Advanced MultiSwap: How to better arbitrage with Solidity
Making multiple swaps across different decentralized exchanges in a single transaction
If you want maximum arbitrage performance, you need to swap tokens between exchanges in a single transaction. Or maybe you just want to save gas on certain swaps you perform regularly. Or maybe you have your own custom use case for swapping between decentralized exchanges. And of course maybe you are just here for the learning aspect.
Whatever your reason may be, MultiSwap is a great way to combine knowledge into one contract. We have previously looked at a MultiSwap that looks like this:
You can find it here. But this time we are going to upgrade it. Instead of having to deploy a new contract for every MultiSwap, we can build a generic MultiSwap contract based on the same concept as before. Then you deploy the contract only once and use it for any arbitraging you like.
To do that, we will still use the same trade from the previous MultiSwap as example. So how does this new advanced MultiSwap look like?
Advanced MultiSwap
// SPDX-License-Identifier: MIT
pragma solidity 0.8.10;
contract AdvancedMultiTrade {
function swap(address[] memory tos, bytes[] memory data) external payable {
require(tos.length > 0 && tos.length == data.length, "Invalid input");
for(uint256 i; i < tos.length; i++) {
(bool success,bytes memory returndata) = tos[i].call{value: address(this).balance, gas: gasleft()}(data[i]);
require(success, string(returndata));
}
}
receive() payable external {}
}
Wow that was easy. How does that work?
What happens here is in Solidity we can call other contracts directly only given the address and the transaction data. In other words, we can have a smart contract where we don't have to predefine which functions on which DEX's are called. Now we can simply pass this information from the outside!
We simply iterate over all target addresses and use the low-level call: tos[i].call{value: address(this).balance, gas: gasleft()}(data[i]).
Note that we pass address(this).balance as value, so any ETH in the contract will always be fully forwarded to the call. And we use gasleft() to forward any remaining gas.
That's great, but how can you use this???
We did indeed shift the complexity from the contract code itself onto how you interact with it. What you need to know is
- which contract addresses do I want to call
- which function on that address I want to call
- and which parameters I want to pass to that function.
And to make matters worse, all of this needs to be in low level encoded data.
The address itself should be easy to get. In our old MultiSwap example for Ropsten on Banchor that was 0xb3fa5dcf7506d146485856439eb5e401e0796b5d. Now we need to figure out which function to call. On a low-level call this is done from the 4-bytes function selector.
One little trick on how to get that is adding the following function to your contract:
function getSelector(string calldata _func) external pure returns (bytes4) {
return bytes4(keccak256(bytes(_func)));
}And now simply call the function with the function name and parameters:
getSelector("convertByPath(address[],uint256,uint256,address,address,uint256)")Great, now we have the function selector which is 0xb77d239b. Now last we need to encode the data for the function parameters.
Once you fully automate your arbitrage, you will want to do this with your favorite choice of library, like Web3.js, Web3.py or ethers.js. Now for testing, you could use this handy online tool here.
Enter the function parameter types separated by comma as well as the values.
- address[],uint256,uint256,address,address,uint256
- [0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE,0x1aCE5DD13Ba14CA42695A905526f2ec366720b13,0xF35cCfbcE1228014F66809EDaFCDB836BFE388f5],1000,1,0x0000000000000000000000000000000000000000,0x0000000000000000000000000000000000000000,0
See the previous MultiSwap example for the details on this here.
Now we the data required for our first call. Simply copy & paste the encoded string after our function selector and we have the first data field complete:
tos: ["0xb3fa5dcf7506d146485856439eb5e401e0796b5d"]
data: ["0xb77d239b00000000000000000000000000000000000000000000000000000000000000c000000000000000000000000000000000000000000000000000000000000003e800000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000003000000000000000000000000eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee0000000000000000000000001ace5dd13ba14ca42695a905526f2ec366720b13000000000000000000000000f35ccfbce1228014f66809edafcdb836bfe388f5"]Constructing the other two calls
The other two calls to SushiSwap and Uniswap follow the exact same principle.
getSelector("swapExactTokensForTokens(uint256,uint256,address[],address,uint256)")will give us the function selector 0x38ed1739. And for the parameter encoding we use:
- uint256,uint256,address[],address,uint256
- 5000000000000000000,2476572156145166857,[0xF35cCfbcE1228014F66809EDaFCDB836BFE388f5,0x9108Ab1bb7D054a3C1Cd62329668536f925397e5],0x2f0cd179a4f3d47eac5a8d22ccb5d76621212616
Note that as recipient address we used the MultiSwap address itself (0x2f0cd179a4f3d47eac5a8d22ccb5d76621212616). Obviously you'll only have this once the contract is deployed, not beforehand. And we of course need it to be the contract itself as recipient, so we can use the funds for the last swap.
