错误:发送到客户端后无法设置标头

Question

我是Node.js的新手，我遇到了一些问题。

我使用的是Node.js 4.10和Express2.4.3。

当我尝试访问http://127.0.0.1:8888/auth/facebook时，我会被重定向到http://127.0.0.1:8888/auth/facebook_callback。

然后我收到了以下错误：

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出了什么问题吗？

Answer 1

Express中的res对象是Node.js's http.ServerResponse (read the http.js source)的子类。在调用res.writeHead(statusCode)之前，您可以随时调用res.setHeader(name, value)。在writeHead之后，标头被烘焙，您只能调用res.write(data)，最后调用res.end(data)。

出现错误" error : Can't set headers after sent“。意味着您已经处于Body或Finished状态，但某些函数试图设置header或statusCode。当您看到此错误时，请尝试查找在某些正文已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。

在本例中，您调用了res.redirect()，这会导致响应结束。然后您的代码抛出一个错误(res.req为null)。由于错误发生在实际的function(req, res, next)中(而不是在回调中)，Connect能够捕捉到它，然后尝试发送一个500错误页面。但是由于头部已经发送，所以node.js的setHeader抛出了您看到的错误。

Node.js/Express响应方法的完整列表以及必须调用它们的时间：

响应必须在Head中，并保留在Head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' (仅限于Express；仅影响特定于Express的methods)
8. res.contentType(type) (仅Express)

Response必须在Head中，并成为Body

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

响应可以在Head/Body中，也可以保留在Body中

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

Response可以是Head/Body中的任何一个，并成为Finished

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

响应可以是Head/Body中的任何一个，并保持其当前状态：

1. res.addTrailers(headers)

响应必须在Head中，并成为Finished

1. return next([err]) (仅限连接/快速)代码中间件(连接/快速only)
2. res.send(body|status[, headers|status[, status]]) (快速only)
3. res.attachment(filename) (快速only)
4. res.sendfile(path[, options[, callback]]) (快速only)
5. res.redirect(url[, status]) ))代码> only)
6. res.cookie(name, val[, options]) (快速only)
7. res.clearCookie(name[, options]) (仅快速only)
8. res.render(view[, options[, fn]]) (仅快速only)
9. res.render(view[, options[, fn]]))<

>H2111

1. [res.partial(view[, options])](http://expressjs.com/2x/guide.html#res.partial(%29) (仅限速成版)

Answer 2

我在一段时间内也遇到了这个错误。我想(希望)我已经想好了，想把它写在这里作为参考。

当您使用app.use方法将中间件添加到connect或express (构建于connect之上)时，您是在connect中将项目附加到Server.prototype.stack (至少使用当前的npm install connect，它看起来与本文发布时的github完全不同)。当服务器收到请求时，它会遍历堆栈，调用(request, response, next)方法。

问题是，如果在其中一个中间件项中写入响应主体或报头(看起来像是因为某种原因)，但没有调用response.end() next()，而您调用了 Server.prototype.handle，那么当核心方法完成时，它将注意到：

1. 堆栈中没有更多的项目，和/或
2. response.headerSent为true。

所以，它抛出了一个错误。但是它抛出的错误只是这个基本响应(来自connect http.js源代码：

res.statusCode = 404;
res.setHeader('Content-Type', 'text/plain');
res.end('Cannot ' + req.method + ' ' + req.url);

在这里，它调用res.setHeader('Content-Type', 'text/plain');，您可能已经在render方法中设置了它，而不调用response.end()，类似于：

response.setHeader("Content-Type", "text/html");
response.write("<p>Hello World</p>");

每件事都需要这样组织：

好的中间件

// middleware that does not modify the response body
var doesNotModifyBody = function(request, response, next) {
  request.params = {
    a: "b"
  };
  // calls next because it hasn't modified the header
  next();
};

// middleware that modify the response body
var doesModifyBody = function(request, response, next) {
  response.setHeader("Content-Type", "text/html");
  response.write("<p>Hello World</p>");
  response.end();
  // doesn't call next()
};

app.use(doesNotModifyBody);
app.use(doesModifyBody);

有问题的中间件

var problemMiddleware = function(request, response, next) {
  response.setHeader("Content-Type", "text/html");
  response.write("<p>Hello World</p>");
  next();
};

有问题的中间件在不调用response.end()和调用next()的情况下设置响应头，这会混淆connect的服务器。

Answer 3

我遇到了同样的问题，并意识到这是因为我在调用res.redirect时没有使用return语句，所以next函数也会在调用后立即被调用：

auth.annonymousOnly = function(req, res, next) {
    if (req.user) res.redirect('/');
    next();
};

这应该是：

auth.annonymousOnly = function(req, res, next) {
    if (req.user) return res.redirect('/');
    next();
};