Add basePath in link component and add/remove it consistently

packages/next/build/webpack-config.ts

@@ -540,7 +540,12 @@ export default async function getBaseWebpackConfig(
 
             let isNextExternal: boolean = false
             if (isLocal) {
-              isNextExternal = /next[/\\]dist[/\\]next-server[/\\]/.test(res)
+              // we need to process next-server/lib/router/router so that
+              // the DefinePlugin can inject process.env values
+              isNextExternal = /next[/\\]dist[/\\]next-server[/\\](?!lib[/\\]router[/\\]router)/.test(
+                res
+              )
+
               if (!isNextExternal) {
                 return callback()
               }

packages/next/build/webpack/loaders/next-serverless-loader.ts

@@ -266,6 +266,7 @@ const nextServerlessLoader: loader.Loader = function() {
         runtimeConfig: runtimeConfig.publicRuntimeConfig || {},
         previewProps: ${encodedPreviewProps},
         env: process.env,
+        basePath: "${basePath}",
         ..._renderOpts
       }
       let _nextData = false

packages/next/client/link.tsx

@@ -9,6 +9,7 @@ import {
   getLocationOrigin,
 } from '../next-server/lib/utils'
 import Router from './router'
+import { addBasePath } from '../next-server/lib/router/router'
 
 function isLocal(href: string) {
   const url = parse(href, false, true)
@@ -161,8 +162,8 @@ class Link extends Component<LinkProps> {
   // as per https://reactjs.org/blog/2018/06/07/you-probably-dont-need-derived-state.html
   formatUrls = memoizedFormatUrl((href, asHref) => {
     return {
-      href: formatUrl(href),
-      as: asHref ? formatUrl(asHref) : asHref,
+      href: addBasePath(formatUrl(href)),
+      as: asHref ? addBasePath(formatUrl(asHref)) : asHref,
     }
   })
 

packages/next/client/router.ts

@@ -36,6 +36,7 @@ const urlPropertyFields = [
   'asPath',
   'components',
   'isFallback',
+  'basePath',
 ]
 const routerEvents = [
   'routeChangeStart',

packages/next/export/index.ts

@@ -238,6 +238,7 @@ export default async function(
     dev: false,
     staticMarkup: false,
     hotReloader: null,
+    basePath: nextConfig.experimental.basePath,
     canonicalBase: nextConfig.amp?.canonicalBase || '',
     isModern: nextConfig.experimental.modern,
     ampValidatorPath: nextConfig.experimental.amp?.validator || undefined,

packages/next/next-server/lib/router/router.ts

@@ -16,10 +16,16 @@ import { isDynamicRoute } from './utils/is-dynamic'
 import { getRouteMatcher } from './utils/route-matcher'
 import { getRouteRegex } from './utils/route-regex'
 
-function addBasePath(path: string): string {
-  // variable is always a string
-  const p = process.env.__NEXT_ROUTER_BASEPATH as string
-  return path.indexOf(p) !== 0 ? p + path : path
+const basePath = process.env.__NEXT_ROUTER_BASEPATH as string
+
+export function addBasePath(path: string): string {
+  return path.indexOf(basePath) !== 0 ? basePath + path : path
+}
+
+function delBasePath(path: string): string {
+  return path.indexOf(basePath) === 0
+    ? path.substr(basePath.length) || '/'
+    : path
 }
 
 function toRoute(path: string): string {
@@ -38,6 +44,7 @@ export type BaseRouter = {
   pathname: string
   query: ParsedUrlQuery
   asPath: string
+  basePath: string
 }
 
 export type NextRouter = BaseRouter &
@@ -133,6 +140,8 @@ export default class Router implements BaseRouter {
   pathname: string
   query: ParsedUrlQuery
   asPath: string
+  basePath: string
+
   /**
    * Map of all components loaded in `Router`
    */
@@ -206,6 +215,7 @@ export default class Router implements BaseRouter {
     this.asPath =
       // @ts-ignore this is temporarily global (attached to window)
       isDynamicRoute(pathname) && __NEXT_DATA__.autoExport ? pathname : as
+    this.basePath = basePath
     this.sub = subscription
     this.clc = null
     this._wrapApp = wrapApp
@@ -361,9 +371,12 @@ export default class Router implements BaseRouter {
 
