Here is all the code that deals with stale? in one place, so that you can see how it works.
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# Sets the etag and/or last_modified on the response and checks it against
# the client request. If the request doesn't match the options provided, the
# request is considered stale and should be generated from scratch. Otherwise,
# it's fresh and we don't need to generate anything and a reply of "304 Not Modified" is sent.
#
# Example:
#
# def show
# @article = Article.find(params[:id])
#
# if stale?(:etag => @article, :last_modified => @article.created_at.utc)
# @statistics = @article.really_expensive_call
# respond_to do |format|
# # all the supported formats
# end
# end
# end
def stale?(options)
fresh_when(options)
!request.fresh?(response)
end
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# Sets the etag, last_modified, or both on the response and renders a
# "304 Not Modified" response if the request is already fresh.
#
# Example:
#
# def show
# @article = Article.find(params[:id])
# fresh_when(:etag => @article, :last_modified => @article.created_at.utc)
# end
#
# This will render the show template if the request isn't sending a matching etag or
# If-Modified-Since header and just a "304 Not Modified" response if there's a match.
def fresh_when(options)
options.assert_valid_keys(:etag, :last_modified)
response.etag = options[:etag] if options[:etag]
response.last_modified = options[:last_modified] if options[:last_modified]
if request.fresh?(response)
head :not_modified
end
end
---
--- RUBY
# Check response freshness (Last-Modified and ETag) against request
# If-Modified-Since and If-None-Match conditions. If both headers are
# supplied, both must match, or the request is not considered fresh.
def fresh?(response)
case
when if_modified_since && if_none_match
not_modified?(response.last_modified) && etag_matches?(response.etag)
when if_modified_since
not_modified?(response.last_modified)
when if_none_match
etag_matches?(response.etag)
else
false
end
end
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def if_modified_since
if since = env['HTTP_IF_MODIFIED_SINCE']
Time.rfc2822(since) rescue nil
end
end
memoize :if_modified_since
def if_none_match
env['HTTP_IF_NONE_MATCH']
end
def not_modified?(modified_at)
if_modified_since && modified_at && if_modified_since >= modified_at
end
def etag_matches?(etag)
if_none_match && if_none_match == etag
end
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def last_modified
if last = headers['Last-Modified']
Time.httpdate(last)
end
end
def last_modified?
headers.include?('Last-Modified')
end
def last_modified=(utc_time)
headers['Last-Modified'] = utc_time.httpdate
end
def etag
headers['ETag']
end
def etag?
headers.include?('ETag')
end
def etag=(etag)
if etag.blank?
headers.delete('ETag')
else
headers['ETag'] = %("#{Digest::MD5.hexdigest(ActiveSupport::Cache.expand_cache_key(etag))}")
end
end
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def self.expand_cache_key(key, namespace = nil)
expanded_cache_key = namespace ? "#{namespace}/" : ""
if ENV["RAILS_CACHE_ID"] || ENV["RAILS_APP_VERSION"]
expanded_cache_key << "#{ENV["RAILS_CACHE_ID"] || ENV["RAILS_APP_VERSION"]}/"
end
expanded_cache_key << case
when key.respond_to?(:cache_key)
key.cache_key
when key.is_a?(Array)
key.collect { |element| expand_cache_key(element) }.to_param
when key
key.to_param
end.to_s
expanded_cache_key
end
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