implementar recurso de base path do next em tempo de execucao

packages/next/src/build/define-env.ts

@@ -224,6 +224,8 @@ export function getDefineEnv({
         }),
     'process.env.__NEXT_MANUAL_CLIENT_BASE_PATH':
       config.experimental.manualClientBasePath ?? false,
+    'process.env.__NEXT_RUNTIME_BASE_PATH_ENABLED':
+      config.experimental.runtimeBasePath ?? false,
     'process.env.__NEXT_CLIENT_ROUTER_DYNAMIC_STALETIME': JSON.stringify(
       isNaN(Number(config.experimental.staleTimes?.dynamic))
         ? 0

packages/next/src/client/add-base-path.ts

@@ -1,9 +1,14 @@
 import { addPathPrefix } from '../shared/lib/router/utils/add-path-prefix'
+import { getRuntimeBasePath } from '../shared/lib/router/utils/runtime-base-path'
 import { normalizePathTrailingSlash } from './normalize-trailing-slash'
 
-const basePath = (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
+const compileTimeBasePath =
+  (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
 
 export function addBasePath(path: string, required?: boolean): string {
+  const basePath = process.env.__NEXT_RUNTIME_BASE_PATH_ENABLED
+    ? getRuntimeBasePath()
+    : compileTimeBasePath
   return normalizePathTrailingSlash(
     process.env.__NEXT_MANUAL_CLIENT_BASE_PATH && !required
       ? path

packages/next/src/client/has-base-path.ts

@@ -1,7 +1,12 @@
 import { pathHasPrefix } from '../shared/lib/router/utils/path-has-prefix'
+import { getRuntimeBasePath } from '../shared/lib/router/utils/runtime-base-path'
 
-const basePath = (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
+const compileTimeBasePath =
+  (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
 
 export function hasBasePath(path: string): boolean {
+  const basePath = process.env.__NEXT_RUNTIME_BASE_PATH_ENABLED
+    ? getRuntimeBasePath()
+    : compileTimeBasePath
   return pathHasPrefix(path, basePath)
 }

packages/next/src/client/index.tsx

@@ -33,6 +33,7 @@ import { ImageConfigContext } from '../shared/lib/image-config-context.shared-ru
 import type { ImageConfigComplete } from '../shared/lib/image-config'
 import { removeBasePath } from './remove-base-path'
 import { hasBasePath } from './has-base-path'
+import { setClientRuntimeBasePath } from '../shared/lib/router/utils/runtime-base-path'
 import { AppRouterContext } from '../shared/lib/app-router-context.shared-runtime'
 import {
   adaptForAppRouterInstance,
@@ -205,6 +206,10 @@ export async function initialize(opts: { devClient?: any } = {}): Promise<{
   )
   window.__NEXT_DATA__ = initialData
 
+  if (process.env.__NEXT_RUNTIME_BASE_PATH_ENABLED) {
+    setClientRuntimeBasePath(initialData.basePath || '')
+  }
+
   defaultLocale = initialData.defaultLocale
   const prefix: string = initialData.assetPrefix || ''
   // With dynamic assetPrefix it's no longer possible to set assetPrefix at the build time

packages/next/src/client/remove-base-path.ts

@@ -1,6 +1,8 @@
+import { getRuntimeBasePath } from '../shared/lib/router/utils/runtime-base-path'
 import { hasBasePath } from './has-base-path'
 
-const basePath = (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
+const compileTimeBasePath =
+  (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
 
 export function removeBasePath(path: string): string {
   if (process.env.__NEXT_MANUAL_CLIENT_BASE_PATH) {
@@ -9,6 +11,10 @@ export function removeBasePath(path: string): string {
     }
   }
 
