Optimize variant decoding (#402)

Author: ruslandoga

lib/ch/row_binary.ex

@@ -754,7 +754,7 @@ defmodule Ch.RowBinary do
   end
 
   defp decoding_type({:variant = v, ts}) do
-    {v, Enum.map(ts, &decoding_type/1)}
+    {v, ts |> Enum.map(&decoding_type/1) |> List.to_tuple()}
   end
 
   defp decoding_type({:map = m, kt, vt}) do
@@ -1397,10 +1397,14 @@ defmodule Ch.RowBinary do
             decode_rows(types_rest, bin, [nil | row], rows, types)
 
           # TODO varint?
-          <<variant_type_index::8, bin::bytes>> ->
-            variant_type = Enum.at(variant_types, variant_type_index)
+          <<variant_type_index::8, bin::bytes>>
+          when variant_type_index < tuple_size(variant_types) ->
+            variant_type = elem(variant_types, variant_type_index)
             decode_rows([variant_type | types_rest], bin, row, rows, types)
 
+          <<variant_type_index::8, _bin::bytes>> ->
+            raise ArgumentError, "invalid Variant type index: #{variant_type_index}"
+
           _ ->
             to_be_continued(rows, bin, [type | types_rest], row)
         end

test/ch/row_binary_test.exs

@@ -300,6 +300,7 @@ defmodule Ch.RowBinaryTest do
         {"Array(LowCardinality(String))", {:array, :string}},
         {"Array(Enum8('hello' = 2, 'world' = 3))",
          {:array, {:enum8, %{2 => "hello", 3 => "world"}}}},
+        {"Variant(String, UInt32)", {:variant, {:string, :u32}}},
         {"Array(Nothing)", {:array, :nothing}},
         {"Nullable(String)", {:nullable, :string}},
         {"Nullable(Float64)", {:nullable, :f64}},
@@ -410,6 +411,12 @@ defmodule Ch.RowBinaryTest do
         decode_rows(<<0>>, [:unsupported])
       end
     end
+
+    test "rejects invalid Variant type indexes" do
+      assert_raise ArgumentError, "invalid Variant type index: 2", fn ->
+        decode_rows(<<2>>, ["Variant(String, UInt32)"])
+      end
+    end
   end
 
   # TODO maybe use stream_data?