From: Lionel Bouton <lionel-subscription@...>
Date: 2007-08-03T04:45:35+09:00
Subject: Re: net::http and caching files

Shea Martin wrote the following on 02.08.2007 20:35 :
> I have just tried about 20 servers (random urls), and have not seen 
> and etag or last_modified on any of them.  Is there really that few of 
> servers which support the two?
>
> Am I doing something wrong?
>
> I am on win32 if it matters.
>
> CODE:
> require 'open-uri'
>
> # h = {}
> # h['If-Modified-Since'] = 'Thu, 09 Aug 2007 17:33:40 GMT'
> http = Net::HTTP.new( "www.google.com" )
> resp, data = http.get( "/index.html" )
> p "r is #{resp}"
> p "code is #{resp.code}"
> resp.each { |k,v| p "#{k} = #{v}" }
>
> #open( "http://google.ca" ) do |f|
> #    p f.last_modified
> #end
>
> exit 0

Of course google won't send you last_modified or etag headers they don't 
have documents to tag with an etag or to mark as generated at a given 
time. If they want to optimize the bandwidth they are far more likeliy 
to use cache-control headers, which they do for their main page with:
"Cache-Control: private"

Look at RSS or Atom feeds, between 1/3 to 1/2 of them have 
"last-modified" headers, they are "modified" when a new article or 
comment is posted...

Lionel.