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Downloading Objects

Last updated: 2022-03-21 14:13:47

    Overview

    This document provides an overview of APIs and SDK code samples related to object download.

    API Operation Description
    GET Object Downloading an object Downloads an object to the local file system.

    SDK API References

    For the parameters and method description of all the APIs in the SDK, see API Documentation.

    Advanced APIs (Recommended)

    Downloading an object (checkpoint restart)

    The advanced version of the GET Object API uses more encapsulated logic to allow you to suspend, resume (via checkpoint restart), or cancel download requests.

    Note:

    • If your .NET Framework version is 4.0 or earlier, advanced APIs are not available. For more information, please see Backward Compatibility.
    • Advanced APIs support concurrent multipart downloads from v5.4.26. To download the latest version of SDK, go to Releases or refer to Getting Started.

    Sample 1. Downloading an object

    using COSXML.Model.Object;
    using COSXML.Auth;
    using COSXML.Transfer;
    using System;
    using COSXML;
    using System.Threading.Tasks;
    namespace COSSnippet
    {
      public class TransferDownloadObjectModel {
         private CosXml cosXml;
         TransferDownloadObjectModel() {
          CosXmlConfig config = new CosXmlConfig.Builder()
            .SetRegion("COS_REGION") // Set the default region. For abbreviations of COS regions, visit https://www.tencentcloud.com/document/product/436/6224?from_cn_redirect=1.
            .Build();
          
          string secretId = "SECRET_ID";   // SecretId of the TencentCloud API. For more information about how to obtain the API key, see https://console.tencentcloud.com/cam/capi.
          string secretKey = "SECRET_KEY"; // SecretKey of the TencentCloud API. For more information about how to obtain the API key, see https://console.tencentcloud.com/cam/capi.
          long durationSecond = 600;          // Validity period of the request signature in seconds
          QCloudCredentialProvider qCloudCredentialProvider = new DefaultQCloudCredentialProvider(secretId, 
            secretKey, durationSecond);
          
          this.cosXml = new CosXmlServer(config, qCloudCredentialProvider);
        }
         /// Download an object via advanced API
        public async Task TransferDownloadObject()
        {
          // Initialize TransferConfig
          TransferConfig transferConfig = new TransferConfig();
          // Manually set the part threshold for advanced APIs to 20 MB (default), which is supported from v5.4.26
          //transferConfig.DivisionForDownload = 20 * 1024 * 1024;
          // Manually set the part size of advanced APIs to 10 MB (default: 5 MB). We recommend you not set the size to a very small value because this may result in frequent retries or unacceptable download speeds.
          //transferConfig.SliceSizeForDownload = 10 * 1024 * 1024;
          
          // Initialize TransferManager
          TransferManager transferManager = new TransferManager(cosXml, transferConfig);
          
          String bucket = "examplebucket-1250000000"; // Bucket name in the format of BucketName-APPID
          String cosPath = "exampleobject"; // 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);
            // Manually set maximum tasks (default: 5) for advanced APIs, which is supported from v5.4.26
          //downloadTask.SetMaxTasks(10);
          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 (COSXML.CosException.CosClientException clientEx)
          {
            // Request failed
            Console.WriteLine("CosClientException: " + clientEx);
          }
          catch (COSXML.CosException.CosServerException serverEx)
          {
            // Request failed
            Console.WriteLine("CosServerException: " + serverEx.GetInfo());
          }
        }
          static void Main(string[] args)
        {
          TransferDownloadObjectModel m = new TransferDownloadObjectModel();
           /// Download an object via advanced API
          m.TransferDownloadObject().Wait();
        }
      }
    }
    
    Note:

    For the complete sample, go to GitHub.

    Sample 2: Setting checkpoint restart for download

    COSXMLDownloadTask downloadTask = new COSXMLDownloadTask(request);
    // Enable checkpoint restart. If an object is not completely downloaded, the download will be started from the checkpoint.
    // If the local file contains content that does not meet the requirements of the current download, the download may fail. You can delete the file and try again.
    downloadTask.SetResumableDownload(true);
    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);
    }
    
    Note:

    For the complete sample, go to GitHub.

    Sample 3: Batch download

    TransferConfig transferConfig = new TransferConfig();
    // Initialize TransferManager
    TransferManager transferManager = new TransferManager(cosXml, transferConfig);
    // Bucket name in the format of `BucketName-APPID`. You can get APPID by referring to https://console.tencentcloud.com/developer.
    string bucket = "examplebucket-1250000000";
    string localDir = System.IO.Path.GetTempPath();// Local file directory
    for (int i = 0; i < 5; i++) {
    // Download an object
    string cosPath = "exampleobject" + i; // Location identifier of an object in the bucket, i.e. the object key
    string localFileName = "my-local-temp-file"; // Filename of the local file
    COSXMLDownloadTask downloadTask = new COSXMLDownloadTask(bucket, cosPath, 
      localDir, localFileName);
    await transferManager.DownloadAsync(downloadTask);
    }
    
    Note:

    For the complete sample, go to GitHub.

