Passthrough SVG images in image resizing

.changeset/two-lions-tickle.md

@@ -0,0 +1,6 @@
+---
+"gitbook-v2": minor
+"gitbook": minor
+---
+
+Pass SVG images through image resizing without resizing them to serve them from optimal host.

packages/gitbook-v2/src/lib/images/checkIsSizableImageURL.ts

@@ -1,27 +1,33 @@
-import { checkIsHttpURL } from '@/lib/urls';
+export enum SizableImageAction {
+    Resize = 'resize',
+    Skip = 'skip',
+    Passthrough = 'passthrough',
+}
 
 /**
  * Check if an image URL is resizable.
  * Skip it for non-http(s) URLs (data, etc).
  * Skip it for SVGs.
  * Skip it for GitBook images (to avoid recursion).
  */
-export function checkIsSizableImageURL(input: string): boolean {
+export function checkIsSizableImageURL(input: string): SizableImageAction {
     if (!URL.canParse(input)) {
-        return false;
-    }
-
-    if (input.includes('/~gitbook/image')) {
-        return false;
+        return SizableImageAction.Skip;
     }
 
     const parsed = new URL(input);
-    if (parsed.pathname.endsWith('.svg') || parsed.pathname.endsWith('.avif')) {
-        return false;
+    if (parsed.protocol !== 'http:' && parsed.protocol !== 'https:') {
+        return SizableImageAction.Skip;
     }
-    if (!checkIsHttpURL(parsed)) {
-        return false;
+    if (parsed.hostname === 'localhost') {
+        return SizableImageAction.Skip;
+    }
+    if (parsed.pathname.includes('/~gitbook/image')) {
+        return SizableImageAction.Skip;
+    }
+    if (parsed.pathname.endsWith('.svg') || parsed.pathname.endsWith('.avif')) {
+        return SizableImageAction.Passthrough;
     }
 
-    return true;
+    return SizableImageAction.Resize;
 }

packages/gitbook-v2/src/lib/images/createImageResizer.ts

@@ -1,7 +1,7 @@
 import 'server-only';
 import { GITBOOK_IMAGE_RESIZE_SIGNING_KEY, GITBOOK_IMAGE_RESIZE_URL } from '../env';
 import type { GitBookLinker } from '../links';
-import { checkIsSizableImageURL } from './checkIsSizableImageURL';
+import { SizableImageAction, checkIsSizableImageURL } from './checkIsSizableImageURL';
 import { getImageSize } from './resizer';
 import { type SignatureVersion, generateImageSignature } from './signatures';
 import type { ImageResizer } from './types';
@@ -24,7 +24,7 @@ export function createImageResizer({
 
     return {
         getResizedImageURL: (urlInput) => {
-            if (!checkIsSizableImageURL(urlInput)) {
+            if (checkIsSizableImageURL(urlInput) === SizableImageAction.Skip) {
                 return null;
             }
 
@@ -64,7 +64,7 @@ export function createImageResizer({
         },
 
         getImageSize: async (input, options) => {
-            if (!checkIsSizableImageURL(input)) {
+            if (checkIsSizableImageURL(input) !== SizableImageAction.Resize) {
                 return null;
             }
 

packages/gitbook-v2/src/lib/images/resizer/resizeImage.ts

@@ -1,7 +1,7 @@
 import 'server-only';
 import assertNever from 'assert-never';
 import { GITBOOK_IMAGE_RESIZE_MODE } from '../../env';
-import { checkIsSizableImageURL } from '../checkIsSizableImageURL';
+import { SizableImageAction, checkIsSizableImageURL } from '../checkIsSizableImageURL';
 import { resizeImageWithCDNCgi } from './cdn-cgi';
 import { resizeImageWithCFFetch } from './cf-fetch';
 import type { CloudflareImageJsonFormat, CloudflareImageOptions } from './types';
@@ -13,7 +13,7 @@ export async function getImageSize(
     input: string,
     defaultSize: Partial<CloudflareImageOptions> = {}
 ): Promise<{ width: number; height: number } | null> {
-    if (!checkIsSizableImageURL(input)) {
+    if (checkIsSizableImageURL(input) !== SizableImageAction.Resize) {
         return null;
     }
 
@@ -48,13 +48,17 @@ export async function resizeImage(
         signal?: AbortSignal;
     }
 ): Promise<Response> {
-    const parsed = new URL(input);
-    if (parsed.protocol === 'data:') {
-        throw new Error('Cannot resize data: URLs');
+    const action = checkIsSizableImageURL(input);
+    if (action === SizableImageAction.Skip) {
+        throw new Error(
+            'Cannot resize this image, this function should have never been called on this url'
+        );
     }
 
-    if (parsed.hostname === 'localhost') {
-        throw new Error('Cannot resize localhost URLs');
+    if (action === SizableImageAction.Passthrough) {
+        return fetch(input, {
+            signal: options.signal,
+        });
     }
 
     switch (GITBOOK_IMAGE_RESIZE_MODE) {

packages/gitbook/src/routes/image.ts

@@ -2,6 +2,7 @@ import {
     CURRENT_SIGNATURE_VERSION,
     type CloudflareImageOptions,
     type SignatureVersion,
+    SizableImageAction,
     checkIsSizableImageURL,
     isSignatureVersion,
     parseImageAPIURL,
@@ -40,7 +41,7 @@ export async function serveResizedImage(
     // Check again if the image can be sized, even though we checked when rendering the Image component
     // Otherwise, it's possible to pass just any link to this endpoint and trigger HTML injection on the domain
     // Also prevent infinite redirects.
-    if (!checkIsSizableImageURL(url)) {
+    if (checkIsSizableImageURL(url) === SizableImageAction.Skip) {
         return new Response('Invalid url parameter', { status: 400 });
     }