Account for Sampled=0 trace header in Active mode

aws-xray-recorder-sdk-apache-http/src/main/java/com/amazonaws/xray/proxies/apache/http/TracedHttpClient.java

@@ -18,6 +18,7 @@
 import com.amazonaws.xray.AWSXRay;
 import com.amazonaws.xray.AWSXRayRecorder;
 import com.amazonaws.xray.entities.Namespace;
+import com.amazonaws.xray.entities.NoOpSubSegment;
 import com.amazonaws.xray.entities.Segment;
 import com.amazonaws.xray.entities.Subsegment;
 import com.amazonaws.xray.entities.TraceHeader;
@@ -104,15 +105,15 @@ public static void addRequestInformation(Subsegment subsegment, HttpRequest requ
         Segment parentSegment = subsegment.getParentSegment();
 
         if (subsegment.shouldPropagate()) {
-            // If the trace is not sampled, passing Parent and Sampled won't matter
+            // If no-op, only propagate root trace ID to not taint sampling decision
             TraceHeader t = TraceHeader.fromEntity(subsegment);
-            if (t.getSampled() != TraceHeader.SampleDecision.SAMPLED) {
+            if (subsegment instanceof NoOpSubSegment) {
                 request.addHeader(
                         TraceHeader.HEADER_KEY,
                         "Root=" + t.getRootTraceId().toString());
             } else {
                 // This will propagate Parent and Sampled
-                request.addHeader(TraceHeader.HEADER_KEY, TraceHeader.fromEntity(subsegment).toString());
+                request.addHeader(TraceHeader.HEADER_KEY, t.toString());
             }
         }
 

aws-xray-recorder-sdk-apache-http/src/test/java/com/amazonaws/xray/proxies/apache/http/TracedHttpClientTest.java

@@ -114,7 +114,7 @@ public void unsampledButForcedPropagation() throws Exception {
 
         verify(getRequestedFor(urlPathEqualTo("/"))
                    .withHeader(TraceHeader.HEADER_KEY,
-                               equalTo("Root=1-67891233-abcdef012345678912345678")));
+                               equalTo("Root=1-67891233-abcdef012345678912345678;Sampled=0")));
     }
 
     @Test

aws-xray-recorder-sdk-aws-sdk-v2/src/main/java/com/amazonaws/xray/interceptors/TracingInterceptor.java

@@ -21,6 +21,7 @@
 import com.amazonaws.xray.entities.EntityDataKeys;
 import com.amazonaws.xray.entities.EntityHeaderKeys;
 import com.amazonaws.xray.entities.Namespace;
+import com.amazonaws.xray.entities.NoOpSubSegment;
 import com.amazonaws.xray.entities.Subsegment;
 import com.amazonaws.xray.entities.TraceHeader;
 import com.amazonaws.xray.handlers.config.AWSOperationHandler;
@@ -296,9 +297,9 @@ public SdkHttpRequest modifyHttpRequest(Context.ModifyHttpRequest context, Execu
             return httpRequest;
         }
 
-        // If the trace is not sampled, passing Parent and Sampled won't matter
+        // If no-op, only propagate root trace ID to not taint sampling decision
         TraceHeader t = TraceHeader.fromEntity(subsegment);
-        if (t.getSampled() != TraceHeader.SampleDecision.SAMPLED) {
+        if (subsegment instanceof NoOpSubSegment) {
             return httpRequest.toBuilder().putHeader(
                     TraceHeader.HEADER_KEY,
                     "Root=" + t.getRootTraceId().toString()).build();
@@ -307,7 +308,7 @@ public SdkHttpRequest modifyHttpRequest(Context.ModifyHttpRequest context, Execu
         // This will propagate Parent and Sampled
         return httpRequest.toBuilder().putHeader(
                 TraceHeader.HEADER_KEY,
-                TraceHeader.fromEntity(subsegment).toString()).build();
+                t.toString()).build();
     }
 
