Change main argument of call promise to be a struct (#29019)

* introduce call args

* bs

* x

* Automated change: Fix sanity tests

* fix

* Simplify naming

* tweak

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

BUILD

@@ -2182,6 +2182,7 @@ grpc_cc_library(
         "grpc_trace",
         "iomgr_port",
         "json",
+        "latch",
         "memory_quota",
         "orphanable",
         "promise",
@@ -4172,6 +4173,7 @@ grpc_cc_library(
     deps = [
         "arena",
         "arena_promise",
+        "capture",
         "config",
         "gpr_base",
         "grpc_base",

build_autogenerated.yaml

@@ -820,6 +820,8 @@ libs:
   - src/core/lib/promise/detail/status.h
   - src/core/lib/promise/detail/switch.h
   - src/core/lib/promise/exec_ctx_wakeup_scheduler.h
+  - src/core/lib/promise/intra_activity_waiter.h
+  - src/core/lib/promise/latch.h
   - src/core/lib/promise/loop.h
   - src/core/lib/promise/map.h
   - src/core/lib/promise/poll.h
@@ -1991,6 +1993,8 @@ libs:
   - src/core/lib/promise/detail/status.h
   - src/core/lib/promise/detail/switch.h
   - src/core/lib/promise/exec_ctx_wakeup_scheduler.h
+  - src/core/lib/promise/intra_activity_waiter.h
+  - src/core/lib/promise/latch.h
   - src/core/lib/promise/loop.h
   - src/core/lib/promise/map.h
   - src/core/lib/promise/poll.h

gRPC-C++.podspec

@@ -789,6 +789,8 @@ Pod::Spec.new do |s|
                       'src/core/lib/promise/detail/status.h',
                       'src/core/lib/promise/detail/switch.h',
                       'src/core/lib/promise/exec_ctx_wakeup_scheduler.h',
+                      'src/core/lib/promise/intra_activity_waiter.h',
+                      'src/core/lib/promise/latch.h',
                       'src/core/lib/promise/loop.h',
                       'src/core/lib/promise/map.h',
                       'src/core/lib/promise/poll.h',
@@ -1590,6 +1592,8 @@ Pod::Spec.new do |s|
                               'src/core/lib/promise/detail/status.h',
                               'src/core/lib/promise/detail/switch.h',
                               'src/core/lib/promise/exec_ctx_wakeup_scheduler.h',
+                              'src/core/lib/promise/intra_activity_waiter.h',
+                              'src/core/lib/promise/latch.h',
                               'src/core/lib/promise/loop.h',
                               'src/core/lib/promise/map.h',
                               'src/core/lib/promise/poll.h',

gRPC-Core.podspec

@@ -1292,6 +1292,8 @@ Pod::Spec.new do |s|
                       'src/core/lib/promise/detail/status.h',
                       'src/core/lib/promise/detail/switch.h',
                       'src/core/lib/promise/exec_ctx_wakeup_scheduler.h',
+                      'src/core/lib/promise/intra_activity_waiter.h',
+                      'src/core/lib/promise/latch.h',
                       'src/core/lib/promise/loop.h',
                       'src/core/lib/promise/map.h',
                       'src/core/lib/promise/poll.h',
@@ -2188,6 +2190,8 @@ Pod::Spec.new do |s|
                               'src/core/lib/promise/detail/status.h',
                               'src/core/lib/promise/detail/switch.h',
                               'src/core/lib/promise/exec_ctx_wakeup_scheduler.h',
+                              'src/core/lib/promise/intra_activity_waiter.h',
+                              'src/core/lib/promise/latch.h',
                               'src/core/lib/promise/loop.h',
                               'src/core/lib/promise/map.h',
                               'src/core/lib/promise/poll.h',

grpc.gemspec

@@ -1211,6 +1211,8 @@ Gem::Specification.new do |s|
   s.files += %w( src/core/lib/promise/detail/status.h )
   s.files += %w( src/core/lib/promise/detail/switch.h )
   s.files += %w( src/core/lib/promise/exec_ctx_wakeup_scheduler.h )
+  s.files += %w( src/core/lib/promise/intra_activity_waiter.h )
+  s.files += %w( src/core/lib/promise/latch.h )
   s.files += %w( src/core/lib/promise/loop.h )
   s.files += %w( src/core/lib/promise/map.h )
   s.files += %w( src/core/lib/promise/poll.h )

package.xml

@@ -1191,6 +1191,8 @@
     <file baseinstalldir="/" name="src/core/lib/promise/detail/status.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/promise/detail/switch.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/promise/exec_ctx_wakeup_scheduler.h" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/promise/intra_activity_waiter.h" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/promise/latch.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/promise/loop.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/promise/map.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/promise/poll.h" role="src" />

src/core/ext/filters/client_idle/client_idle_filter.cc

@@ -76,9 +76,8 @@ class ClientIdleFilter : public ChannelFilter {
   ClientIdleFilter& operator=(ClientIdleFilter&&) = default;
 
   // Construct a promise for one call.
-  ArenaPromise<TrailingMetadata> MakeCallPromise(
+  ArenaPromise<ServerMetadataHandle> MakeCallPromise(
-      ClientInitialMetadata initial_metadata,
+      CallArgs call_args, NextPromiseFactory next_promise_factory) override;
-      NextPromiseFactory next_promise_factory) override;
 
   bool StartTransportOp(grpc_transport_op* op) override;
 
@@ -116,15 +115,14 @@ absl::StatusOr<ClientIdleFilter> ClientIdleFilter::Create(
 }
 
 // Construct a promise for one call.
-ArenaPromise<TrailingMetadata> ClientIdleFilter::MakeCallPromise(
+ArenaPromise<ServerMetadataHandle> ClientIdleFilter::MakeCallPromise(
-    ClientInitialMetadata initial_metadata,
+    CallArgs call_args, NextPromiseFactory next_promise_factory) {
-    NextPromiseFactory next_promise_factory) {
   using Decrementer = std::unique_ptr<ClientIdleFilter, CallCountDecreaser>;
   IncreaseCallCount();
-  return ArenaPromise<TrailingMetadata>(Capture(
+  return ArenaPromise<ServerMetadataHandle>(
-      [](Decrementer*, ArenaPromise<TrailingMetadata>* next)
+      Capture([](Decrementer*, ArenaPromise<ServerMetadataHandle>* next)
-          -> Poll<TrailingMetadata> { return (*next)(); },
+                  -> Poll<ServerMetadataHandle> { return (*next)(); },
-      Decrementer(this), next_promise_factory(std::move(initial_metadata))));
+              Decrementer(this), next_promise_factory(std::move(call_args))));
 }
 
 bool ClientIdleFilter::StartTransportOp(grpc_transport_op* op) {

src/core/ext/filters/http/client_authority_filter.cc

@@ -57,16 +57,17 @@ absl::StatusOr<ClientAuthorityFilter> ClientAuthorityFilter::Create(
   return ClientAuthorityFilter(Slice::FromCopiedString(default_authority_str));
 }
 
