Add initial mempool watching implememtation

4 files changed, 89 insertions, 11 deletions

diff --git a/src/0x.ts b/src/0x.ts
index bc753434c..10db7e158 100644
--- a/src/0x.ts
+++ b/src/0x.ts
@@ -11,6 +11,7 @@ import {assert} from './utils/assert';
 import {AbiDecoder} from './utils/abi_decoder';
 import {intervalUtils} from './utils/interval_utils';
 import {artifacts} from './artifacts';
+import {MempoolWatcher} from './mempool/mempool_watcher';
 import {ExchangeWrapper} from './contract_wrappers/exchange_wrapper';
 import {TokenRegistryWrapper} from './contract_wrappers/token_registry_wrapper';
 import {EtherTokenWrapper} from './contract_wrappers/ether_token_wrapper';
@@ -65,6 +66,10 @@ export class ZeroEx {
      * tokenTransferProxy smart contract.
      */
     public proxy: TokenTransferProxyWrapper;
+    /**
+     * An instance of the MempoolWatcher class containing methods for watching pending events.
+     */
+    public mempool: MempoolWatcher;
     private _web3Wrapper: Web3Wrapper;
     private _abiDecoder: AbiDecoder;
     /**
@@ -191,6 +196,11 @@ export class ZeroEx {
             gasPrice,
         };
         this._web3Wrapper = new Web3Wrapper(provider, defaults);
+        const mempoolPollingIntervalMs = _.isUndefined(config) ? undefined : config.mempoolPollingIntervalMs;
+        this.mempool = new MempoolWatcher(
+            this._web3Wrapper,
+            mempoolPollingIntervalMs,
+        );
         this.token = new TokenWrapper(
             this._web3Wrapper,
             this._abiDecoder,
diff --git a/src/index.ts b/src/index.ts
index 249c20519..7a9b8aa63 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -35,4 +35,6 @@ export {
     OrderTransactionOpts,
     FilterObject,
     LogEvent,
+    DecodedLogEvent,
+    MempoolEventCallback,
 } from './types';
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);
+        });
+    }
+}
diff --git a/src/types.ts b/src/types.ts
index 9ac726ef8..1b32ccdf9 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -37,12 +37,17 @@ export type OrderAddresses = [string, string, string, string, string];
 export type OrderValues = [BigNumber, BigNumber, BigNumber,
                            BigNumber, BigNumber, BigNumber];
 
-export interface LogEvent<ArgsType> extends LogWithDecodedArgs<ArgsType> {
-    removed: boolean;
-}
-export type EventCallbackAsync<ArgsType> = (log: LogEvent<ArgsType>) => Promise<void>;
-export type EventCallbackSync<ArgsType> = (log: LogEvent<ArgsType>) => void;
+export type LogEvent = Web3.LogEntryEvent;
+export type DecodedLogEvent<ArgsType> = Web3.DecodedLogEntryEvent<ArgsType>;
+
+export type EventCallbackAsync<ArgsType> = (log: DecodedLogEvent<ArgsType>) => Promise<void>;
+export type EventCallbackSync<ArgsType> = (log: DecodedLogEvent<ArgsType>) => void;
 export type EventCallback<ArgsType> = EventCallbackSync<ArgsType>|EventCallbackAsync<ArgsType>;
+
+export type MempoolEventCallbackSync = (log: LogEvent) => void;
+export type MempoolEventCallbackAsync = (log: LogEvent) => Promise<void>;
+export type MempoolEventCallback = MempoolEventCallbackSync|MempoolEventCallbackAsync;
+
 export interface ExchangeContract extends Web3.ContractInstance {
     isValidSignature: {
         callAsync: (signerAddressHex: string, dataHex: string, v: number, r: string, s: string,
@@ -394,12 +399,14 @@ export interface JSONRPCPayload {
  * exchangeContractAddress: The address of an exchange contract to use
  * tokenRegistryContractAddress: The address of a token registry contract to use
  * etherTokenContractAddress: The address of an ether token contract to use
+ * mempoolPollingIntervalMs: How often to check for new mempool events
  */
 export interface ZeroExConfig {
     gasPrice?: BigNumber; // Gas price to use with every transaction
     exchangeContractAddress?: string;
     tokenRegistryContractAddress?: string;
     etherTokenContractAddress?: string;
+    mempoolPollingIntervalMs?: number;
 }
 
 export type TransactionReceipt = Web3.TransactionReceipt;
@@ -415,12 +422,7 @@ export interface DecodedLogArgs {
     [argName: string]: ContractEventArg;
 }
 
-export interface DecodedArgs<ArgsType> {
-    args: ArgsType;
-    event: string;
-}
-
-export interface LogWithDecodedArgs<ArgsType> extends Web3.LogEntry, DecodedArgs<ArgsType> {}
+export interface LogWithDecodedArgs<ArgsType> extends Web3.DecodedLogEntry<ArgsType> {}
 
 export interface TransactionReceiptWithDecodedLogs extends Web3.TransactionReceipt {
     logs: Array<LogWithDecodedArgs<DecodedLogArgs>|Web3.LogEntry>;