lua: add a new clear_route_cache option support

api/envoy/extensions/filters/http/lua/v3/lua.proto

@@ -4,6 +4,8 @@ package envoy.extensions.filters.http.lua.v3;
 
 import "envoy/config/core/v3/base.proto";
 
+import "google/protobuf/wrappers.proto";
+
 import "envoy/annotations/deprecation.proto";
 import "udpa/annotations/status.proto";
 import "udpa/annotations/versioning.proto";
@@ -19,6 +21,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // Lua :ref:`configuration overview <config_http_filters_lua>`.
 // [#extension: envoy.filters.http.lua]
 
+// [#next-free-field: 6]
 message Lua {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.filter.http.lua.v2.Lua";
@@ -78,6 +81,12 @@ message Lua {
   //         stat_prefix: bar_script # This emits lua.bar_script.errors etc.
   //
   string stat_prefix = 4;
+
+  // If set to true, the Lua filter will clear the route cache automatically if the request
+  // headers are modified by the Lua script. If set to false, the Lua filter will not clear the
+  // route cache automatically.
+  // Default is true for backward compatibility.
+  google.protobuf.BoolValue clear_route_cache = 5;
 }
 
 message LuaPerRoute {

changelogs/current.yaml

@@ -189,6 +189,11 @@ new_features:
   change: |
     Made the :ref:`credential injector filter <envoy_v3_api_msg_extensions.filters.http.credential_injector.v3.CredentialInjector>`
     work as an upstream filter.
+- area: lua
+  change: |
+    Added :ref:`clear_route_cache <envoy_v3_api_field_extensions.filters.http.lua.v3.Lua.clear_route_cache>` support to
+    control the route cache clearing behavior in the Lua filter.
+
 - area: tcp_proxy
   change: |
     added :ref:`an option <config_network_filters_tcp_proxy_receive_before_connect>` to allow filters to read from the

source/extensions/filters/http/lua/lua_filter.cc

@@ -790,6 +790,8 @@ FilterConfig::FilterConfig(const envoy::extensions::filters::http::lua::v3::Lua&
                            Upstream::ClusterManager& cluster_manager, Api::Api& api,
                            Stats::Scope& scope, const std::string& stats_prefix)
     : cluster_manager_(cluster_manager),
+      clear_route_cache_(
+          proto_config.has_clear_route_cache() ? proto_config.clear_route_cache().value() : true),
       stats_(generateStats(stats_prefix, proto_config.stat_prefix(), scope)) {
   if (proto_config.has_default_source_code()) {
     if (!proto_config.inline_code().empty()) {

source/extensions/filters/http/lua/lua_filter.h

@@ -405,6 +405,7 @@ class FilterConfig : Logger::Loggable<Logger::Id::lua> {
     }
     return nullptr;
   }
+  bool clearRouteCache() const { return clear_route_cache_; }
 
   const LuaFilterStats& stats() const { return stats_; }
 
@@ -417,6 +418,7 @@ class FilterConfig : Logger::Loggable<Logger::Id::lua> {
     return {ALL_LUA_FILTER_STATS(POOL_COUNTER_PREFIX(scope, final_prefix))};
   }
 
+  const bool clear_route_cache_{};
   PerLuaCodeSetupPtr default_lua_code_setup_;
   absl::flat_hash_map<std::string, PerLuaCodeSetupPtr> per_lua_code_setups_map_;
   LuaFilterStats stats_;
@@ -536,7 +538,14 @@ class Filter : public Http::StreamFilter, private Filters::Common::Lua::LuaLogga
     }
     const Buffer::Instance* bufferedBody() override { return callbacks_->decodingBuffer(); }
     void continueIteration() override { return callbacks_->continueDecoding(); }
-    void onHeadersModified() override { callbacks_->downstreamCallbacks()->clearRouteCache(); }
+    void onHeadersModified() override {
+      // Do not clear route cache if clear_route_cache is false or if no downstream callbacks are
+      // available.
+      if (!parent_.config_->clearRouteCache() || !callbacks_->downstreamCallbacks()) {
+        return;
+      }
+      callbacks_->downstreamCallbacks()->clearRouteCache();
+    }
     void respond(Http::ResponseHeaderMapPtr&& headers, Buffer::Instance* body,
                  lua_State* state) override;
 

test/extensions/filters/http/lua/lua_filter_test.cc

@@ -83,8 +83,9 @@ class LuaHttpFilterTest : public testing::Test {
     setupFilter();
   }
 
-  void setupConfig(envoy::extensions::filters::http::lua::v3::Lua& proto_config,
-                   envoy::extensions::filters::http::lua::v3::LuaPerRoute& per_route_proto_config) {
+  void setupConfig(
+      const envoy::extensions::filters::http::lua::v3::Lua& proto_config,
+      const envoy::extensions::filters::http::lua::v3::LuaPerRoute& per_route_proto_config) {
     // Setup filter config for Lua filter.
     config_ = std::make_shared<FilterConfig>(proto_config, tls_, cluster_manager_, api_,
                                              *stats_store_.rootScope(), "test.");
@@ -2735,6 +2736,25 @@ TEST_F(LuaHttpFilterTest, LuaFilterDisabled) {
   EXPECT_FALSE(request_headers_2.has("hello"));
 }
 
+// Test whether the automatic route cache clearing could be disabled.
+TEST_F(LuaHttpFilterTest, DisableAutomaticRouteCacheClearing) {
+  envoy::extensions::filters::http::lua::v3::Lua proto_config;
+  proto_config.mutable_clear_route_cache()->set_value(false);
+  proto_config.mutable_default_source_code()->set_inline_string(ADD_HEADERS_SCRIPT);
+  setupConfig(proto_config, {});
+  setupFilter();
+
+  EXPECT_CALL(decoder_callbacks_.downstream_callbacks_, clearRouteCache()).Times(0);
+
+  ON_CALL(*decoder_callbacks_.route_, mostSpecificPerFilterConfig(_))
+      .WillByDefault(Return(nullptr));
+
+  Http::TestRequestHeaderMapImpl request_headers_1{{":path", "/"}};
+
+  EXPECT_EQ(Http::FilterHeadersStatus::Continue, filter_->decodeHeaders(request_headers_1, true));
+  EXPECT_EQ("world", request_headers_1.get_("hello"));
+}
+
 // Test whether the route can directly reuse the Lua code in the global configuration.
 TEST_F(LuaHttpFilterTest, LuaFilterRefSourceCodes) {
   const std::string SCRIPT_FOR_ROUTE_ONE{R"EOF(