Help Center/ Object Storage Service/ SDK Reference/ Go/ Objects (SDK for Go)/ Object Download Overview (SDK for Go)/ Downloading an Object - Range-Based (SDK for Go)
Updated on 2024-09-05 GMT+08:00
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Downloading an Object - Range-Based (SDK for Go)

Function

This API downloads partial data of an object by specifying a range. If the specified range is from 0 to 1,000, data at the 0th to the 1,000th bytes, 1,001 bytes in total, will be returned. If the specified range is invalid, the whole object data will be returned.

Restrictions

  • To download an object, you must be the bucket owner or have the required permission (obs:object:GetObject in IAM or GetObject in a bucket policy). For details, see Introduction to OBS Access Control, IAM Custom Policies, and Configuring an Object Policy.
  • Objects in the Archive storage class can be downloaded only when they are in the Restored status.
  • If the specified range is invalid (for example, the start or end position is set to a negative integer or the range is larger than the object length), the whole object data will be returned.

Method

func (obsClient ObsClient) GetObject(input *GetObjectInput) (output *GetObjectOutput, err error)

Request Parameters

Table 1 List of request parameters

Parameter

Type

Mandatory (Yes/No)

Description

input

*GetObjectInput

Yes

Explanation:

Input parameters for a partial download. For details, see Table 2.
Table 2 GetObjectInput

Parameter

Type

Mandatory (Yes/No)

Description

Bucket

string

Yes

Explanation:

Bucket name

Restrictions:

  • A bucket name must be unique across all accounts and regions.
  • A bucket name:
    • Must be 3 to 63 characters long and start with a digit or letter. Lowercase letters, digits, hyphens (-), and periods (.) are allowed.
    • Cannot be formatted as an IP address.
    • Cannot start or end with a hyphen (-) or period (.).
    • Cannot contain two consecutive periods (..), for example, my..bucket.
    • Cannot contain a period (.) and a hyphen (-) adjacent to each other, for example, my-.bucket or my.-bucket.
  • If you repeatedly create buckets of the same name in the same region, no error will be reported and the bucket attributes comply with those set in the first creation request.

Default value:

None

Key

string

Yes

Explanation:

Object name. An object is uniquely identified by an object name in a bucket. An object name is a complete path that does not contain the bucket name.

For example, if the address for accessing the object is examplebucket.obs.eu-west-101.myhuaweicloud.com/folder/test.txt, the object name is folder/test.txt.

Value range:

The value must contain 1 to 1,024 characters.

Default value:

None

ResponseCacheControl

string

No

Explanation:

Cache-Control header in the response. It specifies the cache behavior of the web page when the object is downloaded.

Default value:

None

ResponseContentDisposition

string

No

Explanation:

Content-Disposition header in the response. It specifies the name of the object when it is downloaded.

Default value:

None

ResponseContentEncoding

string

No

Explanation:

Content-Encoding header in the response. It specifies the content encoding format when an object is downloaded.

Default value:

None

ResponseContentLanguage

string

No

Explanation:

Content-Language header in the response. It specifies the content language format when an object is downloaded.

Default value:

None

ResponseContentType

string

No

Explanation:

Content-Type header in the response. It specifies the object file type.

Default value:

None

ResponseExpires

string

No

Explanation:

Expires header in the response. It specifies the cache expiration time of the web page when the object is downloaded.

Default value:

None

VersionId

string

No

Explanation:

Object version ID. Example: G001117FCE89978B0000401205D5DC9

Value range:

The value must contain 32 characters.

Default value:

None. If this parameter is left blank, the latest version of the object is obtained.

RangeStart

int64

No

Explanation:

Start position for object download

Value range:

0 to the object length, in bytes.

Default value:

0, indicating the download starts from the first byte of the object.

RangeEnd

int64

No

Explanation:

End position for object download

Value range:

  • The value must be greater than that of RangeStart.
  • The upper limit of the value is the object length minus 1, in bytes.

Default value:

None

IfMatch

string

No

Explanation:

Preset ETag. If the ETag of the object to be downloaded is the same as the preset ETag, the object is returned. Otherwise, an error is returned.

Value range:

The value must contain 32 characters.

Default value:

None

IfNoneMatch

string

No

Explanation:

Preset ETag. If the ETag of the object to be downloaded is different from the preset ETag, the object is returned. Otherwise, an error is returned.

Value range:

The value must contain 32 characters.

Default value:

None

IfModifiedSince

time.Time

No

Explanation:

The object is returned if it has been modified since the specified time; otherwise, an error is returned.

Restrictions:

The time must be in the ISO8601 format, for example, 2018-01-01T00:00:00.000Z.

