Prevent objects from being overwritten by objects that have the same names - Object Storage Service

By default, if you upload an object that has the same name as an existing object, the existing object is overwritten by the uploaded object. This topic describes how to configure the x-oss-forbid-overwrite request header to prevent existing objects from being overwritten by objects with the same names when you copy objects or perform simple upload or multipart upload.

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, endpoints and open ports.
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.

Sample code

The following sample code provides an example on how to prevent existing objects from being overwritten by objects that have the same names when you perform simple upload:

package main

import (
	"log"
	"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 {
		log.Fatalf("Failed to create credentials provider: %v", err)
	}

	// 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. 
	// Specify the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the region to cn-hangzhou. Specify the actual region.
	clientOptions := []oss.ClientOption{oss.SetCredentialsProvider(&provider)}
	clientOptions = append(clientOptions, oss.Region("yourRegion"))
	// Specify the version of the signature algorithm.
	clientOptions = append(clientOptions, oss.AuthVersion(oss.AuthV4))
	client, err := oss.New("yourEndpoint", "", "", clientOptions...)
	if err != nil {
		log.Fatalf("Failed to create OSS client: %v", err)
	}

	// Specify the name of your bucket. 
	bucketName := "yourBucketName"
	bucket, err := client.Bucket(bucketName)
	if err != nil {
		log.Fatalf("Failed to get bucket '%s': %v", bucketName, err)
	}

	// Specify whether to overwrite an existing object with the same name. 
        // By default, if you do not specify oss.ForbidOverWrite, an object that has the same name is overwritten. 
        // If you set oss.ForbidOverWrite to false, an object that has the same name is overwritten. 
        // If you set oss.ForbidOverWrite to true, an object that has the same name is not overwritten. If such an object exists, an error is reported. 
	forbidWrite := oss.ForbidOverWrite(true)

	// Upload the string. 
        // Specify the full path of the object. Do not include the bucket name in the full path. 
	objectName := "yourObjectName"
	objectValue := "yourObjectValue"
	err = bucket.PutObject(objectName, strings.NewReader(objectValue), forbidWrite)
	if err != nil {
		log.Fatalf("Failed to upload object '%s': %v", objectName, err)
	}

	log.Printf("Successfully uploaded object '%s' with value '%s'", objectName, objectValue)
}

Common scenarios

Prevent overwrites in an object copy task

The following sample code provides an example on how to prevent existing objects from being overwritten by newly copied objects that have the same names:

package main

import (
	"log"

	"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 {
		log.Fatalf("Failed to create credentials provider: %v", err)
	}

	// 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. 
	// Specify the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the region to cn-hangzhou. Specify the actual region.
	clientOptions := []oss.ClientOption{oss.SetCredentialsProvider(&provider)}
	clientOptions = append(clientOptions, oss.Region("yourRegion"))
	// Specify the version of the signature algorithm.
	clientOptions = append(clientOptions, oss.AuthVersion(oss.AuthV4))
	client, err := oss.New("yourEndpoint", "", "", clientOptions...)
	if err != nil {
		log.Fatalf("Failed to create OSS client: %v", err)
	}

	// Specify the name of your bucket. 
	bucketName := "yourBucketName"
	// Specify the full path of the source object. Do not include the bucket name in the full path.
	objectName := "yourObjectName"
	// Specify the full path of the destination object. Do not include the bucket name in the full path.
	destObjectName := "yourDestObjectName"

	// Specify the name of the bucket.
	bucket, err := client.Bucket(bucketName)
	if err != nil {
		log.Fatalf("Failed to get bucket '%s': %v", bucketName, err)
	}

	// Specify whether to overwrite an existing object with the same name. 
	// By default, if you do not specify oss.ForbidOverWrite, an object that has the same name is overwritten. 
	// If you set oss.ForbidOverWrite to false, an object that has the same name is overwritten. 
	// If you set oss.ForbidOverWrite to true, an object that has the same name is not overwritten. If such an object exists, an error is reported. 
	forbidWrite := oss.ForbidOverWrite(true)

