c - Haskell:不支持的操作(协议(protocol)族不支持地址族)

Question

我有这段代码连接到本地 Graphite (实际上只是在本地主机上运行的nc -l -p 2023):

getCarbonAddr :: Config -> IO SockAddr
getCarbonAddr cfg = do
    let host = (graphiteHost . graphiteConfig) cfg
    let port = (graphitePort . graphiteConfig) cfg
    -- addrInfos <- getAddrInfo (Just defaultHints)
    addrInfos <- getAddrInfo Nothing
                   (Just host)
                   (Just (show port))
    putStrLn $ "addrInfos: " ++ show addrInfos
    c <- case addrInfos of
           (addrInfo : _) -> return (addrAddress addrInfo)
           _ -> unsupportedAddressError host
    return c
  where
    unsupportedAddressError h = ioError $ userError $
      "unsupported address: " ++ h

主机和端口的配置值分别为“localhost”和2023。当我升级到 Yosemite 后在 OS X 上运行此程序时，我看到以下崩溃:

addrInfos: [AddrInfo {addrFlags = [], addrFamily = AF_INET6, addrSocketType = Datagram, addrProtocol = 17, addrAddress = [::1]:2023, addrCanonName = Nothing},AddrInfo {addrFlags = [], addrFamily = AF_INET6, addrSocketType = Stream, addrProtocol = 6, addrAddress = [::1]:2023, addrCanonName = Nothing},AddrInfo {addrFlags = [], addrFamily = AF_INET, addrSocketType = Datagram, addrProtocol = 17, addrAddress = 127.0.0.1:2023, addrCanonName = Nothing},AddrInfo {addrFlags = [], addrFamily = AF_INET, addrSocketType = Stream, addrProtocol = 6, addrAddress = 127.0.0.1:2023, addrCanonName = Nothing},AddrInfo {addrFlags = [], addrFamily = AF_INET6, addrSocketType = Datagram, addrProtocol = 17, addrAddress = [fe80::1%lo0]:2023, addrCanonName = Nothing},AddrInfo {addrFlags = [], addrFamily = AF_INET6, addrSocketType = Stream, addrProtocol = 6, addrAddress = [fe80::1%lo0]:2023, addrCanonName = Nothing}]
LocalJob: connect: unsupported operation (Address family not supported by protocol family)

这对我来说很奇怪，所以我决定运行这个 C 程序(在 google 上搜索“getaddrinfo”示例，更改主机名和端口，添加 ai_family 的打印):

#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <netinet/in.h>
#include <sys/socket.h>

#ifndef   NI_MAXHOST
#define   NI_MAXHOST 1025
#endif

int main(void)
{
    struct addrinfo *result;
    struct addrinfo *res;
    int error;

    /* resolve the domain name into a list of addresses */
    error = getaddrinfo("localhost", "2023", NULL, &result);
    if (error != 0)
    {
        fprintf(stderr, "error in getaddrinfo: %s\n", gai_strerror(error));
        return EXIT_FAILURE;
    }

    /* loop over all returned results and do inverse lookup */
    for (res = result; res != NULL; res = res->ai_next)
    {
        char hostname[NI_MAXHOST] = "";

        error = getnameinfo(res->ai_addr, res->ai_addrlen, hostname, NI_MAXHOST, NULL, 0, 0);
        if (error != 0)
        {
            fprintf(stderr, "error in getnameinfo: %s\n", gai_strerror(error));
            continue;
        }
        if (*hostname != '\0')
            printf("hostname: %s. ai_family: %i\n", hostname, res->ai_family);
    }

    freeaddrinfo(result);
    return EXIT_SUCCESS;
}

启动后，我看到了以下输出:

➜  getaddrinfotest  ./main
hostname: localhost. ai_family: 30
hostname: localhost. ai_family: 30
hostname: localhost. ai_family: 2
hostname: localhost. ai_family: 2
hostname: localhost. ai_family: 30
hostname: localhost. ai_family: 30

所以，ai_family 30 似乎是一个奇怪的东西。据我了解socket.h sources ，它就是 AF_TIPC 协议(protocol)，这是一个我以前没有听说过的非常罕见的东西。我还打开了haskell的packFamily' sources并惊讶地发现它不能处理 30 的值(不知道 AF_TIPC)。

我的问题是:现在最好的做法是什么？我是否正确地理解了问题？ Haskell 应该更好地处理未知的人工智能家族吗？//谢谢!

更新:我通过提示使用 ipv4 解决了问题:

addrInfos <- getAddrInfo (Just (defaultHints { addrFamily=AF_INET }))
               (Just host)
               (Just (show port))

但我仍然想知道如何“以正确的方式”解决这个问题。

Answer 1

默认情况下，getaddrinfo(及其 Haskell 绑定(bind) getAddrInfo)返回 addrinfo 的链接列表，其中可以包含 IPv4 地址、IPv6 地址或两者的混合。不幸的是，sockets 函数不允许将 IPv4 套接字连接到 IPv6 地址，因此当您迭代地址列表时，您需要创建正确类型的套接字:

addrinfos <- getAddrInfo Nothing (Just hostname) (Just (show port))
let first = head addrinfos
sock <- socket (addrFamily first) Stream defaultProtocol
connect sock (addrAddress first)

请注意如何将(首先是addrFamily)传递给socket函数，以便在正确的协议(protocol)族中创建套接字。

在实际代码中，您需要迭代列表 addrinfos 并尝试连接到 getAddrInfo 返回的所有地址。当您这样做时，不要忘记关闭连接失败的套接字。