getaddrinfo()返回几个相同的结果

在/ etc / hosts我有：

127.0.0.1   localhost.localdomain   localhost
::1     localhost.localdomain   localhost

测试程序：

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

const char* family_to_string(int family)
{
    return family == AF_INET ? "AF_INET"
        : family == AF_INET6 ? "AF_INET6"
        : "<unknown>";
}

const char* socktype_to_string(int socktype)
{
    return socktype == SOCK_STREAM ? "SOCK_STREAM"
        : socktype == SOCK_DGRAM ? "SOCK_DGRAM"
        : "<unknown>";
}

const char* protocol_to_string(int protocol)
{
    return protocol == IPPROTO_TCP ? "IPPROTO_TCP"
        : protocol == IPPROTO_UDP ? "IPPROTO_UDP"
        : "<unknown>";
}

void print_addrinfo(struct addrinfo *ai)
{
    int r;
    char hbuf[NI_MAXHOST],sbuf[NI_MAXSERV];
    r = getnameinfo(ai->ai_addr,ai->ai_addrlen,hbuf,sizeof(hbuf),sbuf,sizeof(sbuf),NI_NUMERICHOST | NI_NUMERICSERV);
    if (r)
    {
        fputs("getnameinfo\n",stderr);
        exit(EXIT_FAILURE);
    }
    const char *family = family_to_string(ai->ai_family);
    const char *socktype = socktype_to_string(ai->ai_socktype);
    const char *protocol = protocol_to_string(ai->ai_protocol);
    const char *family2 = family_to_string(ai->ai_addr->sa_family);
    printf("flags=%i,family=%s,socktype=%s,protocol=%s,host=%s,serv=%s\n",ai->ai_flags,family,socktype,protocol,family2,sbuf);
}

int main(int argc,char *argv[])
{
    (void)argc;
    (void)argv;
    int r;
    struct addrinfo hints;
    struct addrinfo *result,*ai;

    memset(&hints,sizeof(struct addrinfo));
    // hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    r = getaddrinfo("localhost","8000",&hints,&result);
    if (r)
    {
        fputs("getaddrinfo\n",stderr);
        exit(EXIT_FAILURE);
    }

    ai = result;
    while (ai)
    {
        print_addrinfo(ai);
        ai = ai->ai_next;
    }

    exit(EXIT_SUCCESS);
}

当我没有设置hints.ai_family时,它就像预期的那样：

$gcc -Wall -Wextra -Werror -pedantic -pedantic-errors -g -gdwarf-2 -g3 % && ./a.out
flags=0,family=AF_INET6,socktype=SOCK_STREAM,protocol=IPPROTO_TCP,host=::1,serv=8000
flags=0,family=AF_INET,host=127.0.0.1,serv=8000

使用hints.ai_family,它返回两个相同的addrinfo结构：

flags=0,serv=8000

你能解释一下发生了什么吗？我认为提示充当过滤器.也就是说,在这种情况下只返回一个结果.

UPD /etc/nsswitch.conf

# Begin /etc/nsswitch.conf

passwd: compat mymachines systemd
group: compat mymachines systemd
shadow: compat

publickey: files

hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
networks: files

protocols: files
services: files
ethers: files
rpc: files

netgroup: files

# End /etc/nsswitch.conf

在/etc/resolv.conf：

# Generated by resolvconf
search Dlink
nameserver 192.168.0.1

192.168.0.1是我的路由器.我的IP地址是192.168.0.39.

解决方法

从我所看到的：

sysdeps/posix/getaddrinfo.c:2206

int
getaddrinfo (const char *name,const char *service,const struct addrinfo *hints,struct addrinfo **pai)

sysdeps/posix/getaddrinfo.c:2304

last_i = gaih_inet (name,pservice,hints,end,&naddrs,&tmpbuf);

sysdeps/posix/getaddrinfo.c:342

static int
gaih_inet (const char *name,const struct gaih_service *service,const struct addrinfo *req,struct addrinfo **pai,unsigned int *naddrs,struct scratch_buffer *tmpbuf)

sysdeps/posix/getaddrinfo.c:595

rc = __gethostbyname2_r (name,AF_INET,&th,tmpbuf->data,tmpbuf->length,&h,&h_errno);

nss/getXXbyYY_r.c:189

int
INTERNAL (REENTRANT_NAME) (ADD_PARAMS,LOOKUP_TYPE *resbuf,char *buffer,size_t buflen,LOOKUP_TYPE **result H_ERRNO_PARM
                           EXTRA_PARAMS)

nss/getXXbyYY_r.c:316

status = DL_CALL_FCT (fct.l,(ADD_VARIABLES,resbuf,buffer,buflen,&errno H_ERRNO_VAR EXTRA_VARIABLES));

nss/nss_files/files-hosts.c:385

enum nss_status
_nss_files_gethostbyname2_r (const char *name,int af,struct hostent *result,int *errnop,int *herrnop)

nss/nss_files/files-hosts.c:389

return _nss_files_gethostbyname3_r (name,af,result,errnop,herrnop,NULL,NULL);

nss/nss_files/files-hosts.c:334

enum nss_status
_nss_files_gethostbyname3_r (const char *name,int *herrnop,int32_t *ttlp,char **canonp)

这里我们得到第一个匹配,并且 – 如果在/etc/host.conf中打开了多个 – 其余部分：

nss/nss_files/files-hosts.c:352

while ((status = internal_getent (stream,flags))
       == NSS_STATUS_SUCCESS)
  {
    LOOKUP_NAME_CASE (h_name,h_aliases)
  }

if (status == NSS_STATUS_SUCCESS
    && _res_hconf.flags & HCONF_FLAG_MULTI)
  status = gethostbyname3_multi
    (stream,name,flags);

nss/nss_files/files-hosts.c:127

static enum nss_status
gethostbyname3_multi (FILE * stream,const char *name,int flags)

nss/nss_files/files-hosts.c:162

status = internal_getent (stream,&tmp_result_buf,tmp_buffer.data,tmp_buffer.length,flags);

nss/nss_files/files-XXX.c:178

static enum nss_status
internal_getent (FILE *stream,struct STRUCTURE *result,int *errnop H_ERRNO_PROTO
                 EXTRA_ARGS_DECL)

nss/nss_files/files-XXX.c:222

|| ! (parse_result = parse_line (p,data,errnop
                                 EXTRA_ARGS)));

这里我们解析“:: 1 localhost.localdomain localhost”行.我们试图
运行inet_pton over :: 1.那失败了,因为af == AF_INET.然后我们
请注意:: 1是IPv6环回地址,因此我们返回IPv4环回
地址：

nss/nss_files/files-hosts.c:51

LINE_PARSER

nss/nss_files/files-hosts.c:59

if (inet_pton (af == AF_UNSPEC ? AF_INET : af,addr,entdata->host_addr)
    > 0)
  af = af == AF_UNSPEC ? AF_INET : af;
else
  {
    if (...)
      ...
    else if (af == AF_INET
             && inet_pton (AF_INET6,entdata->host_addr) > 0)
      {
        if (...)
          ...
        else if (IN6_IS_ADDR_LOOPBACK (entdata->host_addr))
          {
            in_addr_t localhost = htonl (INADDR_LOOPBACK);
            memcpy (entdata->host_addr,&localhost,sizeof (localhost));
          }

也许有人会在mailing list回复,我们会学到更多.