Smart Contracts & Pricing-Solver

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46// SPDX-License-Identifier: MITpragma solidity ^0.8.24;/// @notice Holds a buyer's funds until both sides agree, or until the deadline/// passes and the buyer takes them back. Deliberately small: every line here is/// a line that has to be audited, and value is on the other side of it.contract Escrow {    address public immutable buyer;    address public immutable seller;    uint256 public immutable deadline;    enum State { Funded, Released, Refunded }    State public state = State.Funded;    error NotParty();    error WrongState();    error TooEarly();    constructor(address _seller, uint256 _deadline) payable {        require(msg.value > 0, "no funds");        buyer = msg.sender;        seller = _seller;        deadline = _deadline;    }    /// Effects before interactions: the state is final before any ether moves,    /// so a malicious receiver that calls back in finds nothing left to take.    function release() external {        if (msg.sender != buyer) revert NotParty();        if (state != State.Funded) revert WrongState();        state = State.Released;        (bool ok, ) = seller.call{value: address(this).balance}("");        require(ok, "transfer failed");    }    function refund() external {        if (msg.sender != buyer) revert NotParty();        if (state != State.Funded) revert WrongState();        if (block.timestamp < deadline) revert TooEarly();        state = State.Refunded;        (bool ok, ) = buyer.call{value: address(this).balance}("");        require(ok, "transfer failed");    }}

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41// SPDX-License-Identifier: MITpragma solidity ^0.8.24;import "forge-std/Test.sol";import "../src/Escrow.sol";/// A reentrant seller. This is the test that matters: it does not check that the/// happy path works, it checks that the obvious attack fails.contract EvilSeller {    Escrow public target;    uint256 public hits;    receive() external payable {        hits++;        if (hits < 2) target.release();   // re-enter mid-transfer    }}contract EscrowTest is Test {    function test_ReentrancyCannotDrain() public {        EvilSeller evil = new EvilSeller();        Escrow escrow = new Escrow{value: 1 ether}(address(evil), block.timestamp + 1 days);        evil.target = escrow;        vm.prank(address(this));        escrow.release();        // The re-entrant call hits WrongState and reverts, so exactly one        // transfer happens and the contract is empty rather than overdrawn.        assertEq(address(escrow).balance, 0);        assertEq(address(evil).balance, 1 ether);    }    function testFuzz_RefundOnlyAfterDeadline(uint256 t) public {        vm.assume(t < 1 days);        Escrow escrow = new Escrow{value: 1 ether}(address(0xBEEF), block.timestamp + 1 days);        vm.warp(block.timestamp + t);        vm.expectRevert(Escrow.TooEarly.selector);        escrow.refund();    }}