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Simple class to automatically detect text file encoding, with English-biased "best guess" heuristic based on byte patterns in the absence of BOM.
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| using System; | |
| using System.Text; | |
| using System.Text.RegularExpressions; | |
| using System.IO; | |
| namespace KlerksSoft | |
| { | |
| public static class TextFileEncodingDetector | |
| { | |
| /* | |
| * Simple class to handle text file encoding woes (in a primarily English-speaking tech | |
| * world). | |
| * | |
| * - This code is fully managed, no shady calls to MLang (the unmanaged codepage | |
| * detection library originally developed for Internet Explorer). | |
| * | |
| * - This class does NOT try to detect arbitrary codepages/charsets, it really only | |
| * aims to differentiate between some of the most common variants of Unicode | |
| * encoding, and a "default" (western / ascii-based) encoding alternative provided | |
| * by the caller. | |
| * | |
| * - As there is no "Reliable" way to distinguish between UTF-8 (without BOM) and | |
| * Windows-1252 (in .Net, also incorrectly called "ASCII") encodings, we use a | |
| * heuristic - so the more of the file we can sample the better the guess. If you | |
| * are going to read the whole file into memory at some point, then best to pass | |
| * in the whole byte byte array directly. Otherwise, decide how to trade off | |
| * reliability against performance / memory usage. | |
| * | |
| * - The UTF-8 detection heuristic only works for western text, as it relies on | |
| * the presence of UTF-8 encoded accented and other characters found in the upper | |
| * ranges of the Latin-1 and (particularly) Windows-1252 codepages. | |
| * | |
| * - For more general detection routines, see existing projects / resources: | |
| * - MLang - Microsoft library originally for IE6, available in Windows XP and later APIs now (I think?) | |
| * - MLang .Net bindings: http://www.codeproject.com/KB/recipes/DetectEncoding.aspx | |
| * - CharDet - Mozilla browser's detection routines | |
| * - Ported to Java then .Net: http://www.conceptdevelopment.net/Localization/NCharDet/ | |
| * - Ported straight to .Net: http://code.google.com/p/chardetsharp/source/browse | |
| * | |
| * Copyright Tao Klerks, 2010-2012, tao@klerks.biz | |
| * Licensed under the modified BSD license: | |
| * | |
| Redistribution and use in source and binary forms, with or without modification, are | |
| permitted provided that the following conditions are met: | |
| - Redistributions of source code must retain the above copyright notice, this list of | |
| conditions and the following disclaimer. | |
| - Redistributions in binary form must reproduce the above copyright notice, this list | |
| of conditions and the following disclaimer in the documentation and/or other materials | |
| provided with the distribution. | |
| - The name of the author may not be used to endorse or promote products derived from | |
| this software without specific prior written permission. | |
| THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, | |
| INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | |
| A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY | |
| DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, | |
| BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR | |
| PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, | |
| WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) | |
| ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY | |
| OF SUCH DAMAGE. | |
| * | |
| * CHANGELOG: | |
| * - 2012-02-03: | |
| * - Simpler methods, removing the silly "DefaultEncoding" parameter (with "??" operator, saves no typing) | |
