feat(tracing): add support for DD_TRACE_PROPAGATION_BEHAVIOR_EXTRACT

BUILD.bazel

@@ -42,6 +42,7 @@ cc_library(
         "src/datadog/parse_util.cpp",
         "src/datadog/parse_util.h",
         "src/datadog/platform_util.h",
+        "src/datadog/propagation_behavior_extract.cpp",
         "src/datadog/propagation_style.cpp",
         "src/datadog/random.cpp",
         "src/datadog/random.h",
@@ -122,6 +123,7 @@ cc_library(
         "include/datadog/logger.h",
         "include/datadog/null_collector.h",
         "include/datadog/optional.h",
+        "include/datadog/propagation_behavior_extract.h",
         "include/datadog/propagation_style.h",
         "include/datadog/rate.h",
         "include/datadog/remote_config/capability.h",

CMakeLists.txt

@@ -151,6 +151,7 @@ target_sources(dd-trace-cpp-objects
       include/datadog/logger.h
       include/datadog/null_collector.h
       include/datadog/optional.h
+      include/datadog/propagation_behavior_extract.h
       include/datadog/propagation_style.h
       include/datadog/rate.h
       include/datadog/runtime_id.h
@@ -196,6 +197,7 @@ target_sources(dd-trace-cpp-objects
     src/datadog/logger.cpp
     src/datadog/msgpack.cpp
     src/datadog/parse_util.cpp
+    src/datadog/propagation_behavior_extract.cpp
     src/datadog/propagation_style.cpp
     src/datadog/random.cpp
     src/datadog/rate.cpp

include/datadog/config.h

@@ -21,6 +21,7 @@ enum class ConfigName : char {
   TAGS,
   EXTRACTION_STYLES,
   INJECTION_STYLES,
+  PROPAGATION_BEHAVIOR_EXTRACT,
   STARTUP_LOGS,
   REPORT_TELEMETRY,
   DELEGATE_SAMPLING,

include/datadog/environment.h

@@ -52,6 +52,7 @@ namespace environment {
         ENV_DEFAULT_RESOLVED_IN_CODE("Defaults to process name when unset."))  \
   MACRO(DD_SPAN_SAMPLING_RULES, ARRAY, "[]")                                   \
   MACRO(DD_SPAN_SAMPLING_RULES_FILE, STRING, "")                               \
+  MACRO(DD_TRACE_PROPAGATION_BEHAVIOR_EXTRACT, STRING, "continue")             \
   MACRO(DD_TRACE_PROPAGATION_STYLE_EXTRACT, ARRAY,                             \
         "datadog,tracecontext,baggage")                                        \
   MACRO(DD_TRACE_PROPAGATION_STYLE_INJECT, ARRAY,                              \

include/datadog/propagation_behavior_extract.h

@@ -0,0 +1,36 @@
+#pragma once
+
+// This component provides an `enum class`, `PropagationBehaviorExtract`, that
+// indicates a trace context extraction or injection format to be used.
+// `TracerConfig` has one `std::vector<PropagationStyle>` for extraction and
+// another for injection. See `tracer_config.h`.
+
+#include "optional.h"
+#include "string_view.h"
+
+// Undefine legacy Windows macro so it can be a value in the enum
+#ifdef IGNORE
+#undef IGNORE
+#endif
+
+namespace datadog {
+namespace tracing {
+
+enum class PropagationBehaviorExtract {
+  // Propagate extracted context normally
+  CONTINUE,
+  // Restart a new trace (new sampling decision, no parent)
+  // Reference previous trace through a span-link
+  RESTART,
+  // Discard entirely incoming context
+  IGNORE,
+};
+
+StringView to_string_view(PropagationBehaviorExtract behavior);
+
+// defaults to CONTINUE if empty or unsupported
+Optional<PropagationBehaviorExtract> parse_propagation_behavior_extract(
+    StringView text);
+
+}  // namespace tracing
+}  // namespace datadog

