AdapterPath

Configure a custom adapter for Next.js to hook into the build process with modifyConfig and onBuildComplete callbacks.

Next.js provides an experimental API that allows you to create custom adapters to hook into the build process. This is useful for deployment platforms or custom build integrations that need to modify the Next.js configuration or process the build output.

Configuration

To use an adapter, specify the path to your adapter module in experimental.adapterPath:

next.config.js

/** @type {import('next').NextConfig} */
const nextConfig = {
  experimental: {
    adapterPath: require.resolve('./my-adapter.js'),
  },
}
 
module.exports = nextConfig

Creating an Adapter

An adapter is a module that exports an object implementing the NextAdapter interface:

export interface NextAdapter {
  name: string
  modifyConfig?: (
    config: NextConfigComplete,
    ctx: {
      phase: PHASE_TYPE
    }
  ) => Promise<NextConfigComplete> | NextConfigComplete
  onBuildComplete?: (ctx: {
    routes: {
      headers: Array<ManifestHeaderRoute>
      redirects: Array<ManifestRedirectRoute>
      rewrites: {
        beforeFiles: Array<ManifestRewriteRoute>
        afterFiles: Array<ManifestRewriteRoute>
        fallback: Array<ManifestRewriteRoute>
      }
      dynamicRoutes: ReadonlyArray<ManifestRoute>
    }
    outputs: AdapterOutputs
    projectDir: string
    repoRoot: string
    distDir: string
    config: NextConfigComplete
    nextVersion: string
  }) => Promise<void> | void
}

Basic Adapter Structure

Here's a minimal adapter example:

my-adapter.js

/** @type {import('next').NextAdapter} */
const adapter = {
  name: 'my-custom-adapter',
 
  async modifyConfig(config, { phase }) {
    // Modify the Next.js config based on the build phase
    if (phase === 'phase-production-build') {
      return {
        ...config,
        // Add your modifications
      }
    }
    return config
  },
 
  async onBuildComplete({
    routes,
    outputs,
    projectDir,
    repoRoot,
    distDir,
    config,
    nextVersion,
  }) {
    // Process the build output
    console.log('Build completed with', outputs.pages.length, 'pages')
 
    // Access different output types
    for (const page of outputs.pages) {
      console.log('Page:', page.pathname, 'at', page.filePath)
    }
 
    for (const apiRoute of outputs.pagesApi) {
      console.log('API Route:', apiRoute.pathname, 'at', apiRoute.filePath)
    }
 
    for (const appPage of outputs.appPages) {
      console.log('App Page:', appPage.pathname, 'at', appPage.filePath)
    }
 
    for (const prerender of outputs.prerenders) {
      console.log('Prerendered:', prerender.pathname)
    }
  },
}
 
module.exports = adapter

API Reference

`modifyConfig(config, context)`

Called for any CLI command that loads the next.config to allow modification of the configuration.

Parameters:

config: The complete Next.js configuration object
context.phase: The current build phase (see phases)

Returns: The modified configuration object (can be async)

`onBuildComplete(context)`

Called after the build process completes with detailed information about routes and outputs.

Parameters:

routes: Object containing route manifests for headers, redirects, rewrites, and dynamic routes
- routes.headers: Array of header route objects with source, sourceRegex, headers, has, missing, and optional priority fields
- routes.redirects: Array of redirect route objects with source, sourceRegex, destination, statusCode, has, missing, and optional priority fields
- routes.rewrites: Object with beforeFiles, afterFiles, and fallback arrays, each containing rewrite route objects with source, sourceRegex, destination, has, and missing fields
- routes.dynamicRoutes: Array of dynamic route objects with source, sourceRegex, destination, has, and missing fields
outputs: Detailed information about all build outputs organized by type
projectDir: Absolute path to the Next.js project directory
repoRoot: Absolute path to the detected repository root
distDir: Absolute path to the build output directory
config: The final Next.js configuration (with modifyConfig applied)
nextVersion: Version of Next.js being used
buildId: Unique identifier for the current build

Output Types

The outputs object contains arrays of different output types:

Pages (`outputs.pages`)

React pages from the pages/ directory:

{
  type: 'PAGES'
  id: string           // Route identifier
  filePath: string     // Path to the built file
  pathname: string     // URL pathname
  sourcePage: string   // Original source file path in pages/ directory
  runtime: 'nodejs' | 'edge'
  assets: Record<string, string>  // Traced dependencies (key: relative path from repo root, value: absolute path)
  wasmAssets?: Record<string, string>  // Bundled wasm files (key: name, value: absolute path)
  config: {
    maxDuration?: number
    preferredRegion?: string | string[]
    env?: Record<string, string>  // Environment variables (edge runtime only)
  }
}

API Routes (`outputs.pagesApi`)

API routes from pages/api/:

