04/18

SushiSwap Explained!

Looking at the implementation details of SushiSwap

You've probably heard of SushiSwap by now. The Uniswap fork brought new features like staking and governance to the exchange. But how exactly are the contracts behind it working?

It's actually not too difficult. Knowing how this works in detail will be a great way to learn about Solidity and Defi.

We will now dive into the implementation details of SushiSwap. Some of the code was modified to be easier to understand. You can always check the full code inside Github.

At its core SushiSwap is just a Uniswap v2 fork. The contract code was copied 1:1 except for a few small differences. If you are curious about how Uniswap v2 works, check out my previous post here. And also keep an eye out for a deep dive into Uniswap v3 in the near future.

In particular SushiSwap is making use of liquidity pool tokens (LP tokens). Check out https://uniswap.org/docs/v2/core-concepts/pools/ under 'Pool tokens' for all details. Essentially LPs are for receiving pro-rata fees accrued in the pool. So you provide liquidity in a pool and get LP tokens minted in return. When the pool is now collecting fees over time, they are evenly distributed to all LP holders at the time of the trade. When you burn your LP tokens, you will receive your share of the pool + the collected fees.

Two changes to the Uniswap code where made by SushiSwap:

The function setFeeTo was called in the deployment and the fee recipient was set to the SushiMaker contract (see below). Once the fee recipient is set, 1/6th of the LP supply growth due to the current trade are minted as protocol fee in the form of pool tokens. Since the trade fee on Uniswap is 0.3%, this will result in a 0.05% fee of every trade going towards the SushiMaker.
A migrator functionality was added (see SushiRoll below).

You can see the full diff between Uniswap's core contracts and how SushiSwap changed them here.

The SushiMaker will receive LP tokens from people trading on SushiSwap. It mostly consists of a convert function which does the following:

Burn the LP tokens for the provided token pair. The result will be receiving proportional amounts of both token0 and token1.
Inside convertStep trade both received tokens into SUSHI. This may require additional steps if there's no direct pool to trade into SUSHI.

The swap itself is performed on the SushiSwap pools itself. Let's see how this is done by examining the _swap function.

function convert(address token0, address token1) external {
  UniV2Pair pair = UniV2Pair(factory.getPair(token0, token1));
  require(address(pair) != address(0), "Invalid pair");

  IERC20(address(pair)).safeTransfer(
      address(pair),
      pair.balanceOf(address(this))
  );

  (uint256 amount0, uint256 amount1) = pair.burn(address(this));

  if (token0 != pair.token0()) {
      (amount0, amount1) = (amount1, amount0);
  }

  _convertStep(token0, token1, amount0, amount1)
}

function _swap(
    address fromToken,
    address toToken,
    uint256 amountIn,
    address to
) internal returns (uint256 amountOut) {
    UniV2Pair pair =
        UniV2Pair(factory.getPair(fromToken, toToken));
    require(address(pair) != address(0), "Cannot convert");

    (uint256 reserve0, uint256 reserve1, ) = pair.getReserves();
    uint256 amountInWithFee = amountIn.mul(997);

    if (fromToken == pair.token0()) {
        amountOut =
            amountInWithFee.mul(reserve1) /
            reserve0.mul(1000).add(amountInWithFee);
        IERC20(fromToken).safeTransfer(address(pair), amountIn);
        pair.swap(0, amountOut, to, new bytes(0));
    } else {
        amountOut =
            amountInWithFee.mul(reserve0) /
            reserve1.mul(1000).add(amountInWithFee);
        IERC20(fromToken).safeTransfer(address(pair), amountIn);
        pair.swap(amountOut, 0, to, new bytes(0));
    }
}

The swap itself is performed on the SushiSwap pools itself. For the trade we are using the low-level Uniswap swap function.

Get the current reserves of both tokens in the pool.
Compute the receiving amount from the reserves and token amount being swapped minus the fees. Calculation is based on the x * y = k curve.

Once the amount out is computed, we can perform the swap. The last step to convert into SUSHI will always call the _swap function by passing the SUSHI token address and sending it to the bar:

_swap(token, sushi, amountIn, bar)

That's it, now we converted all LP tokens into SUSHI. All converted SUSHI are sent to the SushiBar, see next contract.

Inside the SushiBar people can enter with SUSHI, receive xSUSHI and later leave with even more SUSHI. Remember that all SUSHI from the SushiMaker are sent here. So over time the bar will accumulate more and more SUSHI.

Who will receive this SUSHI?

