XRIDescriptor/Expires... maybe a TTL instead?

["Wachob, Gabe" <gwachob@visa.com>]

Mike and I have been discussing the implementation of XRI directories and one issue with the current XRI Descriptor format is the Expires header. If your policy, as a directory, is to put in Expires headers to enable caching for a period of time, then you'll be updating the Expires header on a regular basis (perhaps even every request???).

If you happen to be signing the XRIDescriptor, however, you could get into a new world of hurt. If the Expires header changes every request, then you need to re-sign the response XRIDescriptor every time. It would be really nice to be able to keep a signed copy of the XRIDescriptor for a particular authority resolution and reuse it (at least for a while) to siginficantly reduce the digsig processing. Using a TTL instead of the Expires header (which would cause some extra work on the client side in computing the expiry time) would allow (at least as far as Expires is concerned) caching of signed responses on the server side. 

Now, given the fact that we will have lookahead and proxy resolution, and the fact that the Resolved header could change on a regular basis, I'm not sure this change would have a large impact. But it might. 

Thoughts? (Especially from Dave McAlpin who is writing the trusted resolution spec).

	-Gabe

 
__________________________________________________ 
gwachob@visa.com
Chief Systems Architect
Technology Strategies and Standards
Visa International 
Phone: +1.650.432.3696   Fax: +1.650.554.6817