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[Fizz] Responsive images should not be preloaded with link headers #32445

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Merged
merged 1 commit into from
Feb 21, 2025
Merged

[Fizz] Responsive images should not be preloaded with link headers #32445

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7 changes: 7 additions & 0 deletions packages/react-dom-bindings/src/server/ReactFizzConfigDOM.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2958,6 +2958,9 @@ function pushImg(
if (
headers &&
headers.remainingCapacity > 0 &&
// browsers today don't support preloading responsive images from link headers so we bail out
// if the img has srcset defined
typeof props.srcSet !== 'string' &&
// this is a hueristic similar to capping element preloads to 10 unless explicitly
// fetchPriority="high". We use length here which means it will fit fewer images when
// the urls are long and more when short. arguably byte size is a better hueristic because
Expand Down Expand Up @@ -5703,6 +5706,10 @@ function preload(href: string, as: string, options?: ?PreloadImplOptions) {
if (
headers &&
headers.remainingCapacity > 0 &&
// browsers today don't support preloading responsive images from link headers so we bail out
// if the img has srcset defined
typeof imageSrcSet !== 'string' &&
// We only include high priority images in the link header
fetchPriority === 'high' &&
// Compute the header since we might be able to fit it in the max length
((header = getPreloadAsHeader(href, as, options)),
Expand Down
34 changes: 27 additions & 7 deletions packages/react-dom/src/__tests__/ReactDOMFizzServer-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -3723,23 +3723,43 @@ describe('ReactDOMFizzServer', () => {
});
});

it('encodes img srcset and sizes into preload header params', async () => {
it('omits images from preload headers if they contain srcset and sizes', async () => {
let headers = null;
function onHeaders(x) {
headers = x;
}

function App() {
ReactDOM.preload('presrc', {
ReactDOM.preload('responsive-preload-set-only', {
as: 'image',
fetchPriority: 'high',
imageSrcSet: 'srcset',
});
ReactDOM.preload('responsive-preload', {
as: 'image',
fetchPriority: 'high',
imageSrcSet: 'srcset',
imageSizes: 'sizes',
});
ReactDOM.preload('non-responsive-preload', {
as: 'image',
fetchPriority: 'high',
imageSrcSet: 'presrcset',
imageSizes: 'presizes',
});
return (
<html>
<body>
<img src="src" srcSet="srcset" sizes="sizes" />
<img
src="responsive-img-set-only"
fetchPriority="high"
srcSet="srcset"
/>
<img
src="responsive-img"
fetchPriority="high"
srcSet="srcset"
sizes="sizes"
/>
<img src="non-responsive-img" fetchPriority="high" />
</body>
</html>
);
Expand All @@ -3751,8 +3771,8 @@ describe('ReactDOMFizzServer', () => {

expect(headers).toEqual({
Link: `
<presrc>; rel=preload; as="image"; fetchpriority="high"; imagesrcset="presrcset"; imagesizes="presizes",
<src>; rel=preload; as="image"; imagesrcset="srcset"; imagesizes="sizes"
<non-responsive-preload>; rel=preload; as="image"; fetchpriority="high",
<non-responsive-img>; rel=preload; as="image"; fetchpriority="high"
`
.replaceAll('\n', '')
.trim(),
Expand Down
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