http protocol for caching, not http caching

Larry Masinter writes:

>On the other hand, the HTTP caching group need not actually design or
>promote a particular kind of caching and proxying, or to find ways of
>performing caching or proxying that is more effective than what we
>have currently deployed.
>
>Give us the language, don't write the novels.

I agree 100% with the sentiment and I think we should use it as a design 
parameter for the specification.

We mustn't forget, however, that pretty much any caching scheme will 
require some common primitives that should be incorporated to the 
protocol. The definition of those primitives do not constitute
endorsement of the particular caching schemes that are likely to use
them, any more than supporting jpg/gif files is an endorsement of either
format.

I think pretty much any caching scheme should be able to make do with 
the following set of primitives:

1.- expire headers in a file (e.g. <!-- expires-by "time increment" "date"> 
    whichever occurs first)

    Where time increment = dd:hh:mm:ss
          date = dd/Mmm/yy:hh:mm:ss

2.- forced expires (ie. the server telling a proxy to expire a file.) 
    
3.- cache inform (a proxy telling the server: I intend to cache this document)
    
4.- offer to cache (a proxy saying: I could cache -mirror- this document)

5.- error code document is stale/no longer in cache

6.- verification of staleness (if-modified-since)

7.- forwarding mechanisms (server tells client: document requested also
    lives in XXXX retrieve it from there. This is also very important for 
    mirror sites)
    
8.- SSI remote execution (i.e. a tag within HTML files with the meaning:

    The following bit was generated by an SSI, if you are serving from
    cache (for proxy servers) or requesting this from a proxy (for proxy-
    aware clients) you might want to request the SSI to be executed. 
    Something like:

    <SSI SRC="http://original.server/ssi-bin/ssi-script"> ssi generatad
    stuff </SSI>

Any others? 


Alex



-- 
Alex Lopez-Ortiz                             alopez-o@neumann.UWaterloo.ca
http://daisy.uwaterloo.ca/~alopez-o                     FAX (519)-885-1208
Department of Computer Science                      University of Waterloo
Waterloo, Ontario N2L 3G1                                           Canada

Received on Saturday, 30 December 1995 02:07:25 UTC