Anyone who entered the bar. For entering a user receives xSUSHI which are kind of like the LP tokens for Uniswap. They represent ownership of the SUSHI token in the bar.

The amount of xSUSHI you receive is your transferred SUSHI * total xSUSHI supply / current balance of SUSHI. So if you send 10 SUSHI to the bar which already has 100 SUSHI in it and 200 xSUSHI total supply, you will receive 10 * 200 / 100 = 20 xSUSHI.

function enter(uint256 _amount) external {
  uint256 totalSushi = sushi.balanceOf(address(this));
  uint256 totalShares = totalSupply();

  uint256 mintAmount =
      totalShares == 0 || totalSushi == 0
      ? _amount
      : _amount.mul(totalShares).div(totalSushi);
    
  _mint(msg.sender, mintAmount);
  sushi.transferFrom(
    msg.sender,
    address(this),
    _amount
  );
}

function leave(uint256 _share) external {
    uint256 totalShares = totalSupply();
    uint256 transferAmount = _share
        .mul(sushi.balanceOf(address(this)))
        .div(totalShares);

    _burn(msg.sender, _share);
    sushi.transfer(msg.sender, transferAmount);
}

Now when you leave again, you get your equal share of SUSHI back. This will be at the minimum what you paid in, but considering the bar will accumulate SUSHI over time, it should be more than what you put originally in.

The amount of SUSHI you receive is your transferred xSUSHI * current balance of SUSHI / total xSUSHI supply. So if you send 20 xSUSHI to the bar which has 100 SUSHI in it and 200 xSUSHI total supply, you will receive 20 * 100 / 200 = 10 SUSHI.

Of course you have the SUSHI token contract itself. There's nothing special to it other than being a regular ERC-20 with delegation functionality identical to the COMP token. We've previously discussed COMP governance here. The mentioned Timelock contract is also included in SushiSwap.

The token allows delegating your voting power to some other trusted address. This address can then vote with increased power. Any time you may choose to re-delegate somewhere else.

In the SushiRoll contract a migrator is provided, so people can easily move liquidity from Uniswap to SushiSwap.

With the migrate function, you essentially

Remove liquidity from Uniswap.
Add liquidity in SushiSwap.

Any potential leftover tokens from the token pair will be returned to the user.

function migrate(
    address tokenA,
    address tokenB,
    uint256 liquidity,
    uint256 amountAMin,
    uint256 amountBMin,
    uint256 deadline
) external {
    require(deadline >= block.timestamp, 'SushiSwap: EXPIRED');

    // Remove liquidity from the old router with permit
    (uint256 amountA, uint256 amountB) = removeLiquidity(
        tokenA,
        tokenB,
        liquidity,
        amountAMin,
        amountBMin,
        deadline
    );

    (uint256 pooledAmountA, uint256 pooledAmountB)
        = addLiquidity(tokenA, tokenB, amountA, amountB);

    if (amountA > pooledAmountA) {
        IERC20(tokenA).safeTransfer(msg.sender, amountA - pooledAmountA);
    }
    
    if (amountB > pooledAmountB) {
        IERC20(tokenB).safeTransfer(msg.sender, amountB - pooledAmountB);
    }
}

The MasterChef enables the minting of new SUSHI token. It's the only way that SUSHI tokens are created. This is possible by staking LP tokens inside the MasterChef. The MasterChef is controlled by the owner which originally used to be Chef Nomi, but is since controlled by a 9 person multi-sig belonging to:

SBF_Alameda (FTX CEO)
Rleshner (Compound founder)
0xMaki (Sushiswap GM)
Lawmaster (head of Research at The Block)
CMsholdings (CMS Holdings)
Mattysino (CEO of Sino Global Capital)
mickhagen（Genesis Block founde)
AdamScochran (partner at Cinneamhain Ventures)
zippoxer (Zippo)

Eventually the plan is to move control of the MasterChef to governance. The owner has the power to control the allocations points from pools. What this means is the higher the allocation points of a liquidity pool, the more SUSHI one receives for staking its LP tokens. In the future this might create powerful control to create incentives for participating in special liquidity pools.

The owner can control pool allocations via the add function:

function add(uint256 _allocPoint, IERC20 _lpToken, bool _withUpdate) public onlyOwner;

Ongoing pools can be updated and then mint SUSHI to the people staking the LP tokens using updatePool.

