Object Storage Service:List objects (C# SDK V1)

Prerequisites

Before you begin, make sure that:

• The OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are set with your access credentials

• You have the oss:ListObjects permission. See Attach a custom policy to a RAM user

Usage notes

• The examples use the public endpoint for the China (Hangzhou) region (https://oss-cn-hangzhou.aliyuncs.com). To access OSS from another Alibaba Cloud service in the same region, use the internal endpoint instead. See Regions and endpoints.

• The examples create an OssClient instance using an OSS endpoint. To use a custom domain name or Security Token Service (STS), see Initialization.

Request parameters

When a result set is truncated, result.IsTruncated is true and result.NextMarker contains the starting point for the next request.

List up to 100 objects

ListObjectsRequest returns up to 100 objects by default.

using Aliyun.OSS;

var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
var bucketName = "examplebucket";
const string region = "cn-hangzhou";

var conf = new ClientConfiguration();
conf.SignatureVersion = SignatureVersion.V4;

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

try
{
    var listObjectsRequest = new ListObjectsRequest(bucketName);
    var result = client.ListObjects(listObjectsRequest);

    Console.WriteLine("List objects succeeded");
    foreach (var summary in result.ObjectSummaries)
    {
        Console.WriteLine("File name:{0}", summary.Key);
    }
}
catch (Exception ex)
{
    Console.WriteLine("List objects failed. {0}", ex.Message);
}

List a specific number of objects

Set MaxKeys to control how many objects are returned per request. The default is 100; the maximum is 1000.

using Aliyun.OSS;

var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
var bucketName = "examplebucket";
const string region = "cn-hangzhou";

var conf = new ClientConfiguration();
conf.SignatureVersion = SignatureVersion.V4;

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

try
{
    var listObjectsRequest = new ListObjectsRequest(bucketName)
    {
        MaxKeys = 200,
    };
    var result = client.ListObjects(listObjectsRequest);

    Console.WriteLine("List objects succeeded");
    foreach (var summary in result.ObjectSummaries)
    {
        Console.WriteLine(summary.Key);
    }
}
catch (Exception ex)
{
    Console.WriteLine("List objects failed. {0}", ex.Message);
}

List objects by prefix

Set Prefix to filter results to objects whose keys start with a specific string. This example lists all objects whose keys start with test, paging through the full result set.

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

var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
var bucketName = "examplebucket";
var prefix = "test";
const string region = "cn-hangzhou";

var conf = new ClientConfiguration();
conf.SignatureVersion = SignatureVersion.V4;

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

try
{
    var keys = new List<string>();
    ObjectListing result = null;
    string nextMarker = string.Empty;

    do
    {
        var listObjectsRequest = new ListObjectsRequest(bucketName)
        {
            Marker = nextMarker,
            MaxKeys = 100,
            Prefix = prefix,
        };
        result = client.ListObjects(listObjectsRequest);

        foreach (var summary in result.ObjectSummaries)
        {
            Console.WriteLine(summary.Key);
            keys.Add(summary.Key);
        }

        // Pass NextMarker to the next request to continue listing from where this page left off.
        nextMarker = result.NextMarker;
    } while (result.IsTruncated);

    Console.WriteLine("Listed {0} objects with prefix '{1}' in bucket: {2}", keys.Count, prefix, bucketName);
}
catch (OssException ex)
{
    Console.WriteLine("Failed. Error code: {0}; Error info: {1}. \nRequestID: {2}\tHostID: {3}",
        ex.ErrorCode, ex.Message, ex.RequestId, ex.HostId);
}
catch (Exception ex)
{
    Console.WriteLine("Failed. {0}", ex.Message);
}

List objects after a marker

Set Marker to start listing from a specific position in alphabetical order. Objects whose keys come after the marker value are returned.