include/datadog/tracer.h

@@ -18,6 +18,7 @@
 #include "expected.h"
 #include "id_generator.h"
 #include "optional.h"
+#include "propagation_behavior_extract.h"
 #include "span.h"
 #include "span_config.h"
 #include "tracer_config.h"
@@ -45,6 +46,7 @@ class Tracer {
   Clock clock_;
   std::vector<PropagationStyle> injection_styles_;
   std::vector<PropagationStyle> extraction_styles_;
+  PropagationBehaviorExtract propagation_behavior_extract_;
   Optional<std::string> hostname_;
   std::size_t tags_header_max_size_;
   // Store the tracer configuration in an in-memory file, allowing it to be
@@ -75,6 +77,9 @@ class Tracer {
   // `config`.  If there is no tracing information in `reader`, then return an
   // error with code `Error::NO_SPAN_TO_EXTRACT`.  If a failure occurs, then
   // return an error with some other code.
+  // Depending of the propagation_behavior_restart config, it can continue the
+  // trace, restart a new trace (with link), or discard the span (returning
+  // the same result as if there was no tracing information)
   Expected<Span> extract_span(const DictReader& reader);
   Expected<Span> extract_span(const DictReader& reader,
                               const SpanConfig& config);

include/datadog/tracer_config.h

@@ -16,6 +16,7 @@
 #include "datadog_agent_config.h"
 #include "expected.h"
 #include "http_endpoint_calculation_mode.h"
+#include "propagation_behavior_extract.h"
 #include "propagation_style.h"
 #include "runtime_id.h"
 #include "span_defaults.h"
@@ -107,6 +108,14 @@ struct TracerConfig {
   // environment variables.
   Optional<std::vector<PropagationStyle>> extraction_styles;
 
+  // `propagation_behavior_extract` indicates how to handle incoming trace
+  // context. `continue`: default behavior, all trace contexts are propagated.
+  // `restart`: restart a new trace (new sampling decision) with a span link to
+  // the remote one. baggage is propagated. `ignore`: discard entirely any
+  // existing trace context and start a new trace. Overridden by
+  // DD_TRACE_PROPAGATION_BEHAVIOR_EXTRACT
+  Optional<PropagationBehaviorExtract> propagation_behavior_extract;
+
   // `report_hostname` indicates whether the tracer will include the result of
   // `gethostname` with traces sent to the collector.
   Optional<bool> report_hostname;
@@ -224,6 +233,8 @@ class FinalizedTracerConfig final {
   std::vector<PropagationStyle> injection_styles;
   std::vector<PropagationStyle> extraction_styles;
 
+  PropagationBehaviorExtract propagation_behavior_extract;
+
   bool report_hostname;
   std::size_t tags_header_size;
   std::shared_ptr<Logger> logger;

src/datadog/extracted_data.h

@@ -40,6 +40,7 @@ struct ExtractedData {
   Optional<std::string> additional_datadog_w3c_tracestate;
   // `style` is the extraction style used to obtain this `ExtractedData`. It's
   // for diagnostics.
+  Optional<std::string> tracestate_full;
   Optional<PropagationStyle> style;
   // `headers_examined` are the name/value pairs of HTTP headers (or equivalent
   // request meta-data) that were looked up and had values during the

src/datadog/propagation_behavior_extract.cpp

@@ -0,0 +1,44 @@
+#include <datadog/propagation_behavior_extract.h>
+
+#include <cassert>
+
+#include "json.hpp"
+#include "string_util.h"
+
+namespace datadog {
+namespace tracing {
+
+StringView to_string_view(PropagationBehaviorExtract behavior) {
+  switch (behavior) {
+    case PropagationBehaviorExtract::CONTINUE:
+      return "continue";
+    case PropagationBehaviorExtract::RESTART:
+      return "restart";
+    case PropagationBehaviorExtract::IGNORE:
+      return "ignore";
+    default:
+      std::abort();
+  }
+}
+
+nlohmann::json to_json(PropagationBehaviorExtract behavior) {
+  return to_string_view(behavior);
+}
+
+Optional<PropagationBehaviorExtract> parse_propagation_behavior_extract(
+    StringView text) {
+  auto token = std::string{text};
+  to_lower(token);
+
+  if (token == "continue" || token.empty()) {
+    return PropagationBehaviorExtract::CONTINUE;
+  } else if (token == "restart") {
+    return PropagationBehaviorExtract::RESTART;
+  } else if (token == "ignore") {
+    return PropagationBehaviorExtract::IGNORE;
+  }
+  return nullopt;
+}
+
+}  // namespace tracing
+}  // namespace datadog

