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?
delegatecall to forward it to a second logic contract. As a reminder, delegatecall will execute a function defined in the called contract (logic), but within the context of the calling contract (proxy). In other words, we can have our logic defined separately from our data.
This allows us to change the logic contract without changing the underlying data. All you need to do is change the address of the logic contract defined in our proxy, usually done via governance or at a minimum controlled via a multi-sig wallet.
With this proxy pattern we effectively have upgradability for smart contracts, but it comes with some limitations.
- What if you want to upgrade only a small part of a complex contract? You will still need to upgrade to a completely new logic contract. This makes it more difficult to see what actually changed.
- Reusability of logic contracts by multiple proxies is possible, but it's not very practicable. You can only create identical proxy instances using one logic contract. There is no way to combine logic contracts or use only parts of one.
- You cannot have a modular permission system which for example would allow some entities to only upgrade a subset of existing functions. Instead it's an all or nothing approach.
- One must take special care when accessing data within the logic contract after upgrades, because the data in the proxy contract never changes with upgrades. That means if you were to stop using a state variable in the logic contract, you would still need to keep it in the variable definitions. And when you add state variables, you may only append them to the end of the definitions.
- Logic contracts can easily reach the 24kb max contract size limit.
So this is where diamonds come in. The core idea is identical to the proxy pattern, but with the difference that you can have multiple logic contracts.
- When you have multiple logic contracts, how can the diamond storage know which one to delegate the call to?
- How can multiple logic contracts share the same state without overwriting the data?
- Can the logic contracts share data between each other?
DiamondCut: The managing interface
The diamond storage must implement the diamondCut function. With this function one can (un-)register functions for a specific logic contract. Once a function is registered, the diamond storage can recognize the function selector of any call within its fallback function, retrieve the correct facet address and then run delegatecall for it.
If you remember the PolyNetwork hack, you will know that a function selector collision is possible, meaning two different functions result in the same 4 bytes function signature. This is easily prevented by a simple check which prevents adding function selectors that already exist. The diamond reference implementations perform this check when upgrading.
Great, now we know how the delegatecall works. But how can we ensure the data integrity?
interface IDiamondCut {
enum FacetCutAction {Add, Replace, Remove}
struct FacetCut {
address facetAddress;
FacetCutAction action;
bytes4[] functionSelectors;
}
function diamondCut(
FacetCut[] calldata _diamondCut,
address _init,
bytes calldata _calldata
) external;
}contract FacetA {
struct FacetData {
address owner;
bytes32 dataA;
}
function facetData()
internal
pure
returns(FacetData storage facetData) {
bytes32 storagePosition = keccak256("diamond.storage.FacetA");
assembly {facetData.slot := storagePosition}
}
function setDataA(bytes32 _dataA) external {
FacetData storage facetData = facetData();
require(facetData.owner == msg.sender, "Must be owner.");
facetData.dataA = _dataA;
}
function getDataA() external view returns (bytes32) {
return facetData().dataA;
}
}DiamondStorage: The data keeper
To avoid any storage slot collisions, we can use a simple trick for where to store the data. While usually Solidity will store data in subsequent slots as defined by the state variables, we can also explicitly set the storage slot with assembly.
When doing so we only need to ensure the storage slot is at a unique position which won't create conflicts with other facets. One can easily achieve this by hashing the facet name.
Now whenever we want to read or write FacetData, we don't have to worry about overwriting other facets data, because our storage slot position is unique. And you can of course access this data from any other facet as well, you just need to inherit from FacetA and use the facetData function. That's why it's particularly helpful for creating reusable facets.
However an alternative design would be the AppStorage pattern which we won't go into detail here, but it sacrifices reusability for slightly improved code readability. AppStorage is useful when sharing state variables between facets that are specific to a project and won't be reused in diamonds for other projects or protocols.
DiamondLoupe: Finding out which functions are supported
interface IDiamondLoupe {
struct Facet {
address facetAddress;
bytes4[] functionSelectors;
}
function facets() external view returns (Facet[] memory facets_);
function facetFunctionSelectors(address _facet) external view returns (bytes4[] memory facetFunctionSelectors_);
function facetAddresses() external view returns (address[] memory facetAddresses_);
function facetAddress(bytes4 _functionSelector) external view returns (address facetAddress_);
}While these functions would be optional to have if one was to rely solely on events with something like The Graph, it was still decided to have the loupe within the standard, because they significantly improve the usability with deployed contracts.
So how would you actually implement all this?
How to implement a diamond
There is currently no reference implementation available via the Openzeppelin contracts, but it might happen soon. The EIP author Nick Mudge created three reference implementations which are all audited:
- diamond-1-hardhat (Simple implementation)
- diamond-2-hardhat (Gas-optimized)
- diamond-3-hardhat (Simple loupe functions)
Which one should you choose? They all do the same thing, so it doesn't matter too much. If you plan to do many upgrades and care about gas costs, consider going with diamond-2. It contains some complicated bitwise operations to reduce the storage space and will save you roughly 80,000 gas for every 20 functions added. Otherwise diamond-1 is probably a better choice since the code is much more readable.
