[CallTracer] report transport byte counts directly to `CallTracer`

Instead of passing the transport byte counts back up through the filter
stack to be reported to the `CallTracer`, we now have the transport
pass the transport byte counts directly to the `CallTracer` itself.
This will eventually allow us to avoid unnecessarily storing these byte
counts in cases where no `CallTracer` actually cares about the data, which
will reduce per-call memory.  (In the short term, it actually increases
memory usage, but we can separately do some work to avoid the memory
usage in the transport by removing the `grpc_transport_stream_stats`
struct from the legacy filter API.)

This is a prereq for supporting `CallTracer` in the new call v3 stack,
which does not include the transport byte counts as part of the
receieve-trailing-metadata hook, unlike the legacy filter stack.

This change is controlled by the `call_tracer_in_transport` experiment,
which is enabled by default.

As part of this experiment, we also fix a couple of related bugs:
- On the client side, the chttp2 transport was incorrectly adding
  annotations to the parent `ClientCallTracer` instead of the
  `CallAttemptTracer`.
- The OpenCensus `ServerCallTracer` was incorrectly swapping the values
  of sent and received bytes.

PiperOrigin-RevId: 650728181

BUILD

@@ -2916,6 +2916,7 @@ grpc_cc_library(
         "//src/core:channel_stack_type",
         "//src/core:context",
         "//src/core:error",
+        "//src/core:experiments",
         "//src/core:logging_filter",
         "//src/core:metadata_batch",
         "//src/core:slice",
@@ -4686,6 +4687,7 @@ grpc_cc_library(
         "absl/strings",
     ],
     deps = [
+        "call_tracer",
         "chttp2_bin_encoder",
         "chttp2_legacy_frame",
         "chttp2_varint",

requirements.bazel.txt

@@ -7,7 +7,7 @@ oauth2client==4.1.0
 requests==2.25.1
 urllib3==1.26.18
 chardet==3.0.4
-certifi==2024.7.4
+certifi==2023.7.22
 idna==2.7
 gevent==22.08.0
 zope.event==4.5.0

src/core/ext/transport/chttp2/transport/chttp2_transport.cc

@@ -257,6 +257,7 @@ grpc_core::CopyContextFn g_get_copied_context_fn = nullptr;
 namespace grpc_core {
 
 namespace {
+
 // Initialize a grpc_closure \a c to call \a Fn with \a t and \a error. Holds
 // the passed in reference to \a t until it's moved into Fn.
 template <void (*Fn)(RefCountedPtr<grpc_chttp2_transport>, grpc_error_handle)>
@@ -272,13 +273,12 @@ grpc_closure* InitTransportClosure(RefCountedPtr<grpc_chttp2_transport> t,
       t.release(), nullptr);
   return c;
 }
-}  // namespace
 
-namespace {
 TestOnlyGlobalHttp2TransportInitCallback test_only_init_callback = nullptr;
 TestOnlyGlobalHttp2TransportDestructCallback test_only_destruct_callback =
     nullptr;
 bool test_only_disable_transient_failure_state_notification = false;
+
 }  // namespace
 
 void TestOnlySetGlobalHttp2TransportInitCallback(
@@ -361,6 +361,34 @@ std::string HttpAnnotation::ToString() const {
   return s;
 }
 
+void Chttp2CallTracerWrapper::RecordIncomingBytes(
+    const CallTracerInterface::TransportByteSize& transport_byte_size) {
+  // Update legacy API.
+  stream_->stats.incoming.framing_bytes += transport_byte_size.framing_bytes;
+  stream_->stats.incoming.data_bytes += transport_byte_size.data_bytes;
+  stream_->stats.incoming.header_bytes += transport_byte_size.header_bytes;
+  // Update new API.
+  if (!IsCallTracerInTransportEnabled()) return;
+  auto* call_tracer = stream_->arena->GetContext<CallTracerInterface>();
+  if (call_tracer != nullptr) {
+    call_tracer->RecordIncomingBytes(transport_byte_size);
+  }
+}
+
+void Chttp2CallTracerWrapper::RecordOutgoingBytes(
+    const CallTracerInterface::TransportByteSize& transport_byte_size) {
+  // Update legacy API.
+  stream_->stats.outgoing.framing_bytes += transport_byte_size.framing_bytes;
+  stream_->stats.outgoing.data_bytes += transport_byte_size.data_bytes;
+  stream_->stats.outgoing.header_bytes +=
+      transport_byte_size.header_bytes;  // Update new API.
+  if (!IsCallTracerInTransportEnabled()) return;
+  auto* call_tracer = stream_->arena->GetContext<CallTracerInterface>();
+  if (call_tracer != nullptr) {
+    call_tracer->RecordOutgoingBytes(transport_byte_size);
+  }
+}
+
 }  // namespace grpc_core
 
 //
@@ -814,7 +842,8 @@ grpc_chttp2_stream::grpc_chttp2_stream(grpc_chttp2_transport* t,
         return refcount;
       }()),
       arena(arena),
-      flow_control(&t->flow_control) {
+      flow_control(&t->flow_control),
+      call_tracer_wrapper(this) {
   t->streams_allocated.fetch_add(1, std::memory_order_relaxed);
   if (server_data) {
     id = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(server_data));
@@ -1344,7 +1373,9 @@ static void perform_stream_op_locked(void* stream_op,
   grpc_chttp2_transport* t = s->t.get();
 
   s->traced = op->is_traced;
+  if (!grpc_core::IsCallTracerInTransportEnabled()) {
     s->call_tracer = CallTracerIfSampled(s);
+  }
   s->tcp_tracer = TcpTracerIfSampled(s);
   if (GRPC_TRACE_FLAG_ENABLED(http)) {
     LOG(INFO) << "perform_stream_op_locked[s=" << s << "; op=" << op
@@ -1375,6 +1406,7 @@ static void perform_stream_op_locked(void* stream_op,
   }
 
   if (op->send_initial_metadata) {
+    if (!grpc_core::IsCallTracerInTransportEnabled()) {
       if (s->call_tracer != nullptr) {
         s->call_tracer->RecordAnnotation(
             grpc_core::HttpAnnotation(grpc_core::HttpAnnotation::Type::kStart,
@@ -1382,6 +1414,17 @@ static void perform_stream_op_locked(void* stream_op,
                 .Add(s->t->flow_control.stats())
                 .Add(s->flow_control.stats()));
       }
+    } else if (grpc_core::IsTraceRecordCallopsEnabled()) {
+      auto* call_tracer =
+          s->arena->GetContext<grpc_core::CallTracerInterface>();
+      if (call_tracer != nullptr && call_tracer->IsSampled()) {
+        call_tracer->RecordAnnotation(
+            grpc_core::HttpAnnotation(grpc_core::HttpAnnotation::Type::kStart,
+                                      gpr_now(GPR_CLOCK_REALTIME))
+                .Add(s->t->flow_control.stats())
+                .Add(s->flow_control.stats()));
+      }
+    }
     if (t->is_client && t->channelz_socket != nullptr) {
       t->channelz_socket->RecordStreamStartedFromLocal();
     }
@@ -1464,9 +1507,8 @@ static void perform_stream_op_locked(void* stream_op,
       frame_hdr[3] = static_cast<uint8_t>(len >> 8);
       frame_hdr[4] = static_cast<uint8_t>(len);
 
-      s->stats.outgoing.framing_bytes += GRPC_HEADER_SIZE_IN_BYTES;
-      s->stats.outgoing.data_bytes +=
-          op_payload->send_message.send_message->Length();
+      s->call_tracer_wrapper.RecordOutgoingBytes(
+          {GRPC_HEADER_SIZE_IN_BYTES, len, 0});
       s->next_message_end_offset =
           s->flow_controlled_bytes_written +
           static_cast<int64_t>(s->flow_controlled_buffer.length) +

src/core/ext/transport/chttp2/transport/frame_data.cc

@@ -55,7 +55,7 @@ absl::Status grpc_chttp2_data_parser_begin_frame(uint8_t flags,
 
 void grpc_chttp2_encode_data(uint32_t id, grpc_slice_buffer* inbuf,
                              uint32_t write_bytes, int is_eof,
-                             grpc_transport_one_way_stats* stats,
+                             grpc_core::CallTracerInterface* call_tracer,
                              grpc_slice_buffer* outbuf) {
   grpc_slice hdr;
   uint8_t* p;
@@ -77,7 +77,7 @@ void grpc_chttp2_encode_data(uint32_t id, grpc_slice_buffer* inbuf,
 
   grpc_slice_buffer_move_first_no_ref(inbuf, write_bytes, outbuf);
 
-  stats->framing_bytes += header_size;
+  call_tracer->RecordOutgoingBytes({header_size, 0, 0});
 }
 
 grpc_core::Poll<grpc_error_handle> grpc_deframe_unprocessed_incoming_frames(
@@ -126,8 +126,7 @@ grpc_core::Poll<grpc_error_handle> grpc_deframe_unprocessed_incoming_frames(
   if (min_progress_size != nullptr) *min_progress_size = 0;
 
   if (stream_out != nullptr) {
-    s->stats.incoming.framing_bytes += 5;
-    s->stats.incoming.data_bytes += length;
+    s->call_tracer_wrapper.RecordIncomingBytes({5, length, 0});
     grpc_slice_buffer_move_first_into_buffer(slices, 5, header);
     grpc_slice_buffer_move_first(slices, length, stream_out->c_slice_buffer());
   }

src/core/ext/transport/chttp2/transport/frame_data.h

@@ -33,6 +33,7 @@
 #include "src/core/lib/promise/poll.h"
 #include "src/core/lib/slice/slice_buffer.h"
 #include "src/core/lib/transport/transport.h"
+#include "src/core/telemetry/call_tracer.h"
 
 // start processing a new data frame
 absl::Status grpc_chttp2_data_parser_begin_frame(uint8_t flags,
@@ -49,7 +50,7 @@ grpc_error_handle grpc_chttp2_data_parser_parse(void* parser,
 
 void grpc_chttp2_encode_data(uint32_t id, grpc_slice_buffer* inbuf,
                              uint32_t write_bytes, int is_eof,
-                             grpc_transport_one_way_stats* stats,
+                             grpc_core::CallTracerInterface* call_tracer,
                              grpc_slice_buffer* outbuf);
 
 grpc_core::Poll<grpc_error_handle> grpc_deframe_unprocessed_incoming_frames(

src/core/ext/transport/chttp2/transport/frame_rst_stream.cc

@@ -39,11 +39,13 @@
 #include "src/core/lib/transport/http2_errors.h"
 #include "src/core/lib/transport/metadata_batch.h"
 
