filter state: add an object factory

Signed-off-by: Kuat Yessenov <kuat@google.com>
kyessenov · Aug 15, 2023 · 9a1a3d5 · 9a1a3d5
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diff --git a/docs/root/configuration/advanced/advanced.rst b/docs/root/configuration/advanced/advanced.rst
@@ -5,3 +5,4 @@ Advanced
   :maxdepth: 2
 
   well_known_dynamic_metadata
+  well_known_filter_state
diff --git a/docs/root/configuration/advanced/well_known_filter_state.rst b/docs/root/configuration/advanced/well_known_filter_state.rst
@@ -0,0 +1,12 @@
+.. _well_known_filter_state:
+
+Well Known Filter State Objects
+===============================
+
+The following list of filter state objects are consumed by Envoy extensions:
+
+.. csv-table::
+  :header: Filter state key, Purpose
+  :widths: 1, 3
+
+  ``envoy.tcp_proxy.cluster``, :ref:`TCP proxy <config_network_filters_tcp_proxy>` dynamic cluster selection on a per-connection basis 
diff --git a/docs/root/intro/arch_overview/advanced/data_sharing_between_filters.rst b/docs/root/intro/arch_overview/advanced/data_sharing_between_filters.rst
@@ -90,6 +90,10 @@ addition, it provides a facility to store typed objects in a map
 (``map<string, FilterState::Object>``). The state stored per filter can be
 either write-once (immutable), or write-many (mutable).
 
+See :ref:`the well-known dynamic metadata <well_known_dynamic_metadata>` and
+:ref:`the well-known filter state <well_known_filter_state>` for the reference
+list of the dynamic metadata and the filter state objects.
+
 .. _arch_overview_advanced_filter_state_sharing:
 
 Filter state sharing

diff --git a/envoy/stream_info/BUILD b/envoy/stream_info/BUILD
@@ -34,6 +34,7 @@ envoy_cc_library(
     hdrs = ["filter_state.h"],
     external_deps = ["abseil_optional"],
     deps = [
+        "//envoy/config:typed_config_interface",
         "//source/common/common:fmt_lib",
         "//source/common/common:utility_lib",
         "//source/common/protobuf",

diff --git a/envoy/stream_info/filter_state.h b/envoy/stream_info/filter_state.h
@@ -4,6 +4,7 @@
 #include <vector>
 
 #include "envoy/common/pure.h"
+#include "envoy/config/typed_config.h"
 
 #include "source/common/common/fmt.h"
 #include "source/common/common/utility.h"
@@ -103,6 +104,23 @@ class FilterState {
     virtual absl::optional<std::string> serializeAsString() const { return absl::nullopt; }
   };
 
+  /**
+   * Generic factory for filter state objects. The factory registry uses the
+   * object data name as the index for the object factory. This factory should be used by the
+   * dynamic extensions that cannot use the object constructors directly.
+   */
+  class ObjectFactory : public Config::UntypedFactory {
+  public:
+    // Config::UntypedFactory
+    std::string category() const override { return "filter_state.object"; }
+
+    /**
+     * @return std::unique_ptr<Object> from the serialized object data or nullptr if the input
+     * is malformed.
+     */
+    virtual std::unique_ptr<Object> createFromBytes(absl::string_view data) const PURE;
+  };
+
   struct FilterObject {
     std::shared_ptr<Object> data_;
     StateType state_type_{StateType::ReadOnly};

diff --git a/source/common/tcp_proxy/BUILD b/source/common/tcp_proxy/BUILD
@@ -45,6 +45,7 @@ envoy_cc_library(
         "//envoy/event:dispatcher_interface",
         "//envoy/network:connection_interface",
         "//envoy/network:filter_interface",
+        "//envoy/registry",
         "//envoy/router:router_interface",
         "//envoy/server:filter_config_interface",
         "//envoy/stats:stats_interface",

diff --git a/source/common/tcp_proxy/tcp_proxy.cc b/source/common/tcp_proxy/tcp_proxy.cc
@@ -11,6 +11,7 @@
 #include "envoy/event/timer.h"
 #include "envoy/extensions/filters/network/tcp_proxy/v3/tcp_proxy.pb.h"
 #include "envoy/extensions/filters/network/tcp_proxy/v3/tcp_proxy.pb.validate.h"
+#include "envoy/registry/registry.h"
 #include "envoy/stats/scope.h"
 #include "envoy/upstream/cluster_manager.h"
 #include "envoy/upstream/upstream.h"
@@ -41,6 +42,17 @@ const std::string& PerConnectionCluster::key() {
   CONSTRUCT_ON_FIRST_USE(std::string, "envoy.tcp_proxy.cluster");
 }
 
+class PerConnectionClusterFactory : public StreamInfo::FilterState::ObjectFactory {
+public:
+  std::string name() const override { return PerConnectionCluster::key(); }
+  std::unique_ptr<StreamInfo::FilterState::Object>
+  createFromBytes(absl::string_view data) const override {
+    return std::make_unique<PerConnectionCluster>(data);
+  }
+};
+
+REGISTER_FACTORY(PerConnectionClusterFactory, StreamInfo::FilterState::ObjectFactory);
+
 Config::SimpleRouteImpl::SimpleRouteImpl(const Config& parent, absl::string_view cluster_name)
     : parent_(parent), cluster_name_(cluster_name) {}
 

diff --git a/source/common/tcp_proxy/tcp_proxy.h b/source/common/tcp_proxy/tcp_proxy.h
@@ -374,6 +374,7 @@ class PerConnectionCluster : public StreamInfo::FilterState::Object {
 public:
   PerConnectionCluster(absl::string_view cluster) : cluster_(cluster) {}
   const std::string& value() const { return cluster_; }
+  absl::optional<std::string> serializeAsString() const override { return cluster_; }
   static const std::string& key();
 
 private:

diff --git a/test/common/tcp_proxy/tcp_proxy_test.cc b/test/common/tcp_proxy/tcp_proxy_test.cc
@@ -1410,6 +1410,18 @@ TEST_F(TcpProxyTest, UpstreamStartSecureTransport) {
   filter_->startUpstreamSecureTransport();
 }
 
+TEST(PerConnectionCluster, ObjectFactory) {
+  const std::string name = "envoy.tcp_proxy.cluster";
+  auto* factory =
+      Registry::FactoryRegistry<StreamInfo::FilterState::ObjectFactory>::getFactory(name);
+  ASSERT_NE(nullptr, factory);
+  EXPECT_EQ(name, factory->name());
+  const std::string cluster = "per_connection_cluster";
+  auto object = factory->createFromBytes(cluster);
+  ASSERT_NE(nullptr, object);
+  EXPECT_EQ(cluster, object->serializeAsString());
+}
+
 } // namespace
 } // namespace TcpProxy
 } // namespace Envoy