Object Storage Service:Get object metadata (C++ SDK)

Prerequisites

Before you begin, ensure that you have:

• The oss:GetObject permission on the target object. For more information, see Attach a custom policy to a RAM user

• The OSS C++ SDK installed and an OssClient instance initialized. For more information, see Create an OSSClient instance

Usage notes

• The examples in this topic use the public endpoint for the China (Hangzhou) region. To access OSS from another Alibaba Cloud service in the same region, use the internal endpoint instead. For endpoint details, see Regions and endpoints.

• The examples use EnvironmentVariableCredentialsProvider to load credentials from the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables. Set these variables before running the code.

Get object metadata

The following example calls both GetObjectMeta and HeadObject and prints the returned VersionId.

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

int main(void)
{
    /* Set the endpoint of the region where the bucket is located.
       Example: https://oss-cn-hangzhou.aliyuncs.com for China (Hangzhou). */
    std::string Endpoint = "yourEndpoint";
    /* Set the region ID. Example: cn-hangzhou. */
    std::string Region = "yourRegion";
    /* Specify the bucket name. */
    std::string BucketName = "examplebucket";
    /* Specify the full object path, excluding the bucket name.
       Example: exampledir/exampleobject.txt. */
    std::string ObjectName = "exampledir/exampleobject.txt";

    /* Initialize network resources. */
    InitializeSdk();

    ClientConfiguration conf;
    conf.signatureVersion = SignatureVersionType::V4;
    /* Load credentials from environment variables OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET. */
    auto credentialsProvider = std::make_shared<EnvironmentVariableCredentialsProvider>();
    OssClient client(Endpoint, credentialsProvider, conf);
    client.SetRegion(Region);

    /* GetObjectMeta: retrieve partial metadata (ETag, object size, and last-modified time). */
    GetObjectMetaRequest metaRequest(BucketName, ObjectName);
    metaRequest.setVersionId("yourObjectVersionId");
    auto metaOutcome = client.GetObjectMeta(metaRequest);

    if (!metaOutcome.isSuccess()) {
        std::cout << "GetObjectMeta failed"
                  << ", code: "      << metaOutcome.error().Code()
                  << ", message: "   << metaOutcome.error().Message()
                  << ", requestId: " << metaOutcome.error().RequestId()
                  << std::endl;
        ShutdownSdk();
        return -1;
    }

    auto meta = metaOutcome.result();
    std::cout << "GetObjectMeta succeeded, VersionId: " << meta.VersionId() << std::endl;

    /* HeadObject: retrieve all metadata, including content type, content encoding,
       cache control, and custom headers. */
    HeadObjectRequest headRequest(BucketName, ObjectName);
    headRequest.setVersionId("yourObjectVersionId");
    auto headOutcome = client.HeadObject(headRequest);

    if (!headOutcome.isSuccess()) {
        std::cout << "HeadObject failed"
                  << ", code: "      << headOutcome.error().Code()
                  << ", message: "   << headOutcome.error().Message()
                  << ", requestId: " << headOutcome.error().RequestId()
                  << std::endl;
        ShutdownSdk();
        return -1;
    }

    auto headMeta = headOutcome.result();
    std::cout << "HeadObject succeeded, VersionId: " << headMeta.VersionId() << std::endl;

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

Replace the placeholders with your actual values:

Versioning behavior

When working with versioned objects, be aware of the following behavior:

API reference

• HeadObject

• GetObjectMeta