前言：

昨天，在文章：终于等到你：CYQ.Data V5系列 （ORM数据层，支持.NET Core）最新版本开源了 中，

不小心看到一条留言：

然后就去该地址看了一下，这一看，顺带折腾了一天。

今天，就和大伙分享下折腾的感觉。

在该开源地址中，代码有C++和C#两个版本，编码的整体风格倾向与于C++。

主要的时间，花了在对于检测无BOM的部分，顺带重温了各种编码的基础。

建议在看此文之前，先了解下编码、和BOM的概念。

有BOM的编码检测

对于一个文件，或者字节流，就是一堆二进制：

如果传输的过程，有指定BOM，就是前面两三个字节是固定的255,254之类的，那么解码起来就很简单了。

像之前IOHelper内部读文件的代码是这么写的：

/// <summary>
/// 先自动识别UTF8，否则归到Default编码读取
/// </summary>
/// <returns></returns>
public static string ReadAllText(string fileName)
{
return ReadAllText(fileName, DefaultEncoding);
}
public static string ReadAllText(string fileName, Encoding encoding)
{
try
{
if (!File.Exists(fileName))
{
return string.Empty;
}
Byte[] buff = null;
lock (GetLockObj(fileName.Length))
{
if (!File.Exists(fileName))//多线程情况处理
{
return string.Empty;
}
buff = File.ReadAllBytes(fileName);
}
if (buff.Length == 0) { return ""; }
if (buff[0] == 239 && buff[1] == 187 && buff[2] == 191)
{
return Encoding.UTF8.GetString(buff, 3, buff.Length - 3);
}
else if (buff[0] == 255 && buff[1] == 254)
{
return Encoding.Unicode.GetString(buff, 2, buff.Length - 2);
}
else if (buff[0] == 254 && buff[1] == 255)
{
if (buff.Length > 3 && buff[2] == 0 && buff[3] == 0)
{
return Encoding.UTF32.GetString(buff, 4, buff.Length - 4);
}
return Encoding.BigEndianUnicode.GetString(buff, 2, buff.Length - 2);
}
return encoding.GetString(buff);
}
catch (Exception err)
{
Log.WriteLogToTxt(err);
}
return string.Empty;
}

代码说白了，就是检测BOM头，然后识别编码，用对应的编码解码。

测试的结果：

中文都能正确显示。

windows下文本的另存为只有：ANSI、UTF8､Unicode(UTF16LE)、BigEndianUnicode（UTF16BE）。

这四种有BOM的都是轻松检测了。

 那如果文件或字节没有BOM头呢？如果用默认的编码，由有一定概率会乱码。

无BOM的编码检测

如果一堆字节流，没有指定BOM，就要分析出编码类型，还是挺有难度的。

这需要对各种编码的规则有一定的熟悉度。

先看看网友给出的Github上的 原始源码：

public Encoding DetectEncoding(byte[] buffer, int size)
{
// First check if we have a BOM and return that if so
Encoding encoding = CheckBom(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// Now check for valid UTF8
encoding = CheckUtf8(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// Now try UTF16
encoding = CheckUtf16NewlineChars(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

encoding = CheckUtf16Ascii(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// ANSI or None (binary) then
if (!DoesContainNulls(buffer, size))
{
return Encoding.Ansi;
}

// Found a null, return based on the preference in null_suggests_binary_
return _nullSuggestsBinary ? Encoding.None : Encoding.Ansi;
}

代码流程（和内涵）翻译下来是这样的：

1､检测BOM头，这个很Easy。

2､检测UTF8编码（这个还是很有创意的），如果编码的规则完全符合UTF8,则认为是UTF8。

3､检测字节中是否有换行符（根据换行符中的0的位置，区分是Utf16的BE大尾还是LE小尾）。

这个概率要看字节抽样的长度，带不带换行符。

4､检测字节中，单偶数出现的0的概率，设定了一个期望值来预判（对于中文而言，基本没用），大概是老外写的，只根据英文情况分析的概率。

5､检测字节中，有没有出现0，如果没有，返回系统默认编码（不同系统环境编码是不同的）。

首先，不得不说，原作者还是有一定想法的。

虽然代码中除了UTF8按规则写的分析外，其它的都无法代入中文环境里通过。

但至少思路上，就能得到不少启发。

于是，坑了我大半天，进行重写，改造，代入中文环境测试。

无BOM代码检测的改造过程：

改造后的代码流程是这样的：

public Encoding DetectWithoutBom(byte[] buffer, int size)
{
// Now check for valid UTF8
Encoding encoding = CheckUtf8(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// ANSI or None (binary) then 一个零都没有情况。
if (!ContainsZero(buffer, size))
{
CheckChinese(buffer, size);
return Encoding.Ansi;
}