src/datadog/telemetry/telemetry_impl.cpp

@@ -92,6 +92,8 @@ std::string to_string(datadog::tracing::ConfigName name) {
       return "trace_propagation_style_extract";
     case ConfigName::INJECTION_STYLES:
       return "trace_propagation_style_inject";
+    case ConfigName::PROPAGATION_BEHAVIOR_EXTRACT:
+      return "trace_propagation_behavior_extract";
     case ConfigName::STARTUP_LOGS:
       return "trace_startup_logs_enabled";
     case ConfigName::REPORT_TELEMETRY:

src/datadog/tracer.cpp

@@ -27,6 +27,7 @@
 #include "root_session_id.h"
 #include "span_data.h"
 #include "span_sampler.h"
+#include "string_util.h"
 #include "tags.h"
 #include "telemetry_metrics.h"
 #include "trace_sampler.h"
@@ -61,6 +62,7 @@ Tracer::Tracer(const FinalizedTracerConfig& config,
       clock_(config.clock),
       injection_styles_(config.injection_styles),
       extraction_styles_(config.extraction_styles),
+      propagation_behavior_extract_(config.propagation_behavior_extract),
       tags_header_max_size_(config.tags_header_size),
       baggage_opts_(config.baggage_opts),
       baggage_injection_enabled_(false),
@@ -86,10 +88,12 @@ Tracer::Tracer(const FinalizedTracerConfig& config,
     collector_ = agent;
   }
 
-  for (const auto style : extraction_styles_) {
-    if (style == PropagationStyle::BAGGAGE) {
-      baggage_extraction_enabled_ = true;
-      break;
+  if (propagation_behavior_extract_ != PropagationBehaviorExtract::IGNORE) {
+    for (const auto style : extraction_styles_) {
+      if (style == PropagationStyle::BAGGAGE) {
+        baggage_extraction_enabled_ = true;
+        break;
+      }
     }
   }
 
@@ -172,7 +176,7 @@ void Tracer::store_config(
 
   // clang-format off
   msgpack::pack_map(
-    buffer, 
+    buffer,
     "schema_version", [&](auto& buffer) { msgpack::pack_integer(buffer, std::uint64_t(2)); return Expected<void>{}; },
     "runtime_id", [&](auto& buffer) { return msgpack::pack_string(buffer, runtime_id_.string()); },
     "tracer_version", [&](auto& buffer) { return msgpack::pack_string(buffer, signature_.library_version); },
@@ -229,6 +233,13 @@ Expected<Span> Tracer::extract_span(const DictReader& reader) {
 
 Expected<Span> Tracer::extract_span(const DictReader& reader,
                                     const SpanConfig& config) {
+  // ignore: Discard incoming context, new span with new sampling decision
+  if (propagation_behavior_extract_ == PropagationBehaviorExtract::IGNORE) {
+    return Error{
+        Error::NO_SPAN_TO_EXTRACT,
+        "Ignoring context extraction (propagation_behavior_extract=ignore)"};
+  }
+
   assert(!extraction_styles_.empty());
 
   AuditedReader audited_reader{reader};
@@ -417,37 +428,76 @@ Expected<Span> Tracer::extract_span(const DictReader& reader,
     merged_context.trace_tags.erase(found);
   }
 
