# File lib/rack/sendfile.rb, line 104
    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[type] = url
            body = []
          else
            env['rack.errors'] << "X-Accel-Mapping header missing"
          end
        when 'X-Sendfile', 'X-Lighttpd-Send-File'
          path = F.expand_path(body.to_path)
          headers[type] = path
          body = []
        when '', nil
        else
          env['rack.errors'] << "Unknown x-sendfile variation: '#{variation}'.\n"
        end
      end
      [status, headers, body]
    end