背景：
当加速器(client)拦截了游戏客户端发送的完整数据包(package)时，将package传给中间服务器(mid_server)，经过自己的链路传输数据之后，中间服务器模拟游戏客户端将数据发给游戏服务器(end_server)，目的服务器收到请求后回应，回应的包以同样的方式返回，直到游戏客户端收到数据包。
原理及实现：
1.我们需要三个主机来模拟这个请求：
client_server: IP:192.168.11.104
mid_server: IP:192.168.11.105
end_server: IP:192.168.11.106
程序的流程图：
其中：
1.client_server只是充当普通的udp客户端，不同的是我们发送的数据是一个完整的udp类型的IP数据包
2.end_server模拟的是一台普通的游戏服务器，当有客户请求的时候，它就会回应
3.mid_server代替游戏客户端的请求，将数据包中替换了请求IP和port后发给游戏服务器，获得服务。
当游戏服务器回应数据后，同样再次将数据封装成一个完整的udp的IP数据包，填入相应的服务器IP，服务器端口，客户端IP，客户端端口，将这个数据包作为数据发给client_server
4.client_server将完整的数据包发给游戏服务器。
代码实现：
1.client_server部分：
/*
============================================================================
Name : udp_client.c
Author : huh
Version :
Copyright : ---notice---
Description : Hello World in C, Ansi-style
============================================================================
*/ #include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/ip_icmp.h>
#include <netinet/udp.h> #define MAXLINE 1024*10 int make_message(char *mesg, char sendbuf[], int send_buf_len, uint32_t src_ip, u_int16_t src_port, uint32_t des_ip, u_int16_t des_port); int main()
{
int server_sockfd;
char send_message[MAXLINE];
char recv_message[MAXLINE];
struct sockaddr_in server_address; server_sockfd = socket(AF_INET, SOCK_DGRAM, ); bzero(&server_address,sizeof(server_address));
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = inet_addr("192.168.11.105");
server_address.sin_port = htons(); int mesg_len;
bzero(&send_message, MAXLINE);
mesg_len = make_message("hello world!", send_message, MAXLINE, inet_addr("192.168.11.104"), , inet_addr("192.168.11.106"), ); //printf("send message len:%d\n",strlen(send_message));
sendto(server_sockfd, send_message, mesg_len, , (struct sockaddr *)&server_address, sizeof(server_address)); //将包发出去 bzero(&recv_message, sizeof(recv_message));
int len = recvfrom(server_sockfd, recv_message, MAXLINE, , NULL, NULL);
printf("当前收到的IP数据包的内容：\n");
struct iphdr *ip;
ip = (struct iphdr *)recv_message;
struct udphdr *udp;
udp = (struct udphdr *)(recv_message + sizeof(struct iphdr));
struct in_addr ad;
ad.s_addr = ip->saddr;
printf("src_ip:%s\n",inet_ntoa(ad));
printf("src_port:%d\n",ntohs(udp->source)); ad.s_addr = ip->daddr;
printf("des_ip:%s\n",inet_ntoa(ad));
printf("des_port:%d\n",ntohs(udp->dest));
printf("data:%s\ndata len:%d\n",(recv_message+),len); close(server_sockfd);
return ;
}
udp_client.c
/*
* make_message.c
*
* Created on: 2015年11月18日
* Author: root
*/ #include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/ip_icmp.h>
#include <netinet/udp.h> #define MAXLINE 1024*10 struct udp_front //udp
{
uint32_t srcip;
uint32_t desip;
u_int8_t zero;
u_int8_t protocol;
u_int16_t len;
}; u_int16_t in_chksum(u_int16_t *addr, int len);
u_int16_t udp_check(char *sendbuf, int len, const struct udp_front front);
int make_message(char *mesg, char sendbuf[], int send_buf_len, uint32_t src_ip, u_int16_t src_port, uint32_t des_ip, u_int16_t des_port); //拼接IP数据报
int make_message(char *mesg, char sendbuf[], int send_buf_len, uint32_t src_ip, u_int16_t src_port, uint32_t des_ip, u_int16_t des_port)
{
char message[MAXLINE];
bzero(message, sizeof(message));
strcpy(message,mesg);
printf("message len:%d\n",strlen(message));
struct iphdr *ip;
ip = (struct iphdr *)sendbuf;
