dos.sol

/// @dev A Denial-of-Service (DoS) attack on a Ethereum smart 
/// @dev contract occurs when an attacker floods the contract 
/// @dev with a large number of requests, leading to high gas 
/// @dev costs and rendering the contract unusable. This can 
/// @dev occur in various forms, such as sending many 
/// @dev transactions to a contract in a short period of time, 
/// @dev calling a function repeatedly with high gas costs, 
/// @dev or using reentrancy attacks to repeatedly call a function.

/// @dev To prevent DoS attacks, you can implement rate limiting, 
/// @dev access control checks, or contract incentives that encourage 
/// @dev users to submit proposals in a responsible manner.

pragma solidity >=0.5.0 <0.8.0;

contract Proposal {
    uint256 public proposalCount;
    uint256 public maxProposalsPerMinute;
    uint256 public lastSubmissionTimestamp;

    // limit the number of proposals that can be submitted per minute
    modifier limitProposalsPerMinute() {
        if (proposalCount >= maxProposalsPerMinute) {
            require(now >= lastSubmissionTimestamp + 60 seconds, "Too many proposals submitted in a short period of time. Please try again later.");
        }
        proposalCount++;
        lastSubmissionTimestamp = now;
        _;
    }

    function submitProposal(string memory proposal) public limitProposalsPerMinute {
        // ...
    }
}