ethers.js/utils/utf8.js

var convert = require('./convert.js');

// http://stackoverflow.com/questions/18729405/how-to-convert-utf8-string-to-byte-array
function utf8ToBytes(str) {
    var result = [];
    var offset = 0;
    for (var i = 0; i < str.length; i++) {
        var c = str.charCodeAt(i);
        if (c < 128) {
            result[offset++] = c;
        } else if (c < 2048) {
            result[offset++] = (c >> 6) | 192;
            result[offset++] = (c & 63) | 128;
        } else if (((c & 0xFC00) == 0xD800) && (i + 1) < str.length && ((str.charCodeAt(i + 1) & 0xFC00) == 0xDC00)) {
            // Surrogate Pair
            c = 0x10000 + ((c & 0x03FF) << 10) + (str.charCodeAt(++i) & 0x03FF);
            result[offset++] = (c >> 18) | 240;
            result[offset++] = ((c >> 12) & 63) | 128;
            result[offset++] = ((c >> 6) & 63) | 128;
            result[offset++] = (c & 63) | 128;
        } else {
            result[offset++] = (c >> 12) | 224;
            result[offset++] = ((c >> 6) & 63) | 128;
            result[offset++] = (c & 63) | 128;
        }
    }

    return convert.arrayify(result);
};


// http://stackoverflow.com/questions/13356493/decode-utf-8-with-javascript#13691499
function bytesToUtf8(bytes) {
    bytes = convert.arrayify(bytes);

    var result = '';
    var i = 0;

    // Invalid bytes are ignored
    while(i < bytes.length) {
        var c = bytes[i++];
        if (c >> 7 == 0) {
            // 0xxx xxxx
            result += String.fromCharCode(c);
            continue;
        }

        // Invalid starting byte
        if (c >> 6 == 0x02) { continue; }

        // Multibyte; how many bytes left for thus character?
        var extraLength = null;
        if (c >> 5 == 0x06) {
            extraLength = 1;
        } else if (c >> 4 == 0x0e) {
            extraLength = 2;
        } else if (c >> 3 == 0x1e) {
            extraLength = 3;
        } else if (c >> 2 == 0x3e) {
            extraLength = 4;
        } else if (c >> 1 == 0x7e) {
            extraLength = 5;
        } else {
            continue;
        }

        // Do we have enough bytes in our data?
        if (i + extraLength > bytes.length) {

            // If there is an invalid unprocessed byte, try to continue
            for (; i < bytes.length; i++) {
                if (bytes[i] >> 6 != 0x02) { break; }
            }
            if (i != bytes.length) continue;

            // All leftover bytes are valid.
            return result;
        }

        // Remove the UTF-8 prefix from the char (res)
        var res = c & ((1 << (8 - extraLength - 1)) - 1);

        var count;
        for (count = 0; count < extraLength; count++) {
            var nextChar = bytes[i++];

            // Is the char valid multibyte part?
            if (nextChar >> 6 != 0x02) {break;};
            res = (res << 6) | (nextChar & 0x3f);
        }

        if (count != extraLength) {
            i--;
            continue;
        }

        if (res <= 0xffff) {
            result += String.fromCharCode(res);
            continue;
        }

        res -= 0x10000;
        result += String.fromCharCode(((res >> 10) & 0x3ff) + 0xd800, (res & 0x3ff) + 0xdc00);
    }

    return result;
}

module.exports = {
    toUtf8Bytes: utf8ToBytes,
    toUtf8String: bytesToUtf8,
};