1 files changed, 64 insertions, 0 deletions
diff --git a/src/mempool/mempool_watcher.ts b/src/mempool/mempool_watcher.ts
new file mode 100644
index 000000000..be598c28f
--- /dev/null
+++ b/src/mempool/mempool_watcher.ts
@@ -0,0 +1,64 @@
+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 MempoolWatcher {
+    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, _.isEqual);
+        const newEvents = _.differenceBy(pendingEvents, this._lastMempoolEvents, _.isEqual);
+        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 logWithDecodedArgsEvent = {
+                removed: isRemoved,
+                ...log,
+            };
+            (this._callback as MempoolEventCallback)(logWithDecodedArgsEvent);
+        });
+    }
+}