Object Storage Service:Resumable download

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 use resumable download, you must have the oss:GetObject permission. For more information, see Common examples of RAM policies.

Sample code

The following code provides an example on how to perform resumable download:

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

// 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 = "yourEndpoint";
// 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 = "exampleobject.txt";
// Download the object to D:\\localpath. After the object is downloaded, the local file is named examplefile.txt. If a file with the same name already exists, the downloaded object overwrites the file. Otherwise, the downloaded object is saved in the path. 
// If you do not specify a path for the downloaded object, the downloaded object is saved to the path of the project to which the sample program belongs. 
var downloadFilename = "D:\\localpath\\examplefile.txt";
// Specify the full path of the checkpoint file. Example: D:\\localpath\\examplefile.txt.dcp. 
// The checkpoint file is generated when the download is interrupted. If you want to resume the download task, you must specify the full path of the checkpoint file. After the object is downloaded, the checkpoint file is deleted. 
var checkpointDir = "D:\\localpath\\examplefile.txt.dcp";
// Create an OSSClient instance. 
var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
try
{
    // Configure multiple parameters by using DownloadObjectRequest. 
    DownloadObjectRequest request = new DownloadObjectRequest(bucketName, objectName, downloadFilename)
    {
        // Specify the size of each part to download. Unit: bytes. 
        PartSize = 8 * 1024 * 1024,
        // Specify the number of concurrent threads. 
        ParallelThreadCount = 3,
        // checkpointDir is a file used to store the information about the resumable download progress. If a part fails to be downloaded, you can resume the download task based on the progress that is recorded in the checkpointDir file. If you set checkpointDir to null, resumable download does not take effect and the object is downloaded again if it fails to be downloaded. 
        CheckpointDir = checkpointDir,
    };
    // Start the resumable download. 
    client.ResumableDownloadObject(request);
    Console.WriteLine("Resumable download object:{0} succeeded", objectName);
}
catch (OssException ex)
{
    Console.WriteLine("Failed with error code: {0}; Error info: {1}. \nRequestID:{2}\tHostID:{3}",
        ex.ErrorCode, ex.Message, ex.RequestId, ex.HostId);
}
catch (Exception ex)
{
    Console.WriteLine("Failed with error info: {0}", ex.Message);
}

References

For more information about the API operation that is used to perform resumable download, see GetObject.