Use link from start workflow request for Nexus operations

temporal-sdk/src/main/java/io/temporal/internal/client/RootWorkflowClientInvoker.java

@@ -23,6 +23,7 @@
 import io.temporal.common.interceptors.WorkflowClientCallsInterceptor;
 import io.temporal.internal.client.external.GenericWorkflowClient;
 import io.temporal.internal.common.HeaderUtils;
+import io.temporal.internal.nexus.CurrentNexusOperationContext;
 import io.temporal.payload.context.WorkflowSerializationContext;
 import io.temporal.serviceclient.StatusUtils;
 import io.temporal.worker.WorkflowTaskDispatchHandle;
@@ -95,6 +96,9 @@ public WorkflowStartOutput start(WorkflowStartInput input) {
               e);
         }
       }
+      if (CurrentNexusOperationContext.isNexusContext()) {
+        CurrentNexusOperationContext.get().setStartWorkflowResponseLink(response.getLink());
+      }
       return new WorkflowStartOutput(execution);
     }
   }

temporal-sdk/src/main/java/io/temporal/internal/nexus/CurrentNexusOperationContext.java

@@ -7,6 +7,10 @@
 public final class CurrentNexusOperationContext {
   private static final ThreadLocal<InternalNexusOperationContext> CURRENT = new ThreadLocal<>();
 
+  public static boolean isNexusContext() {
+    return CURRENT.get() != null;
+  }
+
   public static InternalNexusOperationContext get() {
     InternalNexusOperationContext result = CURRENT.get();
     if (result == null) {

temporal-sdk/src/main/java/io/temporal/internal/nexus/InternalNexusOperationContext.java

@@ -1,6 +1,7 @@
 package io.temporal.internal.nexus;
 
 import com.uber.m3.tally.Scope;
+import io.temporal.api.common.v1.Link;
 import io.temporal.client.WorkflowClient;
 import io.temporal.common.interceptors.NexusOperationOutboundCallsInterceptor;
 import io.temporal.nexus.NexusOperationContext;
@@ -11,6 +12,7 @@ public class InternalNexusOperationContext {
   private final Scope metricScope;
   private final WorkflowClient client;
   NexusOperationOutboundCallsInterceptor outboundCalls;
+  Link startWorkflowResponseLink;
 
   public InternalNexusOperationContext(
       String namespace, String taskQueue, Scope metricScope, WorkflowClient client) {
@@ -47,6 +49,14 @@ public NexusOperationContext getUserFacingContext() {
     return new NexusOperationContextImpl();
   }
 
+  public void setStartWorkflowResponseLink(Link link) {
+    this.startWorkflowResponseLink = link;
+  }
+
+  public Link getStartWorkflowResponseLink() {
+    return startWorkflowResponseLink;
+  }
+
   private class NexusOperationContextImpl implements NexusOperationContext {
     @Override
     public Scope getMetricsScope() {

temporal-sdk/src/main/java/io/temporal/nexus/WorkflowRunOperationImpl.java

@@ -41,16 +41,23 @@ public OperationStartResult<R> start(
 
     WorkflowExecution workflowExec = handle.getInvoker().invoke(nexusRequest);
 
-    // Create the link information about the new workflow and return to the caller.
+    // If the start workflow response returned a link use it, otherwise
+    // create the link information about the new workflow and return to the caller.
     Link.WorkflowEvent workflowEventLink =
-        Link.WorkflowEvent.newBuilder()
-            .setNamespace(nexusCtx.getNamespace())
-            .setWorkflowId(workflowExec.getWorkflowId())
-            .setRunId(workflowExec.getRunId())
-            .setEventRef(
-                Link.WorkflowEvent.EventReference.newBuilder()
-                    .setEventType(EventType.EVENT_TYPE_WORKFLOW_EXECUTION_STARTED))
-            .build();
+        nexusCtx.getStartWorkflowResponseLink().hasWorkflowEvent()
+            ? nexusCtx.getStartWorkflowResponseLink().getWorkflowEvent()
+            : null;
+    if (workflowEventLink == null) {
+      workflowEventLink =
+          Link.WorkflowEvent.newBuilder()
+              .setNamespace(nexusCtx.getNamespace())
+              .setWorkflowId(workflowExec.getWorkflowId())
+              .setRunId(workflowExec.getRunId())
+              .setEventRef(
+                  Link.WorkflowEvent.EventReference.newBuilder()
+                      .setEventType(EventType.EVENT_TYPE_WORKFLOW_EXECUTION_STARTED))
+              .build();
+    }
     io.temporal.api.nexus.v1.Link nexusLink = workflowEventToNexusLink(workflowEventLink);
     // Generate the operation token for the new workflow.
     String operationToken;

temporal-sdk/src/test/java/io/temporal/workflow/nexus/WorkflowHandleUseExistingOnConflictTest.java

@@ -3,8 +3,11 @@
 import io.nexusrpc.handler.OperationHandler;
 import io.nexusrpc.handler.OperationImpl;
 import io.nexusrpc.handler.ServiceImpl;
+import io.temporal.api.common.v1.Link;
+import io.temporal.api.enums.v1.EventType;
 import io.temporal.api.enums.v1.WorkflowIdConflictPolicy;
 import io.temporal.client.WorkflowOptions;
+import io.temporal.client.WorkflowStub;
 import io.temporal.nexus.Nexus;
 import io.temporal.nexus.WorkflowRunOperation;
 import io.temporal.testing.internal.SDKTestWorkflowRule;
@@ -14,6 +17,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.UUID;
+import java.util.concurrent.atomic.AtomicInteger;
 import org.junit.*;
 
 public class WorkflowHandleUseExistingOnConflictTest {
@@ -31,6 +35,26 @@ public void testOnConflictUseExisting() {
     String workflowId = UUID.randomUUID().toString();
     String result = workflowStub.execute(workflowId);
     Assert.assertEquals("Hello from operation workflow " + workflowId, result);
+
+    AtomicInteger eventRefLinkCount = new AtomicInteger();
+    AtomicInteger requestIdLinkCount = new AtomicInteger();
+    testWorkflowRule
+        .getHistoryEvents(
+            WorkflowStub.fromTyped(workflowStub).getExecution().getWorkflowId(),
+            EventType.EVENT_TYPE_NEXUS_OPERATION_STARTED)
+        .forEach(
+            event -> {
+              List<Link> links = event.getLinksList();
+              Assert.assertEquals(1, links.size());
+              Link link = links.get(0);
+              if (link.getWorkflowEvent().hasEventRef()) {
+                eventRefLinkCount.getAndIncrement();
+              } else if (link.getWorkflowEvent().hasRequestIdRef()) {
+                requestIdLinkCount.getAndIncrement();
+              }
+            });
+    Assert.assertEquals(1, eventRefLinkCount.get());
+    Assert.assertEquals(4, requestIdLinkCount.get());
   }
 
   public static class TestNexus implements TestWorkflows.TestWorkflow1 {