feat(contracts): add quorum

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

@@ -0,0 +1,98 @@
+// (c) Cartesi and individual authors (see AUTHORS)
+// SPDX-License-Identifier: Apache-2.0 (see LICENSE)
+
+pragma solidity ^0.8.8;
+
+import {AccessControlEnumerable} from "@openzeppelin/contracts/access/AccessControlEnumerable.sol";
+import {EnumerableSet} from "@openzeppelin/contracts/utils/structs/EnumerableSet.sol";
+import {PaymentSplitter} from "@openzeppelin/contracts/finance/PaymentSplitter.sol";
+
+import {AbstractConsensus} from "../AbstractConsensus.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 uses several OpenZeppelin contracts:
+/// `AccessControlEnumerable`, `EnumerableSet`, and `PaymentSplitter`.
+/// For more information on those, please consult OpenZeppelin's official documentation.
+contract Quorum is AbstractConsensus, AccessControlEnumerable, PaymentSplitter {
+    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 Construct a Quorum consensus
+    /// @param _validators the list of validators
+    /// @param _shares the list of shares
+    /// @param _history the history contract
+    constructor(
+        address[] memory _validators,
+        uint256[] memory _shares,
+        IHistory _history
+    ) PaymentSplitter(_validators, _shares) {
+        // 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 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.
+        // If the `add` function returns `true`,
+        // then the message sender was not in the set.
+        if (claimYeas.add(msg.sender)) {
+            // Get the number of validators in favour of the claim,
+            // taking into account the message sender as well.
+            uint256 numOfVotesInFavour = claimYeas.length();
+
+            // Get the number of validators in the quorum.
+            uint256 quorumSize = getRoleMemberCount(VALIDATOR_ROLE);
+
+            // If this claim has now just over half of the quorum's approval,
+            // then we can submit it to the history contract.
+            if (numOfVotesInFavour == 1 + quorumSize / 2) {
+                history.submitClaim(_claimData);
+            }
+        }
+    }
+
+    /// @notice Get the history contract.
+    /// @return The history contract
+    function getHistory() external view returns (IHistory) {
+        return history;
+    }
+
+    function getClaim(
+        address _dapp,
+        bytes calldata _proofContext
+    ) external view override returns (bytes32, uint256, uint256) {
+        return history.getClaim(_dapp, _proofContext);
+    }
+}