http: keep trailers TE header instead of removing it

changelogs/current.yaml

@@ -2,6 +2,10 @@ date: Pending
 
 behavior_changes:
 # *Changes that are expected to cause an incompatibility if applicable; deployment changes are likely required*
+- area: http
+  change: |
+    Force the hop by hop TE header from downstream request headers to "trailers". This change can be temporarily reverted
+    by setting ``envoy.reloadable_features.sanitize_te`` to false.
 
 minor_behavior_changes:
 # *Changes that may cause incompatibilities for some users, but should not for most*

source/common/http/conn_manager_utility.cc

@@ -93,7 +93,7 @@ ConnectionManagerUtility::MutateRequestHeadersResult ConnectionManagerUtility::m
     request_headers.removeConnection();
     request_headers.removeUpgrade();
     if (Runtime::runtimeFeatureEnabled("envoy.reloadable_features.sanitize_te")) {
-      request_headers.removeTE();
+      request_headers.setTE(Http::Headers::get().TEValues.Trailers);
     }
   }
 

test/integration/protocol_integration_test.cc

@@ -806,7 +806,7 @@ TEST_P(DownstreamProtocolIntegrationTest, TeSanitization) {
   auto upstream_headers =
       reinterpret_cast<AutonomousUpstream*>(fake_upstreams_[0].get())->lastRequestHeaders();
   EXPECT_TRUE(upstream_headers != nullptr);
-  EXPECT_EQ("", upstream_headers->getTEValue());
+  EXPECT_EQ("trailers", upstream_headers->getTEValue());
 }
 
 // Regression test for https://github.com/envoyproxy/envoy/issues/10270