perf(web): render resume PDFs in a web worker

apps/web/src/features/resume/export/pdf-document.test.ts

@@ -0,0 +1,69 @@
+import type { PdfWorkerRequest, PdfWorkerResponse } from "./pdf-document";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { sampleResumeData } from "@reactive-resume/schema/resume/sample";
+
+const mocks = vi.hoisted(() => ({ renderHere: vi.fn() }));
+vi.mock("@reactive-resume/pdf/browser", () => ({ createResumePdfBlob: mocks.renderHere }));
+vi.mock("@/libs/resume/section-title-locale", () => ({ createSectionTitleResolverForLocale: async () => () => "" }));
+
+const pageMap = { pages: [{ width: 595, height: 842 }], nodes: [] };
+
+/** Stands in for the browser's Worker: `reply` decides what it sends back for each request. */
+function stubWorker(reply: (request: PdfWorkerRequest, worker: EventTarget) => void) {
+	class FakeWorker extends EventTarget {
+		postMessage(request: PdfWorkerRequest) {
+			queueMicrotask(() => reply(request, this));
+		}
+		terminate() {}
+	}
+	vi.stubGlobal("Worker", FakeWorker);
+}
+
+const respond = (worker: EventTarget, data: PdfWorkerResponse) =>
+	worker.dispatchEvent(new MessageEvent("message", { data }));
+
+beforeEach(() => {
+	vi.resetModules();
+	mocks.renderHere.mockReset();
+});
+
+afterEach(() => {
+	vi.unstubAllGlobals();
+});
+
+describe("createResumePdfBlob", () => {
+	it("renders in the worker and hands back its PDF and page map", async () => {
+		const blob = new Blob(["%PDF"], { type: "application/pdf" });
+		stubWorker((request, worker) => respond(worker, { id: request.id, blob, pageMap }));
+		const { createResumePdfBlob } = await import("./pdf-document");
+		const onPageMap = vi.fn();
+
+		await expect(createResumePdfBlob(sampleResumeData, undefined, undefined, { onPageMap })).resolves.toBe(blob);
+		expect(onPageMap).toHaveBeenCalledWith(pageMap);
+		expect(mocks.renderHere).not.toHaveBeenCalled();
+	});
+
+	it("passes on the worker's failure, so callers can fall back to the server's PDF", async () => {
+		stubWorker((request, worker) => respond(worker, { id: request.id, error: "Fonts could not be loaded: Inter" }));
+		const { createResumePdfBlob } = await import("./pdf-document");
+
+		await expect(createResumePdfBlob(sampleResumeData)).rejects.toThrow("Fonts could not be loaded: Inter");
+	});
+
+	it("renders on the main thread when the worker can't start", async () => {
+		const blob = new Blob(["%PDF"], { type: "application/pdf" });
+		mocks.renderHere.mockImplementation(({ onPageMap }) => {
+			onPageMap(pageMap);
+			return Promise.resolve(blob);
+		});
+		stubWorker((_request, worker) => worker.dispatchEvent(new Event("error")));
+		const { createResumePdfBlob } = await import("./pdf-document");
+		const onPageMap = vi.fn();
+
+		await expect(createResumePdfBlob(sampleResumeData, undefined, undefined, { onPageMap })).resolves.toBe(blob);
+		expect(onPageMap).toHaveBeenCalledWith(pageMap);
+		// Later renders skip the broken worker.
+		await createResumePdfBlob(sampleResumeData);
+		expect(mocks.renderHere).toHaveBeenCalledTimes(2);
+	});
+});

apps/web/src/features/resume/export/pdf-document.ts

@@ -1,7 +1,6 @@
 import type { PageMap } from "@reactive-resume/pdf/page-map";
 import type { ResumeData } from "@reactive-resume/schema/resume/data";
 import type { Template } from "@reactive-resume/schema/templates";
-import { createResumePdfBlob as createPdfBlob } from "@reactive-resume/pdf/browser";
 import { createSectionTitleResolverForLocale } from "@/libs/resume/section-title-locale";
 
 type ResumePdfRenderOptions = {
@@ -13,19 +12,85 @@ type CreateResumePdfBlobExtras = {
 	onPageMap?: (pageMap: PageMap) => void;
 };
 
