Question

我在第一次回调连接时调用“res.writeHead（...）”时总是收到错误“错误：发送后无法设置标题。”：< / p>

var http = require('http');
var connect = require('connect');

var simpleApp = connect();

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

        res.writeHead(200, { 'content-type': 'text/html' });
        res.write('response powered by SIMPLE connect-object as middelware');

        console.log('Pre');
        next();
        console.log('Post');
    })
    .use(function(req, res, next){
        console.log('I am the header guy!');
        next();
    })
    .use('/admin', function(req, res, next){
        console.log('someone entered the admin area....');
        next();
    })
    .use(function(req, res){
        console.log('reached the tail of the "chain of responsibility!!!');
        res.end();
    });

http.createServer(simpleApp).listen(process.env.PORT || 3000);

console.log('Running on port "' + (process.env.PORT || 3000) + '"');

// just a save-guard to stop the process after some time...
setTimeout(function(){
    process.exit(0);
}, 20000);

这是错误信息：

Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (http.js:691:11)
    at ServerResponse.res.setHeader (C:\Users\drt\SkyDrive\Programmierung\nodejs\silkveil\node_modules\connect\lib\patch.js:63:22)
    at next (C:\Users\drt\SkyDrive\Programmierung\nodejs\silkveil\node_modules\connect\lib\proto.js:156:13)
    at Object.handle (C:\Users\drt\SkyDrive\Programmierung\nodejs\silkveil\connectSampleApp.js:13:3)
    at next (C:\Users\drt\SkyDrive\Programmierung\nodejs\silkveil\node_modules\connect\lib\proto.js:193:15)
    at Function.app.handle (C:\Users\drt\SkyDrive\Programmierung\nodejs\silkveil\node_modules\connect\lib\proto.js:201:3)
    at Server.app (C:\Users\drt\SkyDrive\Programmierung\nodejs\silkveil\node_modules\connect\lib\connect.js:65:37)
    at Server.EventEmitter.emit (events.js:98:17)
    at HTTPParser.parser.onIncoming (http.js:2108:12)

当我将“writeHead”代码移动到最后一个回调时，一切都很好：

.use(function(req, res){
        console.log('reached the tail of the "chain of responsibility!!!');
        res.writeHead(200, { 'content-type': 'text/html' });
        res.write('response powered by SIMPLE connect-object as middelware');
        res.end();
    });

所以我的问题是：在使用connect时，是否只允许在最后一次回调中使用writeHead / write？

Answer 1

检查另一个问题。 res.writeHead 基本上在调用res.writeHead之后，标题不能再被修改，而next方法会尝试修改将导致异常的标题。

因此，您可以修改第一个连接回调中的标题，但不允许您编写正文（res.write）。以下代码应该正常工作。简而言之，您可以修改标题，但不能刷新它们。

var http = require('http');
var connect = require('connect');

var simpleApp = connect();

simpleApp
    .use(function(req, res, next){
        res.statusCode = 200;
        res.setHeader( 'content-type', 'text/html' );

        console.log('Pre');
        next();
        console.log('Post');
    })
    .use(function(req, res, next){
        console.log('I am the header guy!');
        next();
    })
    .use('/admin', function(req, res, next){
        console.log('someone entered the admin area....');
        next();
    })
    .use(function(req, res){
        res.write('response powered by SIMPLE connect-object as middelware');
        console.log('reached the tail of the "chain of responsibility!!!');
        res.end();
    });

http.createServer(simpleApp).listen(process.env.PORT || 3000);

console.log('Running on port "' + (process.env.PORT || 3000) + '"');

// just a save-guard to stop the process after some time...
setTimeout(function(){
    process.exit(0);
}, 20000);

Answer 2

您在代码的第一部分中忘记了这一行：

res.end();

如果不起作用，TJ Holowaychuk的评论如下： https://github.com/senchalabs/connect/issues/683#issuecomment-10018892

Nodejs：在第一个connect-callback中连接和“writeHead”

2 个答案: