Merge pull request #24312 from github/repo-sync

repo sync

Author: Octomerger

lib/create-tree.js

@@ -3,38 +3,68 @@ import fs from 'fs/promises'
 
 import Page from './page.js'
 
-export default async function createTree(originalPath, rootPath) {
+export default async function createTree(originalPath, rootPath, previousTree) {
   const basePath = rootPath || originalPath
 
   // On recursive runs, this is processing page.children items in `/<link>` format.
   // If the path exists as is, assume this is a directory with a child index.md.
   // Otherwise, assume it's a child .md file and add `.md` to the path.
   let filepath
+  let mtime
+  // This kills two birds with one stone. We (attempt to) read it as a file,
+  // to find out if it's a directory or a file and whence we know that
+  // we also collect it's modification time.
   try {
-    await fs.access(originalPath)
-    filepath = `${originalPath}/index.md`
-  } catch {
     filepath = `${originalPath}.md`
+    mtime = await getMtime(filepath)
+  } catch (error) {
+    if (error.code !== 'ENOENT') {
+      throw error
+    }
+    filepath = `${originalPath}/index.md`
+    // Note, if this throws, that's quite fine. It usually means that
+    // there's a `index.md` whose `children:` entry lists something that
+    // doesn't exist on disk. So the writer who tries to preview the
+    // page will see the error and it's hopefully clear what's actually
+    // wrong.
+    try {
+      mtime = await getMtime(filepath)
+    } catch (error) {
+      if (error.code === 'ENOENT' && filepath.split(path.sep).includes('early-access')) {
+        // Do not throw an error if Early Access is not available.
+        console.warn(
+          `${filepath} could not be turned into a Page, but is ignored because it's early-access`
+        )
+        return
+      }
+      throw error
+    }
   }
 
   const relativePath = filepath.replace(`${basePath}/`, '')
 
-  // Initialize the Page! This is where the file reads happen.
-  const page = await Page.init({
-    basePath,
-    relativePath,
-    languageCode: 'en',
-  })
+  // Reading in a file from disk is slow and best avoided if we can be
+  // certain it isn't necessary. If the previous tree is known and that
+  // tree's page node's `mtime` hasn't changed, we can use that instead.
+  let page
+  if (previousTree && previousTree.page.mtime === mtime) {
+    // A save! We can use the same exact Page instance from the previous
+    // tree because the assumption is that since the `.md` file it was
+    // created from hasn't changed (on disk) the instance object wouldn't
+    // change.
+    page = previousTree.page
+  } else {
+    // Either the previous tree doesn't exist yet or the modification time
+    // of the file on disk has changed.
+    page = await Page.init({
+      basePath,
+      relativePath,
+      languageCode: 'en',
+      mtime,
+    })
+  }
 
   if (!page) {
-    // Do not throw an error if Early Access is not available.
-    if (relativePath.startsWith('early-access')) {
-      console.warn(
-        `${relativePath} could not be turned into a Page, but is ignore because it's early-access`
-      )
-      return
-    }
-
     throw Error(`Cannot initialize page for ${filepath}`)
   }
 
@@ -49,7 +79,12 @@ export default async function createTree(originalPath, rootPath) {
     item.childPages = (
       await Promise.all(
         item.page.children.map(
-          async (child) => await createTree(path.posix.join(originalPath, child), basePath)
+          async (child, i) =>
+            await createTree(
+              path.posix.join(originalPath, child),
+              basePath,
+              previousTree && previousTree.childPages[i]
+            )
         )
       )
     ).filter(Boolean)
@@ -58,6 +93,22 @@ export default async function createTree(originalPath, rootPath) {
   return item
 }
 
+async function getMtime(filePath) {
+  // Use mtimeMs, which is a regular floating point number, instead of the
+  // mtime which is a Date based on that same number.
+  // Otherwise, if we use the Date instances, we have to compare
+  // them using `oneDate.getTime() === anotherDate.getTime()`.
+  const { mtimeMs } = await fs.stat(filePath)
+  // The `mtimeMs` is a number like `1669827766942.7954`
+  // From the docs:
+  // "The timestamp indicating the last time this file was modified expressed
+  // in nanoseconds since the POSIX Epoch."
+  // But the number isn't actually all that important. We just need it to
+  // later be able to know if it changed. We round it to the nearest
+  // millisecond.
+  return Math.round(mtimeMs)
+}
+
 function assertUniqueChildren(page) {
   if (page.children.length !== new Set(page.children).size) {
     const count = {}

