普通下载（Go SDK）--对象存储-火山引擎

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普通下载（Go SDK）

最近更新时间：2024.02.04 18:30:55首次发布时间：2021.12.31 17:38:36

通过 GetObject 方法可以从指定桶中下载对象。在使用此接口之前，确保拥有对此对象的读访问权限。在使用下载接口的过程中可以通过设置进度条回调来获取目前下载数据进度信息。若需要在下载过程中在客户端限速时，可以使用 tos.RateLimiter 接口，同时可以设置下载过程中返回元数据信息。

注意事项

下载对象前，您必须具有 tos:GetObject 权限，具体操作，请参见权限配置指南。
对于开启多版本的桶，下载指定版本对象时，您必须具有 tos:GetObjectVersion 权限，具体操作，请参见权限配置指南。
如果应用程序会在同一时刻大量下载同一个对象，您的访问速度会受到 TOS 带宽及地域的限制。建议您使用 CDN 产品，提升性能的同时也能降低您的成本。通过 CDN 访问 TOS 的详细信息，请参见使用 CDN 加速访问 TOS 资源。

示例代码

下载数据到内存

以下代码用于下载桶的对象到内存。

package main

import (
   "context"
   "fmt"
   "io/ioutil"
   "sync"
   "time"

   "github.com/volcengine/ve-tos-golang-sdk/v2/tos"
   "github.com/volcengine/ve-tos-golang-sdk/v2/tos/enum"
)

// 自定义进度回调，需要实现 tos.DataTransferStatusChange 接口
type listener struct {
}

func (l *listener) DataTransferStatusChange(event *tos.DataTransferStatus) {
   switch event.Type {
   case enum.DataTransferStarted:
      fmt.Println("Data transfer started")
   case enum.DataTransferRW:
      // Chunk 模式下 TotalBytes 值为 -1
      if event.TotalBytes != -1 {
         fmt.Printf("Once Read:%d,ConsumerBytes/TotalBytes: %d/%d,%d%%\n", event.RWOnceBytes, event.ConsumedBytes, event.TotalBytes, event.ConsumedBytes*100/event.TotalBytes)
      } else {
         fmt.Printf("Once Read:%d,ConsumerBytes:%d\n", event.RWOnceBytes, event.ConsumedBytes)
      }
   case enum.DataTransferSucceed:
      fmt.Printf("Data Transfer Succeed, ConsumerBytes/TotalBytes: %d/%d,%d%%\n", event.ConsumedBytes, event.TotalBytes, event.ConsumedBytes*100/event.TotalBytes)
   case enum.DataTransferFailed:
      fmt.Printf("Data Transfer Failed\n")
   }
}

type rateLimit struct {
   rate     int64
   capacity int64

   currentAmount int64
   sync.Mutex
   lastConsumeTime time.Time
}

func NewDefaultRateLimit(rate int64, capacity int64) tos.RateLimiter {
   return &rateLimit{
      rate:            rate,
      capacity:        capacity,
      lastConsumeTime: time.Now(),
      currentAmount:   capacity,
      Mutex:           sync.Mutex{},
   }
}

func (d *rateLimit) Acquire(want int64) (ok bool, timeToWait time.Duration) {
   d.Lock()
   defer d.Unlock()
   if want > d.capacity {
      want = d.capacity
   }
   increment := int64(time.Now().Sub(d.lastConsumeTime).Seconds() * float64(d.rate))
   if increment+d.currentAmount > d.capacity {
      d.currentAmount = d.capacity
   } else {
      d.currentAmount += increment
   }
   if want > d.currentAmount {
      timeToWaitSec := float64(want-d.currentAmount) / float64(d.rate)
      return false, time.Duration(timeToWaitSec * float64(time.Second))
   }
   d.lastConsumeTime = time.Now()
   d.currentAmount -= want
   return true, 0
}

