Reduce hello-world middleware bundle size from 128k to 88k (#35512)

Moves two utility functions from `server/router.ts` into their own file. This avoids the middleware pulling in the full Next.js router into its bundle.

There are probably more opportunities like this, but this is a good start. Middleware should likely be bundled by a non-chunking optimizing compiler.

packages/next/server/base-server.ts

@@ -42,7 +42,7 @@ import {
 import * as envConfig from '../shared/lib/runtime-config'
 import { DecodeError, normalizeRepeatedSlashes } from '../shared/lib/utils'
 import { isTargetLikeServerless } from './utils'
-import Router, { replaceBasePath, route } from './router'
+import Router, { route } from './router'
 import { setRevalidateHeaders } from './send-payload/revalidate-headers'
 import { IncrementalCache } from './incremental-cache'
 import { execOnce } from '../shared/lib/utils'
@@ -64,6 +64,7 @@ import { addRequestMeta, getRequestMeta } from './request-meta'
 import { createHeaderRoute, createRedirectRoute } from './server-route-utils'
 import { PrerenderManifest } from '../build'
 import { ImageConfigComplete } from '../shared/lib/image-config'
+import { replaceBasePath } from './router-utils'
 
 export type FindComponentsResult = {
   components: LoadComponentsReturnType

packages/next/server/dev/next-dev-server.ts

@@ -41,7 +41,8 @@ import {
 } from '../../shared/lib/router/utils'
 import Server, { WrappedBuildError } from '../next-server'
 import { normalizePagePath } from '../normalize-page-path'
-import Router, { hasBasePath, replaceBasePath, route } from '../router'
+import Router, { route } from '../router'
+import { hasBasePath, replaceBasePath } from '../router-utils'
 import { eventCliSession } from '../../telemetry/events'
 import { Telemetry } from '../../telemetry/storage'
 import { setGlobal } from '../../trace'

packages/next/server/router-utils.ts

@@ -0,0 +1,17 @@
+export function replaceBasePath(pathname: string, basePath: string): string {
+  // ensure basePath is only stripped if it matches exactly
+  // and doesn't contain extra chars e.g. basePath /docs
+  // should replace for /docs, /docs/, /docs/a but not /docsss
+  if (hasBasePath(pathname, basePath)) {
+    pathname = pathname.substr(basePath.length)
+    if (!pathname.startsWith('/')) pathname = `/${pathname}`
+  }
+  return pathname
+}
+
+export function hasBasePath(pathname: string, basePath: string): boolean {
+  return (
+    typeof pathname === 'string' &&
+    (pathname === basePath || pathname.startsWith(basePath + '/'))
+  )
+}

packages/next/server/web/next-url.ts

@@ -1,8 +1,8 @@
 import type { PathLocale } from '../../shared/lib/i18n/normalize-locale-path'
 import type { DomainLocale, I18NConfig } from '../config-shared'
 import { getLocaleMetadata } from '../../shared/lib/i18n/get-locale-metadata'
-import { replaceBasePath } from '../router'
 import cookie from 'next/dist/compiled/cookie'
+import { replaceBasePath } from '../router-utils'
 
 interface Options {
   base?: string | URL

packages/next/shared/lib/router/utils/parse-next-url.ts

@@ -4,7 +4,7 @@ import { parseUrl } from './parse-url'
 import type { NextConfig, DomainLocale } from '../../../../server/config-shared'
 import type { ParsedUrl } from './parse-url'
 import type { PathLocale } from '../../i18n/normalize-locale-path'
-import { hasBasePath, replaceBasePath } from '../../../../server/router'
+import { hasBasePath, replaceBasePath } from '../../../../server/router-utils'
 
 interface Params {
   headers?: { [key: string]: string | string[] | undefined }