ip->ihl = sizeof(struct iphdr) >> ; //首部长度
ip->version = ; //ip协议版本
ip->tos = ; //服务类型字段
ip->tot_len = ; //总长度
ip->id = ; //
ip->frag_off = ;
ip->ttl = ;
ip->protocol = IPPROTO_UDP;
ip->check = ; //内核会算相应的效验和
ip->saddr = src_ip;
ip->daddr = des_ip; struct udp_front front;
front.srcip = src_ip;
front.desip = des_ip;
front.len = htons(+strlen(message));
front.protocol = ;
front.zero = ; struct udphdr *udp;
udp = (struct udphdr *)(sendbuf + sizeof(struct iphdr));
udp->source = htons(src_port); //源端口
udp->dest = htons(des_port); //目的端口
udp->check = ; //效验和，效验整个udp数据报
strcpy((sendbuf++), message);
udp->len = htons(+strlen(message)); //udp数据报总长度 udp->check = udp_check((sendbuf+), +strlen(message), front); ip->tot_len = ( + + strlen(message)); //总长度
printf("ip->tot_len:%d\n",ip->tot_len);
ip->check = in_chksum((unsigned short *)sendbuf, ); return (ip->tot_len);
} //计算udp效验和
unsigned short udp_check(char *sendbuf, int len, const struct udp_front front)
{
char str[MAXLINE];
bzero(&str, MAXLINE);
bcopy(&front, str, sizeof(front));
bcopy(sendbuf, str+sizeof(front), len);
struct udp_front *ptr;
ptr = (struct udp_front *)str;
char *s;
s = (str+);
return in_chksum((unsigned short *)str, sizeof(front)+len);
} //效验和算法
uint16_t in_chksum(uint16_t *addr, int len)
{
int nleft = len;
uint32_t sum = ;
uint16_t *w = addr;
uint16_t answer = ;
//把ICMP报头二进制数据以2字节为单位累加起来
while (nleft > )
{
sum += *w++;
nleft -= ;
}
if (nleft == )
{
*(unsigned char *)(&answer) = *(unsigned char *)w;
sum += answer;
}
sum = (sum>>) + (sum&0xffff);
sum += (sum>>);
answer = ~sum;
return answer;
}
make_message.c
2.mid_server部分：
/*
============================================================================
Name : udp_mid_server.c
Author : huh
Version :
Copyright : ---notice---
Description : Hello World in C, Ansi-style
============================================================================
*/ #include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/ip_icmp.h>
#include <netinet/udp.h> #define MAXLINE 1024*50 #define SERVER_IP "192.168.11.105" //本服务器IP
#define TO_CLI_PORT 8600 //本服务器监听client_server端口
#define TO_END_PORT 8601 //本服务器监听end_server端口 #define END_SERVER_IP "192.168.11.106" //end_server的ip
#define END_SERVER_PORT 8686 //end_server的port struct udp_front //udp
{
uint32_t srcip;
uint32_t desip;
u_int8_t zero;
u_int8_t protocol;
u_int16_t len;
}; uint32_t client_ip;
int client_port; extern u_int16_t in_chksum(u_int16_t *addr, int len);
extern u_int16_t udp_check(char *sendbuf, int len, const struct udp_front front);
extern int make_message(char *mesg, char sendbuf[], int send_buf_len, uint32_t src_ip, u_int16_t src_port, uint32_t des_ip, u_int16_t des_port); void change_src(char sendbuf[], int len, uint32_t src_ip, int src_port)
{
struct iphdr *ip;
ip = (struct iphdr *)sendbuf;
ip->check = ; //内核会算相应的效验和
client_ip = ip->saddr;
ip->saddr = src_ip;
ip->check = in_chksum((unsigned short *)sendbuf, );
;
struct udp_front front;
front.srcip = src_ip;
front.desip = ip->daddr;
front.len = htons(len-);
front.protocol = ;
front.zero = ; struct udphdr *udp;
udp = (struct udphdr *)(sendbuf + sizeof(struct iphdr));
client_port = ntohs(udp->source);
udp->source = htons(src_port); //源端口
udp->check = ; //效验和，效验整个udp数据报
udp->check = udp_check((sendbuf+), len-, front);
} void send_1(int raw_sockfd, char *send_message, int len)
