Linux下实现ping程序

Posted 2021-03-03 Kaleidopink

今天参照大神的代码实现了一个ping程序。
总体是先发送一个ping请求，然后循环四次监听返回。

send_ping函數

1. 將icmp_hdr(icmp消息的header)的指針指向一片內存空間，然後定義各個屬性。通過memcpy函數將要發送的數據複製到data屬性中。

   再通過sendto函數將icmp數據包發送到指定地址

   sendto函數

   #include <sys/types.h>   
   #include <sys/socket.h>
   int sendto(int socketfd, const void * msg, int len, unsigned int flags, const struct sockaddr * to, int tolen);
   

   socketfd:socket套接字描述符

   成功則返回發送的字符數，否則返回-1.

   與之對應的是recvfrom函數

   #include <sys/types.h>   
   #include <sys/socket.h>
   int sendto(int socketfd, void* buffer, int len, unsigned int flags, const struct sockaddr * from, int fromlen);
   

   通過套接字接收信息，存放到buffer中。

handle_packet函數

1. recv_reply函數將返回的ICMP消息存儲在recv_buf中，在處理返回結果時，將一個iphdr類型的指針指向這塊內存進行操作。

   這塊內存信息包含的數據有IP信息頭部長度，數據部分長度。數據部分包含了icmp的頭部信息和數據信息。icmp的起始地址便是recvbuf + ip頭的長度。然後要計算校驗和，如果檢驗和不為0，說明信息出現了錯誤。

   然後還要判斷icmp_id和icmp_type。

贴一下源码

#include<stdio.h>
#include<stdlib.h>
#include<sys/time.h>
#include<unistd.h>   
#include<string.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<netdb.h>
#include<errno.h>
#include<arpa/inet.h>
#include<signal.h>
#include<netinet/in.h>
 
#ifndef _LITTLE_ENDIAN_BITFIELD
#define _LITTLE_ENDIAN_BITFIELD
#endif
 
#define IP_HSIZE sizeof(struct iphdr)   //定义IP_HSIZE为ip头部长度
#define IPVERSION  4   //定义IPVERSION为4，指出用ipv4
 
 
 
#define ICMP_ECHOREPLY 0 //Echo应答
#define ICMP_ECHO      8 //Echo请求
 
#define BUFSIZE 1500     //发送缓存最大值
#define DEFAULT_LEN 56   //ping 消息数据默认大小
 
//数据类型别名
typedef unsigned char u8;
typedef unsigned short u16;
typedef unsigned int u32;
 
//ICMP消息头部

struct icmphdr
{
    u8 type;
    u8 code;
    u16 checksum;
    union
    {
        struct
        {
            u16 id;
            u16 sequence;
        }echo;
        
        u32 gateway;
        struct
        {
            u16 unused;
            u16 mtu;
        }frag; //pmtu发现
    }un;
    u32  icmp_timestamp[2];//时间戳
    //ICMP数据占位符
    u8 data[0];
#define icmp_id un.echo.id
#define icmp_seq un.echo.sequence
};
 
#define ICMP_HSIZE sizeof(struct icmphdr)
struct iphdr
{
#if defined _LITTLE_ENDIAN_BITFIELD
    u8 hlen:4,
ver: 4;
#elif defined _BIG_ENFIAN_BITFELD
    u8 ver:4,
hlen:4;
#endif
    
    u8 tos;
    u16 tot_len;
    u16 id;
    u16 frag_off;
    u8 ttl;
    u8 protocol;
    u16 check;
    u32 saddr;
    u32 daddr;
};
char hello[]="hello this is  a ping test.";
char *hostname; //被ping的主机
int  datalen=DEFAULT_LEN;//ICMP消息携带的数据长度
char sendbuf[BUFSIZE];
char recvbuf[BUFSIZE];
int nsent;//发送的ICMP消息序号
int nrecv;
pid_t pid;//ping程序的进程pid
struct timeval recvtime; //收到ICMP应答的时间戳
int sockfd; //发送和接收原始套接字
struct sockaddr_in dest;//被ping主机的ip
struct sockaddr_in from;//发送ping应答消息的主机ip
 
struct sigaction act_alarm;
struct sigaction act_int;
 
 
//设置的时间是一个结构体，倒计时设置，重复倒时，超时值设为1秒
struct itimerval val_alarm;

void alarm_handler(int);//SIGALRM处理程序
void int_handler(int);//SIGINT处理程序
void set_sighandler();//设置信号处理程序
void send_ping();//发送ping消息
void recv_reply();//接收ping应答
u16 checksum(u8 *buf,int len);//计算校验和
int handle_pkt();//ICMP应答消息处理
void get_statistics(int ,int);//统计ping命令的检测结果
void bail(const char *);//错误报告

void send_ping() {
    struct iphdr* ip_hdr;
    struct icmphdr* icmp_hdr;
    
    icmp_hdr = (struct icmphdr*)(sendbuf);
    icmp_hdr->type = ICMP_ECHO;
    icmp_hdr->code = 0;
    icmp_hdr->icmp_id = pid; //icmp_id = un.id,means process id
    icmp_hdr->icmp_seq = nsent++;
    gettimeofday((struct timeval*)icmp_hdr->icmp_timestamp,NULL);
    