func checkErr(err error) {
   if err != nil {
      if serverErr, ok := err.(*tos.TosServerError); ok {
         fmt.Println("Error:", serverErr.Error())
         fmt.Println("Request ID:", serverErr.RequestID)
         fmt.Println("Response Status Code:", serverErr.StatusCode)
         fmt.Println("Response Header:", serverErr.Header)
         fmt.Println("Response Err Code:", serverErr.Code)
         fmt.Println("Response Err Msg:", serverErr.Message)
      } else if clientErr, ok := err.(*tos.TosClientError); ok {
         fmt.Println("Error:", clientErr.Error())
         fmt.Println("Client Cause Err:", clientErr.Cause.Error())
      } else {
         fmt.Println("Error:", err)
      }
      panic(err)
   }
}

func main() {
   var (
      accessKey = os.Getenv("TOS_ACCESS_KEY")
      secretKey = os.Getenv("TOS_SECRET_KEY")
      // Bucket 对应的 Endpoint，以华北2（北京）为例：https://tos-cn-beijing.volces.com
      endpoint = "https://tos-cn-beijing.volces.com"
      region   = "cn-beijing"
      // 填写 BucketName
      bucketName = "*** Provide your bucket name ***"

      // 下载对象
      objectKey = "example_dir/example.txt"
      ctx       = context.Background()
   )
   // 初始化客户端
   client, err := tos.NewClientV2(endpoint, tos.WithRegion(region), tos.WithCredentials(tos.NewStaticCredentials(accessKey, secretKey)))
   checkErr(err)
   rateLimit1m := int64(1024 * 1024)
   // 下载数据到内存
   getOutput, err := client.GetObjectV2(ctx, &tos.GetObjectV2Input{
      Bucket: bucketName,
      Key:    objectKey,
      // 获取当前下载进度
      DataTransferListener: &listener{},
      // 配置客户端限制
      RateLimiter: NewDefaultRateLimit(rateLimit1m, rateLimit1m),
      // 下载时重写响应头
      ResponseContentType:     "application/json",
      ResponseContentEncoding: "deflate",
   })
   checkErr(err)
   fmt.Println("GetObjectV2 Request ID:", getOutput.RequestID)
   // 下载时前设置的 response content type
   fmt.Println("GetObjectV2 Response ContentType:", getOutput.ContentType)
   // 下载时前设置的 response content encoding
   fmt.Println("GetObjectV2 Response ContentEncoding:", getOutput.ContentEncoding)
   // 下载数据大小
   fmt.Println("GetObjectV2 Response ContentLength", getOutput.ContentLength)
   defer getOutput.Content.Close()
   body, err := ioutil.ReadAll(getOutput.Content)
   checkErr(err)
   // 完成下载
   fmt.Println("Get Object Content:", body)
}

下载数据到本地文件

从 TOS 中下载数据到指定的本地文件路径。

package main

import (
   "context"
   "fmt"

   "github.com/volcengine/ve-tos-golang-sdk/v2/tos"
)

func checkErr(err error) {
   if err != nil {
      if serverErr, ok := err.(*tos.TosServerError); ok {
         fmt.Println("Error:", serverErr.Error())
         fmt.Println("Request ID:", serverErr.RequestID)
         fmt.Println("Response Status Code:", serverErr.StatusCode)
         fmt.Println("Response Header:", serverErr.Header)
         fmt.Println("Response Err Code:", serverErr.Code)
         fmt.Println("Response Err Msg:", serverErr.Message)
      } else if clientErr, ok := err.(*tos.TosClientError); ok {
         fmt.Println("Error:", clientErr.Error())
         fmt.Println("Client Cause Err:", clientErr.Cause.Error())
      } else {
         fmt.Println("Error:", err)
      }
      panic(err)
   }
}

func main() {
   var (
      accessKey = os.Getenv("TOS_ACCESS_KEY")
      secretKey = os.Getenv("TOS_SECRET_KEY")
      // Bucket 对应的 Endpoint，以华北2（北京）为例：https://tos-cn-beijing.volces.com
      endpoint = "https://tos-cn-beijing.volces.com"
      region   = "cn-beijing"
      // 填写 BucketName
      bucketName = "*** Provide your bucket name ***"

