Add support for custom fonts (#2981)

Author: valentin0h

Diff for: .changeset/little-geese-provide.md

@@ -0,0 +1,6 @@
+---
+"gitbook-v2": patch
+"gitbook": patch
+---
+
+Add initial support for loading custom fonts

Diff for: .github/composite/deploy-cloudflare/action.yaml

@@ -50,6 +50,7 @@ runs:
             GITBOOK_IMAGE_RESIZE_SIGNING_KEY: ${{ inputs.opItem }}/GITBOOK_IMAGE_RESIZE_SIGNING_KEY
             GITBOOK_IMAGE_RESIZE_URL: ${{ inputs.opItem }}/GITBOOK_IMAGE_RESIZE_URL
             GITBOOK_ASSETS_PREFIX: ${{ inputs.opItem }}/GITBOOK_ASSETS_PREFIX
+            GITBOOK_FONTS_URL: ${{ inputs.opItem }}/GITBOOK_FONTS_URL
         - name: Build worker
           run: bun run turbo build:v2:cloudflare
           shell: bash

Diff for: .github/composite/deploy-vercel/action.yaml

@@ -55,6 +55,7 @@ runs:
             GITBOOK_IMAGE_RESIZE_SIGNING_KEY: ${{ inputs.opItem }}/GITBOOK_IMAGE_RESIZE_SIGNING_KEY
             GITBOOK_IMAGE_RESIZE_URL: ${{ inputs.opItem }}/GITBOOK_IMAGE_RESIZE_URL
             GITBOOK_ASSETS_PREFIX: ${{ inputs.opItem }}/GITBOOK_ASSETS_PREFIX
+            GITBOOK_FONTS_URL: ${{ inputs.opItem }}/GITBOOK_FONTS_URL
         - name: Build Project Artifacts
           run: bun run vercel build --target=${{ inputs.environment }} --token=${{ inputs.vercelToken }}
           shell: bash
@@ -74,3 +75,4 @@ runs:
           shell: bash
           run: |
               echo "URL: ${{ steps.deploy.outputs.deployment-url }}"
+

Diff for: bun.lock

@@ -33,6 +33,7 @@ const nextConfig = {
         GITBOOK_ASSETS_PREFIX: process.env.GITBOOK_ASSETS_PREFIX,
         GITBOOK_SECRET: process.env.GITBOOK_SECRET,
         GITBOOK_IMAGE_RESIZE_SIGNING_KEY: process.env.GITBOOK_IMAGE_RESIZE_SIGNING_KEY,
+        GITBOOK_FONTS_URL: process.env.GITBOOK_FONTS_URL,
 
         // Next.js envs
         NEXT_SERVER_ACTIONS_ENCRYPTION_KEY: process.env.NEXT_SERVER_ACTIONS_ENCRYPTION_KEY,

Diff for: packages/gitbook-v2/next.config.mjs

@@ -7,6 +7,7 @@ import {
     GITBOOK_APP_URL,
     GITBOOK_ASSETS_URL,
     GITBOOK_DISABLE_TRACKING,
+    GITBOOK_FONTS_URL,
     GITBOOK_ICONS_URL,
     GITBOOK_IMAGE_RESIZE_SIGNING_KEY,
     GITBOOK_INTEGRATIONS_HOST,
@@ -25,6 +26,7 @@ export async function GET(_req: NextRequest) {
         GITBOOK_API_URL,
         GITBOOK_API_PUBLIC_URL,
         GITBOOK_ASSETS_URL,
+        GITBOOK_FONTS_URL,
         GITBOOK_ICONS_URL,
         GITBOOK_USER_AGENT,
         GITBOOK_INTEGRATIONS_HOST,

Diff for: packages/gitbook-v2/src/app/~gitbook/env/route.ts

@@ -64,6 +64,11 @@ export const GITBOOK_DISABLE_TRACKING = Boolean(
 export const GITBOOK_INTEGRATIONS_HOST =
     process.env.GITBOOK_INTEGRATIONS_HOST || 'integrations.gitbook.com';
 
+/**
+ * Hostname for fonts.
+ */
+export const GITBOOK_FONTS_URL = process.env.GITBOOK_FONTS_URL || 'https://fonts.gitbook.com';
+
 /**
  * Endpoint to use for resizing images.
  * It should be a Cloudflare domain with image resizing enabled.

