Retrieve DNS server address error in win32 platform

[qi7chen]

When testing example/http_client,
type command ./http_client http://www.microsoft.com/ got right response in Linux(Ubuntu 14.04) but nothing printed in Windows platform(Windows 7 x64).

With some efforts, I found function ns_get_ip_address_of_nameserver() try to retrieve item under registry HKLM\\SYSTEM\\ControlSet001\\Services\\Tcpip\\Parameters\\Interfaces\, and copy first item's NameServer field as the address of DNS server.
But when got too many interface items(as I shown below) and the NameServer field is an empty string, or the NameServer string contains more than one IP address(seperated by comma token), we cannot retrieve the right DNS server address we want.

[cpq]

Thanks.
As far as I understand, the fix would be to trim the IP on the first comma, is that correct?

[zapline]

But the first ip is not necessarily the best nameserver, 蛋疼

[cpq]

Thanks.
If first IP might not be the best server, what would be the best algorithm to pick one?

[mkmik]

On linux the default behaviour is to to try the second (and the third, see MAXNS) name after attempts number of attempts (default 2), unless the rotate option is present in resolv.conf. On windows I guess there is a similar behaviour but I didn't check.

[qi7chen]

Sorry for my poor English.

Following is code of function ns_get_ip_address_of_nameserver() started at fossa.c line 4384.

static int ns_get_ip_address_of_nameserver(char *name, size_t name_len) {
  int  ret = 0;

#ifdef _WIN32
  int  i;
  LONG  err;
  HKEY  hKey, hSub;
  char  subkey[512], dhcpns[512], ns[512], value[128], *key =
  "SYSTEM\\ControlSet001\\Services\\Tcpip\\Parameters\\Interfaces";

  if ((err = RegOpenKey(HKEY_LOCAL_MACHINE,
      key, &hKey)) != ERROR_SUCCESS) {
    fprintf(stderr, "cannot open reg key %s: %d\n", key, err);
    ret--;
  } else {
    for (ret--, i = 0; RegEnumKey(hKey, i, subkey,
        sizeof(subkey)) == ERROR_SUCCESS; i++) {
      DWORD type, len = sizeof(value);
      if (RegOpenKey(hKey, subkey, &hSub) == ERROR_SUCCESS &&
          (RegQueryValueEx(hSub, "NameServer", 0,
          &type, value, &len) == ERROR_SUCCESS ||
          RegQueryValueEx(hSub, "DhcpNameServer", 0,
          &type, value, &len) == ERROR_SUCCESS)) {
        strncpy(name, value, name_len);
        ret++;
        RegCloseKey(hSub);
        break;
      }
    }
    RegCloseKey(hKey);
  }
#else
  /* linux version */
#endif /* _WIN32 */

  return ret;
}

looking at line strncpy(name, value, name_len),
the value can be an empty string, or IP addresses seperated by comma (e.g 8.8.8.8, 8.8.8.4).

that's the point.