GSN support (#59)

* GSN support

Add base Context contract

Add GSNContext and tests

Add RelayHub deployment to tests

Add RelayProvider integration, complete GSNContext tests

Switch dependency to openzeppelin-gsn-provider

Add default txfee to provider

Add basic signing recipient

Sign more values

Add comment clarifying RelayHub's msg.data

Make context constructors internal

Rename SigningRecipient to GSNRecipientSignedData

Add ERC20Charge recipients

Harcode RelayHub address into GSNContext

Fix Solidity linter errors

Run server from binary, use gsn-helpers to fund it

Migrate to published @openzeppelin/gsn-helpers

Silence false-positive compiler warning

Use GSN helper assertions

Rename meta-tx to gsn, take out of drafts

Merge ERC20 charge recipients into a single one

Rename GSNRecipients to Bouncers

Add GSNBouncerUtils to decouple the bouncers from GSNRecipient

Add _upgradeRelayHub

Store RelayHub address using unstructored storage

Add IRelayHub

Add _withdrawDeposits to GSNRecipient

Add relayHub version to recipient

Make _acceptRelayedCall and _declineRelayedCall easier to use

Rename GSNBouncerUtils to GSNBouncerBase, make it IRelayRecipient

Improve GSNBouncerBase, make pre and post sender-protected and optional

Fix GSNBouncerERC20Fee, add tests

Add missing GSNBouncerSignature test

Override transferFrom in __unstable__ERC20PrimaryAdmin

Rhub address slot reduced by 1

Rename relay hub changed event

Use released gsn-provider

* move gsn to all caps

* update to gsn contracts in solidity/master

* Adapt for ethereum-package

* update gsn related packages

* update dependencies to match contracts repo

* remove mocha bail option

* add changelog entry

* add constructors to mocks

* use unstructured storage for bouncer implementations

CHANGELOG.md

 # Changelog
 
+## 2.2.2 (unreleased)
+
+### New features:
+ * Facilities to make metatransaction-enabled contracts through the Gas Station Network. Backported from [#1844](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1844).
+
 ## 2.2.1 (2019-07-22)
 
 ### Changes:

contracts/GSN/Context.sol

+pragma solidity ^0.5.0;
+
+/*
+ * @dev Provides information about the current execution context, including the
+ * sender of the transaction and its data. While these are generally available
+ * via msg.sender and msg.data, they not should not be accessed in such a direct
+ * manner, since when dealing with GSN meta-transactions the account sending and
+ * paying for execution may not be the actual sender (as far as an application
+ * is concerned).
+ *
+ * This contract is only required for intermediate, library-like contracts.
+ */
+contract Context {
+    // Empty internal constructor, to prevent people from mistakenly deploying
+    // an instance of this contract, with should be used via inheritance.
+    constructor () internal { }
+    // solhint-disable-previous-line no-empty-blocks
+
+    function _msgSender() internal view returns (address) {
+        return msg.sender;
+    }
+
+    function _msgData() internal view returns (bytes memory) {
+        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
+        return msg.data;
+    }
+}

