render.tsx

import { IncomingMessage, ServerResponse } from 'http'
import { ParsedUrlQuery } from 'querystring'
import { PassThrough } from 'stream'
import React from 'react'
import * as ReactDOMServer from 'react-dom/server'
import flush from 'styled-jsx/server'
import Observable from 'next/dist/compiled/zen-observable'
import { warn } from '../build/output/log'
import { UnwrapPromise } from '../lib/coalesced-function'
import {
  GSP_NO_RETURNED_VALUE,
  GSSP_COMPONENT_MEMBER_ERROR,
  GSSP_NO_RETURNED_VALUE,
  STATIC_STATUS_PAGE_GET_INITIAL_PROPS_ERROR,
  SERVER_PROPS_GET_INIT_PROPS_CONFLICT,
  SERVER_PROPS_SSG_CONFLICT,
  SSG_GET_INITIAL_PROPS_CONFLICT,
  UNSTABLE_REVALIDATE_RENAME_ERROR,
} from '../lib/constants'
import { isSerializableProps } from '../lib/is-serializable-props'
import { GetServerSideProps, GetStaticProps, PreviewData } from '../types'
import { isInAmpMode } from '../shared/lib/amp'
import { AmpStateContext } from '../shared/lib/amp-context'
import {
  BODY_RENDER_TARGET,
  SERVER_PROPS_ID,
  STATIC_PROPS_ID,
  STATIC_STATUS_PAGES,
} from '../shared/lib/constants'
import { defaultHead } from '../shared/lib/head'
import { HeadManagerContext } from '../shared/lib/head-manager-context'
import Loadable from '../shared/lib/loadable'
import { LoadableContext } from '../shared/lib/loadable-context'
import postProcess from '../shared/lib/post-process'
import { RouterContext } from '../shared/lib/router-context'
import { NextRouter } from '../shared/lib/router/router'
import { isDynamicRoute } from '../shared/lib/router/utils/is-dynamic'
import {
  AppType,
  ComponentsEnhancer,
  DocumentInitialProps,
  DocumentProps,
  HtmlContext,
  HtmlProps,
  getDisplayName,
  isResSent,
  loadGetInitialProps,
  NextComponentType,
  RenderPage,
  RenderPageResult,
} from '../shared/lib/utils'
import {
  tryGetPreviewData,
  NextApiRequestCookies,
  __ApiPreviewProps,
} from './api-utils'
import { denormalizePagePath } from './denormalize-page-path'
import { FontManifest, getFontDefinitionFromManifest } from './font-utils'
import { LoadComponentsReturnType, ManifestItem } from './load-components'
import { normalizePagePath } from './normalize-page-path'
import optimizeAmp from './optimize-amp'
import {
  allowedStatusCodes,
  getRedirectStatus,
  Redirect,
} from '../lib/load-custom-routes'
import { DomainLocale } from './config'
import { mergeResults, RenderResult, resultsToString } from './utils'

function noRouter() {
  const message =
    'No router instance found. you should only use "next/router" inside the client side of your app. https://nextjs.org/docs/messages/no-router-instance'
  throw new Error(message)
}

class ServerRouter implements NextRouter {
  route: string
  pathname: string
  query: ParsedUrlQuery
  asPath: string
  basePath: string
  events: any
  isFallback: boolean
  locale?: string
  isReady: boolean
  locales?: string[]
  defaultLocale?: string
  domainLocales?: DomainLocale[]
  isPreview: boolean
  isLocaleDomain: boolean

  constructor(
    pathname: string,
    query: ParsedUrlQuery,
    as: string,
    { isFallback }: { isFallback: boolean },
    isReady: boolean,
    basePath: string,
    locale?: string,
    locales?: string[],
    defaultLocale?: string,
    domainLocales?: DomainLocale[],
    isPreview?: boolean,
    isLocaleDomain?: boolean
  ) {
    this.route = pathname.replace(/\/$/, '') || '/'
    this.pathname = pathname
    this.query = query
    this.asPath = as
    this.isFallback = isFallback
    this.basePath = basePath
    this.locale = locale
    this.locales = locales
    this.defaultLocale = defaultLocale
    this.isReady = isReady
    this.domainLocales = domainLocales
    this.isPreview = !!isPreview
    this.isLocaleDomain = !!isLocaleDomain
  }

  push(): any {
    noRouter()
  }
  replace(): any {
    noRouter()
  }
  reload() {
    noRouter()
  }
  back() {
    noRouter()
  }
  prefetch(): any {
    noRouter()
  }
  beforePopState() {
    noRouter()
  }
}

function enhanceComponents(
  options: ComponentsEnhancer,
  App: AppType,
  Component: NextComponentType
): {
  App: AppType
  Component: NextComponentType
} {
  // For backwards compatibility
  if (typeof options === 'function') {
    return {
      App,
      Component: options(Component),
    }
  }