-ArenaPromise<TrailingMetadata> ClientAuthorityFilter::MakeCallPromise(
+ArenaPromise<ServerMetadataHandle> ClientAuthorityFilter::MakeCallPromise(
-    ClientInitialMetadata initial_metadata,
+    CallArgs call_args, NextPromiseFactory next_promise_factory) {
-    NextPromiseFactory next_promise_factory) {
   // If no authority is set, set the default authority.
-  if (initial_metadata->get_pointer(HttpAuthorityMetadata()) == nullptr) {
+  if (call_args.client_initial_metadata->get_pointer(HttpAuthorityMetadata()) ==
-    initial_metadata->Set(HttpAuthorityMetadata(), default_authority_.Ref());
+      nullptr) {
+    call_args.client_initial_metadata->Set(HttpAuthorityMetadata(),
+                                           default_authority_.Ref());
   }
   // We have no asynchronous work, so we can just ask the next promise to run,
   // passing down initial_metadata.
-  return next_promise_factory(std::move(initial_metadata));
+  return next_promise_factory(std::move(call_args));
 }
 
 namespace {

src/core/ext/filters/http/client_authority_filter.h

@@ -37,9 +37,8 @@ class ClientAuthorityFilter final : public ChannelFilter {
       const grpc_channel_args* args, ChannelFilter::Args);
 
   // Construct a promise for one call.
-  ArenaPromise<TrailingMetadata> MakeCallPromise(
+  ArenaPromise<ServerMetadataHandle> MakeCallPromise(
-      ClientInitialMetadata initial_metadata,
+      CallArgs call_args, NextPromiseFactory next_promise_factory) override;
-      NextPromiseFactory next_promise_factory) override;
 
  private:
   explicit ClientAuthorityFilter(Slice default_authority)

src/core/lib/channel/channel_stack.h

@@ -122,9 +122,8 @@ struct grpc_channel_filter {
        - allocation of memory for call data
      There is an on-going migration to move all filters to providing this, and
      then to drop start_transport_stream_op_batch. */
-  grpc_core::ArenaPromise<grpc_core::TrailingMetadata> (*make_call_promise)(
+  grpc_core::ArenaPromise<grpc_core::ServerMetadataHandle> (*make_call_promise)(
-      grpc_channel_element* elem,
+      grpc_channel_element* elem, grpc_core::CallArgs call_args,
-      grpc_core::ClientInitialMetadata initial_metadata,
       grpc_core::NextPromiseFactory next_promise_factory);
   /* Called to handle channel level operations - e.g. new calls, or transport
      closure.

src/core/lib/channel/promise_based_filter.cc

@@ -136,7 +136,7 @@ void ClientCallData::Cancel(grpc_error_handle error) {
   GRPC_ERROR_UNREF(cancelled_error_);
   cancelled_error_ = GRPC_ERROR_REF(error);
   // Stop running the promise.
-  promise_ = ArenaPromise<TrailingMetadata>();
+  promise_ = ArenaPromise<ServerMetadataHandle>();
   // If we have an op queued, fail that op.
   // Record what we've done.
   if (send_initial_state_ == SendInitialState::kQueued) {
@@ -176,10 +176,12 @@ void ClientCallData::StartPromise() {
   {
     ScopedActivity activity(this);
     promise_ = filter->MakeCallPromise(
-        WrapMetadata(send_initial_metadata_batch_->payload
+        CallArgs{
-                         ->send_initial_metadata.send_initial_metadata),
+            WrapMetadata(send_initial_metadata_batch_->payload
-        [this](ClientInitialMetadata initial_metadata) {
+                             ->send_initial_metadata.send_initial_metadata),
-          return MakeNextPromise(std::move(initial_metadata));
+            nullptr},
+        [this](CallArgs call_args) {
+          return MakeNextPromise(std::move(call_args));
         });
   }
   // Poll once.
@@ -203,12 +205,13 @@ void ClientCallData::HookRecvTrailingMetadata(
 // Effectively:
 //   - put the modified initial metadata into the batch to be sent down.
 //   - return a wrapper around PollTrailingMetadata as the promise.
-ArenaPromise<TrailingMetadata> ClientCallData::MakeNextPromise(
+ArenaPromise<ServerMetadataHandle> ClientCallData::MakeNextPromise(
-    ClientInitialMetadata initial_metadata) {
+    CallArgs call_args) {
   GPR_ASSERT(send_initial_state_ == SendInitialState::kQueued);
   send_initial_metadata_batch_->payload->send_initial_metadata
-      .send_initial_metadata = UnwrapMetadata(std::move(initial_metadata));
+      .send_initial_metadata =
-  return ArenaPromise<TrailingMetadata>(
+      UnwrapMetadata(std::move(call_args.client_initial_metadata));
+  return ArenaPromise<ServerMetadataHandle>(
       [this]() { return PollTrailingMetadata(); });
 }
 
@@ -216,7 +219,7 @@ ArenaPromise<TrailingMetadata> ClientCallData::MakeNextPromise(
 // First poll: send the send_initial_metadata op down the stack.
 // All polls: await receiving the trailing metadata, then return it to the
 // application.
-Poll<TrailingMetadata> ClientCallData::PollTrailingMetadata() {
+Poll<ServerMetadataHandle> ClientCallData::PollTrailingMetadata() {
   if (send_initial_state_ == SendInitialState::kQueued) {
     // First poll: pass the send_initial_metadata op down the stack.
     GPR_ASSERT(send_initial_metadata_batch_ != nullptr);
@@ -274,7 +277,7 @@ void ClientCallData::RecvTrailingMetadataReady(grpc_error_handle error) {
   WakeInsideCombiner();
 }
 
