004.UDP--拼接UDP数据包,构造ip头和udp头通信(使用原始套接字)

一.大致流程：

建立一个client端，一个server端，自己构建IP头和UDP头，写入数据(hello,world!)后通过原始套接字(SOCK_RAW)将包发出去。

server端收到数据后，打印UDP数据并发送确认消息(yes)，client收到yes后将其打印。

二.其中：

client端IP：192.168.11.104 端口：8600

server端IP：192.168.11.105 端口：8686

三.注意事项：

1.运行原始套接字socket需要有root权限。

2.注意主机字节序和网络字节序的转

四.涉及的数据结构

1.ip部分的结构图：

2.ip结构体定义：

struct iphdr       /* 该结构体在<netinet/ip.h>中定义 */
  {
#if __BYTE_ORDER == __LITTLE_ENDIAN  /* 如果是小端字节序 */
    unsigned int ihl:;     /*首部长度*/
    unsigned int version:; /* 版本 */
#elif __BYTE_ORDER == __BIG_ENDIAN
    unsigned int version:;
    unsigned int ihl:;
#else
# error    "Please fix <bits/endian.h>"
#endif
    u_int8_t tos;           /* 区分服务 */
    u_int16_t tot_len;      /* 总长度 */
    u_int16_t id;           /* 标识 */
    u_int16_t frag_off;     /* 标志(3位)+片偏移(13位) */
    u_int8_t ttl;           /* 生存时间 */
    u_int8_t protocol;      /* 协议 */
    u_int16_t check;        /* 首部检验和 */
    u_int32_t saddr;        /* 源地址 */
    u_int32_t daddr;        /* 目的地址 */
    /*The options start here. */
  };

 3.udp数据包的结构图：

4.udp结构体定义：

struct udphdr  /* 该结构体在<netiniet/udp.h>中定义 */
{
  u_int16_t source;  /*源端口*/
  u_int16_t dest;    /*目的端口*/
  u_int16_t len;     /*长度*/
  u_int16_t check;   /*校验和*/
};

五.实现如下：

client端：

 /*
  ============================================================================
  Name        : test_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

 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 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 raw_sockfd;
     int size = *;
     char send_message[MAXLINE];
     struct sockaddr_in server_address;
     //创建原始套接字
     raw_sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
     //创建套接字地址
     bzero(&server_address,sizeof(server_address));
     server_address.sin_family = AF_INET;
     server_address.sin_addr.s_addr = inet_addr("192.168.11.105");
     //设置套接字为随数据包含IP首部(设置这个选项后需要我们手动写入IP头)
     setsockopt(raw_sockfd, IPPROTO_IP, IP_HDRINCL, &size, sizeof(size));

     int len;
     bzero(&send_message, sizeof(send_message));
     //拼接完整的UDP数据包(IP头+UDP头+数据)
     int mesg_len = make_message(send_message, MAXLINE, inet_addr("192.168.11.104"), , inet_addr("192.168.11.105"), );
     //将IP数据包发送出去
     sendto(raw_sockfd, send_message, mesg_len, , (struct sockaddr *)&server_address, sizeof(server_address));
     close(raw_sockfd);
     //
     //下面我们开始接受服务器返回的包
     int client_sockfd;
     int server_len;
     char recv_message[MAXLINE];
     struct sockaddr_in server_addr;
     client_sockfd = socket(AF_INET, SOCK_DGRAM, );
     server_addr.sin_family = AF_INET;
     server_addr.sin_addr.s_addr = inet_addr("192.168.11.104");
     server_addr.sin_port = htons();
     server_len = sizeof(server_address);
     bind(client_sockfd, (struct sockaddr *)&server_addr, server_len);

     bzero(&recv_message, sizeof(recv_message));
        len = recvfrom(client_sockfd, recv_message, MAXLINE, , NULL, NULL);
        printf("收到的应答：%s\n",recv_message);
     return ;
 }

 //拼接IP数据报
 int make_message(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[];
     bzero(message, sizeof(message));
     strcpy(message,"hello,world!");
     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 = htons( +  + strlen(message));   //总长度
     printf("ip->tot_len:%d\n",ip->tot_len);
     ip->check = in_chksum((unsigned short *)sendbuf, );

     return ntohs(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;
 }

server端：

server端是一个简单的收包服务器，监听8686端口，当有udp数据包到来时，打印信息并返回给client一个信息。

 #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 HOST_IP "192.168.11.105"
 #define HOST_PORT 8686

 #define MAXLINE 1024*50

 int main()
 {
     int server_sockfd;
     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(HOST_IP);
     server_address.sin_port = htons(HOST_PORT);

     server_len = sizeof(server_address);
     bind(server_sockfd, (struct sockaddr *)&server_address, server_len);

     for( ; ; )
     {
         int len;
         char recv_mesg[MAXLINE];
         char send_mesg[];
         client_len = sizeof(struct sockaddr_in);
         printf("server2 waiting!\n");
         len = recvfrom(server_sockfd, recv_mesg, MAXLINE, , (struct sockaddr *) &client_address, (socklen_t *) &client_len);
         printf("收到包的长度为:%d\n",len);
         printf("%s\n",recv_mesg);
         strcpy(send_mesg,"yes");
         sendto(server_sockfd, send_mesg, strlen(send_mesg), , (struct sockaddr *) &client_address, client_len);  //将包发出去
     }
     return ;
 }

server.c