C++实现分析TCP、UDP、ICMP和IGMP协议

一代码
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <linux/if_packet.h>
#include <netinet/if_ether.h>
#include <netinet/in.h>
#include <unistd.h> //for close


typedef struct _iphdr //定义IP首部
{
    unsigned char h_verlen; //4位首部长度+4位IP版本号
    unsigned char tos; //8位服务类型TOS
    unsigned short total_len; //16位总长度（字节）
    unsigned short ident; //16位标识
    unsigned short frag_and_flags; //3位标志位和13位片偏移
    unsigned char ttl; //8位生存时间 TTL
    unsigned char proto; //8位协议 (TCP, UDP 或其他)
    unsigned short checksum; //16位IP首部校验和
    unsigned int sourceIP; //32位源IP地址
    unsigned int destIP; //32位目的IP地址
}IP_HEADER;

typedef struct _udphdr //定义UDP首部
{
    unsigned short uh_sport;    //16位源端口
    unsigned short uh_dport;    //16位目的端口
    unsigned int uh_len;//16位UDP包长度
    unsigned int uh_sum;//16位校验和
}UDP_HEADER;

typedef struct _tcphdr //定义TCP首部
{
    unsigned short th_sport; //16位源端口
    unsigned short th_dport; //16位目的端口
    unsigned int th_seq; //32位序列号
    unsigned int th_ack; //32位确认号
    unsigned char th_lenres;//4位首部长度/6位保留字
    unsigned char th_flag; //6位标志位
    unsigned short th_win; //16位窗口大小
    unsigned short th_sum; //16位校验和
    unsigned short th_urp; //16位紧急数据偏移量
}TCP_HEADER;

typedef struct _icmphdr {  
    unsigned char  icmp_type;  
    unsigned char icmp_code; /* type sub code */  
    unsigned short icmp_cksum;  
    unsigned short icmp_id;  
    unsigned short icmp_seq;  
    /* This is not the std header, but we reserve space for time */  
    unsigned short icmp_timestamp;  
}ICMP_HEADER;

void analyseIP(IP_HEADER *ip);
void analyseTCP(TCP_HEADER *tcp);
void analyseUDP(UDP_HEADER *udp);
void analyseICMP(ICMP_HEADER *icmp);


int main(void)
{
    int sockfd;
    IP_HEADER *ip;
    char buf[10240];
    ssize_t n;
    /* 如果使用SOCK_DGRAM，则捕获IP的数据报不需要以太网头 */
    if ((sockfd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) == -1)
    {    
        printf("socket error!\n");
        return 1;
    }
    while (1)
    {
        n = recv(sockfd, buf, sizeof(buf), 0);
        if (n == -1)
        {
            printf("recv error!\n");
            break;
        }
        else if (n == 0)
            continue;
        //接收数据不包括数据链路帧头，从IP首部开始接收
        ip = (IP_HEADER *)(buf);
        analyseIP(ip);      //分析IP数据报
        size_t iplen =  (ip->h_verlen & 0x0f) * 4;  //IP数据报长度
        
        if (ip->proto == IPPROTO_TCP)  //分析TCP数据报
        {
            TCP_HEADER *tcp = (TCP_HEADER *)(buf + iplen);
            analyseTCP(tcp);
        }
        else if (ip->proto == IPPROTO_UDP)   //分析UDP数据报
        {
            UDP_HEADER *udp = (UDP_HEADER *)(buf + iplen);
            analyseUDP(udp);
        }
        else if (ip->proto == IPPROTO_ICMP)        //分析ICMP数据报
        {
            ICMP_HEADER *icmp = (ICMP_HEADER *)(buf + iplen);
            analyseICMP(icmp);
        }
        else if (ip->proto == IPPROTO_IGMP)
        {
            printf("IGMP----\n");
        }
        else
        {
            printf("other protocol!\n");
        }        
        printf("\n\n");
    }
    close(sockfd);
    return 0;
}

void analyseIP(IP_HEADER *ip)        //分析出IP数据报的源IP和目的IP
{
    unsigned char* p = (unsigned char*)&ip->sourceIP;
    printf("Source IP\t: %u.%u.%u.%u\n", p[0], p[1], p[2], p[3]);
    p = (unsigned char*)&ip->destIP;
    printf("Destination IP\t: %u.%u.%u.%u\n", p[0], p[1], p[2], p[3]);

}

void analyseTCP(TCP_HEADER *tcp)      //分析出TCP的源端口和目的端口
{
    printf("TCP -----\n");
    printf("Source port: %u\n", ntohs(tcp->th_sport));
    printf("Dest port: %u\n", ntohs(tcp->th_dport));
}

void analyseUDP(UDP_HEADER *udp)        // 分析出UDP的源端口和目的端口
{
    printf("UDP -----\n");
    printf("Source port: %u\n", ntohs(udp->uh_sport));
    printf("Dest port: %u\n", ntohs(udp->uh_dport));
}

void analyseICMP(ICMP_HEADER *icmp)          //分析出ICMP的类型和代码
{
    printf("ICMP -----\n");
    printf("type: %u\n", icmp->icmp_type);
    printf("sub code: %u\n", icmp->icmp_code);
}
二运行
抓包结果如下
C++实现分析TCP、UDP、ICMP和IGMP协议

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