| * - More complete methods | |
| * - Optionally return indication of whether BOM was found in "Detect" methods | |
| * - Provide straight-to-string method for byte arrays (GetStringFromByteArray) | |
| */ | |
| const long _defaultHeuristicSampleSize = 0x10000; //completely arbitrary - inappropriate for high numbers of files / high speed requirements | |
| public static Encoding DetectTextFileEncoding(string InputFilename) | |
| { | |
| using (FileStream textfileStream = File.OpenRead(InputFilename)) | |
| { | |
| return DetectTextFileEncoding(textfileStream, _defaultHeuristicSampleSize); | |
| } | |
| } | |
| public static Encoding DetectTextFileEncoding(FileStream InputFileStream, long HeuristicSampleSize) | |
| { | |
| bool uselessBool = false; | |
| return DetectTextFileEncoding(InputFileStream, _defaultHeuristicSampleSize, out uselessBool); | |
| } | |
| public static Encoding DetectTextFileEncoding(FileStream InputFileStream, long HeuristicSampleSize, out bool HasBOM) | |
| { | |
| if (InputFileStream == null) | |
| throw new ArgumentNullException("Must provide a valid Filestream!", "InputFileStream"); | |
| if (!InputFileStream.CanRead) | |
| throw new ArgumentException("Provided file stream is not readable!", "InputFileStream"); | |
| if (!InputFileStream.CanSeek) | |
| throw new ArgumentException("Provided file stream cannot seek!", "InputFileStream"); | |
| Encoding encodingFound = null; | |
| long originalPos = InputFileStream.Position; | |
| InputFileStream.Position = 0; | |
| //First read only what we need for BOM detection | |
| byte[] bomBytes = new byte[InputFileStream.Length > 4 ? 4 : InputFileStream.Length]; | |
| InputFileStream.Read(bomBytes, 0, bomBytes.Length); | |
| encodingFound = DetectBOMBytes(bomBytes); | |
| if (encodingFound != null) | |
| { | |
| InputFileStream.Position = originalPos; | |
| HasBOM = true; | |
| return encodingFound; | |
| } | |
| //BOM Detection failed, going for heuristics now. | |
| // create sample byte array and populate it | |
| byte[] sampleBytes = new byte[HeuristicSampleSize > InputFileStream.Length ? InputFileStream.Length : HeuristicSampleSize]; | |
| Array.Copy(bomBytes, sampleBytes, bomBytes.Length); | |
| if (InputFileStream.Length > bomBytes.Length) | |
| InputFileStream.Read(sampleBytes, bomBytes.Length, sampleBytes.Length - bomBytes.Length); | |
| InputFileStream.Position = originalPos; | |
| //test byte array content | |
| encodingFound = DetectUnicodeInByteSampleByHeuristics(sampleBytes); | |
| HasBOM = false; | |
| return encodingFound; | |
| } | |
| public static Encoding DetectTextByteArrayEncoding(byte[] TextData) | |
| { | |
| bool uselessBool = false; | |
| return DetectTextByteArrayEncoding(TextData, out uselessBool); | |
| } | |
| public static Encoding DetectTextByteArrayEncoding(byte[] TextData, out bool HasBOM) | |
| { | |
| if (TextData == null) | |
| throw new ArgumentNullException("Must provide a valid text data byte array!", "TextData"); | |
| Encoding encodingFound = null; | |
| encodingFound = DetectBOMBytes(TextData); | |
| if (encodingFound != null) | |
| { | |
| HasBOM = true; | |
| return encodingFound; | |
| } | |
| else | |
| { | |
| //test byte array content | |
| encodingFound = DetectUnicodeInByteSampleByHeuristics(TextData); | |
| HasBOM = false; | |
| return encodingFound; | |
| } | |
| } | |
| public static string GetStringFromByteArray(byte[] TextData, Encoding DefaultEncoding) | |
| { | |
| return GetStringFromByteArray(TextData, DefaultEncoding, _defaultHeuristicSampleSize); | |
| } | |
| public static string GetStringFromByteArray(byte[] TextData, Encoding DefaultEncoding, long MaxHeuristicSampleSize) | |
