407 lines
13 KiB
C#
407 lines
13 KiB
C#
namespace Emby.Server.Implementations.TextEncoding
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{
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// Copyright 2015-2016 Jonathan Bennett <jon@autoitscript.com>
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//
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// https://www.autoitscript.com
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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/// <summary>
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/// Credit: https://github.com/AutoIt/text-encoding-detect
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/// </summary>
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public class TextEncodingDetect
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{
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private readonly byte[] _utf16BeBom =
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{
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0xFE,
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0xFF
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};
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private readonly byte[] _utf16LeBom =
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{
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0xFF,
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0xFE
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};
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private readonly byte[] _utf8Bom =
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{
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0xEF,
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0xBB,
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0xBF
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};
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private bool _nullSuggestsBinary = true;
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private double _utf16ExpectedNullPercent = 70;
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private double _utf16UnexpectedNullPercent = 10;
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public enum CharacterEncoding
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{
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None, // Unknown or binary
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Ansi, // 0-255
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Ascii, // 0-127
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Utf8Bom, // UTF8 with BOM
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Utf8Nobom, // UTF8 without BOM
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Utf16LeBom, // UTF16 LE with BOM
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Utf16LeNoBom, // UTF16 LE without BOM
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Utf16BeBom, // UTF16-BE with BOM
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Utf16BeNoBom // UTF16-BE without BOM
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}
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/// <summary>
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/// Sets if the presence of nulls in a buffer indicate the buffer is binary data rather than text.
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/// </summary>
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public bool NullSuggestsBinary
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{
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set => _nullSuggestsBinary = value;
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}
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public double Utf16ExpectedNullPercent
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{
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set
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{
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if (value > 0 && value < 100)
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{
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_utf16ExpectedNullPercent = value;
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}
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}
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}
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public double Utf16UnexpectedNullPercent
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{
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set
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{
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if (value > 0 && value < 100)
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{
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_utf16UnexpectedNullPercent = value;
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}
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}
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}
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/// <summary>
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/// Gets the BOM length for a given Encoding mode.
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/// </summary>
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/// <param name="encoding"></param>
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/// <returns>The BOM length.</returns>
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public static int GetBomLengthFromEncodingMode(CharacterEncoding encoding)
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{
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int length;
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switch (encoding)
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{
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case CharacterEncoding.Utf16BeBom:
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case CharacterEncoding.Utf16LeBom:
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length = 2;
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break;
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case CharacterEncoding.Utf8Bom:
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length = 3;
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break;
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default:
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length = 0;
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break;
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}
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return length;
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}
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/// <summary>
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/// Checks for a BOM sequence in a byte buffer.
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/// </summary>
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/// <param name="buffer"></param>
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/// <param name="size"></param>
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/// <returns>Encoding type or Encoding.None if no BOM.</returns>
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public CharacterEncoding CheckBom(byte[] buffer, int size)
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{
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// Check for BOM
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if (size >= 2 && buffer[0] == _utf16LeBom[0] && buffer[1] == _utf16LeBom[1])
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{
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return CharacterEncoding.Utf16LeBom;
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}
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if (size >= 2 && buffer[0] == _utf16BeBom[0] && buffer[1] == _utf16BeBom[1])
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{
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return CharacterEncoding.Utf16BeBom;
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}
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if (size >= 3 && buffer[0] == _utf8Bom[0] && buffer[1] == _utf8Bom[1] && buffer[2] == _utf8Bom[2])
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{
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return CharacterEncoding.Utf8Bom;
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}
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return CharacterEncoding.None;
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}
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/// <summary>
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/// Automatically detects the Encoding type of a given byte buffer.
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/// </summary>
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/// <param name="buffer">The byte buffer.</param>
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/// <param name="size">The size of the byte buffer.</param>
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/// <returns>The Encoding type or Encoding.None if unknown.</returns>
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public CharacterEncoding DetectEncoding(byte[] buffer, int size)
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{
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// First check if we have a BOM and return that if so
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CharacterEncoding encoding = CheckBom(buffer, size);
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if (encoding != CharacterEncoding.None)
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{
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return encoding;
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}
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// Now check for valid UTF8
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encoding = CheckUtf8(buffer, size);
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if (encoding != CharacterEncoding.None)
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{
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return encoding;
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}
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// Now try UTF16
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encoding = CheckUtf16NewlineChars(buffer, size);
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if (encoding != CharacterEncoding.None)
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{
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return encoding;
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}
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encoding = CheckUtf16Ascii(buffer, size);
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if (encoding != CharacterEncoding.None)
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{
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return encoding;
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}
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// ANSI or None (binary) then
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if (!DoesContainNulls(buffer, size))
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{
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return CharacterEncoding.Ansi;
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}
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// Found a null, return based on the preference in null_suggests_binary_
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return _nullSuggestsBinary ? CharacterEncoding.None : CharacterEncoding.Ansi;
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}
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/// <summary>
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/// Checks if a buffer contains text that looks like utf16 by scanning for
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/// newline chars that would be present even in non-english text.