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

var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
var bucketName = "examplebucket";
var marker = "exampleobject.txt";
const string region = "cn-hangzhou";

var conf = new ClientConfiguration();
conf.SignatureVersion = SignatureVersion.V4;

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

try
{
    var keys = new List<string>();
    ObjectListing result = null;
    string nextMarker = marker;

    do
    {
        var listObjectsRequest = new ListObjectsRequest(bucketName)
        {
            Marker = nextMarker,
            MaxKeys = 100,
        };
        result = client.ListObjects(listObjectsRequest);

        foreach (var summary in result.ObjectSummaries)
        {
            Console.WriteLine(summary.Key);
            keys.Add(summary.Key);
        }

        // Pass NextMarker to the next request to continue listing from where this page left off.
        nextMarker = result.NextMarker;
    } while (result.IsTruncated);

    Console.WriteLine("List objects succeeded");
}
catch (OssException ex)
{
    Console.WriteLine("Failed. Error code: {0}; Error info: {1}. \nRequestID: {2}\tHostID: {3}",
        ex.ErrorCode, ex.Message, ex.RequestId, ex.HostId);
}
catch (Exception ex)
{
    Console.WriteLine("Failed. {0}", ex.Message);
}

List all objects with pagination

When a bucket contains more objects than MaxKeys allows per response, result.IsTruncated is true. Pass result.NextMarker as the Marker for the next request and repeat until IsTruncated is false.

using Aliyun.OSS;

var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
var bucketName = "examplebucket";
const string region = "cn-hangzhou";

var conf = new ClientConfiguration();
conf.SignatureVersion = SignatureVersion.V4;

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

public void ListAllObjects(string bucketName)
{
    try
    {
        ObjectListing result = null;
        string nextMarker = string.Empty;

        do
        {
            var listObjectsRequest = new ListObjectsRequest(bucketName)
            {
                Marker = nextMarker,
                MaxKeys = 100,
            };
            result = client.ListObjects(listObjectsRequest);

            foreach (var summary in result.ObjectSummaries)
            {
                Console.WriteLine("Name:{0}", summary.Key);
            }

            // Pass NextMarker to the next request to continue listing from where this page left off.
            nextMarker = result.NextMarker;
        } while (result.IsTruncated);
    }
    catch (Exception ex)
    {
        Console.WriteLine("List objects failed. {0}", ex.Message);
    }
}

List objects asynchronously

Use BeginListObjects and EndListObjects to list objects without blocking the calling thread. Implement a callback to process results after the operation completes.

using System;
using System.IO;
using System.Threading;
using Aliyun.OSS;

namespace AsyncListObjects
{
    class Program
    {
        static string endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        static string accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
        static string accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
        static string bucketName = "examplebucket";
        static AutoResetEvent _event = new AutoResetEvent(false);
        const string region = "cn-hangzhou";

        static OssClient CreateClient()
        {
            var conf = new ClientConfiguration();
            conf.SignatureVersion = SignatureVersion.V4;
            var client = new OssClient(endpoint, accessKeyId, accessKeySecret, conf);
            client.SetRegion(region);
            return client;
        }

        static readonly OssClient client = CreateClient();

        static void Main(string[] args)
        {
            AsyncListObjects();
            Console.ReadKey();
        }

        public static void AsyncListObjects()
        {
            try
            {
                var listObjectsRequest = new ListObjectsRequest(bucketName);
                // Begin the async operation and register the callback.
                client.BeginListObjects(listObjectsRequest, ListObjectCallback, null);
                _event.WaitOne();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Async list objects failed. {0}", ex.Message);
            }
        }

        // Called automatically when the listing operation completes.
        private static void ListObjectCallback(IAsyncResult ar)
        {
            try
            {
                var result = client.EndListObjects(ar);
                foreach (var summary in result.ObjectSummaries)
                {
                    Console.WriteLine("Object name: {0}", summary.Key);
                }
                _event.Set();
                Console.WriteLine("Async list objects succeeded");
            }
            catch (Exception ex)
            {
                Console.WriteLine("Async list objects failed. {0}", ex.Message);
            }
        }
    }
}

References

• Complete sample code for synchronous listing: GitHub

• Complete sample code for asynchronous listing: GitHub

• API reference for listing objects: GetBucket (ListObjects)