next.js/packages/next/server/next-dev-server.js

import Server from 'next-server/dist/server/next-server'
import { join } from 'path'
import HotReloader from './hot-reloader'
import {route} from 'next-server/dist/server/router'
import {PHASE_DEVELOPMENT_SERVER} from 'next-server/constants'

export default class DevServer extends Server {
  constructor (options) {
    super(options)
    this.hotReloader = new HotReloader(this.dir, { config: this.nextConfig, buildId: this.buildId })
    this.renderOpts.dev = true
  }

  currentPhase () {
    return PHASE_DEVELOPMENT_SERVER
  }

  readBuildId () {
    return 'development'
  }

  async addExportPathMapRoutes () {
    // Makes `next export` exportPathMap work in development mode.
    // So that the user doesn't have to define a custom server reading the exportPathMap
    if (this.nextConfig.exportPathMap) {
      console.log('Defining routes from exportPathMap')
      const exportPathMap = await this.nextConfig.exportPathMap({}, {dev: true, dir: this.dir, outDir: null, distDir: this.distDir, buildId: this.buildId}) // In development we can't give a default path mapping
      for (const path in exportPathMap) {
        const {page, query = {}} = exportPathMap[path]

        // We use unshift so that we're sure the routes is defined before Next's default routes
        this.router.add({
          match: route(path),
          fn: async (req, res, params, parsedUrl) => {
            const { query: urlQuery } = parsedUrl

            Object.keys(urlQuery)
              .filter(key => query[key] === undefined)
              .forEach(key => console.warn(`Url defines a query parameter '${key}' that is missing in exportPathMap`))

            const mergedQuery = {...urlQuery, ...query}

            await this.render(req, res, page, mergedQuery, parsedUrl)
          }
        })
      }
    }
  }

  async prepare () {
    await super.prepare()
    await this.addExportPathMapRoutes()
    await this.hotReloader.start()
  }

  async close () {
    await this.hotReloader.stop()
  }

  async run (req, res, parsedUrl) {
    const {finished} = await this.hotReloader.run(req, res, parsedUrl)
    if (finished) {
      return
    }

    return super.run(req, res, parsedUrl)
  }

  generateRoutes () {
    const routes = super.generateRoutes()

    // In development we expose all compiled files for react-error-overlay's line show feature
    // We use unshift so that we're sure the routes is defined before Next's default routes
    routes.unshift({
      match: route('/_next/development/:path*'),
      fn: async (req, res, params) => {
        const p = join(this.distDir, ...(params.path || []))
        await this.serveStatic(req, res, p)
      }
    })

    return routes
  }

  async renderToHTML (req, res, pathname, query) {
    const compilationErr = await this.getCompilationError(pathname)
    if (compilationErr) {
      res.statusCode = 500
      return this.renderErrorToHTML(compilationErr, req, res, pathname, query)
    }

    // In dev mode we use on demand entries to compile the page before rendering
    try {
      await this.hotReloader.ensurePage(pathname)
    } catch (err) {
      if (err.code === 'ENOENT') {
        res.statusCode = 404
        return this.renderErrorToHTML(null, req, res, pathname, query)
      }
      if (!this.quiet) console.error(err)
    }

    return super.renderToHTML(req, res, pathname, query)
  }

  async renderErrorToHTML (err, req, res, pathname, query) {
    const compilationErr = await this.getCompilationError(pathname)
    if (compilationErr) {
      res.statusCode = 500
      return super.renderErrorToHTML(compilationErr, req, res, pathname, query)
    }

    try {
      const out = await super.renderErrorToHTML(err, req, res, pathname, query)
      return out
    } catch (err2) {
      if (!this.quiet) console.error(err2)
      res.statusCode = 500
      return super.renderErrorToHTML(err2, req, res, pathname, query)
    }
  }

  sendHTML (req, res, html) {
    // In dev, we should not cache pages for any reason.
    res.setHeader('Cache-Control', 'no-store, must-revalidate')
    return super.sendHTML(req, res, html)
  }

  setImmutableAssetCacheControl (res) {
    res.setHeader('Cache-Control', 'no-store, must-revalidate')
  }

  async getCompilationError (page) {
    const errors = await this.hotReloader.getCompilationErrors(page)
    if (errors.length === 0) return

    // Return the very first error we found.
    return errors[0]
  }
}