class WEBrick::HTTPProxyServer

def perform_proxy_request(req, res, req_class, body_stream = nil)
  uri = req.request_uri
  path = uri.path.dup
  path << "?" << uri.query if uri.query
  header = setup_proxy_header(req, res)
  upstream = setup_upstream_proxy_authentication(req, res, header)
  body_tmp = []
  http = create_net_http(uri, upstream)
  req_fib = Fiber.new do
    http.start do
      if @config[:ProxyTimeout]
        ##################################   these issues are
        http.open_timeout = 30   # secs  #   necessary (maybe because
        http.read_timeout = 60   # secs  #   Ruby's bug, but why?)
        ##################################
      end
      if body_stream && req['transfer-encoding'] =~ /\bchunked\b/i
        header['Transfer-Encoding'] = 'chunked'
      end
      http_req = req_class.new(path, header)
      http_req.body_stream = body_stream if body_stream
      http.request(http_req) do |response|
        # Persistent connection requirements are mysterious for me.
        # So I will close the connection in every response.
        res['proxy-connection'] = "close"
        res['connection'] = "close"
        # stream Net::HTTP::HTTPResponse to WEBrick::HTTPResponse
        res.status = response.code.to_i
        res.chunked = response.chunked?
        choose_header(response, res)
        set_cookie(response, res)
        set_via(res)
        response.read_body do |buf|
          body_tmp << buf
          Fiber.yield # wait for res.body Proc#call
        end
      end # http.request
    end
  end
  req_fib.resume # read HTTP response headers and first chunk of the body
  res.body = ->(socket) do
    while buf = body_tmp.shift
      socket.write(buf)
      buf.clear
      req_fib.resume # continue response.read_body
    end
  end
end