feat(tracing): add DD_TRACE_PROPAGATION_EXTRACT_FIRST

include/datadog/config.h

@@ -22,6 +22,7 @@ enum class ConfigName : char {
   EXTRACTION_STYLES,
   INJECTION_STYLES,
   PROPAGATION_BEHAVIOR_EXTRACT,
+  PROPAGATION_EXTRACT_FIRST,
   STARTUP_LOGS,
   REPORT_TELEMETRY,
   DELEGATE_SAMPLING,

include/datadog/environment.h

@@ -53,6 +53,7 @@ namespace environment {
   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_EXTRACT_FIRST, BOOLEAN, false)                    \
   MACRO(DD_TRACE_PROPAGATION_STYLE_EXTRACT, ARRAY,                             \
         "datadog,tracecontext,baggage")                                        \
   MACRO(DD_TRACE_PROPAGATION_STYLE_INJECT, ARRAY,                              \

include/datadog/tracer.h

@@ -48,6 +48,7 @@ class Tracer {
   std::vector<PropagationStyle> injection_styles_;
   std::vector<PropagationStyle> extraction_styles_;
   PropagationBehaviorExtract propagation_behavior_extract_;
+  bool propagation_extract_first_;
   Optional<std::string> hostname_;
   std::size_t tags_header_max_size_;
   // Store the tracer configuration in an in-memory file, allowing it to be

include/datadog/tracer_config.h

@@ -116,6 +116,11 @@ struct TracerConfig {
   // DD_TRACE_PROPAGATION_BEHAVIOR_EXTRACT
   Optional<PropagationBehaviorExtract> propagation_behavior_extract;
 
+  // `propagation_extract_first` indicates whether extraction stops after the
+  // first successful trace context. Overridden by
+  // DD_TRACE_PROPAGATION_EXTRACT_FIRST.
+  Optional<bool> propagation_extract_first;
+
   // `report_hostname` indicates whether the tracer will include the result of
   // `gethostname` with traces sent to the collector.
   Optional<bool> report_hostname;
@@ -234,6 +239,7 @@ class FinalizedTracerConfig final {
   std::vector<PropagationStyle> extraction_styles;
 
   PropagationBehaviorExtract propagation_behavior_extract;
+  bool propagation_extract_first;
 
   bool report_hostname;
   std::size_t tags_header_size;

src/datadog/telemetry/telemetry_impl.cpp

@@ -94,6 +94,8 @@ std::string to_string(datadog::tracing::ConfigName name) {
       return "trace_propagation_style_inject";
     case ConfigName::PROPAGATION_BEHAVIOR_EXTRACT:
       return "trace_propagation_behavior_extract";
+    case ConfigName::PROPAGATION_EXTRACT_FIRST:
+      return "trace_propagation_extract_first";
     case ConfigName::STARTUP_LOGS:
       return "trace_startup_logs_enabled";
     case ConfigName::REPORT_TELEMETRY:

src/datadog/tracer.cpp

@@ -64,6 +64,7 @@ Tracer::Tracer(const FinalizedTracerConfig& config,
       injection_styles_(config.injection_styles),
       extraction_styles_(config.extraction_styles),
       propagation_behavior_extract_(config.propagation_behavior_extract),
+      propagation_extract_first_(config.propagation_extract_first),
       tags_header_max_size_(config.tags_header_size),
       baggage_opts_(config.baggage_opts),
       baggage_injection_enabled_(false),
@@ -309,7 +310,8 @@ Expected<Span> Tracer::extract_span(const DictReader& reader,
     telemetry::counter::increment(metrics::tracer::trace_context::extracted,
                                   {extracted_tag});
 
-    if (!first_style_with_trace_id && data->trace_id.has_value()) {
+    const bool extracted_trace_context = data->trace_id.has_value();
+    if (!first_style_with_trace_id && extracted_trace_context) {
       first_style_with_trace_id = style;
     }
 
@@ -319,6 +321,10 @@ Expected<Span> Tracer::extract_span(const DictReader& reader,
 
     data->headers_examined = audited_reader.entries_found;
     extracted_contexts.emplace(style, std::move(*data));
+
+    if (propagation_extract_first_ && extracted_trace_context) {
+      break;
+    }
   }
 