-// Given an error, fill in TrailingMetadata to represent that error.
+// Given an error, fill in ServerMetadataHandle to represent that error.
 void ClientCallData::SetStatusFromError(grpc_metadata_batch* metadata,
                                         grpc_error_handle error) {
   grpc_status_code status_code = GRPC_STATUS_UNKNOWN;
@@ -298,13 +301,13 @@ void ClientCallData::WakeInsideCombiner() {
     case SendInitialState::kQueued:
     case SendInitialState::kForwarded: {
       // Poll the promise once since we're waiting for it.
-      Poll<TrailingMetadata> poll;
+      Poll<ServerMetadataHandle> poll;
       {
         ScopedActivity activity(this);
         poll = promise_();
       }
-      if (auto* r = absl::get_if<TrailingMetadata>(&poll)) {
+      if (auto* r = absl::get_if<ServerMetadataHandle>(&poll)) {
-        promise_ = ArenaPromise<TrailingMetadata>();
+        promise_ = ArenaPromise<ServerMetadataHandle>();
         auto* md = UnwrapMetadata(std::move(*r));
         bool destroy_md = true;
         if (recv_trailing_state_ == RecvTrailingState::kComplete) {
@@ -505,7 +508,7 @@ void ServerCallData::Cancel(grpc_error_handle error) {
   GRPC_ERROR_UNREF(cancelled_error_);
   cancelled_error_ = GRPC_ERROR_REF(error);
   // Stop running the promise.
-  promise_ = ArenaPromise<TrailingMetadata>();
+  promise_ = ArenaPromise<ServerMetadataHandle>();
   if (send_trailing_state_ == SendTrailingState::kQueued) {
     send_trailing_state_ = SendTrailingState::kCancelled;
     struct FailBatch : public grpc_closure {
@@ -534,20 +537,20 @@ void ServerCallData::Cancel(grpc_error_handle error) {
 // Effectively:
 //   - put the modified initial metadata into the batch being sent up.
 //   - return a wrapper around PollTrailingMetadata as the promise.
-ArenaPromise<TrailingMetadata> ServerCallData::MakeNextPromise(
+ArenaPromise<ServerMetadataHandle> ServerCallData::MakeNextPromise(
-    ClientInitialMetadata initial_metadata) {
+    CallArgs call_args) {
   GPR_ASSERT(recv_initial_state_ == RecvInitialState::kComplete);
-  GPR_ASSERT(UnwrapMetadata(std::move(initial_metadata)) ==
+  GPR_ASSERT(UnwrapMetadata(std::move(call_args.client_initial_metadata)) ==
              recv_initial_metadata_);
   forward_recv_initial_metadata_callback_ = true;
-  return ArenaPromise<TrailingMetadata>(
+  return ArenaPromise<ServerMetadataHandle>(
       [this]() { return PollTrailingMetadata(); });
 }
 
 // Wrapper to make it look like we're calling the next filter as a promise.
 // All polls: await sending the trailing metadata, then foward it down the
 // stack.
-Poll<TrailingMetadata> ServerCallData::PollTrailingMetadata() {
+Poll<ServerMetadataHandle> ServerCallData::PollTrailingMetadata() {
   switch (send_trailing_state_) {
     case SendTrailingState::kInitial:
       return Pending{};
@@ -587,9 +590,9 @@ void ServerCallData::RecvInitialMetadataReady(grpc_error_handle error) {
   // Construct the promise.
   ChannelFilter* filter = static_cast<ChannelFilter*>(elem()->channel_data);
   promise_ = filter->MakeCallPromise(
-      WrapMetadata(recv_initial_metadata_),
+      CallArgs{WrapMetadata(recv_initial_metadata_), nullptr},
-      [this](ClientInitialMetadata initial_metadata) {
+      [this](CallArgs call_args) {
-        return MakeNextPromise(std::move(initial_metadata));
+        return MakeNextPromise(std::move(call_args));
       });
   // Poll once.
   bool own_error = false;
@@ -610,12 +613,12 @@ void ServerCallData::WakeInsideCombiner(
   bool forward_send_trailing_metadata = false;
   is_polling_ = true;
   if (recv_initial_state_ == RecvInitialState::kComplete) {
-    Poll<TrailingMetadata> poll;
+    Poll<ServerMetadataHandle> poll;
     {
       ScopedActivity activity(this);
       poll = promise_();
     }
-    if (auto* r = absl::get_if<TrailingMetadata>(&poll)) {
+    if (auto* r = absl::get_if<ServerMetadataHandle>(&poll)) {
       auto* md = UnwrapMetadata(std::move(*r));
       bool destroy_md = true;
       switch (send_trailing_state_) {

src/core/lib/channel/promise_based_filter.h

@@ -54,9 +54,8 @@ class ChannelFilter {
   };
 
   // Construct a promise for one call.
-  virtual ArenaPromise<TrailingMetadata> MakeCallPromise(
+  virtual ArenaPromise<ServerMetadataHandle> MakeCallPromise(
-      ClientInitialMetadata initial_metadata,
+      CallArgs call_args, NextPromiseFactory next_promise_factory) = 0;
-      NextPromiseFactory next_promise_factory) = 0;
 
   // Start a legacy transport op
   // Return true if the op was handled, false if it should be passed to the
@@ -205,17 +204,16 @@ class ClientCallData : public BaseCallData {
   // Effectively:
   //   - put the modified initial metadata into the batch to be sent down.
   //   - return a wrapper around PollTrailingMetadata as the promise.
-  ArenaPromise<TrailingMetadata> MakeNextPromise(
+  ArenaPromise<ServerMetadataHandle> MakeNextPromise(CallArgs call_args);
-      ClientInitialMetadata initial_metadata);
   // Wrapper to make it look like we're calling the next filter as a promise.
   // First poll: send the send_initial_metadata op down the stack.
   // All polls: await receiving the trailing metadata, then return it to the
   // application.
-  Poll<TrailingMetadata> PollTrailingMetadata();
+  Poll<ServerMetadataHandle> PollTrailingMetadata();
   static void RecvTrailingMetadataReadyCallback(void* arg,
                                                 grpc_error_handle error);
   void RecvTrailingMetadataReady(grpc_error_handle error);
-  // Given an error, fill in TrailingMetadata to represent that error.
+  // Given an error, fill in ServerMetadataHandle to represent that error.
   void SetStatusFromError(grpc_metadata_batch* metadata,
                           grpc_error_handle error);
   // Wakeup and poll the promise if appropriate.
@@ -223,7 +221,7 @@ class ClientCallData : public BaseCallData {
   void OnWakeup() override;
 
   // Contained promise
-  ArenaPromise<TrailingMetadata> promise_;
+  ArenaPromise<ServerMetadataHandle> promise_;
   // Queued batch containing at least a send_initial_metadata op.
   grpc_transport_stream_op_batch* send_initial_metadata_batch_ = nullptr;
   // Pointer to where trailing metadata will be stored.
@@ -289,12 +287,11 @@ class ServerCallData : public BaseCallData {
   // Effectively:
   //   - put the modified initial metadata into the batch being sent up.
   //   - return a wrapper around PollTrailingMetadata as the promise.
-  ArenaPromise<TrailingMetadata> MakeNextPromise(
+  ArenaPromise<ServerMetadataHandle> MakeNextPromise(CallArgs call_args);
-      ClientInitialMetadata initial_metadata);
   // Wrapper to make it look like we're calling the next filter as a promise.
   // All polls: await sending the trailing metadata, then foward it down the
   // stack.
-  Poll<TrailingMetadata> PollTrailingMetadata();
+  Poll<ServerMetadataHandle> PollTrailingMetadata();
   static void RecvInitialMetadataReadyCallback(void* arg,
                                                grpc_error_handle error);
   void RecvInitialMetadataReady(grpc_error_handle error);
@@ -303,7 +300,7 @@ class ServerCallData : public BaseCallData {
   void OnWakeup() override;
 