The newly minted SUSHI amount per pool depends on the passed blocks since the last update and the set allocation points for the pool. (plus some extra multiplier left out for simplicity in the example on the right)

The calculated sushiReward is then distributed in 10% towards the dev address and the other 90% towards the pool LP stakers.

function updatePool(uint256 _pid) public {
    PoolInfo storage pool = poolInfo[_pid];
    if (block.number <= pool.lastRewardBlock) {
        return;
    }
    uint256 lpSupply = pool.lpToken.balanceOf(address(this));
    if (lpSupply == 0) {
        pool.lastRewardBlock = block.number;
        return;
    }

    uint256 sushiReward = sushiPerBlock
        .mul(pool.allocPoint)
        .div(totalAllocPoint);

    sushi.mint(devaddr, sushiReward.div(10));
    sushi.mint(address(this), sushiReward);

    pool.accSushiPerShare = pool.accSushiPerShare.add(
        sushiReward.mul(1e12).div(lpSupply)
    );
    pool.lastRewardBlock = block.number;
}

function deposit(uint256 _pid, uint256 _amount) public {
    PoolInfo storage pool = poolInfo[_pid];
    UserInfo storage user = userInfo[_pid][msg.sender];
    updatePool(_pid);
    if (user.amount > 0) {
        uint256 pending = user.amount
                .mul(pool.accSushiPerShare)
                .div(1e12)
                .sub(user.rewardDebt);
        safeSushiTransfer(msg.sender, pending);
    }

    pool.lpToken.safeTransferFrom(
        address(msg.sender),
        address(this),
        _amount
    );

    user.amount = user.amount.add(_amount);
    user.rewardDebt = user.amount
        .mul(pool.accSushiPerShare)
        .div(1e12);
}

Using the deposit function users can stake their LP tokens for the provided pool. This will put the user's LP token into the MasterChef contract.

Using the withdraw function users can unstake their LP tokens for the provided pool. In return they will

receive their original LP tokens
get their share of newly minted SUSHI tokens

The amount of minted SUSHI depends on the accSushiPerShare computed previously (see updatePool).

function withdraw(uint256 _pid, uint256 _amount) public {
    PoolInfo storage pool = poolInfo[_pid];
    UserInfo storage user = userInfo[_pid][msg.sender];
    require(user.amount >= _amount, "withdraw: not good");
    updatePool(_pid);
    uint256 pending =
        user.amount
            .mul(pool.accSushiPerShare)
            .div(1e12)
            .sub(user.rewardDebt);
    safeSushiTransfer(msg.sender, pending);
    user.amount = user.amount.sub(_amount);
    user.rewardDebt = user.amount
        .mul(pool.accSushiPerShare)
        .div(1e12);
    pool.lpToken.safeTransfer(address(msg.sender), _amount);
}

Since the SushiSwap creator has since left the field, its future remains uncertain. The token itself maintained a very high market cap and future developments towards decentralized governance may drive SushiSwap further. On the other hand Uniswap v3 is on the horizon and that's certainly not the only competition for SushiSwap.

Markus Waas

Solidity Developer

More great blog posts from Markus Waas

December 2021

12/28
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...
Read more

November 2021

11/30
Deploying Solidity Smart Contracts to Solana
What is Solana and how can you deploy Solidity smart contracts to it?
Solana is a new blockchain focusing on performance. It supports smart contracts like Ethereum which they call Programs. You can develop those in Rust, but there's also a new project now to compile Solidity to Solana. In other words you can deploy your contracts written in Solidity now to Solana!...
Read more
11/14
Smock 2: The powerful mocking tool for Hardhat
Features of smock v2 and how to use them with examples
We’ve covered mocking contracts before as well as the first version of the new mocking tool Smock 2. It simplifies the mocking process greatly and also gives you more testing power. You’ll be able to change the return values for functions as well as changing internal contract storage directly!...
Read more

October 2021

10/23
How to deploy on Evmos: The first EVM chain on Cosmos
Deploying and onboarding users to Evmos
We've covered several Layer 2 sidechains before: Polygon xDAI Binance Smart Chain Aurora Chain (NEAR) Optimism But this time we will do into the exciting new world of Cosmos. Many of the most interesting projects are currently building in the ecosystem and you can expect a lot to happen here in...
Read more
10/15
EIP-2535: A standard for organizing and upgrading a modular smart contract system.
Multi-Facet Proxies for full control over your upgrades
The EIP-2535 standard has several projects already using it, most notably Aavegotchi holding many millions of dollars. What is it and should you use it instead of the commonly used proxy upgrade pattern? What is a diamond? We're not talking about diamond programmer hands here of course. A diamond...
Read more

