def _open_generic_http(self, connection_factory, url, data):
        """Make an HTTP connection using connection_class.

        This is an internal method that should be called from
        open_http() or open_https().

        Arguments:
        - connection_factory should take a host name and return an
          HTTPConnection instance.
        - url is the url to retrieval or a host, relative-path pair.
        - data is payload for a POST request or None.
        """

        user_passwd = None
        proxy_passwd= None
        if isinstance(url, str):
            host, selector = splithost(url)
            if host:
                user_passwd, host = splituser(host)
                host = unquote(host)
            realhost = host
        else:
            host, selector = url
            # check whether the proxy contains authorization information
            proxy_passwd, host = splituser(host)
            # now we proceed with the url we want to obtain
            urltype, rest = splittype(selector)
            url = rest
            user_passwd = None
            if urltype.lower() != 'http':
                realhost = None
            else:
                realhost, rest = splithost(rest)
                if realhost:
                    user_passwd, realhost = splituser(realhost)
                if user_passwd:
                    selector = "%s://%s%s" % (urltype, realhost, rest)
                if proxy_bypass(realhost):
                    host = realhost

        if not host: raise IOError('http error', 'no host given')

        if proxy_passwd:
            proxy_passwd = unquote(proxy_passwd)
            proxy_auth = base64.b64encode(proxy_passwd.encode()).decode('ascii')
        else:
            proxy_auth = None

        if user_passwd:
            user_passwd = unquote(user_passwd)
            auth = base64.b64encode(user_passwd.encode()).decode('ascii')
        else:
            auth = None
        http_conn = connection_factory(host)
        headers = {}
        if proxy_auth:
            headers["Proxy-Authorization"] = "Basic %s" % proxy_auth
        if auth:
            headers["Authorization"] =  "Basic %s" % auth
        if realhost:
            headers["Host"] = realhost

        # Add Connection:close as we don't support persistent connections yet.
        # This helps in closing the socket and avoiding ResourceWarning

        headers["Connection"] = "close"

        for header, value in self.addheaders:
            headers[header] = value

        if data is not None:
            headers["Content-Type"] = "application/x-www-form-urlencoded"
            http_conn.request("POST", selector, data, headers)
        else:
            http_conn.request("GET", selector, headers=headers)

        try:
            response = http_conn.getresponse()
        except http_client.BadStatusLine:
            # something went wrong with the HTTP status line
            raise URLError("http protocol error: bad status line")

        # According to RFC 2616, "2xx" code indicates that the client's
        # request was successfully received, understood, and accepted.
        if 200 <= response.status < 300:
            return addinfourl(response, response.msg, "http:" + url,
                              response.status)
        else:
            return self.http_error(
                url, response.fp,
                response.status, response.reason, response.msg, data)
Make an HTTP connection using connection_class.

        This is an internal method that should be called from
        open_http() or open_https().

        Arguments:
        - connection_factory should take a host name and return an
          HTTPConnection instance.
        - url is the url to retrieval or a host, relative-path pair.
        - data is payload for a POST request or None.