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Object Storage Service:Query object metadata by using OSS SDK for C++

Last Updated:Feb 01, 2024

By default, when you call the HeadObject operation on an Object Storage Service (OSS) object in a versioning-enabled bucket, the metadata of only the current version of the object is returned.

Note

If the current version of the object is a delete marker, OSS returns 404 Not Found. If you specify a version ID in the request, OSS returns the metadata of the specified version of the object.

Usage notes

  • In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access OSS from other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about OSS regions and endpoints, see Regions and endpoints.

  • In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient by using custom domain names or Security Token Service (STS), see Create an OSSClient instance.

  • To query object metadata, you must have the oss:GetObject permission. For more information, see Attach a custom policy to a RAM user.

Examples

The following sample code provides an example on how to query the metadata of an object:

#include <alibabacloud/oss/OssClient.h>
#include <alibabacloud/oss/model/ObjectMetaData.h>
using namespace AlibabaCloud::OSS;

int main(void)
{
    /* Initialize information about the account that is used to access OSS. */
            
    /* Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. */
    std::string Endpoint = "yourEndpoint";
    /* Specify the name of the bucket. Example: examplebucket. */
    std::string BucketName = "examplebucket";
    /* Specify the full path of the object. Do not include the bucket name in the full path. Example: exampledir/exampleobject.txt. */
    std::string ObjectName = "exampledir/exampleobject.txt";

    /* Initialize resources, such as network resources. */
    InitializeSdk();

    ClientConfiguration conf;
    /* Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. */
    auto credentialsProvider = std::make_shared<EnvironmentVariableCredentialsProvider>();
    OssClient client(Endpoint, credentialsProvider, conf);

    /* Query part of the metadata of the object. */
    GetObjectMetaRequest request(BucketName, ObjectName);
    request.setVersionId("yourObjectVersionId");
    auto outcome = client.GetObjectMeta(request);

    if (!outcome.isSuccess()) {
        /* Handle exceptions. */
        std::cout << "GetObjectMeta fail" <<
        ",code:" << outcome.error().Code() <<
        ",message:" << outcome.error().Message() <<
        ",requestId:" << outcome.error().RequestId() << std::endl;
        return -1;
    }
    else { 
            auto metadata = outcome.result();
            std::cout << " get metadata success, VersionId:" << metadata.VersionId() << std::endl;
    }

    /* Query all metadata of the object. */
    HeadObjectRequest request1(BucketName, ObjectName);
    request1.setVersionId("yourObjectVersionId");
    outcome = client.HeadObject(request1);

    if (!outcome.isSuccess()) {
        /* Handle exceptions. */
        std::cout << "HeadObject fail" <<
        ",code:" << outcome.error().Code() <<
        ",message:" << outcome.error().Message() <<
        ",requestId:" << outcome.error().RequestId() << std::endl;
        return -1;
    }
    else { 
            auto headMeta = outcome.result();
            std::cout << " get headMeta success, VersionId:" << headMeta.VersionId() << std::endl;
    }

    /* Release resources, such as network resources. */
    ShutdownSdk();
    return 0;
}

References

For more information about the API operations that you can call to query the metadata of an object, see HeadObject and GetObjectMeta.