August 2021

08/22
MultiSwap: How to 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...
Read more
08/01
The latest tech for scaling your contracts: Optimism
How the blockchain on a blockchain works and how to use it
Have you heard of Optimism? The new Optimistic VM enables Plasma but for smart contracts! What does that mean? Well read on. But what it enables is having a side chain with guarantees of the Ethereum mainnet chain. How cool is that? And you can already use it for several apps on mainnet....
Read more

July 2021

07/10
Ultimate Performance: The Aurora Layer2 Network
Deploying and onboarding users to the Aurora Network powered by NEAR Protocol
We've covered several Layer 2 sidechains before: Polygon xDAI Binance Smart Chain But today might be the fastest of them all. On top it's tightly connected to the NEAR protocol ecosystem, a PoS chain with a scalable sharding design. And of course they have a bridge to Ethereum! What is the Aurora...
Read more

June 2021

06/19
What is ecrecover in Solidity?
A dive into the waters of signatures for smart contracts
Ever wondered what the hell the deal is with the ecrecover command in Solidity? It's all about signatures and keys... What is ecrecover ? You may have seen ecrecover in a Solidity contract before and wondered what exactly the deal with this was. Well you came across the EVM precompile ecrecover....
Read more
06/12
How to use Binance Smart Chain in your Dapp
Deploying and onboarding users to the Binance Smart Chain (BSC)
Defi has been a major contributor to the Binance Smart Chain taking off recently. Along with increasing gas costs on Ethereum mainnet which are actually at one of the lowest levels since a long time at the time of this writing, but will likely pump again at the next ETH price pump. So how does...
Read more

May 2021

05/28
Using the new Uniswap v3 in your contracts
What's new in Uniswap v3 and how to integrate Uniswap v3
If you're not familiar with Uniswap yet, it's a fully decentralized protocol for automated liquidity provision on Ethereum. An easier-to-understand description would be that it's a decentralized exchange (DEX) relying on external liquidity providers that can add tokens to smart contract pools and...
Read more
05/09
What's coming in the London Hardfork?
Looking at all the details of the upcoming fork
The Berlin Hardfork only just went live on April 14th after block 12,224,00. Next up will be the London Hardfork in July which will include EIP-1559 and is scheduled for July 14th (no exact block decided yet). So let's take a look at the new changes and what you need to know as a developer....
Read more

April 2021

04/23
The Ultimate Ethereum Mainnet Deployment Guide
All you need to know to deploy to the Ethereum mainnet
We all love Ethereum, so you've built some great smart contracts. They are tested intensely with unit-tests and on testnets. Now it's finally time to go to mainnet. But this is a tricky business... 1. What exactly is a deployment transaction? First let's quickly discuss what a contract deployment...
Read more
04/04
Solidity Fast Track 2: Continue Learning Solidity Fast
Continuing to learn Solidity fast with the advanced basics
Previously we learned all of the basics in 20 minutes. If you are a complete beginner, start there and then come back here. Now we'll explore some more advanced concepts, but again as fast as possible. 1. Saving money with events We all know gas prices are out of control right now, so it's more...
Read more

March 2021

03/28
What's coming in the Berlin Hardfork?
Looking at all the details of the upcoming fork
The Berlin Hardfork is scheduled for April 14th after block 12,224,00. Later to be followed by the London Hardfork in July which will include EIP-1559. So let's take a look at the new changes and what you need to know as a developer. EIP-2929: Increased gas costs for state access EIP-2929 will...
Read more
03/13
Using 1inch ChiGas tokens to reduce transaction costs
What are gas tokens and example usage for Uniswap v2
Gas prices have been occasionally above 1000 Gwei in the past in peak times. Given an ETH price of over 1000 USD, this can lead to insane real transaction costs. In particular this can be a pain when using onchain DEX's like Uniswap, resulting in hundreds of dollars transaction fees for a single...
Read more
03/07
Openzeppelin Contracts v4 in Review
Taking a look at the new Openzeppelin v4 Release
The Openzeppelin v4 contracts are now available in Beta and most notably come with Solidity 0.8 support. For older compiler versions, you'll need to stick with the older contract versions. The beta tag means there still might be small breaking changes coming for the final v4 version, but you can...
Read more

