Add IPv6 support for gRPC gun adapter

grpc_client/lib/grpc/client/adapters/gun.ex

@@ -94,7 +94,7 @@ defmodule GRPC.Client.Adapters.Gun do
     do: :gun.open_unix(socket_path, open_opts)
 
   defp open(host, port, open_opts),
-    do: :gun.open(String.to_charlist(host), port, open_opts)
+    do: :gun.open(parse_address(host), port, open_opts)
 
   @impl true
   def send_request(stream, message, opts) do
@@ -496,6 +496,15 @@ defmodule GRPC.Client.Adapters.Gun do
     end
   end
 
+  defp parse_address(host) do
+    host = String.to_charlist(host)
+
+    case :inet.parse_address(host) do
+      {:ok, address} -> address
+      {:error, _} -> host
+    end
+  end
+
   defp get_compressor(%{"grpc-encoding" => encoding} = _headers, accepted_compressors) do
     Enum.find(accepted_compressors, nil, fn c -> c.name() == encoding end)
   end

grpc_client/lib/grpc/client/resolver/dns.ex

@@ -46,7 +46,15 @@ defmodule GRPC.Client.Resolver.DNS do
   end
 
   defp lookup_addresses(host) do
-    case adapter().lookup(host, :a) do
+    case lookup_addresses(host, :a) do
+      {:ok, [_ | _] = addrs} -> {:ok, addrs}
+      {:ok, []} -> lookup_addresses(host, :aaaa)
+      other -> other
+    end
+  end
+
+  defp lookup_addresses(host, type) do
+    case adapter().lookup(host, type) do
       {:ok, addrs} when is_list(addrs) -> {:ok, addrs}
       addrs when is_list(addrs) -> {:ok, addrs}
       other -> other

grpc_client/test/grpc/resolver/dns_test.exs

@@ -49,4 +49,23 @@ defmodule GRPC.Client.Resolver.DNSTest do
     assert {"foo", "bar"} in method_names
     assert {"baz", nil} in method_names
   end
+
+  test "resolves AAAA record as fallback when A record returns empty list" do
+    host = "my-service.local"
+    config_name = "_grpc_config." <> host
+
+    DNS.MockAdapter
+    |> expect(:lookup, fn ^host, :a ->
+      {:ok, []}
+    end)
+    |> expect(:lookup, fn ^host, :aaaa ->
+      {:ok, [{0, 0, 0, 0, 0, 0, 0, 1}]}
+    end)
+    |> expect(:lookup, fn ^config_name, :txt ->
+      {:ok, []}
+    end)
+
+    assert {:ok, %{addresses: addrs}} = DNS.resolve(host)
+    assert [%{address: "::1", port: 50051}] = addrs
+  end
 end