node.js download using presigned url - Object Storage Service

By default, objects in an Object Storage Service (OSS) bucket are private and can be accessed only by the object owner. You can use the OSS SDK for Node.js to generate a presigned URL for a GET request. This URL allows other users to temporarily download the object. The URL can be accessed multiple times before it expires. After the URL expires, a new one must be generated.

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.
This topic provides an example of how to retrieve access credentials from environment variables. For more information about how to configure access credentials, see Configure access credentials (Node.js SDK).
To generate a presigned URL for a GET request, you must have the oss:GetObject permission. For more information, see Grant custom permissions to a RAM user.
This topic uses V4 presigned URLs as an example. The maximum validity period is seven days. For more information, see Signature V4 (Recommended).

Process

The process of downloading an object using a presigned URL is as follows:

Code examples

The object owner generates a presigned URL for a GET request.

const OSS = require("ali-oss");

// Define a function to generate a presigned URL.
async function generateSignatureUrl(fileName) {
  // Obtain the presigned URL.
  const client = await new OSS({
      // 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.
      accessKeyId: process.env.OSS_ACCESS_KEY_ID,
      accessKeySecret: process.env.OSS_ACCESS_KEY_SECRET,
      bucket: 'examplebucket',
      // Replace yourregion with the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to oss-cn-hangzhou.
      region: 'oss-cn-hangzhou',
      // Set secure to true to use HTTPS. This prevents the browser from blocking the generated download link.
      secure: true,
      authorizationV4: true
  });

  return await client.signatureUrlV4('GET', 3600, {
      headers: {} // Set the request headers based on the actual request headers.
  }, fileName);
}
// Call the function and pass the file name.
generateSignatureUrl('yourFileName').then(url => {
  console.log('Generated Signature URL:', url);
}).catch(err => {
  console.error('Error generating signature URL:', err);
});

Other users download 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;
}

Other scenarios

Generate a presigned URL with image processing parameters

const OSS = require("ali-oss");

// Define a function to generate a presigned URL.
async function generateSignatureUrl(fileName) {
  // Obtain the presigned URL.
  const client = await new OSS({
    // 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.
    accessKeyId: process.env.OSS_ACCESS_KEY_ID,
    accessKeySecret: process.env.OSS_ACCESS_KEY_SECRET,
    bucket: 'examplebucket',
    // Replace yourregion with the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to oss-cn-hangzhou.
    region: 'oss-cn-hangzhou',
    authorizationV4: true,
    cname: true
  });

  // Generate a signed URL that includes document processing parameters.
  return await client.signatureUrlV4('GET', 3600, {
    headers: {}, // Set the request headers based on the actual request headers.
    queries: {
     "x-oss-process": "image/resize,m_fixed,w_100,h_100" // Add image processing parameters.
    }
  }, fileName);
}

// Call the function and pass the image name.
generateSignatureUrl('test.jpg').then(url => {
  console.log('Generated Signature URL:', url);
}).catch(err => {
  console.error('Error generating signature URL:', err);
});

Generate a presigned URL with a version ID

const OSS = require("ali-oss");

const client = await new OSS({
  // 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.
  accessKeyId: process.env.OSS_ACCESS_KEY_ID,
  accessKeySecret: process.env.OSS_ACCESS_KEY_SECRET,
  bucket: 'examplebucket',
  // Replace yourregion with the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to oss-cn-hangzhou.
  region: 'oss-cn-hangzhou',
  // Set secure to true to use HTTPS. This prevents the browser from blocking the generated download link.
  secure: true,
  authorizationV4: true
});


// Generate a presigned URL.
const signedUrl = await client.signatureUrlV4('GET', 3600, {
  queries:{
    // Specify the version ID of the object.
    "versionId":'yourVersionId'
  }
}, 'demo.pdf');

Generate a presigned URL for download using a custom domain name

The following code provides an example of how to generate a presigned URL for a GET request using a custom domain name.

const OSS = require("ali-oss");

// Define a function to generate a presigned URL.
async function generateSignatureUrl(fileName) {
  // Obtain the presigned URL.
  const client = await new OSS({
      // Use a custom domain name as the endpoint.
      endpoint: 'http://static.example.com', 
      // 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.
      accessKeyId: process.env.OSS_ACCESS_KEY_ID,
      accessKeySecret: process.env.OSS_ACCESS_KEY_SECRET,
      bucket: 'examplebucket',
      // Replace yourregion with the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to oss-cn-hangzhou.
      region: 'oss-cn-hangzhou',
      authorizationV4: true,
      cname: true
  });

  return await client.signatureUrlV4('GET', 3600, {
      headers: {} // Set the request headers based on the actual request headers.
  }, fileName);
}
// Call the function and pass the file name.
generateSignatureUrl('yourFileName').then(url => {
  console.log('Generated Signature URL:', url);
}).catch(err => {
  console.error('Error generating signature URL:', err);
});

References

For more information about the API operation that is used to generate a presigned URL, see GeneratePresignedUrlRequest.