[svc-cfg] Move ServiceConfigChannelArgFilter to promises (#33473)

Co-authored-by: ctiller <ctiller@users.noreply.github.com>

BUILD

@@ -3033,12 +3033,14 @@ grpc_cc_library(
         "xds_orca_service_upb",
         "xds_orca_upb",
         "//src/core:arena",
+        "//src/core:arena_promise",
         "//src/core:channel_args",
         "//src/core:channel_fwd",
         "//src/core:channel_init",
         "//src/core:channel_stack_type",
         "//src/core:closure",
         "//src/core:construct_destruct",
+        "//src/core:context",
         "//src/core:delegating_helper",
         "//src/core:dual_ref_counted",
         "//src/core:env",

src/core/ext/filters/client_channel/service_config_channel_arg_filter.cc

@@ -19,7 +19,8 @@
 
 #include <grpc/support/port_platform.h>
 
-#include <new>
+#include <functional>
+#include <memory>
 #include <string>
 #include <utility>
 
@@ -34,10 +35,12 @@
 #include "src/core/lib/channel/channel_fwd.h"
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/channel/channel_stack_builder.h"
+#include "src/core/lib/channel/context.h"
+#include "src/core/lib/channel/promise_based_filter.h"
 #include "src/core/lib/config/core_configuration.h"
 #include "src/core/lib/gprpp/ref_counted_ptr.h"
-#include "src/core/lib/iomgr/closure.h"
-#include "src/core/lib/iomgr/error.h"
+#include "src/core/lib/promise/arena_promise.h"
+#include "src/core/lib/promise/context.h"
 #include "src/core/lib/resource_quota/arena.h"
 #include "src/core/lib/service_config/service_config.h"
 #include "src/core/lib/service_config/service_config_call_data.h"
@@ -45,20 +48,25 @@
 #include "src/core/lib/service_config/service_config_parser.h"
 #include "src/core/lib/surface/channel_init.h"
 #include "src/core/lib/surface/channel_stack_type.h"
+#include "src/core/lib/transport/metadata_batch.h"
+#include "src/core/lib/transport/transport.h"
 
 namespace grpc_core {
 
 namespace {
 
-class ServiceConfigChannelArgChannelData {
+class ServiceConfigChannelArgFilter : public ChannelFilter {
  public:
-  explicit ServiceConfigChannelArgChannelData(
-      const grpc_channel_element_args* args) {
-    auto service_config_str =
-        args->channel_args.GetOwnedString(GRPC_ARG_SERVICE_CONFIG);
+  static absl::StatusOr<ServiceConfigChannelArgFilter> Create(
+      const ChannelArgs& args, ChannelFilter::Args) {
+    return ServiceConfigChannelArgFilter(args);
+  }
+
+  explicit ServiceConfigChannelArgFilter(const ChannelArgs& args) {
+    auto service_config_str = args.GetOwnedString(GRPC_ARG_SERVICE_CONFIG);
     if (service_config_str.has_value()) {
-      auto service_config = ServiceConfigImpl::Create(
-          args->channel_args, service_config_str->c_str());
+      auto service_config =
+          ServiceConfigImpl::Create(args, *service_config_str);
       if (!service_config.ok()) {
         gpr_log(GPR_ERROR, "%s", service_config.status().ToString().c_str());
       } else {
@@ -67,62 +75,34 @@ class ServiceConfigChannelArgChannelData {
     }
   }
 
-  RefCountedPtr<ServiceConfig> service_config() const {
-    return service_config_;
-  }
+  // Construct a promise for one call.
+  ArenaPromise<ServerMetadataHandle> MakeCallPromise(
+      CallArgs call_args, NextPromiseFactory next_promise_factory) override;
 
  private:
   RefCountedPtr<ServiceConfig> service_config_;
 };
 
-grpc_error_handle ServiceConfigChannelArgInitCallElem(
-    grpc_call_element* elem, const grpc_call_element_args* args) {
-  auto* chand =
-      static_cast<ServiceConfigChannelArgChannelData*>(elem->channel_data);
-  RefCountedPtr<ServiceConfig> service_config = chand->service_config();
+ArenaPromise<ServerMetadataHandle>
+ServiceConfigChannelArgFilter::MakeCallPromise(
+    CallArgs call_args, NextPromiseFactory next_promise_factory) {
   const ServiceConfigParser::ParsedConfigVector* method_configs = nullptr;
-  if (service_config != nullptr) {
-    method_configs = service_config->GetMethodParsedConfigVector(args->path);
+  if (service_config_ != nullptr) {
+    method_configs = service_config_->GetMethodParsedConfigVector(
+        call_args.client_initial_metadata->get_pointer(HttpPathMetadata())
+            ->c_slice());
   }
-  auto* service_config_call_data =
-      args->arena->New<ServiceConfigCallData>(args->arena, args->context);
-  service_config_call_data->SetServiceConfig(std::move(service_config),
-                                             method_configs);
-  return absl::OkStatus();
-}
-
-void ServiceConfigChannelArgDestroyCallElem(
-    grpc_call_element* /*elem*/, const grpc_call_final_info* /*final_info*/,
-    grpc_closure* /*then_schedule_closure*/) {}
-
-grpc_error_handle ServiceConfigChannelArgInitChannelElem(
-    grpc_channel_element* elem, grpc_channel_element_args* args) {
-  ServiceConfigChannelArgChannelData* chand =
-      static_cast<ServiceConfigChannelArgChannelData*>(elem->channel_data);
-  new (chand) ServiceConfigChannelArgChannelData(args);
-  return absl::OkStatus();
-}
-
-void ServiceConfigChannelArgDestroyChannelElem(grpc_channel_element* elem) {
-  ServiceConfigChannelArgChannelData* chand =
-      static_cast<ServiceConfigChannelArgChannelData*>(elem->channel_data);
-  chand->~ServiceConfigChannelArgChannelData();
+  auto* arena = GetContext<Arena>();
+  auto* service_config_call_data = arena->New<ServiceConfigCallData>(
+      arena, GetContext<grpc_call_context_element>());
+  service_config_call_data->SetServiceConfig(service_config_, method_configs);
+  return next_promise_factory(std::move(call_args));
 }
 
-const grpc_channel_filter ServiceConfigChannelArgFilter = {
-    grpc_call_next_op,
-    nullptr,
-    grpc_channel_next_op,
-    0,
-    ServiceConfigChannelArgInitCallElem,
-    grpc_call_stack_ignore_set_pollset_or_pollset_set,
-    ServiceConfigChannelArgDestroyCallElem,
-    sizeof(ServiceConfigChannelArgChannelData),
-    ServiceConfigChannelArgInitChannelElem,
-    grpc_channel_stack_no_post_init,
-    ServiceConfigChannelArgDestroyChannelElem,
-    grpc_channel_next_get_info,
-    "service_config_channel_arg"};
+const grpc_channel_filter kServiceConfigChannelArgFilter =
+    MakePromiseBasedFilter<ServiceConfigChannelArgFilter,
+                           FilterEndpoint::kClient>(
+        "service_config_channel_arg");
 
 }  // namespace
 
@@ -136,7 +116,7 @@ void RegisterServiceConfigChannelArgFilter(
             !channel_args.GetString(GRPC_ARG_SERVICE_CONFIG).has_value()) {
           return true;
         }
-        builder->PrependFilter(&ServiceConfigChannelArgFilter);
+        builder->PrependFilter(&kServiceConfigChannelArgFilter);
         return true;
       });
 }