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/// </summary>
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/// <param name="buffer">The byte buffer.</param>
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/// <param name="size">The size of the byte buffer.</param>
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/// <returns>Encoding.none, Encoding.Utf16LeNoBom or Encoding.Utf16BeNoBom.</returns>
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private static CharacterEncoding CheckUtf16NewlineChars(byte[] buffer, int size)
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{
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if (size < 2)
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{
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return CharacterEncoding.None;
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}
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// Reduce size by 1 so we don't need to worry about bounds checking for pairs of bytes
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size--;
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var leControlChars = 0;
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var beControlChars = 0;
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uint pos = 0;
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while (pos < size)
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{
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byte ch1 = buffer[pos++];
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byte ch2 = buffer[pos++];
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if (ch1 == 0)
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{
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if (ch2 == 0x0a || ch2 == 0x0d)
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{
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++beControlChars;
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}
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}
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else if (ch2 == 0)
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{
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if (ch1 == 0x0a || ch1 == 0x0d)
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{
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++leControlChars;
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}
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}
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// If we are getting both LE and BE control chars then this file is not utf16
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if (leControlChars > 0 && beControlChars > 0)
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{
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return CharacterEncoding.None;
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}
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}
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if (leControlChars > 0)
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{
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return CharacterEncoding.Utf16LeNoBom;
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}
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return beControlChars > 0 ? CharacterEncoding.Utf16BeNoBom : CharacterEncoding.None;
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}
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/// <summary>
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/// Checks if a buffer contains any nulls. Used to check for binary vs text data.
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/// </summary>
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/// <param name="buffer">The byte buffer.</param>
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/// <param name="size">The size of the byte buffer.</param>
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private static bool DoesContainNulls(byte[] buffer, int size)
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{
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uint pos = 0;
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while (pos < size)
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{
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if (buffer[pos++] == 0)
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{
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return true;
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}
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}
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return false;
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}
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/// <summary>
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/// Checks if a buffer contains text that looks like utf16. This is done based
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/// on the use of nulls which in ASCII/script like text can be useful to identify.
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/// </summary>
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/// <param name="buffer">The byte buffer.</param>
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/// <param name="size">The size of the byte buffer.</param>
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/// <returns>Encoding.none, Encoding.Utf16LeNoBom or Encoding.Utf16BeNoBom.</returns>
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private CharacterEncoding CheckUtf16Ascii(byte[] buffer, int size)
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{
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var numOddNulls = 0;
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var numEvenNulls = 0;
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// Get even nulls
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uint pos = 0;
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while (pos < size)
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{
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if (buffer[pos] == 0)
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{
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numEvenNulls++;
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}
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pos += 2;
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}
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// Get odd nulls
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pos = 1;
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while (pos < size)
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{
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if (buffer[pos] == 0)
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{
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numOddNulls++;
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}
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pos += 2;
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}
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double evenNullThreshold = numEvenNulls * 2.0 / size;
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double oddNullThreshold = numOddNulls * 2.0 / size;
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double expectedNullThreshold = _utf16ExpectedNullPercent / 100.0;
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double unexpectedNullThreshold = _utf16UnexpectedNullPercent / 100.0;
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// Lots of odd nulls, low number of even nulls
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if (evenNullThreshold < unexpectedNullThreshold && oddNullThreshold > expectedNullThreshold)
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{
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return CharacterEncoding.Utf16LeNoBom;
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}
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// Lots of even nulls, low number of odd nulls
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if (oddNullThreshold < unexpectedNullThreshold && evenNullThreshold > expectedNullThreshold)
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{
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return CharacterEncoding.Utf16BeNoBom;
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}
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// Don't know
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return CharacterEncoding.None;
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}
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/// <summary>
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/// Checks if a buffer contains valid utf8.
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/// </summary>
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/// <param name="buffer">The byte buffer.</param>
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/// <param name="size">The size of the byte buffer.</param>
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/// <returns>
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/// Encoding type of Encoding.None (invalid UTF8), Encoding.Utf8NoBom (valid utf8 multibyte strings) or
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/// Encoding.ASCII (data in 0.127 range).
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/// </returns>
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/// <returns>2</returns>
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private CharacterEncoding CheckUtf8(byte[] buffer, int size)
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{
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// UTF8 Valid sequences
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// 0xxxxxxx ASCII
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// 110xxxxx 10xxxxxx 2-byte
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// 1110xxxx 10xxxxxx 10xxxxxx 3-byte
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// 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx 4-byte
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//
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// Width in UTF8
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// Decimal Width
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// 0-127 1 byte
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// 194-223 2 bytes
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// 224-239 3 bytes
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// 240-244 4 bytes
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//
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// Subsequent chars are in the range 128-191
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var onlySawAsciiRange = true;
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uint pos = 0;
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while (pos < size)
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{
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byte ch = buffer[pos++];
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if (ch == 0 && _nullSuggestsBinary)
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{
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return CharacterEncoding.None;
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}
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int moreChars;
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if (ch <= 127)
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{
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// 1 byte
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moreChars = 0;
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}
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else if (ch >= 194 && ch <= 223)
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{
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// 2 Byte
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moreChars = 1;
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}
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else if (ch >= 224 && ch <= 239)
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{
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// 3 Byte
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moreChars = 2;
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}
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else if (ch >= 240 && ch <= 244)
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{
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// 4 Byte
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moreChars = 3;
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}
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else
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{
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return CharacterEncoding.None; // Not utf8
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}
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// Check secondary chars are in range if we are expecting any
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while (moreChars > 0 && pos < size)
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{
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onlySawAsciiRange = false; // Seen non-ascii chars now
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ch = buffer[pos++];
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if (ch < 128 || ch > 191)
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{
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return CharacterEncoding.None; // Not utf8
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}
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--moreChars;
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}
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}
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// If we get to here then only valid UTF-8 sequences have been processed
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// If we only saw chars in the range 0-127 then we can't assume UTF8 (the caller will need to decide)
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return onlySawAsciiRange ? CharacterEncoding.Ascii : CharacterEncoding.Utf8Nobom;
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}
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}
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}
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