{
  type: 'PAGES_API'
  id: string
  filePath: string
  pathname: string
  sourcePage: string   // Original relative source file path
  runtime: 'nodejs' | 'edge'
  assets: Record<string, string>
  wasmAssets?: Record<string, string>
  config: {
    maxDuration?: number
    preferredRegion?: string | string[]
    env?: Record<string, string>
  }
}

App Pages (`outputs.appPages`)

React pages from the app/ directory with page.{js,ts,jsx,tsx}:

{
  type: 'APP_PAGE'
  id: string
  filePath: string
  pathname: string     // Includes .rsc suffix for RSC routes
  sourcePage: string   // Original relative source file path
  runtime: 'nodejs' | 'edge'
  assets: Record<string, string>
  wasmAssets?: Record<string, string>
  config: {
    maxDuration?: number
    preferredRegion?: string | string[]
    env?: Record<string, string>
  }
}

App Routes (`outputs.appRoutes`)

API and metadata routes from app/ with route.{js,ts,jsx,tsx}:

{
  type: 'APP_ROUTE'
  id: string
  filePath: string
  pathname: string
  sourcePage: string
  runtime: 'nodejs' | 'edge'
  assets: Record<string, string>
  wasmAssets?: Record<string, string>
  config: {
    maxDuration?: number
    preferredRegion?: string | string[]
    env?: Record<string, string>
  }
}

Prerenders (`outputs.prerenders`)

ISR-enabled routes and static prerenders:

{
  type: 'PRERENDER'
  id: string
  pathname: string
  parentOutputId: string  // ID of the source page/route
  groupId: number        // Revalidation group identifier (prerenders with same groupId revalidate together)
  pprChain?: {
    headers: Record<string, string>  // PPR chain headers (e.g., 'x-nextjs-resume': '1')
  }
  parentFallbackMode?: 'blocking' | false | null  // Fallback mode from getStaticPaths
  fallback?: {
    filePath: string
    initialStatus?: number
    initialHeaders?: Record<string, string | string[]>
    initialExpiration?: number
    initialRevalidate?: number
    postponedState?: string  // PPR postponed state
  }
  config: {
    allowQuery?: string[]     // Allowed query parameters
    allowHeader?: string[]    // Allowed headers for ISR
    bypassFor?: RouteHas[]    // Cache bypass conditions
    renderingMode?: RenderingMode
    bypassToken?: string
  }
}

Static Files (`outputs.staticFiles`)

Static assets and auto-statically optimized pages:

{
  type: 'STATIC_FILE'
  id: string
  filePath: string
  pathname: string
}

Middleware (`outputs.middleware`)

Middleware function (if present):

{
  type: 'MIDDLEWARE'
  id: string
  filePath: string
  pathname: string      // Always '/_middleware'
  sourcePage: string    // Always 'middleware'
  runtime: 'nodejs' | 'edge'
  assets: Record<string, string>
  wasmAssets?: Record<string, string>
  config: {
    maxDuration?: number
    preferredRegion?: string | string[]
    env?: Record<string, string>
    matchers?: Array<{
      source: string
      sourceRegex: string
      has: RouteHas[] | undefined
      missing: RouteHas[] | undefined
    }>
  }
}

Routes Information

The routes object in onBuildComplete provides complete routing information with processed patterns ready for deployment:

Headers

Each header route includes:

source: Original route pattern (e.g., /about)
sourceRegex: Compiled regex for matching requests
headers: Key-value pairs of headers to apply
has: Optional conditions that must be met
missing: Optional conditions that must not be met
priority: Optional flag for internal routes

Redirects

Each redirect route includes:

source: Original route pattern
sourceRegex: Compiled regex for matching
destination: Target URL (can include captured groups)
statusCode: HTTP status code (301, 302, 307, 308)
has: Optional positive conditions
missing: Optional negative conditions
priority: Optional flag for internal routes

Rewrites

Rewrites are categorized into three phases:

beforeFiles: Checked before filesystem (including pages and public files)
afterFiles: Checked after pages/public files but before dynamic routes
fallback: Checked after all other routes

Each rewrite includes source, sourceRegex, destination, has, and missing.

Dynamic Routes

Generated from dynamic route segments (e.g., [slug], [...path]). Each includes:

source: Route pattern
sourceRegex: Compiled regex with named capture groups
destination: Internal destination with parameter substitution
has: Optional positive conditions
missing: Optional negative conditions

Use Cases

Common use cases for adapters include:

Deployment Platform Integration: Automatically configure build outputs for specific hosting platforms
Asset Processing: Transform or optimize build outputs
Monitoring Integration: Collect build metrics and route information
Custom Bundling: Package outputs in platform-specific formats
Build Validation: Ensure outputs meet specific requirements
Route Generation: Use processed route information to generate platform-specific routing configs

experimental.adapterPath

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