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Checking Whether an Object Exists

Last updated: 2022-03-17 15:08:19

    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
    HEAD Object 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.code == 404) {
             console.log('The object does not exist.');
           } else if (err.code == 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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