Object Storage Service:Manage object metadata

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, access credentials are obtained from environment variables. For more information about how to configure access credentials, see Configure access credentials.

• 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 Initialization.

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

Configure object metadata when you upload an object

The following sample code provides an example on how to set object metadata when you upload an object:

package main

import (
    "fmt"
    "os"
    "time"
    "strings"
    "github.com/aliyun/aliyun-oss-go-sdk/oss"
)

func main() {
    /// 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. 
    provider, err := oss.NewEnvironmentVariableCredentialsProvider()
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Create an OSSClient instance. 
    // 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. Specify your actual endpoint. 
    client, err := oss.New("yourEndpoint", "", "", oss.SetCredentialsProvider(&provider)) 
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Specify the name of the bucket. Example: examplebucket. 
    bucket, err := client.Bucket("examplebucket")
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Configure the metadata of the object. Set the expiration time to 23:00:00 January 10, 2049 in GMT, access control list (ACL) to public-read, and MyProp to MyPropVal as user metadata. 
    expires := time.Date(2049, time.January, 10, 23, 0, 0, 0, time.UTC)
    options := []oss.Option{
        oss.Expires(expires),
        oss.ObjectACL(oss.ACLPublicRead),
        oss.Meta("MyProp", "MyPropVal"),
    }

    // Use a data stream to upload the object. 
    // Specify the full path of the object. The full path of the object cannot contain the bucket name. Example: exampledir/exampleobject.txt. 
    err = bucket.PutObject("exampledir/exampleobject.txt", strings.NewReader("MyObjectValue"), options...)
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Query object metadata. 
    props, err := bucket.GetObjectDetailedMeta("exampledir/exampleobject.txt")
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }
    fmt.Println("Object Meta:", props)
}           

Modify object metadata

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

package main

import (
    "fmt"
    "os"
    "github.com/aliyun/aliyun-oss-go-sdk/oss"
)

func main() {
    /// 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. 
    provider, err := oss.NewEnvironmentVariableCredentialsProvider()
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Create an OSSClient instance. 
    // 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. Specify your actual endpoint. 
    client, err := oss.New("yourEndpoint", "", "", oss.SetCredentialsProvider(&provider)) 
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }
    
    // Specify the name of the bucket. Example: examplebucket. 
    bucketName := "examplebucket"
    // Specify the full path of the object. 
    objectName := "exampledir/exampleobject.txt"
    
    bucket, err := client.Bucket(bucketName)
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Modify one object metadata parameter at a time. 
    err = bucket.SetObjectMeta(objectName, oss.Meta("MyMeta", "MyMetaValue1"))
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Modify multiple object metadata parameters at a time. 
    options := []oss.Option{
        oss.Meta("MyMeta", "MyMetaValue2"),
        oss.Meta("MyObjectLocation", "HangZhou"),
    }
    err = bucket.SetObjectMeta(objectName, options...)
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Query object metadata. 
    props, err := bucket.GetObjectDetailedMeta(objectName)
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }
    fmt.Println("Object Meta:", props)
}            

Query object metadata

• Query object metadata, except for the last access time (X-Oss-Last-Access-Time)

  The following code provides an example on how to query object metadata, except for the last access time:

  package main
  
  import (
      "fmt"
      "os"
      "github.com/aliyun/aliyun-oss-go-sdk/oss"
  )
  
  func main() {
      /// 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. 
      provider, err := oss.NewEnvironmentVariableCredentialsProvider()
      if err != nil {
          fmt.Println("Error:", err)
          os.Exit(-1)
      }
  
      // Create an OSSClient instance. 
      // 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. Specify your actual endpoint. 
      client, err := oss.New("yourEndpoint", "", "", oss.SetCredentialsProvider(&provider)) 
      if err != nil {
          fmt.Println("Error:", err)
          os.Exit(-1)
      }
  
      // Specify the name of the bucket. Example: examplebucket. 
      bucketName := "examplebucket"
      // Specify the full path of the object. 
      objectName := "exampledir/exampleobject.txt"
     
      bucket, err := client.Bucket(bucketName)
      if err != nil {
          fmt.Println("Error:", err)
          os.Exit(-1)
      }
  
      // Query object metadata. 
      props, err := bucket.GetObjectDetailedMeta(objectName)
      if err != nil {
          fmt.Println("Error:", err)
          os.Exit(-1)
      }
      fmt.Println("Object Meta:", props)
  }            

• Query object metadata, including the last access time (X-Oss-Last-Access-Time)

  The following code provides an example on how to query object metadata, including the last access time:

  package main
  
  import (
      "fmt"
      "os"
      "github.com/aliyun/aliyun-oss-go-sdk/oss"
  )
  
  func main() {
      /// 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. 
      provider, err := oss.NewEnvironmentVariableCredentialsProvider()
      if err != nil {
          fmt.Println("Error:", err)
          os.Exit(-1)
      }
  
      // Create an OSSClient instance. 
      // 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. Specify your actual endpoint. 
      client, err := oss.New("yourEndpoint", "", "", oss.SetCredentialsProvider(&provider))
      if err != nil {
          fmt.Println("Error:", err)
          os.Exit(-1)
      }
      // Specify the name of the bucket. Example: examplebucket. 
      bucketName := "examplebucket"
      // Specify the full path of the object. 
      objectName := "exampledir/exampleobject.txt"
      
      bucket,err := client.Bucket(bucketName)
      if err != nil {
          fmt.Println("Error:", err)
          os.Exit(-1)
      }
      // Query object metadata. 
      header,err := bucket.GetObjectMeta(objectName)
      if err != nil {
          fmt.Println("Error:", err)
          os.Exit(-1)
      }
      // Query the last access time of the object. 
      fmt.Printf("Last Access Time:%s\n", header.Get("X-Oss-Last-Access-Time"))
  }

References

• For the complete sample code that is used to manage object metadata, visit GitHub.

• For more information about the API operation that you can call to configure object metadata in a simple upload task, see PutObject.
• For more information about the API operation for modifying object metadata, see CopyObject.
• For more information about the API operations that you can call to query the metadata of an object, see GetObjectMeta and HeadObject.

FAQ

When I upload an object to a bucket and set metadata for the object simultaneously, how do I prevent an existing object with the same name in the bucket from being overwritten?

You can use one of the following methods to prevent objects with the same name in the bucket from being overwritten:

• Enable versioning

  If you enable versioning for the bucket, OSS keeps the existing object with the same name as a previous version and stores the object that you upload as the current version. You can recover to a previous version at any time. For more information, see Enable versioning.

• Include the x-oss-forbid-overwrite header in the upload request

  You can include the x-oss-forbid-overwrite header in the upload request and set the header to true. If you upload an object that has the same name as an existing object, the upload fails and OSS returns the FileAlreadyExists error. For more information, see PutObject.