{
struct sockaddr_in server_addr;
bzero(&server_addr,sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = inet_addr(END_SERVER_IP); change_src(send_message, len, inet_addr(SERVER_IP), TO_END_PORT);
sendto(raw_sockfd, send_message, len, , (struct sockaddr *) &server_addr, sizeof(server_addr)); //将包发出去
printf("前往end_server的包已经出发！\n");
} int main()
{
int size = *;
int server_len, client_len;
struct sockaddr_in server_address;
struct sockaddr_in client_address; //接收client_server端数据的套接字
//监听端口：8600
int server_sockfd;
server_sockfd = socket(AF_INET, SOCK_DGRAM, );
bzero(&server_address,sizeof(server_address));
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = inet_addr(SERVER_IP);
server_address.sin_port = htons(TO_CLI_PORT);
server_len = sizeof(server_address);
bind(server_sockfd, (struct sockaddr *)&server_address, server_len); //发送给end_server的原始套接字
int raw_sockfd;
raw_sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
setsockopt(raw_sockfd, IPPROTO_IP, IP_HDRINCL, &size, sizeof(size)); //接收end_server端数据的套接字
//监听端口：8601
int end_sockfd;
end_sockfd = socket(AF_INET, SOCK_DGRAM, );
bzero(&server_address,sizeof(server_address));
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = inet_addr(SERVER_IP);
server_address.sin_port = htons(TO_END_PORT);
server_len = sizeof(server_address);
bind(end_sockfd, (struct sockaddr *)&server_address, server_len); char recv_mesg[MAXLINE];
char send_mesg[MAXLINE];
for( ; ; )
{
int len;
client_len = sizeof(struct sockaddr_in);
printf("server waiting!\n");
//接收来自client_server的包
bzero(&client_address, sizeof(client_address));
len = recvfrom(server_sockfd, recv_mesg, MAXLINE, , (struct sockaddr *) &client_address, (socklen_t *) &client_len);
printf("来自client_server的IP数据包的长度为:%d\n",len); //将接收到的数据作为一个完整的IP包发给end_server
send_1(raw_sockfd, recv_mesg, len); //接收来自end_server的回应包，并将数据存在recv_mesg里面
bzero(recv_mesg, sizeof(recv_mesg));
len = recvfrom(end_sockfd, recv_mesg, MAXLINE, , NULL, NULL);
printf("收到来自end_server的应答：%s,长度：%d\n",recv_mesg,len); //现在将end_server给我的包拼接好后发给client_server.
printf("client:%d\n",client_port);
bzero(send_mesg,sizeof(send_mesg));
int mesg_len = make_message(recv_mesg, send_mesg, MAXLINE, inet_addr(END_SERVER_IP), END_SERVER_PORT, client_ip, client_port);
sendto(server_sockfd, send_mesg, mesg_len, , (struct sockaddr *) &client_address, client_len); }
return ;
}
udp_mid_server.c
/*
* make_message.c
*
* Created on: 2015年11月18日
* Author: root
*/ #include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/ip_icmp.h>
#include <netinet/udp.h> #define MAXLINE 1024*10 struct udp_front //udp
{
uint32_t srcip;
uint32_t desip;
u_int8_t zero;
u_int8_t protocol;
u_int16_t len;
}; u_int16_t in_chksum(u_int16_t *addr, int len);
u_int16_t udp_check(char *sendbuf, int len, const struct udp_front front); //拼接IP数据报
int make_message(char *mesg, char sendbuf[], int send_buf_len, uint32_t src_ip, u_int16_t src_port, uint32_t des_ip, u_int16_t des_port)
{
char message[MAXLINE];
bzero(message, sizeof(message));
strcpy(message,mesg);
printf("message len:%d\n",strlen(message));
struct iphdr *ip;
ip = (struct iphdr *)sendbuf;
ip->ihl = sizeof(struct iphdr) >> ; //首部长度
ip->version = ; //ip协议版本
ip->tos = ; //服务类型字段
ip->tot_len = ; //总长度
ip->id = ; //
ip->frag_off = ;
ip->ttl = ;
ip->protocol = IPPROTO_UDP;