      // 下载指定文件名的文件
      objectKey = "example_dir/example.txt"
      ctx       = context.Background()
   )
   // 初始化客户端
   client, err := tos.NewClientV2(endpoint, tos.WithRegion(region), tos.WithCredentials(tos.NewStaticCredentials(accessKey, secretKey)))
   checkErr(err)

   // 下载文件到指定的路径，示例中下载文件到 example_dir/example.txt
   getObjectToFileOutput, err := client.GetObjectToFile(ctx, &tos.GetObjectToFileInput{
      GetObjectV2Input: tos.GetObjectV2Input{
         Bucket: bucketName,
         Key:    objectKey,
      },
      FilePath: "example_dir/example.txt",
   })
   checkErr(err)
   fmt.Println("GetObjectToFile Request ID:", getObjectToFileOutput.RequestID)
   fmt.Println("GetObjectToFile File Size:", getObjectToFileOutput.ContentLength)
}

下载时重写 HTTP 响应头

以下代码用于下载桶中的对象 object-test，并重写 HTTP 响应头。

package main

import (
   "context"
   "fmt"
   "io/ioutil"

   "github.com/volcengine/ve-tos-golang-sdk/v2/tos"
)

func checkErr(err error) {
   if err != nil {
      if serverErr, ok := err.(*tos.TosServerError); ok {
         fmt.Println("Error:", serverErr.Error())
         fmt.Println("Request ID:", serverErr.RequestID)
         fmt.Println("Response Status Code:", serverErr.StatusCode)
         fmt.Println("Response Header:", serverErr.Header)
         fmt.Println("Response Err Code:", serverErr.Code)
         fmt.Println("Response Err Msg:", serverErr.Message)
      } else if clientErr, ok := err.(*tos.TosClientError); ok {
         fmt.Println("Error:", clientErr.Error())
         fmt.Println("Client Cause Err:", clientErr.Cause.Error())
      } else {
         fmt.Println("Error:", err)
      }
      panic(err)
   }
}

func main() {
   var (
      accessKey = os.Getenv("TOS_ACCESS_KEY")
      secretKey = os.Getenv("TOS_SECRET_KEY")
      // Bucket 对应的 Endpoint，以华北2（北京）为例：https://tos-cn-beijing.volces.com
      endpoint = "https://tos-cn-beijing.volces.com"
      region   = "cn-beijing"
      // 填写 BucketName
      bucketName = "*** Provide your bucket name ***"

      // 下载对象
      objectKey = "example_dir/example.txt"
      ctx       = context.Background()
   )
   // 初始化客户端
   client, err := tos.NewClientV2(endpoint, tos.WithRegion(region), tos.WithCredentials(tos.NewStaticCredentials(accessKey, secretKey)))
   checkErr(err)
   // 下载数据到内存
   getOutput, err := client.GetObjectV2(ctx, &tos.GetObjectV2Input{
      Bucket: bucketName,
      Key:    objectKey,
      // 下载时重写响应头
      ResponseContentType:     "application/json",
      ResponseContentEncoding: "deflate",
   })
   checkErr(err)
   fmt.Println("GetObjectV2 Request ID:", getOutput.RequestID)
   // 下载时前设置的 response content type
   fmt.Println("GetObjectV2 Response ContentType:", getOutput.ContentType)
   // 下载时前设置的 response content encoding
   fmt.Println("GetObjectV2 Response ContentEncoding:", getOutput.ContentEncoding)
   // 下载数据大小
   fmt.Println("GetObjectV2 Response ContentLength", getOutput.ContentLength)
   defer getOutput.Content.Close()
   body, err := ioutil.ReadAll(getOutput.Content)
   checkErr(err)
   // 完成下载
   fmt.Println("Get Object Content:", body)
}

配置进度条

下载时可通过实现 tos.DataTransferStatusChange 接口接收下载进度，代码示例如下。

package main

import (
   "context"
   "fmt"
   "io/ioutil"

