This repo uses forge from Foundry.
There are a few tests written for this code, most of which are normal unit
tests, but also one that tests the rugpull.
If you do not want spoilers, do not open the test file.
The full spoiler is in SPOILER.md.
To run all tests run
$ forge test
The code here represents a Match Making (MM) contract that is NOT ready for production.
The basic idea is to allow users to buy and sell from a pair of tokens T1 and T2, by sending Sell and Buy orders at a specified price.
A sell order gives T1 and receives T2. A buy order gives T2 and receives T1.
To simplify the contract, the price is specified as "the amount of T2 per 10^9 T1" to give some granularity without using FixedPoint libraries. Therefore, the amount of tokens someone receives for a certain order is:
- Sell: (Quantity * Price) / 10^9
- Buy: (Quantity * 10^9) / Price
An order is only considered valid if the person would receive at least 1 of the other token.
We keep two order arrays:
- The Sell orders, sorted in decreasing order.
- The Buy orders, sorted in increasing order.
A match will try to match the last element of each array, therefore the lowest Sell and the highest Buy. For simplicity, only orders with the same price can match.
An order may be partially filled. In this case, the desired quantity of that order decreases by the received amount. If the updated order is invalid, it is removed from the book.
Known problems and assumptions that are not part of the intended problem of this submission:
- Since orders only match if they have the same price, even order pairs such as (Sell at 10, Buy at 15) would not match. We assume that someone can easily arbitrage this by buying at 10 from the first order and selling at 15 to the second.
- Someone can DoS the contract by placing many orders of the minimum amount of tokens that make an order valid. Conceptually this is not a problem if we assume gas is free (for the sake of the exercise in this submission), since those orders would partially match other orders and everything would still work, only requiring more transactions.
- Some orders may take a long time to match. If an order never matches, a user can simply cancel their order.