Google App Engine not generating 304, instead generating 200 always

2
votes

Google App engine always generates 200 for the url /test.js and test.js is not a static resource, but a url pattern for dynamically generated content. The content will expire after N hours and a fresh content will be generated.

I've tried with Last-Modified, ETag and Cache-Control. None seems to work.

Request

Request URL:http://localhost:8081/test.js
Request Method:GET
Status Code: 200 OK
Accept:*/*
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Cache-Control:max-age=0
Connection:keep-alive
Host:localhost:8081
If-Modified-Since:Fri, 18 Oct 2013 14:10:39 GMT
If-None-Match:"1B2M2Y8AsgTpgAmY7PhCfg"
Referer:http://localhost:8080/
User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.101 Safari/537.36

Response Headers


cache-control:public, max-age=360000
Content-Length:2
content-type:application/script; charset=utf-8
Date:Fri, 18 Oct 2013 14:10:40 GMT
etag:"1B2M2Y8AsgTpgAmY7PhCfg"
expires:Tue, 22 Oct 2013 18:10:40 GMT
last-modified:Fri, 18 Oct 2013 14:10:40 GMT
Server:Development/2.0
2
google-app-enginecaching
What is it that you're trying to do? You've left so many details out that it's unlikely someone is going to guess right. – Dave W. Smith

2 Answers

0
votes

Your request has Cache-Control:max-age=0, so any intermediate caches (incl. the browser-cache) won't serve cached content. This is likely a result of a setting in your browser.

For requests with revalidate headers (If-X), you need to have the logic in place to act properly. To save bandwidth, this is pretty simple with webob (which is used by webapp2 and other frameworks) and the conditional-response setting. Avoiding computation as well depends a little more on what you're doing, but webob helps here too.

Redbot is a really useful tool for checking HTTP cache behaviour.

0
votes

Refer to this for HTTP status: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

200 is just the correct HTTP OK status, that doesn't have any interpretation on whether the resource is static or not. (Try any dynamic web page out there like e.g. facebook) and you will notice it's 200. Having a response of 200 is perfectly normal

for 304 it's "Not Modified" - As mentioned in w3 "The 304 response MUST NOT contain a message-body". This is not what you want.

In your case your concern should be to set the correct expiry time for these http header (do it within your program code), so that the browser always request for a fresh copy of content after the expiry time (e.g. after 1 hour):

cache-control:public, max-age=3600
expires:Tue, 20 Oct 2013 18:10:40 GMT