Fix image format handling and enhance PageCoverImage component (#3527)

Co-authored-by: Nicolas Dorseuil <nicolas@gitbook.io>

packages/gitbook/src/components/PageBody/PageCover.tsx

@@ -43,31 +43,30 @@ export async function PageCover(props: {
 
     const getImage = async (resolved: ResolvedContentRef | null, returnNull = false) => {
         if (!resolved && returnNull) return;
-        const [attrs, size] = await Promise.all([
-            getImageAttributes({
-                sizes,
-                source: resolved
-                    ? {
-                          src: resolved.href,
-                          size: resolved.file?.dimensions ?? null,
-                      }
-                    : {
-                          src: defaultPageCover.src,
-                          size: {
-                              width: defaultPageCover.width,
-                              height: defaultPageCover.height,
-                          },
+        // If we don't have a size for the image, we want to calculate it so that we can use srcSet
+        const size =
+            resolved?.file?.dimensions ??
+            (await context.imageResizer?.getImageSize(resolved?.href || defaultPageCover.src, {}));
+        const attrs = await getImageAttributes({
+            sizes,
+            source: resolved
+                ? {
+                      src: resolved.href,
+                      size: size ?? null,
+                  }
+                : {
+                      src: defaultPageCover.src,
+                      size: {
+                          width: defaultPageCover.width,
+                          height: defaultPageCover.height,
                       },
-                quality: 100,
-                resize: context.imageResizer ?? false,
-            }),
-            context.imageResizer
-                ?.getImageSize(resolved?.href || defaultPageCover.src, {})
-                .then((size) => size ?? undefined),
-        ]);
+                  },
+            quality: 100,
+            resize: context.imageResizer ?? false,
+        });
         return {
             ...attrs,
-            size,
+            size: size ?? undefined,
         };
     };
 

packages/gitbook/src/components/PageBody/PageCoverImage.tsx

@@ -44,6 +44,8 @@ export function PageCoverImage({ imgs, y }: { imgs: Images; y: number }) {
         <div className="h-full w-full overflow-hidden" ref={containerRef}>
             <img
                 src={imgs.light.src}
+                srcSet={imgs.light.srcSet}
+                sizes={imgs.light.sizes}
                 fetchPriority="high"
                 alt="Page cover"
                 className={tcls('w-full', 'object-cover', imgs.dark ? 'dark:hidden' : '')}
@@ -55,6 +57,8 @@ export function PageCoverImage({ imgs, y }: { imgs: Images; y: number }) {
             {imgs.dark && (
                 <img
                     src={imgs.dark.src}
+                    srcSet={imgs.dark.srcSet}
+                    sizes={imgs.dark.sizes}
                     fetchPriority="low"
                     alt="Page cover"
                     className={tcls('w-full', 'object-cover', 'dark:inline', 'hidden')}

packages/gitbook/src/routes/image.ts

@@ -87,6 +87,8 @@ export async function serveResizedImage(
         options.height = Number(height);
     }
 
+    const longestEdgeValue = Math.max(options.width || 0, options.height || 0);
+
     const dpr = requestURL.searchParams.get('dpr');
     if (dpr) {
         options.dpr = Number(dpr);
@@ -99,10 +101,14 @@ export async function serveResizedImage(
 
     // Check the Accept header to handle content negotiation
     const accept = request.headers.get('accept');
-    if (accept && /image\/avif/.test(accept)) {
+    // We use transform image, max size for avif should be 1600
+    // https://developers.cloudflare.com/images/transform-images/#limits-per-format
+    if (accept && /image\/avif/.test(accept) && longestEdgeValue <= 1600) {
         options.format = 'avif';
-    } else if (accept && /image\/webp/.test(accept)) {
+        options.dpr = chooseDPR(longestEdgeValue, 1600, options.dpr);
+    } else if (accept && /image\/webp/.test(accept) && longestEdgeValue <= 1920) {
         options.format = 'webp';
+        options.dpr = chooseDPR(longestEdgeValue, 1920, options.dpr);
     }
 
     try {
@@ -119,6 +125,19 @@ export async function serveResizedImage(
     }
 }
 
+/**
+ * Choose the appropriate device pixel ratio (DPR) based on the longest edge of the image.
+ * This function ensures that the DPR is within a reasonable range (1 to 3).
+ * This is only used for AVIF/WebP formats to avoid issues with Cloudflare resizing.
+ * It means that dpr may not be respected for avif/webp formats, but it will also improve the cache hit ratio.
+ */
+function chooseDPR(longestEdgeValue: number, maxAllowedSize: number, wantedDpr?: number): number {
+    const maxDprBySize = Math.floor(maxAllowedSize / longestEdgeValue);
+    const clampedDpr = Math.min(wantedDpr ?? 1, 3); // Limit to a maximum of 3, default to 1 if not specified
+    // Ensure that the DPR is within the allowed range
+    return Math.max(1, Math.min(maxDprBySize, clampedDpr));
+}
+
 /**
  * Parse the image signature version from a query param. Returns null if the version is invalid.
  */