/*
* Copyright (C) 2010 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 java.util.Hashtable;
import com.google.zxing.DecodeHintType;
/**
* Common string-related functions.
*
* @author Sean Owen
*/
public final class StringUtils {
private static final String PLATFORM_DEFAULT_ENCODING =
System.getProperty("file.encoding");
public static final String SHIFT_JIS = "SJIS";
private static final String EUC_JP = "EUC_JP";
private static final String UTF8 = "UTF8";
private static final String ISO88591 = "ISO8859_1";
private static final boolean ASSUME_SHIFT_JIS =
SHIFT_JIS.equalsIgnoreCase(PLATFORM_DEFAULT_ENCODING) ||
EUC_JP.equalsIgnoreCase(PLATFORM_DEFAULT_ENCODING);
private StringUtils() {}
/**
* @param bytes bytes encoding a string, whose encoding should be guessed
* @param hints decode hints if applicable
* @return name of guessed encoding; at the moment will only guess one of:
* {@link #SHIFT_JIS}, {@link #UTF8}, {@link #ISO88591}, or the platform
* default encoding if none of these can possibly be correct
*/
public static String guessEncoding(byte[] bytes, Hashtable hints) {
if (hints != null) {
String characterSet = (String) hints.get(DecodeHintType.CHARACTER_SET);
if (characterSet != null) {
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.
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;
for (int i = 0;
i < length && (canBeISO88591 || canBeShiftJIS || canBeUTF8);
i++) {
int value = bytes[i] & 0xFF;
// UTF-8 stuff
if (value >= 0x80 && value <= 0xBF) {
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;
}
}
}
// 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;
}
// 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) {
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.
}
}
} else {
lastWasPossibleDoubleByteStart = false;
}
}
if (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 (canBeUTF8 && sawUTF8Start) {
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)) {
return SHIFT_JIS;
}
// Otherwise, we default to ISO-8859-1 unless we know it can't be
if (!sawLatin1Supplement && canBeISO88591) {
return ISO88591;
}
// Otherwise, we take a wild guess with platform encoding
return PLATFORM_DEFAULT_ENCODING;
}
}