UDP、IMCP、ARP协议通过netmap解析的实现。

上一篇文章我们讲了一个异步的线程池大概需要如何去实现，现在的话，我们如何来解析一个UDP的包。

环境的搭配

这个环境的问题困扰了很久，这个netmap已经不再更新了，支持Ubuntu16.04-Ubuntu18.04的系统内核，我们需要按照这样的步骤去安装我们的netmap

建立Ubuntu虚拟机的过程，我们就略过了。

切换到su用户下，先去安装我们的编译的环境

apt-get install build-essential

安装完我们的编译工具之后，就需要看看我们的环境是否已经安装git工具。

git --version

没有安装，就需要安装一下我们需要的git工具。

apt-get install git

安装成功以后，我们开始拉取netmap的代码

git clone git://github.com/luigirizzo/netmap.git

拉取代码这个过程可能会遇到一个问题，就是443连接失败的问题，这个问题可以通过魔法上网解决，或者是多尝试几次就好了。

等待拉取代码成功以后，我们来进行netmap的编译和安装。

cd netmap
./configure

这里我们可能会遇到一个问题

Cannot find full kernel sources.
***
*** Please note that most distributions provide separate packages for kernel
*** headers and sources. Once you know the path to kernel sources, you can
*** rerun this script with the additional
***
*** --kernel-sources=/path/to/sources

当我们遇到这个问题的时候，就需要下载一下我们的内核头文件。

apt-get install -y linux-headers-$(uname -r)

拉取内核头文件成功以后，就可以进行netmap的编译了。

./configure
make & make install
insmod netmap.ko

等待运行完毕，这样就完成了netmap的环境搭配。

udp协议解析的代码编写

看一下一个UDP的数据帧是什么样的？

定义我们需要的结构体

以太网头

#define ETH_ALEN 6
struct ethhr{
    unsigned char h_dest[ETH_ALEN];
    unsigned char h_source[ETH_ALEN];
    unsigned short h_proto;
}

ip头

struct iphdr {
	unsigned char version : 4,
		hdrlen : 4;
	unsigned char tos;
	unsigned short tot_len;
	unsigned short id;
	unsigned short flag : 3,
		flag_off : 13;
	unsigned char ttl;
	unsigned char protocol;
	unsigned short check;
	unsigned int saddr;
	unsigned int daddr;
};

UDP协议

struct udphdr {
	unsigned short source;
	unsigned short dest;
	unsigned short len;
	unsigned short check;
};

最后拼接成UDP协议

struct udppkt {
	struct ethhdr eh;
	struct iphdr ip;
	struct udphdr udp;
	unsigned char body[0];
};

arp协议

struct arphdr {
	unsigned short h_type;
	unsigned short h_proto;
	unsigned char h_addrlen;
	unsigned char protolen;
	unsigned short oper;
	unsigned char smac[ETH_ALEN];
	unsigned int sip;
	unsigned char dmac[ETH_ALEN];
	unsigned int dip;
};

arp包

struct arppkt {
	struct ethhdr eh;
	struct arphdr arp;
};

icmp协议

struct icmphdr {
	unsigned char type;
	unsigned char code;
	unsigned short check;
	unsigned short identifier;
	unsigned short seq;
	unsigned char data[32];
};

icmp协议包

struct icmppkt {
	struct ethhdr eh;
	struct iphdr ip;
	struct icmphdr icmp;
};

编写我们解析包的代码

这样定义完我们需要的结构体，就可以编写我们的代码了

最终代码如下:

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

#include <sys/poll.h>
#include <arpa/inet.h>

#define NETMAP_WITH_LIBS

#include <net/netmap_user.h>
#pragma pack(1)

