fix(master): ensure url_parser does not fail on missing txt record (#261)

* fix url parser to avid failing on missing txt record

* Fix lookup value parsing

* Fix warning

* fix comments

---------

Co-authored-by: NI\akerezsi <[email protected]>

Author: kkerezsi

lib/mongo/url_parser.ex

@@ -155,8 +155,8 @@ defmodule Mongo.UrlParser do
          {:ok, {_, _, _, _, _, srv_record}} <-
            :inet_res.getbyname(~c"_mongodb._tcp." ++ url_char, :srv),
          {:ok, host} <- get_host_srv(srv_record),
-         {:ok, {_, _, _, _, _, txt_record}} <- :inet_res.getbyname(url_char, :txt),
-         txt <- "#{orig_options}&#{txt_record}&ssl=true" do
+         {:ok, txt_record} <- resolve_txt_record(url_char),
+         txt <- build_params(orig_options, txt_record) do
       frags
       |> Map.put("seeds", host)
       |> Map.put("options", txt)
@@ -167,6 +167,24 @@ defmodule Mongo.UrlParser do
 
   defp resolve_srv_url(frags), do: frags
 
+  defp build_params(orig_options, nil) do
+    "#{orig_options}&ssl=true"
+  end
+
+  defp build_params(orig_options, txt_record) do
+    "#{orig_options}&#{txt_record}&ssl=true"
+  end
+
+  defp resolve_txt_record(url_char) do
+    case :inet_res.lookup(url_char, :in, :txt) do
+      [[txt_record] | _] ->
+        {:ok, txt_record}
+
+      _other ->
+        {:ok, nil}
+    end
+  end
+
   @spec get_host_srv([{term, term, term, term}]) :: {:ok, String.t()}
   defp get_host_srv(srv) when is_list(srv) do
     hosts = Enum.map_join(srv, ",", fn {_, _, port, host} -> "#{host}:#{port}" end)