I am trying to speed up some ajax calls by facilitating ETags. What I've got at the moment works sometimes (ajax calls that are 304 not modified take 40ms instead of 100ms).
However, what I am noticing is, that chrome apparently only sends the If-None-Match header just for one request but doees never send it on Windows machines. This is quite a pity, as the resource this is about I am loading quite frequently to check for changes. Having ETags work all the time would be really helpful in that case.
Here's what is happening on the wire:
GET /api/book/all/READ HTTP/1.1
Host: something
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.110 Safari/537.36
Accept: */*
Referer: http://something/
Accept-Encoding: gzip, deflate, sdch
Accept-Language: de,en-US;q=0.8,en;q=0.6
Cookie: PHPSESSID=something
and the response:
HTTP/1.1 200 OK
Date: Mon, 04 Apr 2016 06:00:17 GMT
Server: Apache
Expires: Thu, 19 Nov 1981 08:52:00 GMT
ETag: "1"
Cache-Control: "max-age=0, must-revalidate"
Vary: Accept-Encoding
Content-Encoding: gzip
Keep-Alive: timeout=2, max=995
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: application/json;charset=utf8
(as a side note, the ETag value I use refers to the version of the data - each time the data is modified, the version is incremented)
In the next request, on Mac, Chrome will send the appropriate If-None-Match header, and the API will respond with a 304 not modified. However, the second time that resource is being loaded, there will not be any If-None-Match header again.
On Windows, Chrome will just not send the If-None-Match header and therefore the server will respond with the full payload.
The way I would like to have it, is that the browser would always send the If-None-Match header, so that the backend can do a proper job to decide if the cached API response is still fresh.
on mac, this is how the second request (where the If-None-Match header is sent) looks:
GET /api/book/all/READ HTTP/1.1
Host: something
Connection: keep-alive
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.110 Safari/537.36
Accept: */*
Referer: http://something/
Accept-Encoding: gzip, deflate, sdch
Accept-Language: de,en-US;q=0.8,en;q=0.6
Cookie: PHPSESSID=something
If-None-Match: "1"
and the response:
HTTP/1.1 304 Not Modified
Date: Mon, 04 Apr 2016 05:27:19 GMT
Server: Apache
Connection: Keep-Alive
Keep-Alive: timeout=2, max=1000
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Vary: Accept-Encoding
