CharsetRecog_2022.java

// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html#License
/*
*******************************************************************************
* Copyright (C) 2005 - 2012, International Business Machines Corporation and  *
* others. All Rights Reserved.                                                *
*******************************************************************************
*/
package org.apache.tika.parser.txt;

/**
 * class CharsetRecog_2022  part of the ICU charset detection imlementation.
 * This is a superclass for the individual detectors for
 * each of the detectable members of the ISO 2022 family
 * of encodings.
 * <p>
 * The separate classes are nested within this class.
 */
abstract class CharsetRecog_2022 extends CharsetRecognizer {


    /**
     * Matching function shared among the 2022 detectors JP, CN and KR
     * Counts up the number of legal an unrecognized escape sequences in
     * the sample of text, and computes a score based on the total number &
     * the proportion that fit the encoding.
     *
     * @param text            the byte buffer containing text to analyse
     * @param textLen         the size of the text in the byte.
     * @param escapeSequences the byte escape sequences to test for.
     * @return match quality, in the range of 0-100.
     */
    int match(byte[] text, int textLen, byte[][] escapeSequences) {
        int i, j;
        int escN;
        int hits = 0;
        int misses = 0;
        int shifts = 0;
        int quality;
        scanInput:
        for (i = 0; i < textLen; i++) {
            if (text[i] == 0x1b) {
                checkEscapes:
                for (escN = 0; escN < escapeSequences.length; escN++) {
                    byte[] seq = escapeSequences[escN];

                    if ((textLen - i) < seq.length) {
                        continue checkEscapes;
                    }

                    for (j = 1; j < seq.length; j++) {
                        if (seq[j] != text[i + j]) {
                            continue checkEscapes;
                        }
                    }

                    hits++;
                    i += seq.length - 1;
                    continue scanInput;
                }

                misses++;
            }

            if (text[i] == 0x0e || text[i] == 0x0f) {
                // Shift in/out
                shifts++;
            }
        }

        if (hits == 0) {
            return 0;
        }

        //
        // Initial quality is based on relative proportion of recongized vs.
        //   unrecognized escape sequences.
        //   All good:  quality = 100;
        //   half or less good: quality = 0;
        //   linear inbetween.
        quality = (100 * hits - 100 * misses) / (hits + misses);

        // Back off quality if there were too few escape sequences seen.
        //   Include shifts in this computation, so that KR does not get penalized
        //   for having only a single Escape sequence, but many shifts.
        if (hits + shifts < 5) {
            quality -= (5 - (hits + shifts)) * 10;
        }

        if (quality < 0) {
            quality = 0;
        }
        return quality;
    }


    static class CharsetRecog_2022JP extends CharsetRecog_2022 {
        private byte[][] escapeSequences = {
                {0x1b, 0x24, 0x28, 0x43},   // KS X 1001:1992
                {0x1b, 0x24, 0x28, 0x44},   // JIS X 212-1990
                {0x1b, 0x24, 0x40},         // JIS C 6226-1978
                {0x1b, 0x24, 0x41},         // GB 2312-80
                {0x1b, 0x24, 0x42},         // JIS X 208-1983
                {0x1b, 0x26, 0x40},         // JIS X 208 1990, 1997
                {0x1b, 0x28, 0x42},         // ASCII
                {0x1b, 0x28, 0x48},         // JIS-Roman
                {0x1b, 0x28, 0x49},         // Half-width katakana
                {0x1b, 0x28, 0x4a},         // JIS-Roman
                {0x1b, 0x2e, 0x41},         // ISO 8859-1
                {0x1b, 0x2e, 0x46}          // ISO 8859-7
        };

        String getName() {
            return "ISO-2022-JP";
        }

        CharsetMatch match(CharsetDetector det) {
            int confidence = match(det.fInputBytes, det.fInputLen, escapeSequences);
            return confidence == 0 ? null : new CharsetMatch(det, this, confidence);
        }
    }

    static class CharsetRecog_2022KR extends CharsetRecog_2022 {
        private byte[][] escapeSequences = {
                {0x1b, 0x24, 0x29, 0x43}
        };

        String getName() {
            return "ISO-2022-KR";
        }

        CharsetMatch match(CharsetDetector det) {
            int confidence = match(det.fInputBytes, det.fInputLen, escapeSequences);
            return confidence == 0 ? null : new CharsetMatch(det, this, confidence);
        }
    }

    static class CharsetRecog_2022CN extends CharsetRecog_2022 {
        private byte[][] escapeSequences = {
                {0x1b, 0x24, 0x29, 0x41},   // GB 2312-80
                {0x1b, 0x24, 0x29, 0x47},   // CNS 11643-1992 Plane 1
                {0x1b, 0x24, 0x2A, 0x48},   // CNS 11643-1992 Plane 2
                {0x1b, 0x24, 0x29, 0x45},   // ISO-IR-165
                {0x1b, 0x24, 0x2B, 0x49},   // CNS 11643-1992 Plane 3
                {0x1b, 0x24, 0x2B, 0x4A},   // CNS 11643-1992 Plane 4
                {0x1b, 0x24, 0x2B, 0x4B},   // CNS 11643-1992 Plane 5
                {0x1b, 0x24, 0x2B, 0x4C},   // CNS 11643-1992 Plane 6
                {0x1b, 0x24, 0x2B, 0x4D},   // CNS 11643-1992 Plane 7
                {0x1b, 0x4e},               // SS2
                {0x1b, 0x4f},               // SS3
        };

        String getName() {
            return "ISO-2022-CN";
        }

        CharsetMatch match(CharsetDetector det) {
            int confidence = match(det.fInputBytes, det.fInputLen, escapeSequences);
            return confidence == 0 ? null : new CharsetMatch(det, this, confidence);
        }
    }

}