More explicit typing for IncrementalCache API (vercel#26941)

Make the typing for `IncrementalCache` more explicit. With streaming, we’ll want to stream page data as well as HTML. This is a bit complicated now because we’re overloading `pageData` for both redirects and pages.

This PR makes the different types explicit. With streaming, the data for redirects is synchronously available, while the data for pages will become a stream.

A follow up PR will add a “stream through” cache in front of `IncrementalCache`

packages/next/server/incremental-cache.ts

@@ -9,15 +9,25 @@ function toRoute(pathname: string): string {
   return pathname.replace(/\/$/, '').replace(/\/index$/, '') || '/'
 }
 
-type IncrementalCacheValue = {
-  html?: string
-  pageData?: any
-  isStale?: boolean
-  isNotFound?: boolean
-  isRedirect?: boolean
+interface CachedRedirectValue {
+  kind: 'REDIRECT'
+  props: Object
+}
+
+interface CachedPageValue {
+  kind: 'PAGE'
+  html: string
+  pageData: Object
+}
+
+export type IncrementalCacheValue = CachedRedirectValue | CachedPageValue
+
+type IncrementalCacheEntry = {
   curRevalidate?: number | false
   // milliseconds to revalidate after
   revalidateAfter: number | false
+  isStale?: boolean
+  value: IncrementalCacheValue | null
 }
 
 export class IncrementalCache {
@@ -29,7 +39,7 @@ export class IncrementalCache {
   }
 
   prerenderManifest: PrerenderManifest
-  cache: LRUCache<string, IncrementalCacheValue>
+  cache: LRUCache<string, IncrementalCacheEntry>
   locales?: string[]
 
   constructor({
@@ -73,10 +83,10 @@ export class IncrementalCache {
     this.cache = new LRUCache({
       // default to 50MB limit
       max: max || 50 * 1024 * 1024,
-      length(val) {
-        if (val.isNotFound || val.isRedirect) return 25
+      length({ value }) {
+        if (!value || value.kind === 'REDIRECT') return 25
         // rough estimate of size of cache value
-        return val.html!.length + JSON.stringify(val.pageData).length
+        return value.html.length + JSON.stringify(value.pageData).length
       },
     })
   }
@@ -112,16 +122,16 @@ export class IncrementalCache {
   }
 
   // get data from cache if available
-  async get(pathname: string): Promise<IncrementalCacheValue | void> {
-    if (this.incrementalOptions.dev) return
+  async get(pathname: string): Promise<IncrementalCacheEntry | null> {
+    if (this.incrementalOptions.dev) return null
     pathname = normalizePagePath(pathname)
 
     let data = this.cache.get(pathname)
 
     // let's check the disk for seed data
     if (!data) {
       if (this.prerenderManifest.notFoundRoutes.includes(pathname)) {
-        return { isNotFound: true, revalidateAfter: false }
+        return { revalidateAfter: false, value: null }
       }
 
       try {
@@ -134,15 +144,21 @@ export class IncrementalCache {
         )
 
         data = {
-          html,
-          pageData,
           revalidateAfter: this.calculateRevalidate(pathname),
+          value: {
+            kind: 'PAGE',
+            html,
+            pageData,
+          },
         }
         this.cache.set(pathname, data)
       } catch (_) {
         // unable to get data from disk
       }
     }
+    if (!data) {
+      return null
+    }
 
     if (
       data &&
@@ -164,12 +180,7 @@ export class IncrementalCache {
   // populate the incremental cache with new data
   async set(
     pathname: string,
-    data: {
-      html?: string
-      pageData?: any
-      isNotFound?: boolean
-      isRedirect?: boolean
-    },
+    data: IncrementalCacheValue | null,
     revalidateSeconds?: number | false
   ) {
     if (this.incrementalOptions.dev) return
@@ -188,17 +199,13 @@ export class IncrementalCache {
 
     pathname = normalizePagePath(pathname)
     this.cache.set(pathname, {
-      ...data,
       revalidateAfter: this.calculateRevalidate(pathname),
+      value: data,
     })
 