ip->check = ; //内核会算相应的效验和
ip->saddr = src_ip;
ip->daddr = des_ip; struct udp_front front;
front.srcip = src_ip;
front.desip = des_ip;
front.len = htons(+strlen(message));
front.protocol = ;
front.zero = ; struct udphdr *udp;
udp = (struct udphdr *)(sendbuf + sizeof(struct iphdr));
udp->source = htons(src_port); //源端口
udp->dest = htons(des_port); //目的端口
udp->check = ; //效验和，效验整个udp数据报
strcpy((sendbuf++), message);
udp->len = htons(+strlen(message)); //udp数据报总长度 udp->check = udp_check((sendbuf+), +strlen(message), front); ip->tot_len = ( + + strlen(message)); //总长度
printf("ip->tot_len:%d\n",ip->tot_len);
ip->check = in_chksum((unsigned short *)sendbuf, ); return (ip->tot_len);
} //计算udp效验和
unsigned short udp_check(char *sendbuf, int len, const struct udp_front front)
{
char str[MAXLINE];
bzero(&str, MAXLINE);
bcopy(&front, str, sizeof(front));
bcopy(sendbuf, str+sizeof(front), len);
struct udp_front *ptr;
ptr = (struct udp_front *)str;
char *s;
s = (str+);
return in_chksum((unsigned short *)str, sizeof(front)+len);
} //效验和算法
uint16_t in_chksum(uint16_t *addr, int len)
{
int nleft = len;
uint32_t sum = ;
uint16_t *w = addr;
uint16_t answer = ;
//把ICMP报头二进制数据以2字节为单位累加起来
while (nleft > )
{
sum += *w++;
nleft -= ;
}
if (nleft == )
{
*(unsigned char *)(&answer) = *(unsigned char *)w;
sum += answer;
}
sum = (sum>>) + (sum&0xffff);
sum += (sum>>);
answer = ~sum;
return answer;
}
make_message.c
3.end_srever部分：
/*
============================================================================
Name : udp_end_server.c
Author : huh
Version :
Copyright : ---notice---
Description : Hello World in C, Ansi-style
============================================================================
*/ #include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h> #define MAXLINE 1024*50 #define SERVER_IP "192.168.11.106" //本服务器IP
#define SERVER_PORT 8686 //本服务器监听端口 int main()
{
int server_sockfd;
char recv_mesg[MAXLINE];
int server_len, client_len;
struct sockaddr_in server_address;
struct sockaddr_in client_address; server_sockfd = socket(AF_INET, SOCK_DGRAM, );
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = inet_addr(SERVER_IP);
server_address.sin_port = htons(SERVER_PORT);
server_len = sizeof(server_address);
bind(server_sockfd, (struct sockaddr *)&server_address, server_len); //我们会将收到的数据加上"by end server!",再返回给客户端
while()
{
int len;
client_len = sizeof(struct sockaddr_in);
printf("end server waiting!\n");
bzero(recv_mesg, sizeof(recv_mesg));
len = recvfrom(server_sockfd, recv_mesg, MAXLINE, , (struct sockaddr *) &client_address, (socklen_t *) &client_len);
printf("收到mid_server包的长度为:%d,内容为:%s\n", len, recv_mesg);
strcpy(recv_mesg+len," by end_server!");
len = strlen(recv_mesg);
sendto(server_sockfd, recv_mesg, len, , (struct sockaddr *) &client_address, client_len); //将包发出去
printf("往mid_server回应的包已经出发!\n");
}
return ;
}
udp_end_server.c
监听中间服务器显示的结果：
[root@mid_server ~]# tcpdump -nn udp and host 192.168.11.105
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
22:25:24.085794 IP 192.168.11.104.45375 > 192.168.11.105.8600: UDP, length 40
22:25:24.086092 IP 192.168.11.105.8601 > 192.168.11.106.8686: UDP, length 12
22:25:24.086632 IP 192.168.11.106.8686 > 192.168.11.105.8601: UDP, length 27
22:25:24.086891 IP 192.168.11.105.8600 > 192.168.11.104.45375: UDP, length 55