fix: capture cache tags during request handling and don't rely on tag manifest created for prerendered pages

Author: pieh

Diff for: CONTRIBUTING.md

@@ -38,7 +38,6 @@ For a simple next.js app
 ```
 /___netlify-server-handler
 ├── .netlify
-│   ├── tags-manifest.json
 │   └── dist // the compiled runtime code
 │       └── run
 │           ├── handlers

Diff for: src/build/content/server.ts

@@ -311,47 +311,6 @@ export const copyNextDependencies = async (ctx: PluginContext): Promise<void> =>
   })
 }
 
-export const writeTagsManifest = async (ctx: PluginContext): Promise<void> => {
-  const manifest = await ctx.getPrerenderManifest()
-
-  const routes = Object.entries(manifest.routes).map(async ([route, definition]) => {
-    let tags
-
-    // app router
-    if (definition.dataRoute?.endsWith('.rsc')) {
-      const path = join(ctx.publishDir, `server/app/${route === '/' ? '/index' : route}.meta`)
-      try {
-        const file = await readFile(path, 'utf-8')
-        const meta = JSON.parse(file)
-        tags = meta.headers['x-next-cache-tags']
-      } catch {
-        // Parallel route default layout has no prerendered page, so don't warn about it
-        if (!definition.dataRoute?.endsWith('/default.rsc')) {
-          console.log(`Unable to read cache tags for: ${path}`)
-        }
-      }
-    }
-
-    // pages router
-    if (definition.dataRoute?.endsWith('.json')) {
-      tags = `_N_T_${route}`
-    }
-
-    // route handler
-    if (definition.dataRoute === null) {
-      tags = definition.initialHeaders?.['x-next-cache-tags']
-    }
-
-    return [route, tags]
-  })
-
-  await writeFile(
-    join(ctx.serverHandlerDir, '.netlify/tags-manifest.json'),
-    JSON.stringify(Object.fromEntries(await Promise.all(routes))),
-    'utf-8',
-  )
-}
-
 /**
  * Generates a copy of the middleware manifest without any middleware in it. We
  * do this because we'll run middleware in an edge function, and we don't want

Diff for: src/build/functions/server.ts

@@ -10,7 +10,6 @@ import {
   copyNextDependencies,
   copyNextServerCode,
   verifyHandlerDirStructure,
-  writeTagsManifest,
 } from '../content/server.js'
 import { PluginContext, SERVER_HANDLER_NAME } from '../plugin-context.js'
 
@@ -138,7 +137,6 @@ export const createServerHandler = async (ctx: PluginContext) => {
 
     await copyNextServerCode(ctx)
     await copyNextDependencies(ctx)
-    await writeTagsManifest(ctx)
     await copyHandlerDependencies(ctx)
     await writeHandlerManifest(ctx)
     await writePackageMetadata(ctx)

Diff for: src/run/config.ts

@@ -38,9 +38,3 @@ export const setRunConfig = (config: NextConfigComplete) => {
   // set config
   process.env.__NEXT_PRIVATE_STANDALONE_CONFIG = JSON.stringify(config)
 }
-
-export type TagsManifest = Record<string, string>
-
-export const getTagsManifest = async (): Promise<TagsManifest> => {
-  return JSON.parse(await readFile(resolve(PLUGIN_DIR, '.netlify/tags-manifest.json'), 'utf-8'))
-}

Diff for: src/run/handlers/cache.cts

@@ -109,6 +109,44 @@ export class NetlifyCacheHandler implements CacheHandler {
     return restOfRouteValue
   }
 
+  private captureCacheTags(cacheValue: NetlifyIncrementalCacheValue | null, key: string) {
+    if (!cacheValue) {
+      return
+    }
+
+    const requestContext = getRequestContext()
+    // Bail if we can't get request context
+    if (!requestContext) {
+      return
+    }
+
+    // Bail if we already have cache tags - `captureCacheTags()` is called on both `CacheHandler.get` and `CacheHandler.set`
+    // that's because `CacheHandler.get` might not have a cache value (cache miss or on-demand revalidation) in which case
+    // response is generated in blocking way and we need to capture cache tags from the cache value we are setting.
+    // If both `CacheHandler.get` and `CacheHandler.set` are called in the same request, we want to use cache tags from
+    // first `CacheHandler.get` and not from following `CacheHandler.set` as this is pattern for Stale-while-revalidate behavior
+    // and stale response is served while new one is generated.
+    if (requestContext.responseCacheTags) {
+      return
+    }
+
+    if (
+      cacheValue.kind === 'PAGE' ||
+      cacheValue.kind === 'APP_PAGE' ||
+      cacheValue.kind === 'ROUTE'
+    ) {
+      if (cacheValue.headers?.[NEXT_CACHE_TAGS_HEADER]) {
+        const cacheTags = (cacheValue.headers[NEXT_CACHE_TAGS_HEADER] as string).split(',')
+        requestContext.responseCacheTags = cacheTags
+      } else if (cacheValue.kind === 'PAGE' && typeof cacheValue.pageData === 'object') {
+        // pages router doesn't have cache tags headers in PAGE cache value
+        // so we need to generate appropriate cache tags for it
