SushiSwap Settlement

This repository contains solidity contracts to enable limit orders for SushiSwap.

Overview

Typically AMMs only settle orders with market price, which represents a significant limitation compared to orderbook driven exchanges. SushiSwap addresses this critical AMM pain point with the release of the limit order feature.

Contracts in this repo help you submit a limit order with a lower price than what it is now. Later, when the price gets lower enough to meet the requirement of your order, it gets settled.

Contracts

Limit orders on SushiSwap work in a completely decentralized manner, without the need of any centralized authority. The system consists of two contracts: OrderBook and Settlement.

OrderBook

OrderBook is deployed at 0x460c3749ea885617afb9a375ca36d1487781efb3 on kovan and rinkeby testnets.

OrderBook keeps limit orders that users have submitted. Anyone can call createOrder() to create a limit order with the amount to sell and the minimum price. He/she needs to approve the amount to sell for the Settlement contract.

To reduce users' gas fee, OrderBook isn't deployed on the mainnet. The one on kovan testnet is used for production.

Settlement

Settlement is deployed at 0x44c9c1b05139bbc49045852d6e671c5a9f37078a on the Ethereum mainnet, kovan and rinkeby testnets.

Settlement is in charge of swapping tokens for orders. Anyone can call fillOrder() to fill the order submitted. We'll call this caller a 'relayer'. Relayers need to call it with proper parameters to meet the minimum price requirement set in the order. If the call is successful, fee will be transferred to the relayer.

The maker of an order can cancel it with cancelOrder() on Settlement.

It is possible to fill only a certain amount of tokens, not all. In most cases, submitted orders will reside on the OrderBook and their amount will be filled by different callers in different blocks.

Incentives

Relayer

Settlement is a wrapper contract around UniswapV2Router02. Every function in this contract has a duplicated version in the Settlement with an extra parameter args. If args is not empty, it is used for filling orders; see Settlement.fillOrders() for details.

So, users for SushiSwap can choose to be a relayer or not. If he/she decided to do so, calling any swap functions in Settlement will benefit them. Otherwise, he/she can just call functions in UniswapV2Router02 without receiving any fee.

Fee

For every fillOrder() call, 0.2% fee of the amount sold is charged. Out of the fee, 20% goes to xSUSHI holders and the remainder to the relayer. The fee is deducted prior to the swap.

Let's assume Alice created an order to sell 1 ETH with the minimum price of 500 DAI. Current price of ETH is 400 DAI so this order cannot be filled right away. Leter, when the market price goes up to 500 DAI, Bob is trying to fill the entire amount of this order as a relayer.

If the call is successful, amounts of tokens transferred are:

• Limit Order Fee: 1 ETH x 0.2% x 80% = 0.0016 ETH (goes to Bob; relayer)
• Limit Order Fee Split: 1 ETH x 0.2% x 20% = 0.0004 ETH (goes to xSUSHI)
• Swap Fee: (1 ETH - 0.002 ETH) x 0.3% = 0.002994 ETH (goes to the liquidity provider)
• ETH Amount Sold: 1 ETH - 0.002 ETH - 0.002994 ETH = 0.995006 ETH (goes to the liquidity pool)
• DAI Amount Bought: 0.995006 ETH x 500 DAI = 497.503 DAI (goes to Alice; maker)

License

MIT