[call v3] add missing channelz updates in subchannel (#37086)

Closes #37086

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/37086 from markdroth:call_v3_subchannel_channelz e5cde30f8c
PiperOrigin-RevId: 648499878

src/core/client_channel/subchannel.cc

@@ -97,14 +97,11 @@ using ::grpc_event_engine::experimental::EventEngine;
 // ConnectedSubchannel
 //
 
-ConnectedSubchannel::ConnectedSubchannel(
-    const ChannelArgs& args,
-    RefCountedPtr<channelz::SubchannelNode> channelz_subchannel)
+ConnectedSubchannel::ConnectedSubchannel(const ChannelArgs& args)
     : RefCounted<ConnectedSubchannel>(
           GRPC_TRACE_FLAG_ENABLED(subchannel_refcount) ? "ConnectedSubchannel"
                                                        : nullptr),
-      args_(args),
-      channelz_subchannel_(std::move(channelz_subchannel)) {}
+      args_(args) {}
 
 //
 // LegacyConnectedSubchannel
@@ -114,14 +111,19 @@ class LegacyConnectedSubchannel : public ConnectedSubchannel {
  public:
   LegacyConnectedSubchannel(
       RefCountedPtr<grpc_channel_stack> channel_stack, const ChannelArgs& args,
-      RefCountedPtr<channelz::SubchannelNode> channelz_subchannel)
-      : ConnectedSubchannel(args, std::move(channelz_subchannel)),
+      RefCountedPtr<channelz::SubchannelNode> channelz_node)
+      : ConnectedSubchannel(args),
+        channelz_node_(std::move(channelz_node)),
         channel_stack_(std::move(channel_stack)) {}
 
   ~LegacyConnectedSubchannel() override {
     channel_stack_.reset(DEBUG_LOCATION, "ConnectedSubchannel");
   }
 
+  channelz::SubchannelNode* channelz_node() const {
+    return channelz_node_.get();
+  }
+
   void StartWatch(
       grpc_pollset_set* interested_parties,
       OrphanablePtr<ConnectivityStateWatcherInterface> watcher) override {
@@ -162,6 +164,7 @@ class LegacyConnectedSubchannel : public ConnectedSubchannel {
   }
 
  private:
+  RefCountedPtr<channelz::SubchannelNode> channelz_node_;
   RefCountedPtr<grpc_channel_stack> channel_stack_;
 };
 
@@ -191,9 +194,8 @@ class NewConnectedSubchannel : public ConnectedSubchannel {
   NewConnectedSubchannel(
       RefCountedPtr<UnstartedCallDestination> call_destination,
       RefCountedPtr<TransportCallDestination> transport,
-      const ChannelArgs& args,
-      RefCountedPtr<channelz::SubchannelNode> channelz_subchannel)
-      : ConnectedSubchannel(args, std::move(channelz_subchannel)),
+      const ChannelArgs& args)
+      : ConnectedSubchannel(args),
         call_destination_(std::move(call_destination)),
         transport_(std::move(transport)) {}
 
@@ -240,7 +242,8 @@ RefCountedPtr<SubchannelCall> SubchannelCall::Create(Args args,
 }
 
