Cache the shared app shell HTML

tests/server/RenderHtml.test.ts

@@ -0,0 +1,60 @@
+import fs from "fs/promises";
+import os from "os";
+import path from "path";
+import { afterEach, describe, expect, test } from "vitest";
+import {
+  clearAppShellContentCache,
+  getAppShellContent,
+  setAppShellCacheHeaders,
+} from "../../src/server/RenderHtml";
+
+describe("RenderHtml", () => {
+  const originalGitCommit = process.env.GIT_COMMIT;
+  let tempDir: string | null = null;
+
+  afterEach(async () => {
+    process.env.GIT_COMMIT = originalGitCommit;
+    clearAppShellContentCache();
+
+    if (tempDir) {
+      await fs.rm(tempDir, { recursive: true, force: true });
+      tempDir = null;
+    }
+  });
+
+  test("reuses cached app shell content", async () => {
+    tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "render-html-"));
+    const htmlPath = path.join(tempDir, "index.html");
+    await fs.writeFile(
+      htmlPath,
+      "<script>window.GIT_COMMIT = <%- gitCommit %>;</script>",
+      "utf8",
+    );
+
+    process.env.GIT_COMMIT = "first";
+    const first = await getAppShellContent(htmlPath);
+
+    process.env.GIT_COMMIT = "second";
+    const second = await getAppShellContent(htmlPath);
+
+    expect(first).toContain('"first"');
+    expect(second).toBe(first);
+    expect(second).not.toContain('"second"');
+  });
+
+  test("sets shared-cache headers for the app shell", () => {
+    const headers = new Map<string, string>();
+    const response = {
+      setHeader(name: string, value: string) {
+        headers.set(name, value);
+      },
+    } as any;
+
+    setAppShellCacheHeaders(response);
+
+    expect(headers.get("Cache-Control")).toBe(
+      "public, max-age=0, s-maxage=300, stale-while-revalidate=86400",
+    );
+    expect(headers.get("Content-Type")).toBe("text/html");
+  });
+});