Tutorial: Order Matching Bot

Introduction

Order Matching Bots (Matching Bots) are responsible for matching two orders that cross or a taker order against the AMM. Specifically, this includes:

• Market Orders: Market Buy and Market Sell

• Limit Orders: Limit Buy and Limit Sell

Matching Bots receive a small compensation for each order that they successfully fill.

See Keepers & Decentralised Orderbook for a technical explanation of how the decentralised orderbook (DLOB) and matching incentives work.

Matching Bots are similar to Tutorial: Order Trigger Bot in that they:

• also maintain a local copy of the Decentralised Limit Orderbook (DLOB);

• do not require the operator to manage collateral; and

• receive a small reward for performing their duties.

Getting Started

The reference implementation of the Order Matching Bot is available here .

Follow the instructions at Keeper Bots to set the required environment variables and make sure a ClearingHouseUser is initialized.

Start the Matching Bot:

yarn run dev:filler

Technical Explanation

Step 1: Get nodes from the DLOB that are ready to be filled

Market orders that are sent on the Drift Protocol first go through the Just-In-Time (JIT) Auctions. After the auction period, Matching Bots step in to fill orders for a small reward.

The DLOB implementation includes a method for getting orders ready to be filled:

const market = this.clearingHouse.getMarketAccounts()[0]; // get a MarketAccount
 
const oraclePriceData = this.driftClient.getOracleDataForMarket(marketIndex);
const oracleIsValid = isOracleValid(
    market.amm,
    oraclePriceData,
    this.driftClient.getStateAccount().oracleGuardRails,
    this.slotSubscriber.getSlot()
);
 
const vAsk = calculateAskPrice(market, oraclePriceData);
const vBid = calculateBidPrice(market, oraclePriceData);
 
const nodesToFill = this.dlob.findNodesToFill(
    marketIndex,
    vBid,
    vAsk,
    this.slotSubscriber.getSlot(),
    oracleIsValid ? oraclePriceData : undefined
);

Step 2: Filter for fillable nodes

To avoid trying to fill orders that aren’t ready to be filled, filter out orders that are too small to fill

if (
    !nodeToFill.makerNode &&
    (isVariant(nodeToFill.node.order.orderType, "limit") ||
        isVariant(nodeToFill.node.order.orderType, "triggerLimit"))
) {
    const baseAssetAmountMarketCanExecute =
        calculateBaseAssetAmountMarketCanExecute(
            market,
            nodeToFill.node.order,
            oraclePriceData
        );
 
    if (
        baseAssetAmountMarketCanExecute.lt(market.amm.baseAssetAmountStepSize)
    ) {
        // skip order
        continue;
    }
}

Step 3: Call fill_order on DriftClient

const user = this.userMap.get(nodeToFill.node.userAccount.toString());
const txSig = await this.driftClient.fillOrder(
    nodeToFill.node.userAccount,
    user.getUserAccount(),
    nodeToFill.node.order,
    undefined
);