Object Storage Service:Obtain file metadata (C# SDK V2)

Prerequisites

Before you begin, make sure you have:

• A versioning-enabled OSS bucket

• The oss:GetObject permission on the target object. For details, see Grant custom permissions to a RAM user

• The OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables set with valid AccessKey credentials

Note: The examples below use the China (Hangzhou) region (cn-hangzhou) with a public endpoint. If your application runs on an Alibaba Cloud service in the same region as your bucket, use an internal endpoint to reduce latency and avoid data transfer charges. For supported regions and endpoints, see OSS regions and endpoints.

Retrieve all object metadata

Use HeadObjectAsync to get the complete set of metadata for a specific object version. The response includes all standard HTTP headers and any custom metadata stored with the object.

using OSS = AlibabaCloud.OSS.V2;

var region = "cn-hangzhou";         // Region where the bucket is located
var endpoint = null as string;      // Optional: override the default endpoint
var bucket = "<your-bucket-name>";  // Replace with your bucket name
var key = "<your-object-key>";      // Replace with your object key

// Initialize the client with credentials from environment variables
var cfg = OSS.Configuration.LoadDefault();
cfg.CredentialsProvider = new OSS.Credentials.EnvironmentVariableCredentialsProvider();
cfg.Region = region;
if (endpoint != null)
{
    cfg.Endpoint = endpoint;
}

using var client = new OSS.Client(cfg);

try
{
    var result = await client.HeadObjectAsync(new OSS.Models.HeadObjectRequest()
    {
        Bucket = bucket,
        Key = key,
    });

    Console.WriteLine($"Status code: {result.StatusCode}");
    Console.WriteLine($"Request ID:  {result.RequestId}");

    // Access specific metadata fields from the response headers
    Console.WriteLine($"Content-Type:    {result.Headers["Content-Type"]}");
    Console.WriteLine($"Content-Length:  {result.Headers["Content-Length"]}");
    Console.WriteLine($"ETag:            {result.Headers["ETag"]}");
    Console.WriteLine($"Last-Modified:   {result.Headers["Last-Modified"]}");
    Console.WriteLine($"Version ID:      {result.Headers["x-oss-version-id"]}");
}
catch (Exception ex)
{
    Console.WriteLine($"Request failed: {ex.Message}");
}

Replace the following placeholders:

For the complete sample, see HeadObject.cs.

Retrieve partial object metadata

Use GetObjectMetaAsync when you only need a lightweight check — for example, to verify file size before downloading, or to confirm integrity using the CRC checksum. This operation returns only the following five fields and does not return the object body.

using OSS = AlibabaCloud.OSS.V2;

var region = "cn-hangzhou";         // Region where the bucket is located
var endpoint = null as string;      // Optional: override the default endpoint
var bucket = "<your-bucket-name>";  // Replace with your bucket name
var key = "<your-object-key>";      // Replace with your object key

// Initialize the client with credentials from environment variables
var cfg = OSS.Configuration.LoadDefault();
cfg.CredentialsProvider = new OSS.Credentials.EnvironmentVariableCredentialsProvider();
cfg.Region = region;
if (endpoint != null)
{
    cfg.Endpoint = endpoint;
}

using var client = new OSS.Client(cfg);

try
{
    var result = await client.GetObjectMetaAsync(new OSS.Models.GetObjectMetaRequest()
    {
        Bucket = bucket,
        Key = key,
    });

    Console.WriteLine($"Status code:    {result.StatusCode}");
    Console.WriteLine($"Request ID:     {result.RequestId}");
    Console.WriteLine($"Content-Length: {result.Headers["Content-Length"]}");
    Console.WriteLine($"ETag:           {result.Headers["ETag"]}");
    Console.WriteLine($"Last-Modified:  {result.Headers["Last-Modified"]}");
    Console.WriteLine($"Version ID:     {result.Headers["x-oss-version-id"]}");
    Console.WriteLine($"CRC-64:         {result.Headers["x-oss-hash-crc64ecma"]}");
}
catch (Exception ex)
{
    Console.WriteLine($"Request failed: {ex.Message}");
}

Replace the placeholders <your-bucket-name> and <your-object-key> as described in the table above.

For the complete sample, see GetObjectMeta.cs.