   ExtractedData merged_context;

src/datadog/tracer_config.cpp

@@ -243,6 +243,11 @@ Expected<TracerConfig> load_tracer_env_config(Logger &logger) {
         propagation_behavior_extract.value());
   }
 
+  if (auto propagation_extract_first =
+          lookup(environment::DD_TRACE_PROPAGATION_EXTRACT_FIRST)) {
+    env_cfg.propagation_extract_first = !falsy(*propagation_extract_first);
+  }
+
   try {
     const auto global_styles =
         styles_from_env(environment::DD_TRACE_PROPAGATION_STYLE);
@@ -421,6 +426,12 @@ Expected<FinalizedTracerConfig> finalize_config(const TracerConfig &user_config,
         return std::string{to_string_view(behavior)};
       });
 
+  final_config.propagation_extract_first = resolve_and_record_config(
+      env_config->propagation_extract_first,
+      user_config.propagation_extract_first, &final_config.metadata,
+      ConfigName::PROPAGATION_EXTRACT_FIRST, false,
+      [](const bool &value) { return to_string(value); });
+
   final_config.runtime_id = user_config.runtime_id;
   final_config.root_session_id = user_config.root_session_id;
   final_config.process_tags = user_config.process_tags;

supported-configurations.json

@@ -210,6 +210,13 @@
         "type": "string"
       }
     ],
+    "DD_TRACE_PROPAGATION_EXTRACT_FIRST": [
+      {
+        "default": "false",
+        "implementation": "A",
+        "type": "boolean"
+      }
+    ],
     "DD_TRACE_PROPAGATION_STYLE": [
       {
         "default": "datadog,tracecontext,baggage",

test/test_tracer.cpp

@@ -31,6 +31,7 @@
 #include <type_traits>
 #include <utility>
 
+#include "common/environment.h"
 #include "matchers.h"
 #include "mocks/collectors.h"
 #include "mocks/dict_readers.h"
@@ -70,6 +71,9 @@ TEST_TRACER("tracer span defaults") {
   config.name = "test.thing";
   config.tags = {{"some.thing", "thing value"},
                  {"another.thing", "another value"}};
+  // The test does not cover telemetry. Disabling it prevents an asynchronous
+  // request to a local agent from racing the logger assertion below.
+  config.telemetry.enabled = false;
 
   const auto collector = std::make_shared<MockCollector>();
   config.collector = collector;
@@ -1545,6 +1549,32 @@ TEST_TRACER("span extraction") {
   }
 }
 
+TEST_TRACER(
+    "extract first tries later styles after an unsuccessful extraction") {
+  const datadog::test::EnvGuard guard{"DD_TRACE_PROPAGATION_EXTRACT_FIRST",
+                                      "true"};
+  TracerConfig config;
+  config.service = "testsvc";
+  config.collector = std::make_shared<NullCollector>();
+  config.telemetry.enabled = false;
+  config.extraction_styles = std::vector<PropagationStyle>{
+      PropagationStyle::DATADOG, PropagationStyle::W3C};
+
+  const auto finalized_config = finalize_config(config);
+  REQUIRE(finalized_config);
+  Tracer tracer{*finalized_config};
+
+  const std::unordered_map<std::string, std::string> headers{
+      {"traceparent",
+       "00-00000000000000000000000000000001-0000000000000002-01"},
+  };
+
+  MockDictReader reader{headers};
+  const auto span = tracer.extract_span(reader);
+  REQUIRE(span);
+  CHECK(span->parent_id() == 2);
+}
+
 TEST_TRACER("continue extraction resumes the extracted trace") {
   TracerConfig config;
   config.service = "testsvc";
@@ -2019,6 +2049,7 @@ TEST_TRACER("heterogeneous extraction") {
     std::vector<PropagationStyle> injection_styles;
     std::unordered_map<std::string, std::string> extracted_headers;
     std::unordered_map<std::string, std::string> expected_injected_headers;
+    bool extract_first = false;
   };
 
