Obtaining Object Metadata (SDK for Node.js)

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Function

Object metadata contains a set of name-value pairs that are used for describing and managing objects.

Currently, only the system-defined metadata is supported. System-defined metadata consists of system-controlled metadata and user-controlled metadata. The kind of metadata like Last-Modified is controlled by the system and cannot be modified. However, the kind of metadata configured for objects such as ContentLanguage can be modified by calling APIs.

This API sends a HEAD request for obtaining object 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.
To learn about the mappings between OBS regions and endpoints, see Regions and Endpoints.

Method

ObsClient.getObjectMetadata(params)

Request Parameters

**Table 1** List of request parameters
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 with 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. Value range: The value can contain 3 to 63 characters. 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 of the object 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. Restrictions: None Value range: The value can contain 1 to 1,024 characters. Default value: None
VersionId	string	No	Explanation: Object version ID, for example, G001117FCE89978B0000401205D5DC9A Restrictions: None Value range: The value must contain 32 characters. Default value: None
Origin	string	No	Explanation: Origin of the cross-domain request specified in the preflight request. It is usually a domain name. Restrictions: Each origin can contain at most one wildcard character (). Value range: None Default value*: None
RequestHeader	string	No	Explanation: HTTP headers that can be used in cross-origin requests. Only CORS requests matching the allowed headers are valid. Restrictions: Each header can contain at most one wildcard character (). Spaces, ampersands (&), colons (:), less-than signs (<), and full-width characters are not allowed. Value range: None Default value*: None
SseC	string	Yes when SSE-C is used	Explanation: SSE-C is used for decrypting objects. Restrictions: Only AES256 is supported. Value range: AES256 Default value: None
SseCKey	string	Yes when SSE-C is used	Explanation: Key used for decrypting objects when SSE-C is used Restrictions: A Base64-encoded, 256-bit value, for example, K7QkYpBkM5+hca27fsNkUnNVaobncnLht/rCB2o/9Cw= Value range: None Default value: None

Responses

**Table 2** Responses
Type	Description
Table 3 NOTE: This API returns a Promise response, which requires the Promise or async/await syntax.	Explanation: Returned results. For details, see Table 3.

**Table 3** Response
Parameter	Type	Description
CommonMsg	ICommonMsg	Explanation: Common information generated after an API call is complete, including the HTTP status code and error code. For details, see Table 4.
InterfaceResult	Table 5	Explanation: Results outputted for a successful call. For details, see Table 5. Restrictions: This parameter is not included if the value of Status is greater than 300.

**Table 4** ICommonMsg
Parameter	Type	Description
Status	number	Explanation: HTTP status code returned by the OBS server. Value range: A status code is a group of digits indicating the status of a response. It ranges from 2xx (indicating successes) to 4xx or 5xx (indicating errors). For details, see Status Codes.
Code	string	Explanation: Error code returned by the OBS server.
Message	string	Explanation: Error description returned by the OBS server.
HostId	string	Explanation: Request server ID returned by the OBS server.
RequestId	string	Explanation: Request ID returned by the OBS server.
Id2	string	Explanation: Request ID2 returned by the OBS server.
Indicator	string	Explanation: Error code details returned by the OBS server.