This is the core logic of the diamond-1 for adding and removing functions with some checks removed for better readability:
struct FacetAddressAndSelectorPosition {
address facetAddress;
uint16 selectorPosition;
}
struct DiamondStorage {
// function selector => facet address and selector position in selectors array
mapping(bytes4 => FacetAddressAndSelectorPosition) facetAddressAndSelectorPosition;
bytes4[] selectors;
}Basically one maintains an array of all available function signatures with a respective mapping which holds the facet address. The position in the mapping is required when removing a function again.
Adding functions
To add a new function is then as simple as
- adding it to the array
- updating the mapping
- incrementing the total function count
You can find the full source code example here.
function addFunctions(
address _facetAddr,
bytes4[] memory _functionSelectors
) internal {
DiamondStorage storage ds = diamondStorage();
uint16 selectorCount = uint16(ds.selectors.length);
for (uint256 idx; idx < _functionSelectors.length; idx++) {
bytes4 selector = _functionSelectors[idx];
ds.facetAddressAndSelectorPosition[selector] =
FacetAddressAndSelectorPosition(_facetAddr, selectorCount);
ds.selectors.push(selector);
selectorCount++;
}
}function removeFunctions(
address _facetAddr,
bytes4[] memory _functionSelectors
) internal {
DiamondStorage storage ds = diamondStorage();
uint256 selectorCount = ds.selectors.length;
for (uint256 idx; idx < _functionSelectors.length; idx++) {
bytes4 selector = _functionSelectors[idx];
FacetAddressAndSelectorPosition memory old =
ds.facetAddressAndSelectorPosition[selector];
selectorCount--;
if (old.selectorPosition != selectorCount) {
// replace selector with last selector
bytes4 lastSelector = ds.selectors[selectorCount];
ds.selectors[old.selectorPosition] = lastSelector;
ds.facetAddressAndSelectorPosition[lastSelector]
.selectorPosition = old.selectorPosition;
}
// delete last selector
ds.selectors.pop();
delete ds.facetAddressAndSelectorPosition[selector];
}
}Removing functions
Now for removing a function, you can find out the position in the array by checking its position from the mapping (selectorPosition).
When removing elements from the middle of an array in Solidity, one creates empty slots in the array. That's why we also have to copy over the currently last selector to the empty slot and call pop.
You can find the full source code example here.
How to implement the Diamond Storage?
The storage itself consists mainly of the fallback function which
- takes the function selector from msg.sig
- reads the responsible facet address from our mapping which is stored at the predefined slot
DIAMOND_STORAGE_POSITIONto not collide with any other data - forwards the call to the facet using delegatecall
You can find the full source code example here.
fallback() external payable {
LibDiamond.DiamondStorage storage ds;
bytes32 position = LibDiamond.DIAMOND_STORAGE_POSITION;
assembly {
ds.slot := position
}
address facet =
ds.facetAddressAndSelectorPosition[msg.sig].facetAddress;
require(facet != address(0));
assembly {
calldatacopy(0, 0, calldatasize())
let result := delegatecall(
gas(),
facet,
0,
calldatasize(),
0,
0,
)
returndatacopy(0, 0, returndatasize())
switch result
case 0 {
revert(0, returndatasize())
}
default {
return(0, returndatasize())
}
}
}This is also how you would use this yourself, make the diamond storage your main contract and add to it any facets you require. A small repository which gives you an example on how people are using that is here.
Should you use Diamonds?
Now with all that said, which one is better, proxy upgrade patterns or diamonds? Let's look at the pros and cons.
Pros:
- Facet reusability
- Modular upgradability
- Modular permission system
- Storage slot management
- Avoiding max contract size issues
Cons:
- More Complexity
- Harder to maintain
- Not many big real life projects yet
- Not supported by tools like Etherscan, but an alternative for at least Etherscan exists: Louper
The bottom line is diamonds are still bleeding edge and not a finalized or widely used standard. If the proxy upgrade pattern is good enough for you, go with that one. It will be easier to implement, maintain and Etherscan comes with full proxy support.
But if you want to take advantage of the additional features from diamonds, this is a perfectly reasonable alternative by now. A diamond is useful for organizing contract functionality into different sets of functionality that are accessible at the same address and share the same state variables. Say someone wants to implement ERC721 and ERC1155 in the same contract. It could be implemented as a diamond with one ERC721Facet and one ERC1155Facet. Plus any custom functionality could be added with more facets.
Diamonds might see more usage in the future once contract systems require more sophistication and tools are supporting it.
Solidity Developer
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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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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:...
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...
How to get a Solidity developer job?
There are many ways to get a Solidity job and it might be easier than you think!
You have mastered the basics of Solidity, created your first few useful projects and now want to get your hands on some real-world projects. Getting a Solidity developer job might be easier than you think. There are generally plenty of options to choose from and often times not a lot of...
Design Pattern Solidity: Mock contracts for testing
Why you should make fun of your contracts
Mock objects are a common design pattern in object-oriented programming. Coming from the old French word 'mocquer' with the meaning of 'making fun of', it evolved to 'imitating something real' which is actually what we are doing in programming. Please only make fun of your smart contracts if you...
