feat(core): Refactor disabled tracing propagator

Author: PerfectSlayer

dd-trace-core/src/main/java/datadog/trace/core/CoreTracer.java

@@ -6,7 +6,6 @@
 import static datadog.trace.api.DDTags.DSM_ENABLED;
 import static datadog.trace.api.DDTags.PROFILING_CONTEXT_ENGINE;
 import static datadog.trace.bootstrap.instrumentation.api.AgentPropagation.DSM_CONCERN;
-import static datadog.trace.bootstrap.instrumentation.api.AgentPropagation.STANDALONE_ASM_CONCERN;
 import static datadog.trace.bootstrap.instrumentation.api.AgentPropagation.TRACING_CONCERN;
 import static datadog.trace.bootstrap.instrumentation.api.AgentPropagation.XRAY_TRACING_CONCERN;
 import static datadog.trace.common.metrics.MetricsAggregatorFactory.createMetricsAggregator;
@@ -85,7 +84,6 @@
 import datadog.trace.core.monitor.HealthMetrics;
 import datadog.trace.core.monitor.MonitoringImpl;
 import datadog.trace.core.monitor.TracerHealthMetrics;
-import datadog.trace.core.propagation.ApmTracingDisabledPropagator;
 import datadog.trace.core.propagation.ExtractedContext;
 import datadog.trace.core.propagation.HttpCodec;
 import datadog.trace.core.propagation.PropagationTags;
@@ -714,19 +712,11 @@ private CoreTracer(
     // Register context propagators
     HttpCodec.Extractor tracingExtractor =
         extractor == null ? HttpCodec.createExtractor(config, this::captureTraceConfig) : extractor;
-    TracingPropagator tracingPropagator = new TracingPropagator(injector, tracingExtractor);
-    // Check if apm tracing is disabled:
-    // If disabled, use the APM tracing disabled propagator by default that will limit tracing
-    // concern
-    // injection and delegate to the tracing propagator if needed,
-    // If disabled, the most common case, use the usual tracing propagator by default.
-    boolean apmTracingDisabled = !config.isApmTracingEnabled();
-    boolean dsm = config.isDataStreamsEnabled();
-    Propagators.register(
-        STANDALONE_ASM_CONCERN, new ApmTracingDisabledPropagator(), apmTracingDisabled);
-    Propagators.register(TRACING_CONCERN, tracingPropagator, !apmTracingDisabled);
+    TracingPropagator tracingPropagator =
+        new TracingPropagator(config.isApmTracingEnabled(), injector, tracingExtractor);
+    Propagators.register(TRACING_CONCERN, tracingPropagator);
     Propagators.register(XRAY_TRACING_CONCERN, new XRayPropagator(config), false);
-    if (dsm) {
+    if (config.isDataStreamsEnabled()) {
       Propagators.register(DSM_CONCERN, this.dataStreamsMonitoring.propagator());
     }
 

dd-trace-core/src/main/java/datadog/trace/core/propagation/ApmTracingDisabledPropagator.java

@@ -1,5 +1,6 @@
 package datadog.trace.core.propagation;
 
+import static datadog.trace.api.ProductTraceSource.UNSET;
 import static datadog.trace.bootstrap.instrumentation.api.AgentSpan.fromContext;
 import static datadog.trace.bootstrap.instrumentation.api.AgentSpan.fromSpanContext;
 
@@ -19,16 +20,19 @@
 /** Propagator for tracing concern. */
 @ParametersAreNonnullByDefault
 public class TracingPropagator implements Propagator {
+  private final boolean enabled;
   private final Injector injector;
   private final Extractor extractor;
 
   /**
    * Constructor.
    *
+   * @param enabled Whether APM tracing is enabled.
    * @param injector The {@link Injector} used for tracing context injection.
    * @param extractor The {@link Extractor} used for tracing context extraction.
    */
-  public TracingPropagator(Injector injector, Extractor extractor) {
+  public TracingPropagator(boolean enabled, Injector injector, Extractor extractor) {
+    this.enabled = enabled;
     this.injector = injector;
     this.extractor = extractor;
   }
@@ -46,8 +50,12 @@ public <C> void inject(Context context, C carrier, CarrierSetter<C> setter) {
     AgentSpanContext spanContext = span.context();
     if (spanContext instanceof DDSpanContext) {
       DDSpanContext ddSpanContext = (DDSpanContext) spanContext;
+      // Stop injection if tracing is disabled and tracing span is coming from tracing only
+      if (!this.enabled && ddSpanContext.getPropagationTags().getTraceSource() == UNSET) {
+        return;
+      }
       ddSpanContext.getTraceCollector().setSamplingPriorityIfNecessary();
-      this.injector.inject(ddSpanContext, carrier, setter::set);
+      this.injector.inject(ddSpanContext, carrier, setter);
     }
   }