    Sample 4: Limiting single-URL download speed

    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"; // 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
           
    GetObjectRequest request = new GetObjectRequest(bucket, 
           cosPath, localDir, localFileName);
    request.LimitTraffic(8 * 1000 * 1024); // Limit the speed to 1 MB/s.
    COSXMLDownloadTask downloadTask = new COSXMLDownloadTask(request);
    await transferManager.DownloadAsync(downloadTask);
    
    Note:

    For the complete sample, go to GitHub.

    Sample 5: Downloading objects from a folder

    using COSXML.Common;
    using COSXML.CosException;
    using COSXML.Model;
    using COSXML.Model.Object;
    using COSXML.Model.Tag;
    using COSXML.Model.Bucket;
    using COSXML.Model.Service;
    using COSXML.Utils;
    using COSXML.Auth;
    using COSXML.Transfer;
    using System;
    using COSXML;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;
    using System.Reflection;
    using System.Text;
    using System.Threading;
    using System.Threading.Tasks;
    namespace COSSnippet
    {
     public class TransferDownloadObjectModel {
        private CosXml cosXml;
       private string nextMarker;
        TransferDownloadObjectModel() {
         CosXmlConfig config = new CosXmlConfig.Builder()
           .SetRegion("COS_REGION") // Set the default region. For abbreviations of COS regions, visit https://www.tencentcloud.com/document/product/436/6224?from_cn_redirect=1.
           .Build();
           
         string secretId = "SECRET_ID";   // SecretId of the TencentCloud API. For more information about how to obtain the API key, see https://console.tencentcloud.com/cam/capi.
         string secretKey = "SECRET_KEY"; // SecretKey of the TencentCloud API. For more information about how to obtain the API key, see https://console.tencentcloud.com/cam/capi.
         long durationSecond = 600;          // Validity period of each request signature in seconds
         QCloudCredentialProvider qCloudCredentialProvider = new DefaultQCloudCredentialProvider(secretId, 
           secretKey, durationSecond);
           
         this.cosXml = new CosXmlServer(config, qCloudCredentialProvider);
     }
        public void GetObjectsFromFolder()
    {
       // Note: There is no actual API for downloading objects from a folder in COS
       // You can download objects from a folder or perform other similar operations by a combination of listing specified prefixes and downloading all the listed object keys.
       // Next, list objects and download them asynchronously.
        String nextMarker = null;
       
        List<string>  downloadList = new List<string>();
        string bucket = "examplebucket-1250000000";
        string prefix = "folder1/"; // Specify a prefix.
        // Request until there is no next page of data
        do
        {
            // Bucket name in the format of `BucketName-APPID`. You can get APPID by referring to https://console.tencentcloud.com/developer.
            GetBucketRequest listRequest = new GetBucketRequest(bucket);
            // Obtain all objects and subdirectories in folder1/.
            listRequest.SetPrefix(prefix);
            listRequest.SetMarker(nextMarker);
            // Execute the list object request.
            GetBucketResult listResult = cosXml.GetBucket(listRequest);
            ListBucket info = listResult.listBucket;
            // List objects
            List<ListBucket.Contents> objects = info.contentsList;
            // nextMarker for the next page
            nextMarker = info.nextMarker;
            
            // List objects
            foreach (var content in objects)
            {
            downloadList.Add(content.key);
            Console.WriteLine("adding key:" + content.key);
            }
      } while (nextMarker != null);
        Console.WriteLine("download list construct done, " + downloadList.Count + " objects added");
            TransferConfig transferConfig = new TransferConfig();
        TransferManager transferManager = new TransferManager(cosXml, transferConfig);
        string localDir = System.IO.Path.GetTempPath();// Local file directory
      
        List<Task> taskList = new List<Task>();
        for (int i = 0; i < downloadList.Count; i++)
        {
            // Traverse the task list and write downloaded contents to the filename_i file.
            COSXMLDownloadTask downloadTask = new COSXMLDownloadTask(bucket, downloadList[i], 
                localDir, "filename_" + i.ToString());
            // Download asynchronously and add to the task list.
            Task task = transferManager.DownloadAsync(downloadTask);
            taskList.Add(task); 
        }
        Console.WriteLine("download tasks submitted, total " + taskList.Count + " tasks added");
        
        //Wait for all tasks in TaskList to finish.
        foreach(Task task in taskList)
        {
            task.Wait();
            Console.WriteLine("download completed");
        }
     }
          static void Main(string[] args)
         {
           TransferDownloadObjectModel m = new TransferDownloadObjectModel();
           /// Download objects from the folder in batches.
           m.GetObjectsFromFolder();
         }
       }
    }
    
    Note:

    For the complete sample, go to GitHub.

