JavaScript错误：将标头发送到客户端后无法设置标头

Question

我对Node.js相当陌生，遇到了一些问题。

我正在使用Node.js 4.10和Express 2.4.3。

当我尝试访问http://127.0.0.1:8888/auth/facebook时，我将重定向至http://127.0.0.1:8888/auth/facebook_callback。

然后，我收到以下错误：

Error: Can't render headers after they are sent to the client.
    at ServerResponse.<anonymous> (http.js:573:11)
    at ServerResponse._renderHeaders (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:64:25)
    at ServerResponse.writeHead (http.js:813:20)
    at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/auth.strategies/facebook.js:28:15
    at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/index.js:113:13
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/strategyExecutor.js:45:39)
    at [object Object].pass (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/authExecutionScope.js:32:3)
    at [object Object].halt (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/authExecutionScope.js:29:8)
    at [object Object].redirect (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/authExecutionScope.js:16:8)
    at [object Object].<anonymous> (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/auth.strategies/facebook.js:77:15)
Error: Can't set headers after they are sent.
    at ServerResponse.<anonymous> (http.js:527:11)
    at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:195:11)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:150:23)
    at param (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:189:13)
    at pass (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:191:10)
    at Object.router [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:197:6)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
    at Object.auth [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/index.js:153:7)
Error: Can't set headers after they are sent.
    at ServerResponse.<anonymous> (http.js:527:11)
    at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:207:9)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:150:23)
    at param (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:189:13)
    at pass (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:191:10)
    at Object.router [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/router.js:197:6)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
    at Object.auth [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/index.js:153:7)
Error: Can't set headers after they are sent.
    at ServerResponse.<anonymous> (http.js:527:11)
    at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:150:23)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:207:9)
    at Object.auth [as handle] (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect-auth/lib/index.js:153:7)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
    at HTTPServer.handle (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:211:3)
    at Object.handle (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:105:14)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
Error: Can't set headers after they are sent.
    at ServerResponse.<anonymous> (http.js:527:11)
    at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:150:23)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:207:9)
    at HTTPServer.handle (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:211:3)
    at Object.handle (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:105:14)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:198:15)
    at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session.js:323:9
    at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session.js:338:9

node.js:134
        throw e; // process.nextTick error, or 'error' event on first tick
        ^
Error: Can't set headers after they are sent.
    at ServerResponse.<anonymous> (http.js:527:11)
    at ServerResponse.setHeader (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/patch.js:50:20)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:162:13)
    at next (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/http.js:207:9)
    at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session.js:323:9
    at /home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session.js:338:9
    at Array.<anonymous> (/home/eugene/public_html/all_things_node/projects/fb2/node_modules/connect/lib/middleware/session/memory.js:57:7)
    at EventEmitter._tickCallback (node.js:126:26)

以下是我的代码：

var fbId= "XXX";
var fbSecret= "XXXXXX";
var fbCallbackAddress= "http://127.0.0.1:8888/auth/facebook_callback"

var cookieSecret = "node";     // enter a random hash for security

var express= require('express');
var auth = require('connect-auth')
var app = express.createServer();


app.configure(function(){
    app.use(express.bodyParser());
    app.use(express.methodOverride());
    app.use(express.cookieParser());
    app.use(express.session({secret: cookieSecret}));
    app.use(auth([
        auth.Facebook({
            appId : fbId,
            appSecret: fbSecret,
            callback: fbCallbackAddress,
            scope: 'offline_access,email,user_about_me,user_activities,manage_pages,publish_stream',
            failedUri: '/noauth'
        })
    ]));
    app.use(app.router);
});


app.get('/auth/facebook', function(req, res) {
  req.authenticate("facebook", function(error, authenticated) {
    if (authenticated) {
      res.redirect("/great");
      console.log("ok cool.");
      console.log(res['req']['session']);
    }
  });
});

app.get('/noauth', function(req, res) {
  console.log('Authentication Failed');
  res.send('Authentication Failed');
});

app.get('/great', function( req, res) {
  res.send('Supercoolstuff');
});

app.listen(8888);

我可以知道我的代码有什么问题吗？

Answer 1

resExpress中的对象是Node.js的http.ServerResponse子类（请阅读http.js源代码）。允许您拨打任意数量的电话res.setHeader(name, value)，直到致电为止res.writeHead(statusCode)。之后writeHead，将标题放进去，您只能调用res.write(data)，最后res.end(data)。

错误“错误：发送标头后无法设置标头”。表示您已经处于“正文”或“完成”状态，但是某些函数试图设置标头或statusCode。当您看到此错误时，请尝试查找在某些正文已被写入之后尝试发送标头的任何内容。例如，查找意外调用两次的回调，或发送正文后发生的任何错误。

在您的情况下，您致电res.redirect()，这导致响应变为“完成”。然后，您的代码引发了错误（res.reqis
null）。并且由于该错误发生在您的实际错误function(req, res, next)（而不是回调）之内，因此Connect能够捕获该错误，然后尝试发送500错误页面。但是，由于已经发送了标头，所以Node.js
setHeader抛出了您看到的错误。

Node.js / Express响应方法的完整列表以及何时调用它们：

回复必须在 标题中， 并保持在 标题中 ：

1. res.writeContinue()
2. res.statusCode = 404
3. res.setHeader(name, value)
4. res.getHeader(name)
5. res.removeHeader(name)
6. res.header(key[, val]) （Express only）
7. res.charset = ‘utf-8’ （仅Express；仅影响Express特定的方法）
8. res.contentType(type) （Express only）

响应必须在头脑中，然后变成身体：

res.writeHead(statusCode, [reasonPhrase], [headers])

响应可以是头部/身体，也可以是身体：

res.write(chunk, encoding='utf8')

响应可以是Head / Body，也可以是Finished：

res.end([data], [encoding])

响应可以处于Head / Body，也可以保持其当前状态：

res.addTrailers(headers)

响应必须在标题中，并已完成：

1. return next([err]) （仅连接/快速）
2. 中间件中的任何异常function(req, res, next)（仅适用于Connect / Express）
3. res.send(body|status[, headers|status[, status]]) （Express only）
4. res.attachment(filename) （Express only）
5. res.sendfile(path[, options[, callback]]) （Express only）
6. res.json(obj[, headers|status[, status]]) （Express only）
7. res.redirect(url[, status]) （Express only）
8. res.cookie(name, val[, options]) （Express only）
9. res.clearCookie(name[, options]) （Express only）
10. res.render(view[, options[, fn]]) （Express only）
11. res.partial(view[, options]) （Express only）