仍然是一个 "Multiple Dispose" 问题，尽管已得到处理

Question

在我的一些项目中，我一直在使用一对经过验证的数据encryption/decryption方法（加密方法粘贴在下面）。但我一直被这个关于 memoryStream 对象的烦人的 CA2202 警告 ("Do not dispose objects multiple times") 所困扰。我相信我以适当的方式处理了这个问题，但是每当我运行在 Visual Studio 中进行分析时，我仍然会收到警告。它从来没有在生产代码中抛出异常，但我仍然想一劳永逸地摆脱警告。那可能吗？还是我应该忽略它？提前致谢。

public static string Encrypt(string clearText, string passPhrase, string saltValue)
{
    byte[] clearTextBytes = Encoding.UTF8.GetBytes(clearText);
    byte[] saltValueBytes = Encoding.UTF8.GetBytes(saltValue);

    Rfc2898DeriveBytes passPhraseDerviedBytes = new Rfc2898DeriveBytes(passPhrase, saltValueBytes);
    byte[] keyBytes = passPhraseDerviedBytes.GetBytes(32);
    byte[] initVectorBytes = passPhraseDerviedBytes.GetBytes(16);

    RijndaelManaged symmetricKey = new RijndaelManaged() { Mode = CipherMode.CBC };
    ICryptoTransform encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes);

    byte[] cipherTextBytes = null;
    MemoryStream memoryStream = null;
    try
    {
        memoryStream = new MemoryStream();
        using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
        {
            cryptoStream.Write(clearTextBytes, 0, clearTextBytes.Length);
            cryptoStream.FlushFinalBlock();
            cipherTextBytes = memoryStream.ToArray();
        }
    }
    finally
    {
        if (memoryStream != null)
        {
            memoryStream.Dispose();
        }
    }

    return Convert.ToBase64String(cipherTextBytes);
}

Answer 1

因为CryptoStream关闭了memoryStream

您正在使用构造函数

public CryptoStream(Stream stream, ICryptoTransform transform, CryptoStreamMode mode)
    : this(stream, transform, mode, false) {
}

调用

public CryptoStream(Stream stream, ICryptoTransform transform, CryptoStreamMode mode, bool leaveOpen) {
    _stream = stream;
    _leaveOpen = leaveOpen;
    //...
}

_leaveOpen和_stream后来用在Dispose

protected override void Dispose(bool disposing) {
    try {
        if (!_leaveOpen) {
            _stream.Close();
        }
        //...
    }
}

您可以删除 memoryStream.Dispose();，或将 true 作为参数传递给 CryptoStream 构造函数

using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write, true)) { }

github source code reference

Answer 2

问题是对 CryptoStream.Dispose 的调用可以 调用给定流上的处置：

protected override void Dispose(bool disposing) 
{
    try 
    {
        if (disposing) 
        {
            if (!_finalBlockTransformed) 
            {
                FlushFinalBlock();
            }
            if (!_leaveOpen) 
            {
                _stream.Close();
            }
        }
    }
    ...
}

如果你使用带4个参数的构造函数：

CryptoStream(Stream stream, ICryptoTransform transform, CryptoStreamMode mode, bool leaveOpen)

最后一个参数决定流是否关闭。依次调用 Close() ，默认情况下还会调用 Dispose:

public virtual void Close()
{
    /* These are correct, but we'd have to fix PipeStream & NetworkStream very carefully.
    Contract.Ensures(CanRead == false);
    Contract.Ensures(CanWrite == false);
    Contract.Ensures(CanSeek == false);
    */

    Dispose(true);
    GC.SuppressFinalize(this);
}

因此，检查似乎无法正确确定具体的 Stream 实现是否会被 Disposed，而回过头来认为它会被处理 - 就是这种情况。

但是请注意，在大多数情况下，处理两次、一次或零次 MemoryStream 并不重要。

仍然是一个 "Multiple Dispose" 问题，尽管已得到处理

Still A "Multiple Dispose" Issue, Even Though Handled

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c#

ca2202