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Object Storage Service:Range download

Last Updated:Sep 05, 2023

You can use range download to download a specified range of data from 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, 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 perform range download, you must have the oss:GetObject permission. For more information, see Common examples of RAM policies.

Specify a valid range to download

The following sample code provides an example on how to specify a valid range to download data:

package main

import (
  "fmt"
  "os"
  "io/ioutil"
  "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. 
    bucket, err := client.Bucket("yourBucketName")
    if err != nil {
       fmt.Println("Error:", err)
       os.Exit(-1)
  }

  // Query the data that is within the range from byte 15 to byte 35, which includes a total of 21 bytes. 
  // If the specified value range is invalid, the entire object is downloaded. For example, if the specified range includes a negative number or the specified value is greater than the object size, all content of the object is downloaded. 
  // Specify the full path of the object. Do not include the bucket name in the full path. 
  body, err := bucket.GetObject("yourObjectName", oss.Range(15, 35))
  if err != nil {
    fmt.Println("Error:", err)
    os.Exit(-1)
  }
  // You must close the obtained stream after the object is read. Otherwise, connection leaks may occur. Consequently, no connections are available and an exception occurs. 
  defer body.Close()

  data, err := ioutil.ReadAll(body)
  if err != nil {
    fmt.Println("Error:", err)
    os.Exit(-1)
  }
  fmt.Println("data:", string(data))
}

Specify an invalid range to download data

For an object whose size is 1,000 bytes, the valid range is from byte 0 to byte 999. If the specified range is not within the range of byte 0 to byte 999, the range does not take effect. In this case, OSS returns HTTP status code 200 and the data of the entire object. The following examples show invalid requests and the returned results:

  • If you set Range: bytes to 500-2000, the value at the end of the range is invalid. In this case, OSS returns HTTP status code 200 and the data of the entire object.

  • If you set Range: bytes to 1000-2000, the value at the start of the range is invalid. In this case, OSS returns HTTP status code 200 and the data of the entire object.

Specify standard behaviors to download data by range

If you add x-oss-range-behavior:standard to the request header, the download behavior is modified when the specified range is not within the valid range. For an object whose size is 1,000 bytes:

  • If you set Range: bytes to 500-2000, the value at the end of the range is invalid. In this case, OSS returns HTTP status code 206 and the data that is within the range of byte 500 to byte 999.

  • If you set Range: bytes to 1000-2000, the value at the start of the range is invalid. In this case, OSS returns HTTP status code 416 and the InvalidRange error code.

The following sample code provides an example on how to specify standard behaviors to download data by range:

package main

import (
    "fmt"
    "io/ioutil"
    "os"
    "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. 
    bucket, err := client.Bucket("yourBucketName")
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Upload 1,000 bytes. 
    strContent := ""
    for i := 0; i < 100; i++ {
        strContent += "abcdefghij"
    }

    fmt.Printf("content len:%d\n", len(strContent))

    // Upload the string. 
    // Specify the full path of the object. Do not include the bucket name in the full path. 
    err = bucket.PutObject("yourObjectName", strings.NewReader(strContent))
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // If you specify a range from byte 500 to byte 2000, the value at the end of the range is invalid. Then, OSS returns HTTP status code 206 and the data that is within the range from byte 500 to byte 999. 
    // If you specify a range from byte 1000 to byte 2000, the value at the start of the range is invalid. Then, OSS returns HTTP status code 416 and error code InvalidRange. 
    body, err := bucket.GetObject("<yourObjectName>", oss.Range(500, 2000), oss.RangeBehavior("standard"))
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // You must close the obtained stream after the object is read. Otherwise, connection leaks may occur. Consequently, no connections are available and an exception occurs. 
    defer body.Close()
    data, err := ioutil.ReadAll(body)
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    if len(data) != 500 {
        fmt.Println("read data error, len:%d", len(data))
        os.Exit(-1)
    }
    fmt.Println("data:", string(data))
}

References

  • For the complete sample code that is used to perform range download, visit GitHub.

  • For more information about the API operation that you can call to perform range download, see GetObject.