Serve web worker assets with cache-busting (#10831)

Serve code editor worker files with proper
cache-busting via buildHash in the URL path, following the same
pattern used for application bundles.

Worker files are now served at /{buildHash}/editor/workers/* where
buildHash is derived from env.packageInfo.buildNum:
- Development: Number.MAX_SAFE_INTEGER (9007199254740991)
- Distribution: Actual build number from package.json

This ensures browsers and CDNs fetch fresh worker files when OSD
is upgraded, preventing stale cache issues that could cause version
mismatches between application code and worker threads.

Changes:
- Add worker_config.ts with buildHash-based URL generation helpers
- Register static worker route at /{buildHash}/editor/workers/*
- Add test coverage for worker route registration

Signed-off-by: Daniel Rowe <[email protected]>

Author: d-buckner

packages/osd-monaco/src/index.ts

@@ -38,3 +38,4 @@ import * as BarePluginApi from 'monaco-editor/esm/vs/editor/editor.api';
 export { BarePluginApi };
 import './monaco_environment';
 export * from './worker_store';
+export { WORKER_FILES, getWorkerUrl, getWorkerUrls, WorkerId } from './worker_config';

packages/osd-monaco/src/worker_config.ts

@@ -0,0 +1,42 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Worker filenames (relative paths).
+ * Monaco package only defines its worker files, not server routing.
+ */
+export const WORKER_FILES = {
+  ppl: 'ppl.editor.worker.js',
+  json: 'json.editor.worker.js',
+  xjson: 'xjson.editor.worker.js',
+} as const;
+
+export type WorkerId = keyof typeof WORKER_FILES;
+
+/**
+ * Get the full URL for a worker by its ID.
+ *
+ * @param workerId - The worker identifier
+ * @param buildHash - The build hash for cache-busting (e.g., buildNum.toString())
+ * @returns The full URL for the worker, or undefined if not found
+ */
+export function getWorkerUrl(workerId: string, buildHash: string): string | undefined {
+  const filename = WORKER_FILES[workerId as WorkerId];
+  return filename ? `/${buildHash}/editor/workers/${filename}` : undefined;
+}
+
+/**
+ * Helper to generate all worker URLs with the given buildHash.
+ *
+ * @param buildHash - The build hash for cache-busting (e.g., buildNum.toString())
+ * @returns Object with all worker URLs
+ */
+export function getWorkerUrls(buildHash: string) {
+  return {
+    ppl: `/${buildHash}/editor/workers/${WORKER_FILES.ppl}`,
+    json: `/${buildHash}/editor/workers/${WORKER_FILES.json}`,
+    xjson: `/${buildHash}/editor/workers/${WORKER_FILES.xjson}`,
+  } as const;
+}

src/core/server/core_app/core_app.test.ts

@@ -79,4 +79,15 @@ describe('CoreApp', () => {
       );
     });
   });
+
+  describe('static routes', () => {
+    it('registers code editor worker static directory with buildHash', () => {
+      coreApp.setup(internalCoreSetup);
+
+      expect(internalCoreSetup.http.registerStaticDir).toHaveBeenCalledWith(
+        expect.stringMatching(/^\/\d+\/editor\/workers\/\{path\*\}$/),
+        expect.stringContaining('node_modules/@osd/monaco/target/public')
+      );
+    });
+  });
 });

src/core/server/core_app/core_app.ts

@@ -38,7 +38,9 @@ import { Logger } from '../logging';
 /** @internal */
 export class CoreApp {
   private readonly logger: Logger;
+  private readonly coreContext: CoreContext;
   constructor(core: CoreContext) {
+    this.coreContext = core;
     this.logger = core.logger.get('core-app');
   }
   setup(coreSetup: InternalCoreSetup) {
@@ -94,5 +96,14 @@ export class CoreApp {
       '/node_modules/@osd/ui-framework/dist/{path*}',
       fromRoot('node_modules/@osd/ui-framework/dist')
     );
+
+    // Register worker files directory for code editor with buildHash for cache-busting
+    // Serves from: build/opensearch-dashboards/node_modules/@osd/monaco/target/public/
+    // Uses buildNum for cache invalidation on version changes (same pattern as bundles)
+    const buildHash = this.coreContext.env.packageInfo.buildNum.toString();
+    coreSetup.http.registerStaticDir(
+      `/${buildHash}/editor/workers/{path*}`,
+      fromRoot('node_modules/@osd/monaco/target/public')
+    );
   }
 }