Sample code: time.Now().Add(time.Duration(24) * time.Hour)

Default value:

None

IfUnmodifiedSince

time.Time

No

Explanation:

The object is returned if it has not been modified since the specified time; otherwise, an error is returned.

Restrictions:

The time must be in the ISO8601 format, for example, 2018-01-01T00:00:00.000Z.

Sample code: time.Now().Add(time.Duration(24) * time.Hour)

Default value:

None

SseHeader

SseCHeader

No

Explanation:

Server-side decryption headers. For details, see Table 3.

Restrictions:

If the object uploaded to a server is encrypted with the key provided by the client, the key must also be provided in the message for downloading the object.
Table 3 SseCHeader

Parameter

Type

Mandatory (Yes/No)

Description

Encryption

string

Yes if used as a request parameter

Explanation:

SSE-C used for encrypting objects

Value range:

AES256, indicating objects are encrypted using SSE-C

Default value:

None

Key

string

Yes if used as a request parameter

Explanation:

Key for encrypting the object when SSE-C is used

Restrictions:

The value is a Base64-encoded 256-bit key, for example, K7QkYpBkM5+hca27fsNkUnNVaobncnLht/rCB2o/9Cw=.

Default value:

None

KeyMD5

string

No if used as a request parameter

Explanation:

MD5 value of the key for encrypting objects when SSE-C is used. This value is used to check whether any error occurs during the transmission of the key.

Restrictions:

The value is encrypted by MD5 and then encoded by Base64, for example, 4XvB3tbNTN+tIEVa0/fGaQ==.

Default value:

None

Responses

Table 4 List of returned results

Parameter

Type

Description

output

*GetObjectOutput

Explanation:

Returned results. For details, see Table 5.

err

error

Explanation:

Error messages returned by the API
Table 5 GetObjectOutput

Parameter

Type

Description

StatusCode

int

Explanation:

HTTP status code

Value range:

A status code is a group of digits that can be 2xx (indicating successes) or 4xx or 5xx (indicating errors). It indicates the status of a response. For more information, see Status Code.

Default value:

None

RequestId

string

Explanation:

Request ID returned by the OBS server

Default value:

None

ResponseHeaders

map[string][]string

Explanation:

HTTP response headers

Default value:

None

Body

io.ReadCloser

Explanation:

Object data stream to download

Default value:

None

DeleteMarker

bool

Explanation:

Whether the deleted object is a delete marker

Value range:

  • true: The deleted object is a delete marker.
  • false: The deleted object is not a delete marker.

Default value:

false

StorageClass

StorageClassType

Explanation:

Object storage class

Value range:

See Table 6.

Default value:

None

AllowOrigin

string

Explanation:

If Origin in the request meets the CORS rules of the bucket, AllowedOrigin specified in the CORS rules is returned. AllowedOrigin indicates the origin from which the requests can access the bucket.

Restrictions:

Domain name of the origin. Each origin can contain only one wildcard character (*), for example, https://*.vbs.example.com.

Default value:

None

AllowHeader

string

Explanation:

If RequestHeader in the request meets the CORS rules of the bucket, AllowedHeader specified in the CORS rules is returned. AllowedHeader indicates the allowed headers for cross-origin requests. Only CORS requests matching the allowed headers are valid.

Restrictions:

Each header can contain only one wildcard character (*). Spaces, ampersands (&), colons (:), and less-than signs (<) are not allowed.

Default value:

None

AllowMethod

string

Explanation:

AllowedMethod in the CORS rules of the bucket. It specifies the HTTP method of cross-origin requests, that is, the operation type of buckets and objects.

Value range:

The following HTTP methods are supported:

  • GET
  • PUT
  • HEAD
  • POST
  • DELETE

Default value:

None

ExposeHeader

string

Explanation:

ExposeHeader in the CORS rules of the bucket. It specifies the CORS-allowed additional headers in the response. These headers provide additional information to clients. By default, your browser can only access headers Content-Length and Content-Type. If your browser needs to access other headers, add them to a list of the allowed additional headers.

Restrictions:

Spaces, wildcard characters (*), ampersands (&), colons (:), and less-than signs (<) are not allowed.

Default value:

None

MaxAgeSeconds

int

Explanation:

MaxAgeSeconds in the CORS rules of the bucket. It specifies the time your client can cache the response for a cross-origin request.

Restrictions:

Each CORS rule can specify only one value for MaxAgeSeconds.

Value range:

0 to (231 – 1), in seconds

Default value:

100

ContentLength

int64

Explanation:

Object size in bytes

Value range:

The value ranges from 0 TB to 48.8 TB, in bytes.

