[Libevent-users] Re: Some evdns question

[åéé <sunyucong@xxxxxxxxx>]

in case it is useful to anyone,  I will just answer my own question:

1) no need to free evdns_request* and evdns_getaddrinfo_request*

2)  I have a somewhat ip-agnostic version of reverse resolution example here.
handling IN6ADDR_LOOPBACK and INADDR_LOOPBACK is left as reader exercise.

typedef struct addr_name_query_s {
  sockaddr_storage addr;
  socklen_t addrlen;
  struct evdns_request *req;
} addr_name_query_t;

// Reverse DNS lookup.
void on_addr_name_result(int err, char type, int count,
                         int ttl, void *addresses, void *arg)
{

  auto query = (addr_name_query_t *)arg;

  if (err) {
    debug(dns, "DNS reverse lookup fail: %s.\n", evdns_err_to_string(err));
  } else if (count == 0) {
    debug(dns, "DNS reverse lookup returns no result.\n");
  } else {
    auto result = *((char **)addresses);
    debug(dns, "DNS reverse lookup result: %d: %s\n", type, result);
    // Got result, do something with it.
  }
  delete query;
}

// Start a reverse lookup.
void query_name_by_addr(object_t *ob)
{
  auto query = new addr_name_query_t;

  const char *addr = query_ip_number(ob);
  debug(dns, "query_name_by_addr: starting lookup for %s.\n", addr);
  free_string(addr);

  // By the time resolve finish, ob may be already gone, we have to
  // copy the address.
  memcpy(&query->addr, &ob->interactive->addr, ob->interactive->addrlen);
  query->addrlen = ob->interactive->addrlen;

  // Check for mapped/compact v4 address, if we are querying for v6 address.
  if (query->addr.ss_family == AF_INET6) {
    in6_addr *addr6 = &(((sockaddr_in6 *)(&query->addr))->sin6_addr);
    if (IN6_IS_ADDR_V4MAPPED(addr6) || IN6_IS_ADDR_V4COMPAT(addr6)) {
      in_addr *addr4 = &((in_addr *)(addr6))[3];
      debug(dns, "Found mapped v4 address, using extracted v4 address
to resolve.\n")
      query->req = evdns_base_resolve_reverse(
                     g_dns_base, addr4, 0,
                     on_addr_name_result, query);
    } else {
      query->req = evdns_base_resolve_reverse_ipv6(
                     g_dns_base, addr6, 0,
                     on_addr_name_result, query);
    }
  } else {
    in_addr *addr4 = &((sockaddr_in *)&query->addr)->sin_addr;
    query->req = evdns_base_resolve_reverse(
                   g_dns_base, addr4, 0, on_addr_name_result, query);
  }
}


On Wed, Jun 26, 2013 at 7:54 PM, åéé <sunyucong@xxxxxxxxx> wrote:
>
> Hi,
>
> There are a bunch of questions that I couldn't find answers from the
> document, hope someone can share some insight
>
> 1) do I need to FREE returned  struct evdns_request*  in the callback?
>  what about struct evdns_getaddrinfo_request * ?  these things are not
> very clear in the doc, and I by chance found evutil_freeaddrinfo ,
> then I kinda guess I need to free that too.
>
> 2) since there is no evdns_getnameinfo (why?), what function could I
> use to reverse resolve address protocol independently ?  More
> importantly , neither evdns_resolve_reverse or
> evdns_resolve_reverse_ipv6 works with /etc/hosts file,  so things like
> "::1" and "127.0.0.1" is probmatic.
>
> Thanks.
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