fix: add stale cache handling to fetchCached function

Author: LadyBluenotes

src/utils/cache.server.ts

@@ -2,6 +2,7 @@ import LRUCache from 'lru-cache'
 
 declare global {
   var docCache: LRUCache<string, unknown>
+  var docStaleCache: LRUCache<string, unknown>
 }
 
 const docCache =
@@ -12,20 +13,42 @@ const docCache =
     ttl: process.env.NODE_ENV === 'production' ? 1 : 1000000,
   }))
 
+const docStaleCache =
+  globalThis.docStaleCache ||
+  (globalThis.docStaleCache = new LRUCache<string, unknown>({
+    max: 300,
+  }))
+
 export async function fetchCached<T>(opts: {
   fn: () => Promise<T>
   key: string
   ttl: number
+  staleOnError?: boolean
 }): Promise<T> {
   if (docCache.has(opts.key)) {
     return docCache.get(opts.key) as T
   }
 
-  const result = await opts.fn()
+  try {
+    const result = await opts.fn()
 
-  docCache.set(opts.key, result, {
-    ttl: opts.ttl,
-  })
+    docCache.set(opts.key, result, {
+      ttl: opts.ttl,
+    })
 
-  return result
+    if (opts.staleOnError) {
+      docStaleCache.set(opts.key, result)
+    }
+
+    return result
+  } catch (error) {
+    if (opts.staleOnError && docStaleCache.has(opts.key)) {
+      console.warn(
+        `[fetchCached] Serving stale value for key '${opts.key}' after fetch error`,
+      )
+      return docStaleCache.get(opts.key) as T
+    }
+
+    throw error
+  }
 }

src/utils/documents.server.ts

@@ -423,6 +423,7 @@ export function fetchApiContents(
   return fetchCached({
     key: `${repoPair}:${branch}:${startingPath}`,
     ttl: isDev ? 1 : 10 * 60 * 1000, // 10 minute
+    staleOnError: true,
     fn: () => {
       return isDev
         ? fetchApiContentsFs(repoPair, startingPath)