从 Window Azure 存储下载加密文件

Question

我创建了一个 MVC WebRole Window Azure 应用程序，我在其中使用 SymmetricAlgorithm (Rijndael) 将加密文件上传到 Azure blob 存储

控制器>动作是

[HttpPost]
public ActionResult UploadImage_post(HttpPostedFileBase fileBase)
{
    if (fileBase.ContentLength > 0)
    {
       // Retrieve a reference to a container 
       Microsoft.WindowsAzure.StorageClient.CloudBlobContainer blobContainer =
              _myBlobStorageService.GetCloudBlobContainer();

       Microsoft.WindowsAzure.StorageClient.CloudBlob blob =
                blobContainer.GetBlobReference(fileBase.FileName);
       using (BlobStream blobStream = blob.OpenWrite())
       {
             string encryptionKey = //somekey;
             byte[] file = new byte[fileBase.ContentLength];
             EncDecAlgo.EncryptBlobFile(file, blobStream, encryptionKey);
       }
    }
}

public void EncryptBlobFile(byte[] file, BlobStream bs, string key)
    {
        PasswordDeriveBytes pdb = new PasswordDeriveBytes(key,
            new byte[] {0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 
        0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76});
        Rijndael alg = Rijndael.Create();

        alg.Key = pdb.GetBytes(32);
        alg.IV = pdb.GetBytes(16);

        CryptoStream cs = new CryptoStream(bs,
           alg.CreateEncryptor(), CryptoStreamMode.Write);

        foreach (var data in file)
        {
            cs.WriteByte((byte)data);
        }

        cs.Close();
        bs.Close();
    }

上述文件加密工作正常。

用于下载代码

 public ActionResult DownloadFile(string filename)
    {
        // Retrieve reference to a previously created container.
        Microsoft.WindowsAzure.StorageClient.CloudBlobContainer blobContainer =
         _myBlobStorageService.GetCloudBlobContainer();

        Microsoft.WindowsAzure.StorageClient.CloudBlob blob =
            blobContainer.GetBlobReference(filename);
        blob.FetchAttributes();
        string encryptionKey = //same key used in encryption;
        using (BlobStream blobStream = blob.OpenRead())
        {
            EncDecAlgo.DecryptBlobFile(blobStream, encryptionKey, filename);
        }
    }

    public static void DecryptBlobFile(BlobStream bs, string key, string filePath)
    {
        try
        {
            PasswordDeriveBytes pdb = new PasswordDeriveBytes(key,
                new byte[] {0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 
        0x64, 0x76, 0x65, 0x64, 0x65, 0x76});

        Rijndael alg = Rijndael.Create();

        alg.Key = pdb.GetBytes(32);
        alg.IV =  pdb.GetBytes(16);

        CryptoStream cs = new CryptoStream(bs,
            alg.CreateDecryptor(), CryptoStreamMode.Read);

        // Decrypt & Download Here
        System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=" + Path.GetFileName(filePath));
        System.Web.HttpContext.Current.Response.ContentType = "application/" + Path.GetExtension(filePath).Replace(".", "");


        int data;
        while ((data = cs.ReadByte()) != -1)
        {
            if (data != 0)
            {
            }
            System.Web.HttpContext.Current.Response.OutputStream.WriteByte((byte)data);
            System.Web.HttpContext.Current.Response.Flush();

        }
        cs.Close();
        bs.Close();
        }
        catch
        {
        }
    }

下载时出现以下错误

Server cannot set content type after HTTP headers have been sent.

请提出一些解决方案。

Answer 1

这应该相当简单，希望这足以让你开始：

public class CloudFileResult : ActionResult
{
  private string m_FileName;
  private CloudBlobContainer m_Container;

  public CloudFileResult(string imageName, CloudBlobContainer container)
  {
    if (string.IsNullOrEmpty(imageName))
    {
      throw new ArgumentNullException("imageName");
    }
    if (container == null)
    {
      throw new ArgumentNullException("container");
    }

    m_FileName = imageName;
    m_Container = container;
  }

  public override void ExecuteResult(ControllerContext context)
  {
    context.HttpContext.Response.Clear();
    var blockBlob = m_Container.GetBlockBlobReference(m_FileName);
    blockBlob.FetchAttributes();
    context.HttpContext.Response.ContentType = blockBlob.Metadata["ContentType"];
    const string key = "my secret";
    using (var pdb = new Rfc2898DeriveBytes(key, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 }))
    {
      using (var alg = RijndaelManaged.Create())
      {
        alg.Key = pdb.GetBytes(32);
        alg.IV = pdb.GetBytes(16);
        using (var stream = new CryptoStream(context.HttpContext.Response.OutputStream, alg.CreateDecryptor(), CryptoStreamMode.Write))
        {
          blockBlob.DownloadToStream(stream);
        }
      }
    }
  }
}

static void UploadFileToCloud(CloudBlobContainer container, HttpPostedFileBase file)
{
  const string key = "my secret";
  using (var pdb = new Rfc2898DeriveBytes(key, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 }))
  {
    using (var alg = RijndaelManaged.Create())
    {
      alg.Key = pdb.GetBytes(32);
      alg.IV = pdb.GetBytes(16);

      var blockBlob = container.GetBlockBlobReference(file.FileName);
      using (var stream = new CryptoStream(file.InputStream, alg.CreateEncryptor(), CryptoStreamMode.Read))
      {
        blockBlob.UploadFromStream(stream);
      }
      blockBlob.Metadata.Add("ContentType", file.ContentType);
      blockBlob.SetMetadata();
    }
  }
}

static CloudBlobContainer GetContainer()
{
  string connection = "DefaultEndpointsProtocol=http;AccountName=AzureAccount;AccountKey=AzureAccountKey;";
  var account = CloudStorageAccount.Parse(connection);
  var client = account.CreateCloudBlobClient();
  var container = client.GetContainerReference("container");
  return container;
}

至于下载你可以简单使用：

[HttpGet]
public ActionResult Index(string fileName)
{
  if (!string.IsNullOrEmpty(fileName))
  {
    return new CloudFileResult(fileName, GetContainer());
  }
  return View();
}

指针：

• 我更喜欢使用托管加密算法
• 我将原始文件的内容类型存储在 blob 元数据中（因此您知道如何提供它）
• catch {} 让我毛骨悚然，至少在某处记录异常
• 与其玩弄 HttpContext.Response，不如创建自定义 ActionResult
• 始终丢弃 IDisposable 的东西