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Core barcode encoding/decoding library
/*
* Copyright 2007 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.qrcode.decoder;
import com.google.zxing.FormatException;
import com.google.zxing.common.BitSource;
import com.google.zxing.common.CharacterSetECI;
import com.google.zxing.common.DecoderResult;
import com.google.zxing.common.StringUtils;
import java.io.UnsupportedEncodingException;
import java.util.Hashtable;
import java.util.Vector;
/**
* QR Codes can encode text as bits in one of several modes, and can use multiple modes
* in one QR Code. This class decodes the bits back into text.
*
* See ISO 18004:2006, 6.4.3 - 6.4.7
*
* @author Sean Owen
*/
final class DecodedBitStreamParser {
/**
* See ISO 18004:2006, 6.4.4 Table 5
*/
private static final char[] ALPHANUMERIC_CHARS = {
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B',
'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
' ', '$', '%', '*', '+', '-', '.', '/', ':'
};
private static final int GB2312_SUBSET = 1;
private DecodedBitStreamParser() {
}
static DecoderResult decode(byte[] bytes, Version version, ErrorCorrectionLevel ecLevel, Hashtable hints)
throws FormatException {
BitSource bits = new BitSource(bytes);
StringBuffer result = new StringBuffer(50);
CharacterSetECI currentCharacterSetECI = null;
boolean fc1InEffect = false;
Vector byteSegments = new Vector(1);
Mode mode;
do {
// While still another segment to read...
if (bits.available() < 4) {
// OK, assume we're done. Really, a TERMINATOR mode should have been recorded here
mode = Mode.TERMINATOR;
} else {
try {
mode = Mode.forBits(bits.readBits(4)); // mode is encoded by 4 bits
} catch (IllegalArgumentException iae) {
throw FormatException.getFormatInstance();
}
}
if (!mode.equals(Mode.TERMINATOR)) {
if (mode.equals(Mode.FNC1_FIRST_POSITION) || mode.equals(Mode.FNC1_SECOND_POSITION)) {
// We do little with FNC1 except alter the parsed result a bit according to the spec
fc1InEffect = true;
} else if (mode.equals(Mode.STRUCTURED_APPEND)) {
// not really supported; all we do is ignore it
// Read next 8 bits (symbol sequence #) and 8 bits (parity data), then continue
bits.readBits(16);
} else if (mode.equals(Mode.ECI)) {
// Count doesn't apply to ECI
int value = parseECIValue(bits);
currentCharacterSetECI = CharacterSetECI.getCharacterSetECIByValue(value);
if (currentCharacterSetECI == null) {
throw FormatException.getFormatInstance();
}
} else {
// First handle Hanzi mode which does not start with character count
if (mode.equals(Mode.HANZI)) {
//chinese mode contains a sub set indicator right after mode indicator
int subset = bits.readBits(4);
int countHanzi = bits.readBits(mode.getCharacterCountBits(version));
if (subset == GB2312_SUBSET) {
decodeHanziSegment(bits, result, countHanzi);
}
} else {
// "Normal" QR code modes:
// How many characters will follow, encoded in this mode?
int count = bits.readBits(mode.getCharacterCountBits(version));
if (mode.equals(Mode.NUMERIC)) {
decodeNumericSegment(bits, result, count);
} else if (mode.equals(Mode.ALPHANUMERIC)) {
decodeAlphanumericSegment(bits, result, count, fc1InEffect);
} else if (mode.equals(Mode.BYTE)) {
decodeByteSegment(bits, result, count, currentCharacterSetECI, byteSegments, hints);
} else if (mode.equals(Mode.KANJI)) {
decodeKanjiSegment(bits, result, count);
} else {
throw FormatException.getFormatInstance();
}
}
}
}
} while (!mode.equals(Mode.TERMINATOR));
return new DecoderResult(bytes,
result.toString(),
byteSegments.isEmpty() ? null : byteSegments,
ecLevel == null ? null : ecLevel.toString());
}
/**
* See specification GBT 18284-2000
*/
private static void decodeHanziSegment(BitSource bits,
StringBuffer result,
int count) throws FormatException {
// Don't crash trying to read more bits than we have available.
if (count * 13 > bits.available()) {
throw FormatException.getFormatInstance();
}
// Each character will require 2 bytes. Read the characters as 2-byte pairs
// and decode as GB2312 afterwards
byte[] buffer = new byte[2 * count];
int offset = 0;
while (count > 0) {
// Each 13 bits encodes a 2-byte character
int twoBytes = bits.readBits(13);
int assembledTwoBytes = ((twoBytes / 0x060) << 8) | (twoBytes % 0x060);
if (assembledTwoBytes < 0x003BF) {
// In the 0xA1A1 to 0xAAFE range
assembledTwoBytes += 0x0A1A1;
} else {
// In the 0xB0A1 to 0xFAFE range
assembledTwoBytes += 0x0A6A1;
}
buffer[offset] = (byte) ((assembledTwoBytes >> 8) & 0xFF);
buffer[offset + 1] = (byte) (assembledTwoBytes & 0xFF);
offset += 2;
count--;
}
try {
result.append(new String(buffer, StringUtils.GB2312));
} catch (UnsupportedEncodingException uee) {
throw FormatException.getFormatInstance();
}
}
private static void decodeKanjiSegment(BitSource bits,
StringBuffer result,
int count) throws FormatException {
// Don't crash trying to read more bits than we have available.
