deprecate `envoy.reloadable_features.upstream_wait_for_response_heade…

…rs_before_disabling_read` (#35502)

Remove
`envoy.reloadable_features.upstream_wait_for_response_headers_before_disabling_read`
and update change log.

Risk Level: low
Testing: N/A
Docs Changes: N/A
Release Notes: Yes
Platform Specific Features: N/A
Fixes #30427

Signed-off-by: Dan Zhang <danzh@google.com>
Co-authored-by: Dan Zhang <danzh@google.com>

changelogs/current.yaml

@@ -80,6 +80,10 @@ removed_config_or_runtime:
 - area: stateful_session
   change: |
     Removed ``envoy.reloadable_features.stateful_session_encode_ttl_in_cookie`` runtime flag and legacy code paths.
+- area: upstream flow control
+  change: |
+    Removed ``envoy.reloadable_features.upstream_wait_for_response_headers_before_disabling_read`` runtime flag
+    and legacy code paths.
 
 new_features:
 - area: tls

source/common/router/upstream_request.cc

@@ -94,8 +94,6 @@ UpstreamRequest::UpstreamRequest(RouterFilterInterface& parent,
       record_timeout_budget_(parent_.cluster()->timeoutBudgetStats().has_value()),
       cleaned_up_(false), had_upstream_(false),
       stream_options_({can_send_early_data, can_use_http3}), grpc_rq_success_deferred_(false),
-      upstream_wait_for_response_headers_before_disabling_read_(Runtime::runtimeFeatureEnabled(
-          "envoy.reloadable_features.upstream_wait_for_response_headers_before_disabling_read")),
       enable_half_close_(enable_half_close) {
   if (auto tracing_config = parent_.callbacks()->tracingConfig(); tracing_config.has_value()) {
     if (tracing_config->spawnUpstreamSpan() || parent_.config().start_child_span_) {
@@ -717,17 +715,6 @@ void UpstreamRequest::clearRequestEncoder() {
 }
 
 void UpstreamRequest::readDisableOrDefer(bool disable) {
-  if (!upstream_wait_for_response_headers_before_disabling_read_) {
-    if (disable) {
-      parent_.cluster()->trafficStats()->upstream_flow_control_paused_reading_total_.inc();
-      upstream_->readDisable(true);
-    } else {
-      parent_.cluster()->trafficStats()->upstream_flow_control_resumed_reading_total_.inc();
-      upstream_->readDisable(false);
-    }
-    return;
-  }
-
   if (disable) {
     // See comments on deferred_read_disabling_count_ for when we do and don't defer.
     if (parent_.downstreamResponseStarted()) {

source/common/router/upstream_request.h

@@ -256,7 +256,6 @@ class UpstreamRequest : public Logger::Loggable<Logger::Id::router>,
   bool had_upstream_ : 1;
   Http::ConnectionPool::Instance::StreamOptions stream_options_;
   bool grpc_rq_success_deferred_ : 1;
-  bool upstream_wait_for_response_headers_before_disabling_read_ : 1;
   bool enable_half_close_ : 1;
 };
 

source/common/runtime/runtime_features.cc

@@ -92,7 +92,6 @@ RUNTIME_GUARD(envoy_reloadable_features_udp_socket_apply_aggregated_read_limit);
 RUNTIME_GUARD(envoy_reloadable_features_uhv_allow_malformed_url_encoding);
 RUNTIME_GUARD(envoy_reloadable_features_upstream_allow_connect_with_2xx);
 RUNTIME_GUARD(envoy_reloadable_features_upstream_remote_address_use_connection);
-RUNTIME_GUARD(envoy_reloadable_features_upstream_wait_for_response_headers_before_disabling_read);
 RUNTIME_GUARD(envoy_reloadable_features_use_http3_header_normalisation);
 RUNTIME_GUARD(envoy_reloadable_features_use_typed_metadata_in_proxy_protocol_listener);
 RUNTIME_GUARD(envoy_reloadable_features_validate_connect);

test/integration/multiplexed_integration_test.cc

@@ -2927,8 +2927,6 @@ TEST_P(MultiplexedIntegrationTest, PerTryTimeoutWhileDownstreamStopsReading) {
   if (downstreamProtocol() != Http::CodecType::HTTP2) {
     return;
   }
-  config_helper_.addRuntimeOverride(
-      "envoy.reloadable_features.upstream_wait_for_response_headers_before_disabling_read", "true");
 
   config_helper_.addConfigModifier([](envoy::config::bootstrap::v3::Bootstrap& bootstrap) -> void {
     RELEASE_ASSERT(bootstrap.mutable_static_resources()->listeners_size() >= 1, "");