cancels context propagation

Author: dmehala

BUILD.bazel

@@ -42,6 +42,7 @@ cc_library(
       "src/datadog/string_util.cpp",
       "src/datadog/tag_propagation.cpp",
       "src/datadog/tags.cpp",
+      "src/datadog/trace_source.cpp",
       "src/datadog/telemetry_metrics.cpp",
       "src/datadog/threaded_event_scheduler.cpp",
       "src/datadog/tracer_config.cpp",
@@ -117,6 +118,7 @@ cc_library(
       "include/datadog/tracer_config.h",
       "include/datadog/tracer_signature.h",
       "include/datadog/trace_id.h",
+      "include/datadog/trace_source.h",
       "include/datadog/trace_sampler_config.h",
       "include/datadog/trace_segment.h",
       "include/datadog/version.h",

include/datadog/dict_writer.h

@@ -21,6 +21,9 @@ class DictWriter {
   // implementation may, but is not required to, overwrite any previous value at
   // `key`.
   virtual void set(StringView key, StringView value) = 0;
+
+  // Removes the entry associated with the given key.
+  virtual void erase(StringView){};
 };
 
 }  // namespace tracing

src/datadog/tags.h

@@ -46,7 +46,7 @@ extern const std::string apm_enabled;   // _dd.apm.enabled
 
 // Return whether the specified `tag_name` is reserved for use internal to this
 // library.
-constexpr inline bool is_internal(StringView tag_name) {
+inline bool is_internal(StringView tag_name) {
   return starts_with(tag_name, "_dd.");
 }
 

src/datadog/trace_segment.cpp

@@ -359,6 +359,18 @@ bool TraceSegment::inject(DictWriter& writer, const SpanData& span,
   //  - sampling priority is DROP
   if (!tracing_enabled_) {
     if (ts_tag_found == local_root_tags.cend() && sampling_priority <= 0) {
+      writer.erase("x-datadog-trace-id");
+      writer.erase("x-datadog-parent-id");
+      writer.erase("x-datadog-sampling-priority");
+      writer.erase("x-datadog-origin");
+      writer.erase("x-datadog-trace-id");
+      writer.erase("x-datadog-tags");
+      writer.erase("x-b3-traceid");
+      writer.erase("x-b3-spanid");
+      writer.erase("x-b3-sampled");
+      writer.erase("x-datadog-origin");
+      writer.erase("traceparent");
+      writer.erase("tracestate");
       return false;
     }
   }

test/mocks/dict_writers.h

@@ -14,4 +14,6 @@ struct MockDictWriter : public DictWriter {
   void set(StringView key, StringView value) override {
     items.insert_or_assign(std::string(key), std::string(value));
   }
+
+  void erase(StringView key) override { items.erase(std::string(key)); }
 };

test/test_span.cpp

@@ -485,6 +485,32 @@ TEST_SPAN("injection") {
   };
   Tracer tracer{*finalized_config, std::make_shared<Generator>(42)};
 
+  SECTION("APM Disabled cancel context propagation") {
+    config.tracing_enabled = false;
+    auto finalized_config = finalize_config(config);
+
+    Tracer apm_disabled_tracer{*finalized_config,
+                               std::make_shared<Generator>(42)};
+
+    auto apm_span = tracer.create_span();
+    MockDictWriter writer;
+    apm_span.inject(writer);
+
+    REQUIRE(writer.items.empty() == false);
+
+    // Consume the span that MUST be kept for service liveness.
+    {
+      apm_disabled_tracer.create_span();
+    }
+
+    auto span = apm_disabled_tracer.create_span();
+
+    // reuse the same writer. Since span generated from apm_disabled_tracer is
+    // not marked by a product injection should be cancelled.
+    span.inject(writer);
+    CHECK(writer.items.empty());
+  }
+
   SECTION("trace ID, parent ID ,and sampling priority") {
     auto span = tracer.create_span();
     REQUIRE(span.trace_id() == 42);