path: root/src/mempool/event_watcher.ts

import * as Web3 from 'web3';
import * as _ from 'lodash';
import {Web3Wrapper} from '../web3_wrapper';
import {BlockParamLiteral, EventCallback, MempoolEventCallback} from '../types';
import {AbiDecoder} from '../utils/abi_decoder';
import {intervalUtils} from '../utils/interval_utils';

const DEFAULT_MEMPOOL_POLLING_INTERVAL = 200;

export class EventWatcher {
    private _web3Wrapper: Web3Wrapper;
    private _pollingIntervalMs: number;
    private _intervalId: NodeJS.Timer;
    private _lastMempoolEvents: Web3.LogEntry[] = [];
    private _callback?: MempoolEventCallback;
    constructor(web3Wrapper: Web3Wrapper, pollingIntervalMs: undefined|number) {
        this._web3Wrapper = web3Wrapper;
        this._pollingIntervalMs = _.isUndefined(pollingIntervalMs) ?
                                  DEFAULT_MEMPOOL_POLLING_INTERVAL :
                                  pollingIntervalMs;
    }
    public subscribe(callback: MempoolEventCallback): void {
        this._callback = callback;
        this._intervalId = intervalUtils.setAsyncExcludingInterval(
            this._pollForMempoolEventsAsync.bind(this), this._pollingIntervalMs);
    }
    public unsubscribe(): void {
        delete this._callback;
        intervalUtils.clearAsyncExcludingInterval(this._intervalId);
    }
    private async _pollForMempoolEventsAsync(): Promise<void> {
        const pendingEvents = await this._getMempoolEventsAsync();
        if (pendingEvents.length === 0) {
            // HACK: Sometimes when node rebuilds the pending block we get back the empty result.
            // We don't want to emit a lot of removal events and bring them back after a couple of miliseconds,
            // that's why we just ignore those cases.
            return;
        }
        const removedEvents = _.differenceBy(this._lastMempoolEvents, pendingEvents, JSON.stringify);
        const newEvents = _.differenceBy(pendingEvents, this._lastMempoolEvents, JSON.stringify);
        let isRemoved = true;
        this._emitDifferences(removedEvents, isRemoved);
        isRemoved = false;
        this._emitDifferences(newEvents, isRemoved);
        this._lastMempoolEvents = pendingEvents;
    }
    private async _getMempoolEventsAsync(): Promise<Web3.LogEntry[]> {
        const mempoolFilter = {
            fromBlock: BlockParamLiteral.Pending,
            toBlock: BlockParamLiteral.Pending,
        };
        const pendingEvents = await this._web3Wrapper.getLogsAsync(mempoolFilter);
        return pendingEvents;
    }
    private _emitDifferences(logs: Web3.LogEntry[], isRemoved: boolean): void {
        _.forEach(logs, log => {
            const logEvent = {
                removed: isRemoved,
                ...log,
            };
            if (!_.isUndefined(this._callback)) {
                this._callback(logEvent);
            }
        });
    }
}