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    Object Storage Service：使用預簽名URL下載（C# SDK V2）

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    Object Storage Service：使用預簽名URL下載（C# SDK V2）

    更新時間：Aug 06, 2025

    預設情況下，OSS Bucket中的檔案是私人的，僅檔案擁有者可訪問。本文介紹如何使用OSS C# SDK產生帶有到期時間的GET方法預簽名URL，以允許他人臨時下載檔案。在有效期間內可多次訪問，超期後需重建。

    注意事項

    • 本文範例程式碼以華東1（杭州）的地區IDcn-hangzhou為例，預設使用外網Endpoint，如果您希望通過與OSS同地區的其他阿里雲產品訪問OSS，請使用內網Endpoint。關於OSS支援的Region與Endpoint的對應關係，請參見OSS地區和訪問網域名稱。

    • 預簽名URL無需許可權即可產生，但僅當您擁有oss:GetObject許可權時，第三方才能通過該預簽名URL成功下載檔案。具體授權操作，請參見為RAM使用者授權自訂的權限原則。

    使用過程

    使用預簽名URL下載檔案的過程如下：

    範例程式碼

    1. 檔案擁有者產生GET方法的預簽名URL。

      using OSS = AlibabaCloud.OSS.V2;  // 為阿里雲OSS SDK建立別名，簡化後續使用

var region = "cn-hangzhou";  // 必須項，設定Bucket所在的地區（Region）。以華東1（杭州）為例，Region填寫為cn-hangzhou
var endpoint = null as string;  // 可選項，指定訪問OSS服務的網域名稱。以華東1（杭州）為例，Endpoint填寫為https://oss-cn-hangzhou.aliyuncs.com
var bucket = "your bucket name";  // 必須項，Bucket名稱
var key = "your object name";  // 必須項，需要產生預簽名URL的目標對象名稱

// 載入OSS SDK的預設配置，此配置會自動從環境變數中讀取憑證資訊（如AccessKey）
var cfg = OSS.Configuration.LoadDefault();
// 顯式設定使用環境變數擷取憑證，用於身分識別驗證（格式：OSS_ACCESS_KEY_ID、OSS_ACCESS_KEY_SECRET）
cfg.CredentialsProvider = new OSS.Credentials.EnvironmentVariableCredentialsProvider();
// 設定配置的Bucket地區
cfg.Region = region;   
// 若已指定了endpoint，則覆蓋預設的endpoint 
if(endpoint != null) 
{
    cfg.Endpoint = endpoint;
} 

// 使用配置資訊建立OSS用戶端執行個體
using var client = new OSS.Client(cfg); 

// 調用Presign方法產生預簽名URL
var result = client.Presign(new OSS.Models.GetObjectRequest()
{
    Bucket = bucket,
    Key = key,
});

using var hc = new HttpClient();  // 使用HttpClient發送HTTP請求擷取對象內容
var httpResult = await hc.GetAsync(result.Url);  // 發送GET請求到預簽名URL
var stream = await httpResult.Content.ReadAsStreamAsync();  // 讀取響應內容為流 
using var reader = new StreamReader(stream);  // 使用StreamReader將流轉換為字串
var got = await reader.ReadToEndAsync();

// 列印操作完成提示
Console.WriteLine("GetObject done");
Console.WriteLine($"StatusCode: {httpResult.StatusCode}");  //HTTP響應狀態代碼

    2. 其他人使用GET方法的預簽名URL下載檔案。

      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) {
        // 替換為產生的GET方法的預簽名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=LTAI****************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a******************************************************";
        // 填寫檔案儲存的目標路徑，包括檔案名稱和副檔名。
        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");

        // 檢查響應代碼
        int responseCode = httpConn.getResponseCode();
        if (responseCode == HttpURLConnection.HTTP_OK) {
            // 輸入資料流
            InputStream inputStream = new BufferedInputStream(httpConn.getInputStream());
            // 輸出資料流
            FileOutputStream outputStream = new FileOutputStream(savePath);

            byte[] buffer = new byte[4096]; // 緩衝區
            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"; // 檔案將在下載時使用的檔案名稱

fetch(fileURL)
    .then(response => {
        if (!response.ok) {
            throw new Error(`Server replied HTTP code: ${response.status}`);
        }
        return response.blob(); // 將響應轉換為 blob
    })
    .then(blob => {
        const link = document.createElement('a');
        link.href = window.URL.createObjectURL(blob);
        link.download = savePath; // 設定下載檔案的名字
        document.body.appendChild(link); // 此步驟確保連結存在於文檔中
        link.click(); // 類比點擊下載連結
        link.remove(); // 完成後移除連結
        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"; // 修改後的儲存路徑
        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 {
        // 定義檔案 URL 和儲存路徑（修改為有效路徑）
        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"; // 請替換為您的使用者名稱
        
        // 建立 URL 對象
        NSURL *url = [NSURL URLWithString:fileURL];
        
        // 建立下載任務
        NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            // 錯誤處理
            if (error) {
                NSLog(@"Error during download: %@", error.localizedDescription);
                return;
            }
            
            // 檢查資料
            if (!data) {
                NSLog(@"No data received.");
                return;
            }
            
            // 儲存檔案
            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);
            }
        }];
        
        // 啟動任務
        [task resume];
        
        // 讓主線程繼續運行以便非同步請求能夠完成
        [[NSRunLoop currentRunLoop] run];
    }
    return 0;
}

    相關文檔

    關於使用預簽名URL下載的完整範例程式碼，請參見PresignGetObject.cs。