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Checking Whether an Object Exists

Last updated: 2024-02-05 10:54:57

    Overview

    This document provides an overview of the API and sample code for quickly checking whether an object exists in a bucket. The sample code actually calls the HEAD Object COS API and is a simplified version of the API.
    In addition to checking whether an object exists, HEAD Object returns object metadata. To view the SDK API that contains the full functionality of HEAD Object, please see Querying Object Metadata.
    API
    Operation
    Description
    Querying object metadata
    Queries the metadata of an object.

    Description

    The API is used to check whether an object exists in a bucket, which can be implemented by encapsulating the cos.headObject method.

    Sample request

    
    function doesObjectExist() {
    cos.headObject({
    Bucket: 'examplebucket-1250000000', /* Your bucket name. Required. */
    Region: 'COS_REGION', /* Bucket region, such as `ap-beijing`. Required. */
    Key: '1.jpg', /* Object key stored in the bucket (such as `1.jpg` and `a/b/test.txt`). Required. */
    }, function(err, data) {
    if (data) {
    console.log('The object exists.');
    } else if (err.statusCode == 404) {
    console.log('The object does not exist.');
    } else if (err.statusCode == 403) {
    console.log ('no permission to read the object');
    }
    });
    }

    Parameter description

    Parameter
    Description
    Type
    Required
    Bucket
    Bucket name in the format of BucketName-APPID.
    String
    Yes
    Region
    Bucket region. For the enumerated values, please see Regions and Access Endpoints.
    String
    Yes
    Key
    Object key (object name), the unique ID of an object in a bucket. For more information, please see Object Overview.
    String
    Yes
    IfModifiedSince
    Required modification time. Metadata is returned only if the object has been modified after the specified time. Otherwise, 304 is returned.
    String
    No

    Callback function description

    function(err, data) { ... }
    Parameter
    Description
    Type
    err
    Error code, which is returned when an error (network error or service error) occurs. If the request is successful, this parameter is empty. For more information, please see Error Codes.
    Object
    - statusCode
    HTTP status code, such as 200, 403, and 404.
    Number
    - headers
    Headers.
    Object
    data
    Content returned when the request is successful. If the request fails, this parameter is empty.
    Object
    - statusCode
    HTTP status code, such as 200 and 304. 304 is returned if no modification is made after the specified time.
    Number
    - headers
    Headers.
    Object
    - x-cos-object-type
    Whether an object is appendable. Enumerated values: normal, appendable. The default value normal is not displayed.
    String
    - x-cos-storage-class
    Storage class of the object, such as STANDARD (default), STANDARD_IA, ARCHIVE, and DEEP_ARCHIVE. For more information, please see Storage Class Overview. Note that STANDARD is not displayed if returned.
    String
    - x-cos-meta-*
    User-defined metadata.
    String
    - NotModified
    Whether an object hasn’t been modified after the specified time.
    Boolean
    - ETag
    MD5 checksum of the object. The value of ETag can be used to check whether the object was corrupted during the upload.
    Example: "09cba091df696af91549de27b8e7d0f6"
    Note that double quotation marks are required at the beginning and the end.
    String
    - VersionId
    Version ID of the uploaded object if versioning is enabled for its bucket. If versioning is not enabled, this parameter is not returned.
    String
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