上一篇文章我們講了一個異步的線程池大概需要如何去實現，現在的話，我們如何來解析一個UDP的包。
環境的搭配
這個環境的問題困擾了很久，這個netmap已經不再更新了，支持Ubuntu16.04-Ubuntu18.04的系統內核，我們需要按照這樣的步驟去安裝我們的netmap
建立Ubuntu虛擬機的過程，我們就略過了。
切換到su用戶下，先去安裝我們的編譯的環境
apt-get install build-essential
安裝完我們的編譯工具之後，就需要看看我們的環境是否已經安裝git工具。
git --version
沒有安裝，就需要安裝一下我們需要的git工具。
apt-get install git
安裝成功以後，我們開始拉取netmap的代碼
git clone git://github.com/luigirizzo/netmap.git
拉取代碼這個過程可能會遇到一個問題，就是443連接失敗的問題，這個問題可以通過魔法上網解決，或者是多嘗試幾次就好了。
等待拉取代碼成功以後，我們來進行netmap的編譯和安裝。
cd netmap
./configure
這裏我們可能會遇到一個問題
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
當我們遇到這個問題的時候，就需要下載一下我們的內核頭文件。
apt-get install -y linux-headers-$(uname -r)
拉取內核頭文件成功以後，就可以進行netmap的編譯了。
./configure
make & make install
insmod netmap.ko
等待運行完畢，這樣就完成了netmap的環境搭配。
udp協議解析的代碼編寫
看一下一個UDP的數據幀是什麼樣的？
定義我們需要的結構體
以太網頭
#define ETH_ALEN 6
struct ethhr{
unsigned char h_dest[ETH_ALEN];
unsigned char h_source[ETH_ALEN];
unsigned short h_proto;
}
ip頭
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協議
struct udphdr {
unsigned short source;
unsigned short dest;
unsigned short len;
unsigned short check;
};
最後拼接成UDP協議
struct udppkt {
struct ethhdr eh;
struct iphdr ip;
struct udphdr udp;
unsigned char body[0];
};
arp協議
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協議
struct icmphdr {
unsigned char type;
unsigned char code;
unsigned short check;
unsigned short identifier;
unsigned short seq;
unsigned char data[32];
};
icmp協議包
struct icmppkt {
struct ethhdr eh;
struct iphdr ip;
struct icmphdr icmp;
};
編寫我們解析包的代碼
這樣定義完我們需要的結構體，就可以編寫我們的代碼了
最終代碼如下:
#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) {
//獲取收到的包
stream = nm_nextpkt(nmr, &h);
//強轉爲以太網頭
eh = (struct ethhdr*)stream;
//如果是IP協議
if (ntohs(eh->h_proto) == PROTO_IP) {
//強轉爲udp的包
struct udppkt *udp = (struct udppkt*)stream;
//判斷是否爲UDP協議
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 //判斷是否爲ICMP的包
} else if (udp->ip.protocol == PROTO_ICMP) {
//強轉爲 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協議的話
} 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));
}
}
}
}
}
這樣就通過使用netmap完成了icmp和arp，以及UDP包的解析。