Dovecot Failed to init dict: dict redis: Invalid IP - redis

Question

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? :/

Answer 1

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)_/¯