NodeJS/express: Cache and 304 status code

问题:

When I reload a website made with express, I get a blank page with Safari (not with Chrome) because the NodeJS server sends me a 304 status code.

How to solve this?

Of course, this could also be just a problem of Safari, but actually it works on all other websites fine, so it has to be a problem on my NodeJS server, too.

To generate the pages, I'm using Jade with res.render.

Update: It seems like this problem occurs because Safari sends 'cache-control': 'max-age=0' on reload.

Update 2: I now have a workaround, but is there a better solution? Workaround:

app.get('/:language(' + content.languageSelector + ')/:page', function (req, res)
{
    // Disable caching for content files
    res.header("Cache-Control", "no-cache, no-store, must-revalidate");
    res.header("Pragma", "no-cache");
    res.header("Expires", 0);

    // rendering stuff here…
}

Update 3: So the complete code part is currently:

app.get('/:language(' + content.languageSelector + ')/:page', pageHandle);

function pageHandle (req, res)
{
    var language = req.params.language;
    var thisPage = content.getPage(req.params.page, language);

    if (thisPage)
    {
        // Disable caching for content files
        res.header("Cache-Control", "no-cache, no-store, must-revalidate");
        res.header("Pragma", "no-cache");
        res.header("Expires", 0);

        res.render(thisPage.file + '_' + language, {
            thisPage : thisPage,
            language: language,
            languages: content.languages,
            navigation: content.navigation,
            footerNavigation: content.footerNavigation,
            currentYear: new Date().getFullYear()
        });
    }
    else
    {
        error404Handling(req, res);
    }
}

回答1:

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/

回答2:

As you said, Safari sends Cache-Control: max-age=0 on reload. Express (or more specifically, Express's dependency, node-fresh) considers the cache stale when Cache-Control: no-cache headers are received, but it doesn't do the same for Cache-Control: max-age=0. From what I can tell, it probably should. But I'm not an expert on caching.

The fix is to change (what is currently) line 37 of node-fresh/index.js from

if (cc && cc.indexOf('no-cache') !== -1) return false;  

to

if (cc && (cc.indexOf('no-cache') !== -1 ||
  cc.indexOf('max-age=0') !== -1)) return false;

I forked node-fresh and express to include this fix in my project's package.json via npm, you could do the same. Here are my forks, for example:

https://github.com/stratusdata/node-fresh https://github.com/stratusdata/express#safari-reload-fix

The safari-reload-fix branch is based on the 3.4.7 tag.

回答3:

I had the same problem in Safari and Chrome (the only ones I've tested) but I just did something that seems to work, at least I haven't been able to reproduce the problem since I added the solution. What I did was add a metatag to the header with a generated timstamp. Doesn't seem right but it's simple :)

<meta name="304workaround" content="2013-10-24 21:17:23">

Update P.S As far as I can tell, the problem disappears when I remove my node proxy (by proxy i mean both express.vhost and http-proxy module), which is weird...

回答4:

Try using private browsing in Safari or deleting your entire cache/cookies.

I've had some similar issues using chrome when the browser thought it had the website in its cache but actually had not.

The part of the http request that makes the server respond a 304 is the etag. Seems like Safari is sending the right etag without having the corresponding cache.

回答5:

Old question, I know. Disabling the cache facility is not needed and not the best way to manage the problem. By disabling the cache facility the server needs to work harder and generates more traffic. Also the browser and device needs to work harder, especially on mobile devices this could be a problem.

The empty page can be easily solved by using Shift key+reload button at the browser.

The empty page can be a result of:

• a bug in your code
• while testing you served an empty page (you can't remember) that is cached by the browser
• a bug in Safari (if so, please report it to Apple and don't try to fix it yourself)

Try first the Shift keyboard key + reload button and see if the problem still exists and review your code.

回答6:

This... This is the easiest way...

function force200Responses(req, res, next) { req.headers['if-none-match'] = 'no-match-for-this'; next(); }

app.use(force200Responses)

Future me, you are welcome.