Withdrawal patterns in Blockchain / Solidity - Mini Project: Build & Apply

Withdrawal Patterns

📖 Scenario: You are building a simple smart contract that manages user balances and allows withdrawals. To keep the contract safe, you want to implement a withdrawal pattern that prevents common security issues like reentrancy attacks.

🎯 Goal: Create a smart contract that stores user balances, allows deposits, and implements a safe withdrawal pattern where users can withdraw their funds securely.

📋 What You'll Learn

Create a mapping called balances to store user balances.

Create a function deposit that lets users add funds to their balance.

Create a function withdraw that lets users withdraw their balance safely using the withdrawal pattern.

Use the withdrawal pattern by first setting the user's balance to zero before sending funds.

💡 Why This Matters

🌍 Real World

Withdrawal patterns are essential in smart contracts to protect user funds and prevent attacks like reentrancy.

💼 Career

Understanding safe withdrawal patterns is critical for blockchain developers to write secure contracts and protect assets.

1

Set up the balances mapping

Create a public mapping called balances that maps address to uint to store user balances.

Blockchain / Solidity

// Your code here

Need a hint?

Use mapping(address => uint) public balances; to store balances for each user address.

2

Add deposit function

Create a public payable function called deposit that increases the sender's balance by msg.value.

Blockchain / Solidity

mapping(address => uint) public balances;
// Your code here

Need a hint?

Use balances[msg.sender] += msg.value; inside the deposit function.

3

Add safe withdraw function

Create a public function called withdraw that lets the sender withdraw their entire balance safely. First, store the sender's balance in a local variable amount. Then set the sender's balance to zero. Finally, send amount to the sender using payable(msg.sender).transfer(amount);.

Blockchain / Solidity

mapping(address => uint) public balances;

function deposit() public payable {
    balances[msg.sender] += msg.value;
}

// Your code here

Need a hint?

Remember to set the balance to zero before transferring funds to prevent reentrancy.

4

Test withdrawal output

Add a public view function called getBalance that returns the balance of the sender. Then, write a comment showing the expected output after a deposit of 1 ether and a withdrawal.

Blockchain / Solidity

mapping(address => uint) public balances;

function deposit() public payable {
    balances[msg.sender] += msg.value;
}

function withdraw() public {
    uint amount = balances[msg.sender];
    require(amount > 0, "No balance to withdraw");
    balances[msg.sender] = 0;
    payable(msg.sender).transfer(amount);
}

// Your code here

Need a hint?

The getBalance function helps check the user's balance after withdrawal.