  return {
    App: options.enhanceApp ? options.enhanceApp(App) : App,
    Component: options.enhanceComponent
      ? options.enhanceComponent(Component)
      : Component,
  }
}

export type RenderOptsPartial = {
  buildId: string
  canonicalBase: string
  runtimeConfig?: { [key: string]: any }
  assetPrefix?: string
  err?: Error | null
  nextExport?: boolean
  dev?: boolean
  ampPath?: string
  ErrorDebug?: React.ComponentType<{ error: Error }>
  ampValidator?: (html: string, pathname: string) => Promise<void>
  ampSkipValidation?: boolean
  ampOptimizerConfig?: { [key: string]: any }
  isDataReq?: boolean
  params?: ParsedUrlQuery
  previewProps: __ApiPreviewProps
  basePath: string
  unstable_runtimeJS?: false
  unstable_JsPreload?: false
  optimizeFonts: boolean
  fontManifest?: FontManifest
  optimizeImages: boolean
  optimizeCss: any
  devOnlyCacheBusterQueryString?: string
  resolvedUrl?: string
  resolvedAsPath?: string
  distDir?: string
  locale?: string
  locales?: string[]
  defaultLocale?: string
  domainLocales?: DomainLocale[]
  disableOptimizedLoading?: boolean
  requireStaticHTML?: boolean
  concurrentFeatures?: boolean
  customServer?: boolean
}

export type RenderOpts = LoadComponentsReturnType & RenderOptsPartial

const invalidKeysMsg = (methodName: string, invalidKeys: string[]) => {
  return (
    `Additional keys were returned from \`${methodName}\`. Properties intended for your component must be nested under the \`props\` key, e.g.:` +
    `\n\n\treturn { props: { title: 'My Title', content: '...' } }` +
    `\n\nKeys that need to be moved: ${invalidKeys.join(', ')}.` +
    `\nRead more: https://nextjs.org/docs/messages/invalid-getstaticprops-value`
  )
}

function checkRedirectValues(
  redirect: Redirect,
  req: IncomingMessage,
  method: 'getStaticProps' | 'getServerSideProps'
) {
  const { destination, permanent, statusCode, basePath } = redirect
  let errors: string[] = []

  const hasStatusCode = typeof statusCode !== 'undefined'
  const hasPermanent = typeof permanent !== 'undefined'

  if (hasPermanent && hasStatusCode) {
    errors.push(`\`permanent\` and \`statusCode\` can not both be provided`)
  } else if (hasPermanent && typeof permanent !== 'boolean') {
    errors.push(`\`permanent\` must be \`true\` or \`false\``)
  } else if (hasStatusCode && !allowedStatusCodes.has(statusCode!)) {
    errors.push(
      `\`statusCode\` must undefined or one of ${[...allowedStatusCodes].join(
        ', '
      )}`
    )
  }
  const destinationType = typeof destination

  if (destinationType !== 'string') {
    errors.push(
      `\`destination\` should be string but received ${destinationType}`
    )
  }

  const basePathType = typeof basePath

  if (basePathType !== 'undefined' && basePathType !== 'boolean') {
    errors.push(
      `\`basePath\` should be undefined or a false, received ${basePathType}`
    )
  }

  if (errors.length > 0) {
    throw new Error(
      `Invalid redirect object returned from ${method} for ${req.url}\n` +
        errors.join(' and ') +
        '\n' +
        `See more info here: https://nextjs.org/docs/messages/invalid-redirect-gssp`
    )
  }
}

export async function renderToHTML(
  req: IncomingMessage,
  res: ServerResponse,
  pathname: string,
  query: ParsedUrlQuery,
  renderOpts: RenderOpts
): Promise<RenderResult | null> {
  // In dev we invalidate the cache by appending a timestamp to the resource URL.
  // This is a workaround to fix https://github.com/vercel/next.js/issues/5860
  // TODO: remove this workaround when https://bugs.webkit.org/show_bug.cgi?id=187726 is fixed.
  renderOpts.devOnlyCacheBusterQueryString = renderOpts.dev
    ? renderOpts.devOnlyCacheBusterQueryString || `?ts=${Date.now()}`
    : ''

  // don't modify original query object
  query = Object.assign({}, query)

  const {
    err,
    dev = false,
    ampPath = '',
    App,
    Document,
    pageConfig = {},
    Component,
    buildManifest,
    fontManifest,
    reactLoadableManifest,
    ErrorDebug,
    getStaticProps,
    getStaticPaths,
    getServerSideProps,
    isDataReq,
    params,
    previewProps,
    basePath,
    devOnlyCacheBusterQueryString,
    requireStaticHTML,
    concurrentFeatures,
  } = renderOpts

  const getFontDefinition = (url: string): string => {
    if (fontManifest) {
      return getFontDefinitionFromManifest(url, fontManifest)
    }
    return ''
  }

  const callMiddleware = async (method: string, args: any[], props = false) => {
    let results: any = props ? {} : []

