Function resolveRoutes

packages/next-routing/src/resolve-routes.ts:370–987

(
  params: ResolveRoutesParams
)

}

export async function resolveRoutes(
  params: ResolveRoutesParams
): Promise<ResolveRoutesResult> {
  const {
    url: initialUrl,
    basePath,
    requestBody,
    headers: initialHeaders,
    pathnames,
    routes,
    invokeMiddleware,
    buildId,
    i18n,
  } = params

  const { shouldNormalizeNextData } = routes

  let currentUrl = new URL(initialUrl.toString())
  let currentRequestHeaders = new Headers(initialHeaders)
  let currentResponseHeaders = new Headers()
  let currentStatus: number | undefined
  const initialOrigin = initialUrl.origin

  // Check if the original URL is a data URL and normalize if so
  let isDataUrl = false
  if (shouldNormalizeNextData) {
    const dataPrefix = `${basePath}/_next/data/${buildId}/`
    isDataUrl = initialUrl.pathname.startsWith(dataPrefix)

    if (isDataUrl) {
      currentUrl = normalizeNextDataUrl(currentUrl, basePath, buildId)
    }
  }

  // Handle i18n locale detection and redirects
  if (i18n && !isDataUrl) {
    const pathname = currentUrl.pathname.startsWith(basePath)
      ? currentUrl.pathname.slice(basePath.length) || '/'
      : currentUrl.pathname

    // Skip locale handling for _next and api routes
    if (!pathname.startsWith('/_next/') && !pathname.startsWith('/api/')) {
      const hostname = currentUrl.hostname
      const cookieHeader = currentRequestHeaders.get('cookie') || undefined
      const acceptLanguageHeader =
        currentRequestHeaders.get('accept-language') || undefined

      // Detect locale from path first
      const pathLocaleResult = normalizeLocalePath(pathname, i18n.locales)
      const localeInPath = !!pathLocaleResult.detectedLocale

      // Detect domain locale
      const domainLocale = detectDomainLocale(i18n.domains, hostname)
      const defaultLocale = domainLocale?.defaultLocale || i18n.defaultLocale

      // Determine target locale if locale detection is enabled
      let targetLocale = pathLocaleResult.detectedLocale || defaultLocale