Can't set headers after they are sent.

[jwerre]

Pardon me if this has been asked a million time but It's not clear how to best handle timeouts. The following script will crash the server since res.send is called after the timeout. I could wrap res.send in an if !res.headersSent but it seems a little excessive to do that for every route. I'm not sure how to best handle this situation.

var express = require('express');
var timeout = require('connect-timeout');

var handleTimeout = function (req, res, next) {
    if (!req.timedout) next();
};

var app = express()
    .use(timeout(500))
    .use(handleTimeout)
    .get("/", function (req, res, next) {
        setTimeout(function () {
            // This causes "Error: Can't set headers after they are sent."
            res.send({peaches:"yummy", turnips:"yucky"}); 
        }, 1000);
    })
    .use(handleTimeout)
    .listen(8888, function(){
            console.log('Server started on port 8888');
        });

Error:

Starting child process with 'node timeout.js'
Server started on port 8888
ServiceUnavailableError: Response timeout
    at IncomingMessage.<anonymous> (/Users/jw/Desktop/timeout/node_modules/connect-timeout/index.js:69:8)
    at IncomingMessage.emit (events.js:95:17)
    at null._onTimeout (/Users/jw/Desktop/timeout/node_modules/connect-timeout/index.js:41:11)
    at Timer.listOnTimeout [as ontimeout] (timers.js:112:15)

http.js:689
    throw new Error('Can\'t set headers after they are sent.');
          ^
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (http.js:689:11)
    at ServerResponse.header (/Users/jw/Desktop/timeout/node_modules/express/lib/response.js:718:10)
    at ServerResponse.send (/Users/jw/Desktop/timeout/node_modules/express/lib/response.js:163:12)
    at ServerResponse.json (/Users/jw/Desktop/timeout/node_modules/express/lib/response.js:249:15)
    at ServerResponse.send (/Users/jw/Desktop/timeout/node_modules/express/lib/response.js:151:21)
    at null._onTimeout (timeout/timeout.js:13:17)
    at Timer.listOnTimeout [as ontimeout] (timers.js:112:15)
Program node timeout.js exited with code 8

[dougwilson]

I could wrap res.send in an if !res.headersSent but it seems a little excessive to do that for every route. I'm not sure how to best handle this situation.

There are two solutions:

1. You can do as you suggest: check if the request timed out once your timer fired.
2. When you set your timeout, also add a listener on the timeout event and then clear the timeout so your timer never even fires:

    .get("/", function (req, res, next) {
        var timer = setTimeout(function () {
            res.send({peaches:"yummy", turnips:"yucky"}); 
        }, 1000);
        req.once('timeout', function () {
          clearTimeout(timer);
        });
    })