    if ((Document as any)[`${method}Middleware`]) {
      let middlewareFunc = await (Document as any)[`${method}Middleware`]
      middlewareFunc = middlewareFunc.default || middlewareFunc

      const curResults = await middlewareFunc(...args)
      if (props) {
        for (const result of curResults) {
          results = {
            ...results,
            ...result,
          }
        }
      } else {
        results = curResults
      }
    }
    return results
  }

  const headTags = (...args: any) => callMiddleware('headTags', args)

  const isFallback = !!query.__nextFallback
  delete query.__nextFallback
  delete query.__nextLocale
  delete query.__nextDefaultLocale

  const isSSG = !!getStaticProps
  const isBuildTimeSSG = isSSG && renderOpts.nextExport
  const defaultAppGetInitialProps =
    App.getInitialProps === (App as any).origGetInitialProps

  const hasPageGetInitialProps = !!(Component as any).getInitialProps

  const pageIsDynamic = isDynamicRoute(pathname)

  const isAutoExport =
    !hasPageGetInitialProps &&
    defaultAppGetInitialProps &&
    !isSSG &&
    !getServerSideProps

  for (const methodName of [
    'getStaticProps',
    'getServerSideProps',
    'getStaticPaths',
  ]) {
    if ((Component as any)[methodName]) {
      throw new Error(
        `page ${pathname} ${methodName} ${GSSP_COMPONENT_MEMBER_ERROR}`
      )
    }
  }

  if (hasPageGetInitialProps && isSSG) {
    throw new Error(SSG_GET_INITIAL_PROPS_CONFLICT + ` ${pathname}`)
  }

  if (hasPageGetInitialProps && getServerSideProps) {
    throw new Error(SERVER_PROPS_GET_INIT_PROPS_CONFLICT + ` ${pathname}`)
  }

  if (getServerSideProps && isSSG) {
    throw new Error(SERVER_PROPS_SSG_CONFLICT + ` ${pathname}`)
  }

  if (getStaticPaths && !pageIsDynamic) {
    throw new Error(
      `getStaticPaths is only allowed for dynamic SSG pages and was found on '${pathname}'.` +
        `\nRead more: https://nextjs.org/docs/messages/non-dynamic-getstaticpaths-usage`
    )
  }

  if (!!getStaticPaths && !isSSG) {
    throw new Error(
      `getStaticPaths was added without a getStaticProps in ${pathname}. Without getStaticProps, getStaticPaths does nothing`
    )
  }

  if (isSSG && pageIsDynamic && !getStaticPaths) {
    throw new Error(
      `getStaticPaths is required for dynamic SSG pages and is missing for '${pathname}'.` +
        `\nRead more: https://nextjs.org/docs/messages/invalid-getstaticpaths-value`
    )
  }

  let asPath: string = renderOpts.resolvedAsPath || (req.url as string)

  if (dev) {
    const { isValidElementType } = require('react-is')
    if (!isValidElementType(Component)) {
      throw new Error(
        `The default export is not a React Component in page: "${pathname}"`
      )
    }

    if (!isValidElementType(App)) {
      throw new Error(
        `The default export is not a React Component in page: "/_app"`
      )
    }

    if (!isValidElementType(Document)) {
      throw new Error(
        `The default export is not a React Component in page: "/_document"`
      )
    }

    if (isAutoExport || isFallback) {
      // remove query values except ones that will be set during export
      query = {
        ...(query.amp
          ? {
              amp: query.amp,
            }
          : {}),
      }
      asPath = `${pathname}${
        // ensure trailing slash is present for non-dynamic auto-export pages
        req.url!.endsWith('/') && pathname !== '/' && !pageIsDynamic ? '/' : ''
      }`
      req.url = pathname
    }

    if (pathname === '/404' && (hasPageGetInitialProps || getServerSideProps)) {
      throw new Error(
        `\`pages/404\` ${STATIC_STATUS_PAGE_GET_INITIAL_PROPS_ERROR}`
      )
    }
    if (
      STATIC_STATUS_PAGES.includes(pathname) &&
      (hasPageGetInitialProps || getServerSideProps)
    ) {
      throw new Error(
        `\`pages${pathname}\` ${STATIC_STATUS_PAGE_GET_INITIAL_PROPS_ERROR}`
      )
    }
  }

  await Loadable.preloadAll() // Make sure all dynamic imports are loaded

  let isPreview
  let previewData: PreviewData

  if ((isSSG || getServerSideProps) && !isFallback) {
    // Reads of this are cached on the `req` object, so this should resolve
    // instantly. There's no need to pass this data down from a previous
    // invoke, where we'd have to consider server & serverless.
    previewData = tryGetPreviewData(req, res, previewProps)
    isPreview = previewData !== false
  }

