handle empty json

plugin/grpc_provider.go

@@ -603,14 +603,17 @@ func (p *GRPCProvider) Close() error {
 // Decode a DynamicValue from either the JSON or MsgPack encoding.
 func decodeDynamicValue(v *proto.DynamicValue, ty cty.Type) (cty.Value, error) {
 	// always return a valid value
+	var err error
 	res := cty.NullVal(ty)
 	if v == nil {
 		return res, nil
 	}
 
-	if len(v.Msgpack) > 0 {
-		return msgpack.Unmarshal(v.Msgpack, ty)
+	switch {
+	case len(v.Msgpack) > 0:
+		res, err = msgpack.Unmarshal(v.Msgpack, ty)
+	case len(v.Json) > 0:
+		res, err = ctyjson.Unmarshal(v.Json, ty)
 	}
-
-	return ctyjson.Unmarshal(v.Json, ty)
+	return res, err
 }

plugin/grpc_provider_test.go

@@ -310,6 +310,38 @@ func TestGRPCProvider_ReadResourceJSON(t *testing.T) {
 	}
 }
 
+func TestGRPCProvider_ReadEmptyJSON(t *testing.T) {
+	client := mockProviderClient(t)
+	p := &GRPCProvider{
+		client: client,
+	}
+
+	client.EXPECT().ReadResource(
+		gomock.Any(),
+		gomock.Any(),
+	).Return(&proto.ReadResource_Response{
+		NewState: &proto.DynamicValue{
+			Json: []byte(``),
+		},
+	}, nil)
+
+	obj := cty.ObjectVal(map[string]cty.Value{
+		"attr": cty.StringVal("foo"),
+	})
+	resp := p.ReadResource(providers.ReadResourceRequest{
+		TypeName:   "resource",
+		PriorState: obj,
+	})
+
+	checkDiags(t, resp.Diagnostics)
+
+	expected := cty.NullVal(obj.Type())
+
+	if !cmp.Equal(expected, resp.NewState, typeComparer, valueComparer, equateEmpty) {
+		t.Fatal(cmp.Diff(expected, resp.NewState, typeComparer, valueComparer, equateEmpty))
+	}
+}
+
 func TestGRPCProvider_PlanResourceChange(t *testing.T) {
 	client := mockProviderClient(t)
 	p := &GRPCProvider{