+type RenderInput = { data: ResumeData; template?: Template | undefined; renderOptions?: ResumePdfRenderOptions };
+
+export type PdfWorkerRequest = RenderInput & { id: number };
+export type PdfWorkerResponse =
+	| { id: number; blob: Blob; pageMap: PageMap | undefined }
+	| { id: number; error: string };
+
+type Rendered = { blob: Blob; pageMap: PageMap | undefined };
+
+/** The same render on the main thread: where workers aren't available, or the worker failed to start. */
+async function renderHere({ data, template, renderOptions }: RenderInput): Promise<Rendered> {
+	const [{ createResumePdfBlob }, resolveSectionTitle] = await Promise.all([
+		import("@reactive-resume/pdf/browser"),
+		createSectionTitleResolverForLocale(data.metadata.page.locale),
+	]);
+	let pageMap: PageMap | undefined;
+	const blob = await createResumePdfBlob({
+		data,
+		template,
+		...(renderOptions ? { renderOptions } : {}),
+		resolveSectionTitle,
+		onPageMap: (map) => {
+			pageMap = map;
+		},
+	});
+	return { blob, pageMap };
+}
+
+type Pending = { input: RenderInput; resolve(value: Rendered): void; reject(error: Error): void };
+
+// ponytail: one worker renders in order, so a preview can wait behind one thumbnail (~0.25 s); a second worker
+// for thumbnails costs another engine and font set in memory.
+let worker: Worker | null | undefined;
+let nextId = 0;
+const pending = new Map<number, Pending>();
+
+function getWorker(): Worker | null {
+	if (worker !== undefined) return worker;
+	worker = null;
+	if (typeof Worker === "undefined") return worker;
+	try {
+		worker = new Worker(new URL("./pdf.worker.ts", import.meta.url), { type: "module", name: "resume-pdf" });
+	} catch {
+		return worker;
+	}
+	worker.addEventListener("message", ({ data: response }: MessageEvent<PdfWorkerResponse>) => {
+		const request = pending.get(response.id);
+		if (!request) return;
+		pending.delete(response.id);
+		if ("error" in response) request.reject(new Error(response.error));
+		else request.resolve({ blob: response.blob, pageMap: response.pageMap });
+	});
+	// Every render is caught inside the worker, so an error here means it couldn't start: render here instead.
+	worker.addEventListener("error", () => {
+		worker?.terminate();
+		worker = null;
+		for (const request of pending.values()) renderHere(request.input).then(request.resolve, request.reject);
+		pending.clear();
+	});
+	return worker;
+}
+
+function render(input: RenderInput): Promise<Rendered> {
+	const target = getWorker();
+	if (!target) return renderHere(input);
+	const id = ++nextId;
+	return new Promise((resolve, reject) => {
+		pending.set(id, { input, resolve, reject });
+		target.postMessage({ ...input, id } satisfies PdfWorkerRequest);
+	});
+}
+
 export const createResumePdfBlob = async (
 	data: ResumeData,
 	template?: Template,
 	renderOptions?: ResumePdfRenderOptions,
 	{ onPageMap }: CreateResumePdfBlobExtras = {},
 ) => {
-	const sectionTitleResolver = await createSectionTitleResolverForLocale(data.metadata.page.locale);
-
-	return createPdfBlob({
-		data,
-		template,
-		...(renderOptions ? { renderOptions } : {}),
-		resolveSectionTitle: sectionTitleResolver,
-		onPageMap,
-	});
+	const { blob, pageMap } = await render({ data, template, ...(renderOptions ? { renderOptions } : {}) });
+	if (pageMap) onPageMap?.(pageMap);
+	return blob;
 };

apps/web/src/features/resume/export/pdf.worker.ts

@@ -0,0 +1,26 @@
+/// <reference lib="webworker" />
+
+import type { PageMap } from "@reactive-resume/pdf/page-map";
+import type { PdfWorkerRequest, PdfWorkerResponse } from "./pdf-document";
+import { createResumePdfBlob } from "@reactive-resume/pdf/browser";
+import { createSectionTitleResolverForLocale } from "@/libs/resume/section-title-locale";
+
+// Renders off the main thread, so typing, scrolling and the gallery stay smooth while a page is laid out.
+self.addEventListener("message", async ({ data: request }: MessageEvent<PdfWorkerRequest>) => {
+	const { id, data, template, renderOptions } = request;
+	try {
+		let pageMap: PageMap | undefined;
+		const blob = await createResumePdfBlob({
+			data,
+			template,
+			renderOptions,
+			resolveSectionTitle: await createSectionTitleResolverForLocale(data.metadata.page.locale),
+			onPageMap: (map) => {
+				pageMap = map;
+			},
+		});
+		self.postMessage({ id, blob, pageMap } satisfies PdfWorkerResponse);
+	} catch (error) {
+		self.postMessage({ id, error: error instanceof Error ? error.message : String(error) } satisfies PdfWorkerResponse);
+	}
+});