OpenTracing Shim: Full multiple parent support. (#4916)

* Full multiple parent support.

This includes:

* The Baggage union of ALL parents is used.
* All parents are added as Links, in order to preserve
  the OpenTracing reference type as an attribute
  (either CHILD_OF or FOLLOWS_FROM).

* Update opentracing-shim/src/main/java/io/opentelemetry/opentracingshim/SpanBuilderShim.java

Co-authored-by: jack-berg <[email protected]>

* Update opentracing-shim/src/main/java/io/opentelemetry/opentracingshim/SpanBuilderShim.java

Co-authored-by: jack-berg <[email protected]>

* Update opentracing-shim/src/main/java/io/opentelemetry/opentracingshim/SpanBuilderShim.java

Co-authored-by: jack-berg <[email protected]>

* Apply feedback.

* More feedback.

Co-authored-by: jack-berg <[email protected]>

Author: carlosalberto

opentracing-shim/build.gradle.kts

@@ -12,6 +12,8 @@ dependencies {
   api("io.opentracing:opentracing-api")
   implementation(project(":semconv"))
 
+  annotationProcessor("com.google.auto.value:auto-value")
+
   testImplementation(project(":sdk:testing"))
 }
 

opentracing-shim/src/main/java/io/opentelemetry/opentracingshim/SpanBuilderShim.java

@@ -10,32 +10,35 @@
 import static io.opentelemetry.api.common.AttributeKey.longKey;
 import static io.opentelemetry.api.common.AttributeKey.stringKey;
 
+import com.google.auto.value.AutoValue;
 import io.opentelemetry.api.baggage.Baggage;
+import io.opentelemetry.api.baggage.BaggageBuilder;
 import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.trace.SpanKind;
 import io.opentelemetry.api.trace.StatusCode;
 import io.opentelemetry.context.Context;
+import io.opentelemetry.semconv.trace.attributes.SemanticAttributes;
+import io.opentracing.References;
 import io.opentracing.Span;
 import io.opentracing.SpanContext;
 import io.opentracing.Tracer.SpanBuilder;
 import io.opentracing.tag.Tag;
 import io.opentracing.tag.Tags;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
 
 final class SpanBuilderShim extends BaseShimObject implements SpanBuilder {
   private final String spanName;
 
-  // The parent will be either a Span or a SpanContext.
-  // Inherited baggage is supported only for the main parent.
-  @Nullable private SpanShim parentSpan;
-  @Nullable private SpanContextShim parentSpanContext;
+  // *All* parents are saved in this list.
+  private List<SpanParentInfo> allParents = Collections.emptyList();
   private boolean ignoreActiveSpan;
 
-  private final List<io.opentelemetry.api.trace.SpanContext> parentLinks = new ArrayList<>();
-
   @SuppressWarnings("rawtypes")
   private final List<AttributeKey> spanBuilderAttributeKeys = new ArrayList<>();
 
@@ -44,6 +47,15 @@ final class SpanBuilderShim extends BaseShimObject implements SpanBuilder {
   private boolean error;
   private long startTimestampMicros;
 
+  private static final Attributes CHILD_OF_ATTR =
+      Attributes.of(
+          SemanticAttributes.OPENTRACING_REF_TYPE,
+          SemanticAttributes.OpentracingRefTypeValues.CHILD_OF);
+  private static final Attributes FOLLOWS_FROM_ATTR =
+      Attributes.of(
+          SemanticAttributes.OPENTRACING_REF_TYPE,
+          SemanticAttributes.OpentracingRefTypeValues.FOLLOWS_FROM);
+
   public SpanBuilderShim(TelemetryInfo telemetryInfo, String spanName) {
     super(telemetryInfo);
     this.spanName = spanName;
@@ -57,19 +69,12 @@ public SpanBuilder asChildOf(Span parent) {
 
     // TODO - Verify we handle a no-op Span
     SpanShim spanShim = ShimUtil.getSpanShim(parent);
-
-    if (parentSpan == null && parentSpanContext == null) {
-      parentSpan = spanShim;
-    } else {
-      parentLinks.add(spanShim.getSpan().getSpanContext());
-    }
-
-    return this;
+    return addReference(References.CHILD_OF, spanShim.context());
   }
 
   @Override
   public SpanBuilder asChildOf(SpanContext parent) {
-    return addReference(null, parent);
+    return addReference(References.CHILD_OF, parent);
   }
 
   @Override
@@ -78,13 +83,30 @@ public SpanBuilder addReference(@Nullable String referenceType, SpanContext refe
       return this;
     }
 
-    // TODO - Use referenceType
+    ReferenceType refType;
+    if (References.CHILD_OF.equals(referenceType)) {
+      refType = ReferenceType.CHILD_OF;
+    } else if (References.FOLLOWS_FROM.equals(referenceType)) {
+      refType = ReferenceType.FOLLOWS_FROM;
+    } else {
+      // Discard references with unrecognized type.
+      return this;
+    }
+
     SpanContextShim contextShim = ShimUtil.getContextShim(referencedContext);
 
