Raise a nice error for bad wire types

Closes #339.

Author: whatyouhide

lib/protobuf/decoder.ex

@@ -109,12 +109,10 @@ defmodule Protobuf.Decoder do
         skip_delimited(rest, message, props, groups)
 
       wire_32bits() ->
-        <<_skip::bits-32, rest::bits>> = rest
-        skip_field(rest, message, props, groups)
+        rest |> skip_bits(32) |> skip_field(message, props, groups)
 
       wire_64bits() ->
-        <<_skip::bits-64, rest::bits>> = rest
-        skip_field(rest, message, props, groups)
+        rest |> skip_bits(64) |> skip_field(message, props, groups)
 
       wire_type ->
         message =
@@ -140,6 +138,13 @@ defmodule Protobuf.Decoder do
     skip_field(rest, message, props, groups)
   end
 
+  defp skip_bits(binary, length) do
+    case binary do
+      <<_::bits-size(length), rest::bits>> -> rest
+      _ -> raise DecodeError, message: "insufficient data for skipping #{length} bits"
+    end
+  end
+
   defdecoderp decode_varint(field_number, message, props) do
     handle_value(rest, field_number, wire_varint(), value, message, props)
   end

test/protobuf/decoder_test.exs

@@ -221,6 +221,13 @@ defmodule Protobuf.DecoderTest do
     end
   end
 
+  # Regression for #339
+  test "raises a nice error in some cases" do
+    assert_raise Protobuf.DecodeError, "insufficient data for skipping 32 bits", fn ->
+      Decoder.decode("{}", TestMsg.Oneof)
+    end
+  end
+
   describe "groups" do
     test "skips all groups and their fields" do
       a = <<8, 42>>

test/protobuf/protoc/cli_integration_test.exs

@@ -102,6 +102,23 @@ defmodule Protobuf.Protoc.CLIIntegrationTest do
         assert [{Foo.User, docs}] = modules_and_docs
         assert {:docs_v1, _, :elixir, _, :hidden, _, _} = docs
       end
+
+      defp get_docs_and_clean_modules_on_exit(path) do
+        modules_and_docs =
+          path
+          |> Code.compile_file()
+          |> Enum.map(fn {mod, bytecode} ->
+            {mod, fetch_docs_from_bytecode(bytecode)}
+          end)
+
+        on_exit(fn ->
+          modules_and_docs
+          |> Enum.map(fn {mod, _bytecode} -> mod end)
+          |> TestHelpers.purge_modules()
+        end)
+
+        modules_and_docs
+      end
     end
 
     test "package_prefix mypkg", %{tmp_dir: tmp_dir, proto_path: proto_path} do
@@ -323,21 +340,4 @@ defmodule Protobuf.Protoc.CLIIntegrationTest do
 
     modules
   end
-
-  defp get_docs_and_clean_modules_on_exit(path) do
-    modules_and_docs =
-      path
-      |> Code.compile_file()
-      |> Enum.map(fn {mod, bytecode} ->
-        {mod, fetch_docs_from_bytecode(bytecode)}
-      end)
-
-    on_exit(fn ->
-      modules_and_docs
-      |> Enum.map(fn {mod, _bytecode} -> mod end)
-      |> TestHelpers.purge_modules()
-    end)
-
-    modules_and_docs
-  end
 end