make the slippage percentage customizable by integrator

packages/asset-buyer/src/asset_buyer.ts

@@ -13,6 +13,7 @@ import {
     AssetBuyerError,
     AssetBuyerOrdersAndFillableAmounts,
     BuyQuote,
+    BuyQuoteRequestOpts,
     OrderFetcher,
     OrderFetcherResponse,
 } from './types';
@@ -160,12 +161,13 @@ export class AssetBuyer {
      */
     public async getBuyQuoteAsync(
         assetBuyAmount: BigNumber,
-        feePercentage: number = constants.DEFAULT_FEE_PERCENTAGE,
+        options: Partial<BuyQuoteRequestOpts>,
-        forceOrderRefresh: boolean = false,
     ): Promise<BuyQuote> {
+        const { feePercentage, forceOrderRefresh, slippagePercentage } = { ...options, ...constants.DEFAULT_BUY_QUOTE_REQUEST_OPTS };
         assert.isBigNumber('assetBuyAmount', assetBuyAmount);
         assert.isNumber('feePercentage', feePercentage);
         assert.isBoolean('forceOrderRefresh', forceOrderRefresh);
+        assert.isNumber('feePercentage', slippagePercentage);
         // we should refresh if:
         // we do not have any orders OR
         // we are forced to OR
@@ -185,13 +187,11 @@ export class AssetBuyer {
             ordersAndFillableAmounts = this
                 ._currentOrdersAndFillableAmountsIfExists as AssetBuyerOrdersAndFillableAmounts;
         }
-        // TODO: optimization
-        // make the slippage percentage customizable by integrator
         const buyQuote = buyQuoteCalculator.calculate(
             ordersAndFillableAmounts,
             assetBuyAmount,
             feePercentage,
-            constants.DEFAULT_SLIPPAGE_PERCENTAGE,
+            slippagePercentage,
         );
         return buyQuote;
     }

packages/asset-buyer/src/constants.ts

@@ -1,11 +1,18 @@
 import { BigNumber } from '@0xproject/utils';
 
+import { BuyQuoteRequestOpts } from './types';
+
+const DEFAULT_BUY_QUOTE_REQUEST_OPTS: BuyQuoteRequestOpts = {
+    feePercentage: 0,
+    forceOrderRefresh: false,
+    slippagePercentage: 0.2, // 20% slippage protection
+};
+
 export const constants = {
     ZERO_AMOUNT: new BigNumber(0),
     NULL_ADDRESS: '0x0000000000000000000000000000000000000000',
     MAINNET_NETWORK_ID: 1,
-    DEFAULT_SLIPPAGE_PERCENTAGE: 0.2, // 20% slippage protection
     DEFAULT_ORDER_REFRESH_INTERVAL_MS: 10000, // 10 seconds
-    DEFAULT_FEE_PERCENTAGE: 0,
     ETHER_TOKEN_DECIMALS: 18,
+    DEFAULT_BUY_QUOTE_REQUEST_OPTS,
 };

packages/asset-buyer/src/types.ts

@@ -52,6 +52,12 @@ export interface BuyQuote {
     feePercentage?: number;
 }
 
+export interface BuyQuoteRequestOpts {
+    feePercentage: number;
+    forceOrderRefresh: boolean;
+    slippagePercentage: number;
+}
+
 /**
  * Possible errors thrown by an AssetBuyer instance or associated static methods.
  */