使用< byte>C# 10和.NET 6字符串插值、编译器处理程序降低模式将byte[]或ReadOnlySpan格式化为string

umuewwlo  于 2022-11-19  发布在  .NET
关注(0)|答案(3)|浏览(235)

我想使用一些自定义的格式化参数将byte[]ReadOnlySpan<byte>字节格式化为字符串。比如,将S化为Base64。为此,长度总是固定为某个已知的常量。
我想使用https://devblogs.microsoft.com/dotnet/string-interpolation-in-c-10-and-net-6/中描述的现代C# 10和.NET 6字符串格式化功能。内置类型实现了ISpanFormattable,因此我想在这里引入新的格式化参数,但使用了编译器handler lowering pattern
我从那篇文章中提取了一些代码,并在嵌入的代码中做了一些修改,如下所示。它也位于https://dotnetfiddle.net/svyQKD
如代码中所示,我获得了byte[]的直接方法调用,但ReadOnlySpan<byte>的调用没有成功。
有人知道怎么做吗?
我怀疑我需要InterpolatedStringHandler。但如果是这样的话,那么看起来我不知道如何实现一个。所有的提示和代码技巧可能会有帮助。我已经在这个问题上停留了一段时间,现在已经进入凌晨。:)

using System;
using System.Globalization;
using System.Runtime.CompilerServices;

public class Program
{
    public sealed class ExampleCustomFormatter: IFormatProvider, ICustomFormatter
    {
        public object? GetFormat(Type? formatType) => formatType == typeof(ICustomFormatter) ? this : null;
        public string Format(string? format, object? arg, IFormatProvider? formatProvider) => format == "S" && arg is byte[] i ? Convert.ToBase64String(i) : arg is IFormattable formattable ? formattable.ToString(format, formatProvider) : arg?.ToString() ?? string.Empty;
    }

    public static class StringExtensions
    {
        public static string FormatString(byte[] buffer) => string.Create(new ExampleCustomFormatter(), stackalloc char[64], $"{buffer:S}");

        // How to make this work? Maybe needs to have TryWrite 
        // public static string FormatString2(ReadOnlySpan<byte> buffer) => string.Create(new ExampleCustomFormatter(), stackalloc char[64], $"{buffer:S}");
    }

    [InterpolatedStringHandler]
    public ref struct BinaryMessageInterpolatedStringHandler
    {
        private readonly DefaultInterpolatedStringHandler handler;

        public BinaryMessageInterpolatedStringHandler(int literalLength, int formattedCount, bool predicate, out bool handlerIsValid)
        {
            handler = default;

            if(predicate)
            {
                handlerIsValid = false;
                return;
            }

            handlerIsValid = true;
            handler = new DefaultInterpolatedStringHandler(literalLength, formattedCount);
        }

        public void AppendLiteral(string s) => handler.AppendLiteral(s);

        public void AppendFormatted<T>(T t) => handler.AppendFormatted(t);

        public override string ToString() => handler.ToStringAndClear();
    }

    public static void Main()
    {
        byte[] test1 = new byte[1] { 0x55 };
        ReadOnlySpan<byte> test2 = new byte[1] { 0x55 };

        // How to make this work? Now it prints "System.Byte[]".
        Console.WriteLine($"{test1:S}");

        // This works.
        Console.WriteLine(StringExtensions.FormatString(test1));

        // How to make this work? This does not compile. (Yes, signature problem. How to define it?).
        // Console.WriteLine($"{test2:S}");

        // How to make this work? This does not compile. (Yes, signature problem. How to define it?).

        // Console.WriteLine(StringExtensions.FormatString(test2));
    }
}
oxiaedzo

oxiaedzo1#

我玩了这个,因为我也有兴趣了解这些处理程序,所以考虑我的答案与一些怀疑。
Console.WriteLine($"{test2:S}");(和StringExtensions.FormatString2)上的构建错误CS0306 The type 'ReadOnlySpan<byte>' may not be used as a type argument源于(我相信)编译器生成的对DefaultInterpolatedStringHandler.AppendFormatted<T>的调用,该调用带有非法的泛型类型参数ReadOnlySpan<byte>ReadOnlySpanref structref struct不能用作类型参数)。
正如您链接的Stephen Toub的博客中所解释的,编译器会很乐意扩展任何插值字符串以使用DefaultInterpolatedStringHandler(如果它愿意的话),这就是为什么您可以使用带有Console.WriteLine的插值字符串,即使它没有带DefaultInterpolatedStringHandler参数的重载:

