server/render.js

import { join } from 'path'
import { createElement } from 'react'
import { renderToString, renderToStaticMarkup } from 'react-dom/server'
import send from 'send'
import generateETag from 'etag'
import fresh from 'fresh'
import requirePage from './require'
import { Router } from '../lib/router'
import { loadGetInitialProps, isResSent } from '../lib/utils'
import { getAvailableChunks } from './utils'
import Head, { defaultHead } from '../lib/head'
import App from '../lib/app'
import ErrorDebug from '../lib/error-debug'
import { flushChunks } from '../lib/dynamic'

const logger = console

export async function render (req, res, pathname, query, opts) {
  const html = await renderToHTML(req, res, pathname, query, opts)
  sendHTML(req, res, html, req.method, opts)
}

export function renderToHTML (req, res, pathname, query, opts) {
  return doRender(req, res, pathname, query, opts)
}

export async function renderError (err, req, res, pathname, query, opts) {
  const html = await renderErrorToHTML(err, req, res, query, opts)
  sendHTML(req, res, html, req.method, opts)
}

export function renderErrorToHTML (err, req, res, pathname, query, opts = {}) {
  return doRender(req, res, pathname, query, { ...opts, err, page: '/_error' })
}

async function doRender (req, res, pathname, query, {
  err,
  page,
  buildId,
  buildStats,
  hotReloader,
  assetPrefix,
  availableChunks,
  dist,
  dir = process.cwd(),
  dev = false,
  staticMarkup = false,
  nextExport = false
} = {}) {
  page = page || pathname

  if (hotReloader) { // In dev mode we use on demand entries to compile the page before rendering
    await ensurePage(page, { dir, hotReloader })
  }

  const documentPath = join(dir, dist, 'dist', 'bundles', 'pages', '_document')

  let Component = requirePage(page, {dir, dist})
  let Document = require(documentPath)
  Component = Component.default || Component
  Document = Document.default || Document
  const asPath = req.url
  const ctx = { err, req, res, pathname, query, asPath }
  const props = await loadGetInitialProps(Component, ctx)

  // the response might be finshed on the getinitialprops call
  if (isResSent(res)) return

  const renderPage = (enhancer = Page => Page) => {
    const app = createElement(App, {
      Component: enhancer(Component),
      props,
      router: new Router(pathname, query, asPath)
    })

    const render = staticMarkup ? renderToStaticMarkup : renderToString

    let html
    let head
    let errorHtml = ''

    try {
      if (err && dev) {
        errorHtml = render(createElement(ErrorDebug, { error: err }))
      } else if (err) {
        errorHtml = render(app)
      } else {
        html = render(app)
      }
    } finally {
      head = Head.rewind() || defaultHead()
    }
    const chunks = loadChunks({ dev, dir, dist, availableChunks })

    return { html, head, errorHtml, chunks }
  }

  const docProps = await loadGetInitialProps(Document, { ...ctx, renderPage })

  if (isResSent(res)) return

  if (!Document.prototype || !Document.prototype.isReactComponent) throw new Error('_document.js is not exporting a React element')
  const doc = createElement(Document, {
    __NEXT_DATA__: {
      props,
      page, // the rendered page
      pathname, // the requested path
      query,
      buildId,
      buildStats,
      assetPrefix,
      nextExport,
      err: (err) ? serializeError(dev, err) : null
    },
    dev,
    dir,
    staticMarkup,
    ...docProps
  })

  return '<!DOCTYPE html>' + renderToStaticMarkup(doc)
}

export async function renderScriptError (req, res, page, error) {
  // Asks CDNs and others to not to cache the errored page
  res.setHeader('Cache-Control', 'no-store, must-revalidate')

  if (error.code === 'ENOENT') {
    res.statusCode = 404
    res.end('404 - Not Found')
    return
  }

  logger.error(error.stack)
  res.statusCode = 500
  res.end('500 - Internal Error')
}

export function sendHTML (req, res, html, method, { dev }) {
  if (isResSent(res)) return
  const etag = generateETag(html)

  if (fresh(req.headers, { etag })) {
    res.statusCode = 304
    res.end()
    return
  }

  if (dev) {
    // In dev, we should not cache pages for any reason.
    // That's why we do this.
    res.setHeader('Cache-Control', 'no-store, must-revalidate')
  }

  res.setHeader('ETag', etag)
  if (!res.getHeader('Content-Type')) {
    res.setHeader('Content-Type', 'text/html; charset=utf-8')
  }
  res.setHeader('Content-Length', Buffer.byteLength(html))
  res.end(method === 'HEAD' ? null : html)
}

export function sendJSON (res, obj, method) {
  if (isResSent(res)) return

  const json = JSON.stringify(obj)
  res.setHeader('Content-Type', 'application/json')
  res.setHeader('Content-Length', Buffer.byteLength(json))
  res.end(method === 'HEAD' ? null : json)
}

function errorToJSON (err) {
  const { name, message, stack } = err
  const json = { name, message, stack }

  if (err.module) {
    // rawRequest contains the filename of the module which has the error.
    const { rawRequest } = err.module
    json.module = { rawRequest }
  }

  return json
}

function serializeError (dev, err) {
  if (dev) {
    return errorToJSON(err)
  }

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

export function serveStatic (req, res, path) {
  return new Promise((resolve, reject) => {
    send(req, path)
    .on('directory', () => {
      // We don't allow directories to be read.
      const err = new Error('No directory access')
      err.code = 'ENOENT'
      reject(err)
    })
    .on('error', reject)
    .pipe(res)
    .on('finish', resolve)
  })
}

async function ensurePage (page, { dir, hotReloader }) {
  if (page === '/_error') return

  await hotReloader.ensurePage(page)
}

function loadChunks ({ dev, dir, dist, availableChunks }) {
  const flushedChunks = flushChunks()
  const response = {
    names: [],
    filenames: []
  }

  if (dev) {
    availableChunks = getAvailableChunks(dir, dist)
  }

  for (var chunk of flushedChunks) {
    const filename = availableChunks[chunk]
    if (filename) {
      response.names.push(chunk)
      response.filenames.push(filename)
    }
  }

  return response
}