fix(fetch-cache): fix additional typo, add type & data validation

packages/next/src/server/lib/incremental-cache/fetch-cache.ts

@@ -1,6 +1,14 @@
 import type { CacheHandler, CacheHandlerContext, CacheHandlerValue } from './'
+import type {
+  CachedFetchValue,
+  IncrementalCacheValue,
+} from '../../response-cache'
 
 import LRUCache from 'next/dist/compiled/lru-cache'
+
+import { z } from 'next/dist/compiled/zod'
+import type zod from 'next/dist/compiled/zod'
+
 import {
   CACHE_ONE_YEAR,
   NEXT_CACHE_SOFT_TAGS_HEADER,
@@ -23,6 +31,18 @@ const CACHE_REVALIDATE_HEADER = 'x-vercel-revalidate' as const
 const CACHE_FETCH_URL_HEADER = 'x-vercel-cache-item-name' as const
 const CACHE_CONTROL_VALUE_HEADER = 'x-vercel-cache-control' as const
 
+const zCachedFetchValue: zod.ZodType<CachedFetchValue> = z.object({
+  kind: z.literal('FETCH'),
+  data: z.object({
+    headers: z.record(z.string()),
+    body: z.string(),
+    url: z.string(),
+    status: z.number().optional(),
+  }),
+  tags: z.array(z.string()).optional(),
+  revalidate: z.number(),
+})
+
 export default class FetchCache implements CacheHandler {
   private headers: Record<string, string>
   private cacheEndpoint?: string
@@ -233,19 +253,20 @@ export default class FetchCache implements CacheHandler {
           throw new Error(`invalid response from cache ${res.status}`)
         }
 
-        const cached = await res.json()
+        const cached: IncrementalCacheValue = await res.json()
+        const cachedParsed = zCachedFetchValue.safeParse(cached)
 
-        if (!cached || cached.kind !== 'FETCH') {
+        if (!cached || !cachedParsed.success) {
           this.debug && console.log({ cached })
-          throw new Error(`invalid cache value`)
+          throw new Error('invalid cache value')
         }
 
         // if new tags were specified, merge those tags to the existing tags
         if (cached.kind === 'FETCH') {
           cached.tags ??= []
           for (const tag of tags ?? []) {
             if (!cached.tags.includes(tag)) {
-              cached.tag.push(tag)
+              cached.tags.push(tag)
             }
           }
         }