fix: move activity input JSON.parse inside try-catch for proper error handling

The JSON.parse call for deserializing activity input was positioned outside
the try-catch block in ActivityExecutor.execute(). When encodedInput contained
malformed JSON, the SyntaxError bypassed the activityFailed log (EventId 605)
and propagated with no activity context (name, orchestrationId).

Move JSON.parse inside the existing try-catch so all activity execution
failures — including input deserialization errors — are logged consistently
and re-thrown with proper context.

Add unit tests for malformed JSON input, undefined input, and empty string
input edge cases.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Copilot

packages/durabletask-js/src/worker/activity-executor.ts

@@ -32,10 +32,14 @@ export class ActivityExecutor {
     // Log activity start (EventId 603)
     WorkerLogs.activityStarted(this._logger, orchestrationId, name);
 
-    const activityInput = encodedInput ? JSON.parse(encodedInput) : undefined;
     const ctx = new ActivityContext(orchestrationId, taskId);
 
     try {
+      // Deserialize the input inside the try-catch so that malformed JSON
+      // is reported through the same activityFailed log path (EventId 605)
+      // as any other activity execution error.
+      const activityInput = encodedInput ? JSON.parse(encodedInput) : undefined;
+
       // Execute the activity function
       let activityOutput = fn(ctx, activityInput);
 

packages/durabletask-js/test/activity_executor.spec.ts

@@ -53,12 +53,62 @@ describe("Activity Executor", () => {
     expect(caughtException).not.toBeNull();
     expect(caughtException?.message).toMatch(/Bogus/);
   });
+
+  it("should throw and log activityFailed when input is malformed JSON", async () => {
+    const testActivity = (_: ActivityContext, input: any) => {
+      return input;
+    };
+
+    const loggerSpy = createSpyLogger();
+    const [executor, name] = getActivityExecutor(testActivity, loggerSpy);
+
+    const malformedJson = "{not valid json";
+
+    await expect(executor.execute(TEST_INSTANCE_ID, name, TEST_TASK_ID, malformedJson))
+      .rejects.toThrow(SyntaxError);
+
+    // Verify the activityFailed log (EventId 605) was emitted
+    expect(loggerSpy.error).toHaveBeenCalled();
+    const errorCall = loggerSpy.error.mock.calls[0][0];
+    expect(errorCall).toContain(name);
+    expect(errorCall).toContain(TEST_INSTANCE_ID);
+    expect(errorCall).toContain("failed");
+  });
+
+  it("should handle undefined input without error", async () => {
+    const testActivity = (_: ActivityContext, input: any) => {
+      return input;
+    };
+
+    const [executor, name] = getActivityExecutor(testActivity);
+    const result = await executor.execute(TEST_INSTANCE_ID, name, TEST_TASK_ID, undefined);
+    expect(result).toBeUndefined();
+  });
+
+  it("should handle empty string input without error", async () => {
+    const testActivity = (_: ActivityContext, input: any) => {
+      return input;
+    };
+
+    const [executor, name] = getActivityExecutor(testActivity);
+    const result = await executor.execute(TEST_INSTANCE_ID, name, TEST_TASK_ID, "");
+    expect(result).toBeUndefined();
+  });
 });
 
 // Activity = Callable[[ActivityContext, TInput], TOutput]
-function getActivityExecutor(fn: TActivity<any, any>): [ActivityExecutor, string] {
+function getActivityExecutor(fn: TActivity<any, any>, logger?: any): [ActivityExecutor, string] {
   const registry = new Registry();
   const name = registry.addActivity(fn);
-  const executor = new ActivityExecutor(registry, testLogger);
+  const executor = new ActivityExecutor(registry, logger ?? testLogger);
   return [executor, name];
 }
+
+function createSpyLogger() {
+  return {
+    error: jest.fn(),
+    warn: jest.fn(),
+    info: jest.fn(),
+    debug: jest.fn(),
+  };
+}