       // If url and as provided as an object representation,
       // we'll format them into the string version here.
-      const url = typeof _url === 'object' ? formatWithValidation(_url) : _url
+      let url = typeof _url === 'object' ? formatWithValidation(_url) : _url
       let as = typeof _as === 'object' ? formatWithValidation(_as) : _as
 
+      url = addBasePath(url)
+      as = addBasePath(as)
+
       // Add the ending slash to the paths. So, we can serve the
       // "<page>/index.html" directly for the SSR page.
       if (process.env.__NEXT_EXPORT_TRAILING_SLASH) {
@@ -386,7 +399,7 @@ export default class Router implements BaseRouter {
       if (!options._h && this.onlyAHashChange(as)) {
         this.asPath = as
         Router.events.emit('hashChangeStart', as)
-        this.changeState(method, url, addBasePath(as), options)
+        this.changeState(method, url, as, options)
         this.scrollToHash(as)
         Router.events.emit('hashChangeComplete', as)
         return resolve(true)
@@ -458,7 +471,7 @@ export default class Router implements BaseRouter {
         }
 
         Router.events.emit('beforeHistoryChange', as)
-        this.changeState(method, url, addBasePath(as), options)
+        this.changeState(method, url, as, options)
 
         if (process.env.NODE_ENV !== 'production') {
           const appComp: any = this.components['/_app'].Component
@@ -737,12 +750,10 @@ export default class Router implements BaseRouter {
       if (process.env.NODE_ENV !== 'production') {
         return
       }
-
+      const route = delBasePath(toRoute(pathname))
       Promise.all([
-        this.pageLoader.prefetchData(url, asPath),
-        this.pageLoader[options.priority ? 'loadPage' : 'prefetch'](
-          toRoute(pathname)
-        ),
+        this.pageLoader.prefetchData(url, delBasePath(asPath)),
+        this.pageLoader[options.priority ? 'loadPage' : 'prefetch'](route),
       ]).then(() => resolve(), reject)
     })
   }
@@ -752,6 +763,7 @@ export default class Router implements BaseRouter {
     const cancel = (this.clc = () => {
       cancelled = true
     })
+    route = delBasePath(route)
 
     const componentResult = await this.pageLoader.loadPage(route)
 

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

@@ -123,6 +123,7 @@ export default class Server {
     previewProps: __ApiPreviewProps
     customServer?: boolean
     ampOptimizerConfig?: { [key: string]: any }
+    basePath: string
   }
   private compression?: Middleware
   private onErrorMiddleware?: ({ err }: { err: Error }) => Promise<void>
@@ -179,6 +180,7 @@ export default class Server {
       previewProps: this.getPreviewProps(),
       customServer: customServer === true ? true : undefined,
       ampOptimizerConfig: this.nextConfig.experimental.amp?.optimizer,
+      basePath: this.nextConfig.experimental.basePath,
     }
 
     // Only the `publicRuntimeConfig` key is exposed to the client side
@@ -265,14 +267,15 @@ export default class Server {
       parsedUrl.query = parseQs(parsedUrl.query)
     }
 
-    if (parsedUrl.pathname!.startsWith(this.nextConfig.experimental.basePath)) {
+    const { basePath } = this.nextConfig.experimental
+
+    // if basePath is set require it be present
+    if (basePath && !req.url!.startsWith(basePath)) {
+      return this.render404(req, res, parsedUrl)
+    } else {
       // If replace ends up replacing the full url it'll be `undefined`, meaning we have to default it to `/`
-      parsedUrl.pathname =
-        parsedUrl.pathname!.replace(
-          this.nextConfig.experimental.basePath,
-          ''
-        ) || '/'
-      req.url = req.url!.replace(this.nextConfig.experimental.basePath, '')
+      parsedUrl.pathname = parsedUrl.pathname!.replace(basePath, '') || '/'
+      req.url = req.url!.replace(basePath, '')
     }
 