  // url will always be set
  const routerIsReady = !!(
    getServerSideProps ||
    hasPageGetInitialProps ||
    (!defaultAppGetInitialProps && !isSSG)
  )
  const router = new ServerRouter(
    pathname,
    query,
    asPath,
    {
      isFallback: isFallback,
    },
    routerIsReady,
    basePath,
    renderOpts.locale,
    renderOpts.locales,
    renderOpts.defaultLocale,
    renderOpts.domainLocales,
    isPreview,
    (req as any).__nextIsLocaleDomain
  )
  const ctx = {
    err,
    req: isAutoExport ? undefined : req,
    res: isAutoExport ? undefined : res,
    pathname,
    query,
    asPath,
    locale: renderOpts.locale,
    locales: renderOpts.locales,
    defaultLocale: renderOpts.defaultLocale,
    AppTree: (props: any) => {
      return (
        <AppContainer>
          <App {...props} Component={Component} router={router} />
        </AppContainer>
      )
    },
  }
  let props: any

  const ampState = {
    ampFirst: pageConfig.amp === true,
    hasQuery: Boolean(query.amp),
    hybrid: pageConfig.amp === 'hybrid',
  }

  const inAmpMode = isInAmpMode(ampState)

  const reactLoadableModules: string[] = []

  let head: JSX.Element[] = defaultHead(inAmpMode)

  let scriptLoader: any = {}
  const nextExport =
    !isSSG && (renderOpts.nextExport || (dev && (isAutoExport || isFallback)))

  const AppContainer = ({ children }: { children: JSX.Element }) => (
    <RouterContext.Provider value={router}>
      <AmpStateContext.Provider value={ampState}>
        <HeadManagerContext.Provider
          value={{
            updateHead: (state) => {
              head = state
            },
            updateScripts: (scripts) => {
              scriptLoader = scripts
            },
            scripts: {},
            mountedInstances: new Set(),
          }}
        >
          <LoadableContext.Provider
            value={(moduleName) => reactLoadableModules.push(moduleName)}
          >
            {children}
          </LoadableContext.Provider>
        </HeadManagerContext.Provider>
      </AmpStateContext.Provider>
    </RouterContext.Provider>
  )

  try {
    props = await loadGetInitialProps(App, {
      AppTree: ctx.AppTree,
      Component,
      router,
      ctx,
    })

    if ((isSSG || getServerSideProps) && isPreview) {
      props.__N_PREVIEW = true
    }

    if (isSSG) {
      props[STATIC_PROPS_ID] = true
    }

    if (isSSG && !isFallback) {
      let data: UnwrapPromise<ReturnType<GetStaticProps>>

      try {
        data = await getStaticProps!({
          ...(pageIsDynamic ? { params: query as ParsedUrlQuery } : undefined),
          ...(isPreview
            ? { preview: true, previewData: previewData }
            : undefined),
          locales: renderOpts.locales,
          locale: renderOpts.locale,
          defaultLocale: renderOpts.defaultLocale,
        })
      } catch (staticPropsError) {
        // remove not found error code to prevent triggering legacy
        // 404 rendering
        if (staticPropsError.code === 'ENOENT') {
          delete staticPropsError.code
        }
        throw staticPropsError
      }

      if (data == null) {
        throw new Error(GSP_NO_RETURNED_VALUE)
      }

      const invalidKeys = Object.keys(data).filter(
        (key) =>
          key !== 'revalidate' &&
          key !== 'props' &&
          key !== 'redirect' &&
          key !== 'notFound'
      )

      if (invalidKeys.includes('unstable_revalidate')) {
        throw new Error(UNSTABLE_REVALIDATE_RENAME_ERROR)
      }

      if (invalidKeys.length) {
        throw new Error(invalidKeysMsg('getStaticProps', invalidKeys))
      }

      if (process.env.NODE_ENV !== 'production') {
        if (
          typeof (data as any).notFound !== 'undefined' &&
          typeof (data as any).redirect !== 'undefined'
        ) {
          throw new Error(
            `\`redirect\` and \`notFound\` can not both be returned from ${
              isSSG ? 'getStaticProps' : 'getServerSideProps'
            } at the same time. Page: ${pathname}\nSee more info here: https://nextjs.org/docs/messages/gssp-mixed-not-found-redirect`
          )
        }
      }

      if ('notFound' in data && data.notFound) {
        if (pathname === '/404') {
          throw new Error(
            `The /404 page can not return notFound in "getStaticProps", please remove it to continue!`
          )
        }

        ;(renderOpts as any).isNotFound = true
      }

      if (
        'redirect' in data &&
        data.redirect &&
        typeof data.redirect === 'object'
      ) {
        checkRedirectValues(data.redirect as Redirect, req, 'getStaticProps')

        if (isBuildTimeSSG) {
          throw new Error(
            `\`redirect\` can not be returned from getStaticProps during prerendering (${req.url})\n` +
              `See more info here: https://nextjs.org/docs/messages/gsp-redirect-during-prerender`
          )
        }

