For some reason, it might be spending most of my time sitting at the end of a long thin piece of string connecting me to the rest of the universe, but it might also have been watching people pound on my RSS feeds every five minutes, I've been trying to write cache-friendly Nevow resources. This involves setting two HTTP headers, "Last-Modifed" and "ETag". At the moment I'm setting both of these headers using my data source (files in the file system). However, this has left me with a bit of a quandry about my docFactory templates. When my templates change, so should my Last-Modified and ETag headers. Otherwise clients using caches will see my old templates more or less indefinitely, at least on pages I don't subsequently change, because their conditional GET requests complete with correct If-Modified-Since and If-None-Match headers will tell the server never to send a fresh copy of the data. So, I'm faced with the problem of dating my templates or otherwise detecting when they change and I can't think of a good way. Some thoughts: 1. use file timestamps on the template files Pros: Fits OK with the way I deal with the rest of the website data Cons: Reduces flexibility. I can't think of a good way to do this with Stan templates. I also can't think of a good way to do this without restarting the server when my templates change. (I do currently do this, but would prefer not to.) 2. generate the ETag header based on a hash of page contents Pros: As best I can tell, this is how the ETag header is really meant to be generated, ideally it signals octect equality and should change if, for example, Nevow for some reason starts pretty-printing output. Cons: rend.Page.renderHTTP seems to make this really hard -- even if you set the bufferedflag = True, rend.Page.afterRender doesn't seem to have any way to access the result of the render. (Correct me if I'm wrong.) Also, this doesn't help with the Last-Modified date, which means I'm not helping HTTP/1.0 caches very much, unless I store the date the hash changed somewhere. 3. store the templates in some kind of object store and date-stamp them there. Pros: This might well let me change templates without restarting the server. Cons: It imposes a maintainence burden whereby I have to update the objet database with new templates. I like to have a copy of my website and templates on two different servers, and as best I can tell, no object database is going to like being copied to a remote server without me killing all associated processes on the remote server first, so there's a deployment problem. 4. hash the template so that a changed template means a changed hash Pros: This is probably nearly as good as hashing the page content, accuracy-wise. Cons: I don't have any idea how to hash a DocFactory object effectively. Hashing the DocFactory still leaves me vulnerable to changes in Nevow's rendering. Hashing the DocFactory won't tell me to update Last-Modified unless I store the date that the DocFactory changed somewhere. Anyone got any thoughts or has anyone solved this problem before? Help with implementing 2 (how do I get the page contents in order to hash them) or 4 (how can I hash a DocFactory object) also appreciated. -Mary