Kickstart your Dapp frontend development with create-eth-app
An overview on how to use the app and its features
Last time we looked at the big picture of Solidity and already mentioned the create-eth-app. Now you will find out how to use it, what features are integrated and additional ideas on how to expand on it. Started by Paul Razvan Berg, the founder of sablier, this app will kickstart your frontend...
The big picture of Solidity and Blockchain development in 2020
Overview of the most important technologies, services and tools that you need to know
Now, I do not know about you, but I remember when I first started with Solidity development being very confused by all the tools and services and how they work in connection with one another. If you are like me, this overview will help you understand the big picture of Solidity development. As I...
Design Pattern Solidity: Free up unused storage
Why you should clean up after yourself
You may or may not be used to a garbage collectors in your previous programming language. There is no such thing in Solidity and even if there was a similar concept, you would still be better off managing state data yourself. Only you as a programmer can know exactly which data will not be used...
How to setup Solidity Developer Environment on Windows
What you need to know about developing on Windows
Using Windows for development, especially for Solidity development, can be a pain sometimes, but it does not have to be. Once you have configured your environment properly, it can actually be extremely efficient and Windows is a very, very stable OS, so your overall experience can be amazing. The...
Avoiding out of gas for Truffle tests
How you do not have to worry about gas in tests anymore
You have probably seen this error message a lot of times: Error: VM Exception while processing transaction: out of gas Disclaimer : Unfortunately, this does not always actually mean what it is saying when using Truffle , especially for older versions. It can occur for various reasons and might be...
Design Pattern Solidity: Stages
How you can design stages in your contract
Closely related to the concept of finite-state machines, this pattern will help you restrict functions in your contract. You will find a lot of situations where it might be useful. Any time a contract should allow function calls only in certain stages. Let's look at an example: contract Pool {...
Web3 1.2.5: Revert reason strings
How to use the new feature
A new Web3 version was just released and it comes with a new feature that should make your life easier. With the latest version 1.2.5, you can now see the the revert reason if you use the new handleRevert option. You can activate it easily by using web3.eth.handleRevert = true . Now when you use...
Gaining back control of the internet
How Ocelot is decentralizing cloud computing
I recently came across an ambitious company that will completely redefine the way we are using the internet. Or rather, the way we are using its underlying infrastructure which ultimately is the internet. While looking at their offering, I also learned how to get anonymous cloud machines, you...
Devcon 5 - Review
Impressions from the conference
I had a lot to catch up on after Devcon. Also things didn't go quite as planned, so please excuse my delayed review! This year's Devcon was certainly stormy with a big typhoon warning already on day 1. Luckily (for us, not the people in Tokyo), it went right past Osaka. Nevertheless, a lot of...
Devcon 5 - Information, Events, Links, Telegram
What you need to know
Devcon 5 is coming up soon and there are already lots of events available, information about Osaka and more. Here is a short overview: Events Events Calendar Events Google Docs Events Kickback Most events are in all three, but if you really want to see all, you will have to look at all three...
Design Pattern Solidity: Off-chain beats on-chain
Why you should do as much as possible off-chain
As you might have realized, Ethereum transactions are anything but cheap. In particular, if you are computing complex things or storing a lot of data. That means sometimes we cannot put all logic inside Solidity. Instead, we can utilize off-chain computations to help us. A very simple example...
Design Pattern Solidity: Initialize Contract after Deployment
How to use the Initializable pattern
There are a few reasons why you might want to initialize a contract after deployment and not directly by passing constructor arguments. But first let's look at an example: contract MyCrowdsale { uint256 rate; function initialize(uint256 _rate) public { rate = _rate; } } What's the advantage over...
Consensys Blockchain Jobs Report
What the current blockchain job market looks like
Consensys published their blockchain jobs report which you can checkout in their Blockchain Developer Job Kit. The most interesting aspects are Blockchain developer jobs have been growing at a rate of 33x of the previous year according to LinkedIns jobs report Typical salary is about...
Provable — Randomness Oracle
How the Oraclize random number generator works
One particularly interesting approach by Provable is the usage of a hardware security device, namely the Ledger Nano S. It uses a trusted execution environment to generate random numbers and provides a Provable Connector Contract as interface. How to use the Provable Randomness Oracle? Use the...
Solidity Design Patterns: Multiply before Dividing
Why the correct order matters!
There has been a lot of progress since the beginning of Ethereum about best practices in Solidity. Unfortunately, I have the feeling that most of the knowledge is within the circle of experienced people and there aren’t that many online resources about it. That is why I would like to start this...
Devcon 5 Applications closing in one week
Devcon 5 Applications closing
Watch out for the Devcon 5 applications. You only have one week left to apply either as Buidler Student Scholarship Press Devcon is by far the biggest and most impressive Ethereum conference in the world. And it's full of developers! I am especially excited about the cool location this year in...
Randomness and the Blockchain
How to achieve secure randomness for Solidity smart contracts?
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...