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Better encoding guessing from Alex

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git-svn-id: https://zxing.googlecode.com/svn/trunk@2157 59b500cc-1b3d-0410-9834-0bbf25fbcc57
This commit is contained in:
srowen 2012-02-04 12:24:26 +00:00
parent d265ccff56
commit 5d89cc30fc
3 changed files with 189 additions and 94 deletions
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2
AUTHORS
View file

@ -4,6 +4,7 @@ in alphabetical order.
Agustín Delgado (Servinform S.A.)
Aitor Almeida (University of Deusto)
Alasdair Mackintosh (Google)
Alex Dupre
Alexander Martin (Haase & Martin GmbH)
Andreas Pillath
Andrew Walbran (Google)
@ -20,6 +21,7 @@ Dave MacLachlan (Google)
David Phillip Oster (Google)
David Albert (Bug Labs)
David Olivier
dawalker (Google)
Diego Pierotto
drejc83
Eduardo Castillejo (University of Deusto)

209
core/src/com/google/zxing/common/StringUtils.java
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@ -24,6 +24,7 @@ import com.google.zxing.DecodeHintType;
* Common string-related functions.
*
* @author Sean Owen
* @author Alex Dupre
*/
public final class StringUtils {
@ -54,30 +55,33 @@ public final class StringUtils {
return characterSet;
}
}
// Does it start with the UTF-8 byte order mark? then guess it's UTF-8
if (bytes.length > 3 &&
bytes[0] == (byte) 0xEF &&
bytes[1] == (byte) 0xBB &&
bytes[2] == (byte) 0xBF) {
return UTF8;
}
// For now, merely tries to distinguish ISO-8859-1, UTF-8 and Shift_JIS,
// which should be by far the most common encodings. ISO-8859-1
// should not have bytes in the 0x80 - 0x9F range, while Shift_JIS
// uses this as a first byte of a two-byte character. If we see this
// followed by a valid second byte in Shift_JIS, assume it is Shift_JIS.
// If we see something else in that second byte, we'll make the risky guess
// that it's UTF-8.
// which should be by far the most common encodings.
int length = bytes.length;
boolean canBeISO88591 = true;
boolean canBeShiftJIS = true;
boolean canBeUTF8 = true;
int utf8BytesLeft = 0;
int maybeDoubleByteCount = 0;
int maybeSingleByteKatakanaCount = 0;
boolean sawLatin1Supplement = false;
boolean sawUTF8Start = false;
boolean lastWasPossibleDoubleByteStart = false;
//int utf8LowChars = 0;
int utf2BytesChars = 0;
int utf3BytesChars = 0;
int utf4BytesChars = 0;
int sjisBytesLeft = 0;
//int sjisLowChars = 0;
int sjisKatakanaChars = 0;
//int sjisDoubleBytesChars = 0;
int sjisCurKatakanaWordLength = 0;
int sjisCurDoubleBytesWordLength = 0;
int sjisMaxKatakanaWordLength = 0;
int sjisMaxDoubleBytesWordLength = 0;
//int isoLowChars = 0;
//int isoHighChars = 0;
int isoHighOther = 0;
boolean utf8bom = bytes.length > 3 &&
bytes[0] == (byte) 0xEF &&
bytes[1] == (byte) 0xBB &&
bytes[2] == (byte) 0xBF;
for (int i = 0;
i < length && (canBeISO88591 || canBeShiftJIS || canBeUTF8);
@ -86,105 +90,122 @@ public final class StringUtils {
int value = bytes[i] & 0xFF;
// UTF-8 stuff
if (value >= 0x80 && value <= 0xBF) {
if (canBeUTF8) {
if (utf8BytesLeft > 0) {
utf8BytesLeft--;
}
} else {
if (utf8BytesLeft > 0) {
canBeUTF8 = false;
}
if (value >= 0xC0 && value <= 0xFD) {
sawUTF8Start = true;
int valueCopy = value;
while ((valueCopy & 0x40) != 0) {
utf8BytesLeft++;
valueCopy <<= 1;
if ((value & 0x80) == 0) {
canBeUTF8 = false;
} else {
utf8BytesLeft--;
}
}
} else if ((value & 0x80) != 0) {
if ((value & 0x40) == 0) {
canBeUTF8 = false;
} else {
utf8BytesLeft++;
if ((value & 0x20) == 0) {
utf2BytesChars++;
} else {
utf8BytesLeft++;
if ((value & 0x10) == 0) {
utf3BytesChars++;
} else {
utf8BytesLeft++;
if ((value & 0x08) == 0) {
utf4BytesChars++;
} else {
canBeUTF8 = false;
}
}
}
}
} //else {
//utf8LowChars++;
//}
}
// ISO-8859-1 stuff
if ((value == 0xC2 || value == 0xC3) && i < length - 1) {
// This is really a poor hack. The slightly more exotic characters people might want to put in
// a QR Code, by which I mean the Latin-1 supplement characters (e.g. u-umlaut) have encodings
// that start with 0xC2 followed by [0xA0,0xBF], or start with 0xC3 followed by [0x80,0xBF].