contracts/GSN/GSNContext.sol

+pragma solidity ^0.5.0;
+
+import "@openzeppelin/upgrades/contracts/Initializable.sol";
+import "./Context.sol";
+
+/*
+ * @dev Enables GSN support on `Context` contracts by recognizing calls from
+ * RelayHub and extracting the actual sender and call data from the received
+ * calldata.
+ *
+ * > This contract does not perform all required tasks to implement a GSN
+ * recipient contract: end users should use `GSNRecipient` instead.
+ */
+contract GSNContext is Initializable, Context {
+    // We use a random storage slot to allow proxy contracts to enable GSN support in an upgrade without changing their
+    // storage layout. This value is calculated as: keccak256('gsn.relayhub.address'), minus 1.
+    bytes32 private constant RELAY_HUB_ADDRESS_STORAGE_SLOT = 0x06b7792c761dcc05af1761f0315ce8b01ac39c16cc934eb0b2f7a8e71414f262;
+
+    event RelayHubChanged(address indexed oldRelayHub, address indexed newRelayHub);
+
+    function initialize() public initializer {
+        _upgradeRelayHub(0xD216153c06E857cD7f72665E0aF1d7D82172F494);
+    }
+
+    function _getRelayHub() internal view returns (address relayHub) {
+        bytes32 slot = RELAY_HUB_ADDRESS_STORAGE_SLOT;
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            relayHub := sload(slot)
+        }
+    }
+
+    function _upgradeRelayHub(address newRelayHub) internal {
+        address currentRelayHub = _getRelayHub();
+        require(newRelayHub != address(0), "GSNContext: new RelayHub is the zero address");
+        require(newRelayHub != currentRelayHub, "GSNContext: new RelayHub is the current one");
+
+        emit RelayHubChanged(currentRelayHub, newRelayHub);
+
+        bytes32 slot = RELAY_HUB_ADDRESS_STORAGE_SLOT;
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            sstore(slot, newRelayHub)
+        }
+    }
+
+    // Overrides for Context's functions: when called from RelayHub, sender and
+    // data require some pre-processing: the actual sender is stored at the end
+    // of the call data, which in turns means it needs to be removed from it
+    // when handling said data.
+
+    function _msgSender() internal view returns (address) {
+        if (msg.sender != _getRelayHub()) {
+            return msg.sender;
+        } else {
+            return _getRelayedCallSender();
+        }
+    }
+
+    function _msgData() internal view returns (bytes memory) {
+        if (msg.sender != _getRelayHub()) {
+            return msg.data;
+        } else {
+            return _getRelayedCallData();
+        }
+    }
+
+    function _getRelayedCallSender() private pure returns (address result) {
+        // We need to read 20 bytes (an address) located at array index msg.data.length - 20. In memory, the array
+        // is prefixed with a 32-byte length value, so we first add 32 to get the memory read index. However, doing
+        // so would leave the address in the upper 20 bytes of the 32-byte word, which is inconvenient and would
+        // require bit shifting. We therefore subtract 12 from the read index so the address lands on the lower 20
+        // bytes. This can always be done due to the 32-byte prefix.
+
+        // The final memory read index is msg.data.length - 20 + 32 - 12 = msg.data.length. Using inline assembly is the
+        // easiest/most-efficient way to perform this operation.
+
+        // These fields are not accessible from assembly
+        bytes memory array = msg.data;
+        uint256 index = msg.data.length;
+
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            // Load the 32 bytes word from memory with the address on the lower 20 bytes, and mask those.
+            result := and(mload(add(array, index)), 0xffffffffffffffffffffffffffffffffffffffff)
+        }
+        return result;
+    }
+
+    function _getRelayedCallData() private pure returns (bytes memory) {
+        // RelayHub appends the sender address at the end of the calldata, so in order to retrieve the actual msg.data,
+        // we must strip the last 20 bytes (length of an address type) from it.
+
+        uint256 actualDataLength = msg.data.length - 20;
+        bytes memory actualData = new bytes(actualDataLength);
+
+        for (uint256 i = 0; i < actualDataLength; ++i) {
+            actualData[i] = msg.data[i];
+        }
+
+        return actualData;
+    }
+}

contracts/GSN/GSNRecipient.sol

+pragma solidity ^0.5.0;
+
+import "@openzeppelin/upgrades/contracts/Initializable.sol";
+import "./IRelayRecipient.sol";
+import "./GSNContext.sol";
+import "./bouncers/GSNBouncerBase.sol";
+import "./IRelayHub.sol";
+
+/*
+ * @dev Base GSN recipient contract, adding the recipient interface and enabling
+ * GSN support. Not all interface methods are implemented, derived contracts
+ * must do so themselves.
+ */
+contract GSNRecipient is Initializable, IRelayRecipient, GSNContext, GSNBouncerBase {
+    function initialize() public initializer {
+        GSNContext.initialize();
+    }
+
+    function getHubAddr() public view returns (address) {
+        return _getRelayHub();
+    }
+
+    // This function is view for future-proofing, it may require reading from
+    // storage in the future.
+    function relayHubVersion() public view returns (string memory) {
+        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
+        return "1.0.0";
+    }
+
+    function _withdrawDeposits(uint256 amount, address payable payee) internal {
+        IRelayHub(_getRelayHub()).withdraw(amount, payee);
+    }
+}

