call (Rack::Sendfile)

# File lib/rack/sendfile.rb, line 112
    def call(env)
      status, headers, body = @app.call(env)
      if body.respond_to?(:to_path)
        case type = variation(env)
        when 'X-Accel-Redirect'
          path = F.expand_path(body.to_path)
          if url = map_accel_path(env, path)
            headers[CONTENT_LENGTH] = '0'
            headers[type] = url
            obody = body
            body = Rack::BodyProxy.new([]) do
              obody.close if obody.respond_to?(:close)
            end
          else
            env['rack.errors'].puts "X-Accel-Mapping header missing"
          end
        when 'X-Sendfile', 'X-Lighttpd-Send-File'
          path = F.expand_path(body.to_path)
          headers[CONTENT_LENGTH] = '0'
          headers[type] = path
          obody = body
          body = Rack::BodyProxy.new([]) do
            obody.close if obody.respond_to?(:close)
          end
        when '', nil
        else
          env['rack.errors'].puts "Unknown x-sendfile variation: '#{type}'.\n"
        end
      end
      [status, headers, body]
    end