February 2021

02/27
EIP-3156: Creating a standard for Flash Loans
A new standard for flash loans unifying the interface + wrappers for existing ecosystems
As we've discussed last week, flash loans are a commonly used pattern for hacks. But what exactly are they and how are they implemented in the contracts? As of right now each protocol has its own way of implementing flash loans. With EIP-3156 we will get a standardized interface. The standard was...
Read more
02/14
Tornado.cash: A story of anonymity and zk-SNARKs
What is Tornado.cash, how to use it and the future
With the recent Yearn vault v1 hack from just a few days ago, we can see a new pattern of hacks emerging: 1. Get anonymous ETH via tornado.cash. 2. Use the ETH to pay for the hack transaction(s). 3. Use a flash loan to decrease capital requirements. 4. Create some imbalances given the large...
Read more
02/07
High Stakes Roulette on Ethereum
Learn by Example: Building a secure High Stakes Roulette
It's always best to learn with examples. So let's build a little online casino on the blockchain. We'll also make it secure enough to allow playing in really high stakes by adding a secure randomness generator. Let's discuss the overall design first. Designing the contract Before we program...
Read more

January 2021

01/30
How to implement generalized meta transactions
We'll explore a powerful design for meta transactions based on 0x
Enabling meta transactions inside your contract is a powerful addition. Requiring users to hold ETH to pay for gas has always been and still is one of the biggest user onboarding challenges. Who knows how many more people would be using Ethereum right now if it was just a simple click? But...
Read more
01/24
Utilizing Bitmaps to dramatically save on Gas
A simple pattern which can save you a lot of money
As you may know the most expensive operation in Ethereum is storing data (SSTORE). So you should always look for ways to reduce the storage requirements. Let's explore a particularly useful one: Bitmaps. How to implement a simple Bitmap Let's assume we want to store 10 boolean values. Usually you...
Read more
01/16
Using the new Uniswap v2 as oracle in your contracts
How does the Uniswap v2 oracle function and how to integrate with it
We've covered Uniswap previously here. But let's go through the basics first again. What is UniSwap? If you're not familiar with Uniswap yet, it's a fully decentralized protocol for automated liquidity provision on Ethereum. An easier-to-understand description would be that it's a decentralized...
Read more
01/10
Smock: The powerful mocking tool for Hardhat
Features of smock and how to use them with examples
We’ve covered mocking contracts before, but now there’s an additional great tool available: smock. It simplifies the mocking process greatly and also gives you more testing power. You’ll be able to change the return values for functions as well as changing internal contract storage directly! How...
Read more
01/03
How to build and use ERC-721 tokens in 2021
An intro for devs to the uniquely identifying token standard and its future
The ERC-721 standard has been around for a while now. Originally made popular by blockchain games, it's more and more used for other applications like Defi. But what exactly is it? A non-fungible token (NFT) is a uniquely identifying token. The word non-fungible implies you cannot just replace...
Read more

December 2020

12/26
Trustless token management with Set Protocol
How to integrate token sets in your contracts
With Set Protocol you can create baskets of tokens that give users different levels of exposure to underlying assets (currently only ERC-20 tokens). Set Protocol and their TokenSet functionality is the perfect example for making use of the new paradigm of Defi and composability. You can let...
Read more
12/18
Exploring the new Solidity 0.8 Release
And how to upgrade your contracts to Solidity 0.8
We are getting closer to that Solidity 1.0 release (unless of course after 0.9 comes 0.10). Now Solidity 0.8 has been released only 5 months after the 0.7 release! Let's explore how you can migrate your contracts today... New features & how to use them Let's look at the two big new features which...
Read more
12/12
How to build and use ERC-1155 tokens
An intro to the new standard for having many tokens in one
ERC-1155 allows you to send multiple different token classes in one transactions. You can imagine it as transferring Chinese Yuan and US Dollars in a single transfer. ERC-1155 is most commonly known for being used in games, but there are many more use cases for it. First of all though, what are...
Read more
12/05
Leveraging the power of Bitcoins with RSK
Learn how RSK works and how to deploy your smart contracts to it
I'm always interested in what other ways one can use their blockchain and Solidity skills. While many projects are still only in the planning or in testnet status, with Rootstock (RSK) you can transfer mainnet Bitcoins to an EVM sidechain and vice-versa already today. Utilizing the power of the...
Read more