        ;(data as any).props = {
          __N_REDIRECT: data.redirect.destination,
          __N_REDIRECT_STATUS: getRedirectStatus(data.redirect),
        }
        if (typeof data.redirect.basePath !== 'undefined') {
          ;(data as any).props.__N_REDIRECT_BASE_PATH = data.redirect.basePath
        }
        ;(renderOpts as any).isRedirect = true
      }

      if (
        (dev || isBuildTimeSSG) &&
        !(renderOpts as any).isNotFound &&
        !isSerializableProps(pathname, 'getStaticProps', (data as any).props)
      ) {
        // this fn should throw an error instead of ever returning `false`
        throw new Error(
          'invariant: getStaticProps did not return valid props. Please report this.'
        )
      }

      if ('revalidate' in data) {
        if (typeof data.revalidate === 'number') {
          if (!Number.isInteger(data.revalidate)) {
            throw new Error(
              `A page's revalidate option must be seconds expressed as a natural number for ${req.url}. Mixed numbers, such as '${data.revalidate}', cannot be used.` +
                `\nTry changing the value to '${Math.ceil(
                  data.revalidate
                )}' or using \`Math.ceil()\` if you're computing the value.`
            )
          } else if (data.revalidate <= 0) {
            throw new Error(
              `A page's revalidate option can not be less than or equal to zero for ${req.url}. A revalidate option of zero means to revalidate after _every_ request, and implies stale data cannot be tolerated.` +
                `\n\nTo never revalidate, you can set revalidate to \`false\` (only ran once at build-time).` +
                `\nTo revalidate as soon as possible, you can set the value to \`1\`.`
            )
          } else if (data.revalidate > 31536000) {
            // if it's greater than a year for some reason error
            console.warn(
              `Warning: A page's revalidate option was set to more than a year for ${req.url}. This may have been done in error.` +
                `\nTo only run getStaticProps at build-time and not revalidate at runtime, you can set \`revalidate\` to \`false\`!`
            )
          }
        } else if (data.revalidate === true) {
          // When enabled, revalidate after 1 second. This value is optimal for
          // the most up-to-date page possible, but without a 1-to-1
          // request-refresh ratio.
          data.revalidate = 1
        } else if (
          data.revalidate === false ||
          typeof data.revalidate === 'undefined'
        ) {
          // By default, we never revalidate.
          data.revalidate = false
        } else {
          throw new Error(
            `A page's revalidate option must be seconds expressed as a natural number. Mixed numbers and strings cannot be used. Received '${JSON.stringify(
              data.revalidate
            )}' for ${req.url}`
          )
        }
      } else {
        // By default, we never revalidate.
        ;(data as any).revalidate = false
      }

      props.pageProps = Object.assign(
        {},
        props.pageProps,
        'props' in data ? data.props : undefined
      )

      // pass up revalidate and props for export
      // TODO: change this to a different passing mechanism
      ;(renderOpts as any).revalidate =
        'revalidate' in data ? data.revalidate : undefined
      ;(renderOpts as any).pageData = props

      // this must come after revalidate is added to renderOpts
      if ((renderOpts as any).isNotFound) {
        return null
      }
    }

    if (getServerSideProps) {
      props[SERVER_PROPS_ID] = true
    }

    if (getServerSideProps && !isFallback) {
      let data: UnwrapPromise<ReturnType<GetServerSideProps>>

      try {
        data = await getServerSideProps({
          req: req as IncomingMessage & {
            cookies: NextApiRequestCookies
          },
          res,
          query,
          resolvedUrl: renderOpts.resolvedUrl as string,
          ...(pageIsDynamic ? { params: params as ParsedUrlQuery } : undefined),
          ...(previewData !== false
            ? { preview: true, previewData: previewData }
            : undefined),
          locales: renderOpts.locales,
          locale: renderOpts.locale,
          defaultLocale: renderOpts.defaultLocale,
        })
      } catch (serverSidePropsError) {
        // remove not found error code to prevent triggering legacy
        // 404 rendering
        if (serverSidePropsError.code === 'ENOENT') {
          delete serverSidePropsError.code
        }
        throw serverSidePropsError
      }

      if (data == null) {
        throw new Error(GSSP_NO_RETURNED_VALUE)
      }

      const invalidKeys = Object.keys(data).filter(
        (key) => key !== 'props' && key !== 'redirect' && key !== 'notFound'
      )

      if ((data as any).unstable_notFound) {
        throw new Error(
          `unstable_notFound has been renamed to notFound, please update the field to continue. Page: ${pathname}`
        )
      }
      if ((data as any).unstable_redirect) {
        throw new Error(
          `unstable_redirect has been renamed to redirect, please update the field to continue. Page: ${pathname}`
        )
      }

      if (invalidKeys.length) {
        throw new Error(invalidKeysMsg('getServerSideProps', invalidKeys))
      }

      if ('notFound' in data && data.notFound) {
        if (pathname === '/404') {
          throw new Error(
            `The /404 page can not return notFound in "getStaticProps", please remove it to continue!`
          )
        }

