Object Storage Service:Download an object by using a signed URL (Go SDK V1)

Precautions

• In this topic, the public endpoint of the China (Hangzhou) region is used. To access OSS from other Alibaba Cloud services in the same region, use an internal endpoint. For details about supported regions and endpoints, see Regions and endpoints.

• The examples in this topic show how to read access credentials from environment variables. For more information about how to configure access credentials, see Configure access credentials (Go SDK V1).

• 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 Configuration examples for common scenarios.

• You do not need specific permissions to generate a presigned URL. However, to allow others to use the presigned URL to download an object, you must have the oss:GetObject permission. For more information, see Common examples of RAM policies.

• The examples in this topic use V4 signed URLs. The maximum validity period is 7 days. For more information, see Signature V4 (recommended).

Process

The following flowchart shows how to download an object by using a presigned URL.

Sample code

1. The object owner generates a signed URL for a GET request.

   package main
   
   import (
   	"log"
   
   	"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.Printf("Error: %v\n", err)
   	}
   
   	// Create an OSSClient instance.
   	// Set yourEndpoint to the endpoint of the bucket. For example, for a bucket in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. For other regions, set the endpoint as needed.
   	// Set yourRegion to the region where the bucket is located. For example, for a bucket in the China (Hangzhou) region, set the region to cn-hangzhou. For other regions, set the region as needed.
   	clientOptions := []oss.ClientOption{oss.SetCredentialsProvider(&provider)}
   	clientOptions = append(clientOptions, oss.Region("cn-hangzhou"))
   	// Set the signature version.
   	clientOptions = append(clientOptions, oss.AuthVersion(oss.AuthV4))
   	client, err := oss.New("yourEndpoint", "", "", clientOptions...)
   	if err != nil {
   		log.Printf("Error: %v\n", err)
   	}
   
   	// Specify the bucket name, for example, examplebucket.
   	bucketName := "examplebucket"
   	// Specify the object name, for example, exampleobject.txt. The object name cannot contain the bucket name.
   	objectName := "exampleobject.txt"
   	// Download the object to a local file and save it to the specified local path. If the specified local file exists, it is overwritten. If the file does not exist, it is created.
   	bucket, err := client.Bucket(bucketName)
   	if err != nil {
   		log.Printf("Error: %v\n", err)
   	}
   
   	// Generate a signed URL for downloading the object and set the validity period of the signed URL to 600 seconds.
   	signedURL, err := bucket.SignURL(objectName, oss.HTTPGet, 600)
   	if err != nil {
   		log.Printf("Error: %v\n", err)
   	}
   	log.Printf("Sign Url:%s\n", signedURL)
   }
   

2. Other users download the object using the signed URL for the GET request.

   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) {
           // Specify the presigned URL that allows HTTP GET requests. 
           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******************************************************";
           // Specify the path in which the downloaded object is stored, including the object 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");
   
           // Specify the response code.
           int responseCode = httpConn.getResponseCode();
           if (responseCode == HttpURLConnection.HTTP_OK) {
               // Configure the input stream.
               InputStream inputStream = new BufferedInputStream(httpConn.getInputStream());
               // Configure the output stream.
               FileOutputStream outputStream = new FileOutputStream(savePath);
   
               byte[] buffer=new byte[4096]; // Specify the size of the 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"; // Specify the name of the downloaded object.
   
   fetch(fileURL)
       .then(response => {
           if (!response.ok) {
               throw new Error(`Server replied HTTP code: ${response.status}`);
           }
           return response.blob(); // Change the type of the response to blob.
       })
       .then(blob => {
           const link = document.createElement('a');
           link.href = window.URL.createObjectURL(blob);
           link.download=savePath; // Specify the name of the downloaded object.
           document.body.appendChild(link); // This step ensures that the presigned URL exists in the document.
           link.click(); // Click the presigned URL to simulate the object download.
           link.remove(); // Remove the presigned URL after the object is downloaded.
           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"; // Specify the path in which you want to store the downloaded object.
           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 {
           // Specify the presigned URL and the path in which you want to store the object.
           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 your_username with your username.
           
           // Create a URL object.
           NSURL *url = [NSURL URLWithString:fileURL];
           
           // Create an object download task.
           NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
               // Handle errors.
               if (error) {
                   NSLog(@"Error during download: %@", error.localizedDescription);
                   return;
               }
               
               // Check the data in the object.
               if (!data) {
                   NSLog(@"No data received.");
                   return;
               }
               
               // Save the object.
               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 object download task.
           [task resume];
           
           // Continue to run the main thread to complete the asynchronous request.
           [[NSRunLoop currentRunLoop] run];
       }
       return 0;
   }

Other scenarios

package main

import (
	"log"

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

	// Create an OSSClient instance.
	// Set yourEndpoint to the endpoint of the bucket. For example, for a bucket in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. For other regions, set the endpoint as needed.
	// Set yourRegion to the region where the bucket is located. For example, for a bucket in the China (Hangzhou) region, set the region to cn-hangzhou. For other regions, set the region as needed.
	clientOptions := []oss.ClientOption{oss.SetCredentialsProvider(&provider)}
	clientOptions = append(clientOptions, oss.Region("cn-hangzhou"))
	// Set the signature version.
	clientOptions = append(clientOptions, oss.AuthVersion(oss.AuthV4))
	client, err := oss.New("yourEndpoint", "", "", clientOptions...)
	if err != nil {
		log.Printf("Error: %v", err)
	}

	// Specify the bucket name, for example, examplebucket.
	bucketName := "examplebucket"
	// Specify the full path of the object, for example, exampledir/exampleobject.txt. The full path cannot contain the bucket name.
	objectName := "exampledir/exampleobject.txt"
	// Download the object to a local file and save it to the specified local path. If the specified local file exists, it is overwritten. If the file does not exist, it is created.
	bucket, err := client.Bucket(bucketName)
	if err != nil {
		log.Printf("Error: %v", err)
	}

	// Specify the version ID of the file to download.
	options := []oss.Option{
		oss.VersionId("CAEQEhiBgIDmgPf8mxgiIDA1YjZlNDIxY2ZmMzQ1MmU5MTM1Y2M4Yzk4******"),
	}

	// Generate a signed URL for downloading the object and set the validity period of the signed URL to 600 seconds.
	signedURL, err := bucket.SignURL(objectName, oss.HTTPGet, 600, options...)
	if err != nil {
		log.Printf("Error: %v", err)
	}
	log.Printf("Sign Url:%s\n", signedURL)
}

References

• For the complete sample code that shows how to download an object using a signed URL, see GitHub example.

• For more information about the API operation that you can call to download an object using a signed URL, see SignURL.