05/15

How to integrate Wormhole in your smart contracts

Entering a New Era of Blockchain Interoperability

Wormhole began as a token bridge between Ethereum and Solana and has since expanded into a decentralized interoperability protocol for multiple blockchain ecosystems. Wormhole now supports many chains like Ethereum, Cosmos, Polkadot, Injective and many more.

It makes cross-chain communication easy and efficient. Let's explore how it works and then let's send some cross-chain messages between EVM chains in Solidity!

How does Wormhole work?

The fundamental architecture is straight-forward. It consists of:

Wormchain: A Proof of Authority chain controlled by the Guardians.
VAAs: The Verified Action Approvals are the signed messages from the Guardians.
Relayers: The entities actually submitting the signed entities to various chains, you can use your own here as well.
Blockchains: Any blockchain connected to Wormhole.

Why not Proof of Stake (PoS) for the Wormchain?

While you might think for decentralization concerns, PoS would be a better candidate for the Wormchain, it comes with issues for such a protocol.

Network security: PoS systems are designed primarily for achieving consensus within a single blockchain environment. Interoperability protocols like Wormhole are responsible for verifying transactions and information across multiple blockchains. The security assumptions and requirements may be different in a multi-chain environment and PoS may not be best suited to address these complexities.
Unclear security properties: When a PoS system is applied to a decentralized oracle network, it is not immediately clear how the network's security would be affected. As PoS relies on validators who stake their tokens to participate in the consensus process, there may be concerns about the overall security if a majority of validators collude or if the amount staked is insufficient to provide adequate economic security. This contrasts with the security guarantees provided by the underlying blockchains, which may have different consensus mechanisms and security assumptions.
Challenges in achieving outlined goals: A PoS system may introduce complexities as it would require the integration of a native token and a staking mechanism that needs to be compatible with multiple blockchains. This added complexity may make it more difficult to achieve the desired level of decentralization and seamless interoperability.

The Guardian Network

All these things considered, a Proof of Authority (PoA) system was chosen for the Wormchain. It's a purpose-built Cosmos blockchain run by 19 validators, called guardians. 2/3 of the signatures are needed for consensus in the guardian network, meaning 13 signatures need to be verified on-chain, which remains reasonable from a gas-cost and security perspective.

This group of validators is responsible for creating the Verifiable Action Assertions (VAAs). Guardians observe on-chain events, process them, and create a VAA that gets signed by a threshold of Guardians. The VAA then serves as a cryptographically verifiable proof that can be relayed to other chains and executed accordingly.

Rather than securing the network with tokenomics, it was deemed better to initially secure the network by 'involving robust companies which are heavily invested in the success of De-Fi as a whole'. The 19 Guardians are not anonymous or small--they are many of the largest and most widely-known validator companies in cryptocurrency. The current list of Guardians can be viewed here and includes big names like 01 Node, Chorus One, ChainLayer, Figment and Jump.

The Relayers

Relayers are vital components in Wormhole's cross-chain processes, enabling the delivery of VAAs to their destination chains. Unlike other interoperability protocols, Wormhole does not rely on a specific relaying methodology, giving developers the freedom to choose the most suitable strategy for their needs. There are three common relaying strategies: client-side relaying, specialized relayers, and generic relayers. Each strategy has its own set of advantages and drawbacks, catering to different application requirements and user experiences.

Let's send a message from Goerli -> Sepolia

Now let's try and use Wormhole. We can now even send messages from one Ethereum testnet to another Ethereum testnet.

The general flow will be:

Emit message on Goerli using already existing Wormhole contracts.
Guardians are monitoring emitted messages. Once they detect a new one, they will create and sign a VAA.
We can retrieve the VAA and submit to our receiving Sepolia contract. (this step can be abstracted away via generic relayers, we'll use those afterwards)
The Sepolia contract verifies the signature, chain id and emitter address. If all is correct, the message can be stored/processed.

Note that in all examples I'm using the current testnet versions. As Wormhole is in active development, changes to the interfaces may happen.

1. Sending the Message from Goerli

Let's start by sending the message on the Goerli testnet. We'll deploy the GoerliMessageSender contract first. We can import the Wormhole interface from the Wormhole Repository: https://github.com/wormhole-foundation/wormhole. All deployed contracts can be found here.

The interface has a publishMessage and a messageFee function we'll need.

function publishMessage(
    uint32 nonce,
    bytes memory payload,
    uint8 consistencyLevel
) external payable returns (uint64 sequence);

It takes in the following arguments:

nonce: A number assigned to each message. You can use the same nonce, if you want to batch submit multiple messages in one. We'll only submit a single message, so we can just pass a nonce of 1.
Consistency: The level of finality the guardians will reach before signing the message. For our test case purposes, 200 is fine which means instant. More information about finality can be found here.
Payload: The actual message to send as raw bytes.

