使用IPv6的getaddrinfo()没有意义

Question

我不明白为什么getaddrinfo不返回有效的IPv6地址。

在我的系统中，下面的代码是打印22:B8:00:00:00:00:00:00:00:00:00:00:00:00，但我希望在某个地方出现01，因为localhost应该解析为::1。

同时，sa_data只有14个字节，而IPv6地址是16个字节，因此似乎最后几个字节总是被截断，而函数不能返回IPv6地址？

有人能解释一下发生了什么事吗？我应该如何在IPv6中使用这个函数？

#include <stdio.h>
#include <WinSock2.h>
#include <WS2TCPIP.h>
#pragma comment(lib, "WS2_32")

int main(int argc, char *argv[])
{
    WSADATA wsadata;
    WSAStartup(0x0002, &wsadata);
    addrinfo addr_hints = { 0, PF_INET6, SOCK_DGRAM, IPPROTO_UDP }, *addrs_out;
    getaddrinfo("localhost", "8888", &addr_hints, &addrs_out);
    fprintf(stderr,
        "%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X\n",
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 0]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 1]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 2]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 3]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 4]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 5]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 6]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 7]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 8]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 9]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[10]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[11]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[12]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[13]));
    freeaddrinfo(addrs_out);
    return 0;
}

Answer 1

sockaddr结构定义以供参考：

struct sockaddr {
    ushort  sa_family;
    char    sa_data[14];
};


struct sockaddr_in6 {
    short   sin6_family;
    u_short sin6_port;
    u_long  sin6_flowinfo;
    struct  in6_addr sin6_addr;
    u_long  sin6_scope_id;
};

当ai_family == AF_INET6 ai_addr实际上指向一个struct sockaddr_in6时。您要打印的前几个字节是sin6_port和sin6_flowinfo。后面是IPv6地址。

编辑以添加：

您可以直接将ai_addr与bind()和getnameinfo()等函数一起使用。您通常不需要深入了解结构定义的细节。例如，我会使用getnameinfo()和NI_NUMERICHOST来获得可打印的地址。

Answer 2

索卡德尔不被严格解释为指向sockaddr结构的指针。这种结构在不同的称谓族中被不同的解释。

因此，我们首先需要检查sa_family of sockaddr或ai_family从addrinfo (在这个基础上它必须相等)，并根据这个需要“重新解释”从sockaddr (类似于void*指针)到实际结构的指针。就说用联合吧：

addrinfo *addrs_out, *addr;

if (getaddrinfo("localhost", "8888", 0, &addrs_out) == NOERROR)
{
    addr = addrs_out;

    CHAR buf[256], *sz, srv[128];
    ULONG n;
    PUCHAR Byte;

    do 
    {
        union {
            sockaddr* ai_addr;
            SOCKADDR_IN* pa;
            SOCKADDR_IN6* pa6;
        };

        ai_addr = addr->ai_addr;

        if (addr->ai_family != ai_addr->sa_family)
        {
            __debugbreak();
        }

        switch (addr->ai_family)
        {
        case AF_INET6:
            Byte = pa6->sin6_addr.u.Byte, n = RTL_NUMBER_OF(pa6->sin6_addr.u.Byte), sz = buf;
            do 
            {
                sz += sprintf(sz, "%02X:", *Byte++);
            } while (--n);

            sz[-1] = 0;
            DbgPrint("AF_INET6: %s\n", buf);
            break;

        case AF_INET:
            if (0 <= RtlIpv4AddressToStringExA(&pa->sin_addr.S_un.S_addr, pa->sin_port, buf, &(n = RTL_NUMBER_OF(buf))))
            {
                DbgPrint("AF_INET: %s\n", buf);
            }
            break;
        }

        // alt print
        if (getnameinfo(ai_addr, (socklen_t)addr->ai_addrlen, buf, RTL_NUMBER_OF(buf), srv, RTL_NUMBER_OF(srv), NI_NUMERICHOST ) == NOERROR)
        {
            DbgPrint("%s:%s\n", buf, srv);
        }

    } while (addr = addr->ai_next);

    freeaddrinfo(addrs_out);
}