C# 克隆编码但关闭BOM表

假设我有一个编码：

Encoding enc;

当此编码传递给我时，它将被设置为发出BOM表。我对BOMs不感兴趣。我的系统中的编码是用头处理的

假设编码是不可变的。。。我想创建一个与现有编码完全匹配的新编码，但不再发出BOM表

因此，我可以避免以下不匹配：

var data = "áéíóúñ";
var enc = Encoding.UTF8;
long count1 = (long) enc.GetByteCount(data);
long count2;
using(var ms = new MemoryStream())
using(var sw = new StreamWriter(ms, enc))
{
    sw.Write(data);
    sw.Flush();
    count2 = ms.Length;
}
count1.Dump(); //12
count2.Dump(); //15 , oops... BOM was also written

如果您事先不知道编码，那么您需要一些额外的逻辑，例如

switch(enc.CodePage) {
case 65001:
    enc = UTF8Encoding(false);
    break;
case 1200:
    enc = UnicodeEncoding(false, false);
    break;
case 1201:
    enc = UnicodeEncoding(true, false);
    break;
case 12000:
    enc = UTF32Encoding(false, false);
    break;
case 12001:
    enc = UTF32Encoding(true, false);
    break;
default:
    // pass through the original enc unchanged
}

---

根据@leppie的评论，R#帮助我编写了一个抑制BOM的包装器。。。复制在这里，以防有人认为这是个好主意。。。考虑到@ChristianHayter显然已经给出了一个更简单（而且显然）完整的答案，使用它可能是一个好主意

public class EncodingWrapper : Encoding
{
    private readonly Encoding innerEncoding;
    private readonly bool suppressPreamble;
    private static readonly byte[] EmptyBuffer = new byte[0];

    public EncodingWrapper(Encoding innerEncoding, bool suppressPreamble)
    {
        this.innerEncoding = innerEncoding;
        this.suppressPreamble = suppressPreamble;
    }

    public override byte[] GetPreamble()
    {
        return suppressPreamble ? EmptyBuffer : innerEncoding.GetPreamble();
    }

    public override int CodePage
    {
        get { return innerEncoding.CodePage; }
    }
    public override bool IsSingleByte
    {
        get { return innerEncoding.IsSingleByte; }
    }

    public override bool IsMailNewsSave
    {
        get { return innerEncoding.IsMailNewsSave; }
    }

    public override bool IsMailNewsDisplay
    {
        get { return innerEncoding.IsMailNewsDisplay; }
    }

    public override bool IsBrowserSave
    {
        get { return innerEncoding.IsBrowserSave; }
    }

    public override bool IsBrowserDisplay
    {
        get { return innerEncoding.IsBrowserDisplay; }
    }

    public override int WindowsCodePage
    {
        get { return innerEncoding.WindowsCodePage; }
    }

    public override string WebName
    {
        get { return innerEncoding.WebName; }
    }

    public override string HeaderName
    {
        get { return innerEncoding.HeaderName; }
    }

    public override string EncodingName
    {
        get { return innerEncoding.EncodingName; }
    }

    public override string BodyName
    {
        get { return innerEncoding.BodyName; }
    }

    public override string GetString(byte[] bytes, int index, int count)
    {
        return innerEncoding.GetString(bytes, index, count);
    }

    public override string GetString(byte[] bytes)
    {
        return innerEncoding.GetString(bytes);
    }

    public override int GetMaxCharCount(int byteCount)
    {
        return innerEncoding.GetMaxCharCount(byteCount);
    }

    public override int GetMaxByteCount(int charCount)
    {
        return innerEncoding.GetMaxByteCount(charCount);
    }

    public override Encoder GetEncoder()
    {
        return innerEncoding.GetEncoder();
    }

    public override Decoder GetDecoder()
    {
        return innerEncoding.GetDecoder();
    }

    public override bool IsAlwaysNormalized(NormalizationForm form)
    {
        return innerEncoding.IsAlwaysNormalized(form);
    }