-grpc_slice grpc_chttp2_rst_stream_create(uint32_t id, uint32_t code,
-                                         grpc_transport_one_way_stats* stats) {
+grpc_slice grpc_chttp2_rst_stream_create(
+    uint32_t id, uint32_t code, grpc_core::CallTracerInterface* call_tracer) {
   static const size_t frame_size = 13;
   grpc_slice slice = GRPC_SLICE_MALLOC(frame_size);
-  if (stats != nullptr) stats->framing_bytes += frame_size;
+  if (call_tracer != nullptr) {
+    call_tracer->RecordOutgoingBytes({frame_size, 0, 0});
+  }
   uint8_t* p = GRPC_SLICE_START_PTR(slice);
 
   // Frame size.
@@ -70,10 +72,10 @@ grpc_slice grpc_chttp2_rst_stream_create(uint32_t id, uint32_t code,
 
 void grpc_chttp2_add_rst_stream_to_next_write(
     grpc_chttp2_transport* t, uint32_t id, uint32_t code,
-    grpc_transport_one_way_stats* stats) {
+    grpc_core::CallTracerInterface* call_tracer) {
   t->num_pending_induced_frames++;
   grpc_slice_buffer_add(&t->qbuf,
-                        grpc_chttp2_rst_stream_create(id, code, stats));
+                        grpc_chttp2_rst_stream_create(id, code, call_tracer));
 }
 
 grpc_error_handle grpc_chttp2_rst_stream_parser_begin_frame(
@@ -102,7 +104,8 @@ grpc_error_handle grpc_chttp2_rst_stream_parser_parse(void* parser,
     cur++;
     p->byte++;
   }
-  s->stats.incoming.framing_bytes += static_cast<uint64_t>(end - cur);
+  uint64_t framing_bytes = static_cast<uint64_t>(end - cur);
+  s->call_tracer_wrapper.RecordIncomingBytes({framing_bytes, 0, 0});
 
   if (p->byte == 4) {
     CHECK(is_last);

src/core/ext/transport/chttp2/transport/frame_rst_stream.h

@@ -27,20 +27,22 @@
 #include "src/core/ext/transport/chttp2/transport/legacy_frame.h"
 #include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/transport/transport.h"
+#include "src/core/telemetry/call_tracer.h"
 
 struct grpc_chttp2_rst_stream_parser {
   uint8_t byte;
   uint8_t reason_bytes[4];
 };
-grpc_slice grpc_chttp2_rst_stream_create(uint32_t stream_id, uint32_t code,
-                                         grpc_transport_one_way_stats* stats);
+grpc_slice grpc_chttp2_rst_stream_create(
+    uint32_t stream_id, uint32_t code,
+    grpc_core::CallTracerInterface* call_tracer);
 
 // Adds RST_STREAM frame to t->qbuf (buffer for the next write). Should be
 // called when we want to add RST_STREAM and we are not in
 // write_action_begin_locked.
 void grpc_chttp2_add_rst_stream_to_next_write(
     grpc_chttp2_transport* t, uint32_t id, uint32_t code,
-    grpc_transport_one_way_stats* stats);
+    grpc_core::CallTracerInterface* call_tracer);
 
 grpc_error_handle grpc_chttp2_rst_stream_parser_begin_frame(
     grpc_chttp2_rst_stream_parser* parser, uint32_t length, uint8_t flags);

src/core/ext/transport/chttp2/transport/frame_window_update.cc

@@ -32,10 +32,13 @@
 #include "src/core/ext/transport/chttp2/transport/internal.h"
 
 grpc_slice grpc_chttp2_window_update_create(
-    uint32_t id, uint32_t window_delta, grpc_transport_one_way_stats* stats) {
+    uint32_t id, uint32_t window_delta,
+    grpc_core::CallTracerInterface* call_tracer) {
   static const size_t frame_size = 13;
   grpc_slice slice = GRPC_SLICE_MALLOC(frame_size);
-  stats->framing_bytes += frame_size;
+  if (call_tracer != nullptr) {
+    call_tracer->RecordOutgoingBytes({frame_size, 0, 0});
+  }
   uint8_t* p = GRPC_SLICE_START_PTR(slice);
 
   CHECK(window_delta);
@@ -84,7 +87,8 @@ grpc_error_handle grpc_chttp2_window_update_parser_parse(
   }
 
   if (s != nullptr) {
-    s->stats.incoming.framing_bytes += static_cast<uint32_t>(end - cur);
+    uint64_t framing_bytes = static_cast<uint32_t>(end - cur);
+    s->call_tracer_wrapper.RecordIncomingBytes({framing_bytes, 0, 0});
   }
 
   if (p->byte == 4) {

src/core/ext/transport/chttp2/transport/frame_window_update.h

@@ -27,6 +27,7 @@
 #include "src/core/ext/transport/chttp2/transport/legacy_frame.h"
 #include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/transport/transport.h"
+#include "src/core/telemetry/call_tracer.h"
 
 struct grpc_chttp2_window_update_parser {
   uint8_t byte;
@@ -34,7 +35,8 @@ struct grpc_chttp2_window_update_parser {
   uint32_t amount;
 };
 grpc_slice grpc_chttp2_window_update_create(
-    uint32_t id, uint32_t window_delta, grpc_transport_one_way_stats* stats);
+    uint32_t id, uint32_t window_delta,
+    grpc_core::CallTracerInterface* call_tracer);
 
 grpc_error_handle grpc_chttp2_window_update_parser_begin_frame(
     grpc_chttp2_window_update_parser* parser, uint32_t length, uint8_t flags);

src/core/ext/transport/chttp2/transport/hpack_encoder.cc

@@ -87,7 +87,7 @@ void HPackCompressor::Frame(const EncodeHeaderOptions& options,
   if (options.is_end_of_stream) {
     flags |= GRPC_CHTTP2_DATA_FLAG_END_STREAM;
   }
-  options.stats->header_bytes += raw.Length();
+  options.call_tracer->RecordOutgoingBytes({0, 0, raw.Length()});
   while (frame_type == GRPC_CHTTP2_FRAME_HEADER || raw.Length() > 0) {
     // per the HTTP/2 spec:
     //   A HEADERS frame without the END_HEADERS flag set MUST be followed by
@@ -101,7 +101,7 @@ void HPackCompressor::Frame(const EncodeHeaderOptions& options,
     }
     FillHeader(grpc_slice_buffer_tiny_add(output, kHeadersFrameHeaderSize),
                frame_type, options.stream_id, len, flags);
-    options.stats->framing_bytes += kHeadersFrameHeaderSize;
+    options.call_tracer->RecordOutgoingBytes({kHeadersFrameHeaderSize, 0, 0});
     grpc_slice_buffer_move_first(raw.c_slice_buffer(), len, output);
 
     frame_type = GRPC_CHTTP2_FRAME_CONTINUATION;

src/core/ext/transport/chttp2/transport/hpack_encoder.h

@@ -42,6 +42,7 @@
 #include "src/core/lib/transport/metadata_compression_traits.h"
 #include "src/core/lib/transport/timeout_encoding.h"
 #include "src/core/lib/transport/transport.h"
+#include "src/core/telemetry/call_tracer.h"
 
 namespace grpc_core {
 
@@ -353,7 +354,7 @@ class HPackCompressor {
     bool is_end_of_stream;
     bool use_true_binary_metadata;
     size_t max_frame_size;
-    grpc_transport_one_way_stats* stats;
+    CallTracerInterface* call_tracer;
   };
 
   template <typename HeaderSet>

src/core/ext/transport/chttp2/transport/internal.h

@@ -554,6 +554,51 @@ typedef enum {
   GRPC_METADATA_PUBLISHED_AT_CLOSE
 } grpc_published_metadata_method;
 
+namespace grpc_core {
+
+// A CallTracer wrapper that updates both the legacy and new APIs for
+// transport byte sizes.
+// TODO(ctiller): This can go away as part of removing the
+// grpc_transport_stream_stats struct.
+class Chttp2CallTracerWrapper final : public CallTracerInterface {
+ public:
+  explicit Chttp2CallTracerWrapper(grpc_chttp2_stream* stream)
+      : stream_(stream) {}
+
+  void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) override;
+  void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) override;
+
+  // Everything else is a no-op.
+  void RecordSendInitialMetadata(
+      grpc_metadata_batch* /*send_initial_metadata*/) override {}
+  void RecordSendTrailingMetadata(
+      grpc_metadata_batch* /*send_trailing_metadata*/) override {}
+  void RecordSendMessage(const SliceBuffer& /*send_message*/) override {}
+  void RecordSendCompressedMessage(
+      const SliceBuffer& /*send_compressed_message*/) override {}
+  void RecordReceivedInitialMetadata(
+      grpc_metadata_batch* /*recv_initial_metadata*/) override {}
+  void RecordReceivedMessage(const SliceBuffer& /*recv_message*/) override {}
+  void RecordReceivedDecompressedMessage(
+      const SliceBuffer& /*recv_decompressed_message*/) override {}
+  void RecordCancel(grpc_error_handle /*cancel_error*/) override {}
+  std::shared_ptr<TcpTracerInterface> StartNewTcpTrace() override {
+    return nullptr;
+  }
+  void RecordAnnotation(absl::string_view /*annotation*/) override {}
+  void RecordAnnotation(const Annotation& /*annotation*/) override {}
+  std::string TraceId() override { return ""; }
+  std::string SpanId() override { return ""; }
+  bool IsSampled() override { return false; }
+
+ private:
+  grpc_chttp2_stream* stream_;
+};
+
+}  // namespace grpc_core
+
 struct grpc_chttp2_stream {
   grpc_chttp2_stream(grpc_chttp2_transport* t, grpc_stream_refcount* refcount,
                      const void* server_data, grpc_core::Arena* arena);
@@ -653,7 +698,11 @@ struct grpc_chttp2_stream {
   /// Number of times written
   int64_t write_counter = 0;
 
+  grpc_core::Chttp2CallTracerWrapper call_tracer_wrapper;
+
   /// Only set when enabled.
+  // TODO(roth): Remove this when the call_tracer_in_transport
+  // experiment finishes rolling out.
   grpc_core::CallTracerAnnotationInterface* call_tracer = nullptr;
 
   /// Only set when enabled.