+  const basePath = process.env.__NEXT_RUNTIME_BASE_PATH_ENABLED
+    ? getRuntimeBasePath()
+    : compileTimeBasePath
+
   // Can't trim the basePath if it has zero length!
   if (basePath.length === 0) return path
 

packages/next/src/server/config-schema.ts

@@ -268,6 +268,7 @@ export const experimentalSchema = {
   largePageDataBytes: z.number().optional(),
   linkNoTouchStart: z.boolean().optional(),
   manualClientBasePath: z.boolean().optional(),
+  runtimeBasePath: z.boolean().optional(),
   middlewarePrefetch: z.enum(['strict', 'flexible']).optional(),
   proxyPrefetch: z.enum(['strict', 'flexible']).optional(),
   middlewareClientMaxBodySize: zSizeLimit.optional(),

packages/next/src/server/config-shared.ts

@@ -512,6 +512,23 @@ export interface ExperimentalConfig {
   middlewarePrefetch?: 'strict' | 'flexible'
   proxyPrefetch?: 'strict' | 'flexible'
   manualClientBasePath?: boolean
+  /**
+   * Read the basePath from the `x-base-path` request header at runtime instead
+   * of taking it from `next.config.js` at build time.
+   *
+   * When enabled:
+   * - The server reads `x-base-path` from the incoming request, uses it for
+   *   the duration of the render, and writes it into `__NEXT_DATA__.basePath`.
+   * - The client picks the value up from `__NEXT_DATA__.basePath` and uses
+   *   it for every `addBasePath` / `removeBasePath` call (Link, router.push,
+   *   `_next/data` URLs, page chunk URLs).
+   *
+   * Intended for multi-tenant apps where a single Next.js deployment serves
+   * several sites that live behind different URL prefixes on the same host
+   * (e.g. `/site-a/*`, `/site-b/*`), with an edge function rewriting the URI
+   * and injecting `x-base-path` per request.
+   */
+  runtimeBasePath?: boolean
   /**
    * CSS Chunking strategy. Defaults to `true` ("loose" mode), which guesses dependencies
    * between CSS files to keep ordering of them.
@@ -1933,6 +1950,7 @@ export const defaultConfig = Object.freeze({
     proxyPrefetch: 'flexible',
     optimisticClientCache: true,
     manualClientBasePath: false,
+    runtimeBasePath: false,
     cpus: Math.max(
       1,
       (Number(process.env.CIRCLE_NODE_TOTAL) ||

packages/next/src/server/render.tsx

@@ -107,6 +107,24 @@ import { extractNextErrorCode } from '../lib/error-telemetry-utils'
 import type { DeepReadonly } from '../shared/lib/deep-readonly'
 import type { PagesDevOverlayBridgeType } from '../next-devtools/userspace/pages/pages-dev-overlay-setup'
 import { getScriptNonceFromHeader } from './app-render/get-script-nonce-from-header'
+import {
+  getRuntimeBasePath,
+  runWithRuntimeBasePath,
+} from '../shared/lib/router/utils/runtime-base-path'
+
+const RUNTIME_BASE_PATH_HEADER = 'x-base-path'
+
+function readRuntimeBasePathHeader(req: IncomingMessage): string {
+  const raw = req.headers[RUNTIME_BASE_PATH_HEADER]
+  const value = Array.isArray(raw) ? raw[0] : raw
+  if (!value) return ''
+  const trimmed = value.trim()
+  if (!trimmed || trimmed === '/') return ''
+  const withLeadingSlash = trimmed.startsWith('/') ? trimmed : `/${trimmed}`
+  return withLeadingSlash.endsWith('/')
+    ? withLeadingSlash.slice(0, -1)
+    : withLeadingSlash
+}
 