   "github.com/volcengine/ve-tos-golang-sdk/v2/tos"
   "github.com/volcengine/ve-tos-golang-sdk/v2/tos/enum"
)

// 自定义进度回调，需要实现 tos.DataTransferStatusChange 接口
type listener struct {
}

func (l *listener) DataTransferStatusChange(event *tos.DataTransferStatus) {
   switch event.Type {
   case enum.DataTransferStarted:
      fmt.Println("Data transfer started")
   case enum.DataTransferRW:
      // Chunk 模式下 TotalBytes 值为 -1
      if event.TotalBytes != -1 {
         fmt.Printf("Once Read:%d,ConsumerBytes/TotalBytes: %d/%d,%d%%\n", event.RWOnceBytes, event.ConsumedBytes, event.TotalBytes, event.ConsumedBytes*100/event.TotalBytes)
      } else {
         fmt.Printf("Once Read:%d,ConsumerBytes:%d\n", event.RWOnceBytes, event.ConsumedBytes)
      }
   case enum.DataTransferSucceed:
      fmt.Printf("Data Transfer Succeed, ConsumerBytes/TotalBytes: %d/%d,%d%%\n", event.ConsumedBytes, event.TotalBytes, event.ConsumedBytes*100/event.TotalBytes)
   case enum.DataTransferFailed:
      fmt.Printf("Data Transfer Failed\n")
   }
}

func checkErr(err error) {
   if err != nil {
      if serverErr, ok := err.(*tos.TosServerError); ok {
         fmt.Println("Error:", serverErr.Error())
         fmt.Println("Request ID:", serverErr.RequestID)
         fmt.Println("Response Status Code:", serverErr.StatusCode)
         fmt.Println("Response Header:", serverErr.Header)
         fmt.Println("Response Err Code:", serverErr.Code)
         fmt.Println("Response Err Msg:", serverErr.Message)
      } else if clientErr, ok := err.(*tos.TosClientError); ok {
         fmt.Println("Error:", clientErr.Error())
         fmt.Println("Client Cause Err:", clientErr.Cause.Error())
      } else {
         fmt.Println("Error:", err)
      }
      panic(err)
   }
}

func main() {
   var (
      accessKey = os.Getenv("TOS_ACCESS_KEY")
      secretKey = os.Getenv("TOS_SECRET_KEY")
      // Bucket 对应的 Endpoint，以华北2（北京）为例：https://tos-cn-beijing.volces.com
      endpoint = "https://tos-cn-beijing.volces.com"
      region   = "cn-beijing"
      // 填写 BucketName
      bucketName = "*** Provide your bucket name ***"

      // 下载对象
      objectKey = "example_dir/example.txt"
      ctx       = context.Background()
   )
   // 初始化客户端
   client, err := tos.NewClientV2(endpoint, tos.WithRegion(region), tos.WithCredentials(tos.NewStaticCredentials(accessKey, secretKey)))
   checkErr(err)
   // 下载数据到内存
   getOutput, err := client.GetObjectV2(ctx, &tos.GetObjectV2Input{
      Bucket: bucketName,
      Key:    objectKey,
      // 获取当前下载进度
      DataTransferListener: &listener{},
   })
   checkErr(err)
   fmt.Println("GetObjectV2 Request ID:", getOutput.RequestID)
   // 下载时前设置的 response content type
   fmt.Println("GetObjectV2 Response ContentType:", getOutput.ContentType)
   // 下载时前设置的 response content encoding
   fmt.Println("GetObjectV2 Response ContentEncoding:", getOutput.ContentEncoding)
   // 下载数据大小
   fmt.Println("GetObjectV2 Response ContentLength", getOutput.ContentLength)
   defer getOutput.Content.Close()
   body, err := ioutil.ReadAll(getOutput.Content)
   checkErr(err)
   // 完成下载
   fmt.Println("Get Object Content:", body)
}

