Wallet Contract — Secure ETH Custody (Solidity + Foundry)

A minimal, fully-tested Ethereum wallet smart contract for secure ETH deposits, owner-restricted withdrawals, and ownership transfers.
Built with Solidity 0.8.20 and Foundry, this project demonstrates clean contract architecture and production-grade testing.

---

Table of Contents

• Overview
• Features
• Contract Architecture
• Events
• Access Control
• Testing (Foundry)
• Running Tests
• Project Structure
• Security Considerations
• Future Improvements
• License

---

Overview

This wallet contract implements core Ethereum concepts:

• ownership & access control
• ETH deposits & withdrawals
• event logging
• fallback & receive handlers
• comprehensive unit tests (Foundry)

It serves as a learning-friendly yet production-accurate example of on-chain value management, similar to real wallets, treasuries, escrow systems, and DeFi modules.

---

Features

• Deposit ETH using deposit() or direct transfers
• Track last deposit (amount, sender, timestamp)
• Owner-only withdrawals (restricted via modifier)
• Ownership transfer with changeOwner()
• Fully compatible with ETH transfers (receive & fallback)
• Complete Foundry test suite covering:
  • deposits
  • withdrawals
  • reverts
  • permission checks
  • ownership changes

---

Contract Architecture

Core Variables

• owner — address controlling the wallet
• Deposit tracking:
  • lastDepositAmount
  • lastDepositTime
  • lastDepositFrom

Key Functions

• deposit() — external payable ETH deposit
• withdraw(uint256 amount) — owner-only withdrawal
• changeOwner(address newOwner) — assign new owner
• getLastDeposit() — deposit info
• getTotalBalance() — contract ETH balance

Fallback Handlers

• receive() — accepts plain ETH transfers
• fallback() — catches unknown calldata

---

Events

Event	Description
Deposit(address from, uint256 amount, uint256 timestamp)	Emitted when ETH is deposited
Withdrawal(address to, uint256 amount, uint256 timestamp)	Emitted when owner withdraws ETH
OwnerChanged(address oldOwner, address newOwner, uint256 timestamp)	Emitted when ownership changes

---

Access Control

The wallet uses a strict permission model:

• Only the owner can withdraw funds
• Only the owner can change ownership

Enforced via: require(msg.sender == owner, "Only owner can call this function");

Unauthorized access attempts revert immediately.

Testing (Foundry)

This project includes a 9-test Foundry suite validating:

• correct owner initialization
• deposit mechanics
• last deposit tracking
• owner-only withdrawals
• insufficient balance reverts
• unauthorized access reverts
• ownership transfers
• new owner permissions

Foundry cheatcodes used:

vm.deal() — fund accounts

vm.prank() — simulate msg.sender

vm.expectRevert() — check revert messages

assertEq() — validate state/balances

Running Tests

1. Install Foundry curl -L https://foundry.paradigm.xyz | bash foundryup

2. Build forge build

3. Run tests forge test -vv

Project Structure

Main smart contract path: wallet-contract/src/Wallet.sol Test smart contract path: wallet-contract/test/Wallet.t.sol

Security Considerations

No reentrancy risk (transfer() gas stipend = 2300)

Only owner may withdraw funds

Ownership cannot be set to zero address

Minimal state surface

Assumes trusted owner (centralized wallet model)

Future Improvements

Multi-signature support

ERC20 support

Pausable withdrawals

Emergency admin features

EIP-712 meta-transactions

Withdrawal recipient parameter

Full deposit history tracking

License

MIT License — free to use, modify, and distribute.