src/core/ext/transport/chttp2/transport/parsing.cc

@@ -555,7 +555,7 @@ static grpc_error_handle init_data_frame_parser(grpc_chttp2_transport* t) {
     return init_non_header_skip_frame_parser(t);
   }
   s->received_bytes += t->incoming_frame_size;
-  s->stats.incoming.framing_bytes += 9;
+  s->call_tracer_wrapper.RecordIncomingBytes({9, 0, 0});
   if (s->read_closed) {
     return init_non_header_skip_frame_parser(t);
   }
@@ -574,7 +574,7 @@ error_handler:
                                    absl_status_to_grpc_error(status));
     grpc_chttp2_add_rst_stream_to_next_write(t, t->incoming_stream_id,
                                              GRPC_HTTP2_PROTOCOL_ERROR,
-                                             &s->stats.outgoing);
+                                             &s->call_tracer_wrapper);
     return init_non_header_skip_frame_parser(t);
   } else {
     return absl_status_to_grpc_error(status);
@@ -725,7 +725,7 @@ static grpc_error_handle init_header_frame_parser(grpc_chttp2_transport* t,
     t->incoming_stream = s;
   }
   DCHECK_NE(s, nullptr);
-  s->stats.incoming.framing_bytes += 9;
+  s->call_tracer_wrapper.RecordIncomingBytes({9, 0, 0});
   if (GPR_UNLIKELY(s->read_closed)) {
     GRPC_CHTTP2_IF_TRACING(ERROR)
         << "skipping already closed grpc_chttp2_stream header";
@@ -796,7 +796,7 @@ static grpc_error_handle init_window_update_frame_parser(
       }
       return init_non_header_skip_frame_parser(t);
     }
-    s->stats.incoming.framing_bytes += 9;
+    s->call_tracer_wrapper.RecordIncomingBytes({9, 0, 0});
   }
   t->parser = grpc_chttp2_transport::Parser{
       "window_update", grpc_chttp2_window_update_parser_parse,
@@ -822,7 +822,7 @@ static grpc_error_handle init_rst_stream_parser(grpc_chttp2_transport* t) {
   if (!t->incoming_stream) {
     return init_non_header_skip_frame_parser(t);
   }
-  s->stats.incoming.framing_bytes += 9;
+  s->call_tracer_wrapper.RecordIncomingBytes({9, 0, 0});
   t->parser = grpc_chttp2_transport::Parser{
       "rst_stream", grpc_chttp2_rst_stream_parser_parse, &t->simple.rst_stream};
   if (!t->is_client && grpc_core::IsRstpitEnabled()) {
@@ -918,7 +918,7 @@ static void force_client_rst_stream(void* sp, grpc_error_handle /*error*/) {
   grpc_chttp2_transport* t = s->t.get();
   if (!s->write_closed) {
     grpc_chttp2_add_rst_stream_to_next_write(t, s->id, GRPC_HTTP2_NO_ERROR,
-                                             &s->stats.outgoing);
+                                             &s->call_tracer_wrapper);
     grpc_chttp2_initiate_write(t, GRPC_CHTTP2_INITIATE_WRITE_FORCE_RST_STREAM);
     grpc_chttp2_mark_stream_closed(t, s, true, true, absl::OkStatus());
   }
@@ -933,9 +933,12 @@ grpc_error_handle grpc_chttp2_header_parser_parse(void* hpack_parser,
   auto* parser = static_cast<grpc_core::HPackParser*>(hpack_parser);
   grpc_core::CallTracerAnnotationInterface* call_tracer = nullptr;
   if (s != nullptr) {
-    s->stats.incoming.header_bytes += GRPC_SLICE_LENGTH(slice);
+    s->call_tracer_wrapper.RecordIncomingBytes(
+        {0, 0, GRPC_SLICE_LENGTH(slice)});
     call_tracer =
-        s->arena->GetContext<grpc_core::CallTracerAnnotationInterface>();
+        grpc_core::IsCallTracerInTransportEnabled()
+            ? s->arena->GetContext<grpc_core::CallTracerInterface>()
+            : s->arena->GetContext<grpc_core::CallTracerAnnotationInterface>();
   }
   grpc_error_handle error = parser->Parse(
       slice, is_last != 0, absl::BitGenRef(t->bitgen), call_tracer);

src/core/ext/transport/chttp2/transport/writing.cc

@@ -296,10 +296,9 @@ class WriteContext {
     uint32_t transport_announce = t_->flow_control.MaybeSendUpdate(
         t_->outbuf.c_slice_buffer()->count > 0);
     if (transport_announce) {
-      grpc_transport_one_way_stats throwaway_stats;
-      grpc_slice_buffer_add(t_->outbuf.c_slice_buffer(),
-                            grpc_chttp2_window_update_create(
-                                0, transport_announce, &throwaway_stats));
+      grpc_slice_buffer_add(
+          t_->outbuf.c_slice_buffer(),
+          grpc_chttp2_window_update_create(0, transport_announce, nullptr));
       grpc_chttp2_reset_ping_clock(t_);
     }
   }
@@ -411,7 +410,7 @@ class DataSendContext {
                      s_->send_trailing_metadata != nullptr &&
                      s_->send_trailing_metadata->empty();
     grpc_chttp2_encode_data(s_->id, &s_->flow_controlled_buffer, send_bytes,
-                            is_last_frame_, &s_->stats.outgoing,
+                            is_last_frame_, &s_->call_tracer_wrapper,
                             t_->outbuf.c_slice_buffer());
     sfc_upd_.SentData(send_bytes);
     s_->sending_bytes += send_bytes;
@@ -470,8 +469,7 @@ class StreamWriteContext {
               t_->settings.peer()
                   .allow_true_binary_metadata(),     // use_true_binary_metadata
               t_->settings.peer().max_frame_size(),  // max_frame_size
-              &s_->stats.outgoing                    // stats
-          },
+              &s_->call_tracer_wrapper},
           *s_->send_initial_metadata, t_->outbuf.c_slice_buffer());
       grpc_chttp2_reset_ping_clock(t_);
       write_context_->IncInitialMetadataWrites();
@@ -483,6 +481,7 @@ class StreamWriteContext {
     grpc_chttp2_complete_closure_step(t_, &s_->send_initial_metadata_finished,
                                       absl::OkStatus(),
                                       "send_initial_metadata_finished");
+    if (!grpc_core::IsCallTracerInTransportEnabled()) {
       if (s_->call_tracer) {
         grpc_core::HttpAnnotation::WriteStats write_stats;
         write_stats.target_write_size = write_context_->target_write_size();
@@ -494,6 +493,21 @@ class StreamWriteContext {
                 .Add(s_->flow_control.stats())
                 .Add(write_stats));
       }
+    } else if (grpc_core::IsTraceRecordCallopsEnabled()) {
+      auto* call_tracer =
+          s_->arena->GetContext<grpc_core::CallTracerInterface>();
+      if (call_tracer != nullptr && call_tracer->IsSampled()) {
+        grpc_core::HttpAnnotation::WriteStats write_stats;
+        write_stats.target_write_size = write_context_->target_write_size();
+        call_tracer->RecordAnnotation(
+            grpc_core::HttpAnnotation(
+                grpc_core::HttpAnnotation::Type::kHeadWritten,
+                gpr_now(GPR_CLOCK_REALTIME))
+                .Add(s_->t->flow_control.stats())
+                .Add(s_->flow_control.stats())
+                .Add(write_stats));
+      }
+    }
   }
 
   void FlushWindowUpdates() {
@@ -503,9 +517,10 @@ class StreamWriteContext {
     const uint32_t stream_announce = s_->flow_control.MaybeSendUpdate();
     if (stream_announce == 0) return;
 
-    grpc_slice_buffer_add(t_->outbuf.c_slice_buffer(),
-                          grpc_chttp2_window_update_create(
-                              s_->id, stream_announce, &s_->stats.outgoing));
+    grpc_slice_buffer_add(
+        t_->outbuf.c_slice_buffer(),
+        grpc_chttp2_window_update_create(s_->id, stream_announce,
+                                         &s_->call_tracer_wrapper));
     grpc_chttp2_reset_ping_clock(t_);
     write_context_->IncWindowUpdateWrites();
   }
@@ -558,12 +573,13 @@ class StreamWriteContext {
     GRPC_CHTTP2_IF_TRACING(INFO) << "sending trailing_metadata";
     if (s_->send_trailing_metadata->empty()) {
       grpc_chttp2_encode_data(s_->id, &s_->flow_controlled_buffer, 0, true,
-                              &s_->stats.outgoing, t_->outbuf.c_slice_buffer());
+                              &s_->call_tracer_wrapper,
+                              t_->outbuf.c_slice_buffer());
     } else {
       t_->hpack_compressor.EncodeHeaders(
           grpc_core::HPackCompressor::EncodeHeaderOptions{
               s_->id, true, t_->settings.peer().allow_true_binary_metadata(),
-              t_->settings.peer().max_frame_size(), &s_->stats.outgoing},
+              t_->settings.peer().max_frame_size(), &s_->call_tracer_wrapper},
           *s_->send_trailing_metadata, t_->outbuf.c_slice_buffer());
     }
     write_context_->IncTrailingMetadataWrites();
@@ -627,10 +643,11 @@ class StreamWriteContext {
       grpc_slice_buffer_add(
           t_->outbuf.c_slice_buffer(),
           grpc_chttp2_rst_stream_create(s_->id, GRPC_HTTP2_NO_ERROR,
-                                        &s_->stats.outgoing));
+                                        &s_->call_tracer_wrapper));
     }
     grpc_chttp2_mark_stream_closed(t_, s_, !t_->is_client, true,
                                    absl::OkStatus());
+    if (!grpc_core::IsCallTracerInTransportEnabled()) {
       if (s_->call_tracer) {
         s_->call_tracer->RecordAnnotation(
             grpc_core::HttpAnnotation(grpc_core::HttpAnnotation::Type::kEnd,
@@ -638,6 +655,17 @@ class StreamWriteContext {
                 .Add(s_->t->flow_control.stats())
                 .Add(s_->flow_control.stats()));
       }
+    } else if (grpc_core::IsTraceRecordCallopsEnabled()) {
+      auto* call_tracer =
+          s_->arena->GetContext<grpc_core::CallTracerInterface>();
+      if (call_tracer != nullptr && call_tracer->IsSampled()) {
+        call_tracer->RecordAnnotation(
+            grpc_core::HttpAnnotation(grpc_core::HttpAnnotation::Type::kEnd,
+                                      gpr_now(GPR_CLOCK_REALTIME))
+                .Add(s_->t->flow_control.stats())
+                .Add(s_->flow_control.stats()));
+      }
+    }
   }
 
