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DocumentationCloud Object StorageSDK DocumentationNode.js SDKObject OperationsDownloading Objects
Downloading Objects
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Last updated: 2024-02-04 11:37:31
Downloading Objects
Last updated: 2024-02-04 11:37:31
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Overview

Note:
This API is used to read object content. To download a file using your browser, you should first get a download URL through the cos.getObjectUrl method. For more information, please see Pre-signed URLs.
This document provides an overview of APIs and SDK code samples related to object downloads.
API
Operation
Description
Downloading an object
Downloads an object to the local file system.

Simple Operations

Downloading a Single Object

Description

This API (GET Object) is used to download an object in a COS bucket to a local file system. To call this API, you need to have permission to read the object, or the object is set to public-read.

Sample code

cos.getObject({
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */
    Key: '1.jpg',  /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
}, function(err, data) {
    console.log(err || data.Body);
});
Getting file content with Range specified
cos.getObject({
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */
    Key: '1.jpg',  /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
    Range: 'bytes=1-3', /*Optional*/
}, function(err, data) {
    console.log(err || data.Body);
});
Download the file to a specified path:
cos.getObject({
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */
    Key: '1.jpg',  /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
    Output: './exampleobject',
}, function(err, data) {
    console.log(err || data);
});
Download the file to a specified write file stream:
cos.getObject({
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */
    Key: '1.jpg',  /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
    Output: fs.createWriteStream('./exampleobject'),
}, function(err, data) {
    console.log(err || data);
});
Downloading an object (limiting single-URL speed):
Note:
For more information about the speed limits on object downloads, please see Single-URL Speed Limits.
cos.getObject({
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */
    Key: '1.jpg',  /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
    Headers: {
      'x-cos-traffic-limit': 819200, // The speed range is 819200 to 838860800, that is 100 KB/s to 100 MB/s. If the value is not within this range, 400 will be returned.
    },
}, function(err, data) {
    console.log(err || data.Body);
});

Parameter description

Parameter
Description
Type
Required
Bucket
Bucket name in the format of BucketName-APPID
String
Yes
Region
Bucket region. For the enumerated values, please see Regions and Access Endpoints.
String
Yes
Key
Object key (object name), the unique ID of an object in a bucket. For more information, please see Object Overview.
String
Yes
Output
An output file path or a write stream. If this parameter is specified, the full content will be written to data in the callback function.
String/WriteStream
No
ResponseContentType
Sets the Content-Type parameter in the response header.
String
No
ResponseContentLanguage
Sets the Content-Language parameter in the response header.
String
No
ResponseExpires
Sets the Content-Expires parameter in the response header.
String
No
ResponseCacheControl
Sets the Cache-Control parameter in the response header.
String
No
ResponseContentDisposition
Sets the Content-Disposition parameter in the response header.
String
No
ResponseContentEncoding
Sets the Content-Encoding parameter in the response header.
String
No
Range
Byte range of the object as defined in RFC 2616. The range value must be in the format of bytes=first-last, where both first and last are offsets starting from 0. For example, bytes=0-9 means that you want to copy the first 10 bytes of data of the source object. If this parameter is not specified, the entire object will be downloaded.
String
No
If-Modified-Since
If the object is modified after the specified time, the corresponding object metadata will be returned; otherwise, "304 (not modified)" will be returned.
String
No
If-Unmodified-Since
If the object is not modified after the specified time, the object will be returned; otherwise, "412 (precondition failed)" will be returned.
String
No
IfMatch
The object will be returned only if the value of ETag matches the specified content; otherwise, "412 (precondition failed)" will be returned.
String
No
IfNoneMatch
The file will be returned only if the value of ETag does not match the specified content; otherwise, "304 (not modified)" will be returned.
String
No
VersionId
Version ID of the object to download
String
No
onProgress
Callback of the progress. Attributes of the response object progressData are as follows:
Function
No
- progressData.loaded
Size of the downloaded parts, in bytes
Number
No
- progressData.total
Size of the entire object, in bytes
Number
No
- progressData.speed
Download speed, in bytes/s
Number
No
- progressData.percent
Percentage of the file download progress, in decimal form. For example, 0.5 means 50% has been downloaded.
Number
No

Callback function description

function(err, data) { ... }
Parameter
Description
Type
err
Object returned when an error (network error or service error) occurs. If the request is successful, this is null. For more information, see Error Codes.
Object
- statusCode
HTTP status code, such as 200, 403, and 404.
Number
- headers
Headers.
Object
data
Content returned when the request is successful. If the request fails, this parameter is empty.
Object
- statusCode
Returns an HTTP status code, such as 200, 304, 403, and 404
Number
- headers
Headers.
Object
- Cache-Control
Cache directives as defined in RFC 2616. It will be returned only if it is contained in the object metadata or specified through the request parameter.
String
- Content-Disposition
Filename as defined in RFC 2616. It will be returned only if it is contained in the object metadata or specified through the request parameter.
String
- ContentEncoding
Encoding format as defined in RFC 2616. It will be returned only if it is contained in the object metadata or specified through the request parameter.
String
- Expires
Cache expiration time as defined in RFC 2616. It will be returned only if it is contained in the object metadata or specified through the request parameter.
string
- x-cos-storage-class
Storage class of the object. Enumerated values: STANDARD, STANDARD_IA, ARCHIVE
Note: If this header is not returned, the storage class is automatically set to STANDARD
String
- x-cos-meta-*
User-defined metadata
String
- NotModified
This attribute will be returned if the request contains IfModifiedSince. If the file has been modified, false will be returned. If not, true will be returned.
Boolean
- ETag
MD5 checksum of the object. The value of ETag can be used to check whether the object was corrupted during the upload.
Example: "09cba091df696af91549de27b8e7d0f6"
Note that double quotation marks are required at the beginning and the end.
String
- VersionId
Version ID of the uploaded object if versioning is enabled for its bucket. If versioning is not enabled, this parameter is not returned.
String
- Body
Content of the returned file. The default form is buffer.
Buffer