   // Contained promise
-  ArenaPromise<TrailingMetadata> promise_;
+  ArenaPromise<ServerMetadataHandle> promise_;
   // Pointer to where initial metadata will be stored.
   grpc_metadata_batch* recv_initial_metadata_ = nullptr;
   // Closure to call when we're done with the trailing metadata.
@@ -366,10 +363,10 @@ MakePromiseBasedFilter(const char* name) {
         static_cast<CallData*>(elem->call_data)->StartBatch(batch);
       },
       // make_call_promise
-      [](grpc_channel_element* elem, ClientInitialMetadata initial_metadata,
+      [](grpc_channel_element* elem, CallArgs call_args,
          NextPromiseFactory next_promise_factory) {
         return static_cast<F*>(elem->channel_data)
-            ->MakeCallPromise(std::move(initial_metadata),
+            ->MakeCallPromise(std::move(call_args),
                               std::move(next_promise_factory));
       },
       // start_transport_op

src/core/lib/security/authorization/grpc_server_authz_filter.cc

@@ -49,7 +49,7 @@ absl::StatusOr<GrpcServerAuthzFilter> GrpcServerAuthzFilter::Create(
 }
 
 bool GrpcServerAuthzFilter::IsAuthorized(
-    const ClientInitialMetadata& initial_metadata) {
+    const ClientMetadataHandle& initial_metadata) {
   EvaluateArgs args(initial_metadata.get(), &per_channel_evaluate_args_);
   if (GRPC_TRACE_FLAG_ENABLED(grpc_authz_trace)) {
     gpr_log(GPR_DEBUG,
@@ -92,14 +92,13 @@ bool GrpcServerAuthzFilter::IsAuthorized(
   return false;
 }
 
-ArenaPromise<TrailingMetadata> GrpcServerAuthzFilter::MakeCallPromise(
+ArenaPromise<ServerMetadataHandle> GrpcServerAuthzFilter::MakeCallPromise(
-    ClientInitialMetadata initial_metadata,
+    CallArgs call_args, NextPromiseFactory next_promise_factory) {
-    NextPromiseFactory next_promise_factory) {
+  if (!IsAuthorized(call_args.client_initial_metadata)) {
-  if (!IsAuthorized(initial_metadata)) {
+    return ArenaPromise<ServerMetadataHandle>(Immediate(ServerMetadataHandle(
-    return ArenaPromise<TrailingMetadata>(Immediate(TrailingMetadata(
         absl::PermissionDeniedError("Unauthorized RPC request rejected."))));
   }
-  return next_promise_factory(std::move(initial_metadata));
+  return next_promise_factory(std::move(call_args));
 }
 
 const grpc_channel_filter GrpcServerAuthzFilter::kFilterVtable =

src/core/lib/security/authorization/grpc_server_authz_filter.h

@@ -30,16 +30,15 @@ class GrpcServerAuthzFilter final : public ChannelFilter {
   static absl::StatusOr<GrpcServerAuthzFilter> Create(
       const grpc_channel_args* args, ChannelFilter::Args);
 
-  ArenaPromise<TrailingMetadata> MakeCallPromise(
+  ArenaPromise<ServerMetadataHandle> MakeCallPromise(
-      ClientInitialMetadata initial_metadata,
+      CallArgs call_args, NextPromiseFactory next_promise_factory) override;
-      NextPromiseFactory next_promise_factory) override;
 
  private:
   GrpcServerAuthzFilter(
       RefCountedPtr<grpc_auth_context> auth_context, grpc_endpoint* endpoint,
       RefCountedPtr<grpc_authorization_policy_provider> provider);
 
-  bool IsAuthorized(const ClientInitialMetadata& initial_metadata);
+  bool IsAuthorized(const ClientMetadataHandle& initial_metadata);
 
   RefCountedPtr<grpc_auth_context> auth_context_;
   EvaluateArgs::PerChannelArgs per_channel_evaluate_args_;

src/core/lib/security/credentials/call_creds_util.cc

@@ -31,7 +31,7 @@ struct ServiceUrlAndMethod {
 };
 
 ServiceUrlAndMethod MakeServiceUrlAndMethod(
-    const ClientInitialMetadata& initial_metadata,
+    const ClientMetadataHandle& initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs* args) {
   auto service =
       initial_metadata->get_pointer(HttpPathMetadata())->as_string_view();
@@ -65,13 +65,13 @@ ServiceUrlAndMethod MakeServiceUrlAndMethod(
 }  // namespace
 
 std::string MakeJwtServiceUrl(
-    const ClientInitialMetadata& initial_metadata,
+    const ClientMetadataHandle& initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs* args) {
   return MakeServiceUrlAndMethod(initial_metadata, args).service_url;
 }
 
 grpc_auth_metadata_context MakePluginAuthMetadataContext(
-    const ClientInitialMetadata& initial_metadata,
+    const ClientMetadataHandle& initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs* args) {
   auto fields = MakeServiceUrlAndMethod(initial_metadata, args);
   grpc_auth_metadata_context ctx;

src/core/lib/security/credentials/call_creds_util.h

@@ -29,12 +29,12 @@ namespace grpc_core {
 
 // Helper function to construct service URL for jwt call creds.
 std::string MakeJwtServiceUrl(
-    const ClientInitialMetadata& initial_metadata,
+    const ClientMetadataHandle& initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs* args);
 
 // Helper function to construct context for plugin call creds.
 grpc_auth_metadata_context MakePluginAuthMetadataContext(
-    const ClientInitialMetadata& initial_metadata,
+    const ClientMetadataHandle& initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs* args);
 
 }  // namespace grpc_core

src/core/lib/security/credentials/composite/composite_credentials.cc

@@ -43,15 +43,15 @@ const char kCredentialsTypeComposite[] = "composite";
 
 /* -- Composite call credentials. -- */
 
-grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
 grpc_composite_call_credentials::GetRequestMetadata(
-    grpc_core::ClientInitialMetadata initial_metadata,
+    grpc_core::ClientMetadataHandle initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs* args) {
   auto self = Ref();
   return TrySeqIter(
       inner_.begin(), inner_.end(), std::move(initial_metadata),
       [self, args](const grpc_core::RefCountedPtr<grpc_call_credentials>& creds,
-                   grpc_core::ClientInitialMetadata initial_metadata) {
+                   grpc_core::ClientMetadataHandle initial_metadata) {
         return creds->GetRequestMetadata(std::move(initial_metadata), args);
       });
 }

src/core/lib/security/credentials/composite/composite_credentials.h

@@ -90,8 +90,8 @@ class grpc_composite_call_credentials : public grpc_call_credentials {
       grpc_core::RefCountedPtr<grpc_call_credentials> creds2);
   ~grpc_composite_call_credentials() override = default;
 