     res.statusCode = 200

packages/next/next-server/server/render.tsx

@@ -54,6 +54,7 @@ class ServerRouter implements NextRouter {
   pathname: string
   query: ParsedUrlQuery
   asPath: string
+  basePath: string
   events: any
   isFallback: boolean
   // TODO: Remove in the next major version, as this would mean the user is adding event listeners in server-side `render` method
@@ -63,14 +64,15 @@ class ServerRouter implements NextRouter {
     pathname: string,
     query: ParsedUrlQuery,
     as: string,
-    { isFallback }: { isFallback: boolean }
+    { isFallback }: { isFallback: boolean },
+    basePath: string
   ) {
     this.route = pathname.replace(/\/$/, '') || '/'
     this.pathname = pathname
     this.query = query
     this.asPath = as
-
     this.isFallback = isFallback
+    this.basePath = basePath
   }
   push(): any {
     noRouter()
@@ -156,6 +158,7 @@ export type RenderOptsPartial = {
   isDataReq?: boolean
   params?: ParsedUrlQuery
   previewProps: __ApiPreviewProps
+  basePath: string
 }
 
 export type RenderOpts = LoadComponentsReturnType & RenderOptsPartial
@@ -309,6 +312,7 @@ export async function renderToHTML(
     isDataReq,
     params,
     previewProps,
+    basePath,
   } = renderOpts
 
   const callMiddleware = async (method: string, args: any[], props = false) => {
@@ -452,10 +456,16 @@ export async function renderToHTML(
   await Loadable.preloadAll() // Make sure all dynamic imports are loaded
 
   // url will always be set
-  const asPath = req.url as string
-  const router = new ServerRouter(pathname, query, asPath, {
-    isFallback: isFallback,
-  })
+  const asPath: string = req.url as string
+  const router = new ServerRouter(
+    pathname,
+    query,
+    asPath,
+    {
+      isFallback: isFallback,
+    },
+    basePath
+  )
   const ctx = {
     err,
     req: isAutoExport ? undefined : req,

test/integration/basepath/pages/hello.js

@@ -1,9 +1,13 @@
 import Link from 'next/link'
+import { useRouter } from 'next/router'
 
 export default () => (
-  <Link href="/other-page">
-    <a id="other-page-link">
-      <h1>Hello World</h1>
-    </a>
-  </Link>
+  <>
+    <Link href="/other-page">
+      <a id="other-page-link">
+        <h1>Hello World</h1>
+      </a>
+    </Link>
+    <div id="base-path">{useRouter().basePath}</div>
+  </>
 )

test/integration/basepath/test/index.test.js

@@ -2,6 +2,7 @@
 /* global jasmine */
 import webdriver from 'next-webdriver'
 import { join } from 'path'
+import url from 'url'
 import {
   nextServer,
   launchApp,
@@ -49,6 +50,19 @@ const runTests = (context, dev = false) => {
     }
   })
 
+  it('should have correct href for a link', async () => {
+    const browser = await webdriver(context.appPort, '/docs/hello')
+    const href = await browser.elementByCss('a').getAttribute('href')
+    const { pathname } = url.parse(href)
+    expect(pathname).toBe('/docs/other-page')
+  })
+
+  it('should show 404 for page not under the /docs prefix', async () => {
+    const text = await renderViaHTTP(context.appPort, '/hello')
+    expect(text).not.toContain('Hello World')
+    expect(text).toContain('This page could not be found')
+  })
+
   it('should show the other-page page under the /docs prefix', async () => {
     const browser = await webdriver(context.appPort, '/docs/other-page')
     try {
@@ -59,6 +73,12 @@ const runTests = (context, dev = false) => {
     }
   })
 
+  it('should have basePath field on Router', async () => {
+    const html = await renderViaHTTP(context.appPort, '/docs/hello')
+    const $ = cheerio.load(html)
+    expect($('#base-path').text()).toBe('/docs')
+  })
+
   it('should navigate to the page without refresh', async () => {
     const browser = await webdriver(context.appPort, '/docs/hello')
     try {

test/integration/size-limit/test/index.test.js

@@ -100,7 +100,7 @@ describe('Production response size', () => {
     )
 
     // These numbers are without gzip compression!
-    const delta = responseSizesBytes - 165 * 1024
+    const delta = responseSizesBytes - 166 * 1024
     expect(delta).toBeLessThanOrEqual(1024) // don't increase size more than 1kb
     expect(delta).toBeGreaterThanOrEqual(-1024) // don't decrease size more than 1kb without updating target
   })