The return value will be a sequence identifier number that we can use to retrieve the signed VAA.

function messageFee() external view returns (uint256);

The messageFee function gives us the cost for sending such a message. On testnet this is currently zero, so you won't need to pass any ETH, but if your message publishing fails for unknown reasons, it may be because you forgot to send ETH along.

As for the getMessageForAddress, we'll get to that in a moment.

// SPDX-License-Identifier: MIT
pragma solidity 0.8.20;

import "https://github.com/wormhole-foundation/wormhole/blob/1c0a1d7b63fc61dc751537c6c2c4d153725d1dc0/ethereum/relayers/contracts/interfaces/IWormhole.sol";

contract GoerliMessageSender {
    struct MyMessage {
        address recipient;
        string message;
    }

    address private whAddr = 0x706abc4E45D419950511e474C7B9Ed348A4a716c;
    IWormhole public immutable wormhole = IWormhole(whAddr);

    uint256 public lastMessageSequence;

    function getMessageForAddress(address recipient, string calldata message) external pure returns (bytes memory) {
        return abi.encode(MyMessage(recipient, message));
    }

    function sendMessage(
        bytes memory fullMessage
    ) public payable {
        lastMessageSequence = wormhole.publishMessage{
            value: wormhole.messageFee()
        }(1, fullMessage, 200);
    }

    function emitterAddress() public view returns (bytes32) {
        return bytes32(uint256(uint160(address(this))));
    }
}

And we'll need the emitterAddress view function. This is just for our own convenience and converts our contract address into bytes32. We'll need that to retrieve the VAA as well as double checking the emitter address on the receiver side.

// SPDX-License-Identifier: MIT
pragma solidity 0.8.20;

import "https://github.com/wormhole-foundation/wormhole/blob/1c0a1d7b63fc61dc751537c6c2c4d153725d1dc0/ethereum/relayers/contracts/interfaces/IWormhole.sol";
import "https://github.com/wormhole-foundation/wormhole/blob/1c0a1d7b63fc61dc751537c6c2c4d153725d1dc0/ethereum/relayers/contracts/interfaces/IWormholeReceiver.sol";

contract SepoliaMessageReceiver is IWormholeReceiver {
    address private whAddr = 0x4a8bc80Ed5a4067f1CCf107057b8270E0cC11A78;
    IWormhole public immutable wormhole = IWormhole(whAddr);

    struct MyMessage {
        address recipient;
        string message;
    }

    mapping(uint16 => bytes32) public registeredContracts;
    mapping(bytes32 => bool) public hasProcessedMessage;
    string[] public messageHistory;

    function registerEmitter(uint16 chainId, bytes32 emitterAddress) public {
        // require(msg.sender == owner);
        registeredContracts[chainId] = emitterAddress;
    }

    function receiveWormholeMessages(
        bytes[] memory signedVaas,
        bytes[] memory
    ) public payable override {
        (IWormhole.VM memory parsed, bool valid, string memory reason)
            = wormhole.parseAndVerifyVM(signedVaas[0]);

        require(valid, reason);
        require(
            registeredContracts[parsed.emitterChainId] == parsed.emitterAddress,
            "Emitter address not valid"
        );

        require(!hasProcessedMessage[parsed.hash]);

        MyMessage memory message = abi.decode(parsed.payload, (MyMessage));
        require(message.recipient == address(this));

        hasProcessedMessage[parsed.hash] = true;
        messageHistory.push(message.message);
    }

    function getFullMessageHistory() public view returns (string[] memory) {
        return messageHistory;
    }
}

2. Receiving the Message on Sepolia

Now we can create a contract to receive the message. We'll implement the IWormholeReceiver interface for that.

Technically we could define our own interface, since we are just submitting the signed VAA ourselves, but it's always good to follow some standards. And the interface when using generic relayers is the receiveWormholeMessages function that takes in the signed VAAs as array. So let's use that!

In our case we only send a single message, so we can just take the first element of the signedVAAs. Using wormhole.parseAndVerifyVM we will receive the results.

struct VM {
    uint8 version;
    uint32 timestamp;
    uint32 nonce;
    uint16 emitterChainId;
    bytes32 emitterAddress;
    uint64 sequence;
    uint8 consistencyLevel;
    bytes payload;
    uint32 guardianSetIndex;
    Signature[] signatures;
    bytes32 hash;
}

The payload will be the actual message.
The hash is an identifier that can be used to avoid replaying the message more than once, see our hasProcessedMessage mapping.
The emitter chain id and address can be used to make sure the message comes from the contract we care about. You will have to register the expected emitter addresses and chain ids first, see our registeredContracts mapping.
It's also best practice to encode the supposed recipient inside the payload message. You can do that for example using a struct and using abi.decode to get the struct back in Solidity. And then ensure that the recipient is actually our current contract.

