Download an object to a stream with C# SDK V1 - Object Storage Service

Streaming download reads an object's content incrementally as a stream, rather than loading the entire object into memory at once. This approach suits large objects or objects that take a long time to transfer.

Prerequisites

Before you begin, make sure you have:

An OSS bucket with at least one object to download
The oss:GetObject permission. For setup instructions, see Attach a custom policy to a RAM user
The OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables set with your AccessKey ID and AccessKey secret

Usage notes

The example uses the public endpoint for the China (Hangzhou) region. To access OSS from another Alibaba Cloud service in the same region, use the internal endpoint instead. For a full list of endpoints, see Regions and endpoints.
The example creates an OssClient instance using an OSS endpoint. To create an instance using a custom domain name or Security Token Service (STS), see Initialization.

Download an object as a stream

The following example calls GetObject to download an object. The method returns an OssObject, which includes the bucket name, object name, object metadata, and a Content stream. The code reads from that stream in 1024-byte chunks and writes each chunk to a local file.

using Aliyun.OSS;
using Aliyun.OSS.Common;

// Specify the endpoint for the region where your bucket is located.
// Example: https://oss-cn-hangzhou.aliyuncs.com
var endpoint = "yourEndpoint";

// Load access credentials from environment variables.
var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");

// Replace the following values with your actual bucket name, object path, and local output path.
var bucketName = "examplebucket";
var objectName = "exampledir/exampleobject.txt";
var downloadFilename = "D:\\localpath\\examplefile.txt";

// Specify the region where your bucket is located. Example: cn-hangzhou
const string region = "cn-hangzhou";

// Create a ClientConfiguration instance and enable signature algorithm V4.
var conf = new ClientConfiguration();
conf.SignatureVersion = SignatureVersion.V4;

// Create an OssClient instance.
var client = new OssClient(endpoint, accessKeyId, accessKeySecret, conf);
client.SetRegion(region);

try
{
    // Call GetObject to download the object.
    // OssObject.Content is a readable stream containing the object data.
    var obj = client.GetObject(bucketName, objectName);
    using (var requestStream = obj.Content)
    {
        byte[] buf = new byte[1024];
        var fs = File.Open(downloadFilename, FileMode.OpenOrCreate);
        var len = 0;

        // Read the stream in 1024-byte increments and write each chunk to the local file.
        while ((len = requestStream.Read(buf, 0, 1024)) != 0)
        {
            fs.Write(buf, 0, len);
        }
        fs.Close();
    }
    Console.WriteLine("Get object succeeded");
}
catch (Exception ex)
{
    Console.WriteLine("Get object failed. {0}", ex.Message);
}

What's next

For the complete sample code, see GetObjectSample.cs on GitHub.
For the full API reference, see GetObject.