📜 [專欄新文章] Reason Why You Should Use EIP1167 Proxy Contract. (With Tutorial)
✍️ Ping Chen
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EIP1167 minimal proxy contract is a standardized, gas-efficient way to deploy a bunch of contract clones from a factory.
1. Who may consider using EIP1167
For some DApp that are creating clones of a contract for its users, a “factory pattern” is usually introduced. Users simply interact with the factory to get a copy. For example, Gnosis Multisig Wallet has a factory. So, instead of copy-and-paste the source code to Remix, compile, key in some parameters, and deploy it by yourself, you can just ask the factory to create a wallet for you since the contract code has already been on-chain.
The problem is: we need standalone contract instances for each user, but then we’ll have many copies of the same bytecode on the blockchain, which seems redundant. Take multisig wallet as an example, different multisig wallet instances have separate addresses to receive assets and store the wallet’s owners’ addresses, but they can share the same program logic by referring to the same library. We call them ‘proxy contracts’.
One of the most famous proxy contract users is Uniswap. It also has a factory pattern to create exchanges for each ERC20 tokens. Different from Gnosis Multisig, Uniswap only has one exchange instance that contains full bytecode as the program logic, and the remainders are all proxies. So, when you go to Etherscan to check out the code, you’ll see a short bytecode, which is unlikely an implementation of an exchange.
0x3660006000376110006000366000732157a7894439191e520825fe9399ab8655e0f7085af41558576110006000f3
What it does is blindly relay every incoming transaction to the reference contract 0x2157a7894439191e520825fe9399ab8655e0f708by delegatecall.
Every proxy is a 100% replica of that contract but serving for different tokens.
The length of the creation code of Uniswap exchange implementation is 12468 bytes. A proxy contract, however, has only 46 bytes, which is much more gas efficient. So, if your DApp is in a scenario of creating copies of a contract, no matter for each user, each token, or what else, you may consider using proxy contracts to save gas.
2. Why use EIP1167
According to the proposal, EIP is a “minimal proxy contract”. It is currently the known shortest(in bytecode) and lowest gas consumption overhead implementation of proxy contract. Though most ERCs are protocols or interfaces, EIP1167 is the “best practice” of a proxy contract. It uses some EVM black magic to optimize performance.
EIP1167 not only minimizes length, but it is also literally a “minimal” proxy that does nothing but proxying. It minimizes trust. Unlike other upgradable proxy contracts that rely on the honesty of their administrator (who can change the implementation), address in EIP1167 is hardcoded in bytecode and remain unchangeable.
That brings convenience to the community.
Etherscan automatically displays code for EIP1167 proxies.
When you see an EIP1167 proxy, you can definitely regard it as the contract that it points to. For instance, if Etherscan finds a contract meets the format of EIP1167, and the reference implementation’s code has been published, it will automatically use that code for the proxy contract. Unfortunately, non-standard EIP1167 proxies like Uniswap will not benefit from this kind of network effect.
3. How to upgrade a contract to EIP1167 compatible
*Please read all the steps before use, otherwise there might have problems.
A. Build a clone factory
For Vyper, there’s a function create_with_code_of(address)that creates a proxy and returns its address. For Solidity, you may find a reference implementation here.
function createClone(address target) internal returns (address result){ bytes20 targetBytes = bytes20(target); assembly { let clone := mload(0x40) mstore(clone, 0x3d602d80600a3d3981f3363d3d373d3d3d363d73000000000000000000000000) mstore(add(clone, 0x14), targetBytes) mstore(add(clone, 0x28), 0x5af43d82803e903d91602b57fd5bf30000000000000000000000000000000000) result := create(0, clone, 0x37) }}
You can either deploy the implementation contract first or deploy it with the factory’s constructor. I’ll suggest the former, so you can optimize it with higher runs.
contract WalletFactory is CloneFactory { address Template = "0xc0ffee"; function createWallet() external returns (address newWallet) { newWallet = createClone(Template); }}
B. Replace constructor with initializer
When it comes to a contract, there are two kinds of code: creation code and runtime code. Runtime code is the actual business logic stored in the contract’s code slot. Creation code, on the other hand, is runtime code plus an initialization process. When you compile a solidity source code, the output bytecode you get is creation code. And the permanent bytecode you can find on the blockchain is runtime code.