Diff for: packages/gitbook-v2/src/lib/env/globals.ts

@@ -73,7 +73,6 @@
     "devDependencies": {
         "@argos-ci/playwright": "^4.3.0",
         "@cloudflare/next-on-pages": "1.13.7",
-        "vercel": "^39.3.0",
         "@cloudflare/workers-types": "^4.20241230.0",
         "@playwright/test": "^1.51.1",
         "@types/js-cookie": "^3.0.6",
@@ -93,8 +92,10 @@
         "jsonwebtoken": "^9.0.2",
         "postcss": "^8",
         "psi": "^4.1.0",
+        "stylelint": "^16.16.0",
         "tailwindcss": "^3.4.0",
         "ts-essentials": "^10.0.1",
-        "typescript": "^5.5.3"
+        "typescript": "^5.5.3",
+        "vercel": "^39.3.0"
     }
 }

Diff for: packages/gitbook/package.json

@@ -21,8 +21,10 @@ import {
     hexToRgb,
 } from '@gitbook/colors';
 import { IconStyle, IconsProvider } from '@gitbook/icons';
+import * as ReactDOM from 'react-dom';
 
-import { fontNotoColorEmoji, fonts, ibmPlexMono } from '@/fonts';
+import { getFontData } from '@/fonts';
+import { fontNotoColorEmoji, ibmPlexMono } from '@/fonts/default';
 import { getSpaceLanguage } from '@/intl/server';
 import { getAssetURL } from '@/lib/assets';
 import { tcls } from '@/lib/tailwind';
@@ -31,7 +33,7 @@ import { ClientContexts } from './ClientContexts';
 
 import '@gitbook/icons/style.css';
 import './globals.css';
-import { GITBOOK_ICONS_TOKEN, GITBOOK_ICONS_URL } from '@v2/lib/env';
+import { GITBOOK_FONTS_URL, GITBOOK_ICONS_TOKEN, GITBOOK_ICONS_URL } from '@v2/lib/env';
 
 /**
  * Layout shared between the content and the PDF renderer.
@@ -48,6 +50,22 @@ export async function CustomizationRootLayout(props: {
     const mixColor = getTintMixColor(customization.styling.primaryColor, tintColor);
     const sidebarStyles = getSidebarStyles(customization);
     const { infoColor, successColor, warningColor, dangerColor } = getSemanticColors(customization);
+    const fontData = getFontData(customization.styling.font);
+
+    // Preconnect and preload custom fonts if needed
+    if (fontData.type === 'custom') {
+        ReactDOM.preconnect(GITBOOK_FONTS_URL);
+        fontData.preloadSources
+            .flatMap((face) => face.sources)
+            .forEach(({ url, format }) => {
+                ReactDOM.preload(url, {
+                    as: 'font',
+                    crossOrigin: 'anonymous',
+                    fetchPriority: 'high',
+                    type: format ? `font/${format}` : undefined,
+                });
+            });
+    }
 
     return (
         <html
@@ -66,16 +84,18 @@ export async function CustomizationRootLayout(props: {
                 sidebarStyles.list && `sidebar-list-${sidebarStyles.list}`,
                 'links' in customization.styling && `links-${customization.styling.links}`,
                 fontNotoColorEmoji.variable,
-                typeof customization.styling.font === 'string'
-                    ? fonts[customization.styling.font].variable
-                    : '',
-                ibmPlexMono.variable
+                ibmPlexMono.variable,
+                fontData.type === 'default' ? fontData.variable : 'font-custom'
             )}
         >
             <head>
                 {customization.privacyPolicy.url ? (
                     <link rel="privacy-policy" href={customization.privacyPolicy.url} />
                 ) : null}
+
+                {/* Inject custom font @font-face rules */}
+                {fontData.type === 'custom' ? <style>{fontData.fontFaceRules}</style> : null}
+
                 <style
                     nonce={
                         //Since I can't get the nonce to work for inline styles, we need to allow unsafe-inline