   WriteContext* const write_context_;

src/core/lib/experiments/experiments.cc

@@ -114,7 +114,7 @@ const ExperimentMetadata g_experiment_metadata[] = {
      additional_constraints_call_status_override_on_cancellation, nullptr, 0,
      true, true},
     {"call_tracer_in_transport", description_call_tracer_in_transport,
-     additional_constraints_call_tracer_in_transport, nullptr, 0, false, true},
+     additional_constraints_call_tracer_in_transport, nullptr, 0, true, true},
     {"canary_client_privacy", description_canary_client_privacy,
      additional_constraints_canary_client_privacy, nullptr, 0, false, false},
     {"client_privacy", description_client_privacy,
@@ -264,7 +264,7 @@ const ExperimentMetadata g_experiment_metadata[] = {
      additional_constraints_call_status_override_on_cancellation, nullptr, 0,
      true, true},
     {"call_tracer_in_transport", description_call_tracer_in_transport,
-     additional_constraints_call_tracer_in_transport, nullptr, 0, false, true},
+     additional_constraints_call_tracer_in_transport, nullptr, 0, true, true},
     {"canary_client_privacy", description_canary_client_privacy,
      additional_constraints_canary_client_privacy, nullptr, 0, false, false},
     {"client_privacy", description_client_privacy,
@@ -414,7 +414,7 @@ const ExperimentMetadata g_experiment_metadata[] = {
      additional_constraints_call_status_override_on_cancellation, nullptr, 0,
      true, true},
     {"call_tracer_in_transport", description_call_tracer_in_transport,
-     additional_constraints_call_tracer_in_transport, nullptr, 0, false, true},
+     additional_constraints_call_tracer_in_transport, nullptr, 0, true, true},
     {"canary_client_privacy", description_canary_client_privacy,
      additional_constraints_canary_client_privacy, nullptr, 0, false, false},
     {"client_privacy", description_client_privacy,

src/core/lib/experiments/experiments.h

@@ -59,7 +59,8 @@ namespace grpc_core {
 #if defined(GRPC_CFSTREAM)
 #define GRPC_EXPERIMENT_IS_INCLUDED_CALL_STATUS_OVERRIDE_ON_CANCELLATION
 inline bool IsCallStatusOverrideOnCancellationEnabled() { return true; }
-inline bool IsCallTracerInTransportEnabled() { return false; }
+#define GRPC_EXPERIMENT_IS_INCLUDED_CALL_TRACER_IN_TRANSPORT
+inline bool IsCallTracerInTransportEnabled() { return true; }
 inline bool IsCanaryClientPrivacyEnabled() { return false; }
 inline bool IsClientPrivacyEnabled() { return false; }
 inline bool IsEventEngineClientEnabled() { return false; }
@@ -89,7 +90,8 @@ inline bool IsWorkSerializerDispatchEnabled() { return false; }
 #elif defined(GPR_WINDOWS)
 #define GRPC_EXPERIMENT_IS_INCLUDED_CALL_STATUS_OVERRIDE_ON_CANCELLATION
 inline bool IsCallStatusOverrideOnCancellationEnabled() { return true; }
-inline bool IsCallTracerInTransportEnabled() { return false; }
+#define GRPC_EXPERIMENT_IS_INCLUDED_CALL_TRACER_IN_TRANSPORT
+inline bool IsCallTracerInTransportEnabled() { return true; }
 inline bool IsCanaryClientPrivacyEnabled() { return false; }
 inline bool IsClientPrivacyEnabled() { return false; }
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_CLIENT
@@ -122,7 +124,8 @@ inline bool IsWorkSerializerDispatchEnabled() { return false; }
 #else
 #define GRPC_EXPERIMENT_IS_INCLUDED_CALL_STATUS_OVERRIDE_ON_CANCELLATION
 inline bool IsCallStatusOverrideOnCancellationEnabled() { return true; }
-inline bool IsCallTracerInTransportEnabled() { return false; }
+#define GRPC_EXPERIMENT_IS_INCLUDED_CALL_TRACER_IN_TRANSPORT
+inline bool IsCallTracerInTransportEnabled() { return true; }
 inline bool IsCanaryClientPrivacyEnabled() { return false; }
 inline bool IsClientPrivacyEnabled() { return false; }
 inline bool IsEventEngineClientEnabled() { return false; }

src/core/lib/experiments/rollouts.yaml

@@ -42,6 +42,8 @@
 
 - name: call_status_override_on_cancellation
   default: true
+- name: call_tracer_in_transport
+  default: true
 - name: call_v3
   default: false
 - name: canary_client_privacy

src/core/telemetry/call_tracer.cc

@@ -32,6 +32,15 @@
 
 namespace grpc_core {
 
+CallTracerInterface::TransportByteSize&
+CallTracerInterface::TransportByteSize::operator+=(
+    const CallTracerInterface::TransportByteSize& other) {
+  framing_bytes += other.framing_bytes;
+  data_bytes += other.data_bytes;
+  header_bytes += other.header_bytes;
+  return *this;
+}
+
 //
 // ServerCallTracerFactory
 //
@@ -42,6 +51,7 @@ ServerCallTracerFactory* g_server_call_tracer_factory_ = nullptr;
 
 const char* kServerCallTracerFactoryChannelArgName =
     "grpc.experimental.server_call_tracer_factory";
+
 }  // namespace
 
 ServerCallTracerFactory* ServerCallTracerFactory::Get(
@@ -139,6 +149,18 @@ class DelegatingClientCallTracer : public ClientCallTracer {
         tracer->RecordEnd(latency);
       }
     }
+    void RecordIncomingBytes(
+        const TransportByteSize& transport_byte_size) override {
+      for (auto* tracer : tracers_) {
+        tracer->RecordIncomingBytes(transport_byte_size);
+      }
+    }
+    void RecordOutgoingBytes(
+        const TransportByteSize& transport_byte_size) override {
+      for (auto* tracer : tracers_) {
+        tracer->RecordOutgoingBytes(transport_byte_size);
+      }
+    }
     void RecordAnnotation(absl::string_view annotation) override {
       for (auto* tracer : tracers_) {
         tracer->RecordAnnotation(annotation);
@@ -271,6 +293,18 @@ class DelegatingServerCallTracer : public ServerCallTracer {
       tracer->RecordEnd(final_info);
     }
   }
+  void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) override {
+    for (auto* tracer : tracers_) {
+      tracer->RecordIncomingBytes(transport_byte_size);
+    }
+  }
+  void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) override {
+    for (auto* tracer : tracers_) {
+      tracer->RecordOutgoingBytes(transport_byte_size);
+    }
+  }
   void RecordAnnotation(absl::string_view annotation) override {
     for (auto* tracer : tracers_) {
       tracer->RecordAnnotation(annotation);

src/core/telemetry/call_tracer.h

@@ -110,6 +110,19 @@ class CallTracerInterface : public CallTracerAnnotationInterface {
   virtual void RecordReceivedDecompressedMessage(
       const SliceBuffer& recv_decompressed_message) = 0;
   virtual void RecordCancel(grpc_error_handle cancel_error) = 0;
+
+  struct TransportByteSize {
+    uint64_t framing_bytes = 0;
+    uint64_t data_bytes = 0;
+    uint64_t header_bytes = 0;
+
+    TransportByteSize& operator+=(const TransportByteSize& other);
+  };
+  virtual void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) = 0;
+  virtual void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) = 0;
+
   // Traces a new TCP transport attempt for this call attempt. Note the TCP
   // transport may finish tracing and unref the TCP tracer before or after the
   // call completion in gRPC core. No TCP tracing when null is returned.
@@ -144,6 +157,8 @@ class ClientCallTracer : public CallTracerAnnotationInterface {
     // will be null.
     virtual void RecordReceivedTrailingMetadata(
         absl::Status status, grpc_metadata_batch* recv_trailing_metadata,
+        // TODO(roth): Remove this argument when the
+        // call_tracer_in_transport experiment finishes rolling out.
         const grpc_transport_stream_stats* transport_stream_stats) = 0;
     // Should be the last API call to the object. Once invoked, the tracer
     // library is free to destroy the object.

src/cpp/ext/filters/census/client_filter.cc

@@ -53,6 +53,7 @@
 
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/channel/channel_stack.h"
+#include "src/core/lib/experiments/experiments.h"
 #include "src/core/lib/gprpp/sync.h"
 #include "src/core/lib/promise/context.h"
 #include "src/core/lib/resource_quota/arena.h"
@@ -214,17 +215,18 @@ void OpenCensusCallTracer::OpenCensusCallAttemptTracer::
     tags.emplace_back(ClientMethodTagKey(), std::string(parent_->method_));
     tags.emplace_back(ClientStatusTagKey(),
                       absl::StatusCodeToString(status_code_));
+    uint64_t outgoing_bytes = 0;
+    uint64_t incoming_bytes = 0;
+    if (grpc_core::IsCallTracerInTransportEnabled()) {
+      outgoing_bytes = outgoing_bytes_.load();
+      incoming_bytes = incoming_bytes_.load();
+    } else if (transport_stream_stats != nullptr) {
+      outgoing_bytes = transport_stream_stats->outgoing.data_bytes;
+      incoming_bytes = transport_stream_stats->incoming.data_bytes;
+    }
     ::opencensus::stats::Record(
-        // TODO(yashykt): Recording zeros here when transport_stream_stats is
-        // nullptr is unfortunate and should be fixed.
-        {{RpcClientSentBytesPerRpc(),
-          static_cast<double>(transport_stream_stats != nullptr
-                                  ? transport_stream_stats->outgoing.data_bytes
-                                  : 0)},
-         {RpcClientReceivedBytesPerRpc(),
-          static_cast<double>(transport_stream_stats != nullptr
-                                  ? transport_stream_stats->incoming.data_bytes
-                                  : 0)},
+        {{RpcClientSentBytesPerRpc(), static_cast<double>(outgoing_bytes)},
+         {RpcClientReceivedBytesPerRpc(), static_cast<double>(incoming_bytes)},
          {RpcClientServerLatency(),
           ToDoubleMilliseconds(absl::Nanoseconds(elapsed_time))},
          {RpcClientRoundtripLatency(),
@@ -233,6 +235,16 @@ void OpenCensusCallTracer::OpenCensusCallAttemptTracer::
   }
 }
 
+void OpenCensusCallTracer::OpenCensusCallAttemptTracer::RecordIncomingBytes(
+    const TransportByteSize& transport_byte_size) {
+  incoming_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
+void OpenCensusCallTracer::OpenCensusCallAttemptTracer::RecordOutgoingBytes(
+    const TransportByteSize& transport_byte_size) {
+  outgoing_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
 void OpenCensusCallTracer::OpenCensusCallAttemptTracer::RecordCancel(
     absl::Status /*cancel_error*/) {}
 

src/cpp/ext/filters/census/open_census_call_tracer.h

@@ -21,6 +21,7 @@
 
 #include <stdint.h>
 
+#include <atomic>
 #include <memory>
 #include <string>
 
@@ -96,6 +97,10 @@ class OpenCensusCallTracer : public grpc_core::ClientCallTracer {
     void RecordReceivedTrailingMetadata(
         absl::Status status, grpc_metadata_batch* recv_trailing_metadata,
         const grpc_transport_stream_stats* transport_stream_stats) override;
+    void RecordIncomingBytes(
+        const TransportByteSize& transport_byte_size) override;
+    void RecordOutgoingBytes(
+        const TransportByteSize& transport_byte_size) override;
     void RecordCancel(grpc_error_handle cancel_error) override;
     void RecordEnd(const gpr_timespec& /*latency*/) override;
     void RecordAnnotation(absl::string_view annotation) override;
@@ -121,6 +126,12 @@ class OpenCensusCallTracer : public grpc_core::ClientCallTracer {
     uint64_t sent_message_count_ = 0;
     // End status code
     absl::StatusCode status_code_;
+    // TODO(roth, ctiller): Won't need atomic here once chttp2 is migrated
+    // to promises, after which we can ensure that the transport invokes
+    // the RecordIncomingBytes() and RecordOutgoingBytes() methods inside
+    // the call's party.
+    std::atomic<uint64_t> incoming_bytes_{0};
+    std::atomic<uint64_t> outgoing_bytes_{0};
   };
 
   explicit OpenCensusCallTracer(grpc_core::Slice path, grpc_core::Arena* arena,

src/cpp/ext/filters/census/server_call_tracer.cc

@@ -21,6 +21,7 @@
 #include <stdint.h>
 #include <string.h>
 
+#include <atomic>
 #include <memory>
 #include <string>
 #include <utility>
@@ -154,6 +155,11 @@ class OpenCensusServerCallTracer : public grpc_core::ServerCallTracer {
 
   void RecordEnd(const grpc_call_final_info* final_info) override;
 