if (count * 13 > bits.available()) {
throw FormatException.getFormatInstance();
}
// Each character will require 2 bytes. Read the characters as 2-byte pairs
// and decode as Shift_JIS afterwards
byte[] buffer = new byte[2 * count];
int offset = 0;
while (count > 0) {
// Each 13 bits encodes a 2-byte character
int twoBytes = bits.readBits(13);
int assembledTwoBytes = ((twoBytes / 0x0C0) << 8) | (twoBytes % 0x0C0);
if (assembledTwoBytes < 0x01F00) {
// In the 0x8140 to 0x9FFC range
assembledTwoBytes += 0x08140;
} else {
// In the 0xE040 to 0xEBBF range
assembledTwoBytes += 0x0C140;
}
buffer[offset] = (byte) (assembledTwoBytes >> 8);
buffer[offset + 1] = (byte) assembledTwoBytes;
offset += 2;
count--;
}
// Shift_JIS may not be supported in some environments:
try {
result.append(new String(buffer, StringUtils.SHIFT_JIS));
} catch (UnsupportedEncodingException uee) {
throw FormatException.getFormatInstance();
}
}
private static void decodeByteSegment(BitSource bits,
StringBuffer result,
int count,
CharacterSetECI currentCharacterSetECI,
Vector byteSegments,
Hashtable hints) throws FormatException {
// Don't crash trying to read more bits than we have available.
if (count << 3 > bits.available()) {
throw FormatException.getFormatInstance();
}
byte[] readBytes = new byte[count];
for (int i = 0; i < count; i++) {
readBytes[i] = (byte) bits.readBits(8);
}
String encoding;
if (currentCharacterSetECI == null) {
// The spec isn't clear on this mode; see
// section 6.4.5: t does not say which encoding to assuming
// upon decoding. I have seen ISO-8859-1 used as well as
// Shift_JIS -- without anything like an ECI designator to
// give a hint.
encoding = StringUtils.guessEncoding(readBytes, hints);
} else {
encoding = currentCharacterSetECI.getEncodingName();
}
try {
result.append(new String(readBytes, encoding));
} catch (UnsupportedEncodingException uce) {
throw FormatException.getFormatInstance();
}
byteSegments.addElement(readBytes);
}
private static char toAlphaNumericChar(int value) throws FormatException {
if (value >= ALPHANUMERIC_CHARS.length) {
throw FormatException.getFormatInstance();
}
return ALPHANUMERIC_CHARS[value];
}
private static void decodeAlphanumericSegment(BitSource bits,
StringBuffer result,
int count,
boolean fc1InEffect) throws FormatException {
// Read two characters at a time
int start = result.length();
while (count > 1) {
int nextTwoCharsBits = bits.readBits(11);
result.append(toAlphaNumericChar(nextTwoCharsBits / 45));
result.append(toAlphaNumericChar(nextTwoCharsBits % 45));
count -= 2;
}
if (count == 1) {
// special case: one character left
result.append(toAlphaNumericChar(bits.readBits(6)));
}
// See section 6.4.8.1, 6.4.8.2
if (fc1InEffect) {
// We need to massage the result a bit if in an FNC1 mode:
for (int i = start; i < result.length(); i++) {
if (result.charAt(i) == '%') {
if (i < result.length() - 1 && result.charAt(i + 1) == '%') {
// %% is rendered as %
result.deleteCharAt(i + 1);
} else {
// In alpha mode, % should be converted to FNC1 separator 0x1D
result.setCharAt(i, (char) 0x1D);
}
}
}
}
}
private static void decodeNumericSegment(BitSource bits,
StringBuffer result,
int count) throws FormatException {
// Read three digits at a time
while (count >= 3) {
// Each 10 bits encodes three digits
int threeDigitsBits = bits.readBits(10);
if (threeDigitsBits >= 1000) {
throw FormatException.getFormatInstance();
}
result.append(toAlphaNumericChar(threeDigitsBits / 100));
result.append(toAlphaNumericChar((threeDigitsBits / 10) % 10));
result.append(toAlphaNumericChar(threeDigitsBits % 10));
count -= 3;
}
if (count == 2) {
// Two digits left over to read, encoded in 7 bits
int twoDigitsBits = bits.readBits(7);
if (twoDigitsBits >= 100) {
throw FormatException.getFormatInstance();
}
result.append(toAlphaNumericChar(twoDigitsBits / 10));
result.append(toAlphaNumericChar(twoDigitsBits % 10));
} else if (count == 1) {
// One digit left over to read
int digitBits = bits.readBits(4);
if (digitBits >= 10) {
throw FormatException.getFormatInstance();
}
result.append(toAlphaNumericChar(digitBits));
}
}
private static int parseECIValue(BitSource bits) {
int firstByte = bits.readBits(8);
if ((firstByte & 0x80) == 0) {
// just one byte
return firstByte & 0x7F;
} else if ((firstByte & 0xC0) == 0x80) {
// two bytes
int secondByte = bits.readBits(8);
return ((firstByte & 0x3F) << 8) | secondByte;
} else if ((firstByte & 0xE0) == 0xC0) {
// three bytes
int secondThirdBytes = bits.readBits(16);
return ((firstByte & 0x1F) << 16) | secondThirdBytes;
}
throw new IllegalArgumentException("Bad ECI bits starting with byte " + firstByte);
}
}
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