webu/lib/utils/bloom.js

IrChain JavaScript API, middleware to talk to a irchain node over RPC

/*jshint bitwise: false*/

/*
    This file is part of webu.js.

    webu.js is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    webu.js is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with webu.js.  If not, see <http://www.gnu.org/licenses/>.
*/

/**
 * @file bloom.js
 * @author Bas van Kervel <bas@ethereum.org>
 * @date 2017
 */

/**
 * irchain bloom filter support.
 *
 * @module bloom
 * @class [bloom] bloom
 */

var utils = require('./utils.js');
var sha3 = require('./sha3.js');

function codePointToInt(codePoint) {
    if (codePoint >= 48 && codePoint <= 57) { /*['0'..'9'] -> [0..9]*/
        return codePoint - 48;
    }

    if (codePoint >= 65 && codePoint <= 70) { /*['A'..'F'] -> [10..15]*/
        return codePoint - 55;
    }

    if (codePoint >= 97 && codePoint <= 102) { /*['a'..'f'] -> [10..15]*/
        return codePoint - 87;
    }

    throw 'invalid bloom';
}

function testBytes(bloom, bytes) {
    var hash = sha3(bytes, {encoding: 'hex'});

    for (var i = 0; i < 12; i += 4) {
        // calculate bit position in bloom fiter that must be active
        var bitpos = ((parseInt(hash.substr(i, 2), 16) << 8) +
            parseInt(hash.substr((i + 2), 2), 16)) & 2047;

        // test if bitpos in bloom is active
        var code = codePointToInt(
            bloom.charCodeAt(bloom.length - 1 - Math.floor(bitpos / 4)));
        var offset = 1 << (bitpos % 4);

        if ((code & offset) !== offset) {
            return false;
        }
    }

    return true;
}

/**
 * Returns true if address is part of the given bloom.
 * note: false positives are possible.
 *
 * @method testAddress
 * @param bloom
 * @param {String} address in hex notation
 * @returns {Boolean} topic is (probably) part of the block
 */
var testAddress = function(bloom, address) {
    if (!utils.isBloom(bloom)) throw 'invalid bloom';
    if (!utils.isAddress(address)) throw 'invalid address';

    return testBytes(bloom, address);
};

/**
 * Returns true if the topic is part of the given bloom.
 * note: false positives are possible.
 *
 * @method hasTopic
 * @returns {Boolean} topic is (probably) part of the block
 * @param bloom
 * @param topic
 */
var testTopic = function(bloom, topic) {
    if (!utils.isBloom(bloom)) throw 'invalid bloom';
    if (!utils.isTopic(topic)) throw 'invalid topic';

    return testBytes(bloom, topic);
};

module.exports = {
    testAddress: testAddress,
    testTopic: testTopic,
};