Add links to OpenCensus spans after span start

Author: thswlsqls

CHANGELOG.md

@@ -9,6 +9,11 @@
 * Logging: Output event name in `SystemOutLogRecordExporter`
   ([#8609](https://github.com/open-telemetry/opentelemetry-java/pull/8609))
 
+### Shims
+
+* Add OpenCensus links to the OpenTelemetry span instead of logging a warning and dropping them
+  ([#8635](https://github.com/open-telemetry/opentelemetry-java/pull/8635))
+
 ## Version 1.64.0 (2026-07-10)
 
 ### API

opencensus-shim/README.md

@@ -38,8 +38,3 @@ SdkMeterProvider.builder()
     .registerMetricReader(OpenCensusMetrics.attachTo(PeriodicMetricReader.create(metricExporter)))
     .build();
 ```
-
-## Known Problems
-
-* OpenCensus links added after an OpenCensus span is created will not be
-exported, as OpenTelemetry only supports links added when a span is created.

opencensus-shim/src/main/java/io/opentelemetry/opencensusshim/OpenTelemetrySpanImpl.java

@@ -39,20 +39,21 @@
 import io.opencensus.trace.MessageEvent;
 import io.opencensus.trace.Span;
 import io.opencensus.trace.Status;
+import io.opencensus.trace.TraceOptions;
+import io.opencensus.trace.Tracestate;
 import io.opentelemetry.api.common.AttributeKey;
 import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.common.AttributesBuilder;
 import io.opentelemetry.api.trace.SpanContext;
 import io.opentelemetry.api.trace.StatusCode;
 import java.util.EnumSet;
 import java.util.Map;
-import java.util.logging.Logger;
 
 class OpenTelemetrySpanImpl extends Span
     implements io.opentelemetry.api.trace.Span, DelegatingSpan {
-  private static final Logger LOGGER = Logger.getLogger(OpenTelemetrySpanImpl.class.getName());
   private static final EnumSet<Span.Options> RECORD_EVENTS_SPAN_OPTIONS =
       EnumSet.of(Span.Options.RECORD_EVENTS);
+  private static final Tracestate OC_TRACESTATE_DEFAULT = Tracestate.builder().build();
 
   private final io.opentelemetry.api.trace.Span otelSpan;
 
@@ -104,7 +105,20 @@ public void addAnnotation(Annotation annotation) {
 
   @Override
   public void addLink(Link link) {
-    LOGGER.warning("OpenTelemetry does not support links added after a span is created.");
+    Preconditions.checkNotNull(link, "link");
+    AttributesBuilder attributesBuilder = Attributes.builder();
+    mapAttributes(link.getAttributes(), attributesBuilder);
+    // DelegatingSpan does not override addLink, so DelegatingSpan.super.addLink(..) would call the
+    // no-op default method of Span and drop the link. Call the delegate directly instead.
+    getDelegate()
+        .addLink(
+            mapSpanContext(
+                io.opencensus.trace.SpanContext.create(
+                    link.getTraceId(),
+                    link.getSpanId(),
+                    TraceOptions.DEFAULT,
+                    OC_TRACESTATE_DEFAULT)),
+            attributesBuilder.build());
   }
 
   @Override

opencensus-shim/src/test/java/io/opentelemetry/opencensusshim/OpenTelemetrySpanImplTest.java

@@ -5,16 +5,27 @@
 
 package io.opentelemetry.opencensusshim;
 
+import static io.opentelemetry.api.common.AttributeKey.stringKey;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
+import io.opencensus.trace.AttributeValue;
+import io.opencensus.trace.Link;
+import io.opencensus.trace.SpanId;
 import io.opencensus.trace.Status;
+import io.opencensus.trace.TraceId;
+import io.opencensus.trace.TraceOptions;
+import io.opencensus.trace.Tracestate;
+import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.trace.Span;
 import io.opentelemetry.api.trace.SpanContext;
 import io.opentelemetry.api.trace.StatusCode;
+import io.opentelemetry.api.trace.TraceFlags;
+import io.opentelemetry.api.trace.TraceState;
+import java.util.Collections;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.Mock;
@@ -26,6 +37,9 @@
 @MockitoSettings(strictness = Strictness.LENIENT)
 class OpenTelemetrySpanImplTest {
 
+  private static final String TRACE_ID = "0123456789abcdef0123456789abcdef";
+  private static final String SPAN_ID = "fedcba9876543210";
+
   @Mock private Span otelSpan;
 
   private OpenTelemetrySpanImpl shimSpan() {
@@ -47,4 +61,35 @@ void setStatus_withoutDescription_setsCodeOnly() {
     verify(otelSpan).setStatus(StatusCode.OK);
     verify(otelSpan, never()).setStatus(any(StatusCode.class), anyString());
   }
+
+  @Test
+  void addLink_delegatesToOtelSpan() {
+    shimSpan().addLink(Link.fromSpanContext(ocSpanContext(), Link.Type.CHILD_LINKED_SPAN));
+
+    verify(otelSpan).addLink(expectedOtelSpanContext(), Attributes.empty());
+  }
+
+  @Test
+  void addLink_mapsAttributes() {
+    shimSpan()
+        .addLink(
+            Link.fromSpanContext(
+                ocSpanContext(),
+                Link.Type.PARENT_LINKED_SPAN,
+                Collections.singletonMap("key", AttributeValue.stringAttributeValue("value"))));
+
+    verify(otelSpan).addLink(expectedOtelSpanContext(), Attributes.of(stringKey("key"), "value"));
+  }
+
+  private static io.opencensus.trace.SpanContext ocSpanContext() {
+    return io.opencensus.trace.SpanContext.create(
+        TraceId.fromLowerBase16(TRACE_ID),
+        SpanId.fromLowerBase16(SPAN_ID),
+        TraceOptions.DEFAULT,
+        Tracestate.builder().build());
+  }
+
+  private static SpanContext expectedOtelSpanContext() {
+    return SpanContext.create(TRACE_ID, SPAN_ID, TraceFlags.getDefault(), TraceState.getDefault());
+  }
 }