By default, objects in an Object Storage Service (OSS) bucket are private. Only the object owner can access them. You can use the OSS SDK for Python to generate a presigned URL for a GET request that includes a specified expiration time. This allows other users to temporarily download the object. The URL can be used multiple times before it expires. After the URL expires, you must generate a new one.
Notes
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 use access credentials that are configured as environment variables. For more information about how to configure access credentials, see Configure access credentials.
The examples in this topic show how to use an OSS endpoint to create an OSSClient instance. If you want to create an OSSClient instance using a custom domain name or Security Token Service (STS), see Initialization (Python SDK V1).
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:GetObjectpermission. For more information, see Common examples of RAM policies.The examples in this topic use V4 presigned URLs. The maximum validity period for a V4 presigned URL is seven days. For more information, see Signature V4 (Recommended).
Process
The following procedure describes how to download an object using a presigned URL:
Sample code
The object owner generates a presigned URL for a GET request.
# -*- coding: utf-8 -*- import oss2 from oss2.credentials import EnvironmentVariableCredentialsProvider # Obtain access credentials from environment variables. Before you run this code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are set. auth = oss2.ProviderAuthV4(EnvironmentVariableCredentialsProvider()) # Set Endpoint to the endpoint of the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. endpoint = "https://oss-cn-hangzhou.aliyuncs.com" # Set region to the region ID that corresponds to the endpoint, for example, cn-hangzhou. Note: This parameter is required for V4 signatures. region = "cn-hangzhou" # Set yourBucketName to the name of the bucket. bucket = oss2.Bucket(auth, endpoint, "yourBucketName", region=region) # Set object_name to the full path of the object. The full path cannot contain the bucket name. object_name = 'exampledir/exampleobject.txt' # Generate a presigned URL to download the file. The URL is valid for 600 seconds. # When you generate a presigned URL, OSS escapes the forward slashes (/) in the full path of the object by default. This makes the generated signed URL unusable. # Set slash_safe to True. This prevents OSS from escaping the forward slashes (/) in the full path. The generated signed URL can then be used directly. url = bucket.sign_url('GET', object_name, 600, slash_safe=True) print('The presigned URL is: ', url)A user downloads the object using the presigned 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; }