Dovecot Failed to init dict: dict redis: Invalid IP

I'm using Dovecot v2.3.9.3. By looking to the dovecot docs I see that specification for Redis is the following:

redis:param=value:param2=value2:...

Here one of the parameters is host: Redis server host (default: 127.0.0.1).

In my configuration I have specified uri = redis:host=redis:port=6379:

Feb 23 20:48:32 auth: Fatal: dict /etc/dovecot/dovecot-dict-auth.conf.ext: Failed to init dict: dict redis: Invalid IP: redis

redis hostname on my server resolves to the IP without any problem:

# getent hosts redis
192.168.48.2      redis  redis

Is there a way to use hostname (maybe some hidden setting which enables the resolution), or they just bluntly did not implement a support for that? :/

TL;DR

Dovecot redis dict driver accepts undocumented parameter path in which you can specify the unix socket. You may then create a proxy to the hostname redis serving on the tcp port 6379 via the unix socket /run/redis.soc:

socat unix-listen:/run/redis.soc,reuseaddr,fork,perm=0644,user=dovecot tcp:redis:6379 &

Dovecot config becomes:

# Dictionary URI
uri = redis:path=/run/redis.soc

---

The following is my analysis of the problem. I don't code in C, so my understanding was limited.

Code which covers my error (Invalid IP: redis) is the following:

} else if (str_begins(*args, "host=")) {
  if (net_addr2ip(*args+5, &ip) < 0) {
    *error_r = t_strdup_printf("Invalid IP: %s",
              *args+5);
    ret = -1;
  }
}

It relies on the net_addr2ip function which depends on the net_addr2ip_inet4_fast. Both of these functions do not seem to do, what their names are suggesting (they do not turn addr to ip):

static bool net_addr2ip_inet4_fast(const char *addr, struct ip_addr *ip)
{
    uint8_t *saddr = (void *)&ip->u.ip4.s_addr;
    unsigned int i, num;

    if (str_parse_uint(addr, &num, &addr) < 0)
        return FALSE;
    if (*addr == '\0' && num <= 0xffffffff) {
        /* single-number IPv4 address */
        ip->u.ip4.s_addr = htonl(num);
        ip->family = AF_INET;
        return TRUE;
    }

    /* try to parse as a.b.c.d */
    i = 0;
    for (;;) {
        if (num >= 256)
            return FALSE;
        saddr[i] = num;
        if (i == 3)
            break;
        i++;
        if (*addr != '.')
            return FALSE;
        addr++;
        if (str_parse_uint(addr, &num, &addr) < 0)
            return FALSE;
    }
    if (*addr != '\0')
        return FALSE;
    ip->family = AF_INET;
    return TRUE;
}

int net_addr2ip(const char *addr, struct ip_addr *ip)
{
    int ret;

    if (net_addr2ip_inet4_fast(addr, ip))
        return 0;

    if (strchr(addr, ':') != NULL) {
        /* IPv6 */
        T_BEGIN {
            if (addr[0] == '[') {
                /* allow [ipv6 addr] */
                size_t len = strlen(addr);
                if (addr[len-1] == ']')
                    addr = t_strndup(addr+1, len-2);
            }
            ret = inet_pton(AF_INET6, addr, &ip->u.ip6);
        } T_END;
        if (ret == 0)
            return -1;
        ip->family = AF_INET6;
    } else {
        /* IPv4 */
        if (inet_aton(addr, &ip->u.ip4) == 0)
            return -1;
        ip->family = AF_INET;
    }
    return 0;
}

Therefore host parameter in dovecot's redis dict driver cannot be anything else but an IP address ¯_(ツ)_/¯