awl_checksum.c

数据转发,可以根据需要动态改变 阅读您的文件包然后写出其具体功能

#include <string.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <awl_checksum.h>

static unsigned short inline checksum(unsigned short *buffer,int size){

	unsigned long cksum = 0;
	
	while(size>1){
		cksum += *buffer++;
		size  -= sizeof(unsigned short);
	}
	
	if(size){
		cksum += *(unsigned char *)buffer;
	}
	
	cksum = (cksum >> 16) + (cksum & 0xffff);
	cksum += (cksum >> 16);		
	
	return((unsigned short )(~cksum));
}

unsigned int inline tcp_checksum(unsigned long saddr,
   								unsigned long daddr,
								unsigned short *buffer,
								int size)
{
	unsigned long sum = 0;
	char *buf;
	struct tcp_fake_header *tfh;
	int tfh_len = sizeof(struct tcp_fake_header);
	
	buf = (char *)malloc(tfh_len+size);
	tfh = (struct tcp_fake_header *)buf;
	memcpy(buf+tfh_len,buffer,size);
	
	tfh->saddr = saddr;
	tfh->daddr = daddr;
	tfh->mbz = 0;
	tfh->proto = IPPROTO_TCP;
	tfh->header_len = htons(sizeof(struct tcphdr));
	
	sum = checksum((unsigned short*)buf,tfh_len+size);
	free(buf);
	
	return(sum);
}

unsigned int inline ip_checksum(unsigned short *buffer,int size){
	return(checksum(buffer,size));
}