You can use range download to download a specified range of data from an object.

Specify a valid range to download data

The following 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() {
    // 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. 
    // The AccessKey pair of an Alibaba Cloud account has permissions on all API operations. Using these credentials to access Object Storage Service (OSS) is a high-risk operation. We recommend that you use a Resource Access Management (RAM) user to call API operations or perform routine operations and maintenance. To create a RAM user, log on to the RAM console. 
    client, err := oss.New("yourEndpoint", "yourAccessKeyId", "yourAccessKeySecret")
    if err != nil {
       fmt.Println("Error:", err)
       os.Exit(-1)
  }

    // Set yourBucketName to the name of your 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. 
  // Set yourObjectName to the full path of the object. The full path cannot contain the bucket name. 
  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 from byte 0 to byte 999, the range does not take effect. Then, 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. Then, 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. Then, 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. Then, OSS returns HTTP status code 206 and the data that is within the range from byte 500 to byte 999.
  • If you set Range: bytes to 1000-2000, the value at the start of the range is invalid. Then, OSS returns HTTP status code 416 and error code InvalidRange.

The following 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() {
    // 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. 
    // The AccessKey pair of an Alibaba Cloud account has permissions on all API operations. Using these credentials to access OSS is a high-risk operation. We recommend that you use a RAM user to call API operations or perform routine operations and maintenance. To create a RAM user, log on to the RAM console. 
    client, err := oss.New("yourEndpoint", "yourAccessKeyId", "yourAccessKeySecret")
    if err != nil {
        fmt.Println("Error:", err)
        os.Exit(-1)
    }

    // Set yourBucketName to the name of your 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 a string. 
    // Set yourObjectName to the full path of the object. The full path cannot contain the bucket name. 
    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 more information about the complete sample code for range download, visit GitHub.
  • For more information about the API operation that is called to perform range download, see GetObject.