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Object Storage Service:Download objects

Last Updated:Dec 07, 2023

By default, when you call the GetObject operation on an object in a versioning-enabled bucket, only the current version of the object is returned.

Background information

When you call the GetObject operation to download an object in a bucket, you may obtain one of the following results:

  • If the current version of the object is a delete marker, OSS returns 404 Not Found.

  • If a version ID of the object is specified in the request, OSS returns the specified version of the object. If the version ID is set to null in the request, OSS returns the version whose version ID is null.

  • If the version ID specified in the request is the version ID of a delete marker, OSS returns 405 Method Not Allowed.

Usage notes

  • In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access OSS by using other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about the regions and endpoints supported by OSS, see Regions and endpoints.

  • In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient instance by using custom domain names or Security Token Service (STS), see Initialization.

  • To download an object, you must have the oss:GetObject permission. For more information, see Attach a custom policy to a RAM user.

Sample code

The following sample code provides an example on how to download an object:

using System;
using System.IO;
using Aliyun.OSS;

namespace Samples
{
    public class Program
    {
        public static void Main(string[] args)
        {
            // Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
            var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
            // Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. 
            var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
            var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
            // Specify the name of the bucket. Example: examplebucket. 
            var bucketName = "examplebucket";
            // Specify the full path of the object. Do not include the bucket name in the full path. Example: exampledir/exampleobject.txt. 
            var objectName = "exampledir/exampleobject.txt";
            // Specify the full path of the local file that you want to upload. Example: D:\\localpath\\examplefile.txt. 
            var downloadFilename = "D:\\localpath\\examplefile.txt";
            var versionid = "yourArchiveObjectVersionid";
            // Create an OSSClient instance. 
            var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
            try
            {
                // Download the object to a stream. OssObject includes object information, such as the bucket in which the object is stored, the object name, object metadata, and an input stream. 
                var request = new GetObjectRequest(bucketName, objectName)
                {
                    // Specify the version ID of the object. 
                    VersionId = versionid
                };
                var obj = client.GetObject(request);
                using (var requestStream = obj.Content)
                {
                    byte[] buf = new byte[1024];
                    var fs = File.Open(downloadFilename, FileMode.OpenOrCreate);
                    var len = 0;
                    // The input stream can be used to read and download the object content to a local file or to the memory. 
                    while ((len = requestStream.Read(buf, 0, 1024)) != 0)
                    {
                        fs.Write(buf, 0, len);
                    }
                    fs.Close();
                }
                Console.WriteLine("Get object succeeded, vesionid:{0}", versionid);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Get object failed. {0}", ex.Message);
            }
        }
    }
}

References

For more information about the API operation that you can call to download an object, see GetObject.