Backport: Fix(pages-router): restore Content-Length and ETag for /_next/data/ JSON responses (#90304) (#91615)

ijjk · lllomh · web-flow · commit f88cee9604f0 · 2026-03-18T15:53:31.000-07:00
Backports #90304 Co-authored-by: Henry <lllomh@qq.com>
diff --git a/packages/next/src/server/route-modules/pages/pages-handler.ts b/packages/next/src/server/route-modules/pages/pages-handler.ts
@@ -502,16 +502,13 @@ export const getHandler = ({
             return {
               value: {
                 kind: CachedRouteKind.PAGES,
-                html: new RenderResult(
-                  Buffer.from(previousCacheEntry.value.html),
-                  {
-                    contentType: HTML_CONTENT_TYPE_HEADER,
-                    metadata: {
-                      statusCode: previousCacheEntry.value.status,
-                      headers: previousCacheEntry.value.headers,
-                    },
-                  }
-                ),
+                html: new RenderResult(previousCacheEntry.value.html, {
+                  contentType: HTML_CONTENT_TYPE_HEADER,
+                  metadata: {
+                    statusCode: previousCacheEntry.value.status,
+                    headers: previousCacheEntry.value.headers,
+                  },
+                }),
                 pageData: {},
                 status: previousCacheEntry.value.status,
                 headers: previousCacheEntry.value.headers,
@@ -710,13 +707,10 @@ export const getHandler = ({
           // anymore
           result:
             isNextDataRequest && !isErrorPage && !is500Page
-              ? new RenderResult(
-                  Buffer.from(JSON.stringify(result.value.pageData)),
-                  {
-                    contentType: JSON_CONTENT_TYPE_HEADER,
-                    metadata: result.value.html.metadata,
-                  }
-                )
+              ? new RenderResult(JSON.stringify(result.value.pageData), {
+                  contentType: JSON_CONTENT_TYPE_HEADER,
+                  metadata: result.value.html.metadata,
+                })
               : result.value.html,
           generateEtags: nextConfig.generateEtags,
           poweredByHeader: nextConfig.poweredByHeader,
diff --git a/test/e2e/prerender.test.ts b/test/e2e/prerender.test.ts
@@ -2071,7 +2071,10 @@ describe('Prerender', () => {
 
       it('should handle revalidating JSON correctly', async () => {
         const route = `/_next/data/${next.buildId}/blog/post-2/comment-3.json`
-        const initialJson = await renderViaHTTP(next.url, route)
+        const initialRes = await fetchViaHTTP(next.url, route)
+        const initialJson = await initialRes.text()
+        expect(initialRes.headers.get('Content-Length')).toBeDefined()
+        expect(initialRes.headers.get('ETag')).toBeDefined()
         expect(initialJson).toMatch(/post-2/)
         expect(initialJson).toMatch(/comment-3/)
 
@@ -2086,7 +2089,10 @@ describe('Prerender', () => {
         await renderViaHTTP(next.url, route)
 
         await check(async () => {
-          newJson = await renderViaHTTP(next.url, route)
+          const newRes = await fetchViaHTTP(next.url, route)
+          expect(newRes.headers.get('Content-Length')).toBeDefined()
+          expect(newRes.headers.get('ETag')).toBeDefined()
+          newJson = await newRes.text()
           return newJson !== initialJson ? 'success' : newJson
         }, 'success')
 
@@ -2143,7 +2149,10 @@ describe('Prerender', () => {
 
       it('should handle revalidating HTML correctly with blocking and seed', async () => {
         const route = '/blocking-fallback/a'
-        const initialHtml = await renderViaHTTP(next.url, route)
+        const initialRes = await fetchViaHTTP(next.url, route)
+        const initialHtml = await initialRes.text()
+        expect(initialRes.headers.get('Content-Length')).toBeDefined()
+        expect(initialRes.headers.get('ETag')).toBeDefined()
         const $initial = cheerio.load(initialHtml)
         expect($initial('p').text()).toBe('Post: a')
 
@@ -2158,7 +2167,10 @@ describe('Prerender', () => {
         await renderViaHTTP(next.url, route)
 
         await check(async () => {
-          newHtml = await renderViaHTTP(next.url, route)
+          const newRes = await fetchViaHTTP(next.url, route)
+          expect(newRes.headers.get('Content-Length')).toBeDefined()
+          expect(newRes.headers.get('ETag')).toBeDefined()
+          newHtml = await newRes.text()
           return newHtml !== initialHtml ? 'success' : newHtml
         }, 'success')
 
