// ***************************************************************************// An 8051 Based Web Server// icmp.c: ICMP protocol processing// By Mason Kidd 3/14/02// ***************************************************************************#include <string.h>#include "packets.h"#include "ip.h"#include "icmp.h"void tx_icmp_packet(unsigned char tx_type, unsigned char *szData, unsigned char nLength){	unsigned char tx_buf[BUF_LEN];	struct ip_hdr *tx_ip_hdr = (struct ip_hdr *)(tx_buf + sizeof(struct eth_hdr));	struct icmp_hdr *tx_icmp_hdr = (struct icmp_hdr *)(tx_buf + sizeof(struct ip_hdr) + sizeof(struct eth_hdr));	unsigned char *icmp_data = (unsigned char *)(tx_buf + sizeof(struct eth_hdr) + sizeof(struct ip_hdr) + sizeof(struct icmp_hdr));	unsigned int *chksum_hdr = (unsigned int *)tx_icmp_hdr;	int i;	unsigned long chksum = 0;		tx_icmp_hdr->type = tx_type;	tx_icmp_hdr->sequence = 0x01;	for (i = 0; i < nLength; i++)	{		*icmp_data = *szData;		icmp_data++;		szData++;	}	// Compute the checksum	for (i = 0; i < 5; i++, chksum_hdr++)		if (i != 1)			chksum += *chksum_hdr;	chksum = ~((chksum >> 16) + (chksum & 0xffff)); 	tx_icmp_hdr->checksum = (unsigned int)(chksum & 0xffff);	tx_ip_packet(tx_buf, nLength + sizeof(struct icmp_hdr), IP_ICMP);}void rx_icmp_packet(unsigned char *rx_buffer){	struct ip_hdr *rx_ip_hdr = (struct ip_hdr *)(rx_buffer + sizeof(struct eth_hdr));	struct icmp_hdr *rx_icmp_hdr = (struct icmp_hdr *)(rx_buffer + sizeof(struct eth_hdr) + sizeof(struct ip_hdr));	unsigned char *pszData = (unsigned char *)(rx_buffer + sizeof(struct eth_hdr) + sizeof(struct ip_hdr) + sizeof(struct icmp_hdr));	unsigned int nDataLen = rx_ip_hdr->totlen - sizeof(struct icmp_hdr) - sizeof(struct ip_hdr);	// if it's an echo request, send a reply	if (rx_icmp_hdr->type == ICMP_ECHO)	{		// switch source and destination IP's		memcpy(targetMAC, srcMAC, sizeof(unsigned char) * 6);		memcpy(targetIP, srcIP, sizeof(unsigned char) * 4);		tx_icmp_packet(ICMP_ECHOREPLY, pszData, nDataLen);	}	// else discard packet}