Understanding Contract Upgradability In Ethereum Blockchain

Overview

In this blog post, we will delve into an important, yet often overlooked feature in Ethereum smart contracts – upgradability. The Ethereum blockchain as a decentralized platform for applications provides powerful capabilities, but it introduces unique challenges. One such challenge is that once a smart contract is deployed to the blockchain, its code cannot be modified. Hence, a probable solution is making smart contracts upgradeable.

Understanding Upgradability

A contract is termed upgradeable if its functionality can be changed without changing the contract’s address. This implies that any data stored in the contract will not be lost, a critical requirement for any dApp operating in production.

The Proxy Contract Method

The most common method to make a contract upgradeable is by implementing a proxy contract system. The method separates the storage and logic into two separate contracts – a Proxy contract (stores data) and an Implementation contract (stores logic). All external function calls are routed through the Proxy contract, which then delegates the execution to the Implementation contract.

Here's a simple Proxy contract written in Solidity, the commonly used language for Ethereum smart contracts:

pragma solidity ^0.6.0;

contract Proxy {
    address public implementation;

    constructor(address _implementation) public {
        implementation = _implementation;
    }

    fallback() external payable {
        address _impl = implementation;
        require(_impl != address(0));
        assembly {
          let ptr := mload(0x40)
          calldatacopy(ptr, 0, calldatasize())
          let result := delegatecall(gas(), _impl, ptr, calldatasize(), 0, 0)
          let size := returndatasize()
          returndatacopy(ptr, 0, size)

          switch result
          case 0 { revert(ptr, size) }
          default { return(ptr, size) }
        }
    }
}

In the above code snippet, an external function call to the Proxy is redirected to the Implementation contract using low-level delegatecall.

Upgrading the Smart Contract

In a Proxy contract system, upgrading the smart contract involves deploying a new Implementation contract and updating the Implementation address in the Proxy contract. Take note that the data in the Proxy contract remains intact.

function upgrade(address newImplementation) external {
    require(msg.sender == owner, "Only owner can upgrade");
    implementation = newImplementation;
}

In this function, the owner of the contract can change the implementation address to a new version.

Conclusion

The Proxy contract pattern allows for more flexibility in the blockchain environment, and it's a practical solution to one of Ethereum’s hard limitations. Developers need to understand its benefits and potential pitfalls and ensure they balance performance, complexity, and gas costs. Always plan for upgradability.