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import * as Web3 from 'web3';
import * as _ from 'lodash';
import {Web3Wrapper} from '../web3_wrapper';
import {
BlockParamLiteral,
EventCallback,
EventWatcherCallback,
ZeroExError,
} from '../types';
import {AbiDecoder} from '../utils/abi_decoder';
import {intervalUtils} from '../utils/interval_utils';
import {assert} from '../utils/assert';
const DEFAULT_EVENT_POLLING_INTERVAL = 200;
/*
* The EventWatcher watches for blockchain events at the specified block confirmation
* depth.
*/
export class EventWatcher {
private _web3Wrapper: Web3Wrapper;
private _pollingIntervalMs: number;
private _intervalIdIfExists?: NodeJS.Timer;
private _lastEvents: Web3.LogEntry[] = [];
private _callbackIfExistsAsync?: EventWatcherCallback;
private _numConfirmations: number;
constructor(web3Wrapper: Web3Wrapper, pollingIntervalMs: undefined|number, numConfirmations: number) {
this._web3Wrapper = web3Wrapper;
this._numConfirmations = numConfirmations;
this._pollingIntervalMs = _.isUndefined(pollingIntervalMs) ?
DEFAULT_EVENT_POLLING_INTERVAL :
pollingIntervalMs;
}
public subscribe(callback: EventWatcherCallback): void {
assert.isFunction('callback', callback);
if (!_.isUndefined(this._callbackIfExistsAsync)) {
throw new Error(ZeroExError.SubscriptionAlreadyPresent);
}
this._callbackIfExistsAsync = callback;
this._intervalIdIfExists = intervalUtils.setAsyncExcludingInterval(
this._pollForBlockchainEventsAsync.bind(this), this._pollingIntervalMs,
);
}
public unsubscribe(): void {
delete this._callbackIfExistsAsync;
this._lastEvents = [];
if (!_.isUndefined(this._intervalIdIfExists)) {
intervalUtils.clearAsyncExcludingInterval(this._intervalIdIfExists);
}
}
private async _pollForBlockchainEventsAsync(): Promise<void> {
const pendingEvents = await this._getEventsAsync();
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._lastEvents, pendingEvents, JSON.stringify);
const newEvents = _.differenceBy(pendingEvents, this._lastEvents, JSON.stringify);
let isRemoved = true;
await this._emitDifferencesAsync(removedEvents, isRemoved);
isRemoved = false;
await this._emitDifferencesAsync(newEvents, isRemoved);
this._lastEvents = pendingEvents;
}
private async _getEventsAsync(): Promise<Web3.LogEntry[]> {
let latestBlock: BlockParamLiteral|number;
if (this._numConfirmations === 0) {
latestBlock = BlockParamLiteral.Pending;
} else {
const currentBlock = await this._web3Wrapper.getBlockNumberAsync();
latestBlock = currentBlock - this._numConfirmations;
}
const eventFilter = {
fromBlock: latestBlock,
toBlock: latestBlock,
};
const events = await this._web3Wrapper.getLogsAsync(eventFilter);
return events;
}
private async _emitDifferencesAsync(logs: Web3.LogEntry[], isRemoved: boolean): Promise<void> {
for (const log of logs) {
const logEvent = {
removed: isRemoved,
...log,
};
if (!_.isUndefined(this._callbackIfExistsAsync)) {
await this._callbackIfExistsAsync(logEvent);
}
}
}
}
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