Once all checks are passed, you can store the hash as replay protection and process the message.

3. Let's try on Remix!

We can just use Remix to test it. So go to https://remix.ethereum.org/ and add both our contracts.

A. Let's deploy the sender and receiver contract

Let's the deploy the contracts:

First deploy GoerliMessageSender to, you guessed it, the Goerli testnet.
Take the wormhole address for Goerli, select IWormhole from the contracts to deploy in Remix and choose 'At Address'.
Then switch your wallet to the Sepolia testnet and deploy the SepoliaMessageReceiver.

You should now have three contracts in your list as shown on the right. Of course you can use other testnets, but make sure to change the addresses according to https://book.wormhole.com/reference/contracts.html.

B. Let's register the sender with the receiver

Now let's register the sender with the receiver!

Switch back to Goerli and retrieve the emitter address by calling emitterAddress(). We'll need this helper to convert the address into bytes32 which is the expected emitter address type.
With that result, switch back to Sepolia and call registerEmitter(2, emitterAddress) where 2 stands for the chain id of Goerli.

So that means now this specific contract on the Goerli testnet is registered to send a message to us.

C. Let's send the message

Now if we want to send a message, make sure you switch back to Goerli testnet.

Copy the SepoliaMessageReceiver address and call getMessageForAddress(sepoliaMessageReceiverAddress, "Hello World!") which will encode the message for us in a way that let's us verify the intended recipient on the Sepolia side.
Now call messageFee on the IWormhole contract.
Lastly emit the message by calling sendMessage with the result from getMessageForAddress. Also make sure to pass the fee inside the 'VALUE' field. Most likely, especially on the testnets, this will actually be zero and you don't have to worry about it. But for mainnet this might be different.

D. Let's send retrieve the VAA

Great, so now the message was emitted. Unless you use generic relayers (we'll look at those next), you have to relay the message yourself. So let's first retrieve it by going to https://wormhole-v2-testnet-api.certus.one/v1/signed_vaa/2/<emitterAddress>/1. You can find the details for this over at the proto file. This file shows you the publicly available RPC messages for the Wormchain from which we have to retrieve the VAA. For mainnet the available RPCs can be found here.

Wait a few moments for the VAA to appear. Sometimes testnet, unlike mainnet, is also not working perfectly, so you might have to emit the message multiple times for it be picked up. The result should look something like:

{"vaaBytes":"AQAAAAABAK/jB/sgQgOhZXnHlytNy/piP9dWizgbPP9rTpXgS/SOHFq+iW5PzP4j6IyB1UWx/Hos6JW3Bje0jrJgqPljuPsBZFZrWAAAAAEAAgAAAAAAAAAAAAAAACyICfoR/iqwChsK5RTo2NO0QUOGAAAAAAAAAAHIAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAGhvbGE="}

You can verify the VAA on https://vaa.dev/#/parse.

E. Let's submit the VAA

Now to submit the VAA, we have to convert these base64-encoded bytes into raw bytes. You can go to https://cryptii.com/pipes/base64-to-binary, enter the vaaBytes. And on the right choose Bytes with Format Binary and Group By None.

Copy the binary result and call receiveWormholeMessages([copiedBinary],[]). This should succeed.

If you now call getFullMessageHistory() you should see our "Hello World!" message.

How this could be done in a Dapp

To use these cross-chain messages in a Dapp, you can automate the process using the wormhole-sdk. It comes with one obvious downside of course, a user has to manually relay the message, meaning signing two transactions in total with some delay. Not a great UX.

Alternatively you relay the message yourself with some backend server. Or you'll use the generic relayers. Let's try that now!

Sending a Message with Generic Relayers

Take a look at the MockRelayerIntegration, it shows how to use these generic relayers.

