getaddrinfo() returns two identical results

[Yuri Kanivetsky <yuri dot kanivetsky at gmail dot com>]

Hi,

Consider this test program:


    #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,
family=%s, host=%s, serv=%s\n",
               ai->ai_flags, family, socktype, protocol, family2, hbuf, sbuf);
    }

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

        memset(&hints, 0, 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);
    }


In /etc/hosts I have:


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


When I set `hints.ai_family = AF_INET`, I get:


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


Without it:


    flags=0, family=AF_INET6, socktype=SOCK_STREAM,
protocol=IPPROTO_TCP, family=AF_INET6, host=::1, serv=8000
    flags=0, family=AF_INET, socktype=SOCK_STREAM,
protocol=IPPROTO_TCP, family=AF_INET, host=127.0.0.1, serv=8000


>From what I can see, `hints` parameter is supposed to filter results.
Which I cannot reproduce on my machine.

Not sure which info can be of help here. Feel free to ask. I'm running
Arch Linux and glibc-2.26. I haven't used systemd-resolved, and it's
not running.

/etc/resolv.conf:


    # Generated by resolvconf
    search Dlink
    nameserver 192.168.0.1


/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


I'm now building glibc with debugging information, hopefully it'll
shed some light on the matter. But if you've got any ideas what to
check, or possible explanation, feel free to reply.

P.S. Relevant Stack Overflow question:
https://stackoverflow.com/questions/48100853/getaddrinfo-returns-several-identical-results

Regards,
Yuri