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Downloading Objects

Last updated: 2024-02-02 15:51:37

Overview
This document provides an overview of APIs and SDK code samples for downloading an object.
API
Operation
Description
GET Object
Downloading an object
Downloads an object (file) to the local file system
Advanced APIs (Recommended)
Downloading an object
Feature description
The multipart download API automatically downloads data concurrently with Range according to the object size. If you use Range to download an object larger than 16 MB, you can use the PartSize parameter to adjust the part size.
Method prototype
func (s *ObjectService) Download(ctx context.Context, name string, filepath string, opt *MultiDownloadOptions) (*Response, error)
Sample request
package main
﻿
import (
    "context"
    "github.com/tencentyun/cos-go-sdk-v5"
    "net/http"
    "net/url"
    "os"
)
﻿
func main(){
    // Bucket name in the format of `BucketName-APPID` (`APPID` is required), which can be viewed in the COS console at https://console.tencentcloud.com/cos5/bucket.
    // Replace it with your region, which can be viewed in the COS console at https://console.tencentcloud.com/. For more information about regions, visit https://www.tencentcloud.com/document/product/436/6224.
    u, _ := url.Parse("https://examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com")
    b := &cos.BaseURL{BucketURL: u}
    client := cos.NewClient(b, &http.Client{
        Transport: &cos.AuthorizationTransport{
            // Get the key from environment variables
            // Environment variable `SECRETID` refers to the user's `SecretId`, which can be viewed in the CAM console at https://console.tencentcloud.com/cam/capi.
            SecretID: os.Getenv("SECRETID"),  // 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/598/37140?from_cn_redirect=1.
            // Environment variable `SECRETKEY` refers to the user's `SecretKey`, which can be viewed in the CAM console at https://console.tencentcloud.com/cam/capi.
            SecretKey: os.Getenv("SECRETKEY"),  // 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/598/37140?from_cn_redirect=1.
        },
    })
﻿
    key := "exampleobject"
    file := "localfile"
﻿
    opt := &cos.MultiDownloadOptions{
        ThreadPoolSize: 5,
    }
    _, err := client.Object.Download(
        context.Background(), key, file, opt,
    )
    if err != nil{
        panic(err)
    }
}
Field description
type MultiDownloadOptions struct {
    Opt            *ObjectGetOptions
    PartSize       int64
    ThreadPoolSize int
    CheckPoint     bool
    CheckPointFile string
}
Parameter
Description
Type
Required
name
Object key, unique identifier of an object in a bucket. For example, if the object endpoint is examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com/doc/pic.jpg, its object key is doc/pic.jpg.
String
Yes
filepath
Name of the local file
String
Yes
opt
Object download parameter
Struct
No
Opt
Request parameter. For more information, please see ObjectGetOptions.
Struct
No
PartSize
Part size (in MB). If this parameter is not specified or is set to a value smaller than or equal to 0, its value will be automatically determined. In the new version, the default size is 16 (MB).
int64
No
ThreadPoolSize
Size of the thread pool. Default value: 1
Int
No
CheckPoint
Whether to enable checkpoint restart. Default value: false
Bool
No
CheckPointFile
Path to save the download progress file when checkpoint restart is enabled. The default value is &lt;filepath>.cosresumabletask. When the download is completed, this progress file will be cleared.
String
No
Response description
Parameter
Description
Type
*Response
HTTP response, through which you can obtain the response status code, response headers, and other information.
Struct
error
Error message. If no error occurs, nil will be returned.
Struct
Simple Operations
Downloading an object
Feature description
This API (GET Object) is used to download an object (file) to a local file system. Simple downloads and batch downloads are supported.
Method prototype
func (s *ObjectService) Get(ctx context.Context, key string, opt *ObjectGetOptions) (*Response, error)
﻿
func (s *ObjectService) GetToFile(ctx context.Context, key, localfile string, opt *ObjectGetOptions) (*Response, error)
Sample 1: downloading an object
package main
﻿
import (
    "context"
    "github.com/tencentyun/cos-go-sdk-v5"
    "net/http"
    "net/url"
    "io/ioutil"
    "os"
)
﻿
func main(){
    // Bucket name in the format of `BucketName-APPID` (`APPID` is required), which can be viewed in the COS console at https://console.tencentcloud.com/cos5/bucket.
    // Replace it with your region, which can be viewed in the COS console at https://console.tencentcloud.com/. For more information about regions, visit https://www.tencentcloud.com/document/product/436/6224.
    u, _ := url.Parse("https://examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com")
    b := &cos.BaseURL{BucketURL: u}
    client := cos.NewClient(b, &http.Client{
        Transport: &cos.AuthorizationTransport{
            // Get the key from environment variables
            // Environment variable `SECRETID` refers to the user's `SecretId`, which can be viewed in the CAM console at https://console.tencentcloud.com/cam/capi.
            SecretID: os.Getenv("SECRETID"),  // 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/598/37140?from_cn_redirect=1.
            // Environment variable `SECRETKEY` refers to the user's `SecretKey`, which can be viewed in the CAM console at https://console.tencentcloud.com/cam/capi.