-  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
-  GetRequestMetadata(grpc_core::ClientInitialMetadata initial_metadata,
+  GetRequestMetadata(grpc_core::ClientMetadataHandle initial_metadata,
                      const GetRequestMetadataArgs* args) override;
 
   grpc_security_level min_security_level() const override {

src/core/lib/security/credentials/credentials.h

@@ -216,8 +216,8 @@ struct grpc_call_credentials
   ~grpc_call_credentials() override = default;
 
   virtual grpc_core::ArenaPromise<
-      absl::StatusOr<grpc_core::ClientInitialMetadata>>
+      absl::StatusOr<grpc_core::ClientMetadataHandle>>
-  GetRequestMetadata(grpc_core::ClientInitialMetadata initial_metadata,
+  GetRequestMetadata(grpc_core::ClientMetadataHandle initial_metadata,
                      const GetRequestMetadataArgs* args) = 0;
 
   virtual grpc_security_level min_security_level() const {

src/core/lib/security/credentials/fake/fake_credentials.cc

@@ -97,9 +97,9 @@ const char* grpc_fake_transport_get_expected_targets(
 
 /* -- Metadata-only test credentials. -- */
 
-grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
 grpc_md_only_test_credentials::GetRequestMetadata(
-    grpc_core::ClientInitialMetadata initial_metadata,
+    grpc_core::ClientMetadataHandle initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs*) {
   initial_metadata->Append(
       key_.as_string_view(), value_.Ref(),

src/core/lib/security/credentials/fake/fake_credentials.h

@@ -65,8 +65,8 @@ class grpc_md_only_test_credentials : public grpc_call_credentials {
         key_(grpc_core::Slice::FromCopiedString(md_key)),
         value_(grpc_core::Slice::FromCopiedString(md_value)) {}
 
-  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
-  GetRequestMetadata(grpc_core::ClientInitialMetadata initial_metadata,
+  GetRequestMetadata(grpc_core::ClientMetadataHandle initial_metadata,
                      const GetRequestMetadataArgs* args) override;
 
   std::string debug_string() override { return "MD only Test Credentials"; };

src/core/lib/security/credentials/iam/iam_credentials.cc

@@ -31,9 +31,9 @@
 #include "src/core/lib/promise/promise.h"
 #include "src/core/lib/surface/api_trace.h"
 
-grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
 grpc_google_iam_credentials::GetRequestMetadata(
-    grpc_core::ClientInitialMetadata initial_metadata,
+    grpc_core::ClientMetadataHandle initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs*) {
   if (token_.has_value()) {
     initial_metadata->Append(

src/core/lib/security/credentials/iam/iam_credentials.h

@@ -30,8 +30,8 @@ class grpc_google_iam_credentials : public grpc_call_credentials {
   grpc_google_iam_credentials(const char* token,
                               const char* authority_selector);
 
-  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
-  GetRequestMetadata(grpc_core::ClientInitialMetadata initial_metadata,
+  GetRequestMetadata(grpc_core::ClientMetadataHandle initial_metadata,
                      const GetRequestMetadataArgs* args) override;
 
   std::string debug_string() override { return debug_string_; }

src/core/lib/security/credentials/jwt/jwt_credentials.cc

@@ -49,9 +49,9 @@ grpc_service_account_jwt_access_credentials::
   gpr_mu_destroy(&cache_mu_);
 }
 
-grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
 grpc_service_account_jwt_access_credentials::GetRequestMetadata(
-    grpc_core::ClientInitialMetadata initial_metadata,
+    grpc_core::ClientMetadataHandle initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs* args) {
   gpr_timespec refresh_threshold = gpr_time_from_seconds(
       GRPC_SECURE_TOKEN_REFRESH_THRESHOLD_SECS, GPR_TIMESPAN);

src/core/lib/security/credentials/jwt/jwt_credentials.h

@@ -38,8 +38,8 @@ class grpc_service_account_jwt_access_credentials
                                               gpr_timespec token_lifetime);
   ~grpc_service_account_jwt_access_credentials() override;
 
-  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
-  GetRequestMetadata(grpc_core::ClientInitialMetadata initial_metadata,
+  GetRequestMetadata(grpc_core::ClientMetadataHandle initial_metadata,
                      const GetRequestMetadataArgs* args) override;
 
   const gpr_timespec& jwt_lifetime() const { return jwt_lifetime_; }

src/core/lib/security/credentials/oauth2/oauth2_credentials.cc

@@ -281,9 +281,9 @@ void grpc_oauth2_token_fetcher_credentials::on_http_response(
   delete r;
 }
 
-grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
 grpc_oauth2_token_fetcher_credentials::GetRequestMetadata(
-    grpc_core::ClientInitialMetadata initial_metadata,
+    grpc_core::ClientMetadataHandle initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs*) {
   // Check if we can use the cached token.
   absl::optional<grpc_core::Slice> cached_access_token_value;
@@ -328,7 +328,7 @@ grpc_oauth2_token_fetcher_credentials::GetRequestMetadata(
   }
   return
       [pending_request]()
-          -> grpc_core::Poll<absl::StatusOr<grpc_core::ClientInitialMetadata>> {
+          -> grpc_core::Poll<absl::StatusOr<grpc_core::ClientMetadataHandle>> {
         if (!pending_request->done.load(std::memory_order_acquire)) {
           return grpc_core::Pending{};
         }
@@ -696,9 +696,9 @@ grpc_call_credentials* grpc_sts_credentials_create(
 // Oauth2 Access Token credentials.
 //
 
-grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
 grpc_access_token_credentials::GetRequestMetadata(
-    grpc_core::ClientInitialMetadata initial_metadata,
+    grpc_core::ClientMetadataHandle initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs*) {
   initial_metadata->Append(
       GRPC_AUTHORIZATION_METADATA_KEY, access_token_value_.Ref(),

src/core/lib/security/credentials/oauth2/oauth2_credentials.h

@@ -79,9 +79,9 @@ struct grpc_oauth2_pending_get_request_metadata
   std::atomic<bool> done{false};
   grpc_core::Waker waker;
   grpc_polling_entity* pollent;
-  grpc_core::ClientInitialMetadata md;
+  grpc_core::ClientMetadataHandle md;
   struct grpc_oauth2_pending_get_request_metadata* next;
-  absl::StatusOr<grpc_core::ClientInitialMetadata> result;
+  absl::StatusOr<grpc_core::ClientMetadataHandle> result;
 };
 
 // -- Oauth2 Token Fetcher credentials --
@@ -94,8 +94,8 @@ class grpc_oauth2_token_fetcher_credentials : public grpc_call_credentials {
   grpc_oauth2_token_fetcher_credentials();
   ~grpc_oauth2_token_fetcher_credentials() override;
 
-  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
-  GetRequestMetadata(grpc_core::ClientInitialMetadata initial_metadata,
+  GetRequestMetadata(grpc_core::ClientMetadataHandle initial_metadata,
                      const GetRequestMetadataArgs* args) override;
 
   void on_http_response(grpc_credentials_metadata_request* r,
@@ -152,8 +152,8 @@ class grpc_access_token_credentials final : public grpc_call_credentials {
  public:
   explicit grpc_access_token_credentials(const char* access_token);
 