-    if (parentSpan == null && parentSpanContext == null) {
-      parentSpanContext = contextShim;
+    // Optimization for 99% situations, when there is only one parent.
+    if (allParents.size() == 0) {
+      allParents =
+          Collections.singletonList(
+              SpanParentInfo.create(
+                  contextShim.getSpanContext(), contextShim.getBaggage(), refType));
     } else {
-      parentLinks.add(contextShim.getSpanContext());
+      if (allParents.size() == 1) {
+        allParents = new ArrayList<>(allParents);
+      }
+      allParents.add(
+          SpanParentInfo.create(contextShim.getSpanContext(), contextShim.getBaggage(), refType));
     }
 
     return this;
@@ -186,26 +208,26 @@ public SpanBuilder withStartTimestamp(long microseconds) {
   @SuppressWarnings({"rawtypes", "unchecked"})
   @Override
   public Span start() {
-    Baggage baggage = Baggage.empty();
+    Baggage baggage;
     io.opentelemetry.api.trace.SpanBuilder builder = tracer().spanBuilder(spanName);
+    io.opentelemetry.api.trace.SpanContext mainParent = getMainParent(allParents);
 
-    if (ignoreActiveSpan && parentSpan == null && parentSpanContext == null) {
+    if (ignoreActiveSpan && mainParent == null) {
       builder.setNoParent();
-    } else if (parentSpan != null) {
-      builder.setParent(Context.root().with(parentSpan.getSpan()));
-      baggage = ((SpanContextShim) parentSpan.context()).getBaggage();
-    } else if (parentSpanContext != null) {
-      builder.setParent(
-          Context.root()
-              .with(io.opentelemetry.api.trace.Span.wrap(parentSpanContext.getSpanContext())));
-      baggage = parentSpanContext.getBaggage();
+      baggage = Baggage.empty();
+    } else if (mainParent != null) {
+      builder.setParent(Context.root().with(io.opentelemetry.api.trace.Span.wrap(mainParent)));
+      baggage = getAllBaggage(allParents);
     } else {
       // No explicit parent Span, but extracted baggage may be available.
       baggage = Baggage.current();
     }
 
-    for (io.opentelemetry.api.trace.SpanContext link : parentLinks) {
-      builder.addLink(link);
+    // *All* parents are processed as Links, in order to keep the reference type value.
+    for (SpanParentInfo parentInfo : allParents) {
+      builder.addLink(
+          parentInfo.getSpanContext(),
+          parentInfo.getRefType() == ReferenceType.CHILD_OF ? CHILD_OF_ATTR : FOLLOWS_FROM_ATTR);
     }
 
     if (spanKind != null) {
@@ -232,4 +254,62 @@ public Span start() {
 
     return new SpanShim(telemetryInfo(), span, baggage);
   }
+
+  // The first SpanContext with Child Of type in the entire list is used as parent,
+  // else the first SpanContext is used as parent.
+  @Nullable
+  static io.opentelemetry.api.trace.SpanContext getMainParent(List<SpanParentInfo> parents) {
+    if (parents.size() == 0) {
+      return null;
+    }
+
+    SpanParentInfo mainParent = parents.get(0);
+    for (SpanParentInfo parentInfo : parents) {
+      if (parentInfo.getRefType() == ReferenceType.CHILD_OF) {
+        mainParent = parentInfo;
+        break;
+      }
+    }
+
+    return mainParent.getSpanContext();
+  }
+
+  static Baggage getAllBaggage(List<SpanParentInfo> parents) {
+    if (parents.size() == 0) {
+      return Baggage.empty();
+    }
+
+    if (parents.size() == 1) {
+      return parents.get(0).getBaggage();
+    }
+
+    BaggageBuilder builder = Baggage.builder();
+    for (SpanParentInfo parent : parents) {
+      parent.getBaggage().forEach((key, entry) -> builder.put(key, entry.getValue()));
+    }
+
+    return builder.build();
+  }
+
+  @AutoValue
+  @Immutable
+  abstract static class SpanParentInfo {
+    private static SpanParentInfo create(
+        io.opentelemetry.api.trace.SpanContext spanContext,
+        Baggage baggage,
+        ReferenceType refType) {
+      return new AutoValue_SpanBuilderShim_SpanParentInfo(spanContext, baggage, refType);
+    }
+
+    abstract io.opentelemetry.api.trace.SpanContext getSpanContext();
+
+    abstract Baggage getBaggage();
+
+    abstract ReferenceType getRefType();
+  }
+
+  enum ReferenceType {
+    CHILD_OF,
+    FOLLOWS_FROM
+  }
 }