Support Lambda PassThrough trace header propagation

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

@@ -104,7 +104,16 @@ public static void addRequestInformation(Subsegment subsegment, HttpRequest requ
         Segment parentSegment = subsegment.getParentSegment();
 
         if (subsegment.shouldPropagate()) {
-            request.addHeader(TraceHeader.HEADER_KEY, TraceHeader.fromEntity(subsegment).toString());
+            // If the trace is not sampled, passing Parent and Sampled won't matter
+            TraceHeader t = TraceHeader.fromEntity(subsegment);
+            if (t.getSampled() != TraceHeader.SampleDecision.SAMPLED) {
+                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());
+            }
         }
 
         Map<String, Object> requestInformation = new HashMap<>();

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

@@ -99,7 +99,7 @@ public void unsampledPropagation() throws Exception {
 
         verify(getRequestedFor(urlPathEqualTo("/"))
                    .withHeader(TraceHeader.HEADER_KEY,
-                               equalTo("Root=1-00000000-000000000000000000000000;Sampled=0")));
+                               equalTo("Root=1-00000000-000000000000000000000000")));
     }
 
     @Test
@@ -114,7 +114,7 @@ public void unsampledButForcedPropagation() throws Exception {
 
         verify(getRequestedFor(urlPathEqualTo("/"))
                    .withHeader(TraceHeader.HEADER_KEY,
-                               equalTo("Root=1-67891233-abcdef012345678912345678;Sampled=0")));
+                               equalTo("Root=1-67891233-abcdef012345678912345678")));
     }
 
     @Test

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

@@ -296,6 +296,15 @@ public SdkHttpRequest modifyHttpRequest(Context.ModifyHttpRequest context, Execu
             return httpRequest;
         }
 
+        // If the trace is not sampled, passing Parent and Sampled won't matter
+        TraceHeader t = TraceHeader.fromEntity(subsegment);
+        if (t.getSampled() != TraceHeader.SampleDecision.SAMPLED) {
+            return httpRequest.toBuilder().putHeader(
+                    TraceHeader.HEADER_KEY,
+                    "Root=" + t.getRootTraceId().toString()).build();
+        }
+
+        // This will propagate Parent and Sampled
         return httpRequest.toBuilder().putHeader(
                 TraceHeader.HEADER_KEY,
                 TraceHeader.fromEntity(subsegment).toString()).build();

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

@@ -192,7 +192,16 @@ public void beforeRequest(Request<?> request) {
         currentSubsegment.setNamespace(Namespace.AWS.toString());
 
         if (recorder.getCurrentSegment() != null && recorder.getCurrentSubsegment().shouldPropagate()) {
-            request.addHeader(TraceHeader.HEADER_KEY, TraceHeader.fromEntity(currentSubsegment).toString());
+            // If the trace is not sampled, passing Parent and Sampled won't matter
+            TraceHeader t = TraceHeader.fromEntity(currentSubsegment);
+            if (t.getSampled() != TraceHeader.SampleDecision.SAMPLED) {
+                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());
+            }
         }
     }
 

aws-xray-recorder-sdk-aws-sdk/src/test/java/com/amazonaws/xray/handlers/TracingHandlerLambdaTest.java

@@ -137,10 +137,12 @@ public static void lambdaTestHelper(AWSXRayRecorder recorder, String name, boole
         TraceHeader traceHeader = TraceHeader.fromString(request.getHeaders().get(TraceHeader.HEADER_KEY));
         String serviceEntityId = recorder.getCurrentSubsegment().getId();
 
-        assertThat(traceHeader.getSampled()).isEqualTo(
-                subsegment.isSampled() ?
-                        TraceHeader.SampleDecision.SAMPLED :
-                        TraceHeader.SampleDecision.NOT_SAMPLED);
+        if (subsegment.isSampled()) {
+            assertThat(traceHeader.getSampled()).isEqualTo(TraceHeader.SampleDecision.SAMPLED);
+        } else {
+            // Can't assert non-initialized variable to null, assert absence instead
+            assertThat(traceHeader.toString()).doesNotContain("Sampled=");
+        }
         assertThat(traceHeader.getRootTraceId()).isEqualTo(subsegment.getTraceId());
         assertThat(traceHeader.getParentId()).isEqualTo(subsegment.isSampled() ? serviceEntityId : null);
 