    int len = ICMP_HSIZE + strlen(hello);
    icmp_hdr->checksum = 0;
    icmp_hdr->checksum = checksum((u8 *)icmp_hdr, len);
    
    sendto(sockfd, sendbuf, len, 0, (struct sockaddr*)&dest, sizeof(dest));
}

void recv_reply() {
    socklen_t len;
    int n = 0;
    nrecv = 0;
    int errno;
    len = sizeof(from);
    
    while (nrecv < 4) {
        if ((n = recvfrom(sockfd, recvbuf, sizeof(recvbuf), 0, (struct sockaddr*)&from, &len)) < 0) {
            if (errno == EINTR) {
                continue;
            }
            bail("recv from error");
        }
        gettimeofday(&recvtime, NULL);
        
        if (handle_pkt())
            continue;
        
        nrecv++;
    }
    get_statistics(nsent, nrecv);
}

u16 checksum(u8* buf, int len) {
    u32 sum=0;
    u16 *cbuf;
    
    cbuf=(u16 *)buf;
    
    while(len>1)
    {
        sum+=*cbuf++;
        len-=2;
    }
    
    if(len)
        sum+=*(u8 *)cbuf;
    
    sum=(sum>>16)+(sum & 0xffff);
    sum+=(sum>>16);
    
    return ~sum;

}

//handle ip response packet
int handle_pkt() {
    struct iphdr* ip;
    
    ip = (struct iphdr*)recvbuf;
    
    int ip_hlen = ip->hlen << 2;
    u16 ip_datalen = ntohs(ip->tot_len) - ip_hlen; 
    
    struct icmphdr* icmp;
    icmp = (struct icmphdr*)(recvbuf + ip_hlen);
    
    u16 sum = (u16)checksum((u8*)icmp, ip_datalen);
    
    if (sum) {
        printf("check is not equal to 0
");
        return -1;
    }
    
    if (icmp->type != ICMP_ECHOREPLY) {
        return -1;
    }
    if (icmp->icmp_id != pid) {
        return -1;
    }
    
    struct timeval* sendtime = (struct timeval*)icmp->icmp_timestamp;
    double rtt;//round-trip time
    rtt = ((&recvtime)->tv_sec - sendtime->tv_sec) * 1000 + ((&recvtime)->tv_usec - sendtime->tv_usec) / 1000.0;
    
    printf("%dbytes from %s:icmp_seq = %u, ttl = %d, rrt = %.3f ms
",ip_datalen, inet_ntoa(from.sin_addr), nsent, ip->ttl, rtt);
    
    return 0;
}

//signal handler
void set_sighandler() {
    act_alarm.sa_handler=alarm_handler;
    printf("alarm handle signal: %d
", SIGALRM);
    if(sigaction(SIGALRM,&act_alarm,NULL)==-1)  //sigaction()会依参数signum指定的信号编号来设置该信号的处理函数。参数signum指所要捕获信号或忽略的信号，&act代表新设置的信号共用体，NULL代表之前设置的信号处理结构体。这里判断对信号的处理是否成功。
        bail("SIGALRM handler setting fails.");
    
    act_int.sa_handler=int_handler;
    printf("int handler handle signal: %d
", SIGALRM);
    if(sigaction(SIGINT,&act_int,NULL)==-1)
        bail("SIGALRM handler setting fails.");

}

void get_statistics(int nsent, int nrecv) {
    printf("---%s ping statistics-----
",inet_ntoa(dest.sin_addr));
    printf("%d packets transmitted,%d received, %0.0f%% loss
",nsent, nrecv, 1.0 * (nsent - nrecv) / nsent * 100);
}

//error report
void bail(const char* incident) {
    fputs(strerror(errno), stderr);
    fputs(":", stderr);
    fputs(incident, stderr);
    fputc(‘
‘, stderr);
    exit(1);
}

//interupt signal process program
void int_handler(int sig) {
    get_statistics(nsent, nrecv);
    close(sockfd);
    exit(1);
}

void alarm_handler(int signo) {
    send_ping();
}

int main(int argc, char** argv) {
    val_alarm.it_interval.tv_sec = 1;
    val_alarm.it_interval.tv_usec = 0;
    val_alarm.it_value.tv_sec = 0;
    val_alarm.it_value.tv_usec = 1;
    struct hostent* host; //#include <netdb.h>
    int on = 1;
    
    if ((host = gethostbyname(argv[1])) == NULL) {
        perror("can not understand the host name");
        exit(1);
    }
    
    hostname = argv[1];
    memset(&dest, 0, sizeof(dest));
    dest.sin_family = PF_INET;
    dest.sin_port = ntohs(0);
    dest.sin_addr = *(struct in_addr *)host->h_addr_list[0];//h_addr_list is char** type
    
    setuid(getuid());//grant user root authority
    if ((sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0) {
        perror("raw socket created error");
        exit(1);
    }
    
    pid = getpid();
    printf("Pid: %d
", pid);
    set_sighandler();
    printf("Ping %s(%s): %d bytes data in ICMP packets.
", argv[1], inet_ntoa(dest.sin_addr), datalen);
    
    if ((setitimer(ITIMER_REAL, &val_alarm, NULL)) == -1)
        bail("setitimer falied");
    
    recv_reply();
    
    return 0;

}