004.UDP--拼接UDP數據包,構造ip頭和udp頭通信(使用原始套接字)

一.大致流程：

    建立一個client端，一個server端，自己構建IP頭和UDP頭，寫入數據(hello,world!)后通過原始套接字(SOCK_RAW)將包發出去。

server端收到數據后，打印UDP數據並發送確認消息(yes)，client收到yes后將其打印。

二.其中：

client端IP：192.168.11.104 端口：8600

server端IP：192.168.11.105 端口：8686

三.注意事項：

1.運行原始套接字socket需要有root權限。

2.注意主機字節序和網絡字節序的轉

四.涉及的數據結構

1.ip部分的結構圖：

2.ip結構體定義： 

struct iphdr       /* 該結構體在<netinet/ip.h>中定義 */
  {
#if __BYTE_ORDER == __LITTLE_ENDIAN  /* 如果是小端字節序 */
    unsigned int ihl:4;     /*首部長度*/
    unsigned int version:4; /* 版本 */
#elif __BYTE_ORDER == __BIG_ENDIAN
    unsigned int version:4;
    unsigned int ihl:4;
#else
# error    "Please fix <bits/endian.h>"
#endif
    u_int8_t tos;           /* 區分服務 */
    u_int16_t tot_len;      /* 總長度 */
    u_int16_t id;           /* 標識 */
    u_int16_t frag_off;     /* 標志(3位)+片偏移(13位) */
    u_int8_t ttl;           /* 生存時間 */
    u_int8_t protocol;      /* 協議 */
    u_int16_t check;        /* 首部檢驗和 */
    u_int32_t saddr;        /* 源地址 */
    u_int32_t daddr;        /* 目的地址 */
    /*The options start here. */
  };

 3.udp數據包的結構圖： 

4.udp結構體定義： 

struct udphdr  /* 該結構體在<netiniet/udp.h>中定義 */
{
  u_int16_t source;  /*源端口*/
  u_int16_t dest;    /*目的端口*/
  u_int16_t len;     /*長度*/
  u_int16_t check;   /*校驗和*/
};

  

五.實現如下：

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 = 1024*50;
    char send_message[MAXLINE];
    struct sockaddr_in server_address;
    //創建原始套接字
    raw_sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
    //創建套接字地址
    bzero(&server_address,sizeof(server_address));
    server_address.sin_family = AF_INET;
    server_address.sin_addr.s_addr = inet_addr("192.168.11.105");
    //設置套接字為隨數據包含IP首部(設置這個選項后需要我們手動寫入IP頭)
    setsockopt(raw_sockfd, IPPROTO_IP, IP_HDRINCL, &size, sizeof(size));

    int len;
    bzero(&send_message, sizeof(send_message));
    //拼接完整的UDP數據包(IP頭+UDP頭+數據)
    int mesg_len = make_message(send_message, MAXLINE, inet_addr("192.168.11.104"), 8600, inet_addr("192.168.11.105"), 8686);
    //將IP數據包發送出去
    sendto(raw_sockfd, send_message, mesg_len, 0, (struct sockaddr *)&server_address, sizeof(server_address));
    close(raw_sockfd);
    //
    //下面我們開始接受服務器返回的包
    int client_sockfd;
    int server_len;
    char recv_message[MAXLINE];
    struct sockaddr_in server_addr;
    client_sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr("192.168.11.104");
    server_addr.sin_port = htons(8600);
    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, 0, NULL, NULL);
       printf("收到的應答：%s\n",recv_message);
    return 0;
}

//拼接IP數據報
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[1005];
    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) >> 2; //首部長度
    ip->version = 4;   //ip協議版本
    ip->tos = 0;   //服務類型字段
    ip->tot_len = 0;   //總長度
    ip->id = 1000;   //
    ip->frag_off = 0;
    ip->ttl = 128;
    ip->protocol = IPPROTO_UDP;
    ip->check = 0;  //內核會算相應的效驗和
    ip->saddr = src_ip;
    ip->daddr = des_ip;

    struct udp_front front;
    front.srcip = src_ip;
    front.desip = des_ip;
    front.len = htons(8+strlen(message));
    front.protocol = 17;
    front.zero = 0;

    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 = 0;   //效驗和，效驗整個udp數據報
    strcpy((sendbuf+20+8), message);
    udp->len = htons(8+strlen(message)); //udp數據報總長度

    udp->check = udp_check((sendbuf+20), 8+strlen(message), front);

    ip->tot_len = htons(20 + 8 + strlen(message));   //總長度
    printf("ip->tot_len:%d\n",ip->tot_len);
    ip->check = in_chksum((unsigned short *)sendbuf, 20);

    return ntohs(ip->tot_len);
}

//計算udp效驗和
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+20);
    return in_chksum((unsigned short *)str, sizeof(front)+len);
}

//效驗和算法
uint16_t in_chksum(uint16_t *addr, int len)
{
    int nleft = len;
    uint32_t sum = 0;
    uint16_t *w = addr;
    uint16_t answer = 0;
    //把ICMP報頭二進制數據以2字節為單位累加起來
    while (nleft > 1)
    {
        sum += *w++;
        nleft -= 2;
    }
    if (nleft == 1)
    {
        *(unsigned char *)(&answer) = *(unsigned char *)w;
        sum += answer;
    }
    sum = (sum>>16) + (sum&0xffff);
    sum += (sum>>16);
    answer = ~sum;
    return answer;
}

  

server端：

server端是一個簡單的收包服務器，監聽8686端口，當有udp數據包到來時，打印信息並返回給client一個信息。

 

#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, 0);

    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[20];
        client_len = sizeof(struct sockaddr_in);
        printf("server2 waiting!\n");
        len = recvfrom(server_sockfd, recv_mesg, MAXLINE, 0, (struct sockaddr *) &client_address, (socklen_t *) &client_len);
        printf("收到包的長度為:%d\n",len);
        printf("%s\n",recv_mesg);
        strcpy(send_mesg,"yes");
        sendto(server_sockfd, send_mesg, strlen(send_mesg), 0, (struct sockaddr *) &client_address, client_len);  //將包發出去
    }
    return 0;
}