    //public unsafe override int GetChars(byte* bytes, int byteCount, char* chars, int charCount)
    //{
    //    return innerEncoding.GetChars(bytes, byteCount, chars, charCount);
    //}

    public override int GetChars(byte[] bytes, int byteIndex, int byteCount, char[] chars, int charIndex)
    {
        return innerEncoding.GetChars(bytes, byteIndex, byteCount, chars, charIndex);
    }

    public override char[] GetChars(byte[] bytes, int index, int count)
    {
        return innerEncoding.GetChars(bytes, index, count);
    }

    public override char[] GetChars(byte[] bytes)
    {
        return innerEncoding.GetChars(bytes);
    }

    //public override int GetCharCount(byte* bytes, int count)
    //{
    //    return innerEncoding.GetCharCount(bytes, count);
    //}

    public override object Clone()
    {
        return new EncodingWrapper((Encoding)innerEncoding.Clone(), suppressPreamble);
    }

    public override int GetByteCount(string s)
    {
        return innerEncoding.GetByteCount(s);
    }

    public override int GetByteCount(char[] chars)
    {
        return innerEncoding.GetByteCount(chars);
    }

    public override int GetByteCount(char[] chars, int index, int count)
    {
        return innerEncoding.GetByteCount(chars, index, count);
    }

    //public override int GetByteCount(char* chars, int count)
    //{
    //    return innerEncoding.GetByteCount(chars, count);
    //}

    public override byte[] GetBytes(char[] chars)
    {
        return innerEncoding.GetBytes(chars);
    }

    public override byte[] GetBytes(char[] chars, int index, int count)
    {
        return innerEncoding.GetBytes(chars, index, count);
    }

    public override int GetBytes(char[] chars, int charIndex, int charCount, byte[] bytes, int byteIndex)
    {
        return innerEncoding.GetBytes(chars, charIndex, charCount, bytes, byteIndex);
    }

    public override byte[] GetBytes(string s)
    {
        return innerEncoding.GetBytes(s);
    }

    public override int GetBytes(string s, int charIndex, int charCount, byte[] bytes, int byteIndex)
    {
        return innerEncoding.GetBytes(s, charIndex, charCount, bytes, byteIndex);
    }

    //public override int GetBytes(char* chars, int charCount, byte* bytes, int byteCount)
    //{
    //    return innerEncoding.GetBytes(chars, charCount, bytes, byteCount);
    //}

    public override int GetCharCount(byte[] bytes)
    {
        return innerEncoding.GetCharCount(bytes);
    }

    public override int GetCharCount(byte[] bytes, int index, int count)
    {
        return innerEncoding.GetCharCount(bytes, index, count);
    }
}

---

不。我不知道传递给我时的编码是什么。UTF8仅用作示例。我试图在我的问题中澄清这一点。@spender这些是唯一的编码BOM@Esailija明白了。。。注释引用了以前的编辑，但您增加了我的知识，我现在看到这是一个完整的答案。我看到的唯一方法是通过反射更改私有布尔标志（但它们的名称都不同…），如果

GetPreamble

不返回零长度数组，您可以检测是否已设置该标志。或者，您可以实现自己的

编码

对包装和现有包装进行分类，只需重写

GetPreamble

即可返回零长度数组。@leppie这似乎是一个合理的计划。我要试一试，然后再报告。

public class EncodingWrapper : Encoding
{
    private readonly Encoding innerEncoding;
    private readonly bool suppressPreamble;
    private static readonly byte[] EmptyBuffer = new byte[0];

    public EncodingWrapper(Encoding innerEncoding, bool suppressPreamble)
    {
        this.innerEncoding = innerEncoding;
        this.suppressPreamble = suppressPreamble;
    }

    public override byte[] GetPreamble()
    {
        return suppressPreamble ? EmptyBuffer : innerEncoding.GetPreamble();
    }

    public override int CodePage
    {
        get { return innerEncoding.CodePage; }
    }
    public override bool IsSingleByte
    {
        get { return innerEncoding.IsSingleByte; }
    }

    public override bool IsMailNewsSave
    {
        get { return innerEncoding.IsMailNewsSave; }
    }

    public override bool IsMailNewsDisplay
    {
        get { return innerEncoding.IsMailNewsDisplay; }
    }

