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使用签名URL下载

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默认情况下，OSS Bucket中的文件是私有的，仅文件拥有者可访问。您可以使用OSS Node.js SDK生成带有过期时间的GET方法签名URL，以允许他人临时下载文件。在有效期内可多次访问，超期后需重新生成。

注意事项

  • 本文以华东1（杭州）外网Endpoint为例。如果您希望通过与OSS同地域的其他阿里云产品访问OSS，请使用内网Endpoint。关于OSS支持的Region与Endpoint的对应关系，请参见OSS地域和访问域名。

  • 本文以从环境变量读取访问凭证为例。如何配置访问凭证，请参见配置访问凭证。

  • 生成GET方法的签名URL时，您必须具有oss:GetObject权限。具体操作，请参见为RAM用户授权自定义的权限策略。

    说明

    生成签名URL过程中，SDK利用本地存储的密钥信息，根据特定算法计算出签名（signature），然后将其附加到URL上，以确保URL的有效性和安全性。这一系列计算和构造URL的操作都是在客户端完成，不涉及网络请求到服务端。因此，生成签名URL时不需要授予调用者特定权限。但是，为避免第三方用户无法对签名URL授权的资源执行相关操作，需要确保调用生成签名URL接口的身份主体被授予对应的权限。

  • 本文以V4签名URL为例，有效期最大为7天。更多信息，请参见签名版本4（推荐）。

使用过程

使用签名URL下载文件的过程如下：

image

代码示例

  1. 文件拥有者生成GET方法的签名URL。

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

// 定义一个生成签名 URL 的函数
async function generateSignatureUrl(fileName) {
  // 获取签名URL
  const client = await new OSS({
      accessKeyId: 'yourAccessKeyId',
      accessKeySecret: 'yourAccessKeySecret',
      bucket: 'examplebucket',
      region: 'oss-cn-hangzhou',
  });

  return await client.signatureUrlV4('GET', 3600, {
      headers: {} // 请根据实际发送的请求头设置此处的请求头
  }, fileName);
}
// 调用函数并传入文件名
generateSignatureUrl('yourFileName').then(url => {
  console.log('Generated Signature URL:', url);
}).catch(err => {
  console.error('Error generating signature URL:', err);
});

  2. 其他人使用GET方法的签名URL下载文件。

    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=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********"

    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) {
        // 替换为生成的GET方法的签名URL。
        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=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********";
        // 填写文件保存的目标路径，包括文件名和扩展名。
        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");

        // 检查响应代码
        int responseCode = httpConn.getResponseCode();
        if (responseCode == HttpURLConnection.HTTP_OK) {
            // 输入流
            InputStream inputStream = new BufferedInputStream(httpConn.getInputStream());
            // 输出流
            FileOutputStream outputStream = new FileOutputStream(savePath);

            byte[] buffer = new byte[4096]; // 缓冲区
            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=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********";
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=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********"
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=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********"
    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=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********";
const savePath = "C:/downloads/myfile.txt"; // 文件将在下载时使用的文件名

fetch(fileURL)
    .then(response => {
        if (!response.ok) {
            throw new Error(`Server replied HTTP code: ${response.status}`);
        }
        return response.blob(); // 将响应转换为 blob
    })
    .then(blob => {
        const link = document.createElement('a');
        link.href = window.URL.createObjectURL(blob);
        link.download = savePath; // 设置下载文件的名字
        document.body.appendChild(link); // 此步骤确保链接存在于文档中
        link.click(); // 模拟点击下载链接
        link.remove(); // 完成后移除链接
        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"; // 修改后的保存路径
        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 {
        // 定义文件 URL 和保存路径（修改为有效的路径）
        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=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********";
        NSString *savePath = @"/Users/your_username/Desktop/myfile.txt"; // 请替换为您的用户名
        
        // 创建 URL 对象
        NSURL *url = [NSURL URLWithString:fileURL];
        
        // 创建下载任务
        NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            // 错误处理
            if (error) {
                NSLog(@"Error during download: %@", error.localizedDescription);
                return;
            }
            
            // 检查数据
            if (!data) {
                NSLog(@"No data received.");
                return;
            }
            
            // 保存文件
            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);
            }
        }];
        
        // 启动任务
        [task resume];
        
        // 让主线程继续运行以便异步请求能够完成
        [[NSRunLoop currentRunLoop] run];
    }
    return 0;
}

其他场景

生成带图片处理参数的签名URL

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

// 定义一个生成签名 URL 的函数
async function generateSignatureUrl(fileName) {
  // 创建 OSS 客户端
  const client = new OSS({
    accessKeyId: 'yourAccessKeyId',
    accessKeySecret: 'yourAccessKeySecret',
    // 如果你有 STS 令牌，可以加上这行
    // stsToken: 'yourSecurityToken',
    bucket: 'examplebucket',
    region: 'cn-hangzhou',
  });

  // 生成签名 URL
  const url = await client.signatureUrlV4('GET', 3600, {
    headers: {
      'Content-Type': 'application/octet-stream'
    }
  }, fileName);

  return url;
}

// 调用函数并传入文件名
generateSignatureUrl('yourFileName').then(url => {
  console.log('Generated Signature URL:', url);
}).catch(err => {
  console.error('Error generating signature URL:', err);
});

生成带versionId的签名URL

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

const client = await new OSS({
  accessKeyId: 'yourAccessKeyId',
  accessKeySecret: 'yourAccessKeySecret',
  stsToken: 'yourSecurityToken',
  bucket: 'yourBucket',
  region: 'yourRegion',
  // 设置secure为true，使用HTTPS，避免生成的下载链接被浏览器拦截
  secure: true,
});


// 生成签名的URL
const signedUrl = await client.signatureUrlV4('GET', 3600, {
  queries:{
    // 填写 Object 的 versionId
    "versionId":'yourVersionId'
  }
}, 'demo.pdf');

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