**Table 5** GetObjectMetadataOutput
Parameter	Type	Description
RequestId	string	Explanation: Request ID returned by the OBS server
StorageClass	StorageClassType	Explanation: Storage class configured when copying the object. If you do not specify this parameter, the object inherits the storage class of the bucket. Value range: See Table 6.
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 requests can access the bucket. Restrictions: Domain name of the origin. Each origin can contain at most one wildcard character (). 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 at most one wildcard character (). Spaces, ampersands (&), colons (:), less-than signs (<), and full-width characters are not allowed. Default value*: None
AllowMethod	string	Explanation: AllowedMethod in the CORS rules of the bucket. It specifies the HTTP method allowed for 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, asterisks (), ampersands (&), colons (:), less-than signs (<), and full-width characters are not allowed. Default value*: None
MaxAgeSeconds	number	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 contain at most one MaxAgeSeconds. Value range: 0 to (2³¹ – 1), in seconds Default value: 100
ContentLength	number	Explanation: Object size Value range: 0 to (2⁶³ – 1), in bytes Default value: None
ContentType	string	Explanation: MIME type of the object. 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)? (SDK for Node.js) 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	string	Explanation: Time when the object was last modified. 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. It uniquely identifies the content of an object and can be used to check the object integrity. For example, if the ETag is A when an object is uploaded and is B when the object is downloaded, it indicates that the object content has been changed. The ETag reflects changes to the contents of the object, not its metadata. An object created by an upload or copy operation 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: Restoration 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, where expiry-date indicates when the restored object expires. Restrictions: If the object is not in the Archive storage class, this parameter is left blank. Default value: None
Expiration	string	Explanation: Expiration details, for example, "expiry-date=\"Mon, 11 Sep 2023 00:00:00 GMT\"" Default value: None
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: 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 of objects that are in the root directory. Default value: None
Metadata	object	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: The custom metadata cannot exceed 8 KB in total. To measure the size, calculate the sum of bytes of all UTF-8 encoded keys and values. 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 and 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
ObsClient.enums.StorageClassStandard	STANDARD	Standard storage class. 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.
ObsClient.enums.StorageClassWarm	WARM	Infrequent Access storage class. Used for storing data that is semi-frequently accessed (fewer than 12 times a year) but becomes instantly available when needed.
ObsClient.enums.StorageClassCold	COLD	Archive storage class. Used for storing rarely accessed (once a year) data.

Code Examples

You can call ObsClient.getObjectMetadata to obtain the metadata of an object, including its length, MIME type, and custom metadata. The following code shows how to obtain the metadata of object example/objectname in bucket examplebucket:

    
     
       
       
         // Import the OBS library.
// Use npm to install the client.
const ObsClient = require("esdk-obs-nodejs");
// Use the source code to install the client.
// var ObsClient = require('./lib/obs');

// Create an instance of ObsClient.
const obsClient = new ObsClient({
  // 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.
  access_key_id: process.env.ACCESS_KEY_ID,
  secret_access_key: process.env.SECRET_ACCESS_KEY,
  // (Optional) If you use a temporary AK/SK pair and a security token to access OBS, you are advised not to use hard coding, which may result in information leakage. You can obtain an AK/SK pair using environment variables or import an AK/SK pair in other ways.
  // security_token: process.env.SECURITY_TOKEN,
  // Enter the endpoint corresponding to the region where the bucket is located. CN-Hong Kong is used here in this example. Replace it with the one currently in use.
  server: "https://obs.ap-southeast-1.myhuaweicloud.com"
});

async function getObjectMetadata() {
  try {
    const params = {
      // Specify the bucket name.
      Bucket: "examplebucket",
      // Specify the object (example/objectname in this example).
      Key: 'example/objectname',
    };
    // Obtain the object metadata.
    const result = await obsClient.getObjectMetadata(params);
    if (result.CommonMsg.Status <= 300) {
      console.log("Put bucket(%s) successful!", params.Bucket);
      console.log("RequestId: %s", result.CommonMsg.RequestId);
      console.log("StorageClass:%s, ETag:%s, ContentType:%s, ContentLength:%d, LastModified:%s\n",
        result.InterfaceResult.StorageClass, result.InterfaceResult.ETag, result.InterfaceResult.ContentType, 
        result.InterfaceResult.ContentLength, result.InterfaceResult.LastModified);
      // Obtain the custom metadata of the object.
      console.log("Metadata:%v", result.InterfaceResult.Metadata);
      return;
    };
    console.log("An ObsError was found, which means your request sent to OBS was rejected with an error response.");
    console.log("Status: %d", result.CommonMsg.Status);
    console.log("Code: %s", result.CommonMsg.Code);
    console.log("Message: %s", result.CommonMsg.Message);
    console.log("RequestId: %s", result.CommonMsg.RequestId);
  } catch (error) {
    console.log("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.");
    console.log(error);
  };
};

getObjectMetadata();

        

      

    
   