	// Create a copy of the object within the bucket.
	_, err = bucket.CopyObject(objectName, destObjectName, forbidWrite)
	if err != nil {
		log.Fatalf("Failed to copy object from '%s' to '%s': %v", objectName, destObjectName, err)
	}

	log.Printf("Successfully copied object from '%s' to '%s'", objectName, destObjectName)
}

Prevent overwrites in a multipart upload task

The following sample code provides an example on how to prevent an existing object from being overwritten by an object with the same name when you use multipart upload to upload the object:

package main

import (
	"log"
	"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 {
		log.Fatalf("Failed to create credentials provider: %v", err)
	}

	// 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. 
	// Specify the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the region to cn-hangzhou. Specify the actual region.
	clientOptions := []oss.ClientOption{oss.SetCredentialsProvider(&provider)}
	clientOptions = append(clientOptions, oss.Region("yourRegion"))
	// Specify the version of the signature algorithm.
	clientOptions = append(clientOptions, oss.AuthVersion(oss.AuthV4))
	client, err := oss.New("yourEndpoint", "", "", clientOptions...)
	if err != nil {
		log.Fatalf("Failed to create OSS client: %v", err)
	}

	// Specify the name of the bucket. 
	bucketName := "yourBucketName"
	// Specify the full path of the object. Do not include the bucket name in the full path. 
	objectName := "yourObjectName"
	// Specify the full path of the local file. 
	localFilename := "yourLocalFilename"

	// Specify the name of the bucket.
	bucket, err := client.Bucket(bucketName)
	if err != nil {
		log.Fatalf("Failed to get bucket '%s': %v", bucketName, err)
	}

	// Split the object into multiple chunks.
	chunks, err := oss.SplitFileByPartNum(localFilename, 3)
	if err != nil {
		log.Fatalf("Failed to split file: %v", err)
	}

	// Open the local file.
	fd, err := os.Open(localFilename)
	if err != nil {
		log.Fatalf("Failed to open local file '%s': %v", localFilename, err)
	}
	defer fd.Close()

	// Specify whether to overwrite an existing object with the same name. 
	// By default, if you do not specify oss.ForbidOverWrite, an object that has the same name is overwritten. 
	// If you set oss.ForbidOverWrite to false, an object that has the same name is overwritten. 
	// If you set oss.ForbidOverWrite to true, an object that has the same name is not overwritten. If such an object exists, an error is reported. 
	forbidWrite := oss.ForbidOverWrite(true)

	// Step 1: Initiate a multipart upload task. 
	imur, err := bucket.InitiateMultipartUpload(objectName, forbidWrite)
	if err != nil {
		log.Fatalf("Failed to initiate multipart upload for '%s': %v", objectName, err)
	}

	// Step 2: Upload the parts. 
	var parts []oss.UploadPart
	for _, chunk := range chunks {
		fd.Seek(chunk.Offset, os.SEEK_SET)
		// Call the UploadPart method to upload each part. 
		part, err := bucket.UploadPart(imur, fd, chunk.Size, chunk.Number)
		if err != nil {
			log.Fatalf("Failed to upload part %d of '%s': %v", chunk.Number, objectName, err)
		}
		parts = append(parts, part)
	}

	// Step 3: Complete the multipart upload task. Disable overwrites between objects that have the same names. 
	cmur, err := bucket.CompleteMultipartUpload(imur, parts, forbidWrite)
	if err != nil {
		log.Fatalf("Failed to complete multipart upload for '%s': %v", objectName, err)
	}

	log.Printf("Multipart upload completed successfully for '%s'. cmur: %v", objectName, cmur)
}

References

For more information about the API operation that you can call to perform simple upload, see PutObject.
For more information about the API operation that you can call to copy an object, see CopyObject.
For more information about the API operations that you can call to perform multipart upload, see InitiateMultipartUpload and CompleteMultipartUpload.