Do not allocate a tracing context when not fully extracted

Author: amarziali

dd-java-agent/instrumentation/opentelemetry/opentelemetry-1.4/src/test/groovy/opentelemetry14/context/propagation/AbstractPropagatorTest.groovy

@@ -4,6 +4,7 @@ import datadog.trace.agent.test.InstrumentationSpecification
 import datadog.trace.api.DDSpanId
 import datadog.trace.api.DDTraceId
 import io.opentelemetry.api.GlobalOpenTelemetry
+import io.opentelemetry.api.trace.Span
 import io.opentelemetry.context.Context
 import io.opentelemetry.context.ThreadLocalContextStorage
 import io.opentelemetry.context.propagation.TextMapPropagator
@@ -102,6 +103,14 @@ abstract class AbstractPropagatorTest extends InstrumentationSpecification {
     (headers, traceId, spanId, sampling) = values
   }
 
+  def "extraction on missing tracecontext should return an empty context"() {
+    when:
+    def headers = ["User-Agent":"test"]
+    def context = propagator().extract(Context.root(), headers, TextMap.INSTANCE)
+    then:
+    assert Span.fromContextOrNull(context) == null : "Should not have a tracing context"
+  }
+
   def expectedTraceId(String traceId) {
     return DDTraceId.fromHex(traceId)
   }

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

@@ -67,7 +67,7 @@ public <C> Context extract(Context context, C carrier, CarrierVisitor<C> visitor
     }
     TagContext spanContext = this.extractor.extract(carrier, toContextVisitor(visitor));
     // If the extraction fails, return the original context
-    if (spanContext == null) {
+    if (!(spanContext instanceof ExtractedContext)) {
       return context;
     }
     // Otherwise, append a fake span wrapper to context