feat(contracts): add quorum

onchain/rollups/contracts/consensus/quorum/Quorum.sol

@@ -0,0 +1,133 @@
+// Copyright Cartesi Pte. Ltd.
+
+// SPDX-License-Identifier: Apache-2.0
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+pragma solidity ^0.8.8;
+
+import {AccessControlEnumerable} from "@openzeppelin/contracts/access/AccessControlEnumerable.sol";
+import {EnumerableSet} from "@openzeppelin/contracts/utils/structs/EnumerableSet.sol";
+import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+
+import {AbstractConsensus} from "../AbstractConsensus.sol";
+import {IConsensus} from "../IConsensus.sol";
+import {IHistory} from "../../history/IHistory.sol";
+
+/// @title Quorum consensus
+/// @notice A consensus model controlled by a small set of addresses, the validators.
+/// @dev This contract inherits from `AbstractConsensus` and OpenZeppelin's `AccessControlEnumerable` contract.
+/// For more information on `AccessControlEnumerable`, please consult OpenZeppelin's official documentation.
+contract Quorum is AbstractConsensus, AccessControlEnumerable {
+    using EnumerableSet for EnumerableSet.AddressSet;
+
+    /// @notice The validator role.
+    /// @dev Only validators can submit claims.
+    bytes32 public constant VALIDATOR_ROLE = keccak256("VALIDATOR_ROLE");
+
+    /// @notice The history contract.
+    /// @dev See the `getHistory` function.
+    IHistory internal immutable history;
+
+    /// @notice For each claim, the set of validators that agree
+    /// that it should be submitted to the history contract.
+    mapping(bytes => EnumerableSet.AddressSet) internal yeas;
+
+    /// @notice An ERC-20 token transfer failed (`transfer` returned `false`).
+    error ERC20TokenTransferFailed();
+
+    /// @notice Construct a Quorum consensus
+    /// @param _validators the list of validators
+    constructor(IHistory _history, address[] memory _validators) {
+        // Iterate through the array of validators,
+        // and grant to each the validator role.
+        for (uint256 i; i < _validators.length; ++i) {
+            grantRole(VALIDATOR_ROLE, _validators[i]);
+        }
+
+        // Set history.
+        history = _history;
+    }
+
+    /// @notice Get the history contract.
+    /// @return The history contract
+    function getHistory() external view returns (IHistory) {
+        return history;
+    }
+
+    /// @notice Get a claim from the current history.
+    ///         The encoding of `_proofContext` might vary depending on the
+    ///         implementation of the current history contract.
+    /// @inheritdoc IConsensus
+    function getClaim(
+        address _dapp,
+        bytes calldata _proofContext
+    ) external view override returns (bytes32, uint256, uint256) {
+        return history.getClaim(_dapp, _proofContext);
+    }
+
+    /// @notice Submits a claim for voting.
+    ///         If this is the claim that reaches the majority, then
+    ///         the claim is submitted to the history contract.
+    ///         The encoding of `_claimData` might vary depending on the
+    ///         implementation of the current history contract.
+    /// @param _claimData Data for submitting a claim
+    /// @dev Can only be called by a validator,
+    ///      and the `Quorum` contract must have ownership over
+    ///      its current history contract.
+    function submitClaim(
+        bytes calldata _claimData
+    ) external onlyRole(VALIDATOR_ROLE) {
+        // Get the set of validators in favour of the claim
+        EnumerableSet.AddressSet storage claimYeas = yeas[_claimData];
+
+        // Add the message sender to such set.
+        claimYeas.add(msg.sender);
+
+        // Get number of validators in favour of the claim.
+        uint256 numOfVotesInFavour = claimYeas.length();
+
+        // Get the number of validators in the quorum.
+        uint256 quorumSize = getRoleMemberCount(VALIDATOR_ROLE);
+
+        // If this claim already has half of the quorum's approval,
+        // then we can submit it to the history contract.
+        if (numOfVotesInFavour > quorumSize / 2) {
+            history.submitClaim(_claimData);
+        }
+    }
+
+    /// @notice Equally share all tokens from some ERC-20 contract
+    /// amongst all validators in the quorum.
+    /// @param _token The token contract
+    function shareERC20Tokens(IERC20 _token) external {
+        // Get the total amount of ERC-20 tokens held by the quorum.
+        uint256 balance = _token.balanceOf(address(this));
+
+        // Get the number of validators in the quorum.
+        uint256 quorumSize = getRoleMemberCount(VALIDATOR_ROLE);
+
+        // Calculate the share of ERC-20 tokens for each validator.
+        uint256 tokensPerValidator = balance / quorumSize;
+
+        // Iterate through the validator set.
+        for (uint256 i; i < quorumSize; ++i) {
+            // Get the i-th validator.
+            address validator = getRoleMember(VALIDATOR_ROLE, i);
+
+            // Transfer the share of ERC-20 tokens to the i-th validator.
+            bool success = _token.transfer(validator, tokensPerValidator);
+
+            // If the transfer fails, revert.
+            if (!success) {
+                revert ERC20TokenTransferFailed();
+            }
+        }
+    }
+}