Function responseToMiddlewareResult

packages/next-routing/src/middleware.ts:13–204

(
  response: Response,
  requestHeaders: Headers,
  url: URL
)

 * @returns A MiddlewareResult object with processed headers and routing information
 */
export function responseToMiddlewareResult(
  response: Response,
  requestHeaders: Headers,
  url: URL
): MiddlewareResult {
  const result: MiddlewareResult = {}

  // Convert response headers to a mutable record
  const middlewareHeaders: Record<string, string | string[] | undefined> = {}
  response.headers.forEach((value, key) => {
    if (middlewareHeaders[key]) {
      // If header already exists, convert to array
      const existing = middlewareHeaders[key]
      if (Array.isArray(existing)) {
        existing.push(value)
      } else {
        middlewareHeaders[key] = [existing as string, value]
      }
    } else {
      middlewareHeaders[key] = value
    }
  })

  // Handle x-middleware-override-headers
  // This special header contains a comma-separated list of header keys that should be overridden
  if (middlewareHeaders['x-middleware-override-headers']) {
    const overriddenHeaders: Set<string> = new Set()
    let overrideHeaders: string | string[] =
      middlewareHeaders['x-middleware-override-headers']

    if (typeof overrideHeaders === 'string') {
      overrideHeaders = overrideHeaders.split(',')
    }

    for (const key of overrideHeaders) {
      overriddenHeaders.add(key.trim())
    }
    delete middlewareHeaders['x-middleware-override-headers']

    // Delete headers not in the override list
    const headersToDelete: string[] = []
    requestHeaders.forEach((_, key) => {
      if (!overriddenHeaders.has(key)) {
        headersToDelete.push(key)
      }
    })
    for (const key of headersToDelete) {
      requestHeaders.delete(key)
    }

    // Update or add headers from the override list
    for (const key of overriddenHeaders.keys()) {
      const valueKey = 'x-middleware-request-' + key
      const newValue = middlewareHeaders[valueKey]

      if (newValue === undefined || newValue === null) {
        // If no value provided, delete the header
        requestHeaders.delete(key)