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Getting Started
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Last updated: 2025-03-28 10:16:46
Getting Started
Last updated: 2025-03-28 10:16:46
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Resources

Download the XML .NET SDK source code here.
Download XML .NET SDK here.
Find the complete code here.
For the SDK changelog, see Changelog.
For SDK FAQs, see .NET (C#) SDK FAQs.
Note:
If you encounter errors such as non-existent functions or methods when using the SDK, you can update the SDK to the latest version and try again.

Step 1. Integrate the SDK

Environmental dependencies

The .NET SDK is developed based on .NET Standard 2.0.
Windows: Install .NET Core 2.0 or above or .NET Framework 4.5 or above.
For Linux/Mac users: Install .NET Core 2.0 or above.

Installing the SDK

You can install the SDK using NuGet by adding the following to the csproj file in your project:
<PackageReference Include="Tencent.QCloud.Cos.Sdk" Version="5.4.*" />
If .NET CLI is used instead, run the following command:
dotnet add package Tencent.QCloud.Cos.Sdk
If you develop for the target framework .Net Framework 4.0 or below, please download Releases and use COSXML-Compatible.dll.
In your Visual Studio project, click Project > Add Reference > Browse > COSXML-Compatible.dll to add the .NET(C#) SDK.
Note:
The compatible package does not support features such as advanced upload and download. For details, see Backward Compatibility.

Step 2. Initialize COS Services

Caution:
We recommend you use a temporary key as instructed in Generating and Using Temporary Keys to call the SDK for security purposes. When you apply for a temporary key, follow the Notes on Principle of Least Privilege to avoid leaking resources besides your buckets and objects.
If you must use a permanent key, we recommend you follow the Notes on Principle of Least Privilege to limit the scope of permission on the permanent key.
The section below describes how to perform basic COS operations with the .NET SDK, such as initializing a client, creating a bucket, querying a bucket list, uploading an object, querying an object list, downloading an object, and deleting an object.
Note:
For the definition of terms such as SecretId, SecretKey, and Bucket, see COS Glossary.
Namespaces commonly used in this SDK include:
using COSXML;
using COSXML.Auth;
using COSXML.Model.Object;
using COSXML.Model.Bucket;
using COSXML.CosException;
Before making any COS requests, always instantiate the following 3 objects: CosXmlConfig, QCloudCredentialProvider, and CosXmlServer.
CosXmlConfig provides an API to configure SDK.
QCloudCredentialProvider provides an API to set the key information.
CosXmlServer provides APIs to perform operations on COS API services.
Note:
The initialization sample below uses a temporary key. For more information about how to generate and use a temporary key, see Generating and Using Temporary Keys.

1. Initialize a COS service

// Initialize CosXmlConfig. 
string appid = "1250000000";// Set the APPID of your Tencent Cloud account.
string region = "COS_REGION"; // Set the default bucket region.
CosXmlConfig config = new CosXmlConfig.Builder()
  .IsHttps(true)  // Set HTTPS as default request method.
  .SetRegion(region)  // Set the default bucket region.
  .SetDebugLog(true)  // Display logs.
  .Build();  // Create a CosXmlConfig object.

2. Provide access credentials

The SDK supports three types of access credentials: updated temporary keys, unchanging temporary keys, and permanent keys.
Type 1: updated temporary key
Since temporary keys are short term, you can obtain new ones using the following method:
public class CustomQCloudCredentialProvider : DefaultSessionQCloudCredentialProvider
{

  // Even if you do not already have a current temporary key, you can still use this method.
  public CustomQCloudCredentialProvider(): base(null, null, 0L, null) {
    ;
  }

  public override void Refresh()
  {
    //... First, request a temporary key from Tencent Cloud.
    string tmpSecretId = "SECRET_ID"; // SecretId of a temporary key. For more information about how to generate and use a temporary key, visit https://intl.cloud.tencent.com/document/product/436/14048.
    string tmpSecretKey = "SECRET_KEY"; // SecretKey of a temporary key. For more information about how to generate and use a temporary key, visit https://intl.cloud.tencent.com/document/product/436/14048.
    string tmpToken = "COS_TOKEN"; // Token of a temporary key. For more information about how to generate and use a temporary key, visit https://intl.cloud.tencent.com/document/product/436/14048.
    long tmpStartTime = 1546860702;// Start time in seconds of the temporary key’s validity period
    long tmpExpireTime = 1546862502;// End time in seconds of the temporary key’s validity period
    // Call the API to update the key
    SetQCloudCredential(tmpSecretId, tmpSecretKey, 
      String.Format("{0};{1}", tmpStartTime, tmpExpiredTime), tmpToken);
  }
}

QCloudCredentialProvider cosCredentialProvider = new CustomQCloudCredentialProvider();
Type 2: unchanging temporary key (not recommended)
Caution:
This method is not recommended as a request may fail if the temporary key has expired at the time of request.
string tmpSecretId = "SECRET_ID"; // “SecretId of the temporary key”;
string tmpSecretKey = "SECRET_KEY"; // “SecretKey of the temporary key”;
string tmpToken = "COS_TOKEN"; // “Token of the temporary key”;
long tmpExpireTime = 1546862502;// End time in seconds of the temporary key’s validity period
QCloudCredentialProvider cosCredentialProvider = new DefaultSessionQCloudCredentialProvider(
  tmpSecretId, tmpSecretKey, tmpExpireTime, tmpToken);
Type 3: permanent key (not recommended)
string secretId = Environment.GetEnvironmentVariable("SECRET_ID"); // User `SecretId`. We recommend you use a sub-account key and follow the principle of least privilege to reduce risks. For information about how to obtain a sub-account key, visit https://www.tencentcloud.com/document/product/598/32675.
string secretKey = Environment.GetEnvironmentVariable("SECRET_KEY"); // User `SecretKey`. We recommend you use a sub-account key and follow the principle of least privilege to reduce risks. For information about how to obtain a sub-account key, visit https://www.tencentcloud.com/document/product/598/32675.
long durationSecond = 600;          // Validity period of each request signature in seconds
QCloudCredentialProvider cosCredentialProvider = new DefaultQCloudCredentialProvider(
  secretId, secretKey, durationSecond);

