Object metadata includes HTTP headers and user metadata. This topic describes how to set metadata when you upload an object.
Usage notes
In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access OSS by using other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about the regions and endpoints supported by OSS, see Regions and endpoints.
In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient instance by using custom domain names or Security Token Service (STS), see Create an OSSClient instance.
To configure object metadata, you must have the
oss:PutObject
permission. To query object metadata, you must have theoss:GetObject
permission. For more information, see Attach a custom policy to a RAM user.
Configure object metadata
The following code provides an example on how to configure object metadata:
#include <alibabacloud/oss/OssClient.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 of the object. 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);
/* Configure the HTTP headers. */
auto meta = ObjectMetaData();
meta.setContentType("text/plain");
meta.setCacheControl("max-age=3");
/* Configure the user metadata of the object. */
meta.UserMetaData()["meta"] = "meta-value";
std::shared_ptr<std::iostream> content = std::make_shared<std::stringstream>();
*content << "Thank you for using Aliyun Object Storage Service!";
auto outcome = client.PutObject(BucketName, ObjectName, content, meta);
if (!outcome.isSuccess()) {
/* Handle exceptions. */
std::cout << "PutObject fail" <<
",code:" << outcome.error().Code() <<
",message:" << outcome.error().Message() <<
",requestId:" << outcome.error().RequestId() << std::endl;
return -1;
}
/* Release resources, such as network resources. */
ShutdownSdk();
return 0;
}
Query object metadata
The following table describes the methods that you can use to query object metadata.
Method | Description | Advantage |
GetObjectMeta | Queries parts of object metadata such as the ETag value, size, and last modified time of the object. | More lightweight and faster |
HeadObject | Queries all object metadata. | None |
The following sample code provides an example on how to query object metadata:
#include <alibabacloud/oss/OssClient.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 of the object. 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 parts of the object metadata. */
auto outcome = client.GetObjectMeta(BucketName, ObjectName);
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, ETag:" << metadata.ETag() << "; LastModified:"
<< metadata.LastModified() << "; Size:" << metadata.ContentLength() << std::endl;
}
/* Query all object metadata. */
outcome = client.HeadObject(BucketName, ObjectName);
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 <<"headMeta success, ContentType:"
<< headMeta.ContentType() << "; ContentLength:" << headMeta.ContentLength()
<< "; CacheControl:" << headMeta.CacheControl() << std::endl;
}
/* Release resources, such as network resources. */
ShutdownSdk();
return 0;
}
References
For the complete sample code that is used to configure and obtain object metadata, visit GitHub.
For more information about the API operation that you can call to configure object metadata during simple upload, see PutObject.
For more information about the API operations for querying object metadata, see GetObjectMeta and HeadObject.