Downloading multiple objects

Sample code

Download multiple objects with a specified prefix (download objects from a specified directory):
var config = {
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION',  /* Bucket region, such as `ap-beijing`. Required. */ 
}

// Example of how to create a directory recursively. You can implement it by yourself.
function mkdirsSync(dirname) {
  if(fs.existsSync(dirname)) {
    return true;
  }else{
    if(mkdirsSync(path.dirname(dirname))) {
      fs.mkdirSync(dirname);
      return true;
    }
  }
}

// Download a single object
function downloadItem(Key, downloadPath) {
    cos.getObject({
      Bucket: config.Bucket,
      Region: config.Region,
      Key: Key,
      Output: fs.createWriteStream(downloadPath),
    },
    function(err, data) {
        console.log(err || data);
    });
}

// Download multiple objects
function batchDownload(marker = undefined) {
  cos.getBucket({
    Bucket: config.Bucket,
    Region: config.Region,
    Prefix: '1',  // Search for all objects with prefix '1'
    Marker:       marker,
    MaxKeys: 1000,
  },
  function (listError, listResult) {
    if (listError) return console.log(listError);
    // Download to the 'download' directory under this directory
    var localPath = 'download';
    listResult.Contents.forEach(function (item) {
      var downloadPath = path.resolve(localPath, item.Key);
      var pathParse = path.parse(item.Key);
      if (pathParse.dir) {
        // If the downloaded object is in a multi-level directory, create a corresponding directory locally.
        // For example, if the Key is a/b/1.png, create a directory structure 'a/b' locally 
        var mkdir = path.resolve(localPath, pathParse.dir);
        mkdirsSync(mkdir);
        downloadItem(item.Key, downloadPath);
      } else {
        downloadItem(item.Key, downloadPath);
      }
    });
  })
}
batchDownload();

Advanced Operations (Recommended)

Multipart download

Description

This API is used to implement multipart download. It supports concurrent part download.(The sdk version is required to be at least v2.9.14)

Method prototype

Multipart download sample:
var Key = 'test.zip';
cos.downloadFile({
    Bucket: 'examplebucket-1250000000',
    Region: 'ap-beijing',
    Key: Key,
    FilePath: './' + Key, // Local path
    ChunkSize: 1024 * 1024 * 8, // Part size
    ParallelLimit: 5, // Number of concurrent parts
    RetryTimes: 3, // Number of retries for multipart download failures
    TaskId: '123', // TaskId can be automatically generated for canceling the download

    onProgress: function (progressData) {
        console.log(JSON.stringify(progressData));
    },
}, function (err, data) {
    console.log(err || data);
});

// Cancel the download task.
// cos.emit('inner-kill-task', {TaskId: '123'});

Parameter description

Parameter
Description
Type
Required
Bucket
Bucket name, formatted as BucketName-APPID
String
Yes
Region
Bucket region. For the enumerated values, please see Regions and Access Endpoints.
String
Yes
Key
Object key (object name), the unique ID of an object in a bucket. For more information, please see Object Overview.
String
Yes
FilePath
Path to store the downloaded file
String
Yes
ChunkSize
Part size
Number
No
ParallelLimit
Number of parts to download concurrently
Number
No
RetryTimes
Number of retries for multipart download failures
Number
No
onProgress
Download progress
String
No
- progressData.loaded
Size of the uploaded parts, in bytes
Number
No
- progressData.total
Size of the entire file, in bytes
Number
No
- progressData.speed
File upload speed, in bytes/s
Number
No
- progressData.percent
Percentage of the file upload progress, in decimal form. For example, 0.5 means 50% has been uploaded.
Number
No

Callback function description

function(err, data) { ... }
Parameter
Description
Type
err
Error code, which is returned when an error (network error or service error) occurs. If the request is successful, this parameter is empty. For more information, please see Error Codes.
Object
- statusCode
HTTP status code, such as 200, 403, and 404
Number
- headers
Headers
Object
data
Content returned when the request is successful. If the request fails, this parameter is empty.
Object
- statusCode
Returns an HTTP status code, such as 200, 304, 403, and 404
Number
- headers
Headers.
Object
- Cache-Control
Cache directives as defined in RFC 2616. It will be returned only if it is contained in the object metadata or specified through the request parameter.
String
- Content-Disposition
Filename as defined in RFC 2616. It will be returned only if it is contained in the object metadata or specified through the request parameter.
String
- ContentEncoding
Encoding format as defined in RFC 2616. It will be returned only if it is contained in the object metadata or specified through the request parameter.
String
- Expires
Cache expiration time as defined in RFC 2616. It will be returned only if it is contained in the object metadata or specified through the request parameter.
string
- x-cos-storage-class
Storage class of the object. Enumerated values: STANDARD, STANDARD_IA, ARCHIVE
Note: If this header is not returned, the storage class is automatically set to STANDARD
String
- x-cos-meta-*
User-defined metadata
String
- NotModified
This attribute will be returned if the request contains IfModifiedSince. If the file has been modified, false will be returned. If not, true will be returned.
Boolean
- ETag
MD5 checksum of the object. The value of ETag can be used to check whether the object was corrupted during the upload.
Example: "09cba091df696af91549de27b8e7d0f6"
Note that double quotation marks are required at the beginning and the end.
String
- VersionId
Version ID of the uploaded object if versioning is enabled for its bucket. If versioning is not enabled, this parameter is not returned.
String

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