int nextValue = bytes[i + 1] & 0xFF;
if (nextValue <= 0xBF &&
((value == 0xC2 && nextValue >= 0xA0) || (value == 0xC3 && nextValue >= 0x80))) {
sawLatin1Supplement = true;
}
}
if (value >= 0x7F && value <= 0x9F) {
canBeISO88591 = false;
if (canBeISO88591) {
if (value > 0x7F && value < 0xA0) {
canBeISO88591 = false;
} else if (value > 0x9F) {
if (value < 0xC0 || value == 0xD7 || value == 0xF7) {
isoHighOther++;
} //else {
//isoHighChars++;
//}
} //else {
//isoLowChars++;
//}
}
// Shift_JIS stuff
if (value >= 0xA1 && value <= 0xDF) {
// count the number of characters that might be a Shift_JIS single-byte Katakana character
if (!lastWasPossibleDoubleByteStart) {
maybeSingleByteKatakanaCount++;
}
}
if (!lastWasPossibleDoubleByteStart &&
((value >= 0xF0 && value <= 0xFF) || value == 0x80 || value == 0xA0)) {
canBeShiftJIS = false;
}
if ((value >= 0x81 && value <= 0x9F) || (value >= 0xE0 && value <= 0xEF)) {
// These start double-byte characters in Shift_JIS. Let's see if it's followed by a valid
// second byte.
if (lastWasPossibleDoubleByteStart) {
// If we just checked this and the last byte for being a valid double-byte
// char, don't check starting on this byte. If this and the last byte
// formed a valid pair, then this shouldn't be checked to see if it starts
// a double byte pair of course.
lastWasPossibleDoubleByteStart = false;
} else {
// ... otherwise do check to see if this plus the next byte form a valid
// double byte pair encoding a character.
lastWasPossibleDoubleByteStart = true;
if (i >= bytes.length - 1) {
if (canBeShiftJIS) {
if (sjisBytesLeft > 0) {
if (value < 0x40 || value == 0x7F || value > 0xFC) {
canBeShiftJIS = false;
} else {
int nextValue = bytes[i + 1] & 0xFF;
if (nextValue < 0x40 || nextValue > 0xFC) {
canBeShiftJIS = false;
} else {
maybeDoubleByteCount++;
}
// There is some conflicting information out there about which bytes can follow which in
// double-byte Shift_JIS characters. The rule above seems to be the one that matches practice.
sjisBytesLeft--;
}
} else if (value == 0x80 || value == 0xA0 || value > 0xEF) {
canBeShiftJIS = false;
} else if (value > 0xA0 && value < 0xE0) {
sjisKatakanaChars++;
sjisCurDoubleBytesWordLength = 0;
sjisCurKatakanaWordLength++;
if (sjisCurKatakanaWordLength > sjisMaxKatakanaWordLength) {
sjisMaxKatakanaWordLength = sjisCurKatakanaWordLength;
}
} else if (value > 0x7F) {
sjisBytesLeft++;
//sjisDoubleBytesChars++;
sjisCurKatakanaWordLength = 0;
sjisCurDoubleBytesWordLength++;
if (sjisCurDoubleBytesWordLength > sjisMaxDoubleBytesWordLength) {
sjisMaxDoubleBytesWordLength = sjisCurDoubleBytesWordLength;
}
} else {
//sjisLowChars++;
sjisCurKatakanaWordLength = 0;
sjisCurDoubleBytesWordLength = 0;
}
} else {
lastWasPossibleDoubleByteStart = false;
}
}
if (utf8BytesLeft > 0) {
if (canBeUTF8 && utf8BytesLeft > 0) {
canBeUTF8 = false;
}
// Easy -- if assuming Shift_JIS and no evidence it can't be, done
if (canBeShiftJIS && ASSUME_SHIFT_JIS) {
return SHIFT_JIS;
if (canBeShiftJIS && sjisBytesLeft > 0) {
canBeShiftJIS = false;
}
if (canBeUTF8 && sawUTF8Start) {
// Easy -- if there is BOM or at least 1 valid not-single byte character (and no evidence it can't be UTF-8), done
if (canBeUTF8 && (utf8bom || utf2BytesChars + utf3BytesChars + utf4BytesChars > 0)) {
return UTF8;
}
