错误: 无法设置发送到客户端后的标题

I'm fairly new to Node.js and I am having some issues.

I am using Node.js 4.10 and Express 2.4.3.

When I try to access http://127.0.0.1:8888/auth/facebook, i'll be redirected to http://127.0.0.1:8888/auth/facebook_callback.

I then received the following error:

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)

The following is my code:

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);

May I know what is wrong with my code?

转载于:https://stackoverflow.com/questions/7042340/error-cant-set-headers-after-they-are-sent-to-the-client

csdnceshi58
Didn"t forge Google sent me to this question, but newer versions of ExpressJS have res.headersSent boolean which can be used to check if safe to set/send headers
3 年多之前 回复
csdnceshi70
笑故挽风 simple answer from visionmedia: github.com/visionmedia/express/issues/634
接近 9 年之前 回复

20个回答

I ran into this error as well for a while. I think (hope) I've wrapped my head around it, wanted to write it here for reference.

When you add middleware to connect or express (which is built on connect) using the app.use method, you're appending items to Server.prototype.stack in connect (At least with the current npm install connect, which looks quite different from the one github as of this post). When the server gets a request, it iterates over the stack, calling the (request, response, next) method.

The problem is, if in one of the middleware items writes to the response body or headers (it looks like it's either/or for some reason), but doesn't call response.end() and you call next() then as the core Server.prototype.handle method completes, it's going to notice that:

  1. there are no more items in the stack, and/or
  2. that response.headerSent is true.

So, it throws an error. But the error it throws is just this basic response (from the connect http.js source code:

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

Right there, it's calling res.setHeader('Content-Type', 'text/plain');, which you are likely to have set in your render method, without calling response.end(), something like:

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

The way everything needs to be structured is like this:

Good Middleware

// 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);

Problematic Middleware

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

The problematic middleware sets the response header without calling response.end() and calls next(), which confuses connect's server.

csdnceshi70
笑故挽风 You know I have this exact problem due to what you call a problematic middleware, however I need a case where I return response but would like to do further processing in a separate controller as part of the chain, how do I go about suppressing this error?
接近 6 年之前 回复
csdnceshi74
7*4 +1 This is a great explanation, but what about the case when you use res.redirect()? I frequently run into this problem when the middleware is trying to redirect based on some condition. Should middleware not redirect, per your "Good Middleware" example?
接近 8 年之前 回复

I boiled my head over this issue and it has happened due to a careless mistake on handling the callbacks. non returned callbacks cause the response to be set twice.!

My program had a code which validate request and query the DB. after validating if error is there, I was calling back the index.js with the validation errors . And if validation passes it goes ahead and hit the db with success/failure.

    var error = validateRequestDetails("create",queryReq);
    if (error)
        callback(error, null);
   else
    some code 
    callback(null, success);

What was happening is : Incase validation fails the callback get called and response get set. But not returned. So it still continues the method goes to db and hit success/failure . It calls the same callback again causing the response to be set twice now.

So solution is simple, you need to 'return' the callback so that the method don't continue executing, once the error has occurred and hence set the response object once

  var error = validateRequestDetails("create",queryReq);
    if (error)
        callback(error, null);
        return;
    else
       some code 
       callback(null, success);
csdnceshi79
python小菜 Thanks! This turned out to be my problem too. Just did a ctrl+f and found a callback(...) without a return; after it which was eventually causing res.send(...) to be called twice.
4 年多之前 回复

In my case it was a 304 response (caching) that was causing the issue.

Easiest solution:

app.disable('etag');

Alternate solution here if you want more control:

http://vlasenko.org/2011/10/12/expressconnect-static-set-last-modified-to-now-to-avoid-304-not-modified/

weixin_41568110
七度&光 ETags allow the server to not send content that hasn't changed. Turning it off disables this feature. The ETag wikipedia entry (en.wikipedia.org/wiki/HTTP_ETag) has a lengthier explanation.
4 年多之前 回复
csdnceshi56
lrony* Can anyone explain what the implications are for removing the etag header?
4 年多之前 回复
csdnceshi72
谁还没个明天 In my case also 304 response. I a m using Fibers for processing. Any way your answer helps a lot. thank you
6 年多之前 回复

I had this same issue and realised it was because I was calling res.redirect without a return statement, so the next function was also being called immediately afterwards:

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

Which should have been:

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

Add this middlware and it will work

app.use(function(req,res,next){
 var _send = res.send;
var sent = false;
res.send = function(data){
    if(sent) return;
    _send.bind(res)(data);
    sent = true;
};
next();
});

In Typescript, my issue was I didn't close the websocket connection after receiving a message.

WebSocket.on("message", (data) => {
    receivedMessage = true;
    doSomething(data);
    localSocket.close(); //This close the connection, allowing 
});

If you din't get help from above : for noobs The reason behind this error is sending request multiple times let us understand from some cases:- 1. `

module.exports = (req,res,next)=>{
        try{
           const decoded  = jwt.verify(req.body.token,"secret");
           req.userData = decoded;
           next();
        }catch(error){
            return res.status(401).json({message:'Auth failed'});
        }
        next();   
        }

` in the above calling next() twice will raise an error

  1. router.delete('/:orderId', (req, res, next) => { Order.remove({_id:req.params.orderId},(err,data)=>{ if(err){ **res.status(500).json(err);** }else{ res.status(200).json(data); } *res.status(200).json(data);* }) })

here respond is send twice check whether you already sent a response

I had this issue when I was nesting promises. A promise inside of a promise would return 200 to the server, but then the outer promise's catch statement would return a 500. Once I fixed this, the problem went away.

In my case it happens due to multiple callbacks. I have called next() method multiple time during the code

All I had to do in case of this error was res.end().

 auth.annonymousOnly = function(req, res, next) {
 // add other task here   
   res.end();    
  };
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