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用一个using语句替换嵌套的using语句

using-statement c#

0

Christian · 技术社区 · 8 年前

我发现自己在重复这个密码

using (var fileStream = new FileStream(path, FileMode.Open, FileAccess.Read)
{
  using (var aes = AesCryptoServiceProvider() { Key = ... }
  {

    // Read the IV at the beginning of the filestream

    using (var cryptoStream = new CryptoStream(fileStream, aes.CreateDecryptor(), CryptoStreamMode.Read)
    {

      // Actual code only using cryptoStream

    }
  }
}

和

using (var fileStream = new FileStream(path, FileMode.Create, FileAccess.Write)
{
  using (var aes = AesCryptoServiceProvider() { Key = ... }
  {

    // Write the IV at the beginning of the filestream

    using (var cryptoStream = new CryptoStream(fileStream, aes.CreateDecryptor(), CryptoStreamMode.Write)
    {

      // Actual code only using cryptoStream

    }
  }
}

我扪心自问,如果可以用这样的东西来代替这个

using (var cryptoStream = new MyDecryptionStream(path))
{
  // Actual code
}

实际代码可能非常不同。它可以是一个必须保存的图像或XML序列化。

我尝试实现自己的流类,该类将所有方法强制转换为私有属性cryptostream。但这没有成功。它总是在对位处断开,我一开始试着读第四章。

2 回复 | 直到 8 年前

1

N.D.C. 8 年前

这里有一个 非常粗糙 你想做什么的例子。有很多地方可以进行改进,但它是一个你可以指望的工作样本。

首先,我们创建一个实现 IDisposable . 这允许我们在 using 声明。这个类将实例化我们需要的其他三个对象,并处理它们的处理,全部由它自己完成。

class MyCryptoStream : IDisposable
{
    private FileStream fileStream = null;
    private AesCryptoServiceProvider aes = null;
    public CryptoStream cryptoStream = null;

    public enum Mode
    {
        Write,
        Read
    }

    public MyCryptoStream(string filepath, Mode mode, byte[] key, byte[] iv = null)
    {
        if(mode == Mode.Write)
        {
            fileStream = new FileStream(filepath, FileMode.Open, FileAccess.Write);
            fileStream.Write(iv, 0, 16);
            aes = new AesCryptoServiceProvider() { Key = key, IV = iv };

            cryptoStream = new CryptoStream(fileStream, aes.CreateEncryptor(), CryptoStreamMode.Write);
        }
        else
        {
            iv = new byte[16];
            fileStream = new FileStream(filepath, FileMode.Open, FileAccess.Read);
            fileStream.Read(iv, 0, 16);
            aes = new AesCryptoServiceProvider() { Key = key, IV = iv };

            cryptoStream = new CryptoStream(fileStream, aes.CreateDecryptor(), CryptoStreamMode.Read);
        }
    }

    #region IDisposable Support
    private bool disposedValue = false; // To detect redundant calls

    protected virtual void Dispose(bool disposing)
    {
        if (!disposedValue)
        {
            if (disposing)
            {
                if (cryptoStream != null)
                {
                    cryptoStream.Dispose();
                }
                if (aes != null)
                {
                    aes.Dispose();
                }
                if (fileStream != null)
                {
                    fileStream.Dispose();
                }
            }

            // TODO: free unmanaged resources (unmanaged objects) and override a finalizer below.
            // TODO: set large fields to null.

            disposedValue = true;
        }
    }

    // TODO: override a finalizer only if Dispose(bool disposing) above has code to free unmanaged resources.
    // ~UsingReduction() {
    //   // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
    //   Dispose(false);
    // }

    // This code added to correctly implement the disposable pattern.
    public void Dispose()
    {
        // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
        Dispose(true);
        // TODO: uncomment the following line if the finalizer is overridden above.
        // GC.SuppressFinalize(this);
    }
    #endregion

}

现在,我们可以这样使用这个类:

        string path = "..\\..\\test.txt";
        byte[] key = null;
        byte[] iv = null;
        using (AesCryptoServiceProvider myAes = new AesCryptoServiceProvider())
        {
            key = myAes.Key;
            iv = myAes.IV;
        }
        using (MyCryptoStream ur = new MyCryptoStream(path, MyCryptoStream.Mode.Write, key, iv))
        {
            using (StreamWriter sw = new StreamWriter(ur.cryptoStream))
            {
                sw.Write("Test string");
            }
        }
        string text = string.Empty;
        using (MyCryptoStream ur = new MyCryptoStream(path, MyCryptoStream.Mode.Read, key))
        {
            using (StreamReader sr = new StreamReader(ur.cryptoStream))
            {
                text = sr.ReadToEnd();
            }
        }

如果运行这个示例,您可以看到它的写入。 "Test string" 使用 cryptostream ,然后从该文件中读取相同的文本。检查的值 text 我们可以看到它仍然是 “测试字符串” ,表明程序是成功的。

2

1

cwharris 8 年前

助手函数呢?

public static TResult ReadFileUsingCrypto<TResult>(string path, KeyThing key, Func<CryptoStream, TResult> use)
{
    using (var fileStream = new FileStream(path, FileMode.Open, FileAccesa.Read))
    using (var aes = new AesCryptoServiceProvider(){...}))
    using (var cryptoStream = new CryptoStream(fileStream, aes.CreateDecryptor(), CryptoStreamMode.Read))
    {
        return use(cryptoStream);
    }
}

然后

var result = ReadFileUsingCrypto(âmyFileâ, key, crypto => <use crypto here and return result>);