Memoize loadRedirects() with disk (github#22161)

* memoize loadRedirects with disk in development

* no need to await on sync functions

* un-uncomment

* wip

* wip

* cache with max age

* rename redirects memoize cache file

.gitignore

@@ -15,3 +15,4 @@ coverage/
 blc_output.log
 blc_output_internal.log
 broken_links.md
+lib/redirects/.redirects-cache_*.json

lib/redirects/precompile.js

@@ -1,22 +1,53 @@
-import { languageKeys } from '../languages.js'
+import assert from 'assert'
+import fs from 'fs/promises'
+import path from 'path'
+import { isPromise } from 'util/types'
+import { fileURLToPath } from 'url'
+
 import readJsonFile from '../read-json-file.js'
 import { latest } from '../../lib/enterprise-server-releases.js'
 import getExceptionRedirects from './exception-redirects.js'
-const developerRedirects = readJsonFile('./lib/redirects/static/developer.json')
-const latestDevRedirects = {}
-
-// Replace hardcoded 'latest' with real value in the redirected path
-Object.entries(developerRedirects).forEach(([oldPath, newPath]) => {
-  latestDevRedirects[oldPath] = newPath.replace(
-    'enterprise-server@latest',
-    `enterprise-server@${latest}`
-  )
-})
+import { languageKeys } from '../languages.js'
+
+function diskMemoize(filePath, asyncFn, maxAgeSeconds = 60 * 60) {
+  return async (...args) => {
+    try {
+      const stats = await fs.stat(filePath)
+      const ageSeconds = (new Date().getTime() - stats.mtime.getTime()) / 1000
+      if (ageSeconds < maxAgeSeconds) {
+        const value = JSON.parse(await fs.readFile(filePath, 'utf-8'))
+        console.log(`Redirects disk-cache HIT on ${filePath}`)
+        return value
+      }
+      console.log(`Redirects disk-cache ${filePath} too old`)
+    } catch (err) {
+      if (err.code !== 'ENOENT') throw err
+    }
+    console.log(`Redirects disk-cache MISS on ${filePath}`)
+    const promise = asyncFn(...args)
+    assert(isPromise(promise), "memoized function didn't return a promise")
+    return promise.then(async (value) => {
+      await fs.writeFile(filePath, JSON.stringify(value), 'utf-8')
+      return value
+    })
+  }
+}
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+const DISK_CACHE_FILEPATH = path.join(__dirname, `.redirects-cache_${languageKeys.join('_')}.json`)
 
 // This function runs at server warmup and precompiles possible redirect routes.
 // It outputs them in key-value pairs within a neat Javascript object: { oldPath: newPath }
-export default async function precompileRedirects(pageList) {
-  const allRedirects = Object.assign({}, latestDevRedirects)
+const precompileRedirects = diskMemoize(DISK_CACHE_FILEPATH, async (pageList) => {
+  const allRedirects = readJsonFile('./lib/redirects/static/developer.json')
+
+  // Replace hardcoded 'latest' with real value in the redirected path
+  Object.entries(allRedirects).forEach(([oldPath, newPath]) => {
+    allRedirects[oldPath] = newPath.replace(
+      'enterprise-server@latest',
+      `enterprise-server@${latest}`
+    )
+  })
 
   // Exception redirects are those that are essentially unicorn one-offs.
   // For example, we have redirects for documents that used to be on
@@ -35,9 +66,8 @@ export default async function precompileRedirects(pageList) {
 
   // CURRENT PAGES PERMALINKS AND FRONTMATTER
   // create backwards-compatible old paths for page permalinks and frontmatter redirects
-  await Promise.all(
-    pageList.map(async (page) => Object.assign(allRedirects, page.buildRedirects()))
-  )
+  pageList.forEach((page) => Object.assign(allRedirects, page.buildRedirects()))
 
   return allRedirects
-}
+})
+export default precompileRedirects