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Downloading Objects
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Last updated: 2024-02-04 16:51:44
Downloading Objects
Last updated: 2024-02-04 16:51:44
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Overview

This document provides an overview of APIs and SDK code samples for downloading an object.
API
Operation
Description
Downloading an object
Downloads an object to local
Querying object metadata
Queries the metadata of an object

Downloading an object

The download API allows you to pause, resume (via checkpoint restart), or cancel a download task.

Sample code:

    // The advanced download API supports checkpoint restart. Therefore, a HEAD request will be sent before the download to obtain the file information.
    // If you are using a temporary key or accessing with a sub-account, ensure that your permission list includes HeadObject.

    // `CosTransferManger` supports checkpoint restart for download. You only need to ensure the consistency of parameters `bucket`, `cosPath`, and `savePath`.
    // Then the SDK will resume the download from where interrupted.

    // Get `CosTransferManger`
    let cosTransferManger: CosTransferManger = Cos.getDefaultTransferManger();
    //let cosTransferManger: CosTransferManger = Cos.getTransferManger(newRegion);
    // Bucket name in the format of `BucketName-APPID` (`APPID` is required), which can be viewed in the COS console at https://console.cloud.tencent.com/cos5/bucket.
    let bucket = "examplebucket-1250000000";
    let cosPath = "exampleobject"; //Location identifier of the object in the bucket, i.e., the object key
    let downliadPath = "Path of the local file"; // Path of the local file

    // Callback for successful download
    let successCallBack = (header?: object) => {
      // TODO: Logic after successful download
    };
    // Callback for failed download
    let failCallBack = (clientError?: CosXmlClientError, serviceError?: CosXmlServiceError) => {
      // TODO: Logic after failed download
      if (clientError) {
        console.log(clientError);
      }
      if (serviceError) {
        console.log(serviceError);
      }
    };
    // Callback for the download status, through which you can check the task process
    let stateCallBack = (state: TransferState) => {
      // todo notify transfer state
    };
    // Callback for the download progress
    let progressCallBack = (complete: number, target: number) => {
      // todo Do something to download progress...
    };

    // Start the download
    let transferTask:TransferTask = await cosTransferManger.download(
      bucket,
      cosPath,
      downliadPath,
      {
        resultListener: {
          successCallBack: successCallBack,
          failCallBack: failCallBack
        },
        stateCallback: stateCallBack,
        progressCallback: progressCallBack
      }
    );
    // Pause the task
    transferTask.pause();
    // Resume the task
    transferTask.resume();
    // Cancel the task
    transferTask.cancel();

Parameter description

Parameter
Description
Type
Required
bucket
Bucket name in the format of BucketName-APPID. For more information, see Bucket Overview.
String
Yes
cosPath
Object key, which uniquely identifies an object in a bucket. For example, if an object's access endpoint is examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com/doc/picture.jpg, its key is doc/picture.jpg.
String
Yes
savePath
Absolute local path to save the downloaded file
String
Yes
versionId
Version ID of the object to be downloaded
String
No
trafficLimit
Bandwidth limit for a single request in bit/s. Value range: 819200–838860800, i.e., 100 KB/s - 100 MB/s.
Int
No
ResultListener
Callback for the download result (including success and failure)
ResultListener
No
StateCallBack
Callback for the download status
StateCallBack
No
ProgressCallBack
Callback for the download progress
ProgressCallBack
No

Response description

Success: TransferTask is returned. You can pause, resume, or cancel the TransferTask.
Failure: An error (such as authentication failure) occurs, with a CosXmlClientError or CosXmlServiceError exception reported in ResultListener's callback for failure. For more information, see Troubleshooting.
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