base45-web/lib/base45-js.js

Encode/decode base45 data - including non-utf8 compliant data

(function () {
    "use strict";

    const baseSize = 45;
    const baseSizeSquared = 2025;
    const chunkSize = 2;
    const encodedChunkSize = 3;
    const smallEncodedChunkSize = 2;
    const byteSize = 256;

    const encoding = ["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", " ", "$", "%", "*",
        "+", "-", ".", "/", ":"];

    var decoding;

    function encode(byteArrayArg) {

        if (byteArrayArg === null || byteArrayArg === undefined)
            throw new Error("byteArrayArg is null or undefined.");

        //TODO check is array-like?

        const wholeChunkCount = Math.trunc(byteArrayArg.length / chunkSize);
        const resultSize = wholeChunkCount * encodedChunkSize + (byteArrayArg.length % chunkSize === 1 ? smallEncodedChunkSize : 0);

        if (resultSize === 0)
            return "";

        const result = new Array(resultSize);
        var resultIndex = 0;
        const wholeChunkLength = wholeChunkCount * chunkSize;
        for (let i = 0; i < wholeChunkLength;) {
            const value = byteArrayArg[i++] * byteSize + byteArrayArg[i++];
            result[resultIndex++] = encoding[value % baseSize];
            result[resultIndex++] = encoding[Math.trunc(value / baseSize) % baseSize];
            result[resultIndex++] = encoding[Math.trunc(value / baseSizeSquared) % baseSize];
        }

        if (byteArrayArg.length % chunkSize === 0)
            return result.join("");

        result[result.length - 2] = encoding[byteArrayArg[byteArrayArg.length - 1] % baseSize];
        result[result.length - 1] = byteArrayArg[byteArrayArg.length - 1] < baseSize ? encoding[0] : encoding[Math.trunc(byteArrayArg[byteArrayArg.length - 1] / baseSize) % baseSize];

        return result.join("");
    };

    function decode(utf8StringArg) {

        if (utf8StringArg === null || utf8StringArg === undefined)
            throw new Error("utf8StringArg is null or undefined.");

        if (utf8StringArg.length === 0)
            return [];

        var remainderSize = utf8StringArg.length % encodedChunkSize;
        if (remainderSize === 1)
            throw new Error("utf8StringArg has incorrect length.");

        if (decoding === undefined) {
            decoding = {};
            for (let i = 0; i < encoding.length; ++i)
                decoding[encoding[i]] = i;
        }

        const buffer = new Array(utf8StringArg.length);
        for (let i = 0; i < utf8StringArg.length; ++i) {
            const found = decoding[utf8StringArg[i]];
            if (found === undefined)
                throw new Error("Invalid character at position ".concat(i).concat("."));
            buffer[i] = found;
        }

        const wholeChunkCount = Math.trunc(buffer.length / encodedChunkSize);
        var result = new Array(wholeChunkCount * chunkSize + (remainderSize === chunkSize ? 1 : 0));
        var resultIndex = 0;
        const wholeChunkLength = wholeChunkCount * encodedChunkSize;
        for (let i = 0; i < wholeChunkLength;) {
            const val = buffer[i++] + baseSize * buffer[i++] + baseSizeSquared * buffer[i++];
            result[resultIndex++] = Math.trunc(val / byteSize); //result is always in the range 0-255 - % ByteSize omitted.
            result[resultIndex++] = val % byteSize;
        }

        if (remainderSize === 0)
            return result;

        result[result.length - 1] = buffer[buffer.length - 2] + baseSize * buffer[buffer.length - 1]; //result is always in the range 0-255 - % ByteSize omitted.
        return result;
    }

    function decodeToUtf8String(utf8StringArg) {

        var data = decode(utf8StringArg);

        var str = "";
        var count = data.length;
        for (let i= 0; i < count; ++i)
            str += String.fromCharCode(data[i]);

        return str;
    }


    module.exports = {
        encode, decode, decodeToUtf8String
    };

})();