 let tryGetPreviewData: typeof import('./api-utils/node/try-get-preview-data').tryGetPreviewData
 let warn: typeof import('../build/output/log').warn
@@ -1520,6 +1538,9 @@ export async function renderToHTMLImpl(
         notFoundSrcPage && process.env.__NEXT_DEV_SERVER
           ? notFoundSrcPage
           : undefined,
+      basePath: process.env.__NEXT_RUNTIME_BASE_PATH_ENABLED
+        ? getRuntimeBasePath() || undefined
+        : undefined,
     },
     nonce,
     buildManifest: filteredBuildManifest,
@@ -1630,14 +1651,20 @@ export const renderToHTML: PagesRender = (
   sharedContext,
   renderContext
 ) => {
-  return renderToHTMLImpl(
-    req,
-    res,
-    pathname,
-    query,
-    renderOpts,
-    renderOpts,
-    sharedContext,
-    renderContext
-  )
+  const invoke = () =>
+    renderToHTMLImpl(
+      req,
+      res,
+      pathname,
+      query,
+      renderOpts,
+      renderOpts,
+      sharedContext,
+      renderContext
+    )
+
+  if (process.env.__NEXT_RUNTIME_BASE_PATH_ENABLED) {
+    return runWithRuntimeBasePath(readRuntimeBasePathHeader(req), invoke)
+  }
+  return invoke()
 }

packages/next/src/shared/lib/router/router.ts

@@ -807,7 +807,11 @@ export default class Router implements BaseRouter {
     const autoExportDynamic =
       isDynamicRoute(pathname) && self.__NEXT_DATA__.autoExport
 
-    this.basePath = process.env.__NEXT_ROUTER_BASEPATH || ''
+    this.basePath = process.env.__NEXT_RUNTIME_BASE_PATH_ENABLED
+      ? self.__NEXT_DATA__.basePath ||
+        process.env.__NEXT_ROUTER_BASEPATH ||
+        ''
+      : process.env.__NEXT_ROUTER_BASEPATH || ''
     this.sub = subscription
     this.clc = null
     this._wrapApp = wrapApp

packages/next/src/shared/lib/router/utils/runtime-base-path.ts

@@ -0,0 +1,47 @@
+import { createAsyncLocalStorage } from '../../../../server/app-render/async-local-storage'
+
+// Client-side: a single module-scoped value, hydrated from
+// `__NEXT_DATA__.basePath` during client bootstrap. The browser only ever
+// renders one document at a time, so a single mutable value is enough.
+let clientBasePath = ''
+
+// Server-side: a per-request value held in AsyncLocalStorage so concurrent
+// renders don't see each other's basePath. `createAsyncLocalStorage()`
+// returns a no-op implementation in environments without `AsyncLocalStorage`
+// (e.g. browsers), and `getStore()` returns `undefined` there — the client
+// falls through to `clientBasePath`.
+const runtimeBasePathStorage = createAsyncLocalStorage<{ basePath: string }>()
+
+/**
+ * Returns the basePath that should be applied to URLs at this moment.
+ *
+ * On the server, this is the value the current request was rendered with
+ * (set via `runWithRuntimeBasePath`). On the client, this is the value
+ * hydrated from `__NEXT_DATA__.basePath`.
+ *
+ * Only meaningful when `experimental.runtimeBasePath` is enabled.
+ */
+export function getRuntimeBasePath(): string {
+  const store = runtimeBasePathStorage.getStore()
+  if (store) return store.basePath
+  return clientBasePath
+}
+
+/**
+ * Sets the client-side runtime basePath. Should be called exactly once
+ * during client bootstrap, before the router is created.
+ */
+export function setClientRuntimeBasePath(basePath: string): void {
+  clientBasePath = basePath
+}
+
+/**
+ * Runs `fn` with the given basePath as the active runtime basePath.
+ * Used on the server to scope a render to a per-request basePath.
+ */
+export function runWithRuntimeBasePath<R>(
+  basePath: string,
+  fn: () => R
+): R {
+  return runtimeBasePathStorage.run({ basePath }, fn)
+}

packages/next/src/shared/lib/utils.ts

@@ -113,6 +113,12 @@ export type NEXT_DATA = {
   scriptLoader?: any[]
   isPreview?: boolean
   notFoundSrcPage?: string
+  /**
+   * Per-request basePath when `experimental.runtimeBasePath` is enabled.
+   * The client reads this on hydration and uses it for all subsequent
+   * URL building (Link, router navigation, `_next/data` fetches).
+   */
+  basePath?: string
 }
 
 /**