// Now try UTF16  按寻找换行字符先进行判断
encoding = CheckByNewLineChar(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// 没办法了，只能按0出现的次数比率，做大体的预判
encoding = CheckByZeroNumPercent(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// Found a null, return based on the preference in null_suggests_binary_
return Encoding.None;
}

用中文解释流程是这样的：

1､UTF8编码的检测规则，这个是通用的有效，可以保留。

2､调整顺序：先检测字节有没有0字节，若无，补一个是否中文的编码的检测（GB2312､GBK、Big5)。

这个后续有点用。

3､检测换行符：增加UTF-32编码的检测（原来的思路只有UTF16)。

4､预判概率：改造成同时适应中文环境。

测试的结果是这样的：

A、纯中文的：

该测试下，对于BigEndianUnicode的会产生乱码。

B、非纯中文的

一切编码正常通用。

改进后的完整源码：

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;

namespace CYQ.Data.Tool
{
internal static class IOHelper
{
internal static Encoding DefaultEncoding = Encoding.Default;

private static List<object> tenObj = new List<object>(10);
private static List<object> TenObj
{
get
{
if (tenObj.Count == 0)
{
for (int i = 0; i < 10; i++)
{
tenObj.Add(new object());
}
}
return tenObj;
}
}
private static object GetLockObj(int length)
{
int i = length % 9;
return TenObj[i];
}
/// <summary>
/// 先自动识别UTF8，否则归到Default编码读取
/// </summary>
/// <returns></returns>
public static string ReadAllText(string fileName)
{
return ReadAllText(fileName, DefaultEncoding);
}
public static string ReadAllText(string fileName, Encoding encoding)
{
try
{
if (!File.Exists(fileName))
{
return string.Empty;
}
Byte[] buff = null;
lock (GetLockObj(fileName.Length))
{
if (!File.Exists(fileName))//多线程情况处理
{
return string.Empty;
}
buff = File.ReadAllBytes(fileName);
return BytesToText(buff, encoding);
}

}
catch (Exception err)
{
Log.WriteLogToTxt(err);
}
return string.Empty;
}
public static bool Write(string fileName, string text)
{
return Save(fileName, text, false, DefaultEncoding, true);
}
public static bool Write(string fileName, string text, Encoding encode)
{
return Save(fileName, text, false, encode, true);
}
public static bool Append(string fileName, string text)
{
return Save(fileName, text, true, true);
}

internal static bool Save(string fileName, string text, bool isAppend, bool writeLogOnError)
{
return Save(fileName, text, true, DefaultEncoding, writeLogOnError);
}
internal static bool Save(string fileName, string text, bool isAppend, Encoding encode, bool writeLogOnError)
{
try
{
string folder = Path.GetDirectoryName(fileName);
if (!Directory.Exists(folder))
{
Directory.CreateDirectory(folder);
}

lock (GetLockObj(fileName.Length))
{
using (StreamWriter writer = new StreamWriter(fileName, isAppend, encode))
{
writer.Write(text);
}
}
return true;
}
catch (Exception err)
{
if (writeLogOnError)
{
Log.WriteLogToTxt(err);
}
else
{
Error.Throw("IOHelper.Save() : " + err.Message);
}
}
return false;
}

internal static bool Delete(string fileName)
{
try
{
if (File.Exists(fileName))
{
lock (GetLockObj(fileName.Length))
{
if (File.Exists(fileName))
{
File.Delete(fileName);
return true;
}
}
}
}
catch
{

}
return false;
}

public static bool IsLastFileWriteTimeChanged(string fileName, ref DateTime compareTimeUtc)
{
bool isChanged = false;
IOInfo info = new IOInfo(fileName);
if (info.Exists && info.LastWriteTimeUtc != compareTimeUtc)
{
isChanged = true;
compareTimeUtc = info.LastWriteTimeUtc;
}
return isChanged;
}
public static string BytesToText(byte[] buff, Encoding encoding)
{
if (buff.Length == 0) { return ""; }
//if (buff[0] == 239 && buff[1] == 187 && buff[2] == 191)
//{
//    return Encoding.UTF8.GetString(buff, 3, buff.Length - 3);
//}
//else if (buff[0] == 255 && buff[1] == 254)
//{
//    return Encoding.Unicode.GetString(buff, 2, buff.Length - 2);
//}
//else if (buff[0] == 254 && buff[1] == 255)
//{
//    if (buff.Length > 3 && buff[2] == 0 && buff[3] == 0)
//    {
//        return Encoding.UTF32.GetString(buff, 4, buff.Length - 4);
//    }
//    return Encoding.BigEndianUnicode.GetString(buff, 2, buff.Length - 2);
//}
//else
//{
TextEncodingDetect detect = new TextEncodingDetect();

