transformation: fix issue where content-type is removed (#11)

* added a failing test
* fix failed test

Author: yuval-k

source/extensions/filters/http/transformation/transformation_filter.cc

@@ -226,7 +226,10 @@ void TransformationFilter::transformTemplate(
 
     if (body.length() > 0) {
       (this->*addData)(body);
-    } else {
+    } else if (!transformation.has_passthrough()) {
+      // only remove content type if the request is not passthrough.
+      // This means that the empty body is a result of the transformation.
+      // so the content type should be removed
       header_map.removeContentType();
     }
   } catch (nlohmann::json::parse_error &e) {

test/extensions/filters/http/transformation/transformation_filter_test.cc

@@ -63,7 +63,7 @@ class TransformationFilterTest : public testing::Test {
     initFilter(); // Re-load config.
   }
 
-  Http::TestHeaderMapImpl headers_{
+  Http::TestHeaderMapImpl headers_{{"content-type", "test"},
       {":method", "GET"}, {":authority", "www.solo.io"}, {":path", "/path"}};
 
   NiceMock<Http::MockStreamDecoderFilterCallbacks> filter_callbacks_;
@@ -162,6 +162,24 @@ TEST_F(TransformationFilterTest, HappyPathWithBodyPassthrough) {
   EXPECT_EQ(Http::FilterDataStatus::Continue, res);
 }
 
+
+TEST_F(TransformationFilterTest, BodyPassthroughDoesntRemoveContentType) {
+  auto &transformation = (*route_config_.mutable_request_transformation());
+  transformation.mutable_transformation_template()->mutable_passthrough();
+  envoy::api::v2::filter::http::InjaTemplate header_value;
+  header_value.set_text("added-value");
+  (*transformation.mutable_transformation_template()->mutable_headers())["added-header"] = header_value;
+  initFilter(); // Re-load config.
+
+  auto resheaders = filter_->decodeHeaders(headers_, false);
+  EXPECT_EQ(Http::FilterHeadersStatus::Continue, resheaders);
+
+  // as this is a passthrough body, transformation should have been triggered
+  // make sure that transformation did not remove content type.
+  EXPECT_EQ("test", headers_.get_("content-type"));
+  EXPECT_EQ("added-value", headers_.get_("added-header"));
+}
+
 TEST_F(TransformationFilterTest, HappyPathWithHeadersBodyTemplate) {
   initFilterWithHeadersBody();