http filter: Add overrideable function to http filter factory interface for specifying FilterDependencies

include/envoy/server/BUILD

@@ -220,6 +220,7 @@ envoy_cc_library(
         "//source/common/common:assert_lib",
         "//source/common/common:macros",
         "//source/common/protobuf",
+        "@envoy_api//envoy/extensions/filters/common/dependency/v3:pkg_cc_proto",
     ],
 )
 

include/envoy/server/filter_config.h

@@ -3,6 +3,7 @@
 #include <functional>
 
 #include "envoy/config/typed_config.h"
+#include "envoy/extensions/filters/common/dependency/v3/dependency.pb.h"
 #include "envoy/http/filter.h"
 #include "envoy/init/manager.h"
 #include "envoy/network/filter.h"
@@ -152,6 +153,9 @@ class NamedUpstreamNetworkFilterConfigFactory : public ProtocolOptionsFactory {
   std::string category() const override { return "envoy.filters.upstream_network"; }
 };
 
+using FilterDependenciesPtr =
+    std::unique_ptr<envoy::extensions::filters::common::dependency::v3::FilterDependencies>;
+
 /**
  * Implemented by each HTTP filter and registered via Registry::registerFactory or the
  * convenience class RegisterFactory.
@@ -201,6 +205,16 @@ class NamedHttpFilterConfigFactory : public ProtocolOptionsFactory {
    * @return bool true if this filter must be the last filter in a filter chain, false otherwise.
    */
   virtual bool isTerminalFilter() { return false; }
+
+  /**
+   * @return FilterDependenciesPtr specification of dependencies required or
+   * provided on the decode and encode paths. This function returns an empty
+   * filter dependencies specification by default, and can be overridden.
+   */
+  virtual FilterDependenciesPtr dependencies() {
+    return std::make_unique<
+        envoy::extensions::filters::common::dependency::v3::FilterDependencies>();
+  }
 };
 
 } // namespace Configuration

test/server/filter_config_test.cc

@@ -8,8 +8,13 @@
 #include "gtest/gtest.h"
 
 namespace Envoy {
+namespace Server {
+namespace Configuration {
 namespace {
 
+using envoy::extensions::filters::common::dependency::v3::Dependency;
+using envoy::extensions::filters::common::dependency::v3::FilterDependencies;
+
 class TestHttpFilterConfigFactory : public Server::Configuration::NamedHttpFilterConfigFactory {
 public:
   TestHttpFilterConfigFactory() = default;
@@ -25,6 +30,14 @@ class TestHttpFilterConfigFactory : public Server::Configuration::NamedHttpFilte
   ProtobufTypes::MessagePtr createEmptyConfigProto() override { return nullptr; }
   ProtobufTypes::MessagePtr createEmptyProtocolOptionsProto() override { return nullptr; }
 
+  FilterDependenciesPtr dependencies() override {
+    FilterDependencies dependencies;
+    Dependency* d = dependencies.add_decode_required();
+    d->set_name("foobar");
+    d->set_type(Dependency::FILTER_STATE_KEY);
+    return std::make_unique<FilterDependencies>(dependencies);
+  }
+
   std::string name() const override { return "envoy.test.http_filter"; }
   std::string configType() override { return ""; };
 };
@@ -38,5 +51,18 @@ TEST(NamedHttpFilterConfigFactoryTest, CreateFilterFactory) {
   factory.createFilterFactoryFromProto(*message, stats_prefix, context);
 }
 
+TEST(NamedHttpFilterConfigFactoryTest, Dependencies) {
+  TestHttpFilterConfigFactory factory;
+  const std::string stats_prefix = "foo";
+  Server::Configuration::MockFactoryContext context;
+  ProtobufTypes::MessagePtr message{new Envoy::ProtobufWkt::Struct()};
+
+  factory.createFilterFactoryFromProto(*message, stats_prefix, context);
+
+  EXPECT_EQ(factory.dependencies()->decode_required().size(), 1);
+}
+
 } // namespace
+} // namespace Configuration
+} // namespace Server
 } // namespace Envoy