[OSM-dev] Caching tiles and expiry header

[Mathieu Arnold]

+--On 5 juillet 2010 17:27:03 +0200 Moataz Elmasry
<zaza1851983ml at googlemail.com> wrote:
| Hello List
| 
| I use http://tile.openstreetmap.org/${z}/${x}/${y}.png to display the map
| in my web application
| I use a filter mechanism in the servlet, where an expiry header and
| maximum age headers are added to the image requests, so that they will be
| cached for a while on the client browser. These are just for common
| images that the application use like tooltip.png and button.png and
| such...These are called from the cache just fine
| 
| Now to do the same for osm tiles I added a proxy through which the tiles
| are requested and then expiry headers are added to these tiles, Say
| http://myapplciation.com/proxy?url=http://tile.openstreetmap.org/${z}/${x
| }/${y}.png. This is the layer address in OpenLayers.Layer.OSM
| 
| An expiry header is added correctly to osm tiles. The problem is that the
| imagename in the request is different than in the response, so if I'm
| requesting |http://tile.openstreetmap.org/16/34687/21558.png I get an
| image called 2736BB16d01.png in my cache. So that by the next call this
| image won't be fetched from the cache and instead called again from the
| server and so on.
| 
| Is there a way to force the browser to load the images from its cache if
| available?

Well, you should not create a new expire header, but you should forward the
expires and etag from the original request, and try to use that etag header
:

$ curl -I http://tile.openstreetmap.org/16/34687/21558.png
HTTP/1.0 200 OK
Date: Mon, 05 Jul 2010 15:27:25 GMT
Server: Apache/2.2.8 (Ubuntu)
ETag: "ae22fe7a91ce525e988b2da52f63a4a4"
Content-Length: 16897
Cache-Control: max-age=18482
Expires: Mon, 05 Jul 2010 20:35:27 GMT
Content-Type: image/png
Age: 1360
X-Cache: HIT from konqi.openstreetmap.org
X-Cache-Lookup: HIT from konqi.openstreetmap.org:3128
Via: 1.1 konqi.openstreetmap.org:3128 (squid/2.7.STABLE7)
Connection: close

$ curl -H 'If-None-Match: "ae22fe7a91ce525e988b2da52f63a4a4"' -I
http://tile.openstreetmap.org/16/34687/21558.png
HTTP/1.0 304 Not Modified
Date: Mon, 05 Jul 2010 15:27:25 GMT
Content-Type: image/png
Expires: Mon, 05 Jul 2010 20:35:27 GMT
ETag: "ae22fe7a91ce525e988b2da52f63a4a4"
Age: 1392
X-Cache: HIT from konqi.openstreetmap.org
X-Cache-Lookup: HIT from konqi.openstreetmap.org:3128
Via: 1.0 konqi.openstreetmap.org:3128 (squid/2.7.STABLE7)
Connection: close


It should be more effective than what you're trying to achieve. (I think.)


-- 
Mathieu Arnold