Default value:

None

CacheControl

string

Explanation:

Cache-Control header in the response. It specifies cache behaviors of the web page when an object is downloaded.

Default value:

None

ContentDisposition

string

Explanation:

Content-Disposition header in the response

Default value:

None

ContentEncoding

string

Explanation:

Content-Encoding header in the response

Default value:

None

ContentLanguage

string

Explanation:

Content-Language header in the response

Default value:

None

ContentType

string

Explanation:

MIME type of the file to be downloaded. MIME type is a standard way of describing a data type and is used by the browser to decide how to display data.

Value range:

See What Is Content-Type (MIME)?

Default value:

If you do not specify this parameter when uploading an object, the SDK determines the object type based on the suffix of the specified object name and automatically assigns a value to this parameter.

Expires

string

Explanation:

Expires header in the response

Default value:

None

LastModified

time.Time

Explanation:

Time when the last modification was made to the object

Restrictions:

The time must be in the ISO8601 format, for example, 2018-01-01T00:00:00.000Z.

Default value:

None

ETag

string

Explanation:

Base64-encoded, 128-bit MD5 value of an object. ETag is the unique identifier of the object content. It can be used to determine whether the object content is changed. For example, if the ETag value is A when an object is uploaded, but changes to B when the object is downloaded, it indicates that the object content has been changed. The ETag reflects changes to the object content, rather than the object metadata. An uploaded or copied object has a unique ETag after being encrypted using MD5.

Restrictions:

If an object is encrypted using server-side encryption, the ETag is not the MD5 value of the object.

Value range:

The value must contain 32 characters.

Default value:

None

VersionId

string

Explanation:

Object version ID

Value range:

The value must contain 32 characters.

Default value:

None

Restore

string

Explanation:

Restore status of an object. For an Archive object that is being restored or has been restored, this header is returned.

For example, ongoing-request="true" indicates that the object is being restored. ongoing-request="false", expiry-date="Wed, 7 Nov 2012 00:00:00 GMT" indicates that the object has been restored. expiry-date indicates when the restored object expires.

Restrictions:

This parameter is only available for Archive objects.

Default value:

None

Expiration

string

Explanation:

Expiration details of the object. Example: "expiry-date=\"Mon, 11 Sep 2023 00:00:00 GMT\""

Default value:

None

SseHeader

SseCHeader or SseKmsHeader

Explanation:

Server-side encryption header information. If SSE-C is used, see Table 7. If SSE-KMS is used, see Table 8.

WebsiteRedirectLocation

string

Explanation:

If the bucket is configured with website hosting, the request for obtaining the object can be redirected to another object in the bucket or an external URL. This parameter specifies the address the request for the object is redirected to.

The request is redirected to object anotherPage.html in the same bucket:

WebsiteRedirectLocation:/anotherPage.html

The request is redirected to an external URL http://www.example.com/:

WebsiteRedirectLocation:http://www.example.com/

OBS obtains the specified value from the header and stores it in the object metadata WebsiteRedirectLocation.

Restrictions:

  • The value must start with a slash (/), http://, or https:// and cannot exceed 2 KB.
  • OBS only supports redirection for objects in the root directory of a bucket.

Default value:

None

Metadata

map[string]string

Explanation:

Custom object metadata. You can add a header starting with x-obs-meta- in the request to define metadata. The custom metadata will be returned in the response when you retrieve the object or query the object metadata.

Restrictions:

  • The custom metadata cannot exceed 8 KB. To measure the custom metadata, sum the number of bytes in the UTF-8 encoding of each key and value.
  • The custom metadata keys are case insensitive, but are stored in lowercase in OBS. The key values are case sensitive.
  • Both custom metadata keys and their values must conform to US-ASCII standards. If non-ASCII or unrecognizable characters are required, they must be encoded or decoded in URL or Base64 on the client, because the server does not perform such operations.

Default value:

None
Table 6 StorageClassType

Constant

Default Value

Description

StorageClassStandard

STANDARD

OBS Standard

Features low access latency and high throughput and is used for storing massive, frequently accessed (multiple times a month) or small objects (< 1 MB) requiring quick response.

StorageClassWarm

WARM

OBS Infrequent Access

Used for storing data that is semi-frequently accessed (fewer than 12 times a year) but is instantly available when needed.

StorageClassCold

COLD

OBS Archive

Used for storing rarely accessed (once a year) data.
Table 7 SseCHeader

Parameter

Type

Mandatory (Yes/No)

Description

Encryption

string

Yes if used as a request parameter

Explanation:

SSE-C used for encrypting objects

Value range:

AES256, indicating objects are encrypted using SSE-C

Default value:

None

Key

string

Yes if used as a request parameter

Explanation:

Key for encrypting the object when SSE-C is used

Restrictions:

The value is a Base64-encoded 256-bit key, for example, K7QkYpBkM5+hca27fsNkUnNVaobncnLht/rCB2o/9Cw=.

