[codesprints] Who knows about web browser caching?

[Bill Fenner <[e-mail]>]

Hey everyone,

  Does anyone know how to encourage a web browser (I'm testing with
Firefox) to validate the etag when clicking on a page?

  I've set USE_ETAGS=True in settings.py, which causes django to
create an etag for each page - and this works fine - here is Firefox
prefetching the history tab for a document:

GET /doc/draft-ietf-ipsecme-ikev2-redirect/history/ HTTP/1.1
Host: merlot.tools.ietf.org:31415
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US;
rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Referer: http://merlot.tools.ietf.org:31415/doc/draft-ietf-ipsecme-ikev2-redirect/
X-Moz: prefetch
Cookie: sessionid=6d82210d7761d52315fd2319be54a5e7

HTTP/1.0 200 OK
Server: WSGIServer/0.1 Python/2.6.6
Content-Length: 12210
Content-Encoding: gzip
Vary: Accept-Encoding, Cookie
Etag: "b33787a30797c25bd3c18f8d1d863ba4"
Date: Sun, 07 Nov 2010 06:36:59 GMT
Content-Type: text/html; charset=utf-8

However, I clicked on a direct link to the same URL, and Firefox
requested it again, without using If-None-Match:


GET /doc/draft-ietf-ipsecme-ikev2-redirect/history/ HTTP/1.1
Host: merlot.tools.ietf.org:31415
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US;
rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Referer: http://merlot.tools.ietf.org:31415/doc/draft-ietf-ipsecme-ikev2-redirect/
Cookie: sessionid=6d82210d7761d52315fd2319be54a5e7

HTTP/1.0 200 OK
Server: WSGIServer/0.1 Python/2.6.6
Content-Length: 12210
Content-Encoding: gzip
Vary: Accept-Encoding, Cookie
Etag: "ba02420d1da3a92ad8f80ce148edb72f"
Date: Sun, 07 Nov 2010 06:37:23 GMT
Content-Type: text/html; charset=utf-8


I also tried adding "Cache-control: private" headers, to try to
encourage Firefox to cache it, but that didn't help.  It does work for
the static files:

GET /css/base2.css HTTP/1.1
Host: merlot.tools.ietf.org:31415
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US;
rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12
Accept: text/css,*/*;q=0.1
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Referer: http://merlot.tools.ietf.org:31415/doc/draft-ietf-ipsecme-ikev2-redirect/history/
Cookie: sessionid=6d82210d7761d52315fd2319be54a5e7
If-None-Match: "b73424ca331305280f9937208d73f862"

HTTP/1.0 304 NOT MODIFIED
Date: Sun, 07 Nov 2010 06:37:24 GMT
Server: WSGIServer/0.1 Python/2.6.6
Content-Length: 0
Content-Type: text/html; charset=utf-8


I realize that the fact that the Etag varies here is going to be a
problem (it's because the Etag is calculated after the gzip), but this
is a separate problem.

Anyone have any ideas?

Thanks,
  Bill