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.. index:: purchase, remote purchase, escrow
********************
Safe Remote Purchase
********************
::
pragma solidity >=0.4.22 <0.6.0;
contract Purchase {
uint public value;
address payable public seller;
address payable public buyer;
enum State { Created, Locked, Inactive }
State public state;
// Ensure that `msg.value` is an even number.
// Division will truncate if it is an odd number.
// Check via multiplication that it wasn't an odd number.
constructor() public payable {
seller = msg.sender;
value = msg.value / 2;
require((2 * value) == msg.value, "Value has to be even.");
}
modifier condition(bool _condition) {
require(_condition);
_;
}
modifier onlyBuyer() {
require(
msg.sender == buyer,
"Only buyer can call this."
);
_;
}
modifier onlySeller() {
require(
msg.sender == seller,
"Only seller can call this."
);
_;
}
modifier inState(State _state) {
require(
state == _state,
"Invalid state."
);
_;
}
event Aborted();
event PurchaseConfirmed();
event ItemReceived();
/// Abort the purchase and reclaim the ether.
/// Can only be called by the seller before
/// the contract is locked.
function abort()
public
onlySeller
inState(State.Created)
{
emit Aborted();
state = State.Inactive;
seller.transfer(address(this).balance);
}
/// Confirm the purchase as buyer.
/// Transaction has to include `2 * value` ether.
/// The ether will be locked until confirmReceived
/// is called.
function confirmPurchase()
public
inState(State.Created)
condition(msg.value == (2 * value))
payable
{
emit PurchaseConfirmed();
buyer = msg.sender;
state = State.Locked;
}
/// Confirm that you (the buyer) received the item.
/// This will release the locked ether.
function confirmReceived()
public
onlyBuyer
inState(State.Locked)
{
emit ItemReceived();
// It is important to change the state first because
// otherwise, the contracts called using `send` below
// can call in again here.
state = State.Inactive;
// NOTE: This actually allows both the buyer and the seller to
// block the refund - the withdraw pattern should be used.
buyer.transfer(value);
seller.transfer(address(this).balance);
}
}
|