Default value:

None

KeyMD5

string

No if used as a request parameter

Explanation:

MD5 value of the key for encrypting objects when SSE-C is used. This value is used to check whether any error occurs during the transmission of the key.

Restrictions:

The value is encrypted by MD5 and then encoded by Base64, for example, 4XvB3tbNTN+tIEVa0/fGaQ==.

Default value:

None
Table 8 SseKmsHeader

Parameter

Type

Mandatory (Yes/No)

Description

Encryption

string

Yes if used as a request parameter

Explanation:

SSE-KMS used for encrypting objects

Value range:

kms, indicating objects are encrypted using SSE-KMS

Default value:

None

Key

string

No if used as a request parameter

Explanation:

ID of the KMS master key when SSE-KMS is used

Value range:

Valid value formats are as follows:

  1. regionID:domainID:key/key_id
  2. key_id

In the preceding formats:

  • regionID indicates the ID of the region where the key is used.
  • domainID indicates the ID of the account where the key is used. To obtain it, see How Do I Get My Account ID and User ID?
  • key_id indicates the ID of the key created on Data Encryption Workshop (DEW).

Default value:

  • If this parameter is not specified, the default master key will be used.
  • If there is no such a default master key, OBS will create one and use it by default.

Code Examples

This example downloads part (length range: 0-1,000 bytes) of example/objectname from examplebucket.

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package main
import (
    "fmt"
    "os"
    obs "github.com/huaweicloud/huaweicloud-sdk-go-obs/obs"
)
func main() {
    // Obtain an AK/SK pair using environment variables or import an AK/SK pair in other ways. Using hard coding may result in leakage.
    // Obtain an AK/SK pair on the management console. For details, see https://support.huaweicloud.com/eu/usermanual-ca/ca_01_0003.html.
    ak := os.Getenv("AccessKeyID")
    sk := os.Getenv("SecretAccessKey")
    // (Optional) If you use a temporary AK/SK pair and a security token to access OBS, you are advised not to use hard coding to reduce leakage risks. You can obtain an AK/SK pair using environment variables or import an AK/SK pair in other ways.
    // securityToken := os.Getenv("SecurityToken")
    // Enter the endpoint corresponding to the bucket. EU-Dublin is used here as an example. Replace it with the one currently in use.
    endPoint := "https://obs.eu-west-101.myhuaweicloud.eu" 
    // Create an obsClient instance.
    // If you use a temporary AK/SK pair and a security token to access OBS, use the obs.WithSecurityToken method to specify a security token when creating an instance.
    obsClient, err := obs.New(ak, sk, endPoint/*, obs.WithSecurityToken(securityToken)*/)
    if err != nil {
        fmt.Printf("Create obsClient error, errMsg: %s", err.Error())
    }
    input := &obs.GetObjectInput{}
    // Specify a bucket name.
    input.Bucket = "examplebucket"
    // Specify the object (example/objectname as an example) to download.
    input.Key = "example/objectname"
    // Specify a range.
    input.RangeStart = 0
    input.RangeEnd = 1000
    // Download the specified part of the object.
    output, err := obsClient.GetObject(input)
    if err == nil {
        // Close output.Body after using it, to avoid connection leakage.
        defer output.Body.Close()
        fmt.Printf("Get object(%s) under the bucket(%s) successful!\n", input.Key, input.Bucket)
        fmt.Printf("StorageClass:%s, ETag:%s, ContentType:%s, ContentLength:%d, LastModified:%s\n",
            output.StorageClass, output.ETag, output.ContentType, output.ContentLength, output.LastModified)
        // Read the object content.
        p := make([]byte, 1024)
        var readErr error
        var readCount int
        for {
            readCount, readErr = output.Body.Read(p)
            if readCount > 0 {
                fmt.Printf("%s", p[:readCount])
            }
            if readErr != nil {
                break
            }
        }
        return
    }
    fmt.Printf("List objects under the bucket(%s) fail!\n", input.Bucket)
    if obsError, ok := err.(obs.ObsError); ok {
        fmt.Println("An ObsError was found, which means your request sent to OBS was rejected with an error response.")
        fmt.Println(obsError.Error())
    } else {
        fmt.Println("An Exception was found, which means the client encountered an internal problem when attempting to communicate with OBS, for example, the client was unable to access the network.")
        fmt.Println(err)
    }
}

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