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| | require 'digest/md5'
module Rack
# Automatically sets the ETag header on all String bodies.
#
# The ETag header is skipped if ETag or Last-Modified headers are sent or if
# a sendfile body (body.responds_to :to_path) is given (since such cases
# should be handled by apache/nginx).
#
# On initialization, you can pass two parameters: a Cache-Control directive
# used when Etag is absent and a directive when it is present. The first
# defaults to nil, while the second defaults to "max-age=0, private, must-revalidate"
class ETag
ETAG_STRING = 'ETag'.freeze
DEFAULT_CACHE_CONTROL = "max-age=0, private, must-revalidate".freeze
def initialize(app, no_cache_control = nil, cache_control = DEFAULT_CACHE_CONTROL)
@app = app
@cache_control = cache_control
@no_cache_control = no_cache_control
end
def call(env)
status, headers, body = @app.call(env)
if etag_status?(status) && etag_body?(body) && !skip_caching?(headers)
original_body = body
digest, new_body = digest_body(body)
body = Rack::BodyProxy.new(new_body) do
original_body.close if original_body.respond_to?(:close)
end
headers[ETAG_STRING] = %(W/"#{digest}") if digest
end
unless headers[CACHE_CONTROL]
if digest
headers[CACHE_CONTROL] = @cache_control if @cache_control
else
headers[CACHE_CONTROL] = @no_cache_control if @no_cache_control
end
end
[status, headers, body]
end
private
def etag_status?(status)
status == 200 || status == 201
end
def etag_body?(body)
!body.respond_to?(:to_path)
end
def skip_caching?(headers)
(headers[CACHE_CONTROL] && headers[CACHE_CONTROL].include?('no-cache')) ||
headers.key?(ETAG_STRING) || headers.key?('Last-Modified')
end
def digest_body(body)
parts = []
digest = nil
body.each do |part|
parts << part
(digest ||= Digest::MD5.new) << part unless part.empty?
end
[digest && digest.hexdigest, parts]
end
end
end
|