Download objects

Simple download of objects

The following code reads an object to a stream:

// Initialize an OSSClient
var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
/// <summary>
// Retrieve an object from the specified bucket on OSS
/// </summary>
/// <param name="bucketName">Name of the bucket where the object to be retrieved is stored</param>
/// <param name="key">Name of the object to be retrieved</param>
/// <param name="objectToDownload">Local path to which the object to be downloaded</param>
public void GetObject(string bucketName, string key, string fileToDownload)
{
    try
    {
        var object = client.GetObject(bucketName, key);
        using (var requestStream = object.Content)
        {
            byte[] buf = new byte[1024];
            var fs = File.Open(fileToDownload, FileMode.OpenOrCreate);
            var len = 0;
            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);
    }
}

Note:

• For complete code, see GitHub.

• OssObject contains object information such as the object’s bucket, object name, metadata, and an input stream.

• The input stream can be used to read the object content to another object or the memory. ObjectMeta contains the ETag, HTTP header, and UserMetadata, which is defined when the object is uploaded.

Multipart object access

The following code uses GetObjectRequest to access an object through multipart read:

// Initialize an OSSClient
var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
public void GetObject(string bucketName, string key, string fileToDownload)
{
    try
    {
        var getObjectRequest = new GetObjectRequest(bucketName, key);
        //Retrieve the 20th to 100th characters of the object, including the 20th character and the 100th character
        getObjectRequest.SetRange(20, 100);
        var object = client.GetObject(getObjectRequest);
        // Write the retrieved data to the fielToDownload object
        using (var requestStream = object.Content)
        {
            byte[] buf = new byte[1024];
            var fs = File.Open(fileToDownload, FileMode.OpenOrCreate);
            var len = 0;
            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);
    }
}

Note:

• For complete code, see GitHub.

• The setRange method of the GetObjectRequest interface specifies the range of the returned object content.

• The setRange method can be used for multipart download and resumable upload.

• You can set the following parameters for GetObjectRequest:

Retrieve the object metadata only

The GetObjectMetadata method can be used to retrieve the ObjectMeta only instead of the body of an object. The code is as follows:

// Initialize an OSSClient
var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
/// <summary>
/// Retrieve the metadata of the object. 
/// </summary>
/// <param name="bucketName">Name of the bucket</param>
/// <param name="key">Name of the object on the OSS</param>
public void GetObjectMetadata(string bucketName, string key)
{
    try
    {
        var metadata = client.GetObjectMetadata(bucketName, key);
        Console.WriteLine("Get object meta succeeded");  
        Console.WriteLine("Content-Type:{0}", metadata.ContentType);
        Console.WriteLine("Cache-Control:{0}", metadata.CacheControl);
    }
    catch (Exception ex)
    {
        Console.WriteLine("Get object meta failed. {0}", ex.Message);
    }
}