ethers.js/utils/rlp.js

//See: https://github.com/ethereum/wiki/wiki/RLP

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

function arrayifyInteger(value) {
    var result = [];
    while (value) {
        result.unshift(value & 0xff);
        value >>= 8;
    }
    return result;
}

function unarrayifyInteger(data, offset, length) {
    var result = 0;
    for (var i = 0; i < length; i++) {
        result = (result * 256) + data[offset + i];
    }
    return result;
}

function _encode(object) {
    if (Array.isArray(object)) {
        var payload = [];
        object.forEach(function(child) {
            payload = payload.concat(_encode(child));
        });

        if (payload.length <= 55) {
            payload.unshift(0xc0 + payload.length)
            return payload;
        }

        var length = arrayifyInteger(payload.length);
        length.unshift(0xf7 + length.length);

        return length.concat(payload);

    } else {
        object = [].slice.call(convert.arrayify(object));

        if (object.length === 1 && object[0] <= 0x7f) {
            return object;

        } else if (object.length <= 55) {
            object.unshift(0x80 + object.length);
            return object
        }

        var length = arrayifyInteger(object.length);
        length.unshift(0xb7 + length.length);

        return length.concat(object);
    }
}

function encode(object) {
    return convert.hexlify(_encode(object));
}

function _decodeChildren(data, offset, childOffset, length) {
    var result = [];

    while (childOffset < offset + 1 + length) {
        var decoded = _decode(data, childOffset);

        result.push(decoded.result);

        childOffset += decoded.consumed;
        if (childOffset > offset + 1 + length) {
            throw new Error('invalid rlp');
        }
    }

    return {consumed: (1 + length), result: result};
}

// returns { consumed: number, result: Object }
function _decode(data, offset) {
    if (data.length === 0) { throw new Error('invalid rlp data'); }

    // Array with extra length prefix
    if (data[offset] >= 0xf8) {
        var lengthLength = data[offset] - 0xf7;
        if (offset + 1 + lengthLength > data.length) {
            throw new Error('too short');
        }

        var length = unarrayifyInteger(data, offset + 1, lengthLength);
        if (offset + 1 + lengthLength + length > data.length) {
            throw new Error('to short');
        }

        return _decodeChildren(data, offset, offset + 1 + lengthLength, lengthLength + length);

    } else if (data[offset] >= 0xc0) {
        var length = data[offset] - 0xc0;
        if (offset + 1 + length > data.length) {
            throw new Error('invalid rlp data');
        }

        return _decodeChildren(data, offset, offset + 1, length);

    } else if (data[offset] >= 0xb8) {
        var lengthLength = data[offset] - 0xb7;
        if (offset + 1 + lengthLength > data.length) {
            throw new Error('invalid rlp data');
        }

        var length = unarrayifyInteger(data, offset + 1, lengthLength);
        if (offset + 1 + lengthLength + length > data.length) {
            throw new Error('invalid rlp data');
        }

        var result = convert.hexlify(data.slice(offset + 1 + lengthLength, offset + 1 + lengthLength + length));
        return { consumed: (1 + lengthLength + length), result: result }

    } else if (data[offset] >= 0x80) {
        var length = data[offset] - 0x80;
        if (offset + 1 + length > data.offset) {
            throw new Error('invlaid rlp data');
        }

        var result = convert.hexlify(data.slice(offset + 1, offset + 1 + length));
        return { consumed: (1 + length), result: result }
    }
    return { consumed: 1, result: convert.hexlify(data[offset]) };
}

function decode(data) {
    data = convert.arrayify(data);
    var decoded = _decode(data, 0);
    if (decoded.consumed !== data.length) {
        throw new Error('invalid rlp data');
    }
    return decoded.result;
}

module.exports = {
    encode: encode,
    decode: decode,
}