        ;(renderOpts as any).isNotFound = true
        return null
      }

      if ('redirect' in data && typeof data.redirect === 'object') {
        checkRedirectValues(
          data.redirect as Redirect,
          req,
          'getServerSideProps'
        )
        ;(data as any).props = {
          __N_REDIRECT: data.redirect.destination,
          __N_REDIRECT_STATUS: getRedirectStatus(data.redirect),
        }
        if (typeof data.redirect.basePath !== 'undefined') {
          ;(data as any).props.__N_REDIRECT_BASE_PATH = data.redirect.basePath
        }
        ;(renderOpts as any).isRedirect = true
      }

      if (
        (dev || isBuildTimeSSG) &&
        !isSerializableProps(
          pathname,
          'getServerSideProps',
          (data as any).props
        )
      ) {
        // this fn should throw an error instead of ever returning `false`
        throw new Error(
          'invariant: getServerSideProps did not return valid props. Please report this.'
        )
      }

      props.pageProps = Object.assign({}, props.pageProps, (data as any).props)
      ;(renderOpts as any).pageData = props
    }
  } catch (dataFetchError) {
    throw dataFetchError
  }

  if (
    !isSSG && // we only show this warning for legacy pages
    !getServerSideProps &&
    process.env.NODE_ENV !== 'production' &&
    Object.keys(props?.pageProps || {}).includes('url')
  ) {
    console.warn(
      `The prop \`url\` is a reserved prop in Next.js for legacy reasons and will be overridden on page ${pathname}\n` +
        `See more info here: https://nextjs.org/docs/messages/reserved-page-prop`
    )
  }

  // Avoid rendering page un-necessarily for getServerSideProps data request
  // and getServerSideProps/getStaticProps redirects
  if ((isDataReq && !isSSG) || (renderOpts as any).isRedirect) {
    return Observable.of(JSON.stringify(props))
  }

  // We don't call getStaticProps or getServerSideProps while generating
  // the fallback so make sure to set pageProps to an empty object
  if (isFallback) {
    props.pageProps = {}
  }

  // the response might be finished on the getInitialProps call
  if (isResSent(res) && !isSSG) return null

  // we preload the buildManifest for auto-export dynamic pages
  // to speed up hydrating query values
  let filteredBuildManifest = buildManifest
  if (isAutoExport && pageIsDynamic) {
    const page = denormalizePagePath(normalizePagePath(pathname))
    // This code would be much cleaner using `immer` and directly pushing into
    // the result from `getPageFiles`, we could maybe consider that in the
    // future.
    if (page in filteredBuildManifest.pages) {
      filteredBuildManifest = {
        ...filteredBuildManifest,
        pages: {
          ...filteredBuildManifest.pages,
          [page]: [
            ...filteredBuildManifest.pages[page],
            ...filteredBuildManifest.lowPriorityFiles.filter((f) =>
              f.includes('_buildManifest')
            ),
          ],
        },
        lowPriorityFiles: filteredBuildManifest.lowPriorityFiles.filter(
          (f) => !f.includes('_buildManifest')
        ),
      }
    }
  }

  const generateStaticHTML = requireStaticHTML || inAmpMode
  const renderToStream = (element: React.ReactElement) =>
    new Promise<RenderResult>((resolve, reject) => {
      const stream = new PassThrough()
      let resolved = false
      const doResolve = () => {
        if (!resolved) {
          resolved = true

          resolve(
            new Observable((observer) => {
              stream.on('data', (chunk) => {
                observer.next(chunk.toString('utf-8'))
              })
              stream.once('end', () => {
                observer.complete()
              })

              startWriting()
              return () => {
                abort()
              }
            })
          )
        }
      }

      const { abort, startWriting } = (
        ReactDOMServer as any
      ).pipeToNodeWritable(element, stream, {
        onError(error: Error) {
          if (!resolved) {
            resolved = true
            reject(error)
          }
          abort()
        },
        onReadyToStream() {
          if (!generateStaticHTML) {
            doResolve()
          }
        },
        onCompleteAll() {
          doResolve()
        },
      })
    }).then(multiplexResult)

  const renderDocument = async () => {
    if (Document.getInitialProps) {
      const renderPage: RenderPage = (
        options: ComponentsEnhancer = {}
      ): RenderPageResult | Promise<RenderPageResult> => {
        if (ctx.err && ErrorDebug) {
          const html = ReactDOMServer.renderToString(
            <ErrorDebug error={ctx.err} />
          )
          return { html, head }
        }

        if (dev && (props.router || props.Component)) {
          throw new Error(
            `'router' and 'Component' can not be returned in getInitialProps from _app.js https://nextjs.org/docs/messages/cant-override-next-props`
          )
        }

        const { App: EnhancedApp, Component: EnhancedComponent } =
          enhanceComponents(options, App, Component)

