upstream: stats scope for dual filters

source/docs/upstream_filters.md

@@ -8,11 +8,13 @@ functionality analysis. Make sure
   * Either the filter does not sendLocalReply, or you test and document how
     sendLocalReply code paths will play with hedging / retries (cut off the
     hedge attempt, and local-reply failures won't trigger retries)
-  * Either the filter does not access streamInfo in a non-cost way, or you test
+  * Either the filter does not access streamInfo in a non-const way, or you test
     and document how the filter interacts with hedging and retries. Note that
     for hedging, a single downstream StreamInfo is accessible in parallel to
     both instances of the upstream filter instance, so it must be resiliant to
     parallel access.
+  * Any code accessing the downstream connection checks to make sure it is
+    present. The downstream connection will not be available for mirrored/shadowed requests.
 
 Once you've done this, you're ready to convert. An example converted filter is the Envoy
 [Buffer](https://github.com/envoyproxy/envoy/blob/main/source/extensions/filters/http/buffer/config.cc)
@@ -25,12 +27,12 @@ Assuming your filter inherits from FactoryBase:
     Please note if you use the init manager or a stats context you *must* get
     them from DualInfo rather than from the server factory context or xDS
     reloads will not work correctly and may leak memory.
-  * Add ``UpstreamMyFilterFactory = MyFilterFactory;`` and
-    ``DECLARE_FACTORY(UpstreamMyFilterFactory`` in your config.h file and
-    ``REGISTER_FACTORY(UpstreamMyFilterFactory,
-                     Server::Configuration::UpstreamHttpFilterConfigFactory){"envoy.my_filter"};`` to
+  * Add ``using UpstreamMyFilterFactory = MyFilterFactory;`` in your config.h file and
+    ``REGISTER_FACTORY(UpstreamMyFilterFactory, Server::Configuration::UpstreamHttpFilterConfigFactory);`` to
     your config.cc file.
   * If your filter is listed in ``source/extensions/extensions_metadata.yaml``
     add ``envoy.filters.http.upstream`` to the filter category.
 
 Your filter should now be available as an upstream filter.
+
+An example PR for conversion is [23071](https://github.com/envoyproxy/envoy/pull/23071)

source/extensions/filters/http/common/factory_base.h

@@ -87,10 +87,11 @@ class DualFactoryBase : public CommonFactoryBase<ConfigProto, RouteConfigProto>,
 
   struct DualInfo {
     DualInfo(Server::Configuration::UpstreamHttpFactoryContext& context)
-        : init_manager(context.initManager()) {}
+        : init_manager(context.initManager()), scope(context.scope()) {}
     DualInfo(Server::Configuration::FactoryContext& context)
-        : init_manager(context.initManager()) {}
+        : init_manager(context.initManager()), scope(context.scope()) {}
     Init::Manager& init_manager;
+    Stats::Scope& scope;
   };
 
   Http::FilterFactoryCb

test/mocks/server/factory_context.cc

@@ -49,6 +49,7 @@ MockFactoryContext::~MockFactoryContext() = default;
 MockUpstreamHttpFactoryContext::MockUpstreamHttpFactoryContext() {
   ON_CALL(*this, getServerFactoryContext()).WillByDefault(ReturnRef(server_factory_context_));
   ON_CALL(*this, initManager()).WillByDefault(ReturnRef(init_manager_));
+  ON_CALL(*this, scope()).WillByDefault(ReturnRef(scope_));
 }
 
 } // namespace Configuration

test/mocks/server/factory_context.h

@@ -91,6 +91,7 @@ class MockUpstreamHttpFactoryContext : public UpstreamHttpFactoryContext {
   MOCK_METHOD(Stats::Scope&, scope, ());
   testing::NiceMock<Init::MockManager> init_manager_;
   testing::NiceMock<MockServerFactoryContext> server_factory_context_;
+  testing::NiceMock<Stats::MockIsolatedStatsStore> scope_;
 };
 
 } // namespace Configuration