配置客户端限速

下载对象时可以通过客户端使用 tos.RateLimiter 接口对下载数据所占用的带宽进行限制，代码如下所示。

package main

import (
   "context"
   "fmt"
   "io/ioutil"
   "sync"
   "time"

   "github.com/volcengine/ve-tos-golang-sdk/v2/tos"
)

type rateLimit struct {
   rate     int64
   capacity int64

   currentAmount int64
   sync.Mutex
   lastConsumeTime time.Time
}

func NewDefaultRateLimit(rate int64, capacity int64) tos.RateLimiter {
   return &rateLimit{
      rate:            rate,
      capacity:        capacity,
      lastConsumeTime: time.Now(),
      currentAmount:   capacity,
      Mutex:           sync.Mutex{},
   }
}

func (d *rateLimit) Acquire(want int64) (ok bool, timeToWait time.Duration) {
   d.Lock()
   defer d.Unlock()
   if want > d.capacity {
      want = d.capacity
   }
   increment := int64(time.Now().Sub(d.lastConsumeTime).Seconds() * float64(d.rate))
   if increment+d.currentAmount > d.capacity {
      d.currentAmount = d.capacity
   } else {
      d.currentAmount += increment
   }
   if want > d.currentAmount {
      timeToWaitSec := float64(want-d.currentAmount) / float64(d.rate)
      return false, time.Duration(timeToWaitSec * float64(time.Second))
   }
   d.lastConsumeTime = time.Now()
   d.currentAmount -= want
   return true, 0
}

func checkErr(err error) {
   if err != nil {
      if serverErr, ok := err.(*tos.TosServerError); ok {
         fmt.Println("Error:", serverErr.Error())
         fmt.Println("Request ID:", serverErr.RequestID)
         fmt.Println("Response Status Code:", serverErr.StatusCode)
         fmt.Println("Response Header:", serverErr.Header)
         fmt.Println("Response Err Code:", serverErr.Code)
         fmt.Println("Response Err Msg:", serverErr.Message)
      } else if clientErr, ok := err.(*tos.TosClientError); ok {
         fmt.Println("Error:", clientErr.Error())
         fmt.Println("Client Cause Err:", clientErr.Cause.Error())
      } else {
         fmt.Println("Error:", err)
      }
      panic(err)
   }
}

func main() {
   var (
      accessKey = os.Getenv("TOS_ACCESS_KEY")
      secretKey = os.Getenv("TOS_SECRET_KEY")
      // Bucket 对应的 Endpoint，以华北2（北京）为例：https://tos-cn-beijing.volces.com
      endpoint = "https://tos-cn-beijing.volces.com"
      region   = "cn-beijing"
      // 填写 BucketName
      bucketName = "*** Provide your bucket name ***"

      // 下载对象
      objectKey = "example_dir/example.txt"
      ctx       = context.Background()
   )
   // 初始化客户端
   client, err := tos.NewClientV2(endpoint, tos.WithRegion(region), tos.WithCredentials(tos.NewStaticCredentials(accessKey, secretKey)))
   checkErr(err)
   rateLimit1m := int64(1024 * 1024)
   // 下载数据到内存
   getOutput, err := client.GetObjectV2(ctx, &tos.GetObjectV2Input{
      Bucket: bucketName,
      Key:    objectKey,
      // 配置客户端限制
      RateLimiter: NewDefaultRateLimit(rateLimit1m, rateLimit1m),
   })
   checkErr(err)
   fmt.Println("GetObjectV2 Request ID:", getOutput.RequestID)
   // 下载时前设置的 response content type
   fmt.Println("GetObjectV2 Response ContentType:", getOutput.ContentType)
   // 下载时前设置的 response content encoding
   fmt.Println("GetObjectV2 Response ContentEncoding:", getOutput.ContentEncoding)
   // 下载数据大小
   fmt.Println("GetObjectV2 Response ContentLength", getOutput.ContentLength)
   defer getOutput.Content.Close()
   body, err := ioutil.ReadAll(getOutput.Content)
   checkErr(err)
   // 完成下载
   fmt.Println("Get Object Content:", body)
}

对象存储