# File lib/rack/content_length.rb, line 12
12:     def call(env)
13:       status, headers, body = @app.call(env)
14:       headers = HeaderHash.new(headers)
15: 
16:       if !STATUS_WITH_NO_ENTITY_BODY.include?(status.to_i) &&
17:          !headers['Content-Length'] &&
18:          !headers['Transfer-Encoding'] &&
19:          (body.respond_to?(:to_ary) || body.respond_to?(:to_str))
20: 
21:         body = [body] if body.respond_to?(:to_str) # rack 0.4 compat
22:         length = body.to_ary.inject(0) { |len, part| len + bytesize(part) }
23:         headers['Content-Length'] = length.to_s
24:       end
25: 
26:       [status, headers, body]
27:     end