文档

https://nextjs.org/docs/advanced-features/custom-server

// server.js
const { createServer } = require('http')
const { parse } = require('url')
const next = require('next')
const dev = process.env.NODE_ENV !== 'production'
const hostname = 'localhost'
const port = 3000
// when using middleware `hostname` and `port` must be provided below
const app = next({ dev, hostname, port })
const handle = app.getRequestHandler()
app.prepare().then(() => {
  createServer(async (req, res) => {
    try {
      // Be sure to pass `true` as the second argument to `url.parse`.
      // This tells it to parse the query portion of the URL.
      const parsedUrl = parse(req.url, true)
      const { pathname, query } = parsedUrl
      if (pathname === '/a') {
        await app.render(req, res, '/a', query)
      } else if (pathname === '/b') {
        await app.render(req, res, '/b', query)
      } else {
        await handle(req, res, parsedUrl)
      }
    } catch (err) {
      console.error('Error occurred handling', req.url, err)
      res.statusCode = 500
      res.end('internal server error')
    }
  }).listen(port, (err) => {
    if (err) throw err
    console.log(`> Ready on http://${hostname}:${port}`)
  })
})

app.render

next-koa

A koa middleware for next.js with some common tools
https://github.com/xinpianchang/next-koa
https://github.dev/xinpianchang/next-koa

useFileSystemPublicRoutes

https://nextjs.org/docs/advanced-features/custom-server#disabling-file-system-routing
不使用nextjs默认的基于文件系统的路由
比如：使用自定义server后，路由归koa接管，关闭nextjs路由

案例

koa-next-www