class Rack::Cache::EntityStore

which becomes the response body’s key.
Implementations are required to calculate a SHA checksum of the data written
Entity stores are used to cache response bodies across requests. All

def bytesize(string); string.bytesize; end 

def bytesize(string); string.bytesize; end

def bytesize(string); string.size; end 

def bytesize(string); string.size; end

def slurp(body)

[ hexdigest, size ].
call it after iteration is complete. Return a two-tuple of the form:
yielding each chunk to the block. If the body responds to close,
Read body calculating the SHA1 checksum and size while 
def slurp(body)
  digest, size = Digest::SHA1.new, 0
  body.each do |part|
    size += bytesize(part)
    digest << part
    yield part
  end
  body.close if body.respond_to? :close
  [digest.hexdigest, size]
end