fix(core): Fix last parent id injection into trace state

Author: PerfectSlayer

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

@@ -1,5 +1,6 @@
 package datadog.trace.core;
 
+import static datadog.trace.api.DDTags.PARENT_ID;
 import static datadog.trace.api.DDTags.SPAN_LINKS;
 import static datadog.trace.api.cache.RadixTreeCache.HTTP_STATUSES;
 import static datadog.trace.bootstrap.instrumentation.api.ErrorPriorities.UNSET;
@@ -145,7 +146,6 @@ public class DDSpanContext
   private volatile int encodedOperationName;
   private volatile int encodedResourceName;
   private volatile CharSequence lastParentId;
-  private final boolean isRemote;
 
   /**
    * Metastruct keys are associated to the current span, they will not propagate to the children
@@ -196,8 +196,7 @@ public DDSpanContext(
         disableSamplingMechanismValidation,
         propagationTags,
         ProfilingContextIntegration.NoOp.INSTANCE,
-        true,
-        false);
+        true);
   }
 
   public DDSpanContext(
@@ -243,8 +242,7 @@ public DDSpanContext(
         disableSamplingMechanismValidation,
         propagationTags,
         ProfilingContextIntegration.NoOp.INSTANCE,
-        injectBaggageAsTags,
-        false);
+        injectBaggageAsTags);
   }
 
   public DDSpanContext(
@@ -290,8 +288,7 @@ public DDSpanContext(
         disableSamplingMechanismValidation,
         propagationTags,
         profilingContextIntegration,
-        true,
-        false);
+        true);
   }
 
   public DDSpanContext(
@@ -316,8 +313,7 @@ public DDSpanContext(
       final boolean disableSamplingMechanismValidation,
       final PropagationTags propagationTags,
       final ProfilingContextIntegration profilingContextIntegration,
-      final boolean injectBaggageAsTags,
-      final boolean isRemote) {
+      final boolean injectBaggageAsTags) {
 
     assert traceCollector != null;
     this.traceCollector = traceCollector;
@@ -376,8 +372,7 @@ public DDSpanContext(
     if (samplingPriority != PrioritySampling.UNSET) {
       setSamplingPriority(samplingPriority, SamplingMechanism.UNKNOWN);
     }
-    setLastParentId(this.propagationTags.getLastParentId());
-    this.isRemote = isRemote;
+    setTag(PARENT_ID, this.propagationTags.getLastParentId());
   }
 
   @Override
@@ -1055,20 +1050,8 @@ public void setMetaStructCurrent(String field, Object value) {
     setMetaStruct(field, value);
   }
 
-  public CharSequence getLastParentId() {
-    return lastParentId;
-  }
-
-  public void setLastParentId(CharSequence lastParentId) {
-    if (lastParentId != null) {
-      synchronized (unsafeTags) {
-        unsafeSetTag("_dd.parent_id", lastParentId);
-      }
-      this.lastParentId = lastParentId;
-    }
-  }
-
+  @Override
   public boolean isRemote() {
-    return isRemote;
+    return false;
   }
 }

dd-trace-core/src/main/java/datadog/trace/core/propagation/W3CHttpCodec.java

@@ -81,17 +81,7 @@ private <C> void injectTraceParent(DDSpanContext context, C carrier, CarrierSett
 
     private <C> void injectTraceState(DDSpanContext context, C carrier, CarrierSetter<C> setter) {
       PropagationTags propagationTags = context.getPropagationTags();
-      if (propagationTags.getLastParentId() == null) {
-        if (context.isRemote()) {
-          CharSequence lastParentId = context.getLastParentId();
-          if (lastParentId != null) {
-            propagationTags.updateLastParentId(lastParentId);
-          }
-        } else {
-          propagationTags.updateLastParentId(DDSpanId.toHexStringPadded(context.getSpanId()));
-        }
-      }
-
+      propagationTags.updateLastParentId(DDSpanId.toHexStringPadded(context.getSpanId()));
       String tracestate = propagationTags.headerValue(W3C);
       if (tracestate != null && !tracestate.isEmpty()) {
         setter.set(carrier, TRACE_STATE_KEY, tracestate);

dd-trace-core/src/test/groovy/datadog/trace/core/CoreSpanBuilderTest.groovy

@@ -374,9 +374,7 @@ class CoreSpanBuilderTest extends DDCoreSpecification {
     span.traceId != extractedContext.traceId
     span.parentId != extractedContext.spanId
     span.samplingPriority() == PrioritySampling.UNSET
-
-
-    assert span.links.size() == 0
+    span.links.empty
   }
 
   def "TagContext should populate default span details"() {

dd-trace-core/src/test/groovy/datadog/trace/core/test/DDCoreSpecification.groovy

@@ -81,8 +81,7 @@ abstract class DDCoreSpecification extends DDSpecification {
       false,
       propagationTags,
       ProfilingContextIntegration.NoOp.INSTANCE,
-      true,
-      false)
+      true)
 
     def span = DDSpan.create("test", timestamp, context, null)
     for (Map.Entry<String, Object> e : tags.entrySet()) {