Add method to add annotations to call tracer (#31901)

include/grpcpp/opencensus.h

@@ -186,6 +186,11 @@ class CensusContext {
     span_.AddAttribute(key, attribute);
   }
 
+  void AddSpanAnnotation(absl::string_view description,
+                         opencensus::trace::AttributesRef attributes) {
+    span_.AddAnnotation(description, attributes);
+  }
+
   const ::opencensus::trace::Span& Span() const { return span_; }
   const ::opencensus::tags::TagMap& tags() const { return tags_; }
 

src/core/lib/channel/call_tracer.h

@@ -75,6 +75,10 @@ class CallTracer {
     // Should be the last API call to the object. Once invoked, the tracer
     // library is free to destroy the object.
     virtual void RecordEnd(const gpr_timespec& latency) = 0;
+    // Records an annotation on the call attempt.
+    // TODO(yashykt): If needed, extend this to attach attributes with
+    // annotations.
+    virtual void RecordAnnotation(absl::string_view annotation) = 0;
   };
 
   virtual ~CallTracer() {}
@@ -87,6 +91,10 @@ class CallTracer {
   // serves as an indication that the call stack is done with all API calls, and
   // the tracer library is free to destroy it after that.
   virtual CallAttemptTracer* StartNewAttempt(bool is_transparent_retry) = 0;
+  // Records an annotation on the call attempt.
+  // TODO(yashykt): If needed, extend this to attach attributes with
+  // annotations.
+  virtual void RecordAnnotation(absl::string_view annotation) = 0;
 };
 
 }  // namespace grpc_core

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

@@ -246,6 +246,11 @@ void OpenCensusCallTracer::OpenCensusCallAttemptTracer::RecordEnd(
   }
 }
 
+void OpenCensusCallTracer::OpenCensusCallAttemptTracer::RecordAnnotation(
+    absl::string_view annotation) {
+  context_.AddSpanAnnotation(annotation, {});
+}
+
 //
 // OpenCensusCallTracer
 //
@@ -312,6 +317,10 @@ OpenCensusCallTracer::StartNewAttempt(bool is_transparent_retry) {
       this, attempt_num, is_transparent_retry, false /* arena_allocated */);
 }
 
+void OpenCensusCallTracer::RecordAnnotation(absl::string_view annotation) {
+  context_.AddSpanAnnotation(annotation, {});
+}
+
 CensusContext OpenCensusCallTracer::CreateCensusContextForCallAttempt() {
   if (!OpenCensusTracingEnabled() || !tracing_enabled_) return CensusContext();
   GPR_DEBUG_ASSERT(context_.Context().IsValid());

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

@@ -81,6 +81,7 @@ class OpenCensusCallTracer : public grpc_core::CallTracer {
         const grpc_transport_stream_stats* transport_stream_stats) override;
     void RecordCancel(grpc_error_handle cancel_error) override;
     void RecordEnd(const gpr_timespec& /*latency*/) override;
+    void RecordAnnotation(absl::string_view annotation) override;
 
     experimental::CensusContext* context() { return &context_; }
 
@@ -108,6 +109,7 @@ class OpenCensusCallTracer : public grpc_core::CallTracer {
   void GenerateContext();
   OpenCensusCallAttemptTracer* StartNewAttempt(
       bool is_transparent_retry) override;
+  void RecordAnnotation(absl::string_view annotation) override;
 
  private:
   experimental::CensusContext CreateCensusContextForCallAttempt();