 SubchannelCall::SubchannelCall(Args args, grpc_error_handle* error)
-    : connected_subchannel_(std::move(args.connected_subchannel)),
+    : connected_subchannel_(args.connected_subchannel
+                                .TakeAsSubclass<LegacyConnectedSubchannel>()),
       deadline_(args.deadline) {
   grpc_call_stack* callstk = SUBCHANNEL_CALL_TO_CALL_STACK(this);
   const grpc_call_element_args call_args = {
@@ -259,7 +262,7 @@ SubchannelCall::SubchannelCall(Args args, grpc_error_handle* error)
     return;
   }
   grpc_call_stack_set_pollset_or_pollset_set(callstk, args.pollent);
-  auto* channelz_node = connected_subchannel_->channelz_subchannel();
+  auto* channelz_node = connected_subchannel_->channelz_node();
   if (channelz_node != nullptr) {
     channelz_node->RecordCallStarted();
   }
@@ -327,13 +330,9 @@ void SubchannelCall::Destroy(void* arg, grpc_error_handle /*error*/) {
 void SubchannelCall::MaybeInterceptRecvTrailingMetadata(
     grpc_transport_stream_op_batch* batch) {
   // only intercept payloads with recv trailing.
-  if (!batch->recv_trailing_metadata) {
-    return;
-  }
+  if (!batch->recv_trailing_metadata) return;
   // only add interceptor is channelz is enabled.
-  if (connected_subchannel_->channelz_subchannel() == nullptr) {
-    return;
-  }
+  if (connected_subchannel_->channelz_node() == nullptr) return;
   GRPC_CLOSURE_INIT(&recv_trailing_metadata_ready_, RecvTrailingMetadataReady,
                     this, grpc_schedule_on_exec_ctx);
   // save some state needed for the interception callback.
@@ -366,13 +365,13 @@ void SubchannelCall::RecvTrailingMetadataReady(void* arg,
   CHECK_NE(call->recv_trailing_metadata_, nullptr);
   grpc_status_code status = GRPC_STATUS_OK;
   GetCallStatus(&status, call->deadline_, call->recv_trailing_metadata_, error);
-  channelz::SubchannelNode* channelz_subchannel =
-      call->connected_subchannel_->channelz_subchannel();
-  CHECK_NE(channelz_subchannel, nullptr);
+  channelz::SubchannelNode* channelz_node =
+      call->connected_subchannel_->channelz_node();
+  CHECK_NE(channelz_node, nullptr);
   if (status == GRPC_STATUS_OK) {
-    channelz_subchannel->RecordCallSucceeded();
+    channelz_node->RecordCallSucceeded();
   } else {
-    channelz_subchannel->RecordCallFailed();
+    channelz_node->RecordCallFailed();
   }
   Closure::Run(DEBUG_LOCATION, call->original_recv_trailing_metadata_, error);
 }
@@ -860,6 +859,24 @@ bool Subchannel::PublishTransportLocked() {
             ->client_transport());
     InterceptionChainBuilder builder(
         connecting_result_.channel_args.SetObject(transport.get()));
+    if (channelz_node_ != nullptr) {
+      // TODO(ctiller): If/when we have a good way to access the subchannel
+      // from a filter (maybe GetContext<Subchannel>?), consider replacing
+      // these two hooks with a filter so that we can avoid storing two
+      // separate refs to the channelz node in each connection.
+      builder.AddOnClientInitialMetadata(
+          [channelz_node = channelz_node_](ClientMetadata&) {
+            channelz_node->RecordCallStarted();
+          });
+      builder.AddOnServerTrailingMetadata(
+          [channelz_node = channelz_node_](ServerMetadata& metadata) {
+            if (IsStatusOk(metadata)) {
+              channelz_node->RecordCallSucceeded();
+            } else {
+              channelz_node->RecordCallFailed();
+            }
+          });
+    }
     CoreConfiguration::Get().channel_init().AddToInterceptionChainBuilder(
         GRPC_CLIENT_SUBCHANNEL, builder);
     auto transport_destination =
@@ -874,8 +891,7 @@ bool Subchannel::PublishTransportLocked() {
       return false;
     }
     connected_subchannel_ = MakeRefCounted<NewConnectedSubchannel>(
-        std::move(*call_destination), std::move(transport_destination), args_,
-        channelz_node_);
+        std::move(*call_destination), std::move(transport_destination), args_);
   }
   connecting_result_.Reset();
   // Publish.

src/core/client_channel/subchannel.h

@@ -66,9 +66,6 @@ class SubchannelCall;
 class ConnectedSubchannel : public RefCounted<ConnectedSubchannel> {
  public:
   const ChannelArgs& args() const { return args_; }
-  channelz::SubchannelNode* channelz_subchannel() const {
-    return channelz_subchannel_.get();
-  }
 
   virtual void StartWatch(
       grpc_pollset_set* interested_parties,
@@ -85,17 +82,14 @@ class ConnectedSubchannel : public RefCounted<ConnectedSubchannel> {
   virtual void Ping(grpc_closure* on_initiate, grpc_closure* on_ack) = 0;
 
  protected:
-  ConnectedSubchannel(
-      const ChannelArgs& args,
-      RefCountedPtr<channelz::SubchannelNode> channelz_subchannel);
+  explicit ConnectedSubchannel(const ChannelArgs& args);
 
  private:
   ChannelArgs args_;
-  // ref counted pointer to the channelz node in this connected subchannel's
-  // owning subchannel.
-  RefCountedPtr<channelz::SubchannelNode> channelz_subchannel_;
 };
 
+class LegacyConnectedSubchannel;
+
 // Implements the interface of RefCounted<>.
 class SubchannelCall final {
  public:
@@ -150,7 +144,7 @@ class SubchannelCall final {
 
   static void Destroy(void* arg, grpc_error_handle error);
 
-  RefCountedPtr<ConnectedSubchannel> connected_subchannel_;
+  RefCountedPtr<LegacyConnectedSubchannel> connected_subchannel_;
   grpc_closure* after_call_stack_destroy_ = nullptr;
   // State needed to support channelz interception of recv trailing metadata.
   grpc_closure recv_trailing_metadata_ready_;