+  void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) override;
+  void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) override;
+
   void RecordAnnotation(absl::string_view annotation) override {
     if (!context_.Span().IsRecording()) {
       return;
@@ -193,6 +199,12 @@ class OpenCensusServerCallTracer : public grpc_core::ServerCallTracer {
   // Buffer needed for grpc_slice to reference it when adding metatdata to
   // response.
   char stats_buf_[kMaxServerStatsLen];
+  // TODO(roth, ctiller): Won't need atomic here once chttp2 is migrated
+  // to promises, after which we can ensure that the transport invokes
+  // the RecordIncomingBytes() and RecordOutgoingBytes() methods inside
+  // the call's party.
+  std::atomic<uint64_t> incoming_bytes_{0};
+  std::atomic<uint64_t> outgoing_bytes_{0};
 };
 
 void OpenCensusServerCallTracer::RecordReceivedInitialMetadata(
@@ -236,8 +248,18 @@ void OpenCensusServerCallTracer::RecordSendTrailingMetadata(
 void OpenCensusServerCallTracer::RecordEnd(
     const grpc_call_final_info* final_info) {
   if (OpenCensusStatsEnabled()) {
-    const uint64_t request_size = GetOutgoingDataSize(final_info);
-    const uint64_t response_size = GetIncomingDataSize(final_info);
+    uint64_t outgoing_bytes;
+    uint64_t incoming_bytes;
+    if (grpc_core::IsCallTracerInTransportEnabled()) {
+      outgoing_bytes = outgoing_bytes_.load();
+      incoming_bytes = incoming_bytes_.load();
+    } else {
+      // Note: We are incorrectly swapping the two values here, which is
+      // a pre-existing bug.  This code will go away as part of the
+      // experiment rollout.
+      outgoing_bytes = GetIncomingDataSize(final_info);
+      incoming_bytes = GetOutgoingDataSize(final_info);
+    }
     double elapsed_time_ms = absl::ToDoubleMilliseconds(elapsed_time_);
     std::vector<std::pair<opencensus::tags::TagKey, std::string>> tags =
         context_.tags().tags();
@@ -246,8 +268,8 @@ void OpenCensusServerCallTracer::RecordEnd(
         ServerStatusTagKey(),
         std::string(StatusCodeToString(final_info->final_status)));
     ::opencensus::stats::Record(
-        {{RpcServerSentBytesPerRpc(), static_cast<double>(response_size)},
-         {RpcServerReceivedBytesPerRpc(), static_cast<double>(request_size)},
+        {{RpcServerSentBytesPerRpc(), static_cast<double>(outgoing_bytes)},
+         {RpcServerReceivedBytesPerRpc(), static_cast<double>(incoming_bytes)},
          {RpcServerServerLatency(), elapsed_time_ms},
          {RpcServerSentMessagesPerRpc(), sent_message_count_},
          {RpcServerReceivedMessagesPerRpc(), recv_message_count_}},
@@ -258,6 +280,16 @@ void OpenCensusServerCallTracer::RecordEnd(
   }
 }
 
+void OpenCensusServerCallTracer::RecordIncomingBytes(
+    const TransportByteSize& transport_byte_size) {
+  incoming_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
+void OpenCensusServerCallTracer::RecordOutgoingBytes(
+    const TransportByteSize& transport_byte_size) {
+  outgoing_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
 //
 // OpenCensusServerCallTracerFactory
 //

src/cpp/ext/otel/BUILD

@@ -76,6 +76,7 @@ grpc_cc_library(
         "//src/core:channel_stack_type",
         "//src/core:context",
         "//src/core:error",
+        "//src/core:experiments",
         "//src/core:match",
         "//src/core:metadata_batch",
         "//src/core:metrics",

src/cpp/ext/otel/otel_client_call_tracer.cc

@@ -47,6 +47,7 @@
 #include "src/core/client_channel/client_channel_filter.h"
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/channel/status_util.h"
+#include "src/core/lib/experiments/experiments.h"
 #include "src/core/lib/gprpp/sync.h"
 #include "src/core/lib/promise/context.h"
 #include "src/core/lib/resource_quota/arena.h"
@@ -162,24 +163,37 @@ void OpenTelemetryPluginImpl::ClientCallTracer::CallAttemptTracer::
         absl::ToDoubleSeconds(absl::Now() - start_time_), labels,
         opentelemetry::context::Context{});
   }
+  uint64_t outgoing_bytes = 0;
+  uint64_t incoming_bytes = 0;
+  if (grpc_core::IsCallTracerInTransportEnabled()) {
+    outgoing_bytes = outgoing_bytes_.load();
+    incoming_bytes = incoming_bytes_.load();
+  } else if (transport_stream_stats != nullptr) {
+    outgoing_bytes = transport_stream_stats->outgoing.data_bytes;
+    incoming_bytes = transport_stream_stats->incoming.data_bytes;
+  }
   if (parent_->otel_plugin_->client_.attempt
           .sent_total_compressed_message_size != nullptr) {
     parent_->otel_plugin_->client_.attempt.sent_total_compressed_message_size
-        ->Record(transport_stream_stats != nullptr
-                     ? transport_stream_stats->outgoing.data_bytes
-                     : 0,
-                 labels, opentelemetry::context::Context{});
+        ->Record(outgoing_bytes, labels, opentelemetry::context::Context{});
   }
   if (parent_->otel_plugin_->client_.attempt
           .rcvd_total_compressed_message_size != nullptr) {
     parent_->otel_plugin_->client_.attempt.rcvd_total_compressed_message_size
-        ->Record(transport_stream_stats != nullptr
-                     ? transport_stream_stats->incoming.data_bytes
-                     : 0,
-                 labels, opentelemetry::context::Context{});
+        ->Record(incoming_bytes, labels, opentelemetry::context::Context{});
   }
 }
 
+void OpenTelemetryPluginImpl::ClientCallTracer::CallAttemptTracer::
+    RecordIncomingBytes(const TransportByteSize& transport_byte_size) {
+  incoming_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
+void OpenTelemetryPluginImpl::ClientCallTracer::CallAttemptTracer::
+    RecordOutgoingBytes(const TransportByteSize& transport_byte_size) {
+  outgoing_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
 void OpenTelemetryPluginImpl::ClientCallTracer::CallAttemptTracer::RecordCancel(
     absl::Status /*cancel_error*/) {}
 

src/cpp/ext/otel/otel_client_call_tracer.h

@@ -84,8 +84,12 @@ class OpenTelemetryPluginImpl::ClientCallTracer
     void RecordReceivedDecompressedMessage(
         const grpc_core::SliceBuffer& recv_decompressed_message) override;
     void RecordReceivedTrailingMetadata(
-        absl::Status status, grpc_metadata_batch* /*recv_trailing_metadata*/,
+        absl::Status status, grpc_metadata_batch* recv_trailing_metadata,
         const grpc_transport_stream_stats* transport_stream_stats) override;
+    void RecordIncomingBytes(
+        const TransportByteSize& transport_byte_size) override;
+    void RecordOutgoingBytes(
+        const TransportByteSize& transport_byte_size) override;
     void RecordCancel(grpc_error_handle cancel_error) override;
     void RecordEnd(const gpr_timespec& /*latency*/) override;
     void RecordAnnotation(absl::string_view /*annotation*/) override;
@@ -109,6 +113,12 @@ class OpenTelemetryPluginImpl::ClientCallTracer
     std::vector<std::unique_ptr<LabelsIterable>>
         injected_labels_from_plugin_options_;
     bool is_trailers_only_ = false;
+    // TODO(roth, ctiller): Won't need atomic here once chttp2 is migrated
+    // to promises, after which we can ensure that the transport invokes
+    // the RecordIncomingBytes() and RecordOutgoingBytes() methods inside
+    // the call's party.
+    std::atomic<uint64_t> incoming_bytes_{0};
+    std::atomic<uint64_t> outgoing_bytes_{0};
   };
 
   ClientCallTracer(

src/cpp/ext/otel/otel_server_call_tracer.cc

@@ -37,6 +37,7 @@
 
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/channel/status_util.h"
+#include "src/core/lib/experiments/experiments.h"
 #include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/slice/slice.h"
 #include "src/core/lib/slice/slice_buffer.h"
@@ -123,16 +124,30 @@ void OpenTelemetryPluginImpl::ServerCallTracer::RecordEnd(
   if (otel_plugin_->server_.call.sent_total_compressed_message_size !=
       nullptr) {
     otel_plugin_->server_.call.sent_total_compressed_message_size->Record(
-        final_info->stats.transport_stream_stats.outgoing.data_bytes, labels,
-        opentelemetry::context::Context{});
+        grpc_core::IsCallTracerInTransportEnabled()
+            ? outgoing_bytes_.load()
+            : final_info->stats.transport_stream_stats.outgoing.data_bytes,
+        labels, opentelemetry::context::Context{});
   }
   if (otel_plugin_->server_.call.rcvd_total_compressed_message_size !=
       nullptr) {
     otel_plugin_->server_.call.rcvd_total_compressed_message_size->Record(
-        final_info->stats.transport_stream_stats.incoming.data_bytes, labels,
-        opentelemetry::context::Context{});
+        grpc_core::IsCallTracerInTransportEnabled()
+            ? incoming_bytes_.load()
+            : final_info->stats.transport_stream_stats.incoming.data_bytes,
+        labels, opentelemetry::context::Context{});
   }
 }
 
+void OpenTelemetryPluginImpl::ServerCallTracer::RecordIncomingBytes(
+    const TransportByteSize& transport_byte_size) {
+  incoming_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
+void OpenTelemetryPluginImpl::ServerCallTracer::RecordOutgoingBytes(
+    const TransportByteSize& transport_byte_size) {
+  outgoing_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
 }  // namespace internal
 }  // namespace grpc

src/cpp/ext/otel/otel_server_call_tracer.h

@@ -100,6 +100,11 @@ class OpenTelemetryPluginImpl::ServerCallTracer
 
   void RecordEnd(const grpc_call_final_info* final_info) override;
 
