Don't execute prefetches for bot user agents (#40435)

Such bots typically navigate websites using hard navigations (as they crawl one URL at a time). Respectively, they do not benefit from prefetches at all, while increasing the cost of both the crawl and operating the site.  ## Bug - [ ] Related issues linked using `fixes #number` - [x] Integration tests added - [ ] Errors have helpful link attached, see `contributing.md`
vercel · Sep 13, 2022 · 421029c · 421029c
1 parent 8bf6a87
commit 421029c
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Showing 6 changed files with 68 additions and 7 deletions.
diff --git a/packages/next/server/base-server.ts b/packages/next/server/base-server.ts
@@ -48,7 +48,8 @@ import Router from './router'
 
 import { setRevalidateHeaders } from './send-payload/revalidate-headers'
 import { execOnce } from '../shared/lib/utils'
-import { isBlockedPage, isBot } from './utils'
+import { isBlockedPage } from './utils'
+import { isBot } from '../shared/lib/router/utils/is-bot'
 import RenderResult from './render-result'
 import { removeTrailingSlash } from '../shared/lib/router/utils/remove-trailing-slash'
 import { denormalizePagePath } from '../shared/lib/page-path/denormalize-page-path'

diff --git a/packages/next/server/utils.ts b/packages/next/server/utils.ts
@@ -17,12 +17,6 @@ export function cleanAmpPath(pathname: string): string {
   return pathname
 }
 
-export function isBot(userAgent: string): boolean {
-  return /Googlebot|Mediapartners-Google|AdsBot-Google|googleweblight|Storebot-Google|Google-PageRenderer|Bingbot|BingPreview|Slurp|DuckDuckBot|baiduspider|yandex|sogou|LinkedInBot|bitlybot|tumblr|vkShare|quora link preview|facebookexternalhit|facebookcatalog|Twitterbot|applebot|redditbot|Slackbot|Discordbot|WhatsApp|SkypeUriPreview|ia_archiver/i.test(
-    userAgent
-  )
-}
-
 export function isTargetLikeServerless(target: string) {
   const isServerless = target === 'serverless'
   const isServerlessTrace = target === 'experimental-serverless-trace'

diff --git a/packages/next/shared/lib/router/router.ts b/packages/next/shared/lib/router/router.ts
@@ -47,6 +47,7 @@ import { hasBasePath } from '../../../client/has-base-path'
 import { getNextPathnameInfo } from './utils/get-next-pathname-info'
 import { formatNextPathnameInfo } from './utils/format-next-pathname-info'
 import { compareRouterStates } from './utils/compare-states'
+import { isBot } from './utils/is-bot'
 
 declare global {
   interface Window {
@@ -2171,6 +2172,12 @@ export default class Router implements BaseRouter {
     asPath: string = url,
     options: PrefetchOptions = {}
   ): Promise<void> {
+    if (typeof window !== 'undefined' && isBot(window.navigator.userAgent)) {
+      // No prefetches for bots that render the link since they are typically navigating
+      // links via the equivalent of a hard navigation and hence never utilize these
+      // prefetches.
+      return
+    }
     let parsed = parseRelativeUrl(url)
 
     let { pathname, query } = parsed

diff --git a/packages/next/shared/lib/router/utils/is-bot.ts b/packages/next/shared/lib/router/utils/is-bot.ts
@@ -0,0 +1,5 @@
+export function isBot(userAgent: string): boolean {
+  return /Googlebot|Mediapartners-Google|AdsBot-Google|googleweblight|Storebot-Google|Google-PageRenderer|Bingbot|BingPreview|Slurp|DuckDuckBot|baiduspider|yandex|sogou|LinkedInBot|bitlybot|tumblr|vkShare|quora link preview|facebookexternalhit|facebookcatalog|Twitterbot|applebot|redditbot|Slackbot|Discordbot|WhatsApp|SkypeUriPreview|ia_archiver/i.test(
+    userAgent
+  )
+}
diff --git a/test/integration/preload-viewport/pages/bot-user-agent.js b/test/integration/preload-viewport/pages/bot-user-agent.js
@@ -0,0 +1,22 @@
+import Head from 'next/head'
+import Link from 'next/link'
+
+export default () => {
+  return (
+    <div>
+      <Head>
+        <script
+          dangerouslySetInnerHTML={{
+            __html: `Object.defineProperty(navigator, 'userAgent', {
+              value: new URLSearchParams(location.search).get("useragent"),
+            });`,
+          }}
+        ></script>
+      </Head>
+      <br />
+      <Link href="/another">
+        <a id="link-another">to /another</a>
+      </Link>
+    </div>
+  )
+}
diff --git a/test/integration/preload-viewport/test/index.test.js b/test/integration/preload-viewport/test/index.test.js
@@ -110,6 +110,38 @@ describe('Prefetching Links in viewport', () => {
     }
   })
 
+  it('should prefetch with non-bot UA', async () => {
+    let browser
+    try {
+      browser = await webdriver(
+        appPort,
+        `/bot-user-agent?useragent=${encodeURIComponent(
+          'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/105.0.0.0 Safari/537.36'
+        )}`
+      )
+      const links = await browser.elementsByCss('link[rel=prefetch]')
+      expect(links).toHaveLength(1)
+    } finally {
+      if (browser) await browser.close()
+    }
+  })
+
+  it('should not prefetch with bot UA', async () => {
+    let browser
+    try {
+      browser = await webdriver(
+        appPort,
+        `/bot-user-agent?useragent=${encodeURIComponent(
+          'Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/W.X.Y.Z Mobile Safari/537.36 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)'
+        )}`
+      )
+      const links = await browser.elementsByCss('link[rel=prefetch]')
+      expect(links).toHaveLength(0)
+    } finally {
+      if (browser) await browser.close()
+    }
+  })
+
   it('should prefetch rewritten href with link in viewport onload', async () => {
     let browser
     try {