            SecretKey: os.Getenv("SECRETKEY"),  // 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/598/37140?from_cn_redirect=1.
        },
    })
﻿
    key := "exampleobject"
    opt := &cos.ObjectGetOptions{
        ResponseContentType: "text/html",
        Range:               "bytes=0-3", // Download the first 4 bytes of data
    }
    // `opt` is optional. It can be set to `nil` unless otherwise specified.
    // 1. Obtain the object from the response body
    resp, err := client.Object.Get(context.Background(), key, opt)
    if err != nil{
        panic(err)
    }
    ioutil.ReadAll(resp.Body)
    resp.Body.Close()
﻿
    // 2. Download the object to the local file system
    _, err = client.Object.GetToFile(context.Background(), key, "example.txt", nil)
    if err != nil{
        panic(err)
    }
}
Sample 2: batch downloading files (downloading a COS directory)
package main
import (
    "context"
    "fmt"
    "net/http"
    "net/url"
    "os"
    "path"
    "strings"
    "sync"
﻿
    "github.com/tencentyun/cos-go-sdk-v5"
)
﻿
func download(wg *sync.WaitGroup, c *cos.Client, keysCh <-chan []string) {
    defer wg.Done()
    for keys := range keysCh {
        key := keys[0]
        filename := keys[1]
        _, err := c.Object.GetToFile(context.Background(), key, filename, nil)
        if err != nil{
            fmt.Println(err)
        }
    }
}
func main(){
    u, _ := url.Parse("https://test-1259654469.cos.ap-guangzhou.myqcloud.com")
    b := &cos.BaseURL{BucketURL: u}
    c := cos.NewClient(b, &http.Client{
            Transport: &cos.AuthorizationTransport{
                // os.Getenv indicates to get the key from environment variables
                SecretID:  os.Getenv("SECRETID"),   // 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/598/37140?from_cn_redirect=1.
                SecretKey: os.Getenv("SECRETKEY"),// 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/598/37140?from_cn_redirect=1.
            },
    })
    // Multi-thread execution
    keysCh := make(chan []string, 3)
    var wg sync.WaitGroup
    threadpool := 3
    for i := 0; i < threadpool; i++ {
            wg.Add(1)
            go download(&wg, c, keysCh)
    }
    isTruncated := true
    prefix := "dir" // Download all files in the `dir` directory
    marker := ""
    localDir := "./local/"
    for isTruncated {
        opt := &cos.BucketGetOptions{
            Prefix:       prefix,
            Marker:       marker,
            EncodingType: "url", // URL code
        }
        // List directories
        v, _, err := c.Bucket.Get(context.Background(), opt)
        if err != nil{
            fmt.Println(err)
            break
        }
        for _, c := range v.Contents {
            key, _ := cos.DecodeURIComponent(c.Key) //EncodingType: "url". Perform URL decoding on the key first.
            localfile := localDir + key
            if _, err := os.Stat(path.Dir(localfile)); err != nil && os.IsNotExist(err) {
                os.MkdirAll(path.Dir(localfile), os.ModePerm)
            }
            // Keys (directories and files) ended with a slash (/) do not need to be downloaded
            if strings.HasSuffix(localfile, "/") {
                continue
            }
            keysCh <- []string{key, localfile}
        }
        marker, _ = cos.DecodeURIComponent(v.NextMarker) // EncodingType: "url". Perform URL decoding on NextMarker first.
        isTruncated = v.IsTruncated
    }
    close(keysCh)
    wg.Wait()
}
Sample 3: limiting single-URL speed
﻿
package main
﻿
import (
    "context"
    "github.com/tencentyun/cos-go-sdk-v5"
    "net/http"
    "net/url"
    "os"
)
﻿
func main(){
    // Bucket name in the format of `BucketName-APPID` (`APPID` is required), which can be viewed in the COS console at https://console.tencentcloud.com/cos5/bucket.
    // Replace it with your region, which can be viewed in the COS console at https://console.tencentcloud.com/. For more information about regions, visit https://www.tencentcloud.com/document/product/436/6224.
    u, _ := url.Parse("https://examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com")
    b := &cos.BaseURL{BucketURL: u}
    client := cos.NewClient(b, &http.Client{
        Transport: &cos.AuthorizationTransport{
            // Get the key from environment variables
            // Environment variable `SECRETID` refers to the user's `SecretId`, which can be viewed in the CAM console at https://console.tencentcloud.com/cam/capi.
            SecretID: os.Getenv("SECRETID"),  // 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/598/37140?from_cn_redirect=1.
            // Environment variable `SECRETKEY` refers to the user's `SecretKey`, which can be viewed in the CAM console at https://console.tencentcloud.com/cam/capi.
            SecretKey: os.Getenv("SECRETKEY"),  // 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/598/37140?from_cn_redirect=1.
        },
    })
﻿
    key := "exampleobject"
    opt := &cos.ObjectGetOptions{
        // 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.
        XCosTrafficLimit: 819200,
    }
    // `opt` is optional. It can be set to `nil` unless otherwise specified.
    // 1. Obtain the object from the response body
    _, err := client.Object.GetToFile(context.Background(), key, "example.txt", opt)
    if err != nil{
        panic(err)
    }
}
Sample 4: obtaining the download progress
The Go SDK allows you to obtain the download progress via a callback. You need to implement the cos.ProgressListener API, which is defined as follows:
const (
    // Data transfer starts.
    ProgressStartedEvent ProgressEventType = iota
    // Transferring data
    ProgressDataEvent
    // Data transfer is completed, which does not mean the completion of the API call.