        const html = ReactDOMServer.renderToString(
          <AppContainer>
            <EnhancedApp
              Component={EnhancedComponent}
              router={router}
              {...props}
            />
          </AppContainer>
        )
        return { html, head }
      }
      const documentCtx = { ...ctx, renderPage }
      const docProps: DocumentInitialProps = await loadGetInitialProps(
        Document,
        documentCtx
      )
      // the response might be finished on the getInitialProps call
      if (isResSent(res) && !isSSG) return null

      if (!docProps || typeof docProps.html !== 'string') {
        const message = `"${getDisplayName(
          Document
        )}.getInitialProps()" should resolve to an object with a "html" prop set with a valid html string`
        throw new Error(message)
      }

      return {
        bodyResult: Observable.of(docProps.html),
        documentElement: (htmlProps: HtmlProps) => (
          <Document {...htmlProps} {...docProps} />
        ),
        head: docProps.head,
        headTags: await headTags(documentCtx),
        styles: docProps.styles,
      }
    } else {
      const content =
        ctx.err && ErrorDebug ? (
          <ErrorDebug error={ctx.err} />
        ) : (
          <AppContainer>
            <App {...props} Component={Component} router={router} />
          </AppContainer>
        )
      const bodyResult = concurrentFeatures
        ? await renderToStream(content)
        : Observable.of(ReactDOMServer.renderToString(content))

      return {
        bodyResult,
        documentElement: () => (Document as any)(),
        head,
        headTags: [],
        // TODO: Experimental styled-jsx 5 support
        styles: [...flush()],
      }
    }
  }

  const documentResult = await renderDocument()
  if (!documentResult) {
    return null
  }

  const dynamicImportsIds = new Set<string | number>()
  const dynamicImports = new Set<string>()

  for (const mod of reactLoadableModules) {
    const manifestItem: ManifestItem = reactLoadableManifest[mod]

    if (manifestItem) {
      dynamicImportsIds.add(manifestItem.id)
      manifestItem.files.forEach((item) => {
        dynamicImports.add(item)
      })
    }
  }

  const hybridAmp = ampState.hybrid

  const docComponentsRendered: DocumentProps['docComponentsRendered'] = {}
  const {
    assetPrefix,
    buildId,
    customServer,
    defaultLocale,
    disableOptimizedLoading,
    domainLocales,
    locale,
    locales,
    runtimeConfig,
  } = renderOpts
  const htmlProps: any = {
    __NEXT_DATA__: {
      props, // The result of getInitialProps
      page: pathname, // The rendered page
      query, // querystring parsed / passed by the user
      buildId, // buildId is used to facilitate caching of page bundles, we send it to the client so that pageloader knows where to load bundles
      assetPrefix: assetPrefix === '' ? undefined : assetPrefix, // send assetPrefix to the client side when configured, otherwise don't sent in the resulting HTML
      runtimeConfig, // runtimeConfig if provided, otherwise don't sent in the resulting HTML
      nextExport: nextExport === true ? true : undefined, // If this is a page exported by `next export`
      autoExport: isAutoExport === true ? true : undefined, // If this is an auto exported page
      isFallback,
      dynamicIds:
        dynamicImportsIds.size === 0
          ? undefined
          : Array.from(dynamicImportsIds),
      err: renderOpts.err ? serializeError(dev, renderOpts.err) : undefined, // Error if one happened, otherwise don't sent in the resulting HTML
      gsp: !!getStaticProps ? true : undefined, // whether the page is getStaticProps
      gssp: !!getServerSideProps ? true : undefined, // whether the page is getServerSideProps
      customServer, // whether the user is using a custom server
      gip: hasPageGetInitialProps ? true : undefined, // whether the page has getInitialProps
      appGip: !defaultAppGetInitialProps ? true : undefined, // whether the _app has getInitialProps
      locale,
      locales,
      defaultLocale,
      domainLocales,
      isPreview: isPreview === true ? true : undefined,
    },
    buildManifest: filteredBuildManifest,
    docComponentsRendered,
    dangerousAsPath: router.asPath,
    canonicalBase:
      !renderOpts.ampPath && (req as any).__nextStrippedLocale
        ? `${renderOpts.canonicalBase || ''}/${renderOpts.locale}`
        : renderOpts.canonicalBase,
    ampPath,
    inAmpMode,
    isDevelopment: !!dev,
    hybridAmp,
    dynamicImports: Array.from(dynamicImports),
    assetPrefix,
    // Only enabled in production as development mode has features relying on HMR (style injection for example)
    unstable_runtimeJS:
      process.env.NODE_ENV === 'production'
        ? pageConfig.unstable_runtimeJS
        : undefined,
    unstable_JsPreload: pageConfig.unstable_JsPreload,
    devOnlyCacheBusterQueryString,
    scriptLoader,
    locale,
    disableOptimizedLoading,
    head: documentResult.head,
    headTags: documentResult?.headTags,
    styles: documentResult.styles,
  }
  const documentHTML = ReactDOMServer.renderToStaticMarkup(
    <AmpStateContext.Provider value={ampState}>
      <HtmlContext.Provider value={htmlProps}>
        {documentResult.documentElement(htmlProps)}
      </HtmlContext.Provider>
    </AmpStateContext.Provider>
  )

