面试题：C#中如何实现自定义的异步文件操作及IO流处理策略

实现思路

C#异步编程模型：
- 使用async和await关键字实现异步操作。async用于标记异步方法，await用于暂停方法执行，直到异步操作完成。例如，在文件读写操作时，使用File.ReadAllBytesAsync和File.WriteAllBytesAsync等异步方法，这样主线程不会被阻塞，提高应用程序的响应性。

IO流处理方式：

对于文件读取，使用FileStream结合BufferedStream来提高读取效率。在读取字节流后，可以通过MemoryStream进行中间处理。例如，在读取文件内容时：

using (var fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
using (var bufferedStream = new BufferedStream(fileStream))
using (var memoryStream = new MemoryStream())
{
    await bufferedStream.CopyToAsync(memoryStream);
    byte[] fileBytes = memoryStream.ToArray();
}

对于文件写入，同样使用FileStream和BufferedStream，将处理后的字节流写入文件。例如：

using (var fileStream = new FileStream(filePath, FileMode.Create, FileAccess.Write))
using (var bufferedStream = new BufferedStream(fileStream))
{
    await bufferedStream.WriteAsync(processedBytes, 0, processedBytes.Length);
}

加密算法的选择：

可以选择AES（高级加密标准）算法，它是一种对称加密算法，具有较高的安全性和性能。在.NET中，可以使用System.Security.Cryptography.Aes类来实现。例如：

using (Aes aesAlg = Aes.Create())
{
    aesAlg.Key = Encoding.UTF8.GetBytes(key);
    aesAlg.IV = Encoding.UTF8.GetBytes(iv);

    ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
    using (MemoryStream msEncrypt = new MemoryStream())
    {
        using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
        {
            csEncrypt.Write(fileBytes, 0, fileBytes.Length);
        }
        byte[] encrypted = msEncrypt.ToArray();
    }
}

解密时则使用CreateDecryptor方法进行反向操作。

核心代码框架

using System;
using System.IO;
using System.Security.Cryptography;
using System.Threading.Tasks;

public class PriorityFileOperation
{
    private const int HighPriority = 1;
    private const int MediumPriority = 2;
    private const int LowPriority = 3;

    // 加密和解密的密钥和IV
    private readonly string key;
    private readonly string iv;

    public PriorityFileOperation(string key, string iv)
    {
        this.key = key;
        this.iv = iv;
    }

    public async Task ReadFileAsync(string filePath, int priority)
    {
        byte[] fileBytes;
        using (var fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
        using (var bufferedStream = new BufferedStream(fileStream))
        using (var memoryStream = new MemoryStream())
        {
            await bufferedStream.CopyToAsync(memoryStream);
            fileBytes = memoryStream.ToArray();
        }

        byte[] decryptedBytes = Decrypt(fileBytes);

        // 处理解密后的文件内容
        // 这里可以添加具体的业务逻辑
    }

    public async Task WriteFileAsync(string filePath, byte[] content, int priority)
    {
        byte[] encryptedBytes = Encrypt(content);

        using (var fileStream = new FileStream(filePath, FileMode.Create, FileAccess.Write))
        using (var bufferedStream = new BufferedStream(fileStream))
        {
            await bufferedStream.WriteAsync(encryptedBytes, 0, encryptedBytes.Length);
        }
    }

    private byte[] Encrypt(byte[] data)
    {
        using (Aes aesAlg = Aes.Create())
        {
            aesAlg.Key = Encoding.UTF8.GetBytes(key);
            aesAlg.IV = Encoding.UTF8.GetBytes(iv);

            ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
            using (MemoryStream msEncrypt = new MemoryStream())
            {
                using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                {
                    csEncrypt.Write(data, 0, data.Length);
                }
                return msEncrypt.ToArray();
            }
        }
    }

    private byte[] Decrypt(byte[] data)
    {
        using (Aes aesAlg = Aes.Create())
        {
            aesAlg.Key = Encoding.UTF8.GetBytes(key);
            aesAlg.IV = Encoding.UTF8.GetBytes(iv);

            ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
            using (MemoryStream msDecrypt = new MemoryStream())
            {
                using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Write))
                {
                    csDecrypt.Write(data, 0, data.Length);
                }
                return msDecrypt.ToArray();
            }
        }
    }
}

使用示例：

class Program
{
    static async Task Main()
    {
        string key = "1234567890123456";
        string iv = "1234567890123456";
        PriorityFileOperation operation = new PriorityFileOperation(key, iv);

        await operation.ReadFileAsync("test.txt", HighPriority);
        byte[] content = System.Text.Encoding.UTF8.GetBytes("Hello, World!");
        await operation.WriteFileAsync("test.txt", content, HighPriority);
    }
}

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面试题：C#中如何实现自定义的异步文件操作及IO流处理策略

知识考点

面试题答案

实现思路

核心代码框架