检测字节流是否是UTF8编码

/// <summary>

///   Determines whether the given <paramref name="inputStream"/>is UTF8 encoding bytes.

/// </summary>

/// <param name="inputStream">

///    The input stream.

///  </param>

/// <returns>

///   <see langword="true"/> if given bystes stream is in UTF8 encoding; otherwise, <see langword="false"/>.

/// </returns>

/// <remarks>

///   All ASCII chars will regards not UTF8 encoding.

/// </remarks>

public static bool IsTextUTF8(ref byte[] inputStream)

{

    int encodingBytesCount = 0;

    bool allTextsAreASCIIChars = true;

    for (int i = 0; i < inputStream.Length; i++)

    {

        byte current = inputStream[i];

        if ((current & 0x80) == 0x80)

        {                   

            allTextsAreASCIIChars = false;

        }

        // First byte

        if (encodingBytesCount == 0)

        {

            if ((current & 0x80) == 0)

            {

                // ASCII chars, from 0x00-0x7F

                continue;

            }

            if ((current & 0xC0) == 0xC0)

            {

                encodingBytesCount = 1;

                current <<= 2;

                // More than two bytes used to encoding a unicode char.

                // Calculate the real length.

                while ((current & 0x80) == 0x80)

                {

                    current <<= 1;

                    encodingBytesCount++;

                }

            }                   

            else

            {

                // Invalid bits structure for UTF8 encoding rule.

                return false;

            }

        }               

        else

        {

            // Following bytes, must start with 10.

            if ((current & 0xC0) == 0x80)

            {                       

                encodingBytesCount--;

            }

            else

            {

                // Invalid bits structure for UTF8 encoding rule.

                return false;

            }

        }

    }

    if (encodingBytesCount != 0)

    {

        // Invalid bits structure for UTF8 encoding rule.

        // Wrong following bytes count.

        return false;

    }

    // Although UTF8 supports encoding for ASCII chars, we regard as a input stream, whose contents are all ASCII as default encoding.

    return !allTextsAreASCIIChars;

}

/// <summary>

///This is a test class for EncodingHelperTest and is intended

///to contain all EncodingHelperTest Unit Tests

///</summary>

[TestClass()]

public class EncodingHelperTest

{

    /// <summary>

    ///  Normal test for this method.

    ///</summary>

    [TestMethod()]

    public void IsTextUTF8Test()

    {

        for (int i = 0; i < 1000; i++)

        {

            List<Char> chars = new List<char>();

            chars.Add(‘中‘);

            List<UnicodeCategory> temp = new List<UnicodeCategory>();

            Random rd = new Random((int)(DateTime.Now.Ticks & 0x7FFFFFFF));

            for (int j = 0; j < 255; j++)

            {

                char ch = (char)rd.Next(0xFFFF);

                UnicodeCategory uc = System.Globalization.CharUnicodeInfo.GetUnicodeCategory(ch);

                if (uc == UnicodeCategory.Surrogate || // Single surrogate could not be encoding correctly.

                    uc == UnicodeCategory.PrivateUse || // Private use blocks should be excluded.

                    uc == UnicodeCategory.OtherNotAssigned

                    )

                {

                    j--;

                }

                else

                {

                    chars.Add(ch);

                    temp.Add(uc);

                }

            }

            string str = new string(chars.ToArray());

            byte[] inputStream = Encoding.UTF8.GetBytes(str);

            bool expected = true;

            bool actual;

            actual = EncodingHelper.IsTextUTF8(ref inputStream);

            Assert.AreEqual(expected, actual, string.Format("UTF8_Assert Fails at:{0}", str));

            inputStream = Encoding.GetEncoding(932).GetBytes(str);

            expected = false;

            actual = EncodingHelper.IsTextUTF8(ref inputStream);

            Assert.AreEqual(expected, actual, string.Format("ShiftJIS_Assert Fails at:{0}", str));

        }

    }

    /// <summary>

    ///   Check with All ASCII chars

    /// </summary>

    [TestMethod]

    public void IsTextUTF8Test_AllASCII()

    {

        string str = "ABCDEFGHKLHSJKLDFHJKLHAJKLSHJKLHAJKLSHDJKLAHSDJKLHAJKLSDHJKLASHDJKLHASJKLDHJKLASD";

        byte[] inputStream = Encoding.UTF8.GetBytes(str);

        bool expected = false;

        bool actual;

        actual = EncodingHelper.IsTextUTF8(ref inputStream);

        Assert.AreEqual(expected, actual, string.Format("UTF8_Assert Fails at:{0}", str));

    }

}