From aedddb5b5feadfbea785b56383174bcf1014225c Mon Sep 17 00:00:00 2001
From: Daniil Bratukhin <dan@pheekus.dev>
Date: Tue, 8 Sep 2026 13:03:48 -0300
Subject: [PATCH] test: stop the mock server sharing _links between concurrent
 requests

FX-287

The resource GET handler wrote `_links` onto the dataset entry itself and
then awaited `addEmbeds` before serializing, so a second GET for the same
resource could overwrite the first one's `_links` while the first was still
resolving embeds. Both responses then carried the last writer's `self`
href. The same sharing also left `_embedded` from a zoomed request on later
unzoomed ones, which needs no race at all. Write both onto a copy instead.

`src/server` had no test group, and the config has no top-level `files`
key, so a test placed there was silently never run. The generator now emits
one group for it.

npx wtr --group server
---
 .scripts/generate-groups.js                   |  8 ++++
 .../router/createResourceGetHandler.test.ts   | 43 +++++++++++++++++++
 src/server/router/createResourceGetHandler.ts |  9 +++-
 web-test-runner.groups.js                     |  4 ++
 4 files changed, 62 insertions(+), 2 deletions(-)
 create mode 100644 src/server/router/createResourceGetHandler.test.ts

diff --git a/.scripts/generate-groups.js b/.scripts/generate-groups.js
index 9cd5e9c5e..2b9c4148b 100644
--- a/.scripts/generate-groups.js
+++ b/.scripts/generate-groups.js
@@ -37,6 +37,14 @@ publicElements.forEach(file => {
   }
 });
 
+// The mock HAL+JSON server is not a component directory, so it gets one group of its own. Without
+// it there is nothing globbing ./src/server, and since the config has no top-level `files` key a
+// test placed there is silently never run.
+groups.push({
+  name: 'server',
+  files: './src/server/**/*.test.ts',
+});
+
 const configURL = new URL('../web-test-runner.groups.js', import.meta.url);
 const config = `export const groups = ${JSON.stringify(groups, null, 2)}`;
 
diff --git a/src/server/router/createResourceGetHandler.test.ts b/src/server/router/createResourceGetHandler.test.ts
new file mode 100644
index 000000000..1ff9bbe45
--- /dev/null
+++ b/src/server/router/createResourceGetHandler.test.ts
@@ -0,0 +1,43 @@
+import type { HandleResult, Router } from 'service-worker-router';
+
+import { createRouter } from '../hapi/index';
+import { expect } from '@open-wc/testing';
+
+type ResponseBody = {
+  _embedded?: Record<string, unknown>;
+  _links: { self: { href: string } };
+};
+
+const base = 'https://demo.api/hapi';
+
+function get(router: Router, url: string): Promise<ResponseBody> {
+  const result = router.handleRequest(new Request(url)) as HandleResult;
+  return result.handlerPromise.then(response => response.json());
+}
+
+describe('createResourceGetHandler', () => {
+  it('gives each of two overlapping requests for one resource its own _links', async () => {
+    const zoomedURL = `${base}/customers/0?zoom=attributes`;
+    const plainURL = `${base}/customers/0`;
+    const router = createRouter();
+
+    // Both requests are dispatched before either is awaited, so the second one runs while the
+    // first is still resolving its embeds.
+    const whenZoomed = get(router, zoomedURL);
+    const whenPlain = get(router, plainURL);
+    const [zoomed, plain] = await Promise.all([whenZoomed, whenPlain]);
+
+    expect(zoomed._links.self).to.have.property('href', zoomedURL);
+    expect(plain._links.self).to.have.property('href', plainURL);
+  });
+
+  it('does not leave _embedded from a zoomed request on a later plain request', async () => {
+    const router = createRouter();
+
+    const zoomed = await get(router, `${base}/customers/0?zoom=attributes`);
+    const plain = await get(router, `${base}/customers/0`);
+
+    expect(zoomed._embedded).to.have.property('fx:attributes');
+    expect(plain).to.not.have.property('_embedded');
+  });
+});
diff --git a/src/server/router/createResourceGetHandler.ts b/src/server/router/createResourceGetHandler.ts
index 84a1d2b1b..8b0005bc2 100644
--- a/src/server/router/createResourceGetHandler.ts
+++ b/src/server/router/createResourceGetHandler.ts
@@ -44,8 +44,13 @@ async function addEmbeds(router: Router, result: Document, zoom: string[][]) {
 export function createResourceGetHandler(router: Router, dataset: Dataset, links: Links) {
   return async ({ params, url }: HandlerContext): Promise<Response> => {
     const { collection, prefix, id } = params;
-    const document = dataset[collection]?.find(v => v.id == id);
-    if (!document) return new Response('Not found', { status: 404 });
+    const storedDocument = dataset[collection]?.find(v => v.id == id);
+    if (!storedDocument) return new Response('Not found', { status: 404 });
+
+    // Serialization happens after `addEmbeds` yields, so `_links` and `_embedded` go onto a copy.
+    // Writing them to the stored document lets two overlapping requests for the same resource
+    // overwrite each other's `_links`, and leaves `_embedded` behind for later unzoomed requests.
+    const document = { ...storedDocument };
 
     const resourceLinks = links[collection]?.(document) ?? {};
     resourceLinks.self = { href: url.toString() };
diff --git a/web-test-runner.groups.js b/web-test-runner.groups.js
index cd68b5b2e..beea8951f 100644
--- a/web-test-runner.groups.js
+++ b/web-test-runner.groups.js
@@ -707,4 +707,8 @@ export const groups = [
     name: 'foxy-webhook-status-card',
     files: './src/elements/public/WebhookStatusCard/**/*.test.ts',
   },
+  {
+    name: 'server',
+    files: './src/server/**/*.test.ts',
+  },
 ];