You once again submit the message like before, but on top you also request relaying the message. In its current version at the time of writing the interface is:

IWormholeRelayer.Send memory request = IWormholeRelayer.Send({
    targetChain: targetChainId,
    targetAddress: relayer.toWormholeFormat(address(destination)),
    refundAddress: relayer.toWormholeFormat(address(refundAddress)), // This will be ignored on the target chain if the intent is to perform a forward
    maxTransactionFee: msg.value - 3 * wormhole.messageFee() - receiverValue,
    receiverValue: receiverValue,
    relayParameters: relayer.getDefaultRelayParams()
});

relayer.send{value: msg.value - 2 * wormhole.messageFee()}(request, nonce, relayer.getDefaultRelayProvider());

You'll need to use the relayer contracts from https://book.wormhole.com/reference/contracts.html#relayer-contracts. At this time they are only available for a few networks, e.g. to send a message from Mumbai testnet (chain id 5) to BSC testnet (chain id 4).

You can test the generic relaying by using the mock relayer:

// SPDX-License-Identifier: MIT
pragma solidity 0.8.20;

import "https://github.com/wormhole-foundation/trustless-generic-relayer/blob/9e282508f796a76a8aef03ba1911b68e03c8f627/ethereum/contracts/mock/MockRelayerIntegration.sol";

contract MyWormholeBSC is MockRelayerIntegration {
    address private wormholeCore = 0x68605AD7b15c732a30b1BbC62BE8F2A509D74b4D;
    address private coreRelayer = 0xda2592C43f2e10cBBA101464326fb132eFD8cB09; 

    constructor() MockRelayerIntegration(wormholeCore, coreRelayer) {}
}

contract MyWormholeMumbai is MockRelayerIntegration {
    address private wormholeCore = 0x0CBE91CF822c73C2315FB05100C2F714765d5c20;
    address private coreRelayer = 0xFAd28FcD3B05B73bBf52A3c4d8b638dFf1c5605c; 

    constructor() MockRelayerIntegration(wormholeCore, coreRelayer) {}
}

Conclusion

Wormhole emerges as an innovative answer to the longstanding issue of blockchain interoperability, setting the stage for unprecedented possibilities within the decentralized applications sphere. Leveraging a cohesive blend of Guardians, Relayers, and xAssets, Wormhole enables smooth cross-chain communication and interaction.

Our recent exploration of this ecosystem provided us with practical insights into the process of sending messages via self-relaying, as exemplified by the successful transmission from the Goerli to Sepolia testnet. Moreover, we delved into the effective use of generic relayers to transport messages from the Mumbai to the BSC testnet. As the Wormhole ecosystem continues to mature and expand, it holds the promise of a more interconnected and versatile blockchain environment for developers and users alike.

Markus Waas

Solidity Developer

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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...
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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: Get anonymous ETH via tornado.cash. Use the ETH to pay for the hack transaction(s). Use a flash loan to decrease capital requirements. Create some imbalances given the large capital and...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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 transaction. 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...
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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...
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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...
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11/21
Sourcify: 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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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:...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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 {...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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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...
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06/23
Randomness and the Blockchain
How to achieve secure randomness for Solidity smart contracts?
Update 2023 : Ethereum transitioned to Proof of Stake! If you are interested in the randomness there, you can now use the updated info over at https://soliditydeveloper.com/prevrandao. When we talk about randomness and blockchain, these are really two problems: How to generate randomness in smart...
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How to integrate Wormhole in your smart contracts

Entering a New Era of Blockchain Interoperability

How does Wormhole ​work?

Why not Proof of Stake (PoS) for the Wormchain?

The Guardian Network

The Relayers

Let's send a message from Goerli -> Sepolia

1. Sending the Message from Goerli

2. Receiving the Message on Sepolia

3. Let's try on Remix!

A. Let's deploy the sender and receiver contract

B. Let's register the sender with the receiver

C. Let's send the message

D. Let's send retrieve the VAA

E. Let's submit the VAA

How this could be done in a Dapp

Sending a Message with Generic Relayers

Conclusion

More great blog posts from Markus Waas

Using ​the Solidity Scholar and other GPT tips

Let's dive into Uniswap v4's new features and integration

All you need to know about the latest opcode addition

A blockchain on a blockchain deep dive

Everything you need to know about Merkle trees and their future

What are the new features and how to use it

How the zero-knowledge tech works and how to use it

What is the new CrossChain support and how can you use it.

What is Hedera and how can you use it.

Blazing fast tests, no more BigNumber.js, only Solidity

How the newly finalized standard works and can help you with Defi

And how to avoid the two step approve + transferFrom with ERC721-Permit (EIP-4494)

Deploying and onboarding users to Moonbeam or Moonriver

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

How to get alerted *before* getting hacked and prevent it

All you need to know to deploy to the Ethereum mainnet

Looking at the implementation details of SushiSwap

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

How does Wormhole work?

Using the Solidity Scholar and other GPT tips

How to get alerted before getting hacked and prevent it