feat(experimental): option to polyfill fetch using undici in Node.js <18

packages/next/package.json

@@ -75,6 +75,7 @@
     "caniuse-lite": "^1.0.30001332",
     "postcss": "8.4.14",
     "styled-jsx": "5.0.6",
+    "undici": "5.10.0",
     "use-sync-external-store": "1.2.0"
   },
   "peerDependencies": {

packages/next/server/config-utils.ts

@@ -139,6 +139,7 @@ export function loadWebpackHook() {
         'next/dist/compiled/@babel/runtime/package.json',
       ],
       ['node-fetch', 'next/dist/compiled/node-fetch'],
+      ['undici', 'next/dist/compiled/undici'],
     ].map(
       // Use dynamic require.resolve to avoid statically analyzable since they're only for build time
       ([request, replacement]) => [request, require.resolve(replacement)]

packages/next/server/node-polyfill-fetch.js

@@ -1,8 +1,18 @@
-import fetch, {
-  Headers,
-  Request,
-  Response,
-} from 'next/dist/compiled/node-fetch'
+let fetch, Headers, Request, Response
+
+if (process.env.NEXT_USE_UNDICI) {
+  const undici = require('next/dist/compiled/undici')
+  fetch = undici.fetch
+  Headers = undici.Headers
+  Request = undici.Request
+  Response = undici.Response
+} else {
+  const nodeFetch = require('next/dist/compiled/node-fetch')
+  fetch = nodeFetch.fetch
+  Headers = nodeFetch.Headers
+  Request = nodeFetch.Request
+  Response = nodeFetch.Response
+}
 
 // Polyfill fetch() in the Node.js environment
 if (!global.fetch) {

packages/next/taskfile.js

@@ -86,6 +86,8 @@ const externals = {
     'next/dist/build/webpack/plugins/terser-webpack-plugin',
 
   // TODO: Add @swc/helpers to externals once @vercel/ncc switch to swc-loader
+
+  undici: 'undici',
 }
 // eslint-disable-next-line camelcase
 externals['node-html-parser'] = 'next/dist/compiled/node-html-parser'
@@ -167,6 +169,14 @@ export async function ncc_node_fetch(task, opts) {
     .target('compiled/node-fetch')
 }
 
+externals['undici'] = 'next/dist/compiled/undici'
+export async function ncc_undici(task, opts) {
+  await task
+    .source(opts.src || relative(__dirname, require.resolve('undici')))
+    .ncc({ packageName: 'undici', externals })
+    .target('compiled/undici')
+}
+
 // eslint-disable-next-line camelcase
 export async function compile_config_schema(task, opts) {
   const { configSchema } = require('./dist/server/config-schema')

packages/next/types/misc.d.ts

@@ -28,6 +28,12 @@ declare module 'next/dist/compiled/node-fetch' {
   export * from 'node-fetch'
 }
 
+declare module 'next/dist/compiled/undici' {
+  import m from 'undici'
+  export default m
+  export * from 'undici'
+}
+
 declare module 'next/dist/compiled/jest-worker' {
   export * from 'jest-worker'
 }