Downloading an Object - Conditional (SDK for Go)_Object Storage Service

Function

When downloading an object, you can specify one or more conditions. Only when the conditions are met, the object will be downloaded. Otherwise, an error code will be returned and the download will fail.

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.
The mapping between OBS regions and endpoints must comply with what is listed in Regions and Endpoints.
Objects in the Archive storage class can be downloaded only when they are in the Restored status.

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 conditional 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.ap-southeast-1.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.
ImageProcess	string	No	Explanation: Image processing command or style. Example for resizing and rotating an image: image/resize,m_fixed,w_100,h_100/rotate,90 Value range: Command format: image/commands Style format: style/style name For details about image processing parameters, see Processing Images. Default value: If no commands are entered, the original image is returned.
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: regionID:domainID:key/key_id key_id In the preceding formats: regionID indicates the ID of the region where the key is used. You can obtain it from Regions and Endpoints. 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). To obtain it, see Viewing a CMK. 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 example/objectname from examplebucket based on a specific condition. In this example, example/objectname can be downloaded only when it is modified after 00:00:00 on December 31, 2022.

    
     
       
       
         package main
import (
    "fmt"
    "os"
    "time"
    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/intl/en-us/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. CN-Hong Kong is used here as an example. Replace it with the one currently in use.
    endPoint := "https://obs.ap-southeast-1.myhuaweicloud.com"
    // 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"
    // Define the IfModifiedSince time.
    layout := "2006/01/02 15:04:05"
    t, err := time.Parse(layout, "2022/12/31 00:00:00")
    if err != nil {
        fmt.Printf("Parse time error, errMsg: %s", err.Error())
    }
    // The object can be downloaded only when it is modified after the specified time. Otherwise, a 304 response without a message subject is returned.
    input.IfModifiedSince = t
    // Download the object.
    output, err := obsClient.GetObject(input)
    if err == nil {
        // Close output.Body 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)
        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)
    }
}

        

      

    
   

Downloading an Object - Conditional (SDK for Go)

Function

Restrictions

Method

Request Parameters

Responses

Code Examples

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