-  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
-  GetRequestMetadata(grpc_core::ClientInitialMetadata initial_metadata,
+  GetRequestMetadata(grpc_core::ClientMetadataHandle initial_metadata,
                      const GetRequestMetadataArgs* args) override;
 
   std::string debug_string() override;

src/core/lib/security/credentials/plugin/plugin_credentials.cc

@@ -60,7 +60,7 @@ std::string grpc_plugin_credentials::debug_string() {
   return debug_str;
 }
 
-absl::StatusOr<grpc_core::ClientInitialMetadata>
+absl::StatusOr<grpc_core::ClientMetadataHandle>
 grpc_plugin_credentials::PendingRequest::ProcessPluginResult(
     const grpc_metadata* md, size_t num_md, grpc_status_code status,
     const char* error_details) {
@@ -96,12 +96,12 @@ grpc_plugin_credentials::PendingRequest::ProcessPluginResult(
             });
       }
       if (!error.ok()) return std::move(error);
-      return grpc_core::ClientInitialMetadata(std::move(md_));
+      return grpc_core::ClientMetadataHandle(std::move(md_));
     }
   }
 }
 
-grpc_core::Poll<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+grpc_core::Poll<absl::StatusOr<grpc_core::ClientMetadataHandle>>
 grpc_plugin_credentials::PendingRequest::PollAsyncResult() {
   if (!ready_.load(std::memory_order_acquire)) {
     return grpc_core::Pending{};
@@ -137,9 +137,9 @@ void grpc_plugin_credentials::PendingRequest::RequestMetadataReady(
   r->waker_.Wakeup();
 }
 
-grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
 grpc_plugin_credentials::GetRequestMetadata(
-    grpc_core::ClientInitialMetadata initial_metadata,
+    grpc_core::ClientMetadataHandle initial_metadata,
     const grpc_call_credentials::GetRequestMetadataArgs* args) {
   if (plugin_.get_metadata == nullptr) {
     return grpc_core::Immediate(std::move(initial_metadata));

src/core/lib/security/credentials/plugin/plugin_credentials.h

@@ -35,8 +35,8 @@ struct grpc_plugin_credentials final : public grpc_call_credentials {
                                    grpc_security_level min_security_level);
   ~grpc_plugin_credentials() override;
 
-  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+  grpc_core::ArenaPromise<absl::StatusOr<grpc_core::ClientMetadataHandle>>
-  GetRequestMetadata(grpc_core::ClientInitialMetadata initial_metadata,
+  GetRequestMetadata(grpc_core::ClientMetadataHandle initial_metadata,
                      const GetRequestMetadataArgs* args) override;
 
   std::string debug_string() override;
@@ -45,7 +45,7 @@ struct grpc_plugin_credentials final : public grpc_call_credentials {
   class PendingRequest : public grpc_core::RefCounted<PendingRequest> {
    public:
     PendingRequest(grpc_core::RefCountedPtr<grpc_plugin_credentials> creds,
-                   grpc_core::ClientInitialMetadata initial_metadata,
+                   grpc_core::ClientMetadataHandle initial_metadata,
                    const grpc_call_credentials::GetRequestMetadataArgs* args)
         : call_creds_(std::move(creds)),
           context_(
@@ -60,11 +60,11 @@ struct grpc_plugin_credentials final : public grpc_call_credentials {
       }
     }
 
-    absl::StatusOr<grpc_core::ClientInitialMetadata> ProcessPluginResult(
+    absl::StatusOr<grpc_core::ClientMetadataHandle> ProcessPluginResult(
         const grpc_metadata* md, size_t num_md, grpc_status_code status,
         const char* error_details);
 
-    grpc_core::Poll<absl::StatusOr<grpc_core::ClientInitialMetadata>>
+    grpc_core::Poll<absl::StatusOr<grpc_core::ClientMetadataHandle>>
     PollAsyncResult();
 
     static void RequestMetadataReady(void* request, const grpc_metadata* md,
@@ -80,7 +80,7 @@ struct grpc_plugin_credentials final : public grpc_call_credentials {
         grpc_core::Activity::current()->MakeNonOwningWaker()};
     grpc_core::RefCountedPtr<grpc_plugin_credentials> call_creds_;
     grpc_auth_metadata_context context_;
-    grpc_core::ClientInitialMetadata md_;
+    grpc_core::ClientMetadataHandle md_;
     // final status
     absl::InlinedVector<grpc_metadata, 2> metadata_;
     std::string error_details_;

src/core/lib/security/transport/auth_filters.h

@@ -41,17 +41,16 @@ class ClientAuthFilter final : public ChannelFilter {
                                                  ChannelFilter::Args);
 
   // Construct a promise for one call.
-  ArenaPromise<TrailingMetadata> MakeCallPromise(
+  ArenaPromise<ServerMetadataHandle> MakeCallPromise(
-      ClientInitialMetadata initial_metadata,
+      CallArgs call_args, NextPromiseFactory next_promise_factory) override;
-      NextPromiseFactory next_promise_factory) override;
 
  private:
   ClientAuthFilter(
       RefCountedPtr<grpc_channel_security_connector> security_connector,
       RefCountedPtr<grpc_auth_context> auth_context);
 
-  ArenaPromise<absl::StatusOr<ClientInitialMetadata>> GetCallCredsMetadata(
+  ArenaPromise<absl::StatusOr<CallArgs>> GetCallCredsMetadata(
-      ClientInitialMetadata initial_metadata);
+      CallArgs call_args);
 
   // Contains refs to security connector and auth context.
   grpc_call_credentials::GetRequestMetadataArgs args_;

src/core/lib/security/transport/client_auth_filter.cc

@@ -31,6 +31,7 @@
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/channel/promise_based_filter.h"
 #include "src/core/lib/gpr/string.h"
+#include "src/core/lib/gprpp/capture.h"
 #include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/promise/promise.h"
@@ -98,8 +99,8 @@ ClientAuthFilter::ClientAuthFilter(
     RefCountedPtr<grpc_auth_context> auth_context)
     : args_{std::move(security_connector), std::move(auth_context)} {}
 
-ArenaPromise<absl::StatusOr<ClientInitialMetadata>>
+ArenaPromise<absl::StatusOr<CallArgs>> ClientAuthFilter::GetCallCredsMetadata(
-ClientAuthFilter::GetCallCredsMetadata(ClientInitialMetadata initial_metadata) {
+    CallArgs call_args) {
   auto* ctx = static_cast<grpc_client_security_context*>(
       GetContext<grpc_call_context_element>()[GRPC_CONTEXT_SECURITY].value);
   grpc_call_credentials* channel_call_creds =
@@ -108,8 +109,7 @@ ClientAuthFilter::GetCallCredsMetadata(ClientInitialMetadata initial_metadata) {
 
   if (channel_call_creds == nullptr && !call_creds_has_md) {
     /* Skip sending metadata altogether. */
-    return Immediate(
+    return Immediate(absl::StatusOr<CallArgs>(std::move(call_args)));
-        absl::StatusOr<ClientInitialMetadata>(std::move(initial_metadata)));
   }
 
