Object Storage Service:OSS SDK for Goを使用してオブジェクトをファイルとしてダウンロードする

バケットから単一のオブジェクトをダウンロードする場合、最終変更時刻またはオブジェクトのETagに基づいて条件を指定できます。 オブジェクトは、これらの条件が満たされる場合にのみダウンロードされます。 それ以外の場合、エラーが返され、ダウンロード操作はトリガーされません。 これにより、不要なネットワーク送信とリソース消費が削減され、ダウンロード効率が向上します。

次の表に、指定できる使用可能な条件を示します。

次のサンプルコードは、条件付きダウンロードの実行方法の例を示しています。

package main

import (
    "log"
    "time"
    
    "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" // Replace yourBucketName with the actual bucket name.
    bucket, err := client.Bucket(bucketName)
    if err != nil {
        log.Fatalf("Failed to get bucket: %v", err)
    }

    // For example, an object was last modified at 18:43:02, November 21, 2023. If the specified time is earlier than the last modified time, the object meets the If-Modified-Since condition and the object is downloaded. 
    date := time.Date(2023, time.November, 21, 18, 43, 2, 0, time.UTC)

    // Specify the full path of the object. Do not include the bucket name in the full path. 
    objectName := "yourObjectName" // Replace yourObjectName with the actual object name.
    localFilePath := "LocalFile" // Specify the full path of the local file in which you want to store the downloaded object.

    // The object is not downloaded if it does not meet the specified conditions. 
    err = bucket.GetObjectToFile(objectName, localFilePath, oss.IfUnmodifiedSince(date))
    if err == nil {
        log.Fatal("Expected an error when the condition is not met, but got nil")
    }

    // The object is downloaded if it meets the specified conditions. 
    err = bucket.GetObjectToFile(objectName, localFilePath, oss.IfModifiedSince(date))
    if err != nil {
        log.Fatalf("Failed to download file: %v", err)
    }

    log.Println("File has been downloaded successfully.")
}

オブジェクトをダウンロードするときに、進行状況バーを使用してダウンロードの進行状況をリアルタイムで表示できます。これにより、オブジェクトのダウンロードを長時間待った後にダウンロードタスクが停止しているかどうかを確認できます。

次のサンプルコードは、examplebucketという名前のバケットからダウンロードされているexampleobject.txtという名前のオブジェクトの進行状況を表示する方法の例を示しています。

package main

import (
	"log"
	"sync/atomic"

	"github.com/aliyun/aliyun-oss-go-sdk/oss"
)

// Specify the progress bar listener. 
type OssProgressListener struct {
	lastProgress int64
}

// Specify the function that is used to handle progress change events. 
func (listener *OssProgressListener) ProgressChanged(event *oss.ProgressEvent) {
	switch event.EventType {
	case oss.TransferStartedEvent:
		log.Printf("Transfer Started, ConsumedBytes: %d, TotalBytes %d.\n",
			event.ConsumedBytes, event.TotalBytes)
	case oss.TransferDataEvent:
		if event.TotalBytes != 0 {
			progress := int64(event.ConsumedBytes * 100 / event.TotalBytes)
			if progress > atomic.LoadInt64(&listener.lastProgress) {
				atomic.StoreInt64(&listener.lastProgress, progress)
				log.Printf("\rTransfer Data, ConsumedBytes: %d, TotalBytes %d, %d%%.",
					event.ConsumedBytes, event.TotalBytes, progress)
			}
		}
	case oss.TransferCompletedEvent:
		log.Printf("\nTransfer Completed, ConsumedBytes: %d, TotalBytes %d.\n",
			event.ConsumedBytes, event.TotalBytes)
	case oss.TransferFailedEvent:
		log.Printf("\nTransfer Failed, ConsumedBytes: %d, TotalBytes %d.\n",
			event.ConsumedBytes, event.TotalBytes)
	default:
	}
}

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("Error: %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("Error: %v", err)
	}

	// Specify the name of the bucket. 
	bucketName := "examplebucket"
	// Specify the full path of the object. Do not include the bucket name in the full path. 
	objectName := "exampleobject.txt"
	// Specify the full path of the local file in which you want to store the downloaded object. If a file that has the same name already exists in the path, the downloaded object overwrites the file. If no file that has the same name exists in the path, the downloaded object is saved in the path. 
	// If you do not specify a local path for the downloaded object, the downloaded object is saved to the path of the project to which the sample program belongs. 
	localFile := "D:\\localpath\\examplefile.txt"

	// Query the name of the bucket. 
	bucket, err := client.Bucket(bucketName)
	if err != nil {
		log.Fatalf("Error: %v", err)
	}

	// Display the progress of the download task. 
	err = bucket.GetObjectToFile(objectName, localFile, oss.Progress(&OssProgressListener{}))
	if err != nil {
		log.Fatalf("Error: %v", err)
	}
	log.Println("Transfer Completed.")
}