cocoon-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Grzegorz Kossakowski <g...@tuffmail.com>
Subject Improving ServletConnection to make it cache-aware
Date Sat, 10 Feb 2007 17:23:36 GMT
Hello,

I would like to discuss making ServletConnection cache-aware. Daniel 
suggested earlier to utilize standard HTTP protocol concepts. I totally 
agree with his opinion and would like to propose solution, but first 
let's discuss requirements.

Requirements
============

Requirements that ServletConnection must meet are really simple:
1. ServletConnection should provide data that can be used for 
constructing small validation object.
2. ServletConnection should expose functionality for checking if 
previous response is still valid taking as input validation object only.
3. We would like ServletConnection to make as few as possible round 
trips in every situation it encounters.

To satisfy these requirements I propose to use concept of HTTP 
conditional gets[1], more precisely If-Modified-Since request-header[2] 
field. This way we have following cases:
* ServletConnection does not have information needed to create 
If-Modified-Since header, but response includes Last-Modified header and 
full content. Validity object can be created.
* ServletConnection does not have information needed to create 
If-Modified-Since header and response does not include Last-Modified 
header but includes full content. Validity object cannot be created.
* ServletConnection does have information needed to create 
If-Modified-Since. Resource has not been modified so 302 status code is 
returned as response and response does not include full content. Thus 
ServletConnection can just tell that content is still valid and can be 
fetched from cache.
* ServletConnection does have information needed to create 
If-Modified-Since. Resource has been modified so  200 status code is 
returned as response and response includes full content. 
ServletConnection tells that cached content is invalid and returns fresh 
content.

Requirements are satisfied:
1. Last-Modified header can be used to construct validation object.
2. Taking date from validation object enables ServletConnection to 
formulate conditional GET and then response HTTP code settles if 
resource is still valid.
3. In every case we have only one round trip.


Implementation proposal
=======================

We should start from making pipelines more HTTP-compliant. This demands 
taking If-Modified-Since headers into account and returning appropriate 
status code when caching pipeline is processed. Behavior of non-caching 
pipelines should not change.

Then we should implement setIfModifiedSince and getIfModifiedSince from 
java.net.URLConnection and construct requests according to value of that 
property. Also getResponseCode method should be implemented.

All changes proposed above will enable us to implement source validation 
of ServletSource very easily.

Comments? Thoughts?



I can start implementing this as soon as we came with agreement on this. 
However, I would like to point out that I'll need some support to make 
changes in pipeline stuff. I've taken a look on code and not everything 
seems to be clear. Any volunteer on the board? ;-)

Last remark. I know that my English is quite poor and it could be that I 
do not express my thoughts clearly enough. I'm really working on it and 
you should not hesitate to ask when something is hard to understand.


[1] http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.3
[2] http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.25


-- 
Grzegorz Kossakowski

Mime
View raw message