+  void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) override;
+  void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) override;
+
   void RecordAnnotation(absl::string_view /*annotation*/) override {
     // Not implemented
   }
@@ -131,6 +136,12 @@ class OpenTelemetryPluginImpl::ServerCallTracer
       injected_labels_from_plugin_options_;
   OpenTelemetryPluginImpl* otel_plugin_;
   std::shared_ptr<OpenTelemetryPluginImpl::ServerScopeConfig> scope_config_;
+  // TODO(roth, ctiller): Won't need atomic here once chttp2 is migrated
+  // to promises, after which we can ensure that the transport invokes
+  // the RecordIncomingBytes() and RecordOutgoingBytes() methods inside
+  // the call's party.
+  std::atomic<uint64_t> incoming_bytes_{0};
+  std::atomic<uint64_t> outgoing_bytes_{0};
 };
 
 }  // namespace internal

src/python/grpcio_observability/grpc_observability/client_call_tracer.cc

@@ -28,6 +28,7 @@
 
 #include <grpc/slice.h>
 
+#include "src/core/lib/experiments/experiments.h"
 #include "src/core/lib/slice/slice.h"
 
 namespace grpc_observability {
@@ -273,19 +274,22 @@ void PythonOpenCensusCallTracer::PythonOpenCensusCallAttemptTracer::
   for (const auto& label : labels_from_peer_) {
     context_.Labels().emplace_back(label);
   }
-  RecordDoubleMetric(
-      kRpcClientSentBytesPerRpcMeasureName,
-      static_cast<double>(transport_stream_stats != nullptr
-                              ? transport_stream_stats->outgoing.data_bytes
-                              : 0),
-      context_.Labels(), parent_->identifier_, parent_->registered_method_,
+  uint64_t incoming_bytes = 0;
+  uint64_t outgoing_bytes = 0;
+  if (grpc_core::IsCallTracerInTransportEnabled()) {
+    incoming_bytes = incoming_bytes_.load();
+    outgoing_bytes = outgoing_bytes_.load();
+  } else if (transport_stream_stats != nullptr) {
+    incoming_bytes = transport_stream_stats->incoming.data_bytes;
+    outgoing_bytes = transport_stream_stats->outgoing.data_bytes;
+  }
+  RecordDoubleMetric(kRpcClientSentBytesPerRpcMeasureName,
+                     static_cast<double>(outgoing_bytes), context_.Labels(),
+                     parent_->identifier_, parent_->registered_method_,
                      /*include_exchange_labels=*/true);
-  RecordDoubleMetric(
-      kRpcClientReceivedBytesPerRpcMeasureName,
-      static_cast<double>(transport_stream_stats != nullptr
-                              ? transport_stream_stats->incoming.data_bytes
-                              : 0),
-      context_.Labels(), parent_->identifier_, parent_->registered_method_,
+  RecordDoubleMetric(kRpcClientReceivedBytesPerRpcMeasureName,
+                     static_cast<double>(incoming_bytes), context_.Labels(),
+                     parent_->identifier_, parent_->registered_method_,
                      /*include_exchange_labels=*/true);
   RecordDoubleMetric(kRpcClientServerLatencyMeasureName,
                      absl::ToDoubleSeconds(absl::Nanoseconds(elapsed_time)),
@@ -302,6 +306,16 @@ void PythonOpenCensusCallTracer::PythonOpenCensusCallAttemptTracer::
                   /*include_exchange_labels=*/true);
 }
 
+void PythonOpenCensusCallTracer::PythonOpenCensusCallAttemptTracer::
+    RecordIncomingBytes(const TransportByteSize& transport_byte_size) {
+  incoming_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
+void PythonOpenCensusCallTracer::PythonOpenCensusCallAttemptTracer::
+    RecordOutgoingBytes(const TransportByteSize& transport_byte_size) {
+  outgoing_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
 void PythonOpenCensusCallTracer::PythonOpenCensusCallAttemptTracer::
     RecordCancel(absl::Status /*cancel_error*/) {}
 

src/python/grpcio_observability/grpc_observability/client_call_tracer.h

@@ -17,6 +17,7 @@
 
 #include <stdint.h>
 
+#include <atomic>
 #include <string>
 
 #include "absl/base/thread_annotations.h"
@@ -69,6 +70,10 @@ class PythonOpenCensusCallTracer : public grpc_core::ClientCallTracer {
     void RecordReceivedTrailingMetadata(
         absl::Status status, grpc_metadata_batch* recv_trailing_metadata,
         const grpc_transport_stream_stats* transport_stream_stats) override;
+    void RecordIncomingBytes(
+        const TransportByteSize& transport_byte_size) override;
+    void RecordOutgoingBytes(
+        const TransportByteSize& transport_byte_size) override;
     void RecordCancel(grpc_error_handle cancel_error) override;
     void RecordEnd(const gpr_timespec& /*latency*/) override;
     void RecordAnnotation(absl::string_view annotation) override;
@@ -97,6 +102,12 @@ class PythonOpenCensusCallTracer : public grpc_core::ClientCallTracer {
         optional_labels_array_;
     std::vector<Label> labels_from_peer_;
     bool is_trailers_only_ = false;
+    // TODO(roth, ctiller): Won't need atomic here once chttp2 is migrated
+    // to promises, after which we can ensure that the transport invokes
+    // the RecordIncomingBytes() and RecordOutgoingBytes() methods inside
+    // the call's party.
+    std::atomic<uint64_t> incoming_bytes_{0};
+    std::atomic<uint64_t> outgoing_bytes_{0};
   };
 
   explicit PythonOpenCensusCallTracer(

src/python/grpcio_observability/grpc_observability/server_call_tracer.cc

@@ -36,6 +36,7 @@
 #include <grpc/support/port_platform.h>
 
 #include "src/core/lib/channel/channel_stack.h"
+#include "src/core/lib/experiments/experiments.h"
 #include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/resource_quota/arena.h"
 #include "src/core/lib/slice/slice.h"
@@ -175,8 +176,15 @@ void PythonOpenCensusServerCallTracer::RecordCancel(
 void PythonOpenCensusServerCallTracer::RecordEnd(
     const grpc_call_final_info* final_info) {
   if (PythonCensusStatsEnabled()) {
-    const uint64_t request_size = GetIncomingDataSize(final_info);
-    const uint64_t response_size = GetOutgoingDataSize(final_info);
+    uint64_t outgoing_bytes;
+    uint64_t incoming_bytes;
+    if (grpc_core::IsCallTracerInTransportEnabled()) {
+      outgoing_bytes = outgoing_bytes_.load();
+      incoming_bytes = incoming_bytes_.load();
+    } else {
+      outgoing_bytes = GetOutgoingDataSize(final_info);
+      incoming_bytes = GetIncomingDataSize(final_info);
+    }
     double elapsed_time_s = absl::ToDoubleSeconds(elapsed_time_);
     context_.Labels().emplace_back(kServerMethod, std::string(method_));
     context_.Labels().emplace_back(
@@ -186,11 +194,11 @@ void PythonOpenCensusServerCallTracer::RecordEnd(
       context_.Labels().emplace_back(label);
     }
     RecordDoubleMetric(kRpcServerSentBytesPerRpcMeasureName,
-                       static_cast<double>(response_size), context_.Labels(),
+                       static_cast<double>(outgoing_bytes), context_.Labels(),
                        identifier_, registered_method_,
                        /*include_exchange_labels=*/true);
     RecordDoubleMetric(kRpcServerReceivedBytesPerRpcMeasureName,
-                       static_cast<double>(request_size), context_.Labels(),
+                       static_cast<double>(incoming_bytes), context_.Labels(),
                        identifier_, registered_method_,
                        /*include_exchange_labels=*/true);
     RecordDoubleMetric(kRpcServerServerLatencyMeasureName, elapsed_time_s,
@@ -218,6 +226,16 @@ void PythonOpenCensusServerCallTracer::RecordEnd(
   delete this;
 }
 
+void PythonOpenCensusServerCallTracer::RecordIncomingBytes(
+    const TransportByteSize& transport_byte_size) {
+  incoming_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
+void PythonOpenCensusServerCallTracer::RecordOutgoingBytes(
+    const TransportByteSize& transport_byte_size) {
+  outgoing_bytes_.fetch_add(transport_byte_size.data_bytes);
+}
+
 void PythonOpenCensusServerCallTracer::RecordAnnotation(
     absl::string_view annotation) {
   if (!context_.GetSpanContext().IsSampled()) {

src/python/grpcio_observability/grpc_observability/server_call_tracer.h

@@ -15,6 +15,8 @@
 #ifndef GRPC_PYTHON_OPENCENSUS_SERVER_CALL_TRACER_H
 #define GRPC_PYTHON_OPENCENSUS_SERVER_CALL_TRACER_H
 
+#include <atomic>
+
 #include "absl/strings/string_view.h"
 #include "absl/strings/strip.h"
 #include "constants.h"
@@ -102,6 +104,12 @@ class PythonOpenCensusServerCallTracer : public grpc_core::ServerCallTracer {
 
   void RecordEnd(const grpc_call_final_info* final_info) override;
 
+  void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) override;
+
+  void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) override;
+
   void RecordAnnotation(absl::string_view annotation) override;
 
   void RecordAnnotation(const Annotation& annotation) override;
@@ -124,6 +132,12 @@ class PythonOpenCensusServerCallTracer : public grpc_core::ServerCallTracer {
   std::vector<Label> labels_from_peer_;
   std::string identifier_;
   bool registered_method_ = false;
+  // TODO(roth, ctiller): Won't need atomic here once chttp2 is migrated
+  // to promises, after which we can ensure that the transport invokes
+  // the RecordIncomingBytes() and RecordOutgoingBytes() methods inside
+  // the call's party.
+  std::atomic<uint64_t> incoming_bytes_{0};
+  std::atomic<uint64_t> outgoing_bytes_{0};
 };
 
 }  // namespace grpc_observability

src/python/grpcio_observability/make_grpcio_observability.py

@@ -90,7 +90,11 @@ BAZEL_DEPS = os.path.join(
 )
 