  if (process.env.NODE_ENV !== 'production') {
    const nonRenderedComponents = []
    const expectedDocComponents = ['Main', 'Head', 'NextScript', 'Html']

    for (const comp of expectedDocComponents) {
      if (!(docComponentsRendered as any)[comp]) {
        nonRenderedComponents.push(comp)
      }
    }
    const plural = nonRenderedComponents.length !== 1 ? 's' : ''

    if (nonRenderedComponents.length) {
      const missingComponentList = nonRenderedComponents
        .map((e) => `<${e} />`)
        .join(', ')
      warn(
        `Your custom Document (pages/_document) did not render all the required subcomponent${plural}.\n` +
          `Missing component${plural}: ${missingComponentList}\n` +
          'Read how to fix here: https://nextjs.org/docs/messages/missing-document-component'
      )
    }
  }

  let results: Array<RenderResult> = []
  const renderTargetIdx = documentHTML.indexOf(BODY_RENDER_TARGET)
  results.push(
    Observable.of(
      '<!DOCTYPE html>' + documentHTML.substring(0, renderTargetIdx)
    )
  )
  if (inAmpMode) {
    results.push(Observable.of('<!-- __NEXT_DATA__ -->'))
  }
  results.push(documentResult.bodyResult)
  results.push(
    Observable.of(
      documentHTML.substring(renderTargetIdx + BODY_RENDER_TARGET.length)
    )
  )

  const postProcessors: Array<((html: string) => Promise<string>) | null> = (
    generateStaticHTML
      ? [
          inAmpMode
            ? async (html: string) => {
                html = await optimizeAmp(html, renderOpts.ampOptimizerConfig)
                if (!renderOpts.ampSkipValidation && renderOpts.ampValidator) {
                  await renderOpts.ampValidator(html, pathname)
                }
                return html
              }
            : null,
          process.env.__NEXT_OPTIMIZE_FONTS ||
          process.env.__NEXT_OPTIMIZE_IMAGES
            ? async (html: string) => {
                return await postProcess(
                  html,
                  { getFontDefinition },
                  {
                    optimizeFonts: renderOpts.optimizeFonts,
                    optimizeImages: renderOpts.optimizeImages,
                  }
                )
              }
            : null,
          renderOpts.optimizeCss
            ? async (html: string) => {
                // eslint-disable-next-line import/no-extraneous-dependencies
                const Critters = require('critters')
                const cssOptimizer = new Critters({
                  ssrMode: true,
                  reduceInlineStyles: false,
                  path: renderOpts.distDir,
                  publicPath: `${renderOpts.assetPrefix}/_next/`,
                  preload: 'media',
                  fonts: false,
                  ...renderOpts.optimizeCss,
                })
                return await cssOptimizer.process(html)
              }
            : null,
          inAmpMode || hybridAmp
            ? async (html: string) => {
                return html.replace(/&amp;amp=1/g, '&amp=1')
              }
            : null,
        ]
      : []
  ).filter(Boolean)

  if (postProcessors.length > 0) {
    let html = await resultsToString(results)
    for (const postProcessor of postProcessors) {
      if (postProcessor) {
        html = await postProcessor(html)
      }
    }
    results = [Observable.of(html)]
  }

  return mergeResults(results)
}

function multiplexResult(result: RenderResult): RenderResult {
  const chunks: Array<string> = []
  const subscribers: Set<ZenObservable.SubscriptionObserver<string>> = new Set()
  let terminator:
    | ((subscriber: ZenObservable.SubscriptionObserver<string>) => void)
    | null = null

  result.subscribe({
    next(chunk) {
      chunks.push(chunk)
      subscribers.forEach((subscriber) => subscriber.next(chunk))
    },
    error(error) {
      if (!terminator) {
        terminator = (subscriber) => subscriber.error(error)
        subscribers.forEach(terminator)
        subscribers.clear()
      }
    },
    complete() {
      if (!terminator) {
        terminator = (subscriber) => subscriber.complete()
        subscribers.forEach(terminator)
        subscribers.clear()
      }
    },
  })

  return new Observable((observer) => {
    for (const chunk of chunks) {
      if (observer.closed) {
        return
      }
      observer.next(chunk)
    }

    if (terminator) {
      terminator(observer)
      return
    }

    subscribers.add(observer)
    return () => {
      subscribers.delete(observer)
    }
  })
}

function errorToJSON(err: Error): Error {
  const { name, message, stack } = err
  return { name, message, stack }
}

function serializeError(
  dev: boolean | undefined,
  err: Error
): Error & { statusCode?: number } {
  if (dev) {
    return errorToJSON(err)
  }

  return {
    name: 'Internal Server Error.',
    message: '500 - Internal Server Error.',
    statusCode: 500,
  }
}