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require 'rack/utils'
module Rack
# Middleware that enables conditional GET using If-None-Match and
# If-Modified-Since. The application should set either or both of the
# Last-Modified or Etag response headers according to RFC 2616. When
# either of the conditions is met, the response body is set to be zero
# length and the response status is set to 304 Not Modified.
#
# Applications that defer response body generation until the body's each
# message is received will avoid response body generation completely when
# a conditional GET matches.
#
# Adapted from Michael Klishin's Merb implementation:
# https://github.com/wycats/merb/blob/master/merb-core/lib/merb-core/rack/middleware/conditional_get.rb
class ConditionalGet
def initialize(app)
@app = app
end
def call(env)
case env[REQUEST_METHOD]
when "GET", "HEAD"
status, headers, body = @app.call(env)
headers = Utils::HeaderHash.new(headers)
if status == 200 && fresh?(env, headers)
status = 304
headers.delete(CONTENT_TYPE)
headers.delete(CONTENT_LENGTH)
original_body = body
body = Rack::BodyProxy.new([]) do
original_body.close if original_body.respond_to?(:close)
end
end
[status, headers, body]
else
@app.call(env)
end
end
private
def fresh?(env, headers)
modified_since = env['HTTP_IF_MODIFIED_SINCE']
none_match = env['HTTP_IF_NONE_MATCH']
return false unless modified_since || none_match
success = true
success &&= modified_since?(to_rfc2822(modified_since), headers) if modified_since
success &&= etag_matches?(none_match, headers) if none_match
success
end
def etag_matches?(none_match, headers)
etag = headers['ETag'] and etag == none_match
end
def modified_since?(modified_since, headers)
last_modified = to_rfc2822(headers['Last-Modified']) and
modified_since and
modified_since >= last_modified
end
def to_rfc2822(since)
# shortest possible valid date is the obsolete: 1 Nov 97 09:55 A
# anything shorter is invalid, this avoids exceptions for common cases
# most common being the empty string
if since && since.length >= 16
# NOTE: there is no trivial way to write this in a non execption way
# _rfc2822 returns a hash but is not that usable
Time.rfc2822(since) rescue nil
else
nil
end
end
end
end
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