ip.c

这是南开大学实验室开发的基于51单片机的TCP-IP通信协议,有较高的参考性

/*
 * Copyright (c) 2003 Electric Application Laboratory of NAN KAI University
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * Author: Li Zhanglin <[e-mail]>
 *
 */

#include "..\GloblDef\GloblDef.h"
#include "..\TCPIP\TCPIPmem.h"
#include "..\TCPIP\IP.h"
#include "..\TCPIP\icmp.h"
#include "..\TCPIP\Netif.h"
#include "..\TCPIP\TCP.h"

/* Check sum calulation. data in buff, size, InSum is initial sum */
WORD CheckSum(WORD DT_XDATA * buff,WORD size,DWORD InSum) REENTRANT_SIG
{
	/* TO DO:in packet memory high part of short is in low memory. add all data in 
	form of 16 bits get a result of 32 bits, add high 16 bits to low 16 bits two 
	times.  get a 16 bits result then complement it. */
									   //注意：
	DWORD cksum = InSum; 
									  //只对偶数的字节数校验
	/* sum all word except the last odd byte(if size is a odd num) */
	WORD DT_XDATA * EndBuf = buff + size/2;	 
	while(buff < EndBuf)	   
	{ 
		/* net order is equeal as host order in mirochip, so no need to change */
		cksum += *(buff++);   //对于INT型指针自加一次地址偏移两个单位(先求总和)
	} 
	
	/**((WORD xdata *)CheckSumInParam) = size;
	*((WORD xdata *)(CheckSumInParam+2)) = buff;
	asmAddCheckSum();
	cksum = CheckSumOutParm;
	*/
	
	/* if has last odd byte. use this byte as the high part of 16 bits, and add. */
	if((size & 0x0001) != 0) 
		cksum += (*buff) & 0xff00;	//对最后的奇数位进行校验

	cksum = (cksum >> 16) + (cksum & 0xffff);  //两次折合把32bit转化为16bibit
	cksum += (cksum >>16); 
	return (WORD)(~cksum); 
}

/* IP input process */
void IPInput(struct SMemHead DT_XDATA *MemHead) REENTRANT_MUL
{
	struct SIPHead DT_XDATA *pIPHead;
	struct SNetIf  DT_XDATA *pNetIf;		/* for search netif list */

	pIPHead = (struct SIPHead DT_XDATA *)(MemHead->pStart);

	/* check ip version */
	if(IP_VERSION(pIPHead) != IP_VERSION_4)	  //如果不是IP包就释放内存
	{
		MemFree(MemHead);
		return;
	}

	/* if checksum is wrong */
	if(CheckSum((WORD DT_XDATA *)pIPHead,(WORD)IP_HEAD_LEN(pIPHead),0) != 0)
	{
		MemFree(MemHead);
		return;
	}

	/* ip packet with options is not supported */
	if(IP_HEAD_LEN(pIPHead) != IP_HEAD_MIN_LEN)	//？？？？注意长度单位是4字节的（5：20byte）
	{
		MemFree(MemHead);
		return;
	}

	/* ip packet fragmented is not supported */
	if((pIPHead->FragmentFlag_Offset & IP_FRAGMENT_OFFSET_MASK)!= 0)
	{
		MemFree(MemHead);
		return;
	}

	
	/* if this packet for us. check all the netif. if a host
	has tow device(tow ip). This packet may come from one device
	but send for the IP of the other deviec. In this case we should
	not drop or forward this packet */
	
	/* if this packet is not for us. forward it */
	if((pNetIf = NetIfFindIP(pIPHead->IPDest)) == NULL)//本机不是目的主机
	{
		#ifdef IP_ENABLE_FORWARD	/* if act as a router */ //如果具有路由功能
		/* We should decrease the IPHead->ttl */
		if(pIPHead->LifeLength != 0)
		{
			pIPHead->LifeLength--;
				
			/* recaculate IP head checksum. there is a easy method
			to recaculate, leave for later version improvment */
			CheckSum((WORD DT_XDATA *)pIPHead,(WORD)IP_HEAD_LEN(pIPHead),0); //应该可以不要校验拉

			/* find a rout( a interface ) */
			if((pNetIf = NetIfFindRout(pIPHead->IPDest)) != NULL) //找到了路由（只要路由表不为空）
			{
				/* forward. send it through this interface. if return FALSE, we
				do not care, the soure of the packet will deel with it. */
				pNetIf->output(MemHead,pNetIf,pIPHead->IPDest);	//进行转发该报
			}
		}
		#endif		
		MemFree(MemHead);
		return;
	}
	else	 //是发给本机的报文
	{
		/* MemHead->pStart set to point uper layer */
		MemHead->pStart += sizeof(struct SIPHead);

		/* pass to the uper layer */
		switch(pIPHead->Protocol)
		{
		case IP_PROTOCOL_TCP:
			TCPInput(MemHead);	//把包传给TCP层
			break;
#if	ICMP_EN
		case IP_PROTOCOL_ICMP:  //把包传给ICMP（PING）层
			ICMPInput(MemHead);
			break;
#endif
		default:			   //否则放弃本包数据
			MemFree(MemHead);
			break;
		}
	}
}

/* out put a ip packet,NOTE:MemHead->pStart point to IPHead.
IPScr IPDest Protocol TotalLen is already filled at uper layer.
To do so TCPCheckSum is easy to generate and pass augument to 
IPOutput is easyer. 
return :
	TURE: send the packt successful. */
BOOL IPOutput(struct SMemHead DT_XDATA * MemHead) REENTRANT_SIG
{
	struct SNetIf  DT_XDATA *pNetIf;
	struct SIPHead DT_XDATA *pIPHead;
	WORD tCheckSum;
	
	pIPHead = (struct SIPHead DT_XDATA *)(MemHead->pStart);	 //把IP报文头放入缓存首部

	/* found a rout */
	if((pNetIf = NetIfFindRout(pIPHead->IPDest)) != NULL) //请求路由
	{
		/* fill IP head */
		pIPHead->CheckSum				= 0; //可以没有下面有        
		pIPHead->FragmentFlag_Offset	= 0;
		pIPHead->FragmentID				= 0;
		pIPHead->LifeLength				= IP_INITIAL_LIFE;
		pIPHead->ServeType				= 0;
		pIPHead->Ver_HeadLen			= (IP_VERSION_4 << 4) + IP_HEAD_MIN_LEN/4;
										 //头部的其余重要信息由上层协议注入
		/* checksum */
		tCheckSum = CheckSum((WORD DT_XDATA *)pIPHead,(WORD)IP_HEAD_LEN(pIPHead),0);
		pIPHead->CheckSum = htons(tCheckSum);//按照网络字节存放（32位数据按低到高发送）

		/* output it */
		return pNetIf->output(MemHead,pNetIf,pIPHead->IPDest);
	}
	else
		return FALSE;
	/* 'MemHead' freeing is at tcp model when it is acked */
}