scrapy中使用讯代理动态转发

scrapy源代码中查找http11.py文件，相对路径为：
Lib/site-packages/scrapy/core/downloader/handlers/http11.py

找到下面内容，注释掉：
if isinstance(agent, self._TunnelingAgent):
   headers.removeHeader(b'Proxy-Authorization')

否则proxy-authorization会被去除，动态转发失效。

自定义下载中间件：
class ProxyIPMiddleware(object):
    '''
    随机更换代理ip
    '''
    def __init__(self):
        self.orderno = "xxxxxxxxxxxx"  # 订单号
        self.secret = "xxxxxxxxxxx"  # 秘钥

    def process_request(self,request,spider):
        print('====ProxyIPMiddleware====')
        protocal = request.url.split(':')[0].strip().lower()
        print(request.url,'protocal:',protocal)
        ip = "forward.xdaili.cn"  # 代理ip
        port = "80"  # 端口号
        ip_port = ip + ":" + port
        proxy = {"http": "http://" + ip_port, "https": "https://" + ip_port}
        timestamp = str(int(time.time()))  # 时间戳
        string = "orderno=" + self.orderno + "," + "secret=" + self.secret + "," + "timestamp=" + timestamp
        md5_string = hashlib.md5(string.encode()).hexdigest()  # md5哈希，得到固定长度的字符串
        sign = md5_string.upper()  # 转换成大写字母
        # 认证信息
        auth = "sign=" + sign + "&" + "orderno=" + self.orderno + "&" + "timestamp=" + timestamp
        print('auth:',auth)
        request.headers['Proxy-Authorization'] = auth
        #HTTP代理，只代理HTTP网站，HTTPS代理，只代理HTTPS网站
        request.meta['proxy'] = proxy[protocal]