     // TODO: This option needs to cease to exist unless it stops mutating the
     // `next build` output's manifest.
-    if (
-      this.incrementalOptions.flushToDisk &&
-      !data.isNotFound &&
-      !data.isRedirect
-    ) {
+    if (this.incrementalOptions.flushToDisk && data?.kind === 'PAGE') {
       try {
         const seedPath = this.getSeedPath(pathname, 'html')
         await promises.mkdir(path.dirname(seedPath), { recursive: true })

packages/next/server/next-server.ts

@@ -73,7 +73,7 @@ import prepareDestination, {
 } from '../shared/lib/router/utils/prepare-destination'
 import { sendPayload, setRevalidateHeaders } from './send-payload'
 import { serveStatic } from './serve-static'
-import { IncrementalCache } from './incremental-cache'
+import { IncrementalCache, IncrementalCacheValue } from './incremental-cache'
 import { execOnce } from '../shared/lib/utils'
 import { isBlockedPage } from './utils'
 import { loadEnvConfig } from '@next/env'
@@ -1653,30 +1653,25 @@ export default class Server {
     }
 
     // Complete the response with cached data if its present
-    const cachedData = ssgCacheKey
+    const cacheEntry = ssgCacheKey
       ? await this.incrementalCache.get(ssgCacheKey)
       : undefined
 
-    if (cachedData) {
-      const data = isDataReq
-        ? JSON.stringify(cachedData.pageData)
-        : cachedData.html
-
+    if (cacheEntry) {
+      const cachedData = cacheEntry.value
       const revalidateOptions = !this.renderOpts.dev
         ? {
             // When the page is 404 cache-control should not be added
             private: isPreviewMode || is404Page,
             stateful: false, // GSP response
             revalidate:
-              cachedData.curRevalidate !== undefined
-                ? cachedData.curRevalidate
+              cacheEntry.curRevalidate !== undefined
+                ? cacheEntry.curRevalidate
                 : /* default to minimum revalidate (this should be an invariant) */ 1,
           }
         : undefined
 
-      if (!isDataReq && cachedData.pageData?.pageProps?.__N_REDIRECT) {
-        await handleRedirect(cachedData.pageData)
-      } else if (cachedData.isNotFound) {
+      if (!cachedData) {
         if (revalidateOptions) {
           setRevalidateHeaders(res, revalidateOptions)
         }
@@ -1689,16 +1684,34 @@ export default class Server {
             query,
           } as UrlWithParsedQuery)
         }
+      } else if (cachedData.kind === 'REDIRECT') {
+        if (isDataReq) {
+          sendPayload(
+            req,
+            res,
+            JSON.stringify(cachedData.props),
+            'json',
+            {
+              generateEtags: this.renderOpts.generateEtags,
+              poweredByHeader: this.renderOpts.poweredByHeader,
+            },
+            revalidateOptions
+          )
+        } else {
+          await handleRedirect(cachedData.props)
+        }
       } else {
         respondWith({
           type: isDataReq ? 'json' : 'html',
-          body: data!,
+          body: isDataReq
+            ? JSON.stringify(cachedData.pageData)
+            : cachedData.html,
           revalidateOptions,
         })
       }
 
       // Stop the request chain here if the data we sent was up-to-date
-      if (!cachedData.isStale) {
+      if (!cacheEntry.isStale) {
         return
       }
     }
@@ -1912,11 +1925,15 @@ export default class Server {
 
     // Update the cache if the head request and cacheable
     if (isOrigin && ssgCacheKey) {
-      await this.incrementalCache.set(
-        ssgCacheKey,
-        { html: html!, pageData, isNotFound, isRedirect },
-        sprRevalidate
-      )
+      let cacheValue: IncrementalCacheValue | null
+      if (isNotFound) {
+        cacheValue = null
+      } else if (isRedirect) {
+        cacheValue = { kind: 'REDIRECT', props: pageData }
+      } else {
+        cacheValue = { kind: 'PAGE', html, pageData }
+      }
+      await this.incrementalCache.set(ssgCacheKey, cacheValue, sprRevalidate)
     }
 
     if (!hasResponded() && isNotFound) {