Missing previous king payout - reward mechanism is broken
Description
When a new player claims the throne, a small portion of the claim fee is intended to be paid to the previous king as an incentive for participation. However, the previousKingPayout is always initialized and left at 0, meaning no funds are never reserved for the former king - even though the code intends to support this mechanic.
function claimThrone() external payable gameNotEnded nonReentrant {
...
@> uint256 previousKingPayout = 0;
....
@> if (currentPlatformFee > (sentAmount - previousKingPayout)) {
@> currentPlatformFee = sentAmount - previousKingPayout;
}
Risk
Likelihood: High
This happens every time a new player claims the throne.
Impact: Medium
The previous king receives no payout, reducing game incentives.
Proof of Concept
function test_previousKingDoesNotGetPayout() public {
vm.prank(player1);
game.claimThrone{value: INITIAL_CLAIM_FEE}();
assertEq(game.currentKing(), player1, "Player1 should be the current king");
assertEq(game.pendingWinnings(player1), 0, "Player1 should not have pending winnings");
uint256 claimFee = game.claimFee();
vm.prank(player2);
game.claimThrone{value: claimFee}();
assertEq(game.currentKing(), player2, "Player2 should be the current king");
assertEq(game.pendingWinnings(player2), 0, "Player2 should not have pending winnings");
assertEq(game.pendingWinnings(player1), 0, "Player1 should have pending winnings as previous king payout");
vm.warp(block.timestamp + game.gracePeriod() + 1);
vm.prank(player3);
game.declareWinner();
assertEq(game.currentKing(), player2, "Player2 should be the current king");
uint256 kingExpectedWinnings = claimFee + INITIAL_CLAIM_FEE - game.platformFeesBalance();
assertEq(game.pendingWinnings(player2), kingExpectedWinnings, "Player2 should not have pending winnings");
assertEq(game.pendingWinnings(player1), 0, "Player1 should have pending winnings as previous king payout");
}
According to documentation, the pendingWinnings data structure stores kings and previous kings balances.
Recommended Mitigation
Calculate the previous king payout and include it in the expected data structure.
- uint256 previousKingPayout = 0;
+ uint256 previousKingPayout = previousKingPayoutFormula();
...
+ pendingWinnings[previousKing] += previousKingPayout;
