fix(config visibility): fix system test related to reporting of trace sampler and span sampler (#272)

* Report trace sampler

* Report span sampler values

* answer to comment, merge instead of passing by ref

* Add more asserts in unit tests

* answer to comments

* rename telemetry_configs to metadata and remove old metadata

Author: anna-git

include/datadog/config.h

@@ -63,11 +63,12 @@ struct ConfigMetadata {
 };
 
 // Returns the final configuration value using the following
-// precedence order: environment > user code > default, and populates two maps:
-// 1. `telemetry_configs`: Records ALL configuration sources that were provided,
-//    ordered from lowest to highest precedence.
-// 2. `metadata`: Records ONLY the winning configuration value (highest
-// precedence). Template Parameters:
+// precedence order: environment > user code > default, and populates metadata:
+// `metadata`: Records ALL configuration sources that were provided,
+//    ordered from lowest to highest precedence. The last entry has the highest
+//    precedence and is the winning value.
+//
+// Template Parameters:
 //   Value: The type of the configuration value
 //   Stringifier: Optional function type to convert Value to string
 //                (defaults to std::nullptr_t, which uses string construction)
@@ -76,10 +77,8 @@ struct ConfigMetadata {
 // Parameters:
 //   from_env: Optional value from environment variables (highest precedence)
 //   from_user: Optional value from user code (middle precedence)
-//   telemetry_configs: Output map that will be populated with all config
-//                      sources found for this config_name, in precedence order
-//   metadata: Output map that will be populated with the winning config value
-//             for this config_name
+//   metadata: Output map that will be populated with all config sources found
+//             for this config_name, in precedence order (last = highest)
 //   config_name: The configuration parameter name identifier
 //   fallback: Optional default value (lowest precedence). Pass nullptr to
 //             indicate no default.
@@ -94,9 +93,7 @@ template <typename Value, typename Stringifier = std::nullptr_t,
           typename DefaultValue = std::nullptr_t>
 Value resolve_and_record_config(
     const Optional<Value>& from_env, const Optional<Value>& from_user,
-    std::unordered_map<ConfigName, std::vector<ConfigMetadata>>*
-        telemetry_configs,
-    std::unordered_map<ConfigName, ConfigMetadata>* metadata,
+    std::unordered_map<ConfigName, std::vector<ConfigMetadata>>* metadata,
     ConfigName config_name, DefaultValue fallback = nullptr,
     Stringifier to_string_fn = nullptr) {
   auto stringify = [&](const Value& v) -> std::string {
@@ -111,13 +108,12 @@ Value resolve_and_record_config(
     }
   };
 
-  std::vector<ConfigMetadata> telemetry_entries;
+  std::vector<ConfigMetadata> metadata_entries;
   Optional<Value> chosen_value;
 
   auto add_entry = [&](ConfigMetadata::Origin origin, const Value& val) {
     std::string val_str = stringify(val);
-    telemetry_entries.emplace_back(
-        ConfigMetadata{config_name, val_str, origin});
+    metadata_entries.emplace_back(ConfigMetadata{config_name, val_str, origin});
     chosen_value = val;
   };
 
@@ -134,9 +130,8 @@ Value resolve_and_record_config(
     add_entry(ConfigMetadata::Origin::ENVIRONMENT_VARIABLE, *from_env);
   }
 
-  (*telemetry_configs)[config_name] = std::move(telemetry_entries);
-  if (!(*telemetry_configs)[config_name].empty()) {
-    (*metadata)[config_name] = (*telemetry_configs)[config_name].back();
+  if (!metadata_entries.empty()) {
+    (*metadata)[config_name] = std::move(metadata_entries);
   }
 
   return chosen_value.value_or(Value{});

include/datadog/datadog_agent_config.h

@@ -85,7 +85,7 @@ class FinalizedDatadogAgentConfig {
   std::chrono::steady_clock::duration request_timeout;
   std::chrono::steady_clock::duration shutdown_timeout;
   std::chrono::steady_clock::duration remote_configuration_poll_interval;
-  std::unordered_map<ConfigName, ConfigMetadata> metadata;
+  std::unordered_map<ConfigName, std::vector<ConfigMetadata>> metadata;
 
   // Origin detection
   Optional<std::string> admission_controller_uid;

include/datadog/span_sampler_config.h

@@ -49,7 +49,7 @@ class FinalizedSpanSamplerConfig {
   };
 
   std::vector<Rule> rules;
-  std::unordered_map<ConfigName, ConfigMetadata> metadata;
+  std::unordered_map<ConfigName, std::vector<ConfigMetadata>> metadata;
 };
 
