From a0c8036cb7883b98467d64b28010fbcb583e611b Mon Sep 17 00:00:00 2001
From: Mike Schore <mike.schore@gmail.com>
Date: Tue, 9 May 2017 15:58:15 -0700
Subject: [PATCH] tracing: add direct support for a span to spawn a child

---
 include/envoy/tracing/http_tracer.h           |  8 ++++++--
 source/common/tracing/http_tracer_impl.h      |  5 +++++
 .../common/tracing/lightstep_tracer_impl.cc   | 19 +++++++++++++++----
 source/common/tracing/lightstep_tracer_impl.h |  4 +++-
 test/mocks/tracing/mocks.h                    |  8 +++++++-
 5 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/include/envoy/tracing/http_tracer.h b/include/envoy/tracing/http_tracer.h
index 295d24c9bca4..cc9e2a47f560 100644
--- a/include/envoy/tracing/http_tracer.h
+++ b/include/envoy/tracing/http_tracer.h
@@ -33,16 +33,20 @@ class Config {
 /*
  * Basic abstraction for span.
  */
+class Span;
+
+typedef std::unique_ptr<Span> SpanPtr;
+
 class Span {
 public:
   virtual ~Span() {}
 
   virtual void setTag(const std::string& name, const std::string& value) PURE;
   virtual void finishSpan() PURE;
+  // virtual void inject(Http::HeaderMap& request_headers) PURE;
+  virtual SpanPtr spawnChild(const std::string& name, SystemTime start_time) PURE;
 };
 
-typedef std::unique_ptr<Span> SpanPtr;
-
 /**
  * Tracing driver is responsible for span creation.
  */
diff --git a/source/common/tracing/http_tracer_impl.h b/source/common/tracing/http_tracer_impl.h
index c2a3ba4c909b..3291ecf96046 100644
--- a/source/common/tracing/http_tracer_impl.h
+++ b/source/common/tracing/http_tracer_impl.h
@@ -87,6 +87,11 @@ class NullSpan : public Tracing::Span {
   // Tracing::Span
   void setTag(const std::string&, const std::string&) override {}
   void finishSpan() override {}
+  SpanPtr spawnChild(const std::string&, SystemTime) override {
+    SpanPtr nullSpan;
+    nullSpan.reset(new NullSpan());
+    return std::move(nullSpan);
+  }
 };
 
 } // Tracing
diff --git a/source/common/tracing/lightstep_tracer_impl.cc b/source/common/tracing/lightstep_tracer_impl.cc
index f0aefbe493b6..888beac38a45 100644
--- a/source/common/tracing/lightstep_tracer_impl.cc
+++ b/source/common/tracing/lightstep_tracer_impl.cc
@@ -14,7 +14,8 @@
 
 namespace Tracing {
 
-LightStepSpan::LightStepSpan(lightstep::Span& span) : span_(span) {}
+LightStepSpan::LightStepSpan(lightstep::Span& span, lightstep::Tracer& tracer)
+    : span_(span), tracer_(tracer) {}
 
 void LightStepSpan::finishSpan() { span_.Finish(); }
 
@@ -22,6 +23,15 @@ void LightStepSpan::setTag(const std::string& name, const std::string& value) {
   span_.SetTag(name, value);
 }
 
+SpanPtr LightStepSpan::spawnChild(const std::string& name, SystemTime start_time) {
+  SpanPtr child_span;
+  lightstep::Span ls_span = tracer_.StartSpan(
+      name, {lightstep::ChildOf(span_.context()), lightstep::StartTimestamp(start_time)});
+  child_span.reset(new LightStepSpan(ls_span, tracer_));
+
+  return std::move(child_span);
+}
+
 LightStepRecorder::LightStepRecorder(const lightstep::TracerImpl& tracer, LightStepDriver& driver,
                                      Event::Dispatcher& dispatcher)
     : builder_(tracer), driver_(driver) {
@@ -133,20 +143,21 @@ SpanPtr LightStepDriver::startSpan(Http::HeaderMap& request_headers,
     lightstep::Span ls_span =
         tracer.StartSpan(operation_name, {lightstep::ChildOf(parent_span_ctx),
                                           lightstep::StartTimestamp(start_time)});
-    active_span.reset(new LightStepSpan(ls_span));
+    active_span.reset(new LightStepSpan(ls_span, tracer));
   } else {
     lightstep::Span ls_span =
         tracer.StartSpan(operation_name, {lightstep::StartTimestamp(start_time)});
-    active_span.reset(new LightStepSpan(ls_span));
+    active_span.reset(new LightStepSpan(ls_span, tracer));
   }
 
-  // Inject newly created span context into HTTP carrier.
+  // Inject newly created span context into HTTP carrier. TODO: move to inject()
   lightstep::BinaryCarrier ctx;
   tracer.Inject(active_span->context(), lightstep::CarrierFormat::LightStepBinaryCarrier,
                 lightstep::ProtoWriter(&ctx));
   const std::string current_span_context = ctx.SerializeAsString();
   request_headers.insertOtSpanContext().value(
       Base64::encode(current_span_context.c_str(), current_span_context.length()));
+  // end TODO
 
   return std::move(active_span);
 }
diff --git a/source/common/tracing/lightstep_tracer_impl.h b/source/common/tracing/lightstep_tracer_impl.h
index 8c44f9d3168e..f01c03923112 100644
--- a/source/common/tracing/lightstep_tracer_impl.h
+++ b/source/common/tracing/lightstep_tracer_impl.h
@@ -28,16 +28,18 @@ struct LightstepTracerStats {
 
 class LightStepSpan : public Span {
 public:
-  LightStepSpan(lightstep::Span& span);
+  LightStepSpan(lightstep::Span& span, lightstep::Tracer& tracer);
 
   // Tracing::Span
   void finishSpan() override;
   void setTag(const std::string& name, const std::string& value) override;
+  SpanPtr spawnChild(const std::string& name, SystemTime start_time) override;
 
   lightstep::SpanContext context() { return span_.context(); }
 
 private:
   lightstep::Span span_;
+  lightstep::Tracer& tracer_;
 };
 
 typedef std::unique_ptr<LightStepSpan> LightStepSpanPtr;
diff --git a/test/mocks/tracing/mocks.h b/test/mocks/tracing/mocks.h
index c0181932f32a..97dcdfc2cf4c 100644
--- a/test/mocks/tracing/mocks.h
+++ b/test/mocks/tracing/mocks.h
@@ -33,6 +33,12 @@ class MockSpan : public Span {
 
   MOCK_METHOD2(setTag, void(const std::string& name, const std::string& value));
   MOCK_METHOD0(finishSpan, void());
+
+  SpanPtr spawnChild(const std::string& name, SystemTime start_time) override {
+    return SpanPtr{spawnChild_(name, start_time)};
+  }
+
+  MOCK_METHOD2(spawnChild_, Span*(const std::string& name, SystemTime start_time));
 };
 
 class MockHttpTracer : public HttpTracer {
@@ -63,4 +69,4 @@ class MockDriver : public Driver {
                                  const std::string& operation_name, SystemTime start_time));
 };
 
-} // Tracing
\ No newline at end of file
+} // Tracing