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Download an object by using a presigned URL (Node.js SDK)

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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:

image

Code examples

  1. 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);
});

  2. 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) {
        // 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;
}

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

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