November 2020

11/29
Solidity Fast Track: Learn Solidity Fast
'Learn X in Y minutes' this time with X = Solidity 0.7 and Y = 20
You might be familiar with the Learn X in Y minutes. For example you could learn JavaScript in 20 minutes at https://learnxinyminutes.com/docs/javascript/. Unfortunately there is no equivalent for Solidity, but this is about to change. Do you have 20 minutes to learn all of the basics? We even...
Read more
11/21
The future of a Decentralized Etherscan
Learn how to use the new Sourcify infrastructure today
We all love Etherscan. It's a great tool to interact with contracts, read the source codes or just see the status of your transactions. But unfortunately as great as it is, we should not forget that it's a centralized service. The website could be taken down any day. This kind of defeats the...
Read more
11/14
Integrating the 0x API into your contracts
How to automatically get the best prices via 0x
How can you add 0x to your contracts to automatically convert between tokens? We have done this in a similar fashion before with Uniswap and Balancer. The 0x API has a bit of a twist. Let's take a look why... Why you want 0x in your contracts? It's simple: Okay, but seriously. Let's see why the...
Read more
11/08
How to build and use ERC-777 tokens
An intro to the new upgraded standard for ERC-20 tokens
The new upgraded standard for ERC-20 tokens is becoming more and more popular. It's fully backwards compatible, you can easily create one using the Openzeppelin contracts and there are many interesting new features not available in ERC-20. Should you upgrade from ERC-20? Well let's look into what...
Read more
11/01
COMP Governance Explained
How Compound's Decentralized Governance is working under the hood
You might have heard about the COMP token launch. With a current market cap of over 350 million USD, the token has accumulated massive value. But what is the actual utility of COMP? It's a governance token. Compound being a fully decentralized system (or at least on the way towards it), has a...
Read more

October 2020

10/25
How to prevent stuck tokens in contracts
And other use cases for the popular EIP-165
Do you remember the beginning of the Dark Forest story? If not, let's look at it again: Somebody sent tokens to a smart contract that was not intended to receive tokens. This perfectly illustrates one of the issues not only with ERC-20 tokens, but generally with smart contracts. How can we find...
Read more
10/18
Understanding the World of Automated Smart Contract Analyzers
What are the best tools today and how can you use them?
As we all know, it's very difficult writing a complex, yet fully secure smart contract. Without the proper methods, chances are you will have many security issues. Automated security testing tools already exist and can be a great help. One of the main challenges for these tools is to maximize...
Read more
10/10
A Long Way To Go: On Gasless Tokens and ERC20-Permit
And how to avoid the two step approve + transferFrom with ERC20-Permit (EIP-2612)!
It's April 2019 in Sydney. Here I am looking for the Edcon Hackathon inside the massive Sydney university complex. It feels like a little city within a city. Of course, I am at the wrong end of the complex and I realize to get to the venue hosting the Hackathon I need to walk 30 minutes to the...
Read more
10/03
Smart Contract Testing with Waffle 3
What are the features of Waffle and how to use them.
Waffle has been a relatively recent new testing framework, but has gained a lot of popularity thanks to its simplicity and speed. Is it worth a try? Absolutely. I wouldn't run and immediately convert every project to it, but you might want to consider it for new ones. It's also actively being...
Read more

September 2020

09/26
How to use xDai in your Dapp
Deploying and onboarding users to xDai to avoid the high gas costs
Gas costs are exploding again, ETH2.0 is still too far away and people are now looking at layer 2 solutions. Here's a good overview of existing layer 2 projects: https://github.com/Awesome-Layer-2/awesome-layer-2. Today we will take a closer look at xDai as a solution for your Dapp. What are...
Read more
09/19
Stack Too Deep
Three words of horror
You just have to add one tiny change in your contracts. You think this will take you only a few seconds. And you are right, adding the code took you less than a minute. All happy about your coding speed you enter the compile command. With such a small change, you are confident your code is...
Read more
09/13
Integrating the new Chainlink contracts
How to use the new price feeder oracles
By now you've probably heard of Chainlink. Maybe you are even participating the current hackathon? In any case adding their new contracts to retrieve price feed data is surprisingly simple. But how does it work? Oracles and decentralization If you're confused about oracles, you're not alone. The...
Read more
09/06
TheGraph: Fixing the Web3 data querying
Why we need TheGraph and how to use it
Previously we looked at the big picture of Solidity and the create-eth-app which already mentioned TheGraph before. This time we will take a closer look at TheGraph which essentially became part of the standard stack for developing Dapps in the last year. But let's first see how we would do...
Read more