#define ETH_ALEN	6
#define PROTO_IP	0x0800
#define PROTO_ARP	0x0806

#define PROTO_UDP	17
#define PROTO_ICMP	1
#define PROTO_IGMP	2

struct ethhdr {
	unsigned char h_dest[ETH_ALEN];
	unsigned char h_source[ETH_ALEN];
	unsigned short h_proto;
};

struct iphdr {
	unsigned char version:4,
			  hdrlen:4;
	unsigned char tos;
	unsigned short tot_len;
	unsigned short id;
	unsigned short flag:3,
			   flag_off:13;
	unsigned char ttl;
	unsigned char protocol;
	unsigned short check;
	unsigned int saddr;
	unsigned int daddr;
};

struct udphdr {
	unsigned short source;
	unsigned short dest;
	unsigned short len;
	unsigned short check;
};

struct udppkt {
	struct ethhdr eh;
	struct iphdr ip;
	struct udphdr udp;
	unsigned char body[0];
};

struct arphdr {
	unsigned short h_type;
	unsigned short h_proto;
	unsigned char h_addrlen;
	unsigned char protolen;
	unsigned short oper;
	unsigned char smac[ETH_ALEN];
	unsigned int sip;
	unsigned char dmac[ETH_ALEN];
	unsigned int dip;
};

struct arppkt {
	struct ethhdr eh;
	struct arphdr arp;
};

struct icmphdr {
	unsigned char type;
	unsigned char code;
	unsigned short check;
	unsigned short identifier;
	unsigned short seq;
	unsigned char data[32];
};

struct icmppkt {
	struct ethhdr eh;
	struct iphdr ip;
	struct icmphdr icmp;
};

void print_mac(unsigned char *mac) {
	int i = 0;
	for (i = 0;i < ETH_ALEN-1;i ++) {
		printf("%02x:", mac[i]);
	}
	printf("%02x", mac[i]);
}

void print_ip(unsigned char *ip) {
	int i = 0;

	for (i = 0;i < 3;i ++) {
		printf("%d.", ip[i]);
	}
	printf("%d", ip[i]);
}

void print_arp(struct arppkt *arp) {
	print_mac(arp->eh.h_dest);
	printf(" ");

	print_mac(arp->eh.h_source);
	printf(" ");

	printf("0x%04x ", ntohs(arp->eh.h_proto));
	printf("  ");

}

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;
}

void echo_arp_pkt(struct arppkt *arp, struct arppkt *arp_rt, char *hmac) {

	memcpy(arp_rt, arp, sizeof(struct arppkt));

	memcpy(arp_rt->eh.h_dest, arp->eh.h_source, ETH_ALEN);
	str2mac(arp_rt->eh.h_source, hmac);
	arp_rt->eh.h_proto = arp->eh.h_proto;

	arp_rt->arp.h_addrlen = 6;
	arp_rt->arp.protolen = 4;
	arp_rt->arp.oper = htons(2);

	str2mac(arp_rt->arp.smac, hmac);
	arp_rt->arp.sip = arp->arp.dip;

	memcpy(arp_rt->arp.dmac, arp->arp.smac, ETH_ALEN);
	arp_rt->arp.dip = arp->arp.sip;

}

void echo_udp_pkt(struct udppkt *udp, struct udppkt *udp_rt) {

	memcpy(udp_rt, udp, sizeof(struct udppkt));

	memcpy(udp_rt->eh.h_dest, udp->eh.h_source, ETH_ALEN);
	memcpy(udp_rt->eh.h_source, udp->eh.h_dest, ETH_ALEN);

	udp_rt->ip.saddr = udp->ip.daddr;
	udp_rt->ip.daddr = udp->ip.saddr;

	udp_rt->udp.source = udp->udp.dest;
	udp_rt->udp.dest = udp->udp.source;

}

unsigned short in_cksum(unsigned short *addr, int len)
{
	register int nleft = len;
	register unsigned short *w = addr;
	register int sum = 0;
	unsigned short answer = 0;

	while (nleft > 1)  {
		sum += *w++;
		nleft -= 2;
	}

	if (nleft == 1) {
		*(u_char *)(&answer) = *(u_char *)w ;
		sum += answer;
	}

	sum = (sum >> 16) + (sum & 0xffff);
	sum += (sum >> 16);
	answer = ~sum;

	return (answer);