    public override bool IsBrowserSave
    {
        get { return innerEncoding.IsBrowserSave; }
    }

    public override bool IsBrowserDisplay
    {
        get { return innerEncoding.IsBrowserDisplay; }
    }

    public override int WindowsCodePage
    {
        get { return innerEncoding.WindowsCodePage; }
    }

    public override string WebName
    {
        get { return innerEncoding.WebName; }
    }

    public override string HeaderName
    {
        get { return innerEncoding.HeaderName; }
    }

    public override string EncodingName
    {
        get { return innerEncoding.EncodingName; }
    }

    public override string BodyName
    {
        get { return innerEncoding.BodyName; }
    }

    public override string GetString(byte[] bytes, int index, int count)
    {
        return innerEncoding.GetString(bytes, index, count);
    }

    public override string GetString(byte[] bytes)
    {
        return innerEncoding.GetString(bytes);
    }

    public override int GetMaxCharCount(int byteCount)
    {
        return innerEncoding.GetMaxCharCount(byteCount);
    }

    public override int GetMaxByteCount(int charCount)
    {
        return innerEncoding.GetMaxByteCount(charCount);
    }

    public override Encoder GetEncoder()
    {
        return innerEncoding.GetEncoder();
    }

    public override Decoder GetDecoder()
    {
        return innerEncoding.GetDecoder();
    }

    public override bool IsAlwaysNormalized(NormalizationForm form)
    {
        return innerEncoding.IsAlwaysNormalized(form);
    }


    //public unsafe override int GetChars(byte* bytes, int byteCount, char* chars, int charCount)
    //{
    //    return innerEncoding.GetChars(bytes, byteCount, chars, charCount);
    //}

    public override int GetChars(byte[] bytes, int byteIndex, int byteCount, char[] chars, int charIndex)
    {
        return innerEncoding.GetChars(bytes, byteIndex, byteCount, chars, charIndex);
    }

    public override char[] GetChars(byte[] bytes, int index, int count)
    {
        return innerEncoding.GetChars(bytes, index, count);
    }

    public override char[] GetChars(byte[] bytes)
    {
        return innerEncoding.GetChars(bytes);
    }

    //public override int GetCharCount(byte* bytes, int count)
    //{
    //    return innerEncoding.GetCharCount(bytes, count);
    //}

    public override object Clone()
    {
        return new EncodingWrapper((Encoding)innerEncoding.Clone(), suppressPreamble);
    }

    public override int GetByteCount(string s)
    {
        return innerEncoding.GetByteCount(s);
    }

    public override int GetByteCount(char[] chars)
    {
        return innerEncoding.GetByteCount(chars);
    }

    public override int GetByteCount(char[] chars, int index, int count)
    {
        return innerEncoding.GetByteCount(chars, index, count);
    }

    //public override int GetByteCount(char* chars, int count)
    //{
    //    return innerEncoding.GetByteCount(chars, count);
    //}

    public override byte[] GetBytes(char[] chars)
    {
        return innerEncoding.GetBytes(chars);
    }

    public override byte[] GetBytes(char[] chars, int index, int count)
    {
        return innerEncoding.GetBytes(chars, index, count);
    }

    public override int GetBytes(char[] chars, int charIndex, int charCount, byte[] bytes, int byteIndex)
    {
        return innerEncoding.GetBytes(chars, charIndex, charCount, bytes, byteIndex);
    }

    public override byte[] GetBytes(string s)
    {
        return innerEncoding.GetBytes(s);
    }

    public override int GetBytes(string s, int charIndex, int charCount, byte[] bytes, int byteIndex)
    {
        return innerEncoding.GetBytes(s, charIndex, charCount, bytes, byteIndex);
    }

    //public override int GetBytes(char* chars, int charCount, byte* bytes, int byteCount)
    //{
    //    return innerEncoding.GetBytes(chars, charCount, bytes, byteCount);
    //}

    public override int GetCharCount(byte[] bytes)
    {
        return innerEncoding.GetCharCount(bytes);
    }

    public override int GetCharCount(byte[] bytes, int index, int count)
    {
        return innerEncoding.GetCharCount(bytes, index, count);
    }
}