CODEWITHSUNDEEP
google-chromehttpcachinggoogle-chrome-devtools
Matt
Matt

Reputation: 141

Why does chrome not request more recent version of cached file?

I have a caching issue. Chrome does not always load newer versions of site assets, most often Javascript files loaded by Require.js. Right now I've been having this problem for over 24 hours with a particular file.

If I load the page with devtools (network tab) open, the offending files typically show a HTTP 200 response, but in the "Size" column it shows "(from cache)". In the Headers details it shows "Provisional headers are shown". Wireshark shows that the file is indeed not requested from the server.

Chrome shows the Last-Modified date of the file as Sat, 06 Dec 2014 01:27:55 GMT, but my below raw request to the server clearly indicates the file has changed much more recently.

If I do a raw request myself I don't see anything in the headers returned by the server that should cause this problem:

GET /js/path/to/file.js HTTP/1.1
Host: static.mydomain.com
User-Agent: Matt

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Vary: Accept-Encoding
Content-Type: application/javascript
Accept-Ranges: bytes
ETag: "4203477418"
Last-Modified: Fri, 16 Jan 2015 18:28:30 GMT
Content-Length: 5704
Date: Fri, 16 Jan 2015 21:05:06 GMT
Server: lighttpd/1.4.33

.... data here ...

The issue has been reported by chrome users on multiple OSes with different versions of chrome, but I do not typically receive reports of caching issues on other browsers. (Right now I'm on "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36")

Edit: The problem seems to be most offensive with files loaded by Require.js, though I have encountered it with javascript directly referenced in the page as well.

What am I missing here? Why won't chrome check for a new version of the file?

Upvotes: 6

Views: 2383

Answers (1)

Matt
Matt

Reputation: 141

As it turns out, browsers have poorly documented behavior regarding caching when the Cache-Control header is not specified in the server response (well, at least when no caching behavior is specified). In general, it seems that in this case a browser determines how long to cache the item for based on the file's last modified date (if declared in the response), the current date, and ????

See: https://webmasters.stackexchange.com/questions/53942/why-is-this-response-being-cached

Sadly, Google's official page on HTTP caching does not mention what happens if the header is not set: https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching

Edit: I ran across some more specific information about the heuristics used, here: What heuristics do browsers use to cache resources not explicitly set to be cachable?

Upvotes: 5

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