Object Storage Service:Usar uma URL pré-assinada para baixar um objeto com o OSS SDK for Python 2.0

Notas de uso

• O código de exemplo neste tópico usa o ID da região cn-hangzhou, correspondente à região China (Hangzhou). O endpoint público é usado por padrão para acessar recursos em um bucket. Para acessar os recursos do bucket a partir de outros serviços da Alibaba Cloud na mesma região onde o bucket está localizado, use o endpoint interno. Para mais informações sobre regiões e endpoints do OSS, consulte Regiões e endpoints.

• Não são necessárias permissões especiais para gerar uma URL pré-assinada. No entanto, para que terceiros baixem o objeto usando essa URL, o usuário que a gera deve possuir a permissão oss:GetObject. Para saber mais sobre como conceder permissões, consulte Conceder permissões personalizadas a um usuário RAM.

• Este tópico usa o algoritmo de assinatura V4 para gerar URLs pré-assinadas com validade de até 7 dias. Para mais detalhes, consulte (Recomendado) Assinaturas V4 em URLs pré-assinadas.

Procedimento

O procedimento a seguir descreve como baixar um objeto usando uma URL pré-assinada:

Definição do método

Chame o método presign para gerar uma URL pré-assinada que concede acesso temporário a um objeto do OSS. Essa URL pode ser usada várias vezes antes de expirar.

A linha abaixo mostra a sintaxe do método presign:

presign(request: GetObjectRequest, **kwargs) → PresignResult

Parâmetros da solicitação

Parâmetros de resposta

Conteúdo de PresignResult

Para obter mais informações sobre o método presign, consulte presign.

Código de exemplo

1. Gere uma URL pré-assinada que permita solicitações HTTP GET:

   import argparse
   import alibabacloud_oss_v2 as oss
   
   # Create a command-line parameter parser and describe the purpose of the script.
   parser = argparse.ArgumentParser(description="presign get object sample")
   
   # Specify the --region parameter to indicate the region in which the bucket is located. This parameter is required.
   parser.add_argument('--region', help='The region in which the bucket is located.', required=True)
   # Specify the --bucket parameter to indicate the name of the bucket in which the object is stored. This parameter is required.
   parser.add_argument('--bucket', help='The name of the bucket.', required=True)
   # Specify the --endpoint parameter to indicate the endpoint of the region in which the bucket is located. This parameter is optional.
   parser.add_argument('--endpoint', help='The domain names that other services can use to access OSS')
   # Specify the --key parameter to indicate the name of the object. This parameter is required.
   parser.add_argument('--key', help='The name of the object.', required=True)
   
   def main():
       # Parse the command-line parameters to obtain the specified values.
       args = parser.parse_args()
   
       # From the environment variables, load the authentication information required to access OSS.
       credentials_provider = oss.credentials.EnvironmentVariableCredentialsProvider()
   
       # Use the default configuration to create a cfg object and specify the credential provider.
       cfg = oss.config.load_default()
       cfg.credentials_provider = credentials_provider
       
       # Set the region attribute of the cfg object to the region provided in the command line.
       cfg.region = args.region
   
       # If a custom endpoint is provided, update the endpoint attribute of the cfg object with the provided endpoint.
       if args.endpoint is not None:
           cfg.endpoint = args.endpoint
   
       # Use the preceding settings to initialize the OSSClient instance.
       client = oss.Client(cfg)
   
       # Initiate a request to generate a presigned URL.
       pre_result = client.presign(
           oss.GetObjectRequest(
               bucket=args.bucket,  # Specify the bucket name.
               key=args.key,        # Specify the object key.
           )
       )
   
       # Display the HTTP method, expiration time, and presigned URL.
       print(f'method: {pre_result.method},'
             f' expiration: {pre_result.expiration.strftime("%Y-%m-%dT%H:%M:%S.000Z")},'
             f' url: {pre_result.url}'
       )
   
       # Display the signed headers.
       for key, value in pre_result.signed_headers.items():
           print(f'signed headers key: {key}, signed headers value: {value}')
   
   # Call the main function to start the processing logic when the script is directly run.
   if __name__ == "__main__":
       main()  # Specify the entry point of the script. The control flow starts here.