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

@@ -18,11 +18,11 @@
 import com.amazonaws.xray.AWSXRayRecorder;
 import com.amazonaws.xray.entities.Entity;
 import com.amazonaws.xray.entities.FacadeSegment;
+import com.amazonaws.xray.entities.NoOpSegment;
 import com.amazonaws.xray.entities.Segment;
 import com.amazonaws.xray.entities.Subsegment;
 import com.amazonaws.xray.entities.SubsegmentImpl;
 import com.amazonaws.xray.entities.TraceHeader;
-import com.amazonaws.xray.entities.TraceHeader.SampleDecision;
 import com.amazonaws.xray.entities.TraceID;
 import com.amazonaws.xray.exceptions.SubsegmentNotFoundException;
 import com.amazonaws.xray.listeners.SegmentListener;
@@ -39,36 +39,44 @@ public class LambdaSegmentContext implements SegmentContext {
     // See: https://github.com/aws/aws-xray-sdk-java/issues/251
     private static final String LAMBDA_TRACE_HEADER_PROP = "com.amazonaws.xray.traceHeader";
 
-    private static TraceHeader getTraceHeaderFromEnvironment() {
+    public static TraceHeader getTraceHeaderFromEnvironment() {
         String lambdaTraceHeaderKey = System.getenv(LAMBDA_TRACE_HEADER_KEY);
         return TraceHeader.fromString(lambdaTraceHeaderKey != null && lambdaTraceHeaderKey.length() > 0 
             ? lambdaTraceHeaderKey 
             : System.getProperty(LAMBDA_TRACE_HEADER_PROP));
     }
 
-    private static boolean isInitializing(TraceHeader traceHeader) {
-        return traceHeader.getRootTraceId() == null || traceHeader.getSampled() == null || traceHeader.getParentId() == null;
-    }
-
-    private static FacadeSegment newFacadeSegment(AWSXRayRecorder recorder, String name) {
-        TraceHeader traceHeader = getTraceHeaderFromEnvironment();
-        if (isInitializing(traceHeader)) {
-            logger.warn(LAMBDA_TRACE_HEADER_KEY + " is missing a trace ID, parent ID, or sampling decision. Subsegment "
-                        + name + " discarded.");
-            return new FacadeSegment(recorder, TraceID.create(recorder), "", SampleDecision.NOT_SAMPLED);
-        }
-        return new FacadeSegment(recorder, traceHeader.getRootTraceId(), traceHeader.getParentId(), traceHeader.getSampled());
-    }
-
+    // SuppressWarnings is needed for passing Root TraceId to noOp segment
+    @SuppressWarnings("nullness")
     @Override
     public Subsegment beginSubsegment(AWSXRayRecorder recorder, String name) {
         if (logger.isDebugEnabled()) {
             logger.debug("Beginning subsegment named: " + name);
         }
 
+        TraceHeader traceHeader = LambdaSegmentContext.getTraceHeaderFromEnvironment();
         Entity entity = getTraceEntity();
-        if (entity == null) { // First subsgment of a subsegment branch.
-            Segment parentSegment = newFacadeSegment(recorder, name);
+        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);
+                }
+            } else {
+                parentSegment = Segment.noOp(TraceID.create(recorder), recorder);
+            }
 
             boolean isRecording = parentSegment.isRecording();
 
@@ -145,6 +153,8 @@ public void endSubsegment(AWSXRayRecorder recorder) {
                     current.getCreator().getEmitter().sendSubsegment((Subsegment) current);
                 }
                 clearTraceEntity();
+            } else if (parentEntity instanceof NoOpSegment) {
+                clearTraceEntity();
             } else {
                 setTraceEntity(current.getParent());
             }

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

@@ -22,7 +22,7 @@
 import java.util.concurrent.locks.ReentrantLock;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
-class NoOpSegment implements Segment {
+public class NoOpSegment implements Segment {
 
     private final TraceID traceId;
     private final AWSXRayRecorder creator;

aws-xray-recorder-sdk-core/src/test/java/com/amazonaws/xray/contexts/LambdaSegmentContextTest.java

