chardet/encoding/iso2022.js

var util = require('util'),
    Match = require ('../match');


/**
 * This is a superclass for the individual detectors for
 * each of the detectable members of the ISO 2022 family
 * of encodings.
 */

function ISO_2022() {};

ISO_2022.prototype.match = function(det) {

    /**
     * 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.
     */

    var i, j;
    var escN;
    var hits   = 0;
    var misses = 0;
    var shifts = 0;
    var quality;

    // TODO: refactor me
    var text = det.fInputBytes;
    var textLen = det.fInputLen;

    scanInput:
        for (i=0; i<textLen; i++) {
            if (text[i] == 0x1b) {
                checkEscapes:
                    for (escN=0; escN < this.escapeSequences.length; escN++) {
                        var seq = this.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 null;
    }

    //
    // 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;

    return quality == 0 ? null : new Match(det, this, quality);
};

module.exports.ISO_2022_JP = function() {
    this.name = function() {
        return "ISO-2022-JP";
    };
    this.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
    ];
};
util.inherits(module.exports.ISO_2022_JP, ISO_2022);



module.exports.ISO_2022_KR = function() {
    this.name = function() {
        return "ISO-2022-KR";
    };
    this.escapeSequences = [
        [ 0x1b, 0x24, 0x29, 0x43 ]
    ];
};
util.inherits(module.exports.ISO_2022_KR, ISO_2022);



module.exports.ISO_2022_CN = function() {
    this.name = function() {
        return "ISO-2022-CN";
    };
    this.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
    ];
};
util.inherits(module.exports.ISO_2022_CN, ISO_2022);