| { | |
| if (TextData == null) | |
| throw new ArgumentNullException("Must provide a valid text data byte array!", "TextData"); | |
| Encoding encodingFound = null; | |
| encodingFound = DetectBOMBytes(TextData); | |
| if (encodingFound != null) | |
| { | |
| //For some reason, the default encodings don't detect/swallow their own preambles!! | |
| return encodingFound.GetString(TextData, encodingFound.GetPreamble().Length, TextData.Length - encodingFound.GetPreamble().Length); | |
| } | |
| else | |
| { | |
| byte[] heuristicSample = null; | |
| if (TextData.Length > MaxHeuristicSampleSize) | |
| { | |
| heuristicSample = new byte[MaxHeuristicSampleSize]; | |
| Array.Copy(TextData, heuristicSample, MaxHeuristicSampleSize); | |
| } | |
| else | |
| { | |
| heuristicSample = TextData; | |
| } | |
| encodingFound = DetectUnicodeInByteSampleByHeuristics(TextData) ?? DefaultEncoding; | |
| return encodingFound.GetString(TextData); | |
| } | |
| } | |
| public static Encoding DetectBOMBytes(byte[] BOMBytes) | |
| { | |
| if (BOMBytes == null) | |
| throw new ArgumentNullException("Must provide a valid BOM byte array!", "BOMBytes"); | |
| if (BOMBytes.Length < 2) | |
| return null; | |
| if (BOMBytes[0] == 0xff | |
| && BOMBytes[1] == 0xfe | |
| && (BOMBytes.Length < 4 | |
| || BOMBytes[2] != 0 | |
| || BOMBytes[3] != 0 | |
| ) | |
| ) | |
| return Encoding.Unicode; | |
| if (BOMBytes[0] == 0xfe | |
| && BOMBytes[1] == 0xff | |
| ) | |
| return Encoding.BigEndianUnicode; | |
| if (BOMBytes.Length < 3) | |
| return null; | |
| if (BOMBytes[0] == 0xef && BOMBytes[1] == 0xbb && BOMBytes[2] == 0xbf) | |
| return Encoding.UTF8; | |
| if (BOMBytes[0] == 0x2b && BOMBytes[1] == 0x2f && BOMBytes[2] == 0x76) | |
| return Encoding.UTF7; | |
| if (BOMBytes.Length < 4) | |
| return null; | |
| if (BOMBytes[0] == 0xff && BOMBytes[1] == 0xfe && BOMBytes[2] == 0 && BOMBytes[3] == 0) | |
| return Encoding.UTF32; | |
| if (BOMBytes[0] == 0 && BOMBytes[1] == 0 && BOMBytes[2] == 0xfe && BOMBytes[3] == 0xff) | |
| return Encoding.GetEncoding(12001); | |
| return null; | |
| } | |
| public static Encoding DetectUnicodeInByteSampleByHeuristics(byte[] SampleBytes) | |
| { | |
| long oddBinaryNullsInSample = 0; | |
| long evenBinaryNullsInSample = 0; | |
| long suspiciousUTF8SequenceCount = 0; | |
| long suspiciousUTF8BytesTotal = 0; | |
| long likelyUSASCIIBytesInSample = 0; | |
| //Cycle through, keeping count of binary null positions, possible UTF-8 | |
| // sequences from upper ranges of Windows-1252, and probable US-ASCII | |
| // character counts. | |
| long currentPos = 0; | |
| int skipUTF8Bytes = 0; | |
| while (currentPos < SampleBytes.Length) | |
| { | |
| //binary null distribution | |
| if (SampleBytes[currentPos] == 0) | |
| { | |
| if (currentPos % 2 == 0) | |
| evenBinaryNullsInSample++; | |
| else | |
| oddBinaryNullsInSample++; | |
| } | |
| //likely US-ASCII characters | |
| if (IsCommonUSASCIIByte(SampleBytes[currentPos])) | |
| likelyUSASCIIBytesInSample++; | |
| //suspicious sequences (look like UTF-8) | |
| if (skipUTF8Bytes == 0) | |
| { | |
| int lengthFound = DetectSuspiciousUTF8SequenceLength(SampleBytes, currentPos); | |
| if (lengthFound > 0) | |
| { | |
| suspiciousUTF8SequenceCount++; | |
| suspiciousUTF8BytesTotal += lengthFound; | |
| skipUTF8Bytes = lengthFound - 1; | |
| } | |
| } | |
| else | |
| { | |
| skipUTF8Bytes--; | |
| } | |
| currentPos++; | |
| } | |
| //1: UTF-16 LE - in english / european environments, this is usually characterized by a | |
| // high proportion of odd binary nulls (starting at 0), with (as this is text) a low | |
| // proportion of even binary nulls. | |
| // The thresholds here used (less than 20% nulls where you expect non-nulls, and more than | |
