UDP 设计实现_udp数据协议设计

七层网络设计

利用netmap拿到传输到服务端的原始数据；它是由mmap将网卡的数据映射到内存中；使用nm_open("eth0",NULL,0,NULL)返回的fd是指向网卡的，当网卡里面来数据时就可以通过fd来知晓，操作数据是操作内存里面的数据

ARP请求

1：客户端会定时的发生arp请求

2：将服务器的IP地址，mac地址记录在客户端的ARP表当中；如果服务器没有回应就不会记录。

ARP表的作用是发送给服务器的包，查看服务器的地址是否在ARP表当中，如果没有就不会进行发送

实现

#include <stdio.h>
 
#include <sys/poll.h>
#include <arpa/inet.h>
 
#define NETMAP_WITH_LIBS
 
#include <net/netmap_user.h>
 
#pragma pack(1)
 
 
#define ETH_ADDR_LENGTH		6
 
#define PROTO_IP			0x0800
#define PROTO_ARP			0x0806
#define PROTO_UDP			17
#define PROTO_ICMP			1
 
 
struct ethhdr {
	unsigned char h_dst[ETH_ADDR_LENGTH];//源mac地址
	unsigned char h_src[ETH_ADDR_LENGTH];//目的mac地址
	unsigned short h_proto;//协议，保存的是上层的协议，是IP协议还是ICMP协议，还是其他的协议
	
}; // 14
 
 
struct iphdr {
 
	unsigned char hdrlen:4,
				  version:4; // 0x45
				  
 
	unsigned char tos;
 
	unsigned short totlen;
	
	unsigned short id;
 
	unsigned short flag_offset; //
 
	unsigned char ttl; //time to livem,默认为64，每过一个网关就减一
	// 0x1234// htons
 
	unsigned char type;//传输层协议是udp,还是tcp,
 
	unsigned short check;//校验值
 
	unsigned int sip;//源ip
	unsigned int dip;//目的Ip
 
}; // 20
 
 
 
struct udphdr {
 
	unsigned short sport;//源端口号
	unsigned short dport;//目的端口号
 
	unsigned short length;//udp总长度
	unsigned short check;
 
}; // 8
 
 
struct udppkt {
 
	struct ethhdr eh; // 14
	struct iphdr ip;  // 20 
	struct udphdr udp; // 8
 
	unsigned char data[0];
 
}; // sizeof(struct udppkt) == 
 
 
struct arphdr {
 
	unsigned short h_type;
	unsigned short h_proto;
 
	unsigned char h_addrlen;
	unsigned char h_protolen;
 
	unsigned short oper;
 
	unsigned char smac[ETH_ADDR_LENGTH];
	unsigned int sip;
 
	unsigned char dmac[ETH_ADDR_LENGTH];
	unsigned int dip;
};
 
struct arppkt {
 
	struct ethhdr eh;
	struct arphdr arp;
 
};
 
 
 
int str2mac(char *mac, char *str) {
 
	char *p = str;
	unsigned char value = 0x0;
	int i = 0;
 
	while (p != '\0') {
		
		if (*p == ':') {
			mac[i++] = value;
			value = 0x0;
		} else {
			
			unsigned char temp = *p;
			if (temp <= '9' && temp >= '0') {
				temp -= '0';
			} else if (temp <= 'f' && temp >= 'a') {
				temp -= 'a';
				temp += 10;
			} else if (temp <= 'F' && temp >= 'A') {
				temp -= 'A';
				temp += 10;
			} else {	
				break;
			}
			value <<= 4;
			value |= temp;
		}
		p ++;
	}
 
	mac[i] = value;
 
	return 0;
}
 
 
//回应arp
void echo_arp_pkt(struct arppkt *arp, struct arppkt *arp_rt, char *mac) {
 
	memcpy(arp_rt, arp, sizeof(struct arppkt));
 
	memcpy(arp_rt->eh.h_dst, arp->eh.h_src, ETH_ADDR_LENGTH);
	str2mac(arp_rt->eh.h_src, mac);
	arp_rt->eh.h_proto = arp->eh.h_proto;
 
	arp_rt->arp.h_addrlen = 6;
	arp_rt->arp.h_protolen = 4;
	arp_rt->arp.oper = htons(2);
	
	str2mac(arp_rt->arp.smac, mac);
	arp_rt->arp.sip = arp->arp.dip;
	
	memcpy(arp_rt->arp.dmac, arp->arp.smac, ETH_ADDR_LENGTH);
	arp_rt->arp.dip = arp->arp.sip;
 
}
 
//
int main() {
 
	struct nm_pkthdr h;
	struct nm_desc *nmr = nm_open("netmap:eth0", NULL, 0, NULL);
	if (nmr == NULL) return -1;
 
	struct pollfd pfd = {0};
	pfd.fd = nmr->fd;
	pfd.events = POLLIN;
 
	while (1) {
 
		int ret = poll(&pfd, 1, -1);
		if (ret < 0) continue;
 
		if (pfd.revents & POLLIN) {
 
			unsigned char *stream = nm_nextpkt(nmr, &h);
 
			struct ethhdr *eh = (struct ethhdr *)stream;
			if (ntohs(eh->h_proto) ==  PROTO_IP) {//如果是IP协议
 
				struct udppkt *udp = (struct udppkt *)stream;
 
				if (udp->ip.type == PROTO_UDP) { //如果是udp协议就直接打印
 
					int udplength = ntohs(udp->udp.length);
 
					udp->data[udplength-8] = '\0';
 
					printf("udp --> %s\n", udp->data);
 
				} else if (udp->ip.type == PROTO_ICMP) {//这个是处理ping的请求
 
					
 
				}
				
 
			} else if (ntohs(eh->h_proto) ==  PROTO_ARP) {//如果是arp协议
 
				struct arppkt *arp = (struct arppkt *)stream;
 
				struct arppkt arp_rt;
 
				if (arp->arp.dip == inet_addr("192.168.0.123")) { //
 
					echo_arp_pkt(arp, &arp_rt, "00:50:56:33:1c:ca");
 
					nm_inject(nmr, &arp_rt, sizeof(arp_rt));
 
					printf("arp ret\n");
				
				}
 
			}
 
		}
 
	}
	
	
 
}