2. Use a URL pré-assinada para baixar o objeto.

   curl

   curl -SO "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI****************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a******************************************************"

   Java

   import java.io.BufferedInputStream;
   import java.io.FileOutputStream;
   import java.io.IOException;
   import java.io.InputStream;
   import java.net.HttpURLConnection;
   import java.net.URL;
   
   public class Demo {
       public static void main(String[] args) {
           // Replace with the generated presigned URL for the GET request.
           String fileURL = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI****************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a******************************************************";
           // Enter the destination path to save the file, including the file name and extension.
           String savePath = "C:/downloads/myfile.txt";
   
           try {
               downloadFile(fileURL, savePath);
               System.out.println("Download completed!");
           } catch (IOException e) {
               System.err.println("Error during download: " + e.getMessage());
           }
       }
   
       private static void downloadFile(String fileURL, String savePath) throws IOException {
           URL url = new URL(fileURL);
           HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
           httpConn.setRequestMethod("GET");
   
           // Check the response code.
           int responseCode = httpConn.getResponseCode();
           if (responseCode == HttpURLConnection.HTTP_OK) {
               // Input stream.
               InputStream inputStream = new BufferedInputStream(httpConn.getInputStream());
               // Output stream.
               FileOutputStream outputStream = new FileOutputStream(savePath);
   
               byte[] buffer = new byte[4096]; // Buffer.
               int bytesRead;
               while ((bytesRead = inputStream.read(buffer)) != -1) {
                   outputStream.write(buffer, 0, bytesRead);
               }
   
               outputStream.close();
               inputStream.close();
           } else {
               System.out.println("No file to download. Server replied HTTP code: " + responseCode);
           }
           httpConn.disconnect();
       }
   }

   Node.js

   const https = require('https');
   const fs = require('fs');
   
   const fileURL = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI****************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a******************************************************";
   const savePath = "C:/downloads/myfile.txt";
   
   https.get(fileURL, (response) => {
       if (response.statusCode === 200) {
           const fileStream = fs.createWriteStream(savePath);
           response.pipe(fileStream);
           
           fileStream.on('finish', () => {
               fileStream.close();
               console.log("Download completed!");
           });
       } else {
           console.error(`Download failed. Server responded with code: ${response.statusCode}`);
       }
   }).on('error', (err) => {
       console.error("Error during download:", err.message);
   });

   Python

   import requests
   
   file_url = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI****************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a******************************************************"
   save_path = "C:/downloads/myfile.txt"
   
   try:
       response = requests.get(file_url, stream=True)
       if response.status_code == 200:
           with open(save_path, 'wb') as f:
               for chunk in response.iter_content(4096):
                   f.write(chunk)
           print("Download completed!")
       else:
           print(f"No file to download. Server replied HTTP code: {response.status_code}")
   except Exception as e:
       print("Error during download:", e)

   Go

   package main
   
   import (
       "io"
       "net/http"
       "os"
   )
   
   func main() {
       fileURL := "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI****************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a******************************************************"
       savePath := "C:/downloads/myfile.txt"
   
       response, err := http.Get(fileURL)
       if err != nil {
           panic(err)
       }
       defer response.Body.Close()
   
       if response.StatusCode == http.StatusOK {
           outFile, err := os.Create(savePath)
           if err != nil {
               panic(err)
           }
           defer outFile.Close()
   
           _, err = io.Copy(outFile, response.Body)
           if err != nil {
               panic(err)
           }
           println("Download completed!")
       } else {
           println("No file to download. Server replied HTTP code:", response.StatusCode)
       }
   }

   JavaScript

   const fileURL = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI****************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a******************************************************";
   const savePath = "C:/downloads/myfile.txt"; // The file name to use for the download.
   