| // 60% nulls where you do expect nulls) are completely arbitrary. | |
| if (((evenBinaryNullsInSample * 2.0) / SampleBytes.Length) < 0.2 | |
| && ((oddBinaryNullsInSample * 2.0) / SampleBytes.Length) > 0.6 | |
| ) | |
| return Encoding.Unicode; | |
| //2: UTF-16 BE - in english / european environments, this is usually characterized by a | |
| // high proportion of even binary nulls (starting at 0), with (as this is text) a low | |
| // proportion of odd binary nulls. | |
| // The thresholds here used (less than 20% nulls where you expect non-nulls, and more than | |
| // 60% nulls where you do expect nulls) are completely arbitrary. | |
| if (((oddBinaryNullsInSample * 2.0) / SampleBytes.Length) < 0.2 | |
| && ((evenBinaryNullsInSample * 2.0) / SampleBytes.Length) > 0.6 | |
| ) | |
| return Encoding.BigEndianUnicode; | |
| //3: UTF-8 - Martin Dürst outlines a method for detecting whether something CAN be UTF-8 content | |
| // using regexp, in his w3c.org unicode FAQ entry: | |
| // http://www.w3.org/International/questions/qa-forms-utf-8 | |
| // adapted here for C#. | |
| string potentiallyMangledString = Encoding.ASCII.GetString(SampleBytes); | |
| Regex UTF8Validator = new Regex(@"\A(" | |
| + @"[\x09\x0A\x0D\x20-\x7E]" | |
| + @"|[\xC2-\xDF][\x80-\xBF]" | |
| + @"|\xE0[\xA0-\xBF][\x80-\xBF]" | |
| + @"|[\xE1-\xEC\xEE\xEF][\x80-\xBF]{2}" | |
| + @"|\xED[\x80-\x9F][\x80-\xBF]" | |
| + @"|\xF0[\x90-\xBF][\x80-\xBF]{2}" | |
| + @"|[\xF1-\xF3][\x80-\xBF]{3}" | |
| + @"|\xF4[\x80-\x8F][\x80-\xBF]{2}" | |
| + @")*\z"); | |
| if (UTF8Validator.IsMatch(potentiallyMangledString)) | |
| { | |
| //Unfortunately, just the fact that it CAN be UTF-8 doesn't tell you much about probabilities. | |
| //If all the characters are in the 0-127 range, no harm done, most western charsets are same as UTF-8 in these ranges. | |
| //If some of the characters were in the upper range (western accented characters), however, they would likely be mangled to 2-byte by the UTF-8 encoding process. | |
| // So, we need to play stats. | |
| // The "Random" likelihood of any pair of randomly generated characters being one | |
| // of these "suspicious" character sequences is: | |
| // 128 / (256 * 256) = 0.2%. | |
| // | |
| // In western text data, that is SIGNIFICANTLY reduced - most text data stays in the <127 | |
| // character range, so we assume that more than 1 in 500,000 of these character | |
| // sequences indicates UTF-8. The number 500,000 is completely arbitrary - so sue me. | |
| // | |
| // We can only assume these character sequences will be rare if we ALSO assume that this | |
| // IS in fact western text - in which case the bulk of the UTF-8 encoded data (that is | |
| // not already suspicious sequences) should be plain US-ASCII bytes. This, I | |
| // arbitrarily decided, should be 80% (a random distribution, eg binary data, would yield | |
| // approx 40%, so the chances of hitting this threshold by accident in random data are | |
| // VERY low). | |
| if ((suspiciousUTF8SequenceCount * 500000.0 / SampleBytes.Length >= 1) //suspicious sequences | |
| && ( | |
| //all suspicious, so cannot evaluate proportion of US-Ascii | |
| SampleBytes.Length - suspiciousUTF8BytesTotal == 0 | |
| || | |
| likelyUSASCIIBytesInSample * 1.0 / (SampleBytes.Length - suspiciousUTF8BytesTotal) >= 0.8 | |
| ) | |
| ) | |
| return Encoding.UTF8; | |
| } | |
| return null; | |
| } | |
| private static bool IsCommonUSASCIIByte(byte testByte) | |
| { | |
| if (testByte == 0x0A //lf | |
| || testByte == 0x0D //cr | |
| || testByte == 0x09 //tab | |
| || (testByte >= 0x20 && testByte <= 0x2F) //common punctuation | |
| || (testByte >= 0x30 && testByte <= 0x39) //digits | |
