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fix(fonts): subset Google Fonts to composition text #2353

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fix(fonts): subset Google Fonts to composition text #2353

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25 changes: 25 additions & 0 deletions packages/producer/src/services/deterministicFonts-textSubset.test.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,25 @@
import { describe, expect, it } from "bun:test";
import { injectDeterministicFontFaces } from "./deterministicFonts.js";

describe("Google Fonts text subsetting", () => {
it("sends the composition character set to the CSS API", async () => {
let requestedUrl = "";
const fetchImpl = (async (input: unknown) => {
requestedUrl = String(input);
return new Response("", { status: 400 });
}) as unknown as typeof fetch;

await injectDeterministicFontFaces(
`<!doctype html><html><head><style>
h1 { font-family: "Noto Performance Test", sans-serif; }
</style></head><body><h1>旅行ランキング</h1></body></html>`,
{ fetchImpl, allowSystemFontCapture: false },
);

const url = new URL(requestedUrl);
const text = url.searchParams.get("text") ?? "";
for (const character of new Set("旅行ランキング")) {
expect(text).toContain(character);
}
});
});
27 changes: 23 additions & 4 deletions packages/producer/src/services/deterministicFonts.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -456,6 +456,7 @@ function buildFontFaceRule(
async function buildFontFaceCss(
requestedFamilies: Map<string, string>,
options: InternalFontFetchOptions,
fontText?: string,
): Promise<{
css: string;
unresolved: string[];
Expand Down Expand Up @@ -483,7 +484,7 @@ async function buildFontFaceCss(
// already covered by the embedded bundle. This ensures that
// compositions requesting e.g. wght@200 get that weight even
// if the bundle only ships 400/700/900.
const googleFaces = await fetchGoogleFont(originalCaseFamily, options);
const googleFaces = await fetchGoogleFont(originalCaseFamily, options, fontText);
for (const face of googleFaces) {
// A weight covered by the embedded bundle is already full-coverage —
// skip it. For weights the bundle lacks, add EVERY subset face (a
Expand All @@ -503,7 +504,7 @@ async function buildFontFaceCss(
}

// Path 2: fetch from Google Fonts (with local cache)
const googleFaces = await fetchGoogleFont(originalCaseFamily, options);
const googleFaces = await fetchGoogleFont(originalCaseFamily, options, fontText);
if (googleFaces.length > 0) {
for (const face of googleFaces) {
rules.push(
Expand Down Expand Up @@ -735,10 +736,12 @@ async function ensureWoff2DataUri(
async function fetchGoogleFont(
familyName: string,
options: InternalFontFetchOptions,
fontText?: string,
): Promise<GoogleFontFace[]> {
const slug = fontSlug(familyName);
const encodedFamily = encodeURIComponent(familyName);
const url = `https://fonts.googleapis.com/css2?family=${encodedFamily}:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;0,700;0,800;0,900;1,400;1,700`;
const textParam = fontText ? `&text=${encodeURIComponent(fontText)}` : "";
const url = `https://fonts.googleapis.com/css2?family=${encodedFamily}:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;0,700;0,800;0,900;1,400;1,700${textParam}`;

let cssText: string;
try {
Expand Down Expand Up @@ -844,6 +847,18 @@ export interface InjectDeterministicFontFacesOptions {
allowSystemFontCapture?: boolean;
}

// Keep the complete CSS request under the broadly supported ~2 KB URL limit.
// Using unique source characters covers static text plus strings authored in
// scripts, while collapsing repeated prose and base64 assets to a tiny set.
const GOOGLE_FONTS_TEXT_MAX_ENCODED_LENGTH = 1_700;

function extractGoogleFontsText(html: string): string | undefined {
const uniqueCharacters = [...new Set(Array.from(html))].join("");
return encodeURIComponent(uniqueCharacters).length <= GOOGLE_FONTS_TEXT_MAX_ENCODED_LENGTH
? uniqueCharacters
: undefined;
}

export async function injectDeterministicFontFaces(
html: string,
options: InjectDeterministicFontFacesOptions = {},
Expand Down Expand Up @@ -871,7 +886,11 @@ export async function injectDeterministicFontFaces(
return html;
}

const { css, unresolved } = await buildFontFaceCss(pendingFamilies, fetchOptions);
const { css, unresolved } = await buildFontFaceCss(
pendingFamilies,
fetchOptions,
extractGoogleFontsText(html),
);
if (unresolved.length > 0 && options.failClosedFontFetch) {
throw new FontFetchError(
unresolved.join(", "),
Expand Down
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