   fetch(fileURL)
       .then(response => {
           if (!response.ok) {
               throw new Error(`Server replied HTTP code: ${response.status}`);
           }
           return response.blob(); // Convert the response to a blob.
       })
       .then(blob => {
           const link = document.createElement('a');
           link.href = window.URL.createObjectURL(blob);
           link.download = savePath; // Set the name of the downloaded file.
           document.body.appendChild(link); // This step ensures that the link exists in the document.
           link.click(); // Simulate a click on the download link.
           link.remove(); // Remove the link after completion.
           console.log("Download completed!");
       })
       .catch(error => {
           console.error("Error during download:", error);
       });

   Android-Java

   import android.os.AsyncTask;
   import android.os.Environment;
   import java.io.BufferedInputStream;
   import java.io.FileOutputStream;
   import java.io.InputStream;
   import java.net.HttpURLConnection;
   import java.net.URL;
   
   public class DownloadTask extends AsyncTask<String, String, String> {
       @Override
       protected String doInBackground(String... params) {
           String fileURL = params[0];
           String savePath = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + "/myfile.txt"; // The modified save path.
           try {
               URL url = new URL(fileURL);
               HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
               httpConn.setRequestMethod("GET");
               int responseCode = httpConn.getResponseCode();
               if (responseCode == HttpURLConnection.HTTP_OK) {
                   InputStream inputStream = new BufferedInputStream(httpConn.getInputStream());
                   FileOutputStream outputStream = new FileOutputStream(savePath);
                   byte[] buffer = new byte[4096];
                   int bytesRead;
                   while ((bytesRead = inputStream.read(buffer)) != -1) {
                       outputStream.write(buffer, 0, bytesRead);
                   }
                   outputStream.close();
                   inputStream.close();
                   return "Download completed!";
               } else {
                   return "No file to download. Server replied HTTP code: " + responseCode;
               }
           } catch (Exception e) {
               return "Error during download: " + e.getMessage();
           }
       }
   }

   Objective-C

   #import <Foundation/Foundation.h>
   
   int main(int argc, const char * argv[]) {
       @autoreleasepool {
           // Define the file URL and save path (change to a valid path).
           NSString *fileURL = @"https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI****************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a******************************************************";
           NSString *savePath = @"/Users/your_username/Desktop/myfile.txt"; // Replace with your username.
           
           // Create a URL object.
           NSURL *url = [NSURL URLWithString:fileURL];
           
           // Create a download task.
           NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
               // Error handling.
               if (error) {
                   NSLog(@"Error during download: %@", error.localizedDescription);
                   return;
               }
               
               // Check the data.
               if (!data) {
                   NSLog(@"No data received.");
                   return;
               }
               
               // Save the file.
               NSError *writeError = nil;
               BOOL success = [data writeToURL:[NSURL fileURLWithPath:savePath] options:NSDataWritingAtomic error:&writeError];
               if (success) {
                   NSLog(@"Download completed!");
               } else {
                   NSLog(@"Error saving file: %@", writeError.localizedDescription);
               }
           }];
           
           // Start the task.
           [task resume];
           
           // Keep the main thread running so that the asynchronous request can be completed.
           [[NSRunLoop currentRunLoop] run];
       }
       return 0;
   }

Cenários comuns

import argparse
import alibabacloud_oss_v2 as oss

# Create a command-line parameter parser and describe the purpose of the script.
parser = argparse.ArgumentParser(description="presign get object sample")

# Specify the --region parameter to indicate the region in which the bucket is located. This parameter is required.
parser.add_argument('--region', help='The region in which the bucket is located.', required=True)
# Specify the --bucket parameter to indicate the name of the bucket in which the object is stored. This parameter is required.
parser.add_argument('--bucket', help='The name of the bucket.', required=True)
# Specify the --endpoint parameter to indicate the endpoint of the region in which the bucket is located. This parameter is optional.
parser.add_argument('--endpoint', help='The domain names that other services can use to access OSS')
# Specify the --key parameter to indicate the name of the object. This parameter is required.
parser.add_argument('--key', help='The name of the object.', required=True)

def main():
    # Parse the command-line parameters to obtain the specified values.
    args = parser.parse_args()

    # From the environment variables, load the authentication information required to access OSS.
    credentials_provider = oss.credentials.EnvironmentVariableCredentialsProvider()