| || (testByte >= 0x3A && testByte <= 0x40) //common punctuation | |
| || (testByte >= 0x41 && testByte <= 0x5A) //capital letters | |
| || (testByte >= 0x5B && testByte <= 0x60) //common punctuation | |
| || (testByte >= 0x61 && testByte <= 0x7A) //lowercase letters | |
| || (testByte >= 0x7B && testByte <= 0x7E) //common punctuation | |
| ) | |
| return true; | |
| else | |
| return false; | |
| } | |
| private static int DetectSuspiciousUTF8SequenceLength(byte[] SampleBytes, long currentPos) | |
| { | |
| int lengthFound = 0; | |
| if (SampleBytes.Length >= currentPos + 1 | |
| && SampleBytes[currentPos] == 0xC2 | |
| ) | |
| { | |
| if (SampleBytes[currentPos + 1] == 0x81 | |
| || SampleBytes[currentPos + 1] == 0x8D | |
| || SampleBytes[currentPos + 1] == 0x8F | |
| ) | |
| lengthFound = 2; | |
| else if (SampleBytes[currentPos + 1] == 0x90 | |
| || SampleBytes[currentPos + 1] == 0x9D | |
| ) | |
| lengthFound = 2; | |
| else if (SampleBytes[currentPos + 1] >= 0xA0 | |
| && SampleBytes[currentPos + 1] <= 0xBF | |
| ) | |
| lengthFound = 2; | |
| } | |
| else if (SampleBytes.Length >= currentPos + 1 | |
| && SampleBytes[currentPos] == 0xC3 | |
| ) | |
| { | |
| if (SampleBytes[currentPos + 1] >= 0x80 | |
| && SampleBytes[currentPos + 1] <= 0xBF | |
| ) | |
| lengthFound = 2; | |
| } | |
| else if (SampleBytes.Length >= currentPos + 1 | |
| && SampleBytes[currentPos] == 0xC5 | |
| ) | |
| { | |
| if (SampleBytes[currentPos + 1] == 0x92 | |
| || SampleBytes[currentPos + 1] == 0x93 | |
| ) | |
| lengthFound = 2; | |
| else if (SampleBytes[currentPos + 1] == 0xA0 | |
| || SampleBytes[currentPos + 1] == 0xA1 | |
| ) | |
| lengthFound = 2; | |
| else if (SampleBytes[currentPos + 1] == 0xB8 | |
| || SampleBytes[currentPos + 1] == 0xBD | |
| || SampleBytes[currentPos + 1] == 0xBE | |
| ) | |
| lengthFound = 2; | |
| } | |
| else if (SampleBytes.Length >= currentPos + 1 | |
| && SampleBytes[currentPos] == 0xC6 | |
| ) | |
| { | |
| if (SampleBytes[currentPos + 1] == 0x92) | |
| lengthFound = 2; | |
| } | |
| else if (SampleBytes.Length >= currentPos + 1 | |
| && SampleBytes[currentPos] == 0xCB | |
| ) | |
| { | |
| if (SampleBytes[currentPos + 1] == 0x86 | |
| || SampleBytes[currentPos + 1] == 0x9C | |
| ) | |
| lengthFound = 2; | |
| } | |
| else if (SampleBytes.Length >= currentPos + 2 | |
| && SampleBytes[currentPos] == 0xE2 | |
| ) | |
| { | |
| if (SampleBytes[currentPos + 1] == 0x80) | |
| { | |
| if (SampleBytes[currentPos + 2] == 0x93 | |
| || SampleBytes[currentPos + 2] == 0x94 | |
| ) | |
| lengthFound = 3; | |
| if (SampleBytes[currentPos + 2] == 0x98 | |
| || SampleBytes[currentPos + 2] == 0x99 | |
| || SampleBytes[currentPos + 2] == 0x9A | |
| ) | |
| lengthFound = 3; | |
| if (SampleBytes[currentPos + 2] == 0x9C | |
| || SampleBytes[currentPos + 2] == 0x9D | |
| || SampleBytes[currentPos + 2] == 0x9E | |
| ) | |
| lengthFound = 3; | |
| if (SampleBytes[currentPos + 2] == 0xA0 | |
| || SampleBytes[currentPos + 2] == 0xA1 | |
| || SampleBytes[currentPos + 2] == 0xA2 | |
| ) | |
| lengthFound = 3; | |
| if (SampleBytes[currentPos + 2] == 0xA6) | |
| lengthFound = 3; | |
| if (SampleBytes[currentPos + 2] == 0xB0) | |
| lengthFound = 3; | |
| if (SampleBytes[currentPos + 2] == 0xB9 | |
| || SampleBytes[currentPos + 2] == 0xBA | |
| ) | |
| lengthFound = 3; | |
| } | |
| else if (SampleBytes[currentPos + 1] == 0x82 | |
| && SampleBytes[currentPos + 2] == 0xAC | |
| ) | |
| lengthFound = 3; | |
| else if (SampleBytes[currentPos + 1] == 0x84 | |
| && SampleBytes[currentPos + 2] == 0xA2 | |
| ) | |
| lengthFound = 3; | |
| } | |
| return lengthFound; | |
| } | |
| } | |
| } |
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