AFHTTPRequestOperation nil响应而不是错误

Question

我正在使用AFHTTPRequestOperation来解析几个HTML页面。 我遇到的问题是，如果我使用错误的端口号，例如，当连接到服务器时，“失败的”错误块不会触发。相反，完成块会触发，但响应字符串为零。 我只是从ASIHTTP切换到AFNetworking，而使用ASIHTTP会产生错误。

当然这应该提供错误？我怎么能陷阱呢？

    NSString *urlString;
    urlString = [NSString stringWithFormat:@"%@://%@:%@/",kHttp,_IP,_Port];
    NSURL *url = [NSURL URLWithString:urlString];

    // Set authorization
    AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
    [httpClient setAuthorizationHeaderWithUsername:_User password:_Pass];

    NSURLRequest *request = [httpClient requestWithMethod:@"POST" path:@"Info.htm" parameters:nil];
    AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
    [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
        if ([self parseInfoLive:operation.responseString])
            _count_parsed++;
        if (_count_parsed == 2)
            [[NSNotificationCenter defaultCenter] postNotificationName:@"downloadsComplete" object:nil];
    }
                                     failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                                         NSLog(@"Error during connection: %@",error.description);
                                         [[NSNotificationCenter defaultCenter] postNotificationName:@"errorConnecting" object:nil];
                                     }];
[operation start];