From 6c7771e4447d6b18e48c97998f5215af1b338f45 Mon Sep 17 00:00:00 2001
From: Malte Ubl <malte.ubl@gmail.com>
Date: Mon, 21 Mar 2022 18:35:18 -0700
Subject: [PATCH] Reduce hello-world middleware bundle size from 128k to 88k

Moves two utiloty functions from `server/router.ts` into their own file. This avoids the middleware pulling in the full Next.js router into its bundle.
---
 packages/next/server/base-server.ts             |  3 ++-
 packages/next/server/dev/next-dev-server.ts     |  3 ++-
 packages/next/server/router-utils.ts            | 17 +++++++++++++++++
 packages/next/server/web/next-url.ts            |  2 +-
 .../shared/lib/router/utils/parse-next-url.ts   |  2 +-
 5 files changed, 23 insertions(+), 4 deletions(-)
 create mode 100644 packages/next/server/router-utils.ts

diff --git a/packages/next/server/base-server.ts b/packages/next/server/base-server.ts
index f02f7db199d..a575e1ad596 100644
--- a/packages/next/server/base-server.ts
+++ b/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
diff --git a/packages/next/server/dev/next-dev-server.ts b/packages/next/server/dev/next-dev-server.ts
index 2a18039e648..b30545ae5bd 100644
--- a/packages/next/server/dev/next-dev-server.ts
+++ b/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'
diff --git a/packages/next/server/router-utils.ts b/packages/next/server/router-utils.ts
new file mode 100644
index 00000000000..630521434fd
--- /dev/null
+++ b/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 + '/'))
+  )
+}
diff --git a/packages/next/server/web/next-url.ts b/packages/next/server/web/next-url.ts
index 532b93e64ab..8ceaea68323 100644
--- a/packages/next/server/web/next-url.ts
+++ b/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
diff --git a/packages/next/shared/lib/router/utils/parse-next-url.ts b/packages/next/shared/lib/router/utils/parse-next-url.ts
index 57985ecfaf0..0e36e4b6191 100644
--- a/packages/next/shared/lib/router/utils/parse-next-url.ts
+++ b/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 }