middleware/index.js

@@ -20,6 +20,7 @@ import handleErrors from './handle-errors.js'
 import handleInvalidPaths from './handle-invalid-paths.js'
 import handleNextDataPath from './handle-next-data-path.js'
 import detectLanguage from './detect-language.js'
+import reloadTree from './reload-tree.js'
 import context from './context.js'
 import shortVersions from './contextualizers/short-versions.js'
 import languageCodeRedirects from './redirects/language-code-redirects.js'
@@ -212,6 +213,7 @@ export default function (app) {
   // *** Config and context for redirects ***
   app.use(reqUtils) // Must come before events
   app.use(instrument(detectLanguage, './detect-language')) // Must come before context, breadcrumbs, find-page, handle-errors, homepages
+  app.use(asyncMiddleware(instrument(reloadTree, './reload-tree'))) // Must come before context
   app.use(asyncMiddleware(instrument(context, './context'))) // Must come before early-access-*, handle-redirects
   app.use(instrument(shortVersions, './contextualizers/short-versions')) // Support version shorthands
 

middleware/reload-tree.js

@@ -0,0 +1,72 @@
+/**
+ * This exists for local previewing. Only.
+ * We load in the entire tree on startup, then that's used for things like
+ * sidebars and breadcrumbs and landing pages and ToC pages (and possibly
+ * more).
+ * When an individual page is requested, we always reload it from disk
+ * in case it has changed. But that's not feasible with all 1k+ pages.
+ *
+ * The core of this middleware calls `createTree()` but by passing the
+ * optional previous tree so that within `createTree` it can opt to
+ * re-use those that haven't changed on disk.
+ *
+ * The intention here is so that things like sidebars can refresh
+ * without having to restart the entire server.
+ */
+
+import path from 'path'
+
+import languages, { languageKeys } from '../lib/languages.js'
+import createTree from '../lib/create-tree.js'
+import warmServer from '../lib/warm-server.js'
+import { loadSiteTree, loadPages, loadPageMap } from '../lib/page-data.js'
+import loadRedirects from '../lib/redirects/precompile.js'
+
+const languagePrefixRegex = new RegExp(`^/(${languageKeys.join('|')})(/|$)`)
+const englishPrefixRegex = /^\/en(\/|$)/
+
+const isDev = process.env.NODE_ENV === 'development'
+
+export default async function reloadTree(req, res, next) {
+  if (!isDev) return next()
+  // Filter out things like `/will/redirect` or `/_next/data/...`
+  if (!languagePrefixRegex.test(req.pagePath)) return next()
+  // We only bother if the loaded URL is something `/en/...`
+  if (!englishPrefixRegex.test(req.pagePath)) return next()
+
+  const warmed = await warmServer()
+  // For all the real English content, this usually takes about 30-60ms on
+  // an Intel MacbookPro.
+  const before = getMtimes(warmed.unversionedTree.en)
+  warmed.unversionedTree.en = await createTree(
+    path.join(languages.en.dir, 'content'),
+    undefined,
+    warmed.unversionedTree.en
+  )
+  const after = getMtimes(warmed.unversionedTree.en)
+  // The next couple of operations are much slower (in total) than
+  // refrehing the tree. So we want to know if the tree changed before
+  // bothering.
+  // If refreshing of the `.en` part of the `unversionedTree` takes 40ms
+  // then the following operations takes about 140ms.
+  if (before !== after) {
+    warmed.siteTree = await loadSiteTree(warmed.unversionedTree)
+    warmed.pageList = await loadPages(warmed.unversionedTree)
+    warmed.pageMap = await loadPageMap(warmed.pageList)
+    warmed.redirects = await loadRedirects(warmed.pageList)
+  }
+
+  return next()
+}
+
+// Given a tree, return a number that represents the mtimes for all pages
+// in the tree.
+// You can use this to compute it before and after the tree is (maybe)
+// mutated and if the numbers *change* you can know the tree changed.
+function getMtimes(tree) {
+  let mtimes = tree.page.mtime
+  for (const child of tree.childPages || []) {
+    mtimes += getMtimes(child)
+  }
+  return mtimes
+}