fix: support segment data in cache entries (#3093)

Author: pieh

src/build/content/prerendered.ts

@@ -5,6 +5,7 @@ import { join } from 'node:path'
 import { trace } from '@opentelemetry/api'
 import { wrapTracer } from '@opentelemetry/api/experimental'
 import { glob } from 'fast-glob'
+import type { RouteMetadata } from 'next-with-cache-handler-v2/dist/export/routes/types.js'
 import pLimit from 'p-limit'
 import { satisfies } from 'semver'
 
@@ -69,21 +70,44 @@ const buildPagesCacheValue = async (
   revalidate: initialRevalidateSeconds,
 })
 
+const RSC_SEGMENTS_DIR_SUFFIX = '.segments'
+const RSC_SEGMENT_SUFFIX = '.segment.rsc'
+
 const buildAppCacheValue = async (
   path: string,
   shouldUseAppPageKind: boolean,
 ): Promise<NetlifyCachedAppPageValue | NetlifyCachedPageValue> => {
-  const meta = JSON.parse(await readFile(`${path}.meta`, 'utf-8'))
+  const meta = JSON.parse(await readFile(`${path}.meta`, 'utf-8')) as RouteMetadata
   const html = await readFile(`${path}.html`, 'utf-8')
 
   // supporting both old and new cache kind for App Router pages - https://github.com/vercel/next.js/pull/65988
   if (shouldUseAppPageKind) {
+    // segments are normalized and outputted separately for each segment, we denormalize it here and stitch
+    // fully constructed segmentData to avoid data fetch waterfalls later in cache handler at runtime
+    // https://github.com/vercel/next.js/blob/def2c6ba75dff754767379afb44c26c30bd3d96b/packages/next/src/server/lib/incremental-cache/file-system-cache.ts#L185
+    let segmentData: NetlifyCachedAppPageValue['segmentData']
+    if (meta.segmentPaths) {
+      const segmentsDir = path + RSC_SEGMENTS_DIR_SUFFIX
+
+      segmentData = Object.fromEntries(
+        await Promise.all(
+          meta.segmentPaths.map(async (segmentPath: string) => {
+            const segmentDataFilePath = segmentsDir + segmentPath + RSC_SEGMENT_SUFFIX
+
+            const segmentContent = await readFile(segmentDataFilePath, 'base64')
+            return [segmentPath, segmentContent]
+          }),
+        ),
+      )
+    }
+
     return {
       kind: 'APP_PAGE',
       html,
       rscData: await readFile(`${path}.rsc`, 'base64').catch(() =>
         readFile(`${path}.prefetch.rsc`, 'base64'),
       ),
+      segmentData,
       ...meta,
     }
   }
@@ -97,7 +121,10 @@ const buildAppCacheValue = async (
   if (
     !meta.status &&
     rsc.includes('NEXT_NOT_FOUND') &&
-    !meta.headers['x-next-cache-tags'].includes('/@')
+    !(
+      typeof meta.headers?.['x-next-cache-tags'] === 'string' &&
+      meta.headers?.['x-next-cache-tags'].includes('/@')
+    )
   ) {
     meta.status = 404
   }

src/run/handlers/cache.cts

@@ -364,7 +364,7 @@ export class NetlifyCacheHandler implements CacheHandlerForMultipleVersions {
             requestContext.isCacheableAppPage = true
           }
 
-          const { revalidate, rscData, ...restOfPageValue } = blob.value
+          const { revalidate, rscData, segmentData, ...restOfPageValue } = blob.value
 
           span.addEvent(blob.value?.kind, { lastModified: blob.lastModified, revalidate, ttl })
 
@@ -375,6 +375,14 @@ export class NetlifyCacheHandler implements CacheHandlerForMultipleVersions {
             value: {
               ...restOfPageValue,
               rscData: rscData ? Buffer.from(rscData, 'base64') : undefined,
+              segmentData: segmentData
+                ? new Map(
+                    Object.entries(segmentData).map(([segmentPath, base64EncodedSegment]) => [
+                      segmentPath,
+                      Buffer.from(base64EncodedSegment, 'base64'),
+                    ]),
+                  )
+                : undefined,
             },
           }
         }
@@ -416,6 +424,14 @@ export class NetlifyCacheHandler implements CacheHandlerForMultipleVersions {
         revalidate: context.revalidate ?? context.cacheControl?.revalidate,
         cacheControl: context.cacheControl,
         rscData: data.rscData?.toString('base64'),
+        segmentData: data.segmentData
+          ? Object.fromEntries(
+              [...data.segmentData.entries()].map(([segmentPath, base64EncodedSegment]) => [
+                segmentPath,
+                base64EncodedSegment.toString('base64'),
+              ]),
+            )
+          : undefined,
       }
     }
 

src/shared/cache-types.cts

@@ -9,6 +9,7 @@ import type {
   IncrementalCachedPageValue,
   IncrementalCacheValue,
 } from 'next/dist/server/response-cache/types.js'
+import type { IncrementalCachedAppPageValue as IncrementalCachedAppPageValueForNewVersions } from 'next-with-cache-handler-v2/dist/server/response-cache/types.js'
 
 export type { CacheHandlerContext } from 'next/dist/server/lib/incremental-cache/index.js'
 
@@ -44,17 +45,19 @@ type IncrementalCachedAppPageValueForMultipleVersions = Omit<
   'kind'
 > & {
   kind: 'APP_PAGE'
-}
+} & Pick<IncrementalCachedAppPageValueForNewVersions, 'segmentData'>
 
 /**
  * Used for storing in blobs and reading from blobs
  */
 export type NetlifyCachedAppPageValue = Omit<
   IncrementalCachedAppPageValueForMultipleVersions,
-  'rscData'
+  'rscData' | 'segmentData'
 > & {
-  // Next.js stores rscData as buffer, while we store it as base64 encoded string
+  // Next.js stores rscData as Buffer, while we store it as base64 encoded string
   rscData: string | undefined
+  // Next.js stores segmentData as Map<string, Buffer>, while we store it as Record<string, string>, where value is base64 encoded string
+  segmentData: Record<string, string> | undefined
   revalidate?: Parameters<CacheHandler['set']>[2]['revalidate']
   cacheControl?: CacheControl
 }