Express 4錯誤：發送標頭后無法設置標頭

Question

我正在嘗試使用Express建立一個簡單的聊天系統。 我剛剛從v.3遷移到v.4，現在收到以下錯誤消息：

   info  - socket.io started
Express server listening on port 3000
GET / 304 790.443 ms - -
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (http.js:707:11)
    at ServerResponse.res.setHeader (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/connect/lib/patch.js:134:22)
    at Object.expressInit [as handle] (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/lib/middleware.js:20:42)
    at next (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/connect/lib/proto.js:174:15)
    at Object.query [as handle] (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/connect/lib/middleware/query.js:43:5)
    at next (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/connect/lib/proto.js:174:15)
    at Function.app.handle (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/connect/lib/proto.js:182:3)
    at Server.app (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/connect/lib/connect.js:67:37)
    at Manager.handleRequest (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/socket.io/lib/manager.js:564:28)
    at Server.<anonymous> (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/socket.io/lib/manager.js:118:10)
GET /javascripts/jquery.min.js 304 7.874 ms - -
GET /javascripts/jquery.min.js 304 7.966 ms - -
GET /javascripts/chat.js 304 4.132 ms - -
GET /javascripts/chat.js 304 4.213 ms - -
GET /socket.io/socket.io.js 404 11.137 ms - 35
GET /stylesheets/style.css 304 1.715 ms - -
GET /stylesheets/style.css 304 1.798 ms - -
Error: Can't set headers after they are sent.
    at SendStream.headersAlreadySent (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:319:13)
    at SendStream.send (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:501:17)
    at onstat (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:600:10)
    at Object.oncomplete (fs.js:107:15)
Error: Can't set headers after they are sent.
    at SendStream.headersAlreadySent (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:319:13)
    at SendStream.send (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:501:17)
    at onstat (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:600:10)
    at Object.oncomplete (fs.js:107:15)
Error: Can't set headers after they are sent.
    at SendStream.headersAlreadySent (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:319:13)
    at SendStream.send (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:501:17)
    at onstat (/Users/bruger/Google Drev/Uni/8. semester/Real-Time-Webapplikationer/0786OS_Code/Chapter 04/section02/awesome-chat/node_modules/express/node_modules/send/index.js:600:10)
    at Object.oncomplete (fs.js:107:15)
   debug - served static content /socket.io.js

當我第一次啟動服務器實例時，一切似乎都很好，直到我進入瀏覽器，然后才出現錯誤。

我一直在嘗試解決有關閱讀幾乎所有有關帖子的問題

Error: Can't set headers after they are sent.

但是我不知道自己在做什么錯？ 這是我設置app.js文件的代碼：

var express = require('express')
  , routes = require('./routes')
  , http = require('http')
  , path = require('path');

var methodOverride = require('method-override')                     
var json = require('json-middleware');                              
var multipart = require('connect-multiparty');                      
var multipartMiddleware = multipart();                              

var app = express();

// Express 4 version
var env = process.env.NODE_ENV || 'development';
if ('development' == env) {
   // configure stuff here
  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(json);                                                    
  app.use('/public/javascripts/chat.js', multipartMiddleware);      
  //app.use(express.bodyParser());                                  
  //app.use(express.methodOverride());                              
  app.use(methodOverride('_method'))
  app.use(app.router);
  app.use(express.static(path.join(__dirname, 'public')));
}


app.get('/', routes.index);

var server = http.createServer(app).listen(app.get('port'), function(){
  console.log("Express server listening on port " + app.get('port'));
});

//routes.sockets.connect(server);
require('./routes/sockets.js').initialize(server);

可能是因為錯誤是在index.js或socket.js文件中生成的，所以我也添加了這些。 Index.js：

exports.index = function(req, res){
  res.render('index', { title: 'Express Chat' });
};

sockets.js：

var io = require('socket.io');

exports.initialize = function(server) {
  io = io.listen(server);
  io.sockets.on("connection", function(socket){
    socket.on('message', function(message){
      message= JSON.parse(message);
      if(message.type == "userMessage"){
        socket.get('nickname', function(err, nickname){
          message.username=nickname;
          socket.broadcast.send(JSON.stringify(message));
          message.type = "myMessage";
          socket.send(JSON.stringify(message));
        });        
      }
    });

    socket.on("set_name", function(data){
      socket.set('nickname', data.name, function(){
        socket.emit('name_set', data);
    socket.send(JSON.stringify({type:'serverMessage', message: 'Welcome to the most interesting chat room on earth!'}));          
      });
    });
  });
}

我是表達和node.js的新手，並且已經兩天了，所以我們將不勝感激！

Answer 1

這種錯誤通常是由於不return的-發送函數，然后在執行過程中稍后的某些操作也會發送數據。

為了減輕這種情況，您應該始終返回發送。

  return socket.send(JSON.stringify(message));

這將確保未設置多個標頭。