And that will give us the second call data:
tos: ["0x1b02da8cb0d097eb8d57a175b88c7d8b47997506"]
data: ["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"]And the same thing for the Uniswap call:
getSelector("exactInputSingle((address,address,uint24,address,uint256,uint256,uint256,uint160))")will give us the function selector 0x414bf389. And for the parameter encoding we use:
- address,address,uint24,address,uint256,uint256,uint256,uint160
- 0x9108Ab1bb7D054a3C1Cd62329668536f925397e5,0xaD6D458402F60fD3Bd25163575031ACDce07538D,3000,0x15ae150d7dC03d3B635EE90b85219dBFe071ED35,1728418389,5000,1,0
Note that since this is the last call, we used our own address as recipient, not the MultiSwap smart contract address.
Which will give us the third and final call data:
tos: ["0xe592427a0aece92de3edee1f18e0157c05861564"]
data: ["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"]<br>And lastly merge all three calls into one:
tos: ["0xb3fa5dcf7506d146485856439eb5e401e0796b5d","0x1b02da8cb0d097eb8d57a175b88c7d8b47997506","0xe592427a0aece92de3edee1f18e0157c05861564"]
data: ["0xb77d239b00000000000000000000000000000000000000000000000000000000000000c000000000000000000000000000000000000000000000000000000000000003e800000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000003000000000000000000000000eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee0000000000000000000000001ace5dd13ba14ca42695a905526f2ec366720b13000000000000000000000000f35ccfbce1228014f66809edafcdb836bfe388f5","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","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"]What about the token.approve?
Good catch. We are indeed requiring the token approvals from the contract to the DEX contract. How you will integrate those the best will depend on your use case. If you already know which tokens you will exclusively trade, just put them into the constructor:
import {IERC20, SafeERC20} from "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/utils/SafeERC20.sol";
contract AdvancedMultiTrade {
using SafeERC20 for IERC20;
constructor() {
IERC20(0xF35cCfbcE1228014F66809EDaFCDB836BFE388f5).safeApprove(address(0x1b02dA8Cb0d097eB8D57A175b88c7D8b47997506), type(uint256).max);
IERC20(0x9108Ab1bb7D054a3C1Cd62329668536f925397e5).safeApprove(address(0xE592427A0AEce92De3Edee1F18E0157C05861564), type(uint256).max);
}
}But of course those approvals are also just calls itself. So you could just make them part of the function call arrays.
Lastly, just pass all calls to the contract (make sure to pass enough ETH as well for our example) and we only need one transaction for the whole swap!
Solidity Developer
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How to get a Solidity developer job?
There are many ways to get a Solidity job and it might be easier than you think!
You have mastered the basics of Solidity, created your first few useful projects and now want to get your hands on some real-world projects. Getting a Solidity developer job might be easier than you think. There are generally plenty of options to choose from and often times not a lot of...
Design Pattern Solidity: Mock contracts for testing
Why you should make fun of your contracts
Mock objects are a common design pattern in object-oriented programming. Coming from the old French word 'mocquer' with the meaning of 'making fun of', it evolved to 'imitating something real' which is actually what we are doing in programming. Please only make fun of your smart contracts if you...
Kickstart your Dapp frontend development with create-eth-app
An overview on how to use the app and its features
Last time we looked at the big picture of Solidity and already mentioned the create-eth-app. Now you will find out how to use it, what features are integrated and additional ideas on how to expand on it. Started by Paul Razvan Berg, the founder of sablier, this app will kickstart your frontend...
The big picture of Solidity and Blockchain development in 2020
Overview of the most important technologies, services and tools that you need to know
Now, I do not know about you, but I remember when I first started with Solidity development being very confused by all the tools and services and how they work in connection with one another. If you are like me, this overview will help you understand the big picture of Solidity development. As I...
Design Pattern Solidity: Free up unused storage
Why you should clean up after yourself
You may or may not be used to a garbage collectors in your previous programming language. There is no such thing in Solidity and even if there was a similar concept, you would still be better off managing state data yourself. Only you as a programmer can know exactly which data will not be used...