contracts/GSN/IRelayRecipient.sol

+pragma solidity ^0.5.0;
+
+/*
+ * @dev Interface for a contract that will be called via the GSN from RelayHub.
+ */
+contract IRelayRecipient {
+    /**
+     * @dev Returns the address of the RelayHub instance this recipient interacts with.
+     */
+    function getHubAddr() public view returns (address);
+
+    function acceptRelayedCall(
+        address relay,
+        address from,
+        bytes calldata encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes calldata approvalData,
+        uint256 maxPossibleCharge
+    )
+        external
+        view
+        returns (uint256, bytes memory);
+
+    function preRelayedCall(bytes calldata context) external returns (bytes32);
+
+    function postRelayedCall(bytes calldata context, bool success, uint actualCharge, bytes32 preRetVal) external;
+}

contracts/GSN/bouncers/GSNBouncerBase.sol

+pragma solidity ^0.5.0;
+
+import "../IRelayRecipient.sol";
+
+/*
+ * @dev Base contract used to implement GSNBouncers.
+ *
+ * > This contract does not perform all required tasks to implement a GSN
+ * recipient contract: end users should use `GSNRecipient` instead.
+ */
+contract GSNBouncerBase is IRelayRecipient {
+    uint256 constant private RELAYED_CALL_ACCEPTED = 0;
+    uint256 constant private RELAYED_CALL_REJECTED = 11;
+
+    // How much gas is forwarded to postRelayedCall
+    uint256 constant internal POST_RELAYED_CALL_MAX_GAS = 100000;
+
+    // Base implementations for pre and post relayedCall: only RelayHub can invoke them, and data is forwarded to the
+    // internal hook.
+
+    /**
+     * @dev See `IRelayRecipient.preRelayedCall`.
+     *
+     * This function should not be overriden directly, use `_preRelayedCall` instead.
+     *
+     * * Requirements:
+     *
+     * - the caller must be the `RelayHub` contract.
+     */
+    function preRelayedCall(bytes calldata context) external returns (bytes32) {
+        require(msg.sender == getHubAddr(), "GSNBouncerBase: caller is not RelayHub");
+        return _preRelayedCall(context);
+    }
+
+    /**
+     * @dev See `IRelayRecipient.postRelayedCall`.
+     *
+     * This function should not be overriden directly, use `_postRelayedCall` instead.
+     *
+     * * Requirements:
+     *
+     * - the caller must be the `RelayHub` contract.
+     */
+    function postRelayedCall(bytes calldata context, bool success, uint256 actualCharge, bytes32 preRetVal) external {
+        require(msg.sender == getHubAddr(), "GSNBouncerBase: caller is not RelayHub");
+        _postRelayedCall(context, success, actualCharge, preRetVal);
+    }
+
+    /**
+     * @dev Return this in acceptRelayedCall to proceed with the execution of a relayed call. Note that this contract
+     * will be charged a fee by RelayHub
+     */
+    function _approveRelayedCall() internal pure returns (uint256, bytes memory) {
+        return _approveRelayedCall("");
+    }
+
+    /**
+     * @dev See `GSNBouncerBase._approveRelayedCall`.
+     *
+     * This overload forwards `context` to _preRelayedCall and _postRelayedCall.
+     */
+    function _approveRelayedCall(bytes memory context) internal pure returns (uint256, bytes memory) {
+        return (RELAYED_CALL_ACCEPTED, context);
+    }
+
+    /**
+     * @dev Return this in acceptRelayedCall to impede execution of a relayed call. No fees will be charged.
+     */
+    function _rejectRelayedCall(uint256 errorCode) internal pure returns (uint256, bytes memory) {
+        return (RELAYED_CALL_REJECTED + errorCode, "");
+    }
+
+    // Empty hooks for pre and post relayed call: users only have to define these if they actually use them.
+
+    function _preRelayedCall(bytes memory) internal returns (bytes32) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    function _postRelayedCall(bytes memory, bool, uint256, bytes32) internal {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    /*
+     * @dev Calculates how much RelaHub will charge a recipient for using `gas` at a `gasPrice`, given a relayer's
+     * `serviceFee`.
+     */
+    function _computeCharge(uint256 gas, uint256 gasPrice, uint256 serviceFee) internal pure returns (uint256) {
+        // The fee is expressed as a percentage. E.g. a value of 40 stands for a 40% fee, so the recipient will be
+        // charged for 1.4 times the spent amount.
+        return (gas * gasPrice * (100 + serviceFee)) / 100;
+    }
+}