   RefCountedPtr<grpc_call_credentials> creds;
@@ -148,12 +148,20 @@ ClientAuthFilter::GetCallCredsMetadata(ClientInitialMetadata initial_metadata) {
         "transfer call credential."));
   }
 
-  return creds->GetRequestMetadata(std::move(initial_metadata), &args_);
+  auto client_initial_metadata = std::move(call_args.client_initial_metadata);
+  return TrySeq(
+      creds->GetRequestMetadata(std::move(client_initial_metadata), &args_),
+      Capture(
+          [](CallArgs* rest_of_args, ClientMetadataHandle new_metadata) {
+            rest_of_args->client_initial_metadata = std::move(new_metadata);
+            return Immediate<absl::StatusOr<CallArgs>>(
+                absl::StatusOr<CallArgs>(std::move(*rest_of_args)));
+          },
+          std::move(call_args)));
 }
 
-ArenaPromise<TrailingMetadata> ClientAuthFilter::MakeCallPromise(
+ArenaPromise<ServerMetadataHandle> ClientAuthFilter::MakeCallPromise(
-    ClientInitialMetadata initial_metadata,
+    CallArgs call_args, NextPromiseFactory next_promise_factory) {
-    NextPromiseFactory next_promise_factory) {
   auto* legacy_ctx = GetContext<grpc_call_context_element>();
   if (legacy_ctx[GRPC_CONTEXT_SECURITY].value == nullptr) {
     legacy_ctx[GRPC_CONTEXT_SECURITY].value =
@@ -166,13 +174,14 @@ ArenaPromise<TrailingMetadata> ClientAuthFilter::MakeCallPromise(
       legacy_ctx[GRPC_CONTEXT_SECURITY].value)
       ->auth_context = args_.auth_context;
 
-  auto* host = initial_metadata->get_pointer(HttpAuthorityMetadata());
+  auto* host =
+      call_args.client_initial_metadata->get_pointer(HttpAuthorityMetadata());
   if (host == nullptr) {
-    return next_promise_factory(std::move(initial_metadata));
+    return next_promise_factory(std::move(call_args));
   }
   return TrySeq(args_.security_connector->CheckCallHost(
                     host->as_string_view(), args_.auth_context.get()),
-                GetCallCredsMetadata(std::move(initial_metadata)),
+                GetCallCredsMetadata(std::move(call_args)),
                 next_promise_factory);
 }
 

src/core/lib/transport/transport.h

@@ -31,6 +31,7 @@
 #include "src/core/lib/iomgr/pollset.h"
 #include "src/core/lib/iomgr/pollset_set.h"
 #include "src/core/lib/promise/arena_promise.h"
+#include "src/core/lib/promise/latch.h"
 #include "src/core/lib/resource_quota/arena.h"
 #include "src/core/lib/slice/slice_internal.h"
 #include "src/core/lib/transport/byte_stream.h"
@@ -99,21 +100,33 @@ class MetadataHandle {
 
 // Trailing metadata type
 // TODO(ctiller): This should be a bespoke instance of MetadataMap<>
-using TrailingMetadata = MetadataHandle<grpc_metadata_batch>;
+using ServerMetadata = grpc_metadata_batch;
+using ServerMetadataHandle = MetadataHandle<ServerMetadata>;
 
 // Ok/not-ok check for trailing metadata, so that it can be used as result types
 // for TrySeq.
-inline bool IsStatusOk(const TrailingMetadata& m) {
+inline bool IsStatusOk(const ServerMetadataHandle& m) {
   return m->get(GrpcStatusMetadata()).value_or(GRPC_STATUS_UNKNOWN) ==
          GRPC_STATUS_OK;
 }
 
 // Client initial metadata type
 // TODO(ctiller): This should be a bespoke instance of MetadataMap<>
-using ClientInitialMetadata = MetadataHandle<grpc_metadata_batch>;
+using ClientMetadata = grpc_metadata_batch;
+using ClientMetadataHandle = MetadataHandle<ClientMetadata>;
+
+// Server initial metadata type
+// TODO(ctiller): This should be a bespoke instance of MetadataMap<>
+using ServerMetadataHandle = MetadataHandle<grpc_metadata_batch>;
+
+struct CallArgs {
+  ClientMetadataHandle client_initial_metadata;
+  Latch<ServerMetadata*>* server_initial_metadata;
+};
 
 using NextPromiseFactory =
-    std::function<ArenaPromise<TrailingMetadata>(ClientInitialMetadata)>;
+    std::function<ArenaPromise<ServerMetadataHandle>(CallArgs)>;
+
 }  // namespace grpc_core
 
 /* forward declarations */

src/core/lib/transport/transport_impl.h

@@ -45,8 +45,8 @@ typedef struct grpc_transport_vtable {
        - allocation of memory for call data (sizeof_stream may be ignored)
      There is an on-going migration to move all filters to providing this, and
      then to drop perform_stream_op. */
-  grpc_core::ArenaPromise<grpc_core::TrailingMetadata> (*make_call_promise)(
+  grpc_core::ArenaPromise<grpc_core::ServerMetadataHandle> (*make_call_promise)(
-      grpc_transport* self, grpc_core::ClientInitialMetadata initial_metadata,
+      grpc_transport* self, grpc_core::ClientMetadataHandle initial_metadata,
       grpc_core::NextPromiseFactory next_promise_factory);
 
   /* implementation of grpc_transport_set_pollset */

test/core/filters/client_authority_filter_test.cc

@@ -71,18 +71,24 @@ TEST(ClientAuthorityFilterTest, PromiseCompletesImmediatelyAndSetsAuthority) {
   // TODO(ctiller): use Activity here, once it's ready.
   TestContext<Arena> context(arena.get());
   auto promise = filter.MakeCallPromise(
-      ClientInitialMetadata::TestOnlyWrap(&initial_metadata_batch),
+      CallArgs{
-      [&](ClientInitialMetadata initial_metadata) {
+          ClientMetadataHandle::TestOnlyWrap(&initial_metadata_batch),
-        EXPECT_EQ(initial_metadata->get_pointer(HttpAuthorityMetadata())
+          nullptr,
+      },
+      [&](CallArgs call_args) {
+        EXPECT_EQ(call_args.client_initial_metadata
+                      ->get_pointer(HttpAuthorityMetadata())
                       ->as_string_view(),
                   "foo.test.google.au");
         seen = true;
-        return ArenaPromise<TrailingMetadata>([&]() -> Poll<TrailingMetadata> {
+        return ArenaPromise<ServerMetadataHandle>(
-          return TrailingMetadata::TestOnlyWrap(&trailing_metadata_batch);
+            [&]() -> Poll<ServerMetadataHandle> {
-        });
+              return ServerMetadataHandle::TestOnlyWrap(
+                  &trailing_metadata_batch);
+            });
       });
   auto result = promise();
-  EXPECT_TRUE(absl::get_if<TrailingMetadata>(&result) != nullptr);
+  EXPECT_TRUE(absl::get_if<ServerMetadataHandle>(&result) != nullptr);
   EXPECT_TRUE(seen);
 }
 
