icmp.c

Keil_C51程序,C8051实现的TCP/IP功能源码

//-----------------------------------------------------------------------------
// Net ICMP.C
//
// This module handles ICMP messages
// Refer to RFC 792, 896, 950, 1122, and 1191
// 处理ICMP报文
//-----------------------------------------------------------------------------
#include <string.h>
#include <stdlib.h>
#include "reg52.h"
#include "net.h"
#include "cksum.h"
#include "ip.h"
#include "serial.h"
#include "icmp.h"

extern UCHAR idata debug;

//------------------------------------------------------------------------
// This builds a ping response message.  It allocates memory for the
// entire outgoing message, including Eth and IP headers.  See "TCP/IP
// Illustrated, Volume 1" Sect 7.2 for info on Ping messages
// PING的返回信息。返回MAC和IP头。
//------------------------------------------------------------------------
void ping_send(UCHAR xdata * inbuf, ULONG ipaddr, UINT len)
{
   	PING_HEADER xdata * ping_in;
   	PING_HEADER xdata * ping_out;
   	UCHAR xdata * outbuf;
            
   	ping_in = (PING_HEADER xdata *)(inbuf + 34);
      
   	// Allocate memory for entire outgoing message
   	outbuf = (UCHAR xdata *)malloc(len + 34);
   	if (outbuf == NULL)
   	{
      	if (debug) SendCommString("PING: Oops, out of memory\r");
      	return;
   	}      
      
   	// Ping response message payload starts at offset 34
   	ping_out = (PING_HEADER xdata *)(outbuf + 34);

   	ping_out->msg_type = 0;//回显应答
   	ping_out->msg_code = 0;//代码0
   	ping_out->checksum = 0;//校验和
   	ping_out->identifier = ping_in->identifier;//标识符，这两个是传送过来的数据
   	ping_out->sequence = ping_in->sequence;//序列号字段
   
   	memcpy(&ping_out->echo_data, &ping_in->echo_data, len - 8);
            
	// Compute checksum over the ICMP header plus
	// optional data and insert complement
	//校验
   	ping_out->checksum = ~cksum(outbuf + 34, len);
                        
   	if (debug) SendCommString("ICMP: Sending response to IP layer\r");

   	ip_send(outbuf, ipaddr, ICMP_TYPE, len);
}


//------------------------------------------------------------------------
// This builds an outgoing ICMP destination port unreachable response
// message.  See See "TCP/IP Illustrated, Volume 1" Sect 6.5.  This
// message is typically sent in response to a UDP message directed
// to a port that has no corresponding application running. 
// Todo: The spec says we should return all options that were in
// the original incoming IP header.  Right now we cut off everything
// after the first 20 bytes. 
// 发送一个未到达信息，这个消息主要用于回应一个UDP信息，如果没有对应的端口。
//------------------------------------------------------------------------
void dest_unreach_send(UCHAR xdata * inbuf, ULONG ipaddr)
{
   	UCHAR xdata * outbuf;
   	ICMP_ERR_HEADER xdata * icmp;
            
   	// Allocate memory for entire outgoing message
   	// including eth and IP haders.  Always 70 bytes
   	outbuf = (UCHAR xdata *)malloc(70);
   	if (outbuf == NULL)
   	{
      	if (debug) SendCommString("ICMP: Oops, out of memory\r");
      	return;
   	}      
      
   	icmp = (ICMP_ERR_HEADER xdata *)(outbuf + 34);
   
   	// Fill in ICMP error message header
   	icmp->msg_type = 3;   // destination unreachable目的地址不对
   	icmp->msg_code = 3;   // port unreachable端口未到达
   	icmp->checksum = 0;
      
   	// Fill in ICMP error message data
   	icmp->msg_data = 0;
           
   	// Copy in 20 byte original incoming IP header
   	// plus 8 bytes of data
   	memcpy(&icmp->echo_data, inbuf + 14, 28);
                               
   	// Compute checksum over the 36 byte long ICMP
   	// header plus data and insert complement
   	icmp->checksum = ~cksum(outbuf + 34, 36);
      
   	// Forward message to the IP layer
   	if (debug) SendCommString("ICMP: Sending dest unreach to IP layer\r");
   	ip_send(outbuf, ipaddr, ICMP_TYPE, 36);
}

//------------------------------------------------------------------------
// This handles incoming ICMP messages.  See "TCP/IP Illustrated,
// Volume 1" Sect 6.2 for discussion of the various ICMP messages
// 处理收到的ICMP信息
//------------------------------------------------------------------------
void icmp_rcve(UCHAR xdata * inbuf, UINT len)
{
   IP_HEADER * ip;
   UCHAR idata msg_type;
   UINT idata temp;
   
   // Allow for 14 bytes eth header
   ip = (IP_HEADER *)(inbuf + 14);
        
   // IP header has been adjusted if necessary to always be 
	// 20 bytes so message starts at an offset of 34
   // Validate checksum of entire ICMP message incl data 
	temp = cksum(inbuf + 34, len);
	
	if (temp != 0xFFFF)
	{
	  	if (debug) SendCommString("ICMP: Error, cksum bad\r");
      return; 
   }
      
   // Switch on the message type
   msg_type = *(inbuf + 34);//消息类型
   switch(msg_type)
   {
      case 3://目的地址未到达
      if (debug) SendCommString("ICMP: Dest unreachable rcvd\r");
      break;

	   case 8://收到，对方要求请求回显
      if (debug) SendCommString("ICMP: Ping rcvd\r");
      ping_send(inbuf, ip->source_ipaddr, len); 
      break;

      default://
      if (debug) SendCommString("ICMP: Error, unknown msg rcvd\r");
      break;
   }
}