4 files changed, 37 insertions, 2 deletions
diff --git a/packages/asset-buyer/src/errors.ts b/packages/asset-buyer/src/errors.ts
new file mode 100644
index 000000000..ec5fe548c
--- /dev/null
+++ b/packages/asset-buyer/src/errors.ts
@@ -0,0 +1,22 @@
+import { BigNumber } from '@0x/utils';
+
+import { AssetBuyerError } from './types';
+
+/**
+ * Error class representing insufficient asset liquidity
+ */
+export class InsufficientAssetLiquidityError extends Error {
+    /**
+     * The amount availabe to fill (in base units) factoring in slippage.
+     */
+    public amountAvailableToFill: BigNumber;
+    /**
+     * @param amountAvailableToFill The amount availabe to fill (in base units) factoring in slippage
+     */
+    constructor(amountAvailableToFill: BigNumber) {
+        super(AssetBuyerError.InsufficientAssetLiquidity);
+        this.amountAvailableToFill = amountAvailableToFill;
+        // Setting prototype so instanceof works.  See https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#extending-built-ins-like-error-array-and-map-may-no-longer-work
+        Object.setPrototypeOf(this, InsufficientAssetLiquidityError.prototype);
+    }
+}
diff --git a/packages/asset-buyer/src/index.ts b/packages/asset-buyer/src/index.ts
index 8418edb42..a42d7e272 100644
--- a/packages/asset-buyer/src/index.ts
+++ b/packages/asset-buyer/src/index.ts
@@ -9,6 +9,7 @@ export { SignedOrder } from '@0x/types';
 export { BigNumber } from '@0x/utils';
 
 export { AssetBuyer } from './asset_buyer';
+export { InsufficientAssetLiquidityError } from './errors';
 export { BasicOrderProvider } from './order_providers/basic_order_provider';
 export { StandardRelayerAPIOrderProvider } from './order_providers/standard_relayer_api_order_provider';
 export {
diff --git a/packages/asset-buyer/src/types.ts b/packages/asset-buyer/src/types.ts
index 3b573edca..d5d6be695 100644
--- a/packages/asset-buyer/src/types.ts
+++ b/packages/asset-buyer/src/types.ts
@@ -102,7 +102,7 @@ export interface AssetBuyerOpts {
 }
 
 /**
- * Possible errors thrown by an AssetBuyer instance or associated static methods.
+ * Possible error messages thrown by an AssetBuyer instance or associated static methods.
  */
 export enum AssetBuyerError {
     NoEtherTokenContractFound = 'NO_ETHER_TOKEN_CONTRACT_FOUND',
diff --git a/packages/asset-buyer/src/utils/buy_quote_calculator.ts b/packages/asset-buyer/src/utils/buy_quote_calculator.ts
index b15b880c2..fcded6ab1 100644
--- a/packages/asset-buyer/src/utils/buy_quote_calculator.ts
+++ b/packages/asset-buyer/src/utils/buy_quote_calculator.ts
@@ -3,6 +3,7 @@ import { BigNumber } from '@0x/utils';
 import * as _ from 'lodash';
 
 import { constants } from '../constants';
+import { InsufficientAssetLiquidityError } from '../errors';
 import { AssetBuyerError, BuyQuote, BuyQuoteInfo, OrdersAndFillableAmounts } from '../types';
 
 import { orderUtils } from './order_utils';
@@ -33,7 +34,18 @@ export const buyQuoteCalculator = {
         });
         // if we do not have enough orders to cover the desired assetBuyAmount, throw
         if (remainingFillAmount.gt(constants.ZERO_AMOUNT)) {
-            throw new Error(AssetBuyerError.InsufficientAssetLiquidity);
+            // We needed the amount they requested to buy, plus the amount for slippage
+            const totalAmountRequested = assetBuyAmount.plus(slippageBufferAmount);
+            const amountAbleToFill = totalAmountRequested.minus(remainingFillAmount);
+            // multiplierNeededWithSlippage represents what we need to multiply the assetBuyAmount by
+            // in order to get the total amount needed considering slippage
+            // i.e. if slippagePercent was 0.2 (20%), multiplierNeededWithSlippage would be 1.2
+            const multiplierNeededWithSlippage = new BigNumber(1).plus(slippagePercentage);
+            // Given amountAvailableToFillConsideringSlippage * multiplierNeededWithSlippage = amountAbleToFill
+            // We divide amountUnableToFill by multiplierNeededWithSlippage to determine amountAvailableToFillConsideringSlippage
+            const amountAvailableToFillConsideringSlippage = amountAbleToFill.div(multiplierNeededWithSlippage).floor();
+
+            throw new InsufficientAssetLiquidityError(amountAvailableToFillConsideringSlippage);
         }
         // if we are not buying ZRX:
         // given the orders calculated above, find the fee-orders that cover the desired assetBuyAmount (with slippage)