IPv6 的 getaddrinfo() 没有意义

Question

我不明白为什么 getaddrinfo 不是 return 有效的 IPv6 地址。

在我的系统上，下面的代码正在打印 22:B8:00:00:00:00:00:00:00:00:00:00:00:00，但我预计某处会出现 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，所以似乎最后几个字节总是被砍掉，函数可以't return 一个 IPv6 地址？

谁能解释一下这是怎么回事？我该如何在 IPv6 上使用此功能？

#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实际指向一个struct sockaddr_in6。您要打印的前几个字节是 sin6_port 和 sin6_flowinfo。 IPv6 地址在后面。

编辑添加：

您可以直接将 ai_addr 与 bind() 和 getnameinfo() 等函数一起使用。您通常不需要深入研究结构定义细节。例如，我会使用 getnameinfo() 和 NI_NUMERICHOST 来获取可打印的地址。

Answer 2

sockaddr are not strictly interpreted to be pointers to a sockaddr structure. The structure is interpreted differently in the context of different address families.

所以我们需要首先检查 sockaddr or ai_family from addrinfo (in this base it must be equal) and based on this need "reinterpret" pointer from sockaddr 的 sa_family（这就像 void* 指针）到真实结构。说为此使用联合：

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);
}

IPv6 的 getaddrinfo() 没有意义

getaddrinfo() with IPv6 not making sense

c

sockets

winapi

ipv6

getaddrinfo