下载文件不成功，找不出原因

直接拷出地址，在浏览中打开能下载，程序 下载，不成功。
options = oss_request_options_create(p);

init_sample_request_options(options, is_cname);
aos_str_set(&bucket, BUCKET_NAME);
aos_str_set(&object, OBJECT_NAME);
headers = aos_table_make(p, 0);
aos_str_set(&file, download_filename);

// aos_string_t url_str("http://xxxx-file.oss-cn-beijing.aliyuncs.com/apps/appFiles/a15e9df939450a7fe9f17517bb4661d2_test.apk");

s = oss_get_object_to_file(options, &bucket, &object, headers, 
                           params, &file, &resp_headers);
//s = oss_get_object_to_file_by_url(options,&url_str, headers, &file, &resp_headers);