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normalizeRewrites

Filters and normalizes rewrite routes from Next.js routing phases into Vercel route format.

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Signature

function normalizeRewrites(routing: {
  beforeFiles: AdapterRoute[];
  afterFiles: AdapterRoute[];
  fallback: AdapterRoute[];
}): {
  beforeFiles: RouteWithSrc[];
  afterFiles: RouteWithSrc[];
  fallback: RouteWithSrc[];
}

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Parameters

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routing
object
required
Object containing rewrite routes from three phases.

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Return value

Returns an object with the same structure, but with routes normalized to Vercel format:
  • beforeFiles: Routes with continue: true and override: true (no check property)
  • afterFiles: Routes with check: true
  • fallback: Routes with check: true

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Example

const convertedRewrites = normalizeRewrites(routing);

// convertedRewrites.beforeFiles[0]:
// {
//   src: '^/blog/(.*)$',
//   dest: '/posts/$1',
//   continue: true,
//   override: true
// }

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modifyWithRewriteHeaders

Modifies rewrite routes by adding x-nextjs-rewritten-path and x-nextjs-rewritten-query headers. Also handles RSC suffix modifications for App Router.

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Signature

function modifyWithRewriteHeaders(
  rewrites: RouteWithSrc[],
  {
    isAfterFilesRewrite = false,
    shouldHandleSegmentPrefetches,
  }: {
    isAfterFilesRewrite?: boolean;
    shouldHandleSegmentPrefetches?: boolean;
  }
): void

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Parameters

​
rewrites
RouteWithSrc[]
required
Array of rewrite routes to modify in place.
​
isAfterFilesRewrite
boolean
default:"false"
Whether these are afterFiles rewrites. When true, adds RSC suffix handling.
​
shouldHandleSegmentPrefetches
boolean
Whether to handle segment prefetches for PPR (Partial Prerendering).

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Behavior

This function mutates the rewrites array by:
  1. Adding rewrite headers to track the original destination
  2. For afterFiles rewrites with App Router: modifies src regex to match RSC suffixes
  3. Skips external rewrites (those with http:// or https:// protocol)
  4. Filters out Next.js internal query params (nxtP*, nxtI*)

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Example

const rewrites = [
  {
    src: '^/api/(.*)$',
    dest: '/external-api/$1?param=value',
  },
];

modifyWithRewriteHeaders(rewrites, {
  shouldHandleSegmentPrefetches: true,
});

// Result:
// {
//   src: '^/api/(.*)$',
//   dest: '/external-api/$1?param=value',
//   headers: {
//     'x-nextjs-rewritten-path': '/external-api/$1',
//     'x-nextjs-rewritten-query': 'param=value'
//   }
// }

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extractRedirects

Extracts redirect routes from routing phases and categorizes them by priority.

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Signature

function extractRedirects(routing: {
  beforeMiddleware: AdapterRoute[];
  beforeFiles: AdapterRoute[];
}): {
  priority: RouteWithSrc[];
  normal: RouteWithSrc[];
}

​
Parameters

​
routing
object
required
Routing configuration containing routes from multiple phases.

​
Return value

Returns an object with two arrays:
​
priority
RouteWithSrc[]
Redirects with priority: true flag. These have continue: true added.
​
normal
RouteWithSrc[]
Standard redirects without priority flag.

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Notes

Only processes routes with redirect status codes: 301, 302, 303, 307, 308.

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extractHeaders

Extracts header routes from routing phases.

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Signature

function extractHeaders(routing: {
  beforeMiddleware: AdapterRoute[];
  beforeFiles: AdapterRoute[];
}): RouteWithSrc[]

​
Parameters

​
routing
object
required
Routing configuration containing routes from multiple phases.

​
Return value

Returns an array of header routes. Each route has:
  • src: Source regex pattern
  • headers: Headers to apply
  • continue: true: Continues to next route
  • important: true: Added if route has priority flag
  • has: Optional conditions
  • missing: Optional negative conditions

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Notes

  • Skips routes that are redirects (have redirect status codes)
  • Skips routes that are rewrites (have destination property)

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normalizeNextDataRoutes

Creates routes to normalize _next/data URLs for middleware data resolving.

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Signature

function normalizeNextDataRoutes(
  config: NextConfig,
  buildId: string,
  shouldHandleMiddlewareDataResolving: boolean,
  isOverride = false
): RouteWithSrc[]

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Parameters

​
config
NextConfig
required
Next.js configuration object.
​
buildId
string
required
Current build identifier.
​
shouldHandleMiddlewareDataResolving
boolean
required
Whether middleware data resolving should be handled. Returns empty array if false.
​
isOverride
boolean
default:"false"
Whether to add override: true to routes.

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Return value

Returns an array of routes that:
  1. Add x-nextjs-data header if missing
  2. Strip _next/data/{buildId}/ prefix from URLs
  3. Normalize /index routes to /

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denormalizeNextDataRoutes

Creates routes to convert normalized URLs back to _next/data format for middleware.

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Signature

function denormalizeNextDataRoutes(
  config: NextConfig,
  buildId: string,
  shouldHandleMiddlewareDataResolving: boolean,
  isOverride = false
): RouteWithSrc[]

​
Parameters

Same as normalizeNextDataRoutes.

​
Return value

Returns an array of routes that convert URLs back to _next/data format when x-nextjs-data header is present.

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extractOnMatchRoutes

Extracts routes for the “hit” handle phase that execute when a match is found.

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Signature

function extractOnMatchRoutes(routing: {
  onMatch: AdapterRoute[];
}): RouteWithSrc[]

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Parameters

​
routing
object
required
Object containing onMatch routes.

​
Return value

Returns an array of routes with:
  • src: Source regex
  • dest: Optional destination
  • headers: Optional headers
  • has/missing: Optional conditions
  • continue: true
  • important: true

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Example

const onMatchRoutes = extractOnMatchRoutes(routing);

// Result:
// [
//   {
//     src: '^/(.*)$',
//     headers: { 'x-custom-header': 'value' },
//     continue: true,
//     important: true
//   }
// ]

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