < sizeof(Udp_packet))
				throw No_udp_packet();
		}


		/******************************
		 ** UDP field read-accessors **
		 ******************************/

		Genode::uint16_t src_port()  { return bswap(_src_port); }
		Genode::uint16_t dst_port()  { return bswap(_dst_port); }
		Genode::uint16_t length()    { return bswap(_length);   }
		Genode::uint16_t checksum()  { return bswap(_checksum); }
		void* data()                 { return &_data;           }


		/***************
		 ** Operators **
		 ***************/

		/**
		 * Placement new.
		 */
		void * operator new(Genode::size_t size, void* addr) {
			return addr; }


		/***************************
		 ** Convenience functions **
		 ***************************/

		/**
		 * UDP checksum is calculated over the udp datagram + an IPv4
		 * pseudo header.
		 *
		 * IPv4 pseudo header:
		 *
		 *  --------------------------------------------------------------
		 * | src-ipaddr | dst-ipaddr | zero-field | prot.-id | udp-length |
		 * |  4 bytes   |  4 bytes   |   1 byte   |  1 byte  |  2 bytes   |
		 *  --------------------------------------------------------------
		 */
		void calc_checksum(Ipv4_packet::Ipv4_address src,
		                   Ipv4_packet::Ipv4_address dst)
		{
			/* have to reset the checksum field for calculation */
			_checksum = 0;

			/*
			 * sum up pseudo header
			 */
			Genode::uint32_t sum = 0;
			for (unsigned i = 0; i < Ipv4_packet::ADDR_LEN; i=i+2) {
				Genode::uint16_t s = src.addr[i] << 8 | src.addr[i + 1];
				Genode::uint16_t d = dst.addr[i] << 8 | dst.addr[i + 1];
				sum += s + d;
			}
			Genode::uint8_t prot[] = { 0, IP_ID };
			sum += bswap(*(Genode::uint16_t*)&prot) + length();

			/*
			 * sum up udp packet itself
			 */
			unsigned max = (length() & 1) ? (length() - 1) : length();
			Genode::uint16_t *udp = (Genode::uint16_t*) this;
			for (unsigned i = 0; i < max; i=i+2)
				sum += bswap(*udp++);

			/* if udp length is odd, append a zero byte */
			if (length() & 1) {
				Genode::uint8_t last[] =
					{ *((Genode::uint8_t*)this + (length()-1)), 0 };
				sum += bswap(*(Genode::uint16_t*)&last);
			}

			/*
			 * keep only the last 16 bits of the 32 bit calculated sum
			 * and add the carries
			 */
			while (sum >> 16)
				sum = (sum & 0xffff) + (sum >> 16);

			/* one's complement of sum */
			_checksum = bswap((Genode::uint16_t) ~sum);
		}
} __attribute__((packed));

#endif /* _UDP_H_ */