}

void echo_icmp_pkt(struct icmppkt *icmp, struct icmppkt *icmp_rt) {

	memcpy(icmp_rt, icmp, sizeof(struct icmppkt));

	icmp_rt->icmp.type = 0x0; //
	icmp_rt->icmp.code = 0x0; //
	icmp_rt->icmp.check = 0x0;

	icmp_rt->ip.saddr = icmp->ip.daddr;
	icmp_rt->ip.daddr = icmp->ip.saddr;

	memcpy(icmp_rt->eh.h_dest, icmp->eh.h_source, ETH_ALEN);
	memcpy(icmp_rt->eh.h_source, icmp->eh.h_dest, ETH_ALEN);

	icmp_rt->icmp.check = in_cksum((unsigned short*)&icmp_rt->icmp, sizeof(struct icmphdr));

}

int main() {

	struct ethhdr *eh;
	struct pollfd pfd = {0};
	struct nm_pkthdr h;
	unsigned char *stream = NULL;

	struct nm_desc *nmr = nm_open("netmap:eth0", NULL, 0, NULL);
	if (nmr == NULL) {
		return -1;
	}

	pfd.fd = nmr->fd;
	pfd.events = POLLIN;

	while (1) {
		int ret = poll(&pfd, 1, -1);
		if (ret < 0) continue;

		if (pfd.revents & POLLIN) {
			//获取收到的包
			stream = nm_nextpkt(nmr, &h);
			//强转为以太网头
			eh = (struct ethhdr*)stream;
			//如果是IP协议
			if (ntohs(eh->h_proto) == PROTO_IP) {
				//强转为udp的包
				struct udppkt *udp = (struct udppkt*)stream;
				//判断是否为UDP协议
				if (udp->ip.protocol == PROTO_UDP) {

					struct in_addr addr;
					addr.s_addr = udp->ip.saddr;

					int udp_length = ntohs(udp->udp.len);
					printf("%s:%d:length:%d, ip_len:%d --> ", inet_ntoa(addr), udp->udp.source,
						udp_length, ntohs(udp->ip.tot_len));

					udp->body[udp_length-8] = '\0';
					printf("udp --> %s\n", udp->body);
#if 1
					struct udppkt udp_rt;
					echo_udp_pkt(udp, &udp_rt);
					nm_inject(nmr, &udp_rt, sizeof(struct udppkt));
#endif			//判断是否为ICMP的包
				} else if (udp->ip.protocol == PROTO_ICMP) {
					//强转为 imcp的包
					struct icmppkt *icmp = (struct icmppkt*)stream;

					printf("icmp ---------- --> %d, %x\n", icmp->icmp.type, icmp->icmp.check);
					if (icmp->icmp.type == 0x08) {
						struct icmppkt icmp_rt = {0};
						echo_icmp_pkt(icmp, &icmp_rt);

						//printf("icmp check %x\n", icmp_rt.icmp.check);
						nm_inject(nmr, &icmp_rt, sizeof(struct icmppkt));
					}
					//如果是IGMP协议的话
				} else if (udp->ip.protocol == PROTO_IGMP) {

				} else {
					printf("other ip packet");
				}

			}  else if (ntohs(eh->h_proto) == PROTO_ARP) {

				struct arppkt *arp = (struct arppkt *)stream;
				struct arppkt arp_rt;

				if (arp->arp.dip == inet_addr("192.168.0.26")) {
					echo_arp_pkt(arp, &arp_rt, "00:50:56:33:1c:ca");
					nm_inject(nmr, &arp_rt, sizeof(struct arppkt));
				}
			}
		}
	}
}

这样就通过使用netmap完成了icmp和arp，以及UDP包的解析。