 # the bazel target to scrape to get list of sources for the build
-BAZEL_DEPS_QUERIES = ["//src/core:slice", "//src/core:ref_counted_string"]
+BAZEL_DEPS_QUERIES = [
+    "//src/core:experiments",
+    "//src/core:slice",
+    "//src/core:ref_counted_string",
+]
 
 
 def _bazel_query(query):

src/python/grpcio_observability/observability_lib_deps.py

@@ -21,6 +21,8 @@ CC_FILES=[
     'grpc_root/src/core/lib/debug/trace.cc',
     'grpc_root/src/core/lib/debug/trace_flags.cc',
     'grpc_root/src/core/lib/event_engine/thread_local.cc',
+    'grpc_root/src/core/lib/experiments/config.cc',
+    'grpc_root/src/core/lib/experiments/experiments.cc',
     'grpc_root/src/core/lib/gprpp/crash.cc',
     'grpc_root/src/core/lib/gprpp/examine_stack.cc',
     'grpc_root/src/core/lib/gprpp/fork.cc',

test/core/end2end/tests/http2_stats.cc

@@ -63,6 +63,11 @@ class FakeCallTracer : public ClientCallTracer {
  public:
   class FakeCallAttemptTracer : public CallAttemptTracer {
    public:
+    FakeCallAttemptTracer() {
+      MutexLock lock(g_mu);
+      incoming_bytes_ = TransportByteSize();
+      outgoing_bytes_ = TransportByteSize();
+    }
     std::string TraceId() override { return ""; }
     std::string SpanId() override { return ""; }
     bool IsSampled() override { return false; }
@@ -83,8 +88,30 @@ class FakeCallTracer : public ClientCallTracer {
         absl::Status /*status*/,
         grpc_metadata_batch* /*recv_trailing_metadata*/,
         const grpc_transport_stream_stats* transport_stream_stats) override {
+      if (IsCallTracerInTransportEnabled()) return;
+      TransportByteSize incoming_bytes = {
+          transport_stream_stats->incoming.framing_bytes,
+          transport_stream_stats->incoming.data_bytes,
+          transport_stream_stats->incoming.header_bytes};
+      TransportByteSize outgoing_bytes = {
+          transport_stream_stats->outgoing.framing_bytes,
+          transport_stream_stats->outgoing.data_bytes,
+          transport_stream_stats->outgoing.header_bytes};
+      MutexLock lock(g_mu);
+      incoming_bytes_ = incoming_bytes;
+      outgoing_bytes_ = outgoing_bytes;
+    }
+
+    void RecordIncomingBytes(
+        const TransportByteSize& transport_byte_size) override {
+      MutexLock lock(g_mu);
+      incoming_bytes_ += transport_byte_size;
+    }
+
+    void RecordOutgoingBytes(
+        const TransportByteSize& transport_byte_size) override {
       MutexLock lock(g_mu);
-      transport_stream_stats_ = *transport_stream_stats;
+      outgoing_bytes_ += transport_byte_size;
     }
 
     void RecordCancel(grpc_error_handle /*cancel_error*/) override {}
@@ -101,14 +128,19 @@ class FakeCallTracer : public ClientCallTracer {
     void SetOptionalLabel(OptionalLabelKey /*key*/,
                           RefCountedStringValue /*value*/) override {}
 
-    static grpc_transport_stream_stats transport_stream_stats() {
+    static TransportByteSize incoming_bytes() {
+      MutexLock lock(g_mu);
+      return incoming_bytes_;
+    }
+
+    static TransportByteSize outgoing_bytes() {
       MutexLock lock(g_mu);
-      return transport_stream_stats_;
+      return outgoing_bytes_;
     }
 
    private:
-    static grpc_transport_stream_stats transport_stream_stats_
-        ABSL_GUARDED_BY(g_mu);
+    static TransportByteSize incoming_bytes_ ABSL_GUARDED_BY(g_mu);
+    static TransportByteSize outgoing_bytes_ ABSL_GUARDED_BY(g_mu);
   };
 
   explicit FakeCallTracer() {}
@@ -126,11 +158,18 @@ class FakeCallTracer : public ClientCallTracer {
   void RecordAnnotation(const Annotation& /*annotation*/) override {}
 };
 
-grpc_transport_stream_stats
-    FakeCallTracer::FakeCallAttemptTracer::transport_stream_stats_;
+CallTracerInterface::TransportByteSize
+    FakeCallTracer::FakeCallAttemptTracer::incoming_bytes_;
+CallTracerInterface::TransportByteSize
+    FakeCallTracer::FakeCallAttemptTracer::outgoing_bytes_;
 
 class FakeServerCallTracer : public ServerCallTracer {
  public:
+  FakeServerCallTracer() {
+    MutexLock lock(g_mu);
+    incoming_bytes_ = TransportByteSize();
+    outgoing_bytes_ = TransportByteSize();
+  }
   ~FakeServerCallTracer() override {}
   void RecordSendInitialMetadata(
       grpc_metadata_batch* /*send_initial_metadata*/) override {}
@@ -152,28 +191,57 @@ class FakeServerCallTracer : public ServerCallTracer {
       grpc_metadata_batch* /*recv_trailing_metadata*/) override {}
 
   void RecordEnd(const grpc_call_final_info* final_info) override {
+    if (!IsCallTracerInTransportEnabled()) {
+      TransportByteSize incoming_bytes = {
+          final_info->stats.transport_stream_stats.incoming.framing_bytes,
+          final_info->stats.transport_stream_stats.incoming.data_bytes,
+          final_info->stats.transport_stream_stats.incoming.header_bytes};
+      TransportByteSize outgoing_bytes = {
+          final_info->stats.transport_stream_stats.outgoing.framing_bytes,
+          final_info->stats.transport_stream_stats.outgoing.data_bytes,
+          final_info->stats.transport_stream_stats.outgoing.header_bytes};
       MutexLock lock(g_mu);
-    transport_stream_stats_ = final_info->stats.transport_stream_stats;
+      incoming_bytes_ = incoming_bytes;
+      outgoing_bytes_ = outgoing_bytes;
+    }
     g_server_call_ended_notify->Notify();
   }
 
+  void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) override {
+    MutexLock lock(g_mu);
+    incoming_bytes_ += transport_byte_size;
+  }
+
+  void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) override {
+    MutexLock lock(g_mu);
+    outgoing_bytes_ += transport_byte_size;
+  }
+
   void RecordAnnotation(absl::string_view /*annotation*/) override {}
   void RecordAnnotation(const Annotation& /*annotation*/) override {}
   std::string TraceId() override { return ""; }
   std::string SpanId() override { return ""; }
   bool IsSampled() override { return false; }
 
-  static grpc_transport_stream_stats transport_stream_stats() {
+  static TransportByteSize incoming_bytes() {
+    MutexLock lock(g_mu);
+    return incoming_bytes_;
+  }
+
+  static TransportByteSize outgoing_bytes() {
     MutexLock lock(g_mu);
-    return transport_stream_stats_;
+    return outgoing_bytes_;
   }
 
  private:
-  static grpc_transport_stream_stats transport_stream_stats_
-      ABSL_GUARDED_BY(g_mu);
+  static TransportByteSize incoming_bytes_ ABSL_GUARDED_BY(g_mu);
+  static TransportByteSize outgoing_bytes_ ABSL_GUARDED_BY(g_mu);
 };
 
-grpc_transport_stream_stats FakeServerCallTracer::transport_stream_stats_;
+CallTracerInterface::TransportByteSize FakeServerCallTracer::incoming_bytes_;
+CallTracerInterface::TransportByteSize FakeServerCallTracer::outgoing_bytes_;
 
 // TODO(yijiem): figure out how to reuse FakeStatsPlugin instead of
 // inheriting and overriding it here.
@@ -238,29 +306,32 @@ CORE_END2END_TEST(Http2FullstackSingleHopTest, StreamStats) {
   g_client_call_ended_notify->WaitForNotificationWithTimeout(absl::Seconds(5));
   g_server_call_ended_notify->WaitForNotificationWithTimeout(absl::Seconds(5));
 
-  auto client_transport_stats =
-      FakeCallTracer::FakeCallAttemptTracer::transport_stream_stats();
-  auto server_transport_stats = FakeServerCallTracer::transport_stream_stats();
-  EXPECT_EQ(client_transport_stats.outgoing.data_bytes,
+  auto client_outgoing_transport_stats =
+      FakeCallTracer::FakeCallAttemptTracer::outgoing_bytes();
+  auto client_incoming_transport_stats =
+      FakeCallTracer::FakeCallAttemptTracer::incoming_bytes();
+  auto server_outgoing_transport_stats = FakeServerCallTracer::outgoing_bytes();
+  auto server_incoming_transport_stats = FakeServerCallTracer::incoming_bytes();
+  EXPECT_EQ(client_outgoing_transport_stats.data_bytes,
             send_from_client.size());
-  EXPECT_EQ(client_transport_stats.incoming.data_bytes,
+  EXPECT_EQ(client_incoming_transport_stats.data_bytes,
             send_from_server.size());
-  EXPECT_EQ(server_transport_stats.outgoing.data_bytes,
+  EXPECT_EQ(server_outgoing_transport_stats.data_bytes,
             send_from_server.size());
-  EXPECT_EQ(server_transport_stats.incoming.data_bytes,
+  EXPECT_EQ(server_incoming_transport_stats.data_bytes,
             send_from_client.size());
   // At the very minimum, we should have 9 bytes from initial header frame, 9
   // bytes from data header frame, 5 bytes from the grpc header on data and 9
   // bytes from the trailing header frame. The actual number might be more due
   // to RST_STREAM (13 bytes) and WINDOW_UPDATE (13 bytes) frames.
-  EXPECT_GE(client_transport_stats.outgoing.framing_bytes, 32);
-  EXPECT_LE(client_transport_stats.outgoing.framing_bytes, 58);
-  EXPECT_GE(client_transport_stats.incoming.framing_bytes, 32);
-  EXPECT_LE(client_transport_stats.incoming.framing_bytes, 58);
-  EXPECT_GE(server_transport_stats.outgoing.framing_bytes, 32);
-  EXPECT_LE(server_transport_stats.outgoing.framing_bytes, 58);
-  EXPECT_GE(server_transport_stats.incoming.framing_bytes, 32);
-  EXPECT_LE(server_transport_stats.incoming.framing_bytes, 58);
+  EXPECT_GE(client_outgoing_transport_stats.framing_bytes, 32);
+  EXPECT_LE(client_outgoing_transport_stats.framing_bytes, 58);
+  EXPECT_GE(client_incoming_transport_stats.framing_bytes, 32);
+  EXPECT_LE(client_incoming_transport_stats.framing_bytes, 58);
+  EXPECT_GE(server_outgoing_transport_stats.framing_bytes, 32);
+  EXPECT_LE(server_outgoing_transport_stats.framing_bytes, 58);
+  EXPECT_GE(server_incoming_transport_stats.framing_bytes, 32);
+  EXPECT_LE(server_incoming_transport_stats.framing_bytes, 58);
 
   delete g_client_call_ended_notify;
   g_client_call_ended_notify = nullptr;

test/core/test_util/fake_stats_plugin.h

@@ -87,6 +87,10 @@ class FakeClientCallTracer : public ClientCallTracer {
         const grpc_transport_stream_stats* /*transport_stream_stats*/)
         override {}
     void RecordEnd(const gpr_timespec& /*latency*/) override { Unref(); }
+    void RecordIncomingBytes(
+        const TransportByteSize& /*transport_byte_size*/) override {}
+    void RecordOutgoingBytes(
+        const TransportByteSize& /*transport_byte_size*/) override {}
     void RecordAnnotation(absl::string_view annotation) override {
       annotation_logger_->push_back(std::string(annotation));
     }
@@ -180,6 +184,10 @@ class FakeServerCallTracer : public ServerCallTracer {
   void RecordReceivedTrailingMetadata(
       grpc_metadata_batch* /*recv_trailing_metadata*/) override {}
   void RecordEnd(const grpc_call_final_info* /*final_info*/) override {}
+  void RecordIncomingBytes(
+      const TransportByteSize& /*transport_byte_size*/) override {}
+  void RecordOutgoingBytes(
+      const TransportByteSize& /*transport_byte_size*/) override {}
   void RecordAnnotation(absl::string_view annotation) override {
     annotation_logger_->push_back(std::string(annotation));
   }

test/core/transport/chttp2/hpack_encoder_test.cc

@@ -148,6 +148,39 @@ static void CrashOnAppendError(absl::string_view, const grpc_core::Slice&) {
   abort();
 }
 
