var  connect = require( 'connect' ); 
 var  http = require( 'http' ); 
 var  app = connect(); 
 // gzip/deflate outgoing responses 

 var  compression = require( 'compression' ); 

 app.use(compression()); 

// store session state in browser cookie 

 var  cookieSession = require( 'cookie-session' ); 

 app.use(cookieSession({ 

    keys: [ 'secret1' ,  'secret2' ] 

 })); 

 // parse urlencoded request bodies into req.body 

 var  bodyParser = require( 'body-parser' ); 

 app.use(bodyParser.urlencoded({extended:  false })); 

 

 // respond to all requests 

 app.use( function (req, res){ 

   res.end( 'Hello from Connect!\n' ); 

 }); 


 //create node.js http server and listen on port 

 http.createServer(app).listen(3000); 

 var  app = connect() // 初始化 

 app.use( function (req, res, next) { 

    // do something 

 })

 // http 服务器，使用 

 http.createServer(app).listen(3000); 

function  handle () { 
   function  app(req, res, next) { app.handle(req, res, next)} 
  app.handle =  function  (req, res, next) { 

    console.log( this ); 

   } 
  app.statck = []; 
   return  app; 

 } 
 var  app = handle(); 
 app()  // ==> { [Function: app] handle: [Function], stack: [] } 
 app.apply({})  // ==>{ [Function: app] handle: [Function], stack: [] } 

 var  merge = require( 'utils-merge' ); 

 module.exports = createServer; 

 var  proto = {}; 

 function  createServer() { 

   // 函数对象，这个对象能调用，能加属性 

   function  app(req, res, next){ app.handle(req, res, next); } 

   merge(app, proto);  // ===等于调用 Object.assign 

   merge(app, EventEmitter.prototype);  // === 等于调用 Object.assign 

   app.route =  '/' ; 

   app.stack = []; 

   return  app; 

 } 

 proto.handle =  function  handle(req, res, out) { 

   var  index = 0; 

   var  protohost = getProtohost(req.url) ||  '' ;  //获得 http://www.baidu.com 

   var  removed =  '' ; 

   var  slashAdded =  false ; 

   var  stack =  this .stack; 

 

   // final function handler 

   var  done = out || finalhandler(req, res, { 

    env: env, 

    onerror: logerror 

   });  // 接口 done(err); 

 

   // store the original URL 

   req.originalUrl = req.originalUrl || req.url; 

 

   function  next(err) { 

    if  (slashAdded) { 

     req.url = req.url.substr(1);  // 除掉 / 之后的字符串 

     slashAdded =  false ;  // 已经拿掉 

    } 

 

    if  (removed.length !== 0) { 

     req.url = protohost + removed + req.url.substr(protohost.length); 

     removed =  '' ; 

    } 

 

    // next callback 

    var  layer = stack[index++]; 

 

    // all done 

    if  (!layer) { 

     defer(done, err);  // 没有中间件，调用 finalhandler 进行处理，如果 err 有值，就返回 404 进行处理 

     return ; 

    } 

 

    // route data 

    var  path = parseUrl(req).pathname ||  '/' ; 

    var  route = layer.route; 

 

    // skip this layer if the route doesn't match 

    if  (path.toLowerCase().substr(0, route.length) !== route.toLowerCase()) { 

     return  next(err);  // 执行下一个 

    } 

 

    // skip if route match does not border "/", ".", or end 

    var  c = path[route.length]; 

    if  (c !== undefined && '/ ' !== c && ' . ' !== c) { 

     return next(err); // 执行下一个 

    } 

 

    // trim off the part of the url that matches the route 

    if (route.length !== 0 && route !== ' / ') { 

     removed = route; 

     req.url = protohost + req.url.substr(protohost.length + removed.length); 

 

     // ensure leading slash 

     if (!protohost && req.url[0] !== ' / ') { 

      req.url = ' /' + req.url; 

      slashAdded =  true ; 

     } 

    } 

 

    // call the layer handle 

    call(layer.handle, route, err, req, res, next); 

   } 

 

   next(); 

 }; 

 function  call(handle, route, err, req, res, next) { 

   var  arity = handle.length; 

   var  error = err; 

   var  hasError = Boolean(err); 

 

   debug( '%s %s : %s' , handle.name ||  '<anonymous>' , route, req.originalUrl); 

 

   try  { 

    if  (hasError && arity === 4) { 

     // error-handling middleware 

     handle(err, req, res, next); 

     return ; 

    }  else  if  (!hasError && arity < 4) { 

     // request-handling middleware 

     handle(req, res, next); 

     return ; 

    } 

   }  catch  (e) { 

    // replace the error 

    error = e; 

   } 

 

   // continue 

   next(error); 

 } 

 proto.use =  function  use(route, fn) { 

   var  handle = fn;  // fn 只是一个函数的话 三种接口 // 1. err, req, res, next 2. req, res, 3, req, res, next 

   var  path = route; 

 

   // default route to '/' 

   if  ( typeof  route !==  'string' ) { 

    handle = route; 

    path =  '/' ; 

   } 

 

   // wrap sub-apps 

   if  ( typeof  handle.handle ===  'function' ) {  // 自定义中的函数对象 

    var  server = handle; 

    server.route = path; 

    handle =  function  (req, res, next) {  // req, res, next 中间件 

     server.handle(req, res, next); 

    }; 

   } 

 

   // wrap vanilla http.Servers 

   if  (handle  instanceof  http.Server) { 

    handle = handle.listeners( 'request' )[0];  // (req, res) // 最后的函数 

   } 

 

   // strip trailing slash 

   if  (path[path.length - 1] ===  '/' ) { 

    path = path.slice(0, -1); 

   } 

 

   // add the middleware 

   debug( 'use %s %s' , path ||  '/' , handle.name ||  'anonymous' ); 

   this .stack.push({ route: path, handle: handle }); 

 

   return  this ; 

 }; 

 /* istanbul ignore next */ 

 var  defer =  typeof  setImmediate ===  'function' 

   ? setImmediate 

   :  function (fn){ process.nextTick(fn.bind.apply(fn, arguments)) } 

 function  () { 

    var  cb = Array.from(arguments)[0]; 

    var  args = Array.from(arguments).splice(1); 

    process.nextTick( function () { 

      cb.apply( null ,args); 

    }) 

 } 

 function (..args){ process.nextTick(fn.bind(...args)) }