**文件管理**
##############################
在NOS中，用户可以通过一系列的接口管理桶(Bucket)中的文件(Object)，比如ListObjects，DeleteObject，CopyObject，DoesObjectExist等。

列出桶中的文件
=============================
您可以使用S3Client.ListObjects列出存储中间中的文件::
    
    void listObjectsWithPrintKeySize(const Aws::S3::S3Client& s3Client,const Aws::String& bucketName){
        Aws::S3::Model::ListObjectsRequest listObjectRequest;
        listObjectRequest.WithBucket(bucketName);
        auto result = s3Client.ListObjects(listObjectRequest);
        if (result.IsSuccess()) {
            for(auto content : result.GetResult().GetContents()){
                std::cout << content.GetKey() << " --> " << content.GetSize() << std::endl;
            }
        } else {
            std::cout << "list Objects failed" << std::endl;
        }
    }
        

上述代码中的ListObjectsRequest中的可选参数如下所示:

+------------------------+-------------------------------------------------------------------------------------------------------------------------+
|参数                    |    说明                                                                                                                 |
+========================+=========================================================================================================================+
| Delimiter              |用于对Object名字进行分组的字符。所有名字包含指定的前缀且第一次出现delimiter字符之间的object作为一组元素。限制长度为10。  |
+------------------------+-------------------------------------------------------------------------------------------------------------------------+
| Prefix                 |限定返回的object key必须以prefix作为前缀。注意使用prefix查询时，返回的key中仍会包含prefix                                |
+------------------------+-------------------------------------------------------------------------------------------------------------------------+
| MaxKeys                |限定此次返回object的最大数，如果不设定，默认为100                                                                        |
+------------------------+-------------------------------------------------------------------------------------------------------------------------+
| Marker                 |设定结果从marker之后按字母排序的第一个开始返回                                                                           |
+------------------------+-------------------------------------------------------------------------------------------------------------------------+

.. note::

	1. 上述表中的参数都是可选参数

判断文件是否存在
============================
您可以使用S3Client.GetObjectMetadata的返回值来判断文件是否存在::

    bool doesObjectExits(const Aws::S3::S3Client& s3Client,const Aws::String& bucketName,const Aws::String& objectName){
        Aws::S3::Model::HeadObjectRequest headObjectRequest;
        headObjectRequest.WithBucket(bucketName).WithKey(objectName);
        auto result = s3Client.HeadObject(headObjectRequest);
        return result.IsSuccess();
    }

删除单个文件
===========================
您可以使用S3Client.DeleteObject删除单个需要删除的文件::

    void deleteObject(const Aws::S3::S3Client& s3Client,const Aws::String& bucketName,const Aws::String& objectName){
        
        Aws::S3::Model::DeleteObjectRequest object_request;
        object_request.WithBucket(bucketName).WithKey(objectName);
        
        auto delete_object_outcome = s3Client.DeleteObject(object_request);
        
        if (delete_object_outcome.IsSuccess())
        {
            std::cout << "Done!" << std::endl;
        }
        else
        {
            std::cout << "DeleteObject error: " <<
            delete_object_outcome.GetError().GetExceptionName() << " " <<
            delete_object_outcome.GetError().GetMessage() << std::endl;
        }
    }


删除多个文件
============================
您可以使用S3Client.DeleteObjects批量删除文件::

    void deleteObjects(const Aws::S3::S3Client& s3Client,const Aws::String& bucketName,const Aws::Vector<Aws::S3::Model::ObjectIdentifier>& objectNames){
        Aws::S3::Model::DeleteObjectsRequest deleteObjectsRequest;
        Aws::S3::Model::Delete deleteObjects;
        deleteObjects.SetObjects(objectNames);
        deleteObjects.SetQuiet(false);
        deleteObjectsRequest.WithBucket(bucketName).WithDelete(deleteObjects);
        auto result = s3Client.DeleteObjects(deleteObjectsRequest);
        if (result.IsSuccess()) {
            for(auto err : result.GetResult().GetErrors()){
                std::cout << "delete err : " << err.GetKey() << " --> " << err.GetMessage() << std::endl;
            }
            for (auto del : result.GetResult().GetDeleted()) {
                std::cout << "delete ok : " << del.GetKey()  << std::endl;
            }
            std::cout << "ok" << std::endl;
        } else {
            std::cout << result.GetError().GetMessage() << std::endl;
            std::cout << "failed" << std::endl;
        }
        
    }

拷贝文件
===========================
您可以使用S3Client.CopyObject拷贝文件::

    void copyObject(const Aws::S3::S3Client& s3Client,const Aws::String& srcBucket,const Aws::String& srcObject,const Aws::String& dstBucket,const Aws::String& dstObject){
        Aws::S3::Model::CopyObjectRequest copyObjectRequest;
        copyObjectRequest.WithBucket(dstBucket).WithKey(dstObject).WithCopySource("/" + srcBucket + "/" + srcObject);
        auto result = s3Client.CopyObject(copyObjectRequest);
        if (result.IsSuccess()) {
            std::cout << "copy done" << std::endl;
        } else {
            std::cout << "copy failed" << std::endl;
        }
    }

.. attention::

	1. 支持跨桶的文件copy


获取文件的文件元信息
==========================
您可以使用S3Client.GetObjectMetadata获取对象的元数据信息::

 
    void getObjectMeta(const Aws::S3::S3Client& s3Client,const Aws::String& bucketName,const Aws::String& objectName){
        Aws::S3::Model::HeadObjectRequest headObjectRequest;
        headObjectRequest.WithBucket(bucketName).WithKey(objectName);
        auto result = s3Client.HeadObject(headObjectRequest);
        if (result.IsSuccess()) {
            for(auto entry : result.GetResult().GetMetadata()){
                std::cout << entry.first << " -- > " << entry.second << std::endl;
            }
        } else {
            std::cout << "failed" << std::endl;
        }
    }


生成私有对象可下载的URL链接
=============================
您可以使用S3Client.GetPreSignedURL获取对象的下载URL::

    void getObjectDonwloadUrl(Aws::S3::S3Client& s3Client,const Aws::String& bucketName,const Aws::String& objectName){
        Aws::String url = s3Client.GeneratePresignedUrl(bucketName, objectName,Aws::Http::HttpMethod::HTTP_GET,20);//最后一个20是过期时间，但是为second
        std::cout << url << std::endl;
    }