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Improve default DNS resolution support for Alpine/musl

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On Alpine (musl libc), /etc/resolv.conf now gets parsed for the first
IPv4 nameserver that works.

Addresses GH-216
This commit is contained in:
Jon Siwek 2018-11-30 19:26:04 -06:00
parent af82e87699
commit 206f12467a
1 changed files with 82 additions and 0 deletions
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82
src/nb_dns.c
View file

@ -144,6 +144,88 @@ nb_dns_init(char *errstr)
return (NULL);
}
if ( _res.nscount == 0 )
{
// Really? Let's try parsing resolv.conf ourselves to see what's
// there. (e.g. musl libc has res_init() that doesn't actually
// parse the config file).
const char* config_file_path = "/etc/resolv.conf";
#ifdef _PATH_RESCONF
config_file_path = _PATH_RESCONF;
#endif
FILE* config_file = fopen(config_file_path, "r");
if ( config_file )
{
char line[128];
char* ns;
while ( fgets(line, sizeof(line), config_file) )
{
ns = strtok(line, " \t\n");
if ( ! ns || strcmp(ns, "nameserver") )
continue;
ns = strtok(0, " \t\n");
if ( ! ns )
continue;
/* XXX support IPv6 */
struct sockaddr_in a;
memset(&a, 0, sizeof(a));
a.sin_family = AF_INET;
a.sin_port = htons(53);
if ( inet_pton(AF_INET, ns, &a.sin_addr) == 1 )
{
memcpy(&nd->server, &a, sizeof(a));
nd->s = socket(nd->server.ss_family, SOCK_DGRAM, 0);
if ( nd->s < 0 )
{
snprintf(errstr, NB_DNS_ERRSIZE, "socket(): %s",
my_strerror(errno));
fclose(config_file);
free(nd);
return (NULL);
}
if ( connect(nd->s, (struct sockaddr *)&nd->server,
nd->server.ss_family == AF_INET ?
sizeof(struct sockaddr_in) :
sizeof(struct sockaddr_in6)) < 0 )
{
char s[INET6_ADDRSTRLEN];
sa_ntop((struct sockaddr*)&nd->server, s, INET6_ADDRSTRLEN);
snprintf(errstr, NB_DNS_ERRSIZE, "connect(%s): %s", s,
my_strerror(errno));
fclose(config_file);
close(nd->s);
free(nd);
return (NULL);
}
fclose(config_file);
return (nd);
}
}
fclose(config_file);
snprintf(errstr, NB_DNS_ERRSIZE, "no valid nameserver found in %s",
config_file_path);
free(nd);
return (NULL);
}
snprintf(errstr, NB_DNS_ERRSIZE, "resolver config file not located");
free(nd);
return (NULL);
}
int i;
for ( i = 0; i < _res.nscount; ++i )