For EIP1167 proxies, we say it ‘clones’ a contract. It actually clones a contract’s runtime code. But if the contract that it is cloning has a constructor, the clone is not 100% precise. So, we need to slightly modify our implementation contract. Replace the constructor with an ‘initializer’, which is part of the permanent code but can only be called once.
// constructorconstructor(address _owner) external { owner = _owner;}// initializerfunction set(address _owner) external { require(owner == address(0)); owner = _owner;}
Mind that initializer is not a constructor, so theoretically it can be called multiple times. You need to maintain the edge case by yourself. Take the code above as an example, when the contract is initialized, the owner must never be set to 0, or anyone can modify it.
C. Don’t assign value outside a function
As mentioned, a creation code contains runtime code and initialization process. A so-called “initialization process” is not only a constructor but also all the variable assignments outside a function. If an EIP1167 proxy points to a contract that assigns value outside a function, it will again have different behavior. We need to remove them.
There are two approaches to solve this problem. The first one is to turn all the variables that need to be assigned to constant. By doing so, they are no longer a variable written in the contract’s storage, but a constant value that hardcoded everywhere it is used.
bytes32 public constant symbol = "4441490000000000000000000000000000000000000000000000000000000000";uint256 public constant decimals = 18;
Second, if you really want to assign a non-constant variable while initializing, then just add it to the initializer.
mapping(address => bool) public isOwner;uint public dailyWithdrawLimit;uint public signaturesRequired;
function set(address[] _owner, uint limit, uint required) external { require(dailyWithdrawLimit == 0 && signaturesRequired == 0); dailyWithdrawLimit = limit; signaturesRequired = required; //DO SOMETHING ELSE}
Our ultimate goal is to eliminate the difference between runtime code and creation code, so EIP1167 proxy can 100% imitate its implementation.
D. Put them all together
A proxy contract pattern splits the deployment process into two. But the factory can combine two steps into one, so users won’t feel different.
contract multisigWallet { //wallet interfaces function set(address[] owners, uint required, uint limit) external;}contract walletFactory is cloneFactory { address constant template = "0xdeadbeef"; function create(address[] owners, uint required, uint limit) external returns (address) { address wallet = createClone(template); multisigWallet(wallet).set(owners, required, limit); return wallet; }}
Since both the factory and the clone/proxy has exactly the same interface, no modification is required for all the existing DApp, webpage, and tools, just enjoy the benefit of proxy contracts!
4. Drawbacks
Though proxy contract can lower the storage fee of deploying multiple clones, it will slightly increase the gas cost of each operation in the future due to the usage of delegatecall. So, if the contract is not so long(in bytes), and you expect it’ll be called millions of times, it’ll eventually be more efficient to not use EIP1167 proxies.
In addition, proxy pattern also introduces a different attack vector to the system. For EIP1167 proxies, trust is minimized since the address they point to is hardcoded in bytecode. But, if the reference contract is not permanent, some problems may happen.
You might ever hear of parity multisig wallet hack. There are multiple proxies(not EIP1167) that refer to the same implementation. However, the wallet has a self-destruct function, which empties both the storage and the code of a contract. Unfortunately, there was a bug in Parity wallet’s access control and someone accidentally gained the ownership of the original implementation. That did not directly steal assets from other parity wallets, but then the hacker deleted the original implementation, making all the remaining wallets a shell without functionality, and lock assets in it forever.
https://cointelegraph.com/news/parity-multisig-wallet-hacked-or-how-come
Conclusion
In brief, the proxy factory pattern helps you to deploy a bunch of contract clones with a considerably lower gas cost. EIP1167 defines a bytecode format standard for minimal proxy and it is supported by Etherscan.
To upgrade a contract to EIP1167 compatible, you have to remove both constructor and variable assignment outside a function. So that runtime code will contain all business logic that proxies may need.
Here’s a use case of EIP1167 proxy contract: create adapters for ERC1155 tokens to support ERC20 interface.
pelith/erc-1155-adapter
References
https://eips.ethereum.org/EIPS/eip-1167
https://blog.openzeppelin.com/on-the-parity-wallet-multisig-hack-405a8c12e8f7/
Donation:
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Reason Why You Should Use EIP1167 Proxy Contract. (With Tutorial) was originally published in Taipei Ethereum Meetup on Medium, where people are continuing the conversation by highlighting and responding to this story.
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