Question

TL;DR This appears to be a browser problem that is fixed in newer (58+) versions.

I'm working on a Node.js/express-based web server and I'm running into a problem where my browser (Firefox 57.0.1 on Mac OS) loads a page twice. I've been googling for tons and tons of other answers and blog posts, but haven't found a solution yet.

Obviously, apart from the double network traffic, this is a problem in an application that performs database work under the hood.

Reproducing the problem

Here's a simple script to replicate the issue:

#!/usr/bin/env node

const express = require('express');

const app = express();
app.disable('etag');

app.listen(3000, () => console.log('\n\n\n\n\nListening on port 3000!'));

app.all('/', function (req, res, next) {
    rn=Math.random();
    console.log('\n'+req.method+' '+req.url);
    console.log('rn='+rn);
    res.send('rn='+rn);
    next();
});

For every request to /, the server generates a random number and returns it to the client. That way, I can see (using console.log()) how many requests are being made and which ones are being rendered in the browser.

When I request http://localhost:3000/, I get the following output in my console:

GET /
rn=0.3196834037080407

GET /
rn=0.8270968825090677

Full HTTP headers

Using Firefox' developer tools, I can see that two identical requests are being made. First request:

Accept: text/html,application/xhtml+xm…plication/xml;q=0.9,*/*;q=0.8
Accept-Encoding: gzip, deflate
Accept-Language: en-US,sv-SE;q=0.5
Cache-Control: max-age=0
Connection: keep-alive
DNT: 1
Host: localhost:3000
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Macintosh; Intel …) Gecko/20100101 Firefox/57.0

First response:

Connection: keep-alive
Content-Length: 21
Content-Type: text/html; charset=utf-8
Date: Mon, 18 Dec 2017 05:44:51 GMT
X-Powered-By: Express

Second request:

Accept: text/html,application/xhtml+xm…plication/xml;q=0.9,*/*;q=0.8
Accept-Encoding: gzip, deflate
Accept-Language: en-US,sv-SE;q=0.5
Cache-Control: no-cache
Connection: keep-alive
DNT: 1
Host: localhost:3000
Pragma: no-cache
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Macintosh; Intel …) Gecko/20100101 Firefox/57.0

The only difference between the first and the second requests are the Cache-Control and Pragma headers.

Second response:

Connection: keep-alive
Content-Length: 21
Content-Type: text/html; charset=utf-8
Date: Mon, 18 Dec 2017 05:44:51 GMT
X-Powered-By: Express

I can actually see Firefox render the first number and then immediately replace it with the second, as if it actually clicks the "Reload" button.

In the developer tools, on the "Stack trace" tab seems to confirm this. Here's the first request:

loadURI/<            chrome://global/content/browser-child.js:354:14
_wrapURIChangeCall   chrome://global/content/browser-child.js:308:7
loadURI              chrome://global/content/browser-child.js:353:5
receiveMessage       chrome://global/content/browser-child.js:288:9

.. and the second request:

reload               chrome://global/content/browser-child.js:366:5
receiveMessage       chrome://global/content/browser-child.js:297:9

Other things I've checked

I've disabled Adblock Plus for localhost. There are no other add-ons installed in the browser.
No other browser I've tried exhibits the same behaviour: Safari on MacOS, Chrome 63 on Windows, Edge, Internet Explorer 11.
There's no cross-origin stuff going on here, it's a simple one-page request.
No javascript involed.
No images, scripts or iframes with empty hrefs.
Both responses are HTTP/200, both requests are GET (i.e. no HEAD thing happening).

Any pointers would be greatly appreciated.

Firefox 57 loads http request twice

0 个答案: