Solidity 103

I have recently been revising Solidity to consolidate the details, and am writing a "WTF Simplified Introduction to Solidity" for beginners to use (programming experts can find other tutorials), with weekly updates of 1-3 lectures.

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in this lesson, we'll introduce Upgradeable Contract, the sample contracts used for teaching are simplified from OpenZeppelin contracts, they may pose security issues, DO NOT USE IN PRODUCTION.

Upgradeable Contract

If you understand proxy contracts, it is easy to understand upgradeable contracts. It is a proxy contract that can change the logic contract.

Simple Implementation

Below we implement a simple upgradeable contract that includes 3 contracts: the proxy contract, the old logic contract, and the new logic contract.

Proxy Contract

This proxy contract is simpler than that in Lecture 46. We didn't use inline assembly in its fallback() function, but only used implementation.delegatecall(msg.data);. Therefore, the callback function does not return a value, but it is sufficient for teaching purposes.

It contains 3 variables:

• implementation: The logic contract address.
• admin: Admin address.
• words: String that can be changed through a function in the logic contract.

It contains 3 functions:

• Constructor: Initializes admin and logic contract addresses.
• fallback(): Callback function, delegates the call to the logic contract.
• upgrade(): The upgrade function, changes the logic contract's address, and can only be called by admin.

// SPDX-License-Identifier: MIT
// wtf.academy
pragma solidity ^0.8.21;

// simple upgradeable contract, the admin could change the logic contract's address by calling the upgrade function, thus changing the contract logic
// FOR TEACHING PURPOSE ONLY, DO NOT USE IN PRODUCTION
contract SimpleUpgrade {
    // logic contract's address
    address public implementation; 

    // admin address
    address public admin;

    // string variable, could be changed by the logic contract's function
    string public words; 

    // constructor, initializing admin address and logic contract's address
    constructor(address _implementation){
        admin = msg.sender;
        implementation = _implementation;
    }

    // fallback function, delegates function call to logic contract
    fallback() external payable {
        (bool success, bytes memory data) = implementation.delegatecall(msg.data);
    }

    // upgrade function, changes the logic contract's address, can only be called by admin
    function upgrade(address newImplementation) external {
        require(msg.sender == admin);
        implementation = newImplementation;
    }
}

Old Logic Contract

This logic contract includes 3 state variables and is consistent with the proxy contract to prevent slot conflicts. It only has one function foo(), which changes the value of words in the proxy contract to "old".

// Logic contract 1
contract Logic1 {
    // State variables consistent with Proxy contract to prevent slot conflicts
    address public implementation; 
    address public admin;
    // String that can be changed through the function of the logic contract  
    string public words; 

    // Change state variables in Proxy contract, selector: 0xc2985578
    function foo() public {
        words = "old";
    }
}

New Logic Contract

This logic contract contains 3 state variables, consistent with the proxy contract to prevent slot conflicts. It has only one function, foo(), which changes the value of words in the proxy contract to "new".

// Logic Contract 2
contract Logic2 {
    // State variables consistent with a proxy contract to prevent slot collisions
    address public implementation; 
    address public admin;
    // String that can be changed through the function of the logic contract  
    string public words; 

    // Change state variables in Proxy contract, selector: 0xc2985578
    function foo() public{
        words = "new";
    }
}

Implementation with Remix

1. Deploy the old and new logic contracts Logic1 and Logic2.

   
   

2. Deploy the upgradeable contract SimpleUpgrade and set the implementation address to the address of the old logic contract.

   

3. Use the selector 0xc2985578 to call the foo() function of the old logic contract Logic1 in the proxy contract and change the value of words to "old".

   

4. Call upgrade() to set the implementation address to the address of the new logic contract Logic2.

   

5. Use the selector 0xc2985578 to call the foo() function of the new logic contract Logic2 in the proxy contract and change the value of words to "new".

   

Summary

In this lesson, we introduced a simple upgradeable contract. It is a proxy contract that can change the logic contract and add upgrade functionality to immutable smart contracts. However, this contract has a problem of selector conflict and poses security risks. Later, we will introduce the upgradeable contract standards that solve this vulnerability: Transparent Proxy and UUPS.