c - getaddrinfo() 返回 2.0.0.0

Question

我正在尝试查找主机名的 IP 地址，即 www.google.com

我调用 getaddrinfo() 扫描列表，创建一个原始 ipv4 icmp 套接字，然后将该套接字绑定(bind)到该地址

当我检查在wireshark中发送的数据包时，无论我传递给getaddrinfo()什么主机名，地址都会显示为2.0.0.0

  int                  skt, errno;
   struct sockaddr_in   addr;
   struct addrinfo      hints;  //prefered addr type(connection)
   struct addrinfo  *   list;   //list of addr structs
   struct addrinfo  *   addrptr;//the one i am gonna use

   struct in_addr test;

    if(servname == NULL){
        fprintf(stderr, "No servname!\n");
        exit(1);
    }

    /*
     * prefered connection type
     */

    bzero(&hints, sizeof(hints));
    hints.ai_flags                = 0;
    hints.ai_family               = AF_INET;
    hints.ai_socktype             = SOCK_RAW;
    hints.ai_protocol             = IPPROTO_ICMP;                 

    /*get IP*/
    if((errno = getaddrinfo(servname, 0, &hints, &list))<0){
        fprintf(stderr, "addrinfo error, lookup fail:  %s",
        gai_strerror(errno));
        exit(1);
    }

   addrptr=list;
   //start scanning 
   while(addrptr){
       //start
       if((skt = socket(addrptr->ai_family, addrptr->ai_socktype, addrptr->ai_protocol))<0){
        perror("socket()");
        exit(1);
       }
           if(skt > 0)
            if(connect(skt,addrptr->ai_addr, addrptr->ai_addrlen)==0)
                break;
            printf("attempt connect\n");
            close (skt);
            addrptr=addrptr->ai_next;
    }


 //once IP has been found set destination address an port=0
 dstaddr.sin_addr.s_addr = ((struct in_addr *)addrptr->ai_addr)->s_addr;
 dstaddr.sin_port        = 0;

Answer 1

您的代码中似乎存在一些错误:

• addrptr=list->ai_next应该是addrptr=addr->ai_next遍历列表。
• 在 while 循环之后，addrptr->ai_addr保存最后找到的条目，而不是 list->ai_addr .
• bind() 成功时返回零，因此您应该检查 if(bind(...) == 0) break;
• 除非我弄错了，bind()用于将套接字绑定(bind)到本地地址。要检查是否可以在某个地址访问主机，请使用 connect()相反。

这是我尝试过的代码:

int main(int argc, const char * argv[])
{
    int                  skt, errno;
    struct addrinfo      hints;  //prefered addr type(connection)
    struct addrinfo  *   list;   //list of addr structs
    struct addrinfo  *   addrptr;//the one i am gonna use

    char *servname = "www.google.com";

    memset(&hints, 0, sizeof(hints));
    hints.ai_flags                = 0;
    hints.ai_family               = AF_INET;
    hints.ai_socktype             = SOCK_RAW;
    hints.ai_protocol             = IPPROTO_ICMP;

    if ((errno = getaddrinfo(servname, 0, &hints, &list))<0){
        fprintf(stderr, "addrinfo error, lookup fail:  %s", gai_strerror(errno));
        exit(1);
    }

    for (addrptr = list; addrptr != NULL; addrptr = addrptr->ai_next) {
        if ((skt = socket(addrptr->ai_family, addrptr->ai_socktype, addrptr->ai_protocol)) == -1)
            continue;
        if(connect(skt,addrptr->ai_addr, addrptr->ai_addrlen) == 0)
            break;
        close (skt);
    }

    if (addrptr != NULL) {
        char host[NI_MAXHOST];
        getnameinfo(addrptr->ai_addr, addrptr->ai_addrlen, host, sizeof(host), NULL, 0, NI_NUMERICHOST);
        printf("%s can be reached at %s\n", servname, host);
    }

    return 0;
}

输出为:“可通过 173.194.113.146 访问 www.google.com”

更新:您复制找到的地址的代码是错误的，应该是

struct sockaddr_in dstaddr;
memcpy(&dstaddr, addrptr->ai_addr, sizeof(dstaddr));
dstaddr.sin_port        = 0;