Object Storage Service:Download a file (C# SDK V1)

Background information

Usage notes

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

Permissions

By default, an Alibaba Cloud account has full permissions. RAM users or RAM roles under an Alibaba Cloud account do not have any permissions by default. The Alibaba Cloud account or account administrator must grant operation permissions through RAM Policy or Bucket policies.

Sample code

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

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

namespace Samples
{
    public class Program
    {
        public static void Main(string[] args)
        {
            // Set yourEndpoint to the Endpoint of the region where the bucket is located. For example, if the bucket is 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 this sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are set.
            var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
            var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
            // Specify the bucket name. Example: examplebucket.
            var bucketName = "examplebucket";
            // Specify the full path of the object. The full path cannot contain the bucket name. Example: exampledir/exampleobject.txt.
            var objectName = "exampledir/exampleobject.txt";
            // Specify the full path of the local file. Example: D:\\localpath\\examplefile.txt.
            var downloadFilename = "D:\\localpath\\examplefile.txt";
            var versionid = "yourArchiveObjectVersionid";
            // Specify the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set the region to cn-hangzhou.
            const string region = "cn-hangzhou";
            
            // Create a ClientConfiguration instance and modify the default parameters as needed.
            var conf = new ClientConfiguration();
            
            // Set the signature version to V4.
            conf.SignatureVersion = SignatureVersion.V4;
            
            // Create an OssClient instance.
            var client = new OssClient(endpoint, accessKeyId, accessKeySecret, conf);
            client.SetRegion(region);
            try
            {
                // Download the file to a stream. OssObject contains various information about the file, such as the bucket where the file is stored, the file name, 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;
                    // Read the content of the file to a file or memory using the input stream.
                    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 used to download files, see GetObject.