+namespace grpc_core {
+
+class FakeCallTracer final : public CallTracerInterface {
+ public:
+  void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) override {}
+  void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) override {}
+  void RecordSendInitialMetadata(
+      grpc_metadata_batch* send_initial_metadata) override {}
+  void RecordSendTrailingMetadata(
+      grpc_metadata_batch* send_trailing_metadata) override {}
+  void RecordSendMessage(const SliceBuffer& send_message) override {}
+  void RecordSendCompressedMessage(
+      const SliceBuffer& send_compressed_message) override {}
+  void RecordReceivedInitialMetadata(
+      grpc_metadata_batch* recv_initial_metadata) override {}
+  void RecordReceivedMessage(const SliceBuffer& recv_message) override {}
+  void RecordReceivedDecompressedMessage(
+      const SliceBuffer& recv_decompressed_message) override {}
+  void RecordCancel(grpc_error_handle cancel_error) override {}
+  std::shared_ptr<TcpTracerInterface> StartNewTcpTrace() override {
+    return nullptr;
+  }
+  void RecordAnnotation(absl::string_view annotation) override {}
+  void RecordAnnotation(const Annotation& annotation) override {}
+  std::string TraceId() override { return ""; }
+  std::string SpanId() override { return ""; }
+  bool IsSampled() override { return false; }
+};
+
+}  // namespace grpc_core
+
 grpc_slice EncodeHeaderIntoBytes(
     bool is_eof,
     const std::vector<std::pair<std::string, std::string>>& header_fields) {
@@ -161,14 +194,13 @@ grpc_slice EncodeHeaderIntoBytes(
              CrashOnAppendError);
   }
 
-  grpc_transport_one_way_stats stats = {};
+  grpc_core::FakeCallTracer call_tracer;
   grpc_core::HPackCompressor::EncodeHeaderOptions hopt{
       0xdeadbeef,  // stream_id
       is_eof,      // is_eof
       false,       // use_true_binary_metadata
       16384,       // max_frame_size
-      &stats       // stats
-  };
+      &call_tracer};
   grpc_slice_buffer output;
   grpc_slice_buffer_init(&output);
 
@@ -306,14 +338,13 @@ static void verify_continuation_headers(const char* key, const char* value,
   b.Append(key, grpc_core::Slice::FromStaticString(value), CrashOnAppendError);
   grpc_slice_buffer_init(&output);
 
-  grpc_transport_one_way_stats stats;
-  stats = {};
+  grpc_core::FakeCallTracer call_tracer;
   grpc_core::HPackCompressor::EncodeHeaderOptions hopt = {
       0xdeadbeef,  // stream_id
       is_eof,      // is_eof
       false,       // use_true_binary_metadata
       150,         // max_frame_size
-      &stats /* stats */};
+      &call_tracer};
   g_compressor->EncodeHeaders(hopt, b, &output);
   verify_frames(output, is_eof);
   grpc_slice_buffer_destroy(&output);
@@ -344,8 +375,7 @@ TEST(HpackEncoderTest, EncodeBinaryAsBase64) {
                "Base64, a tool\nTo encode binary data into "
                "text\nSo it can be shared."),
            CrashOnAppendError);
-  grpc_transport_one_way_stats stats;
-  stats = {};
+  grpc_core::FakeCallTracer call_tracer;
   grpc_slice_buffer output;
   grpc_slice_buffer_init(&output);
   grpc_core::HPackCompressor::EncodeHeaderOptions hopt = {
@@ -353,7 +383,7 @@ TEST(HpackEncoderTest, EncodeBinaryAsBase64) {
       true,        // is_eof
       false,       // use_true_binary_metadata
       150,         // max_frame_size
-      &stats};
+      &call_tracer};
   grpc_core::HPackCompressor compressor;
   compressor.EncodeHeaders(hopt, b, &output);
   grpc_slice_buffer_destroy(&output);
@@ -369,8 +399,7 @@ TEST(HpackEncoderTest, EncodeBinaryAsTrueBinary) {
                "Base64, a tool\nTo encode binary data into "
                "text\nSo it can be shared."),
            CrashOnAppendError);
-  grpc_transport_one_way_stats stats;
-  stats = {};
+  grpc_core::FakeCallTracer call_tracer;
   grpc_slice_buffer output;
   grpc_slice_buffer_init(&output);
   grpc_core::HPackCompressor::EncodeHeaderOptions hopt = {
@@ -378,7 +407,7 @@ TEST(HpackEncoderTest, EncodeBinaryAsTrueBinary) {
       true,        // is_eof
       true,        // use_true_binary_metadata
       150,         // max_frame_size
-      &stats};
+      &call_tracer};
   grpc_core::HPackCompressor compressor;
   compressor.EncodeHeaders(hopt, b, &output);
   grpc_slice_buffer_destroy(&output);

test/cpp/ext/filters/census/stats_plugin_end2end_test.cc

@@ -828,8 +828,11 @@ TEST_F(StatsPluginEnd2EndTest, TestMetadataSizeAnnotations) {
   traces_recorder_->StopRecording();
   auto recorded_spans = traces_recorder_->GetAndClearSpans();
   // Check presence of metadata size annotations in client span.
-  auto sent_span_data =
-      GetSpanByName(recorded_spans, absl::StrCat("Sent.", client_method_name_));
+  auto sent_span_data = GetSpanByName(
+      recorded_spans,
+      absl::StrCat(
+          grpc_core::IsCallTracerInTransportEnabled() ? "Attempt." : "Sent.",
+          client_method_name_));
   ASSERT_NE(sent_span_data, recorded_spans.end());
   EXPECT_TRUE(IsAnnotationPresent(
       sent_span_data,
@@ -871,8 +874,11 @@ TEST_F(StatsPluginEnd2EndTest, TestHttpAnnotations) {
   ::opencensus::trace::exporter::SpanExporterTestPeer::ExportForTesting();
   traces_recorder_->StopRecording();
   auto recorded_spans = traces_recorder_->GetAndClearSpans();
-  auto client_span_data =
-      GetSpanByName(recorded_spans, absl::StrCat("Sent.", client_method_name_));
+  auto client_span_data = GetSpanByName(
+      recorded_spans,
+      absl::StrCat(
+          grpc_core::IsCallTracerInTransportEnabled() ? "Attempt." : "Sent.",
+          client_method_name_));
   ASSERT_NE(client_span_data, recorded_spans.end());
   EXPECT_TRUE(IsAnnotationPresent(client_span_data,
                                   "HttpAnnotation type: Start time: .* "

test/cpp/microbenchmarks/bm_chttp2_hpack.cc

@@ -54,6 +54,39 @@ static grpc_slice MakeSlice(const std::vector<uint8_t>& bytes) {
   return s;
 }
 
+namespace grpc_core {
+
+class FakeCallTracer final : public CallTracerInterface {
+ public:
+  void RecordIncomingBytes(
+      const TransportByteSize& transport_byte_size) override {}
+  void RecordOutgoingBytes(
+      const TransportByteSize& transport_byte_size) override {}
+  void RecordSendInitialMetadata(
+      grpc_metadata_batch* send_initial_metadata) override {}
+  void RecordSendTrailingMetadata(
+      grpc_metadata_batch* send_trailing_metadata) override {}
+  void RecordSendMessage(const SliceBuffer& send_message) override {}
+  void RecordSendCompressedMessage(
+      const SliceBuffer& send_compressed_message) override {}
+  void RecordReceivedInitialMetadata(
+      grpc_metadata_batch* recv_initial_metadata) override {}
+  void RecordReceivedMessage(const SliceBuffer& recv_message) override {}
+  void RecordReceivedDecompressedMessage(
+      const SliceBuffer& recv_decompressed_message) override {}
+  void RecordCancel(grpc_error_handle cancel_error) override {}
+  std::shared_ptr<TcpTracerInterface> StartNewTcpTrace() override {
+    return nullptr;
+  }
+  void RecordAnnotation(absl::string_view annotation) override {}
+  void RecordAnnotation(const Annotation& annotation) override {}
+  std::string TraceId() override { return ""; }
+  std::string SpanId() override { return ""; }
+  bool IsSampled() override { return false; }
+};
+
+}  // namespace grpc_core
+
 ////////////////////////////////////////////////////////////////////////////////
 // HPACK encoder
 //
@@ -80,8 +113,7 @@ static void BM_HpackEncoderEncodeDeadline(benchmark::State& state) {
         saved_now + grpc_core::Duration::Seconds(30));
 
   grpc_core::HPackCompressor c;
-  grpc_transport_one_way_stats stats;
-  stats = {};
+  grpc_core::FakeCallTracer call_tracer;
   grpc_slice_buffer outbuf;
   grpc_slice_buffer_init(&outbuf);
   while (state.KeepRunning()) {
@@ -91,7 +123,7 @@ static void BM_HpackEncoderEncodeDeadline(benchmark::State& state) {
             true,
             false,
             size_t{1024},
-            &stats,
+            &call_tracer,
         },
         b, &outbuf);
     grpc_slice_buffer_reset_and_unref(&outbuf);
@@ -110,8 +142,7 @@ static void BM_HpackEncoderEncodeHeader(benchmark::State& state) {
   Fixture::Prepare(&b);
 
   grpc_core::HPackCompressor c;
-  grpc_transport_one_way_stats stats;
-  stats = {};
+  grpc_core::FakeCallTracer call_tracer;
   grpc_slice_buffer outbuf;
   grpc_slice_buffer_init(&outbuf);
   while (state.KeepRunning()) {
@@ -122,7 +153,7 @@ static void BM_HpackEncoderEncodeHeader(benchmark::State& state) {
             state.range(0) != 0,
             Fixture::kEnableTrueBinary,
             static_cast<size_t>(state.range(1) + kEnsureMaxFrameAtLeast),
-            &stats,
+            &call_tracer,
         },
         b, &outbuf);
     if (!logged_representative_output && state.iterations() > 3) {
@@ -383,9 +414,8 @@ class FromEncoderFixture {
     EncoderFixture::Prepare(&b);
 
     grpc_core::HPackCompressor c;
-    grpc_transport_one_way_stats stats;
+    grpc_core::FakeCallTracer call_tracer;
     std::vector<grpc_slice> out;
-    stats = {};
     bool done = false;
     int i = 0;
     while (!done) {
@@ -397,7 +427,7 @@ class FromEncoderFixture {
               false,
               EncoderFixture::kEnableTrueBinary,
               1024 * 1024,
-              &stats,
+              &call_tracer,
           },
           b, &outbuf);
       if (i == iteration) {