//检测Bom
switch (detect.DetectWithBom(buff))
{
case TextEncodingDetect.Encoding.Utf8Bom:
return Encoding.UTF8.GetString(buff, 3, buff.Length - 3);
case TextEncodingDetect.Encoding.UnicodeBom:
return Encoding.Unicode.GetString(buff, 2, buff.Length - 2);
case TextEncodingDetect.Encoding.BigEndianUnicodeBom:
return Encoding.BigEndianUnicode.GetString(buff, 2, buff.Length - 2);
case TextEncodingDetect.Encoding.Utf32Bom:
return Encoding.UTF32.GetString(buff, 4, buff.Length - 4);
}
if (encoding != DefaultEncoding && encoding != Encoding.ASCII)//自定义设置编码，优先处理。
{
return encoding.GetString(buff);
}
switch (detect.DetectWithoutBom(buff, buff.Length > 1000 ? 1000 : buff.Length))//自动检测。
{

case TextEncodingDetect.Encoding.Utf8Nobom:
return Encoding.UTF8.GetString(buff);

case TextEncodingDetect.Encoding.UnicodeNoBom:
return Encoding.Unicode.GetString(buff);

case TextEncodingDetect.Encoding.BigEndianUnicodeNoBom:
return Encoding.BigEndianUnicode.GetString(buff);

case TextEncodingDetect.Encoding.Utf32NoBom:
return Encoding.UTF32.GetString(buff);

case TextEncodingDetect.Encoding.Ansi:
if (IsChineseEncoding(DefaultEncoding) && !IsChineseEncoding(encoding))
{
if (detect.IsChinese)
{
return Encoding.GetEncoding("gbk").GetString(buff);
}
else//非中文时，默认选一个。
{
return Encoding.Unicode.GetString(buff);
}
}
else
{
return encoding.GetString(buff);
}

case TextEncodingDetect.Encoding.Ascii:
return Encoding.ASCII.GetString(buff);

default:
return encoding.GetString(buff);
}
// }
}
private static bool IsChineseEncoding(Encoding encoding)
{
return encoding == Encoding.GetEncoding("gb2312") || encoding == Encoding.GetEncoding("gbk") || encoding == Encoding.GetEncoding("big5");
}
}
internal class IOInfo : FileSystemInfo
{
public IOInfo(string fileName)
{
base.FullPath = fileName;
}
public override void Delete()
{
}

public override bool Exists
{
get
{
return File.Exists(base.FullPath);
}
}

public override string Name
{
get
{
return null;
}
}
}
/// <summary>
/// 字节文本编码检测
/// </summary>
internal class TextEncodingDetect
{
private readonly byte[] _UTF8Bom =
{
0xEF,
0xBB,
0xBF
};
//utf16le _UnicodeBom
private readonly byte[] _UTF16LeBom =
{
0xFF,
0xFE
};

//utf16be _BigUnicodeBom
private readonly byte[] _UTF16BeBom =
{
0xFE,
0xFF
};

//utf-32le
private readonly byte[] _UTF32LeBom =
{
0xFF,
0xFE,
0x00,
0x00
};
//utf-32Be
//private readonly byte[] _UTF32BeBom =
//{
//    0x00,
//    0x00,
//    0xFE,
//    0xFF
//};
/// <summary>
/// 是否中文
/// </summary>
public bool IsChinese = false;

public enum Encoding
{
None, // Unknown or binary
Ansi, // 0-255
Ascii, // 0-127
Utf8Bom, // UTF8 with BOM
Utf8Nobom, // UTF8 without BOM
UnicodeBom, // UTF16 LE with BOM
UnicodeNoBom, // UTF16 LE without BOM
BigEndianUnicodeBom, // UTF16-BE with BOM
BigEndianUnicodeNoBom, // UTF16-BE without BOM