3. Initialize CosXmlServer

Use CosXmlConfig and QCloudCredentialProvider to initialize the CosXmlServer service class. We recommend you use the service class as a singleton in your project.
CosXml cosXml = new CosXmlServer(config, cosCredentialProvider);

Step 3. Access COS

Creating a bucket

try
{
  String bucket = "examplebucket-1250000000"; // Format: BucketName-APPID
  PutBucketRequest request = new PutBucketRequest(bucket);
  // Execute the request
  PutBucketResult result = cosXml.PutBucket(request);
  // Request succeeded
  Console.WriteLine(result.GetResultInfo());
}
catch (COSXML.CosException.CosClientException clientEx)
{
  // Request failed
  Console.WriteLine("CosClientException: " + clientEx);
}
catch (COSXML.CosException.CosServerException serverEx)
{
  // Request failed
  Console.WriteLine("CosServerException: " + serverEx.GetInfo());
}

Querying the bucket list

try
{
  GetServiceRequest request = new GetServiceRequest();
  // Execute the request
  GetServiceResult result = cosXml.GetService(request);
  // Get the list of all buckets.
  List<ListAllMyBuckets.Bucket> allBuckets = result.listAllMyBuckets.buckets;
}
catch (COSXML.CosException.CosClientException clientEx)
{
  // Request failed
  Console.WriteLine("CosClientException: " + clientEx);
}
catch (COSXML.CosException.CosServerException serverEx)
{
  // Request failed
  Console.WriteLine("CosServerException: " + serverEx.GetInfo());
}

Uploading an object

// Initialize TransferConfig
TransferConfig transferConfig = new TransferConfig();

// Initialize TransferManager
TransferManager transferManager = new TransferManager(cosXml, transferConfig);

String bucket = "examplebucket-1250000000"; // Bucket name in the format of BucketName-APPID
String cosPath = "exampleobject"; // The location identifier of the object in the bucket, i.e., the object key
String srcPath = @"temp-source-file";// Absolute path to the local file

// Upload an object
COSXMLUploadTask uploadTask = new COSXMLUploadTask(bucket, cosPath);
uploadTask.SetSrcPath(srcPath);

uploadTask.progressCallback = delegate (long completed, long total)
{
    Console.WriteLine(String.Format("progress = {0:##.##}%", completed * 100.0 / total));
};

try {
  COSXML.Transfer.COSXMLUploadTask.UploadTaskResult result = await 
    transferManager.UploadAsync(uploadTask);
  Console.WriteLine(result.GetResultInfo());
  string eTag = result.eTag;
} catch (Exception e){
    Console.WriteLine("CosException: " + e);
}

Querying objects

try
{
  String bucket = "examplebucket-1250000000"; // Format: BucketName-APPID
  GetBucketRequest request = new GetBucketRequest(bucket);
  // Execute the request
  GetBucketResult result = cosXml.GetBucket(request);
  // Bucket information
  ListBucket info = result.listBucket;
  if (info.isTruncated) {
    // The data is truncated, and the next marker of the data is recorded.
    this.nextMarker = info.nextMarker;
  }
}
catch (COSXML.CosException.CosClientException clientEx)
{
  // Request failed
  Console.WriteLine("CosClientException: " + clientEx);
}
catch (COSXML.CosException.CosServerException serverEx)
{
  // Request failed
  Console.WriteLine("CosServerException: " + serverEx.GetInfo());
}

Downloading an object

// Initialize TransferConfig
TransferConfig transferConfig = new TransferConfig();

// Initialize TransferManager
TransferManager transferManager = new TransferManager(cosXml, transferConfig);

String bucket = "examplebucket-1250000000"; // Bucket name in the format of BucketName-APPID
String cosPath = "exampleobject"; // The location identifier of the object in the bucket, i.e., the object key
string localDir = System.IO.Path.GetTempPath();// Local file directory
string localFileName = "my-local-temp-file"; // Filename of the local file

// Download an object
COSXMLDownloadTask downloadTask = new COSXMLDownloadTask(bucket, cosPath, 
  localDir, localFileName);

downloadTask.progressCallback = delegate (long completed, long total)
{
    Console.WriteLine(String.Format("progress = {0:##.##}%", completed * 100.0 / total));
};

try {
  COSXML.Transfer.COSXMLDownloadTask.DownloadTaskResult result = await 
    transferManager.DownloadAsync(downloadTask);
  Console.WriteLine(result.GetResultInfo());
  string eTag = result.eTag;
} catch (Exception e){
    Console.WriteLine("CosException: " + e);
}

Deleting an object

try
{
  string bucket = "examplebucket-1250000000"; // Bucket name in the format of BucketName-APPID
  string key = "exampleobject"; // Object key
  DeleteObjectRequest request = new DeleteObjectRequest(bucket, key);
  // Execute the request
  DeleteObjectResult result = cosXml.DeleteObject(request);
  // Request succeeded
  Console.WriteLine(result.GetResultInfo());
}
catch (COSXML.CosException.CosClientException clientEx)
{
  // Request failed
  Console.WriteLine("CosClientException: " + clientEx);
}
catch (COSXML.CosException.CosServerException serverEx)
{
  // Request failed
  Console.WriteLine("CosServerException: " + serverEx.GetInfo());
}

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