// Distinguishing Shift_JIS and ISO-8859-1 can be a little tough. The crude heuristic is:
// - If we saw
// - at least 3 bytes that starts a double-byte value (bytes that are rare in ISO-8859-1), or
// - over 5% of bytes could be single-byte Katakana (also rare in ISO-8859-1),
// - and, saw no sequences that are invalid in Shift_JIS, then we conclude Shift_JIS
if (canBeShiftJIS && (maybeDoubleByteCount >= 3 || 20 * maybeSingleByteKatakanaCount > length)) {
// Easy -- if assuming Shift_JIS or at least 3 valid consecutive not-ascii characters (and no evidence it can't be), done
if (canBeShiftJIS && (ASSUME_SHIFT_JIS || sjisMaxKatakanaWordLength >= 3 || sjisMaxDoubleBytesWordLength >= 3)) {
return SHIFT_JIS;
}
// Otherwise, we default to ISO-8859-1 unless we know it can't be
if (!sawLatin1Supplement && canBeISO88591) {
// Distinguishing Shift_JIS and ISO-8859-1 can be a little tough for short words. The crude heuristic is:
// - If we saw
// - only two consecutive katakana chars in the whole text, or
// - at least 10% of bytes that could be "upper" not-alphanumeric Latin1,
// - then we conclude Shift_JIS, else ISO-8859-1
if (canBeISO88591 && canBeShiftJIS) {
return (sjisMaxKatakanaWordLength == 2 && sjisKatakanaChars == 2) || isoHighOther * 10 >= length
? SHIFT_JIS : ISO88591;
}
// Otherwise, try in order ISO-8859-1, Shift JIS, UTF-8 and fall back to default platform encoding
if (canBeISO88591) {
return ISO88591;
}
if (canBeShiftJIS) {
return SHIFT_JIS;
}
if (canBeUTF8) {
return UTF8;
}
// Otherwise, we take a wild guess with platform encoding
return PLATFORM_DEFAULT_ENCODING;
}

72
core/test/src/com/google/zxing/common/StringUtilsTestCase.java Normal file
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@ -0,0 +1,72 @@
/*
* Copyright 2012 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.zxing.common;
import org.junit.Assert;
import org.junit.Test;
import java.nio.charset.Charset;
public final class StringUtilsTestCase extends Assert {
@Test
public void testShortShiftJIS_1() {
// 金魚
doTest(new byte[] { (byte) 0x8b, (byte) 0xe0, (byte) 0x8b, (byte) 0x9b, }, "SJIS");
}
@Test
public void testShortISO88591_1() {
// båd
doTest(new byte[] { (byte) 0x62, (byte) 0xe5, (byte) 0x64, }, "ISO-8859-1");
}
@Test
public void testMixedShiftJIS_1() {
// Hello Èáë!
doTest(new byte[] { (byte) 0x48, (byte) 0x65, (byte) 0x6c, (byte) 0x6c, (byte) 0x6f,
(byte) 0x20, (byte) 0x8b, (byte) 0xe0, (byte) 0x21, },
"SJIS");
}
private static void doTest(byte[] bytes, String charsetName) {
Charset charset = Charset.forName(charsetName);
String guessedName = StringUtils.guessEncoding(bytes, null);
Charset guessedEncoding = Charset.forName(guessedName);
assertEquals(charset, guessedEncoding);
}
/**
* Utility for printing out a string in given encoding as a Java statement, since it's better
* to write that into the Java source file rather than risk character encoding issues in the
* source file itself
*/
public static void main(String[] args) {
String text = args[0];
Charset charset = Charset.forName(args[1]);
StringBuilder declaration = new StringBuilder();
declaration.append("new byte[] { ");
for (byte b : text.getBytes(charset)) {
declaration.append("(byte) 0x");
declaration.append(Integer.toHexString(b & 0xFF));
declaration.append(", ");
}
declaration.append('}');
System.out.println(declaration);
}
}