    # Use the default configuration to create a cfg object and specify the credential provider.
    cfg = oss.config.load_default()
    cfg.credentials_provider = credentials_provider
    
    # Specify the region attribute of the configuration object based on the command line parameters specified by the user.
    cfg.region = args.region

    # If a custom endpoint is provided, update the endpoint attribute of the cfg object with the provided endpoint.
    if args.endpoint is not None:
        cfg.endpoint = args.endpoint

    # Use the preceding settings to initialize the OSSClient instance.
    client = oss.Client(cfg)

    # Initiate a request to generate a presigned URL.
    # The version_id parameter is optional. You need to specify this parameter only when the bucket that contains the object is versioned.
    pre_result = client.presign(
        oss.GetObjectRequest(
            bucket=args.bucket,  # Specify the bucket name.
            key=args.key,        # Specify the object key.
            version_id='yourVersionId'  # If applicable, specify the version ID of the object.
        )
    )

    # Display the HTTP method, expiration time, and presigned URL.
    print(f'method: {pre_result.method},'
          f' expiration: {pre_result.expiration.strftime("%Y-%m-%dT%H:%M:%S.000Z")},'
          f' url: {pre_result.url}'
    )

    # Display the signed headers.
    for key, value in pre_result.signed_headers.items():
        print(f'signed headers key: {key}, signed headers value: {value}')

# Call the main function to start the processing logic when the script is directly run.
if __name__ == "__main__":
    main()  # Specify the entry point of the script. The control flow starts here.

import argparse
import alibabacloud_oss_v2 as oss

# Create a command-line parameter parser and describe the purpose of the script.
parser = argparse.ArgumentParser(description="presign get object sample")

# Specify the --region parameter to indicate the region in which the bucket is located. This parameter is required.
parser.add_argument('--region', help='The region in which the bucket is located.', required=True)
# Specify the --bucket parameter to indicate the name of the bucket in which the object is stored. This parameter is required.
parser.add_argument('--bucket', help='The name of the bucket.', required=True)
# Specify the --endpoint parameter to indicate the endpoint of the region in which the bucket is located. This parameter is optional.
parser.add_argument('--endpoint', help='The domain names that other services can use to access OSS')
# Specify the --key parameter to indicate the name of the object. This parameter is required.
parser.add_argument('--key', help='The name of the object.', required=True)

def main():
    # Parse the command-line parameters to obtain the specified values.
    args = parser.parse_args()

    # From the environment variables, load the authentication information required to access OSS.
    credentials_provider = oss.credentials.EnvironmentVariableCredentialsProvider()

    # Use the default configuration to create a cfg object and specify the credential provider.
    cfg = oss.config.load_default()
    cfg.credentials_provider = credentials_provider
    
    # Specify the region attribute of the configuration object based on the command line parameters specified by the user.
    cfg.region = args.region

    # Specify the custom endpoint. Example: http://static.example.com
    cfg.endpoint = "http://static.example.com"
    
    # Enable CNAME record resolution.
    cfg.use_cname = True

    # Use the preceding settings to initialize the OSSClient instance.
    client = oss.Client(cfg)

    # Initiate a request to generate a presigned URL.
    pre_result = client.presign(
        oss.GetObjectRequest(
            bucket=args.bucket,  # Specify the bucket name.
            key=args.key,        # Specify the object key.
        )
    )

    # Display the HTTP method, expiration time, and presigned URL.
    print(f'method: {pre_result.method},'
          f' expiration: {pre_result.expiration.strftime("%Y-%m-%dT%H:%M:%S.000Z")},'
          f' url: {pre_result.url}'
    )

    # Display the signed headers.
    for key, value in pre_result.signed_headers.items():
        print(f'signed headers key: {key}, signed headers value: {value}')

# Call the main function to start the processing logic when the script is directly run.
if __name__ == "__main__":
    main()  # Specify the entry point of the script. The control flow starts here.

Referências

• Para obter o código de exemplo completo sobre como baixar um objeto usando uma URL pré-assinada, consulte presigner_get_object.py.