@@ -99,18 +105,24 @@ TEST(ClientAuthorityFilterTest,
   // TODO(ctiller): use Activity here, once it's ready.
   TestContext<Arena> context(arena.get());
   auto promise = filter.MakeCallPromise(
-      ClientInitialMetadata::TestOnlyWrap(&initial_metadata_batch),
+      CallArgs{
-      [&](ClientInitialMetadata initial_metadata) {
+          ClientMetadataHandle::TestOnlyWrap(&initial_metadata_batch),
-        EXPECT_EQ(initial_metadata->get_pointer(HttpAuthorityMetadata())
+          nullptr,
+      },
+      [&](CallArgs call_args) {
+        EXPECT_EQ(call_args.client_initial_metadata
+                      ->get_pointer(HttpAuthorityMetadata())
                       ->as_string_view(),
                   "bar.test.google.au");
         seen = true;
-        return ArenaPromise<TrailingMetadata>([&]() -> Poll<TrailingMetadata> {
+        return ArenaPromise<ServerMetadataHandle>(
-          return TrailingMetadata::TestOnlyWrap(&trailing_metadata_batch);
+            [&]() -> Poll<ServerMetadataHandle> {
-        });
+              return ServerMetadataHandle::TestOnlyWrap(
+                  &trailing_metadata_batch);
+            });
       });
   auto result = promise();
-  EXPECT_TRUE(absl::get_if<TrailingMetadata>(&result) != nullptr);
+  EXPECT_TRUE(absl::get_if<ServerMetadataHandle>(&result) != nullptr);
   EXPECT_TRUE(seen);
 }
 

test/core/security/credentials_test.cc

@@ -450,9 +450,9 @@ class RequestMetadataState : public RefCounted<RequestMetadataState> {
     activity_ = MakeActivity(
         [this, creds] {
           return Seq(creds->GetRequestMetadata(
-                         ClientInitialMetadata::TestOnlyWrap(&md_),
+                         ClientMetadataHandle::TestOnlyWrap(&md_),
                          &get_request_metadata_args_),
-                     [this](absl::StatusOr<ClientInitialMetadata> metadata) {
+                     [this](absl::StatusOr<ClientMetadataHandle> metadata) {
                        if (metadata.ok()) {
                          GPR_ASSERT(metadata->get() == &md_);
                        }
@@ -1771,8 +1771,8 @@ struct fake_call_creds : public grpc_call_credentials {
  public:
   fake_call_creds() : grpc_call_credentials("fake") {}
 
-  ArenaPromise<absl::StatusOr<ClientInitialMetadata>> GetRequestMetadata(
+  ArenaPromise<absl::StatusOr<ClientMetadataHandle>> GetRequestMetadata(
-      ClientInitialMetadata initial_metadata,
+      ClientMetadataHandle initial_metadata,
       const grpc_call_credentials::GetRequestMetadataArgs*) override {
     initial_metadata->Append("foo", Slice::FromStaticString("oof"),
                              [](absl::string_view, const Slice&) { abort(); });

test/core/security/oauth2_utils.cc

@@ -57,10 +57,10 @@ char* grpc_test_fetch_oauth2_token_with_credentials(
       [creds, &initial_metadata, &get_request_metadata_args]() {
         return grpc_core::Map(
             creds->GetRequestMetadata(
-                grpc_core::ClientInitialMetadata::TestOnlyWrap(
+                grpc_core::ClientMetadataHandle::TestOnlyWrap(
                     &initial_metadata),
                 &get_request_metadata_args),
-            [](const absl::StatusOr<grpc_core::ClientInitialMetadata>& s) {
+            [](const absl::StatusOr<grpc_core::ClientMetadataHandle>& s) {
               return s.status();
             });
       },

test/cpp/cocoapods/test/server_context_test_spouse_test.mm

@@ -55,7 +55,7 @@ bool ClientMetadataContains(const grpc::ServerContext& context, const grpc::stri
 
 @implementation ServerContextTestSpouseTest
 
-TEST(ServerContextTestSpouseTest, ClientMetadata) {
+TEST(ServerContextTestSpouseTest, ClientMetadataHandle) {
   grpc::ServerContext context;
   grpc::testing::ServerContextTestSpouse spouse(&context);
 
@@ -81,7 +81,7 @@ TEST(ServerContextTestSpouseTest, InitialMetadata) {
   ASSERT_EQ(metadata, spouse.GetInitialMetadata());
 }
 
-TEST(ServerContextTestSpouseTest, TrailingMetadata) {
+TEST(ServerContextTestSpouseTest, ServerMetadataHandle) {
   grpc::ServerContext context;
   grpc::testing::ServerContextTestSpouse spouse(&context);
   std::multimap<std::string, std::string> metadata;

test/cpp/test/server_context_test_spouse_test.cc

@@ -47,7 +47,7 @@ bool ClientMetadataContains(const ServerContext& context,
   return false;
 }
 
-TEST(ServerContextTestSpouseTest, ClientMetadata) {
+TEST(ServerContextTestSpouseTest, ClientMetadataHandle) {
   ServerContext context;
   ServerContextTestSpouse spouse(&context);
 
@@ -73,7 +73,7 @@ TEST(ServerContextTestSpouseTest, InitialMetadata) {
   ASSERT_EQ(metadata, spouse.GetInitialMetadata());
 }
 
-TEST(ServerContextTestSpouseTest, TrailingMetadata) {
+TEST(ServerContextTestSpouseTest, ServerMetadataHandle) {
   ServerContext context;
   ServerContextTestSpouse spouse(&context);
   std::multimap<std::string, std::string> metadata;

tools/doxygen/Doxyfile.c++.internal

@@ -2190,6 +2190,8 @@ src/core/lib/promise/detail/promise_like.h \
 src/core/lib/promise/detail/status.h \
 src/core/lib/promise/detail/switch.h \
 src/core/lib/promise/exec_ctx_wakeup_scheduler.h \
+src/core/lib/promise/intra_activity_waiter.h \
+src/core/lib/promise/latch.h \
 src/core/lib/promise/loop.h \
 src/core/lib/promise/map.h \
 src/core/lib/promise/poll.h \

tools/doxygen/Doxyfile.core.internal

@@ -1985,6 +1985,8 @@ src/core/lib/promise/detail/promise_like.h \
 src/core/lib/promise/detail/status.h \
 src/core/lib/promise/detail/switch.h \
 src/core/lib/promise/exec_ctx_wakeup_scheduler.h \
+src/core/lib/promise/intra_activity_waiter.h \
+src/core/lib/promise/latch.h \
 src/core/lib/promise/loop.h \
 src/core/lib/promise/map.h \
 src/core/lib/promise/poll.h \