kao 源码浅析:

  • use middleware
  • listen -> callback -> compose
  • handleRequest
  • createContext -> middleware -> response

部分子模块及简要说明

  • koa-compose: 组合和遍历middleware

    // 简化版的 compose，（不含类型检测和异常处理）
module.exports = (middleware) => (context, next) => {
  const dispatch = (i) => {
    let fn = middleware[i]
    if (i === middleware.length) return Promise.resolve()

    try {
      return Promise.resolve(fn(context, function next () {
        return dispatch(i + 1)
      }))
    } catch (err) {
      return Promise.reject(err)
    }
  }
  return dispatch(0);
}

  • on-finished: Execute a callback when a HTTP request closes, finishes, or errors.

    var destroy = require('destroy')
var http = require('http')
var onFinished = require('on-finished')

http.createServer(function onRequest(req, res) {
  var stream = fs.createReadStream('package.json')
  stream.pipe(res)
  onFinished(res, function (err) {
    destroy(stream)
  })
})

  • statuses: HTTP status utility for node.

    status(403) // => 403
status('403') // => 403
status('forbidden') // => 403
status('Forbidden') // => 403

status.empty[200] // => undefined
status.empty[204] // => true
status.empty[304] // => true

  • cookies: Cookies 工具集。

    var http    = require( "http" )
var Cookies = require( "cookies" )

server = http.createServer( function( req, res ) {
  var cookies = new Cookies( req, res, { "keys": keys } )
    , unsigned, signed, tampered

  if ( req.url == "/set" ) {
    cookies
      // set a regular cookie
      .set( "unsigned", "foo", { httpOnly: false } )

      // set a signed cookie
      .set( "signed", "bar", { signed: true } )

      // mimic a signed cookie, but with a bogus signature
      .set( "tampered", "baz" )
      .set( "tampered.sig", "bogus" )

    res.writeHead( 302, { "Location": "/" } )
    return res.end( "Now let's check." )
  }

  unsigned = cookies.get( "unsigned" )
  signed = cookies.get( "signed", { signed: true } )
  tampered = cookies.get( "tampered", { signed: true } )

  assert.equal( unsigned, "foo" )
  assert.equal( signed, "bar" )
  assert.notEqual( tampered, "baz" )
  assert.equal( tampered, undefined )

  res.writeHead( 200, { "Content-Type": "text/plain" } )
  res.end(
    "unsigned expected: foo\n\n" +
    "unsigned actual: " + unsigned + "\n\n" +
    "signed expected: bar\n\n" +
    "signed actual: " + signed + "\n\n" +
    "tampered expected: undefined\n\n"+
    "tampered: " + tampered + "\n\n"
  )
})

  • accepts: Accepts 工具集。

    var accepts = require('accepts')
var http = require('http')

function app(req, res) {
  var accept = accepts(req)

  // the order of this list is significant; should be server preferred order
  switch(accept.type(['json', 'html'])) {
    case 'json':
      res.setHeader('Content-Type', 'application/json')
      res.write('{"hello":"world!"}')
      break
    case 'html':
      res.setHeader('Content-Type', 'text/html')
      res.write('<b>hello, world!</b>')
      break
    default:
      // the fallback is text/plain, so no need to specify it above
      res.setHeader('Content-Type', 'text/plain')
      res.write('hello, world!')
      break
  }

  res.end()
}

http.createServer(app).listen(3000)

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