// This trivial example might not actually construct a DefaultInterpolatedStringHandler
// but the point still stands (it compiles and works)
int x = 3;
Console.WriteLine($"{x}");

一个简单的解决方案是创建一个DefaultInterpolatedStringHandler.AppendFormatted的扩展重载,它接受一个ReadOnlySpan<byte>,但是在这个残酷的世界里,编译器似乎没有检测到它:

public static class PleaseWork
{
    public static void AppendFormatted(
        this ref DefaultInterpolatedStringHandler handler,
        ReadOnlySpan<byte> bytes,
        string? format)
    {
        if (format != "S")
        {
            throw new ArgumentException("Invalid format");
        }

        handler.AppendLiteral(Convert.ToBase64String(bytes));
    }
}

ReadOnlySpan<byte> test2 = new byte[1] { 0x56 };
Console.WriteLine($"{test2:S}"); // nope (CS0306)

所以这里有一个解决方案:用AppendFormatted重载创建一个自定义的InterpolatedStringHandler(就像你已经做的那样)。就像在你的实现中一样,我们可以只 Package 一个DefaultInterpolatedStringHandler(或者一个StringBuilder),这样实际的实现(缓冲区管理等)就留给更聪明的人了。完整的例子:

public class Program
{
    [InterpolatedStringHandler]
    public ref struct WrappingInterpolatedStringHandler
    {
        private DefaultInterpolatedStringHandler handler;

        public WrappingInterpolatedStringHandler(int literalLength, int formattedCount)
        {
            handler = new(literalLength, formattedCount);
        }

        public void AppendLiteral(string s) => handler.AppendLiteral(s);

        public void AppendFormatted<T>(T t, string? format = null)
            => handler.AppendFormatted(t, format);

        // This is necessary otherwise byte[] arg resolves to the generic overload
        public void AppendFormatted(byte[] bytes, string? format = null)
            => AppendFormatted((ReadOnlySpan<byte>)bytes, format);

        public void AppendFormatted(ReadOnlySpan<byte> bytes, string? format)
        {
            if (format != "S")
            {
                throw new ArgumentException("Invalid format");
            }
            
            // This allocates an intermediate string
            handler.AppendLiteral(Convert.ToBase64String(bytes));
        }

        public string ToStringAndClear() => handler.ToStringAndClear();
    }

    public static void Main()
    {
        byte[] test1 = new byte[1] { 0x55 };
        ReadOnlySpan<byte> test2 = new byte[1] { 0x56 };
        Span<byte> test3 = new byte[128];
        test3.Fill(0x55);

        WriteLine($"test1:{test1:S}"); // "test1:VQ=="
        WriteLine($"test2:{test2:S}"); // "test2:Vg=="
        WriteLine($"test3:{test3:S}"); // "test3:<a long base64 string>"
    }

    private static void WriteLine(ref WrappingInterpolatedStringHandler builder)
    {
        // Naturally, Console.WriteLine has no overload taking our custom handler
        // so we need to give it the resulting string
        Console.WriteLine(builder.ToStringAndClear());
    }
}

我们新的AppendFormatted重载调用Convert.ToBase64String,后者正在分配中间string(然后将其复制到DefaultInterpolatedStringHandler的缓冲区中)。这是我们为自己没有管理缓冲区而付出的代价。如果我们不能忍受这样的想法(让实现风险和收益递减见鬼去吧),这里有一个哑处理程序,它将(固定大小)缓冲区作为参数(可以进行堆栈分配):

public class Program
{
    [InterpolatedStringHandler]
    public ref struct MyReallyBadAndUntestedInterpolatedStringHandler
    {
        private readonly Span<char> _buffer;
        private int _charsWritten;

        public MyReallyBadAndUntestedInterpolatedStringHandler(int literalLength, int formattedCount, Span<char> destination)
        {
            _buffer = destination;
            _charsWritten = 0;
        }

        public bool AppendLiteral(string s)
        {
            if (s.AsSpan().TryCopyTo(_buffer.Slice(_charsWritten)))
            {
                _charsWritten += s.Length;
                return true;
            }

