Obtaining Object Metadata (SDK for Go)
Function
Object metadata is a set of name-value pairs that describe the object and is used for object management.
Currently, only the metadata defined by the system is supported. There are two kinds of metadata: system-controlled metadata and user-controlled metadata.
You can use this API to send a HEAD request to the object of a specified bucket to obtain its metadata.
Restrictions
- To obtain object metadata, 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.
- Users with the read permission on an object can perform the HEAD operation to obtain the object metadata. The object metadata is included in the response.
Method
func (obsClient ObsClient) GetObjectMetadata(input *GetObjectMetadataInput) (output *GetObjectMetadataOutput, err error)
Request Parameters
Parameter |
Type |
Mandatory (Yes/No) |
Description |
---|---|---|---|
input |
Yes |
Explanation: Input parameters for obtaining object metadata. For details, see Table 2. |
Parameter |
Type |
Mandatory (Yes/No) |
Description |
---|---|---|---|
Bucket |
string |
Yes |
Explanation: Bucket name Restrictions:
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 |
VersionId |
string |
No |
Explanation: Object version ID, for example, G001117FCE89978B0000401205D5DC9A Value range: The value must contain 32 characters. Default value: None |
SseHeader |
No |
Explanation: Server-side decryption headers. For details, see Table 3. |
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
Parameter |
Type |
Description |
---|---|---|
output |
Explanation: Returned results. For details, see Table 5. |
|
err |
error |
Explanation: Error messages returned by the API |
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 |
StorageClass |
Explanation: Object storage class. If you do not specify this header, the object inherits the storage class of the bucket. 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:
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: 0 to (263 – 1), in bytes Default value: None |
ContentType |
string |
Explanation: MIME type of the object file. 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. |
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: ETag of the object 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 ETag value is A when an object is uploaded but changes to B when the object is downloaded, it indicates that the object content is changed. The ETag reflects changes to the object content, rather than the object metadata. An uploaded object or copied object has a unique ETag. 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 |
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. 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:
Default value: None |
Metadata |
map[string]string |
Explanation: Custom metadata of the object. 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:
Default value: None |
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. |
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 |
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:
In the preceding formats:
Default value:
|
Code Examples
This example returns the metadata of object example/objectname.
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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/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.WithSignature(obs.SignatureObs)/*, obs.WithSecurityToken(securityToken)*/) if err != nil { fmt.Printf("Create obsClient error, errMsg: %s", err.Error()) } input := &obs.GetObjectMetadataInput{} // Specify a bucket name. input.Bucket = "examplebucket" // Specify an object (example/objectname as an example). input.Key = "example/objectname" // Obtain the custom metadata of the object. output, err := obsClient.GetObjectMetadata(input) if err == nil { fmt.Printf("Get object(%s)'s metadata successful with bucket(%s)!\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) // Obtain the custom metadata of the object. fmt.Printf("Metadata:%v\n", output.Metadata) return } fmt.Printf("Get object(%s)'s metadata fail with bucket(%s)!\n", input.Key, 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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