Utf32Bom,//UTF-32LE with BOM
Utf32NoBom //UTF-32 without BOM

}

public Encoding DetectWithBom(byte[] buffer)
{
if (buffer != null)
{
int size = buffer.Length;
// Check for BOM
if (size >= 2 && buffer[0] == _UTF16LeBom[0] && buffer[1] == _UTF16LeBom[1])
{
return Encoding.UnicodeBom;
}

if (size >= 2 && buffer[0] == _UTF16BeBom[0] && buffer[1] == _UTF16BeBom[1])
{
if (size >= 4 && buffer[2] == _UTF32LeBom[2] && buffer[3] == _UTF32LeBom[3])
{
return Encoding.Utf32Bom;
}
return Encoding.BigEndianUnicodeBom;
}

if (size >= 3 && buffer[0] == _UTF8Bom[0] && buffer[1] == _UTF8Bom[1] && buffer[2] == _UTF8Bom[2])
{
return Encoding.Utf8Bom;
}
}
return Encoding.None;
}

/// <summary>
///     Automatically detects the Encoding type of a given byte buffer.
/// </summary>
/// <param name="buffer">The byte buffer.</param>
/// <param name="size">The size of the byte buffer.</param>
/// <returns>The Encoding type or Encoding.None if unknown.</returns>
public Encoding DetectWithoutBom(byte[] buffer, int size)
{
// Now check for valid UTF8
Encoding encoding = CheckUtf8(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// ANSI or None (binary) then 一个零都没有情况。
if (!ContainsZero(buffer, size))
{
CheckChinese(buffer, size);
return Encoding.Ansi;
}

// Now try UTF16  按寻找换行字符先进行判断
encoding = CheckByNewLineChar(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// 没办法了，只能按0出现的次数比率，做大体的预判
encoding = CheckByZeroNumPercent(buffer, size);
if (encoding != Encoding.None)
{
return encoding;
}

// Found a null, return based on the preference in null_suggests_binary_
return Encoding.None;
}

/// <summary>
///     Checks if a buffer contains text that looks like utf16 by scanning for
///     newline chars that would be present even in non-english text.
///     以检测换行符标识来判断。
/// </summary>
/// <param name="buffer">The byte buffer.</param>
/// <param name="size">The size of the byte buffer.</param>
/// <returns>Encoding.none, Encoding.Utf16LeNoBom or Encoding.Utf16BeNoBom.</returns>
private static Encoding CheckByNewLineChar(byte[] buffer, int size)
{
if (size < 2)
{
return Encoding.None;
}

// Reduce size by 1 so we don't need to worry about bounds checking for pairs of bytes
size--;

int le16 = 0;
int be16 = 0;
int le32 = 0;//检测是否utf32le。
int zeroCount = 0;//utf32le 每4位后面多数是0
uint pos = 0;
while (pos < size)
{
byte ch1 = buffer[pos++];
byte ch2 = buffer[pos++];

if (ch1 == 0)
{
if (ch2 == 0x0a || ch2 == 0x0d)//\r \t 换行检测。
{
++be16;
}
}
if (ch2 == 0)
{
zeroCount++;
if (ch1 == 0x0a || ch1 == 0x0d)
{
++le16;
if (pos + 1 <= size && buffer[pos] == 0 && buffer[pos + 1] == 0)
{
++le32;
}

}
}

// If we are getting both LE and BE control chars then this file is not utf16
if (le16 > 0 && be16 > 0)
{
return Encoding.None;
}
}

if (le16 > 0)
{
if (le16 == le32 && buffer.Length % 4 == 0)
{
return Encoding.Utf32NoBom;
}
return Encoding.UnicodeNoBom;
}
else if (be16 > 0)
{
return Encoding.BigEndianUnicodeNoBom;
}
else if (buffer.Length % 4 == 0 && zeroCount >= buffer.Length / 4)
{
return Encoding.Utf32NoBom;
}
return Encoding.None;
}

/// <summary>
/// Checks if a buffer contains any nulls. Used to check for binary vs text data.
/// </summary>
/// <param name="buffer">The byte buffer.</param>
/// <param name="size">The size of the byte buffer.</param>
private static bool ContainsZero(byte[] buffer, int size)
{
uint pos = 0;
while (pos < size)
{
if (buffer[pos++] == 0)
{
return true;
}
}

return false;
}

/// <summary>
///     Checks if a buffer contains text that looks like utf16. This is done based
///     on the use of nulls which in ASCII/script like text can be useful to identify.
///     按照一定的空0数的概率来预测。
/// </summary>
/// <param name="buffer">The byte buffer.</param>
/// <param name="size">The size of the byte buffer.</param>
/// <returns>Encoding.none, Encoding.Utf16LeNoBom or Encoding.Utf16BeNoBom.</returns>
private Encoding CheckByZeroNumPercent(byte[] buffer, int size)
{
//单数
int oddZeroCount = 0;
//双数
int evenZeroCount = 0;

