我无法正确运行聊天应用程序

Question

我知道这是一个着名的问题，但是我的聊天应用程序遇到了问题，事实上它是一个教师，它应该可以工作，但我遇到了问题：

    C:\xampp\htdocs\chat>node app.js
       info  - socket.io started
    Express server listening on port 3000
    GET /chat 200 210ms - 686
    http.js:690
        throw new Error('Can\'t set headers after they are sent.');
              ^
    Error: Can't set headers after they are sent.
        at ServerResponse.OutgoingMessage.setHeader (http.js:690:11)
        at ServerResponse.res.setHeader (C:\xampp\htdocs\chat\node_modules\express\n
    ode_modules\connect\lib\patch.js:59:22)
        at next (C:\xampp\htdocs\chat\node_modules\express\node_modules\connect\lib\
    proto.js:153:13)
        at Function.app.handle (C:\xampp\htdocs\chat\node_modules\express\node_modul
    es\connect\lib\proto.js:198:3)
        at Server.app (C:\xampp\htdocs\chat\node_modules\express\node_modules\connec
    t\lib\connect.js:66:31)
        at Manager.handleRequest (C:\xampp\htdocs\chat\node_modules\socket.io\lib\ma
    nager.js:564:28)
        at Server.<anonymous> (C:\xampp\htdocs\chat\node_modules\socket.io\lib\manag
    er.js:118:10)
        at Server.emit (events.js:117:20)
        at HTTPParser.parser.onIncoming (http.js:2113:12)
        at HTTPParser.parserOnHeadersComplete [as onHeadersComplete] (http.js:122:23
    )

the app.js which runs the server:
    /**
     * Module dependencies.
     */
    var express = require('express')
      , routes = require('./routes')
      , user = require('./routes/user')
      , chat = require('./routes/chat')
      , socketio = require('socket.io')
      , http = require('http')
      , path = require('path');
    var app = express();
    app.configure(function(){
      app.set('port', process.env.PORT || 3000);
      app.set('views', __dirname + '/views');
      app.set('view engine', 'jade');
      app.use(express.favicon());
      app.use(express.logger('dev'));
      app.use(express.bodyParser());
      app.use(express.methodOverride());
      app.use(app.router);
      app.use(express.static(path.join(__dirname, 'public')));
    });
    app.configure('development', function(){
      app.use(express.errorHandler());
    });
    app.get('/', routes.index);
    app.get('/chat', chat.main);
    app.get('/users', user.list);
    var server = app.listen(app.get('port'), function(){
      console.log("Express server listening on port " + app.get('port'));
    });
    var io = socketio.listen(server);
    var clients = {};
    var socketsOfClients = {};
    io.sockets.on('connection', function(socket) {
      socket.on('set username', function(userName) {
        // Is this an existing user name?
        if (clients[userName] === undefined) {
          // Does not exist ... so, proceed
          clients[userName] = socket.id;
          socketsOfClients[socket.id] = userName;
          userNameAvailable(socket.id, userName);
          userJoined(userName);
        } else
        if (clients[userName] === socket.id) {
          // Ignore for now
        } else {
          userNameAlreadyInUse(socket.id, userName);
        }
      });
      socket.on('message', function(msg) {
        var srcUser;
        if (msg.inferSrcUser) {
          // Infer user name based on the socket id
          srcUser = socketsOfClients[socket.id];
        } else {
          srcUser = msg.source;
        }
        if (msg.target == "All") {
          // broadcast
          io.sockets.emit('message',
              {"source": srcUser,
               "message": msg.message,
               "target": msg.target});
        } else {
          // Look up the socket id
          io.sockets.sockets[clients[msg.target]].emit('message', 
              {"source": srcUser,
               "message": msg.message,
               "target": msg.target});
        }})
      socket.on('disconnect', function() {
          var uName = socketsOfClients[socket.id];
          delete socketsOfClients[socket.id];
        delete clients[uName];
        // relay this message to all the clients
        userLeft(uName);
      })
    })
    function userJoined(uName) {
        Object.keys(socketsOfClients).forEach(function(sId) {
            io.sockets.sockets[sId].emit('userJoined', { "userName": uName });
        }) }
    function userLeft(uName) {
        io.sockets.emit('userLeft', { "userName": uName });
    }
    function userNameAvailable(sId, uName) {
      setTimeout(function() {
        console.log('Sending welcome msg to ' + uName + ' at ' + sId);
        io.sockets.sockets[sId].emit('welcome', { "userName" : uName, "currentUsers": JSON.stringify(Object.keys(clients)) });
      }, 500);}
    function userNameAlreadyInUse(sId, uName) {
      setTimeout(function() {
        io.sockets.sockets[sId].emit('error', { "userNameInUse" : true });
      }, 500);
    }

那些是chat.js：

exports.main = function(req, res){
  res.render('chat', { "title" : "Chat Sample" });
};

和user.js

/*
 * GET users listing.
 */
exports.list = function(req, res){
  res.send("respond with a resource");
};

感谢帮助