@@ -22,6 +22,7 @@
 import com.amazonaws.xray.AWSXRayRecorderBuilder;
 import com.amazonaws.xray.emitters.Emitter;
 import com.amazonaws.xray.entities.FacadeSegment;
+import com.amazonaws.xray.entities.NoOpSegment;
 import com.amazonaws.xray.entities.Subsegment;
 import com.amazonaws.xray.exceptions.SubsegmentNotFoundException;
 import com.amazonaws.xray.strategy.LogErrorContextMissingStrategy;
@@ -49,6 +50,10 @@ class LambdaSegmentContextTest {
 
     private static final String MALFORMED_TRACE_HEADER =
         ";;Root=1-57ff426a-80c11c39b0c928905eb0828d;;Parent=1234abcd1234abcd;;;Sampled=1;;;";
+    private static final String MALFORMED_TRACE_HEADER_2 = ";;root-missing;;Parent=1234abcd1234abcd;;;Sampled=1;;;";
+
+    private static final String ROOT_LAMBDA_PASSTHROUGH_TRACE_HEADER =
+        "Root=1-5759e988-bd862e3fe1be46a994272711;Lineage=10:1234abcd:3";
 
     @BeforeEach
     public void setupAWSXRay() {
@@ -63,14 +68,14 @@ public void setupAWSXRay() {
     }
 
     @Test
-    void testBeginSubsegmentWithNullTraceHeaderEnvironmentVariableResultsInAFacadeSegmentParent() {
-        testContextResultsInFacadeSegmentParent();
+    void testBeginSubsegmentWithNullTraceHeaderEnvironmentVariableResultsInANoOpSegmentParent() {
+        testContextResultsInNoOpSegmentParent();
     }
 
     @Test
     @SetEnvironmentVariable(key = "_X_AMZN_TRACE_ID", value = "a")
-    void testBeginSubsegmentWithIncompleteTraceHeaderEnvironmentVariableResultsInAFacadeSegmentParent() {
-        testContextResultsInFacadeSegmentParent();
+    void testBeginSubsegmentWithIncompleteTraceHeaderEnvironmentVariableResultsInANoOpSegmentParent() {
+        testContextResultsInNoOpSegmentParent();
     }
 
     @Test
@@ -85,6 +90,18 @@ void testBeginSubsegmentWithCompleteButMalformedTraceHeaderEnvironmentVariableRe
         testContextResultsInFacadeSegmentParent();
     }
 
+    @Test
+    @SetEnvironmentVariable(key = "_X_AMZN_TRACE_ID", value = MALFORMED_TRACE_HEADER_2)
+    void testBeginSubsegmentWithIncompleteAndMalformedTraceHeaderEnvironmentVariableResultsInANoOpSegmentParent() {
+        testContextResultsInNoOpSegmentParent();
+    }
+
+    @Test
+    @SetEnvironmentVariable(key = "_X_AMZN_TRACE_ID", value = ROOT_LAMBDA_PASSTHROUGH_TRACE_HEADER)
+    void testBeginSubsegmentWithRootLambdaPassthroughTraceHeaderEnvironmentVariableResultsInANoOpSegmentParent() {
+        testContextResultsInNoOpSegmentParent();
+    }
+
     @Test
     @SetEnvironmentVariable(key = "_X_AMZN_TRACE_ID", value = TRACE_HEADER_2)
     void testNotSampledSetsParentToSubsegment() {
@@ -149,4 +166,12 @@ private static void testContextResultsInFacadeSegmentParent() {
         mockContext.endSubsegment(AWSXRay.getGlobalRecorder());
         assertThat(AWSXRay.getTraceEntity()).isNull();
     }
+
+    private static void testContextResultsInNoOpSegmentParent() {
+        LambdaSegmentContext mockContext = new LambdaSegmentContext();
+        assertThat(mockContext.beginSubsegment(AWSXRay.getGlobalRecorder(), "test").getParent())
+            .isInstanceOf(NoOpSegment.class);
+        mockContext.endSubsegment(AWSXRay.getGlobalRecorder());
+        assertThat(AWSXRay.getTraceEntity()).isNull();
+    }
 }