            return false;
        }

        public bool AppendFormatted<T>(T t, ReadOnlySpan<char> format)
        {
            Span<char> buffer = _buffer.Slice(_charsWritten);
            
            if (t is ISpanFormattable formattable)
            {
                bool success = formattable.TryFormat(buffer, out int charsWritten, format, null);
                _charsWritten += charsWritten;
                return success;
            }

            string s = t?.ToString() ?? "";

            if (s.AsSpan().TryCopyTo(buffer))
            {
                _charsWritten += s.Length;
                return true;
            }

            return false;
        }

        // This is necessary otherwise byte[] arg resolves to the generic overload
        public bool AppendFormatted(byte[] bytes, ReadOnlySpan<char> format)
            => AppendFormatted((ReadOnlySpan<byte>)bytes, format);

        public bool AppendFormatted(ReadOnlySpan<byte> bytes, ReadOnlySpan<char> format)
        {
            if (format != "S")
            {
                throw new ArgumentException("Invalid format");
            }

            bool success = Convert.TryToBase64Chars(bytes, _buffer.Slice(_charsWritten), out int charsWritten);
            _charsWritten += charsWritten;
            return success;
        }

        public string ToStringAndClear()
        {
            string result = new string(_buffer.Slice(0, _charsWritten));
            _buffer.Clear();
            _charsWritten = 0;
            return result;
        }
    }

    public static void Main()
    {
        byte[] test1 = new byte[1] { 0x55 };
        ReadOnlySpan<byte> test2 = new byte[1] { 0x56 };
        Span<byte> test3 = new byte[128];
        test3.Fill(0x55);

        Span<char> buffer = stackalloc char[64];
        WriteLine(buffer, $"test1:{test1:S}"); // "test1:VQ=="
        WriteLine(buffer, $"test2:{test2:S}"); // "test2:Vg=="
        WriteLine(buffer, $"test3:{test3:S}"); // "test3:" (the buffer is not big enough)
    }

    private static void WriteLine(
        Span<char> destination,
        [InterpolatedStringHandlerArgument("destination")] ref MyReallyBadAndUntestedInterpolatedStringHandler builder)
    {
        Console.WriteLine(builder.ToStringAndClear());
    }
}

总之,只需调用Console.WriteLine(Convert.ToBase64String(test2)),然后继续:)

ac1kyiln

ac1kyiln2#

您可以使用延伸方法:

using System.Text;

byte[] test1 = new byte[2] { 0x55, 0x34 };
ReadOnlySpan<byte> test2 = new byte[2] { 0x55, 0x34 };

// How to make this work? Now it prints "System.Byte[]".
Console.WriteLine($"{test1.MyFormat()}");

Console.WriteLine($"{test2.MyFormat()}");

public static class MyExtensionMethods
{
    public static string MyFormat(this byte[] value)
    {
        StringBuilder sb = new StringBuilder();
        foreach (byte b in value)
        {
            sb.Append(b).Append(" ");
        }
        return sb.ToString();
    }

    public static string MyFormat(this ReadOnlySpan<byte> value)
    {
        StringBuilder sb = new StringBuilder();
        foreach (byte b in value)
        {
            sb.Append(b).Append(" ");
        }
        return sb.ToString();
    }
}

结果:

85 52
85 52

您也可以尝试使用:

public static class MyExtensionMethods
{
    public static string MyFormat(this byte[] value) => Encoding.Unicode.GetString(value);

    public static string MyFormat(this ReadOnlySpan<byte> value) => Encoding.Unicode.GetString(value);
}
gupuwyp2

gupuwyp23#

如果您真的想像这样使用方法,则需要重写Byte[]类的ToString()方法。
但是您无法在Byte[]类别上覆写方法。您必须继承Byte[]类别,并在衍生的上覆写ToString()方法。
然后,您必须使用衍生类别取代所有的Byte[]对象,使用并不是一个好主意。
因此,没有解决方案为您在这种方式:

// How to make this work? Now it prints "System.Byte[]".
Console.WriteLine($"{test1:S}");

最好的办法是创建一个“outside”方法来格式化Byte[],然后按照格式化的方法进行操作。

  • 同样适用于ReadOnlySpan<byte>

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