August 2020

08/29
Adding Typescript to Truffle and Buidler
How to use TypeChain to utilize the powers of Typescript in your project
Unlike compiled languages, you pretty much have no safeguards when running JavaScript code. You'll only notice errors during runtime and you won't get autocompletion during coding. With Typescript you can get proper typechecking as long as the used library exports its types. Most Ethereum...
Read more
08/22
Integrating Balancer in your contracts
What is Balancer and how to use it
What is Balancer? Balancer is very similar to Uniswap. If you're not familiar with Uniswap or Balancer yet, they are fully decentralized protocols for automated liquidity provision on Ethereum. An easier-to-understand description would be that they are decentralized exchanges (DEX) relying on...
Read more
08/15
Navigating the pitfalls of securely interacting with ERC20 tokens
Figuring out how to securely interact might be harder than you think
You would think calling a few functions on an ERC-20 token is the simplest thing to do, right? Unfortunately I have some bad news, it's not. There are several things to consider and some errors are still pretty common. Let's start with the easy ones. Let's take a very common token: ... Now to...
Read more
08/08
Why you should automatically generate interests from user funds
How to integrate Aave and similar systems in your contracts
If you're writing contracts that use, hold or manage user funds, you might want to consider using those funds for generating free extra income. What's the catch? That's right, it's basically free money and leaving funds unused in a contract is wasting a lot of potential. The way these...
Read more
08/02
How to use Polygon (Matic) in your Dapp
Deploying and onboarding users to Polygon to avoid the high gas costs
Gas costs are exploding again, ETH2.0 is still too far away and people are now looking at layer 2 solutions. Here's a good overview of existing layer 2 projects: https://github.com/Awesome-Layer-2/awesome-layer-2. Today we will take a closer look at Polygon (previously known as Matic) as a...
Read more

July 2020

07/25
Migrating from Truffle to Buidler
And why you should probably keep both.
Why Buidler? Proper debugging is a pain with Truffle. Events are way too difficult to use as logging and they don't even work for reverted transactions (when you would need them most). Buidler gives you a console.log for your contracts which is a game changer. And you'll also get stack traces...
Read more
07/18
Contract factories and clones
How to deploy contracts within contracts as easily and gas-efficient as possible
The factory design pattern is a pretty common pattern used in programming. The idea is simple, instead of creating objects directly, you have an object (the factory) that creates objects for you. In the case of Solidity, an object is a smart contract and so a factory will deploy new contracts for...
Read more
07/12
How to use IPFS in your Dapp?
Using the interplanetary file system in your frontend and contracts
You may have heard about IPFS before, the Interplanetary File System. The concept has existed for quite some time now, but with IPFS you'll get a more reliable data storage, thanks to their internal use of blockchain technology. Filecoin is a new system that is incentivizing storage for IPFS...
Read more

June 2020

06/26
Downsizing contracts to fight the contract size limit
What can you do to prevent your contracts from getting too large?
Why is there a limit? On November 22, 2016 the Spurious Dragon hard-fork introduced EIP-170 which added a smart contract size limit of 24.576 kb. For you as a Solidity developer this means when you add more and more functionality to your contract, at some point you will reach the limit and when...
Read more
06/21
Using EXTCODEHASH to secure your systems
How to safely integrate anyone's smart contract
What is the EXTCODEHASH? The EVM opcode EXTCODEHASH was added on February 28, 2019 via EIP-1052. Not only does it help to reduce external function calls for compiled Solidity contracts, it also adds additional functionality. It gives you the hash of the code from an address. Since only contract...
Read more
06/13
Using the new Uniswap v2 in your contracts
What's new in Uniswap v2 and how to integrate Uniswap v2
Note : For Uniswap 3 check out the tutorial here. What is UniSwap? If you're not familiar with Uniswap yet, it's a fully decentralized protocol for automated liquidity provision on Ethereum. An easier-to-understand description would be that it's a decentralized exchange (DEX) relying on external...
Read more
06/05
Solidity and Truffle Continuous Integration Setup
How to setup Travis or Circle CI for Truffle testing along with useful plugins.
Continuous integration (CI) with Truffle is great for developing once you have a basic set of tests implemented. It allows you to run very long tests, ensure all tests pass before merging a pull request and to keep track of various statistics using additional tools. We will use the Truffle...
Read more

May 2020

05/30
Upcoming Devcon 2021 and other events
The Ethereum Foundation just announced the next Devcon in 2021 in Colombia
Biggest virtual hackathon almost finished First of all, the current HackMoney event has come to an end and it has been a massive success. One can only imagine what kind of cool projects people have built in a 30 days hackathon. All final projects can be seen at:...
Read more
05/17
The Year of the 20: Creating an ERC20 in 2020
How to use the latest and best tools to create an ERC-20 token contract
You know what an ERC-20 is, you probably have created your own versions of it several times (if not, have a look at: ERC-20). But how would you start in 2020 using the latest tools? Let's create a new ERC-2020 token contract with some basic functionality which focuses on simplicity and latest...
Read more
05/10
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...
Read more
05/02
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...
Read more