 Expected<FinalizedSpanSamplerConfig> finalize_config(const SpanSamplerConfig&,

include/datadog/trace_sampler_config.h

@@ -50,7 +50,7 @@ class FinalizedTraceSamplerConfig {
  public:
   double max_per_second;
   std::vector<TraceSamplerRule> rules;
-  std::unordered_map<ConfigName, ConfigMetadata> metadata;
+  std::unordered_map<ConfigName, std::vector<ConfigMetadata>> metadata;
 
  public:
   /// Returns the trace sampler configuration when APM Tracing is disabled.

include/datadog/tracer_config.h

@@ -229,7 +229,7 @@ class FinalizedTracerConfig final {
   std::string integration_name;
   std::string integration_version;
   bool report_traces;
-  std::unordered_map<ConfigName, ConfigMetadata> metadata;
+  std::unordered_map<ConfigName, std::vector<ConfigMetadata>> metadata;
   Baggage::Options baggage_opts;
   HTTPClient::URL agent_url;
   std::shared_ptr<EventScheduler> event_scheduler;

src/datadog/config_manager.cpp

@@ -287,12 +287,18 @@ namespace rc = datadog::remote_config;
 
 ConfigManager::ConfigManager(const FinalizedTracerConfig& config)
     : clock_(config.clock),
-      default_metadata_(config.metadata),
       trace_sampler_(
           std::make_shared<TraceSampler>(config.trace_sampler, clock_)),
       rules_(config.trace_sampler.rules),
       span_defaults_(std::make_shared<SpanDefaults>(config.defaults)),
-      report_traces_(config.report_traces) {}
+      report_traces_(config.report_traces) {
+  // Extract winning value (last entry) from each config's metadata history
+  for (const auto& [name, metadata_vec] : config.metadata) {
+    if (!metadata_vec.empty()) {
+      default_metadata_[name] = metadata_vec.back();
+    }
+  }
+}
 
 rc::Products ConfigManager::get_products() { return rc::product::APM_TRACING; }
 

src/datadog/datadog_agent_config.cpp

@@ -142,8 +142,8 @@ Expected<FinalizedDatadogAgentConfig> finalize_config(
     return std::move(*error);
   }
   result.url = *parsed_url;
-  result.metadata[ConfigName::AGENT_URL] =
-      ConfigMetadata(ConfigName::AGENT_URL, url, origin);
+  result.metadata[ConfigName::AGENT_URL] = {
+      ConfigMetadata(ConfigName::AGENT_URL, url, origin)};
 
   // Starting Datadog Agent 7.62.0, the admission controller inject a unique
   // identifier through `DD_EXTERNAL_ENV`. This uid is used for origin

src/datadog/span_sampler_config.cpp

@@ -228,20 +228,21 @@ Expected<FinalizedSpanSamplerConfig> finalize_config(
   }
 
   FinalizedSpanSamplerConfig result;
-
-  std::vector<SpanSamplerConfig::Rule> rules;
+  Optional<std::vector<SpanSamplerConfig::Rule>> env_rules;
+  Optional<std::vector<SpanSamplerConfig::Rule>> user_rules;
   if (!env_config->rules.empty()) {
-    rules = env_config->rules;
-    result.metadata[ConfigName::SPAN_SAMPLING_RULES] =
-        ConfigMetadata(ConfigName::SPAN_SAMPLING_RULES, to_string(rules),
-                       ConfigMetadata::Origin::ENVIRONMENT_VARIABLE);
-  } else if (!user_config.rules.empty()) {
-    rules = user_config.rules;
-    result.metadata[ConfigName::SPAN_SAMPLING_RULES] =
-        ConfigMetadata(ConfigName::SPAN_SAMPLING_RULES, to_string(rules),
-                       ConfigMetadata::Origin::CODE);
+    env_rules = env_config->rules;
+  }
+  if (!user_config.rules.empty()) {
+    user_rules = user_config.rules;
   }
 
