VRFConsumerV2

Author: Simon Malatrait simon.malatrait@grenoble-inp.org

This contract implements the RNG standard and inherits from VRFConsumerBaseV2 to use Chainlink Verifiable Randomness Mechanism.

It allows to store the random number associated to the requests made.

Chainlink Subscription Method Documentation: https://docs.chain.link/vrf/v2/subscription

Chainlink Subscription Method Network Parameters: https://docs.chain.link/vrf/v2/subscription/supported-networks#arbitrum-mainnet

For SECURITY CONSIDERATIONS, you might also have look to: https://github.com/smartcontractkit/chainlink/blob/develop/contracts/src/v0.8/vrf/VRFConsumerBaseV2.sol

For SECURITY CONSIDERATIONS, you might also have look to: https://github.com/smartcontractkit/chainlink/blob/develop/contracts/src/v0.8/interfaces/VRFCoordinatorV2Interface.sol

State Variables

governor

address public governor;

keyHash

bytes32 public keyHash;

vrfCoordinator

VRFCoordinatorV2Interface public vrfCoordinator;

subscriptionId

uint64 public subscriptionId;

callbackGasLimit

uint32 public callbackGasLimit;

sortitionModule

ISortitionModule public sortitionModule;

numWords

uint32 public numWords;

requestConfirmations

uint16 public requestConfirmations;

lastRequestId

uint256 public lastRequestId;

requestsToRandomWords

mapping(uint256 => uint256) public requestsToRandomWords;

Functions

onlyBySortitionModule

modifier onlyBySortitionModule();

onlyByGovernor

modifier onlyByGovernor();

constructor

Constructs the ChainlinkRNG contract.

https://docs.chain.link/vrf/v2/subscription/examples/get-a-random-number#analyzing-the-contract

constructor(
    address _governor,
    address _vrfCoordinator,
    address _sortitionModule,
    bytes32 _keyHash,
    uint64 _subscriptionId,
    uint16 _requestConfirmations,
    uint32 _callbackGasLimit,
    uint32 _numWords
) VRFConsumerBaseV2(_vrfCoordinator);

Parameters

Name	Type	Description
`_governor`	`address`	The Governor of the contract.
`_vrfCoordinator`	`address`	The address of the VRFCoordinator contract.
`_sortitionModule`	`address`	The address of the SortitionModule contract.
`_keyHash`	`bytes32`	The gas lane key hash value - Defines the maximum gas price you are willing to pay for a request in wei (ID of the off-chain VRF job).
`_subscriptionId`	`uint64`	The unique identifier of the subscription used for funding requests.
`_requestConfirmations`	`uint16`	How many confirmations the Chainlink node should wait before responding.
`_callbackGasLimit`	`uint32`	The limit for how much gas to use for the callback request to the contract's fulfillRandomWords() function.
`_numWords`	`uint32`	How many random values to request.

changeVrfCoordinator

Changes the vrfCoordinator storage variable.

function changeVrfCoordinator(address _vrfCoordinator) external onlyByGovernor;

Parameters

Name	Type	Description
`_vrfCoordinator`	`address`	The new value for the `vrfCoordinator` storage variable.

changeSortitionModule

Changes the sortitionModule storage variable.

function changeSortitionModule(address _sortitionModule) external onlyByGovernor;

Parameters

Name	Type	Description
`_sortitionModule`	`address`	The new value for the `sortitionModule` storage variable.

changeKeyHash

Changes the keyHash storage variable.

function changeKeyHash(bytes32 _keyHash) external onlyByGovernor;

Parameters

Name	Type	Description
`_keyHash`	`bytes32`	The new value for the `keyHash` storage variable.

changeSubscriptionId

Changes the subscriptionId storage variable.

function changeSubscriptionId(uint64 _subscriptionId) external onlyByGovernor;

Parameters

Name	Type	Description
`_subscriptionId`	`uint64`	The new value for the `subscriptionId` storage variable.

changeRequestConfirmations

Changes the requestConfirmations storage variable.

function changeRequestConfirmations(uint16 _requestConfirmations) external onlyByGovernor;

Parameters

Name	Type	Description
`_requestConfirmations`	`uint16`	The new value for the `requestConfirmations` storage variable.

changeCallbackGasLimit

Changes the callbackGasLimit storage variable.

function changeCallbackGasLimit(uint32 _callbackGasLimit) external onlyByGovernor;

Parameters

Name	Type	Description
`_callbackGasLimit`	`uint32`	The new value for the `callbackGasLimit` storage variable.

changeNumWord

Changes the numWords storage variable.

function changeNumWord(uint32 _numWords) external onlyByGovernor;

Parameters

Name	Type	Description
`_numWords`	`uint32`	The new value for the `numWords` storage variable.

requestRandomness

Submit a request to the VRF Coordinator contract with the specified parameters.

Assumes the subscription is funded sufficiently; "Words" refers to unit of data in Computer Science Note Buffer of one requestId, as in RandomizerRNG, which should be enough with the callback function.

function requestRandomness(uint256) external onlyBySortitionModule;

fulfillRandomWords

Callback function used by VRF Coordinator

Stores the random number given by the VRF Coordinator and calls passPhase function on SortitionModule.

function fulfillRandomWords(uint256 _requestId, uint256[] memory _randomWords) internal override;

Parameters

Name	Type	Description
`_requestId`	`uint256`	The same request Id initially returned by `vrfCoordinator.requestRandomWords` and stored in the `lastRequestId` storage variable.
`_randomWords`	`uint256[]`	- array of random results from VRF Coordinator

receiveRandomness

Get the random value associated to lastRequestId

function receiveRandomness(uint256) external view returns (uint256 randomNumber);

Returns

Name	Type	Description
`randomNumber`	`uint256`	The random number. If the value is not ready or has not been required it returns 0.

Events

RequestSent

Emitted when a request is sent to the VRF Coordinator

event RequestSent(uint256 indexed requestId, uint32 numWords);

RequestFulfilled

Emitted when a request has been fulfilled.

event RequestFulfilled(uint256 indexed requestId, uint256[] randomWords);