April 2020

04/27
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...
Read more
04/16
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...
Read more
04/05
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...
Read more

March 2020

03/21
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...
Read more
03/07
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...
Read more

February 2020

02/22
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 {...
Read more

January 2020

01/28
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...
Read more

December 2019

12/12
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...
Read more

October 2019

10/24
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...
Read more

September 2019

09/30
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...
Read more
09/14
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...
Read more
09/01
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...
Read more

July 2019

07/27
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...
Read more
07/27
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...
Read more
07/21
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...
Read more

June 2019

06/29
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...
Read more
06/23
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...
Read more

SushiSwap Explained!

Looking at the implementation details of SushiSwap

The contracts in detail

1. Uniswap v2

2. SushiMaker

3. SushiBar

3. SushiToken

4. SushiRoll (Migrator)

5. MasterChef

updatePool

deposit

withdraw

The Sushi Future

More great blog posts from Markus Waas

Making multiple swaps across different decentralized exchanges in a single transaction

What is Solana and how can you deploy Solidity smart contracts to it?

Features of smock v2 and how to use them with examples

Deploying and onboarding users to Evmos

Multi-Facet Proxies for full control over your upgrades

Making multiple swaps across different decentralized exchanges in a single transaction

How the blockchain on a blockchain works and how to use it

Deploying and onboarding users to the Aurora Network powered by NEAR Protocol

A dive into the waters of signatures for smart contracts

Deploying and onboarding users to the Binance Smart Chain (BSC)

What's new in Uniswap v3 and how to integrate Uniswap v3

Looking at all the details of the upcoming fork

All you need to know to deploy to the Ethereum mainnet

Continuing to learn Solidity fast with the advanced basics

Looking at all the details of the upcoming fork

What are gas tokens and example usage for Uniswap v2

Taking a look at the new Openzeppelin v4 Release

A new standard for flash loans unifying the interface + wrappers for existing ecosystems

What is Tornado.cash, how to use it and the future

Learn by Example: Building a secure High Stakes Roulette

We'll explore a powerful design for meta transactions based on 0x

A simple pattern which can save you a lot of money

How does the Uniswap v2 oracle function and how to integrate with it

Features of smock and how to use them with examples

An intro for devs to the uniquely identifying token standard and its future

How to integrate token sets in your contracts

And how to upgrade your contracts to Solidity 0.8

An intro to the new standard for having many tokens in one

Learn how RSK works and how to deploy your smart contracts to it

'Learn X in Y minutes' this time with X = Solidity 0.7 and Y = 20

Learn how to use the new Sourcify infrastructure today

How to automatically get the best prices via 0x

An intro to the new upgraded standard for ERC-20 tokens

How Compound's Decentralized Governance is working under the hood

And other use cases for the popular EIP-165

What are the best tools today and how can you use them?

And how to avoid the two step approve + transferFrom with ERC20-Permit (EIP-2612)!

What are the features of Waffle and how to use them.

Deploying and onboarding users to xDai to avoid the high gas costs

Three words of horror

How to use the new price feeder oracles

Why we need TheGraph and how to use it

How to use TypeChain to utilize the powers of Typescript in your project

What is Balancer and how to use it

Figuring out how to securely interact might be harder than you think

How to integrate Aave and similar systems in your contracts

Deploying and onboarding users to Polygon to avoid the high gas costs

And why you should probably keep both.

How to deploy contracts within contracts as easily and gas-efficient as possible

Using the interplanetary file system in your frontend and contracts

What can you do to prevent your contracts from getting too large?

How to safely integrate anyone's smart contract

What's new in Uniswap v2 and how to integrate Uniswap v2

How to setup Travis or Circle CI for Truffle testing along with useful plugins.

The Ethereum Foundation just announced the next Devcon in 2021 in Colombia

How to use the latest and best tools to create an ERC-20 token contract

There are many ways to get a Solidity job and it might be easier than you think!

Why you should make fun of your contracts

An overview on how to use the app and its features

Overview of the most important technologies, services and tools that you need to know

Why you should clean up after yourself

What you need to know about developing on Windows

How you do not have to worry about gas in tests anymore

How you can design stages in your contract

How to use the new feature

How Ocelot is decentralizing cloud computing