    Simple Operations

    Downloading an object

    Description

    This API is used to download an object to the local file system.

    Sample 1: simple download of a single object

    using COSXML.Model.Object;
    using COSXML.Auth;
    using System;
    using COSXML;
    namespace COSSnippet
    {
      public class GetObjectModel {
         private CosXml cosXml;
         GetObjectModel() {
          CosXmlConfig config = new CosXmlConfig.Builder()
            .SetRegion("COS_REGION") // Set the default region. For abbreviations of COS regions, visit https://www.tencentcloud.com/document/product/436/6224?from_cn_redirect=1. 
            .Build();
          
          string secretId = "SECRET_ID";   // SecretId of the TencentCloud API. For more information about how to obtain the API key, see https://console.tencentcloud.com/cam/capi.
          string secretKey = "SECRET_KEY"; // SecretKey of the TencentCloud API. For more information about how to obtain the API key, see https://console.tencentcloud.com/cam/capi.
          long durationSecond = 600;          // Validity period of the request signature in seconds
          QCloudCredentialProvider qCloudCredentialProvider = new DefaultQCloudCredentialProvider(secretId, 
            secretKey, durationSecond);
          
          this.cosXml = new CosXmlServer(config, qCloudCredentialProvider);
        }
         /// Download an object
        public void GetObject()
        {
          //.cssg-snippet-body-start:[get-object]
          try
          {
            // Bucket name in the format of `BucketName-APPID`. You can get APPID by referring to https://console.tencentcloud.com/developer.
            string bucket = "examplebucket-1250000000";
            string key = "exampleobject"; // Object key
            string localDir = System.IO.Path.GetTempPath();// Local file directory
            string localFileName = "my-local-temp-file"; // Filename of the local file
            GetObjectRequest request = new GetObjectRequest(bucket, key, localDir, localFileName);
            // Set the progress callback
            request.SetCosProgressCallback(delegate (long completed, long total)
            {
              Console.WriteLine(String.Format("progress = {0:##.##}%", completed * 100.0 / total));
            });
            // Execute the request
            GetObjectResult result = cosXml.GetObject(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());
          }
        }
         static void Main(string[] args)
        {
          GetObjectModel m = new GetObjectModel();
          /// Download an object
          m.GetObject();
        }
      }
    }
    
    Note:

    For the complete sample, go to GitHub.

    Sample 2: downloading an object to memory

    using COSXML.Model.Object;
    using COSXML.Auth;
    using System;
    using COSXML;
    namespace COSSnippet
    {
      public class GetObjectModel {
         private CosXml cosXml;
         GetObjectModel() {
          CosXmlConfig config = new CosXmlConfig.Builder()
            .SetRegion("COS_REGION") // Set the default region. For abbreviations of COS regions, visit https://www.tencentcloud.com/document/product/436/6224?from_cn_redirect=1. 
            .Build();
          
          string secretId = "SECRET_ID";   // SecretId of the TencentCloud API. For more information about how to obtain the API key, see https://console.tencentcloud.com/cam/capi.
          string secretKey = "SECRET_KEY"; // SecretKey of the TencentCloud API. For more information about how to obtain the API key, see https://console.tencentcloud.com/cam/capi.
          long durationSecond = 600;          // Validity period of the request signature in seconds
          QCloudCredentialProvider qCloudCredentialProvider = new DefaultQCloudCredentialProvider(secretId, 
            secretKey, durationSecond);
          
          this.cosXml = new CosXmlServer(config, qCloudCredentialProvider);
        }
         /// Download the returned bytes data
        public void downloadToMem() {
          try
          {
            // Bucket name in the format of `BucketName-APPID`. You can get APPID by referring to https://console.tencentcloud.com/developer.
            string bucket = "examplebucket-1250000000";
            string key = "exampleobject"; // Object key
          
            GetObjectBytesRequest request = new GetObjectBytesRequest(bucket, key);
            // Set the progress callback
            request.SetCosProgressCallback(delegate (long completed, long total)
            {
              Console.WriteLine(String.Format("progress = {0:##.##}%", completed * 100.0 / total));
            });
            // Execute the request
            GetObjectBytesResult result = cosXml.GetObject(request);
            // Get content for the byte array
            byte[] content = result.content;
            // 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());
          }
        }
         // .cssg-methods-pragma
         static void Main(string[] args)
        {
          GetObjectModel m = new GetObjectModel();
           /// Download the object to memory
          m.downloadToMem();
          // .cssg-methods-pragma
        }
      }
    }
    
    Note:

    For the complete sample, go to GitHub.

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