-  // When APM Tracing is disabled, the incoming sampling decision MAY be
-  // overridden based on locally generated spans. As such, the received sampling
-  // decision is intentionally ignored, and the tracer is expected to make its
-  // own decision in accordance with the locally enabled product configuration.
-  Optional<SamplingDecision> sampling_decision;
-  if (tracing_enabled_ && merged_context.sampling_priority) {
-    SamplingDecision decision;
-    decision.priority = *merged_context.sampling_priority;
-    // `decision.mechanism` is null.  We might be able to infer it once we
-    // extract `trace_tags`, but we would have no use for it, so we won't.
-    decision.origin = SamplingDecision::Origin::EXTRACTED;
-
-    sampling_decision = decision;
-  }
+  switch (propagation_behavior_extract_) {
+    case PropagationBehaviorExtract::CONTINUE: {
+      // When APM Tracing is disabled, the incoming sampling decision MAY be
+      // overridden based on locally generated spans. As such, the received
+      // sampling decision is intentionally ignored, and the tracer is expected
+      // to make its own decision in accordance with the locally enabled product
+      // configuration.
+      Optional<SamplingDecision> sampling_decision;
+      if (tracing_enabled_ && merged_context.sampling_priority) {
+        SamplingDecision decision;
+        decision.priority = *merged_context.sampling_priority;
+        // `decision.mechanism` is null.  We might be able to infer it once we
+        // extract `trace_tags`, but we would have no use for it, so we won't.
+        decision.origin = SamplingDecision::Origin::EXTRACTED;
+        sampling_decision = decision;
+      }
 
-  const auto span_data_ptr = span_data.get();
-  telemetry::counter::increment(metrics::tracer::trace_segments_created,
-                                {"new_continued:continued"});
-  const auto segment = std::make_shared<TraceSegment>(
-      logger_, collector_, config_manager_->trace_sampler(), span_sampler_,
-      config_manager_->span_defaults(), config_manager_, runtime_id_,
-      injection_styles_, hostname_, std::move(merged_context.origin),
-      tags_header_max_size_, std::move(merged_context.trace_tags),
-      std::move(sampling_decision),
-      std::move(merged_context.additional_w3c_tracestate),
-      std::move(merged_context.additional_datadog_w3c_tracestate),
-      std::move(span_data), resource_renaming_mode_, tracing_enabled_);
-  Span span{span_data_ptr, segment,
-            [generator = generator_]() { return generator->span_id(); },
-            clock_};
-  return span;
+      const auto span_data_ptr = span_data.get();
+      telemetry::counter::increment(metrics::tracer::trace_segments_created,
+                                    {"new_continued:continued"});
+      const auto segment = std::make_shared<TraceSegment>(
+          logger_, collector_, config_manager_->trace_sampler(), span_sampler_,
+          config_manager_->span_defaults(), config_manager_, runtime_id_,
+          injection_styles_, hostname_, std::move(merged_context.origin),
+          tags_header_max_size_, std::move(merged_context.trace_tags),
+          std::move(sampling_decision),
+          std::move(merged_context.additional_w3c_tracestate),
+          std::move(merged_context.additional_datadog_w3c_tracestate),
+          std::move(span_data), resource_renaming_mode_, tracing_enabled_);
+
+      Span span{span_data_ptr, segment,
+                [generator = generator_]() { return generator->span_id(); },
+                clock_};
+      return span;
+    }
+    case PropagationBehaviorExtract::RESTART: {
+      // restart: create a new trace, with a span link to the previous one
+
+      std::string context_headers{to_string_view(*first_style_with_trace_id)};
+      to_lower(context_headers);
+      auto link_attributes = SpanLinkAttributes{};
+      link_attributes.emplace("reason", "propagation_behavior_extract");
+      link_attributes.emplace("context_headers", std::move(context_headers));
+
+      Optional<std::string> tracestate;
+      if (const auto w3c = extracted_contexts.find(PropagationStyle::W3C);
+          w3c != extracted_contexts.end() &&
+          w3c->second.trace_id == span_data->trace_id) {
+        tracestate = w3c->second.tracestate_full;
+      }
+
+      Optional<std::uint32_t> flags =
+          merged_context.sampling_priority
+              ? Optional<std::uint32_t>(
+                    *merged_context.sampling_priority > 0 ? 1u : 0u)
+              : nullopt;
+
+      auto restarted_span = create_span(config);
+      restarted_span.add_link(
+          SpanContext{span_data->trace_id, span_data->parent_id, tracestate,
+                      flags},
+          link_attributes);
+      return restarted_span;
+    }
+    default:
+      // Should be unreachable
+      return Error{
+          Error::NO_SPAN_TO_EXTRACT,
+          "Ignoring context extraction (propagation_behavior_extract=ignore)"};
+  }
 }
 
 Span Tracer::extract_or_create_span(const DictReader& reader) {