    ProgressCompletedEvent
    // Returned only when an error occurs during data transfer.
    ProgressFailedEvent
)
type ProgressEvent struct {
    EventType     ProgressEventType
    RWBytes       int64  // Number of bytes read at a time
    ConsumedBytes int64  // Number of bytes completed
    TotalBytes    int64  // Total number of bytes
    Err           error  // Error
}
type ProgressListener interface {
    ProgressChangedCallback(event *ProgressEvent)
}
package main
﻿
import (
    "context"
    "fmt"
    "github.com/tencentyun/cos-go-sdk-v5"
    "io/ioutil"
    "net/http"
    "net/url"
    "os"
)
﻿
type SelfListener struct {
}
﻿
// A custom progress callback, which requires the ProgressChangedCallback method to be implemented.
func (l *SelfListener) ProgressChangedCallback(event *cos.ProgressEvent) {
    switch event.EventType {
    case cos.ProgressDataEvent:
        fmt.Printf("\\r[ConsumedBytes/TotalBytes: %d/%d, %d%%]",
            event.ConsumedBytes, event.TotalBytes, event.ConsumedBytes*100/event.TotalBytes)
    case cos.ProgressFailedEvent:
        fmt.Printf("\\nTransfer Failed: %v", event.Err)
    }
}
func main(){
    // Bucket name in the format of `BucketName-APPID` (`APPID` is required), which can be viewed in the COS console at https://console.tencentcloud.com/cos5/bucket.
    // Replace it with your region, which can be viewed in the COS console at https://console.tencentcloud.com/. For more information about regions, visit https://www.tencentcloud.com/document/product/436/6224.
    u, _ := url.Parse("https://examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com")
    b := &cos.BaseURL{BucketURL: u}
    client := cos.NewClient(b, &http.Client{
        Transport: &cos.AuthorizationTransport{
            // Get the key from environment variables
            // Environment variable `SECRETID` refers to the user's `SecretId`, which can be viewed in the CAM console at https://console.tencentcloud.com/cam/capi.
            SecretID: os.Getenv("SECRETID"),  // 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/598/37140?from_cn_redirect=1.
            // Environment variable `SECRETKEY` refers to the user's `SecretKey`, which can be viewed in the CAM console at https://console.tencentcloud.com/cam/capi.
            SecretKey: os.Getenv("SECRETKEY"),  // 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/598/37140?from_cn_redirect=1.
        },
    })
    key := "exampleobject"
    opt := &cos.ObjectGetOptions{
        ResponseContentType: "text/html",
        // View the progress using the default progress listener.
    Listener: &cos.DefaultProgressListener{},
    }
    // `opt` is optional. It can be set to `nil` unless otherwise specified.
    // 1. Obtain the object from the response body
    resp, err := client.Object.Get(context.Background(), key, opt)
    if err != nil{
        panic(err)
    }
    ioutil.ReadAll(resp.Body)
    resp.Body.Close()
﻿
    // 2. Download the object to the local file system
    // Use the custom progress callback method.
    opt.Listener = &SelfListener{}
    _, err = client.Object.GetToFile(context.Background(), key, "example.txt", opt)
    if err != nil{
        panic(err)
    }
}
Field description
type ObjectGetOptions struct {
    ResponseContentType        string 
    ResponseContentLanguage    string 
    ResponseExpires            string 
    ResponseCacheControl       string 
    ResponseContentDisposition string 
    ResponseContentEncoding    string 
    Range                      string 
    IfModifiedSince            string 
    XCosTrafficLimit           int
    Listener                   ProgressListener
}
Parameter
Description
Type
Required
key
ObjectKey is the unique identifier of an object in a bucket. For example, in the object's access domain name examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com/doc/pic.jpg, the ObjectKey is doc/pic.jpg.
string
Yes
localfile
Name of the file downloaded to the local file system
string
Yes
ResponseContentType
Content-Type of the response header
string
No
ResponseContentLanguage
Content-Language of the response header
string
No
ResponseExpires
Content-Expires of the response header
string
No
ResponseCacheControl
Cache-Control of the response header
string
No
ResponseContentDisposition
Content-Disposition of the response header
string
No
ResponseContentEncoding
Content-Encoding of the response header
string
No
Range
Byte range of the file to download. Format: bytes=first-last
string
No
IfModifiedSince
Returned only if the object is modified after the specified time
string
No
XCosTrafficLimit
Speed limit for a single URL
int
No
Listener
Progress callback API
struct
No
Response description
{
    'Body': '',
    'Accept-Ranges': 'bytes',
    'Content-Type': 'application/octet-stream',
    'Content-Length': '16807',
    'Content-Disposition': 'attachment; filename="filename.jpg"',
    'Content-Range': 'bytes 0-16086/16087',
    'ETag': '"9a4802d5c99dafe1c04da0a8e7e166bf"',
    'Last-Modified': 'Wed, 28 Oct 2014 20:30:00 GMT',
    'X-Cos-Request-Id': 'NTg3NzQ3ZmVfYmRjMzVfMzE5N182NzczMQ=='
}
The result can be obtained from the response.
resp, err := client.Object.Get(context.Background(), key, nil)
body, _ := ioutil.ReadAll(resp.Body)
contentType := resp.Header.Get("Content-Type")
contentLength := resp.Header.Get("Content-Length")
etag := resp.Header.Get("ETag")
reqid := resp.Header.Get("X-Cos-Request-Id")
﻿
Parameter
Description
Type
Body
Content of the downloaded file
StreamBody
File metadata
Metadata of the downloaded file, including ETag and X-Cos-Request-Id. The metadata of the configured file is also returned.
String
﻿