// Get even nulls
uint pos = 0;
while (pos < size)
{
if (buffer[pos] == 0)
{
evenZeroCount++;
}

pos += 2;
}

// Get odd nulls
pos = 1;
while (pos < size)
{
if (buffer[pos] == 0)
{
oddZeroCount++;
}

pos += 2;
}

double evenZeroPercent = evenZeroCount * 2.0 / size;
double oddZeroPercent = oddZeroCount * 2.0 / size;

// Lots of odd nulls, low number of even nulls 这里的条件做了修改
if (evenZeroPercent < 0.1 && oddZeroPercent > 0)
{
return Encoding.UnicodeNoBom;
}

// Lots of even nulls, low number of odd nulls 这里的条件也做了修改
if (oddZeroPercent < 0.1 && evenZeroPercent > 0)
{
return Encoding.BigEndianUnicodeNoBom;
}

// Don't know
return Encoding.None;
}

/// <summary>
///     Checks if a buffer contains valid utf8.
///     以UTF8 的字节范围来检测。
/// </summary>
/// <param name="buffer">The byte buffer.</param>
/// <param name="size">The size of the byte buffer.</param>
/// <returns>
///     Encoding type of Encoding.None (invalid UTF8), Encoding.Utf8NoBom (valid utf8 multibyte strings) or
///     Encoding.ASCII (data in 0.127 range).
/// </returns>
/// <returns>2</returns>
private Encoding CheckUtf8(byte[] buffer, int size)
{
// UTF8 Valid sequences
// 0xxxxxxx  ASCII
// 110xxxxx 10xxxxxx  2-byte
// 1110xxxx 10xxxxxx 10xxxxxx  3-byte
// 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx  4-byte
//
// Width in UTF8
// Decimal      Width
// 0-127        1 byte
// 194-223      2 bytes
// 224-239      3 bytes
// 240-244      4 bytes
//
// Subsequent chars are in the range 128-191
bool onlySawAsciiRange = true;
uint pos = 0;

while (pos < size)
{
byte ch = buffer[pos++];

if (ch == 0)
{
return Encoding.None;
}

int moreChars;
if (ch <= 127)
{
// 1 byte
moreChars = 0;
}
else if (ch >= 194 && ch <= 223)
{
// 2 Byte
moreChars = 1;
}
else if (ch >= 224 && ch <= 239)
{
// 3 Byte
moreChars = 2;
}
else if (ch >= 240 && ch <= 244)
{
// 4 Byte
moreChars = 3;
}
else
{
return Encoding.None; // Not utf8
}

// Check secondary chars are in range if we are expecting any
while (moreChars > 0 && pos < size)
{
onlySawAsciiRange = false; // Seen non-ascii chars now

ch = buffer[pos++];
if (ch < 128 || ch > 191)
{
return Encoding.None; // Not utf8
}

--moreChars;
}
}

// If we get to here then only valid UTF-8 sequences have been processed

// If we only saw chars in the range 0-127 then we can't assume UTF8 (the caller will need to decide)
return onlySawAsciiRange ? Encoding.Ascii : Encoding.Utf8Nobom;
}
/// <summary>
/// 是否中文编码（GB2312、GBK、Big5）
/// </summary>
private void CheckChinese(byte[] buffer, int size)
{
IsChinese = false;
if (size < 2)
{
return;
}

// Reduce size by 1 so we don't need to worry about bounds checking for pairs of bytes
size--;
uint pos = 0;
bool isCN = false;
while (pos < size)
{
//GB2312
//0xB0-0xF7(176-247)
//0xA0-0xFE（160-254）

//GBK
//0x81-0xFE（129-254）
//0x40-0xFE（64-254）

//Big5
//0x81-0xFE（129-255）
//0x40-0x7E（64-126）  OR 0xA1－0xFE（161-254）
byte ch1 = buffer[pos++];
byte ch2 = buffer[pos++];
isCN = (ch1 >= 176 && ch1 <= 247 && ch2 >= 160 && ch2 <= 254)
|| (ch1 >= 129 && ch1 <= 254 && ch2 >= 64 && ch2 <= 254)
|| (ch1 >= 129 && ((ch2 >= 64 && ch2 <= 126) || (ch2 >= 161 && ch2 <= 254)));
if (!isCN)
{
return;
}

}
IsChinese = true;
}
}
}

后续更新地址：https://github.com/cyq1162/cyqdata/blob/master/Tool/IOHelper.cs

总结：

1、考虑到UTF7已经过时了，所以直接无视了。

2、对于纯中文情况，UTF16下是BE还是LE，暂时没有想到好的检测方法，所以默认返回了常用的LE，即Unicode。

3、其它一切都安好，全国公开的C#版本，应该就此一份了。