How to setup Solidity Developer Environment on Windows
What you need to know about developing on Windows
Using Windows for development, especially for Solidity development, can be a pain sometimes, but it does not have to be. Once you have configured your environment properly, it can actually be extremely efficient and Windows is a very, very stable OS, so your overall experience can be amazing. The...
Avoiding out of gas for Truffle tests
How you do not have to worry about gas in tests anymore
You have probably seen this error message a lot of times: Error: VM Exception while processing transaction: out of gas Disclaimer : Unfortunately, this does not always actually mean what it is saying when using Truffle , especially for older versions. It can occur for various reasons and might be...
Design Pattern Solidity: Stages
How you can design stages in your contract
Closely related to the concept of finite-state machines, this pattern will help you restrict functions in your contract. You will find a lot of situations where it might be useful. Any time a contract should allow function calls only in certain stages. Let's look at an example: contract Pool {...
Web3 1.2.5: Revert reason strings
How to use the new feature
A new Web3 version was just released and it comes with a new feature that should make your life easier. With the latest version 1.2.5, you can now see the the revert reason if you use the new handleRevert option. You can activate it easily by using web3.eth.handleRevert = true . Now when you use...
Gaining back control of the internet
How Ocelot is decentralizing cloud computing
I recently came across an ambitious company that will completely redefine the way we are using the internet. Or rather, the way we are using its underlying infrastructure which ultimately is the internet. While looking at their offering, I also learned how to get anonymous cloud machines, you...
Devcon 5 - Review
Impressions from the conference
I had a lot to catch up on after Devcon. Also things didn't go quite as planned, so please excuse my delayed review! This year's Devcon was certainly stormy with a big typhoon warning already on day 1. Luckily (for us, not the people in Tokyo), it went right past Osaka. Nevertheless, a lot of...
Devcon 5 - Information, Events, Links, Telegram
What you need to know
Devcon 5 is coming up soon and there are already lots of events available, information about Osaka and more. Here is a short overview: Events Events Calendar Events Google Docs Events Kickback Most events are in all three, but if you really want to see all, you will have to look at all three...
Design Pattern Solidity: Off-chain beats on-chain
Why you should do as much as possible off-chain
As you might have realized, Ethereum transactions are anything but cheap. In particular, if you are computing complex things or storing a lot of data. That means sometimes we cannot put all logic inside Solidity. Instead, we can utilize off-chain computations to help us. A very simple example...
Design Pattern Solidity: Initialize Contract after Deployment
How to use the Initializable pattern
There are a few reasons why you might want to initialize a contract after deployment and not directly by passing constructor arguments. But first let's look at an example: contract MyCrowdsale { uint256 rate; function initialize(uint256 _rate) public { rate = _rate; } } What's the advantage over...
Consensys Blockchain Jobs Report
What the current blockchain job market looks like
Consensys published their blockchain jobs report which you can checkout in their Blockchain Developer Job Kit. The most interesting aspects are Blockchain developer jobs have been growing at a rate of 33x of the previous year according to LinkedIns jobs report Typical salary is about...
Provable — Randomness Oracle
How the Oraclize random number generator works
One particularly interesting approach by Provable is the usage of a hardware security device, namely the Ledger Nano S. It uses a trusted execution environment to generate random numbers and provides a Provable Connector Contract as interface. How to use the Provable Randomness Oracle? Use the...
Solidity Design Patterns: Multiply before Dividing
Why the correct order matters!
There has been a lot of progress since the beginning of Ethereum about best practices in Solidity. Unfortunately, I have the feeling that most of the knowledge is within the circle of experienced people and there aren’t that many online resources about it. That is why I would like to start this...
Devcon 5 Applications closing in one week
Devcon 5 Applications closing
Watch out for the Devcon 5 applications. You only have one week left to apply either as Buidler Student Scholarship Press Devcon is by far the biggest and most impressive Ethereum conference in the world. And it's full of developers! I am especially excited about the cool location this year in...
Randomness and the Blockchain
How to achieve secure randomness for Solidity smart contracts?
When we talk about randomness and blockchain, these are really two problems: 1. How to generate randomness in smart contracts? 2. How to produce randomness for proof-of-stake (POS) systems? Or more generally, how to produce trusted randomness in public distributed systems? There is some overlap...