+  std::vector<SpanSamplerConfig::Rule> rules = resolve_and_record_config(
+      env_rules, user_rules, &result.metadata, ConfigName::SPAN_SAMPLING_RULES,
+      nullptr, [](const std::vector<SpanSamplerConfig::Rule> &r) {
+        return to_string(r);
+      });
+
   for (const auto &rule : rules) {
     auto maybe_rate = Rate::from(rule.sample_rate);
     if (auto *error = maybe_rate.if_error()) {
@@ -276,7 +277,6 @@ Expected<FinalizedSpanSamplerConfig> finalize_config(
     finalized.max_per_second = rule.max_per_second;
     result.rules.push_back(std::move(finalized));
   }
-
   return result;
 }
 

src/datadog/trace_sampler_config.cpp

@@ -162,14 +162,14 @@ Expected<FinalizedTraceSamplerConfig> finalize_config(
 
   if (!env_config->rules.empty()) {
     rules = std::move(env_config->rules);
-    result.metadata[ConfigName::TRACE_SAMPLING_RULES] =
+    result.metadata[ConfigName::TRACE_SAMPLING_RULES] = {
         ConfigMetadata(ConfigName::TRACE_SAMPLING_RULES, to_string(rules),
-                       ConfigMetadata::Origin::ENVIRONMENT_VARIABLE);
+                       ConfigMetadata::Origin::ENVIRONMENT_VARIABLE)};
   } else if (!config.rules.empty()) {
     rules = std::move(config.rules);
-    result.metadata[ConfigName::TRACE_SAMPLING_RULES] =
+    result.metadata[ConfigName::TRACE_SAMPLING_RULES] = {
         ConfigMetadata(ConfigName::TRACE_SAMPLING_RULES, to_string(rules),
-                       ConfigMetadata::Origin::CODE);
+                       ConfigMetadata::Origin::CODE)};
   }
 
   for (const auto &rule : rules) {
@@ -191,27 +191,16 @@ Expected<FinalizedTraceSamplerConfig> finalize_config(
     result.rules.emplace_back(std::move(finalized_rule));
   }
 
-  Optional<double> sample_rate;
-  if (env_config->sample_rate) {
-    sample_rate = env_config->sample_rate;
-    result.metadata[ConfigName::TRACE_SAMPLING_RATE] = ConfigMetadata(
-        ConfigName::TRACE_SAMPLING_RATE, to_string(*sample_rate, 1),
-        ConfigMetadata::Origin::ENVIRONMENT_VARIABLE);
-  } else if (config.sample_rate) {
-    sample_rate = config.sample_rate;
-    result.metadata[ConfigName::TRACE_SAMPLING_RATE] = ConfigMetadata(
-        ConfigName::TRACE_SAMPLING_RATE, to_string(*sample_rate, 1),
-        ConfigMetadata::Origin::CODE);
-  } else {
-    result.metadata[ConfigName::TRACE_SAMPLING_RATE] =
-        ConfigMetadata(ConfigName::TRACE_SAMPLING_RATE, "1.0",
-                       ConfigMetadata::Origin::DEFAULT);
-  }
+  Optional<double> sample_rate = resolve_and_record_config(
+      env_config->sample_rate, config.sample_rate, &result.metadata,
+      ConfigName::TRACE_SAMPLING_RATE, 1.0,
+      [](const double &d) { return to_string(d, 1); });
 
+  bool is_sample_rate_provided = env_config->sample_rate || config.sample_rate;
   // If `sample_rate` was specified, then it translates to a "catch-all" rule
   // appended to the end of `rules`. First, though, we have to make sure the
   // sample rate is valid.
-  if (sample_rate) {
+  if (sample_rate && is_sample_rate_provided) {
     auto maybe_rate = Rate::from(*sample_rate);
     if (auto *error = maybe_rate.if_error()) {
       return error->with_prefix(
@@ -225,11 +214,9 @@ Expected<FinalizedTraceSamplerConfig> finalize_config(
     result.rules.emplace_back(std::move(finalized_rule));
   }
 
-  std::unordered_map<ConfigName, std::vector<ConfigMetadata>>
-      telemetry_configs_tmp;
   double max_per_second = resolve_and_record_config(
-      env_config->max_per_second, config.max_per_second, &telemetry_configs_tmp,
-      &result.metadata, ConfigName::TRACE_SAMPLING_LIMIT, 100.0,
+      env_config->max_per_second, config.max_per_second, &result.metadata,
+      ConfigName::TRACE_SAMPLING_LIMIT, 100.0,
       [](const double &d) { return std::to_string(d); });
 
   const auto allowed_types = {FP_NORMAL, FP_SUBNORMAL};