Object Storage Service:Use .NET to manage object metadata

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.

• To configure object metadata, you must have the oss:PutObject permission. To query object metadata, you must have the oss:GetObject permission. For more information, see Attach a custom policy to a RAM user.

Sample code

The following code provides an example on how to configure, modify, and query object metadata:

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

// 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. 
var bucketName = "examplebucket";
// Specify the full path of the object. Do not include the bucket name in the full path. 
var objectName = "exampleobject.txt";
// Specify the full path of the local object that you want to upload. By default, if you do not specify the full path of the local object, the local object is uploaded from the path of the project to which the sample program belongs. 
var localFilename = "D:\\localpath\\examplefile.txt";
// Create an OSSClient instance. 
var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
try
{
    using (var fs = File.Open(localFilename, FileMode.Open))
    {
        // Create metadata for the object. You can configure HTTP headers for the object. 
        var metadata = new ObjectMetadata()
        {
            // Specify the content type of the object. 
            ContentType = "text/html",
            // Specify the expiration time of the cache in UTC. 
            ExpirationTime = DateTime.Parse("2025-10-12T00:00:00.000Z"),
        };
        // Specify the length of the object content to upload. If the actual object length is greater than the specified length, the object is truncated. Only the content of the specified length is uploaded. If the actual object length is smaller than the specified length, all content of the object is uploaded. 
        metadata.ContentLength = fs.Length;
        // Specify the caching behavior of the web page when the object is downloaded. 
        metadata.CacheControl = "No-Cache";
        // Set mykey1 to myval1. 
        metadata.UserMetadata.Add("mykey1", "myval1");
        // Set mykey2 to myval2. 
        metadata.UserMetadata.Add("mykey2", "myval2");
        var saveAsFilename = "Filetest123.txt";
        var contentDisposition = string.Format("attachment;filename*=utf-8''{0}", HttpUtils.EncodeUri(saveAsFilename, "utf-8"));
        // Specify a default object name when the required content is saved as an object. 
        metadata.ContentDisposition = contentDisposition;
        // Upload the object and configure object metadata. 
        client.PutObject(bucketName, objectName, fs, metadata);
        Console.WriteLine("Put object succeeded");
        // Query object metadata. 
        var oldMeta = client.GetObjectMetadata(bucketName, objectName);
        // Configure new object metadata. 
        var newMeta = new ObjectMetadata()
        {
            ContentType = "application/octet-stream",
            ExpirationTime = DateTime.Parse("2035-11-11T00:00:00.000Z"),
            // Specify the content encoding format of the object when the object is downloaded. 
            ContentEncoding = null,
            CacheControl = ""
        };
        // Configure user metadata. 
        newMeta.UserMetadata.Add("author", "oss");
        newMeta.UserMetadata.Add("flag", "my-flag");
        newMeta.UserMetadata.Add("mykey2", "myval2-modified-value");
        // Use the ModifyObjectMeta method to modify the object metadata. 
        client.ModifyObjectMeta(bucketName, objectName, newMeta);
    }
}
catch (Exception ex)
{
    Console.WriteLine("Put object failed, {0}", ex.Message);
}

References

• For the complete sample code that is used to configure, modify, and obtain object metadata, visit GitHub.

• For more information about the API operation that you can call to configure object metadata during simple upload, see PutObject.

• For more information about the API operation that you can call to modify object metadata when you copy an object, see CopyObject

• For more information about the API operation that you can call to query object metadata, see GetObjectMeta and HeadObject.