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tencent cloud

Recent Pages

Downloading Objects

Overview

Advanced APIs (Recommended)

Downloading an object

Feature description

Method prototype

Sample request

Field description

Response description

Simple Operations

Downloading an object

Feature description

Method prototype

Sample 1: downloading an object

Sample 2: batch downloading files (downloading a COS directory)

Sample 3: limiting single-URL speed

Sample 4: obtaining the download progress

Field description

Response description

Was this page helpful?

Was this page helpful?

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

Parameter	Description	Type	Required
name	Object key, unique identifier of an object in a bucket. For example, if the object endpoint is `examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com/doc/pic.jpg`, its object key is `doc/pic.jpg`.	String	Yes
filepath	Name of the local file	String	Yes
opt	Object download parameter	Struct	No
Opt	Request parameter. For more information, please see ObjectGetOptions.	Struct	No
PartSize	Part size (in MB). If this parameter is not specified or is set to a value smaller than or equal to 0, its value will be automatically determined. In the new version, the default size is 16 (MB).	int64	No
ThreadPoolSize	Size of the thread pool. Default value: `1`	Int	No
CheckPoint	Whether to enable checkpoint restart. Default value: `false`	Bool	No
CheckPointFile	Path to save the download progress file when checkpoint restart is enabled. The default value is `<filepath>.cosresumabletask`. When the download is completed, this progress file will be cleared.	String	No

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Recent Pages

Downloading Objects

Overview

Advanced APIs (Recommended)

Downloading an object

Feature description

Method prototype

Sample request

Field description

Response description

Simple Operations

Downloading an object

Feature description

Method prototype

Sample 1: downloading an object

Sample 2: batch downloading files (downloading a COS directory)

Sample 3: limiting single-URL speed

Sample 4: obtaining the download progress

Field description

Response description

Was this page helpful?

Was this page helpful?