     @Override

aws-xray-recorder-sdk-aws-sdk/src/main/java/com/amazonaws/xray/handlers/TracingHandler.java

@@ -31,6 +31,7 @@
 import com.amazonaws.xray.entities.EntityDataKeys;
 import com.amazonaws.xray.entities.EntityHeaderKeys;
 import com.amazonaws.xray.entities.Namespace;
+import com.amazonaws.xray.entities.NoOpSubSegment;
 import com.amazonaws.xray.entities.Subsegment;
 import com.amazonaws.xray.entities.TraceHeader;
 import com.amazonaws.xray.handlers.config.AWSOperationHandler;
@@ -192,15 +193,15 @@ public void beforeRequest(Request<?> request) {
         currentSubsegment.setNamespace(Namespace.AWS.toString());
 
         if (recorder.getCurrentSegment() != null && recorder.getCurrentSubsegment().shouldPropagate()) {
-            // If the trace is not sampled, passing Parent and Sampled won't matter
+            // If no-op, only propagate root trace ID to not taint sampling decision
             TraceHeader t = TraceHeader.fromEntity(currentSubsegment);
-            if (t.getSampled() != TraceHeader.SampleDecision.SAMPLED) {
+            if (currentSubsegment instanceof NoOpSubSegment) {
                 request.addHeader(
                         TraceHeader.HEADER_KEY,
                         "Root=" + t.getRootTraceId().toString());
             } else {
                 // This will propagate Parent and Sampled
-                request.addHeader(TraceHeader.HEADER_KEY, TraceHeader.fromEntity(currentSubsegment).toString());
+                request.addHeader(TraceHeader.HEADER_KEY, t.toString());
             }
         }
     }

aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/contexts/LambdaSegmentContext.java

@@ -58,24 +58,20 @@ public Subsegment beginSubsegment(AWSXRayRecorder recorder, String name) {
         Entity entity = getTraceEntity();
         if (entity == null) { // First subsegment of a subsegment branch
             Segment parentSegment;
-            // We rely on the AWS SDK to propagate one or both of these
-            // It is therefore possible to get just Root, or Root and Parent
-            if (traceHeader.getRootTraceId() != null) {
-                if (traceHeader.getParentId() != null) {
-                    parentSegment = new FacadeSegment(
-                        recorder,
-                        traceHeader.getRootTraceId(),
-                        traceHeader.getParentId(),
-                        traceHeader.getSampled());
-                } else {
-                    if (logger.isDebugEnabled()) {
-                        logger.debug("Creating No-Op parent segment");
-                    }
-                    TraceID t = traceHeader.getRootTraceId();
-                    parentSegment = Segment.noOp(t, recorder);
-                }
+            // Trace header either takes the structure `Root=...;<extra-data>` or
+            // `Root=...;Parent=...;Sampled=...;<extra-data>`
+            if (traceHeader.getRootTraceId() != null && traceHeader.getParentId() != null && traceHeader.getSampled() != null) {
+                parentSegment = new FacadeSegment(
+                    recorder,
+                    traceHeader.getRootTraceId(),
+                    traceHeader.getParentId(),
+                    traceHeader.getSampled());
             } else {
-                parentSegment = Segment.noOp(TraceID.create(recorder), recorder);
+                if (logger.isDebugEnabled()) {
+                    logger.debug("Creating No-Op parent segment");
+                }
+                TraceID t = traceHeader.getRootTraceId() != null ? traceHeader.getRootTraceId() : TraceID.create(recorder);
+                parentSegment = Segment.noOp(t, recorder);
             }
 
             boolean isRecording = parentSegment.isRecording();

aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/entities/NoOpSubSegment.java

@@ -25,7 +25,7 @@
 import java.util.concurrent.locks.ReentrantLock;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
-class NoOpSubSegment implements Subsegment {
+public class NoOpSubSegment implements Subsegment {
     private final Segment parentSegment;
     private final AWSXRayRecorder creator;
     private final boolean shouldPropagate;