   // clang-format off
@@ -2041,6 +2072,17 @@ TEST_TRACER("heterogeneous extraction") {
      {{"traceparent", "00-00000000000000000000000000000030-000000000000002a-01"},
       {"tracestate", "dd=s:2;p:000000000000002a;o:Kansas;ah:choo,competitor=stuff"}}},
 
+    {__LINE__, "extract first ignores tracestate from subsequent style",
+     {PropagationStyle::DATADOG, PropagationStyle::W3C},
+     {PropagationStyle::W3C},
+     {{"x-datadog-trace-id", "48"}, {"x-datadog-parent-id", "64"},
+      {"x-datadog-origin", "Kansas"}, {"x-datadog-sampling-priority", "2"},
+      {"traceparent", "00-00000000000000000000000000000030-0000000000000040-01"},
+      {"tracestate", "competitor=stuff,dd=o:Nebraska;s:1;ah:choo"}},
+     {{"traceparent", "00-00000000000000000000000000000030-000000000000002a-01"},
+      {"tracestate", "dd=s:2;p:000000000000002a;o:Kansas"}},
+     true},
+
     {__LINE__, "ignore interlopers",
      {PropagationStyle::DATADOG, PropagationStyle::B3, PropagationStyle::W3C},
      {PropagationStyle::W3C},
@@ -2087,8 +2129,12 @@ TEST_TRACER("heterogeneous extraction") {
   config.service = "testsvc";
   config.extraction_styles = test_case.extraction_styles;
   config.injection_styles = test_case.injection_styles;
+  config.telemetry.enabled = false;
   config.logger = std::make_shared<NullLogger>();
 
+  const datadog::test::EnvGuard extract_first{
+      "DD_TRACE_PROPAGATION_EXTRACT_FIRST",
+      test_case.extract_first ? "true" : "false"};
   auto finalized_config = finalize_config(config);
   REQUIRE(finalized_config);
   Tracer tracer{*finalized_config, std::make_shared<MockIDGenerator>()};

test/test_tracer_config.cpp

@@ -1378,6 +1378,55 @@ TRACER_CONFIG_TEST("TracerConfig propagation behavior extract") {
   }
 }
 
+TRACER_CONFIG_TEST("TracerConfig propagation extract first") {
+  TracerConfig config;
+  config.service = "testsvc";
+
+  const auto extract_first_metadata =
+      [](const FinalizedTracerConfig& finalized) {
+        return finalized.metadata.at(ConfigName::PROPAGATION_EXTRACT_FIRST);
+      };
+
+  SECTION("defaults to false") {
+    const auto finalized = finalize_config(config);
+    REQUIRE(finalized);
+    CHECK_FALSE(finalized->propagation_extract_first);
+
+    const auto& metadata = extract_first_metadata(*finalized);
+    REQUIRE(metadata.size() == 1);
+    CHECK(metadata.back().origin == ConfigMetadata::Origin::DEFAULT);
+    CHECK(metadata.back().value == "false");
+  }
+
+  SECTION("uses programmatic configuration") {
+    config.propagation_extract_first = true;
+
+    const auto finalized = finalize_config(config);
+    REQUIRE(finalized);
+    CHECK(finalized->propagation_extract_first);
+
+    const auto& metadata = extract_first_metadata(*finalized);
+    REQUIRE(metadata.size() == 2);
+    CHECK(metadata.back().origin == ConfigMetadata::Origin::CODE);
+    CHECK(metadata.back().value == "true");
+  }
+
+  SECTION("environment configuration overrides programmatic configuration") {
+    const EnvGuard guard{"DD_TRACE_PROPAGATION_EXTRACT_FIRST", "true"};
+    config.propagation_extract_first = false;
+
+    const auto finalized = finalize_config(config);
+    REQUIRE(finalized);
+    CHECK(finalized->propagation_extract_first);
+
+    const auto& metadata = extract_first_metadata(*finalized);
+    REQUIRE(metadata.size() == 3);
+    CHECK(metadata.back().origin ==
+          ConfigMetadata::Origin::ENVIRONMENT_VARIABLE);
+    CHECK(metadata.back().value == "true");
+  }
+}
+
 TRACER_CONFIG_TEST("configure 128-bit trace IDs") {
   TracerConfig config;
   config.service = "testsvc";