+        const cacheTags = [`_N_T_${key === '/index' ? '/' : key}`]
+        requestContext.responseCacheTags = cacheTags
+      }
+    }
+  }
+
   private async injectEntryToPrerenderManifest(
     key: string,
     revalidate: NetlifyCachedPageValue['revalidate'],
@@ -176,6 +214,7 @@ export class NetlifyCacheHandler implements CacheHandler {
       }
 
       this.captureResponseCacheLastModified(blob, key, span)
+      this.captureCacheTags(blob.value, key)
 
       switch (blob.value?.kind) {
         case 'FETCH':
@@ -273,6 +312,10 @@ export class NetlifyCacheHandler implements CacheHandler {
 
       const value = this.transformToStorableObject(data, context)
 
+      // if previous CacheHandler.get call returned null (page was either never rendered on was on-demand revalidated)
+      // and we didn't yet capture cache tags, we try to get cache tags from freshly produced cache value
+      this.captureCacheTags(value, key)
+
       await this.blobStore.setJSON(blobKey, {
         lastModified,
         value,

Diff for: src/run/handlers/request-context.cts

@@ -10,6 +10,7 @@ export type RequestContext = {
   captureServerTiming: boolean
   responseCacheGetLastModified?: number
   responseCacheKey?: string
+  responseCacheTags?: string[]
   usedFsRead?: boolean
   didPagesRouterOnDemandRevalidate?: boolean
   serverTiming?: string

Diff for: src/run/handlers/server.ts

@@ -5,7 +5,6 @@ import { Context } from '@netlify/functions'
 import type { NextConfigComplete } from 'next/dist/server/config-shared.js'
 import type { WorkerRequestHandler } from 'next/dist/server/lib/types.js'
 
-import { getTagsManifest, TagsManifest } from '../config.js'
 import {
   adjustDateHeader,
   setCacheControlHeaders,
@@ -20,7 +19,7 @@ import { getTracer } from './tracer.cjs'
 
 const nextImportPromise = import('../next.cjs')
 
-let nextHandler: WorkerRequestHandler, nextConfig: NextConfigComplete, tagsManifest: TagsManifest
+let nextHandler: WorkerRequestHandler, nextConfig: NextConfigComplete
 
 /**
  * When Next.js proxies requests externally, it writes the response back as-is.
@@ -55,21 +54,11 @@ export default async (request: Request, context: FutureContext) => {
   const tracer = getTracer()
 
   if (!nextHandler) {
-    await tracer.withActiveSpan('initialize next server', async (span) => {
+    await tracer.withActiveSpan('initialize next server', async () => {
       // set the server config
       const { getRunConfig, setRunConfig } = await import('../config.js')
       nextConfig = await getRunConfig()
       setRunConfig(nextConfig)
-      tagsManifest = await getTagsManifest()
-      span.setAttributes(
-        Object.entries(tagsManifest).reduce(
-          (acc, [key, value]) => {
-            acc[`tagsManifest.${key}`] = value
-            return acc
-          },
-          {} as Record<string, string>,
-        ),
-      )
 
       const { getMockedRequestHandlers } = await nextImportPromise
       const url = new URL(request.url)
@@ -124,7 +113,7 @@ export default async (request: Request, context: FutureContext) => {
     await adjustDateHeader({ headers: response.headers, request, span, tracer, requestContext })
 
     setCacheControlHeaders(response.headers, request, requestContext)
-    setCacheTagsHeaders(response.headers, request, tagsManifest, requestContext)
+    setCacheTagsHeaders(response.headers, requestContext)
     setVaryHeaders(response.headers, request, nextConfig)
     setCacheStatusHeader(response.headers)
 

Diff for: src/run/headers.ts

@@ -3,7 +3,6 @@ import type { NextConfigComplete } from 'next/dist/server/config-shared.js'
 
 import { encodeBlobKey } from '../shared/blobkey.js'
 
-import type { TagsManifest } from './config.js'
 import type { RequestContext } from './handlers/request-context.cjs'
 import type { RuntimeTracer } from './handlers/tracer.cjs'
 import { getRegionalBlobStore } from './regional-blob-store.cjs'
@@ -275,21 +274,9 @@ export const setCacheControlHeaders = (
   }
 }
 
-function getCanonicalPathFromCacheKey(cacheKey: string | undefined): string | undefined {
-  return cacheKey === '/index' ? '/' : cacheKey
-}
-
-export const setCacheTagsHeaders = (
-  headers: Headers,
-  request: Request,
-  manifest: TagsManifest,
-  requestContext: RequestContext,
-) => {
-  const path =
-    getCanonicalPathFromCacheKey(requestContext.responseCacheKey) ?? new URL(request.url).pathname
-  const tags = manifest[path]
-  if (tags !== undefined) {
-    headers.set('netlify-cache-tag', tags)
+export const setCacheTagsHeaders = (headers: Headers, requestContext: RequestContext) => {
+  if (requestContext.responseCacheTags) {
+    headers.set('netlify-cache-tag', requestContext.responseCacheTags.join(','))
   }
 }