contracts/GSN/bouncers/GSNBouncerERC20Fee.sol

+pragma solidity ^0.5.0;
+
+import "@openzeppelin/upgrades/contracts/Initializable.sol";
+import "./GSNBouncerBase.sol";
+import "../../math/SafeMath.sol";
+import "../../ownership/Secondary.sol";
+import "../../token/ERC20/SafeERC20.sol";
+import "../../token/ERC20/ERC20.sol";
+import "../../token/ERC20/ERC20Detailed.sol";
+
+contract GSNBouncerERC20Fee is Initializable, GSNBouncerBase {
+    using SafeERC20 for __unstable__ERC20PrimaryAdmin;
+    using SafeMath for uint256;
+
+    enum GSNBouncerERC20FeeErrorCodes {
+        INSUFFICIENT_BALANCE
+    }
+
+    // We use a random storage slot to allow proxy contracts to enable GSN support in an upgrade without changing their
+    // storage layout. This value is calculated as: keccak256('gsn.bouncer.signature.token'), minus 1.
+    bytes32 constant private TOKEN_STORAGE_SLOT = 0xd918b70a5a5c95a8c0cac8acbdd59e1b4acd0645f53c0461d64b41f8825c8828;
+
+    function initialize(string memory name, string memory symbol, uint8 decimals) initializer public {
+        // TODO: Should we inject this token, instead of creating it, in order to make it upgradeable?
+        // However, that would mean removing it from unstable and making in an official contract
+        _setToken(new __unstable__ERC20PrimaryAdmin(name, symbol, decimals));
+    }
+
+    function token() public view returns (IERC20) {
+        return IERC20(_getToken());
+    }
+
+    function _mint(address account, uint256 amount) internal {
+        _getToken().mint(account, amount);
+    }
+
+    function acceptRelayedCall(
+        address,
+        address from,
+        bytes calldata,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256,
+        uint256,
+        bytes calldata,
+        uint256 maxPossibleCharge
+    )
+        external
+        view
+        returns (uint256, bytes memory)
+    {
+        if (_getToken().balanceOf(from) < maxPossibleCharge) {
+            return _rejectRelayedCall(uint256(GSNBouncerERC20FeeErrorCodes.INSUFFICIENT_BALANCE));
+        }
+
+        return _approveRelayedCall(abi.encode(from, maxPossibleCharge, transactionFee, gasPrice));
+    }
+
+    function _preRelayedCall(bytes memory context) internal returns (bytes32) {
+        (address from, uint256 maxPossibleCharge) = abi.decode(context, (address, uint256));
+
+        // The maximum token charge is pre-charged from the user
+        _getToken().safeTransferFrom(from, address(this), maxPossibleCharge);
+    }
+
+    function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal {
+        (address from, uint256 maxPossibleCharge, uint256 transactionFee, uint256 gasPrice) =
+            abi.decode(context, (address, uint256, uint256, uint256));
+
+        // actualCharge is an _estimated_ charge, which assumes postRelayedCall will use all available gas.
+        // This implementation's gas cost can be roughly estimated as 10k gas, for the two SSTORE operations in an
+        // ERC20 transfer.
+        uint256 overestimation = _computeCharge(POST_RELAYED_CALL_MAX_GAS.sub(10000), gasPrice, transactionFee);
+        actualCharge = actualCharge.sub(overestimation);
+
+        // After the relayed call has been executed and the actual charge estimated, the excess pre-charge is returned
+        _getToken().safeTransfer(from, maxPossibleCharge.sub(actualCharge));
+    }
+
+    function _getToken() private view returns (__unstable__ERC20PrimaryAdmin token) {
+      bytes32 slot = TOKEN_STORAGE_SLOT;
+      // solhint-disable-next-line no-inline-assembly
+      assembly {
+        token := sload(slot)
+      }
+    }
+
+    function _setToken(__unstable__ERC20PrimaryAdmin token) private {
+      bytes32 slot = TOKEN_STORAGE_SLOT;
+      // solhint-disable-next-line no-inline-assembly
+      assembly {
+        sstore(slot, token)
+      }
+    }
+}
+
+/**
+ * @title __unstable__ERC20PrimaryAdmin
+ * @dev An ERC20 token owned by another contract, which has minting permissions and can use transferFrom to receive
+ * anyone's tokens. This contract is an internal helper for GSNRecipientERC20Fee, and should not be used
+ * outside of this context.
+ */
+// solhint-disable-next-line contract-name-camelcase
+contract __unstable__ERC20PrimaryAdmin is ERC20, ERC20Detailed, Secondary {
+    uint256 private constant UINT256_MAX = 2**256 - 1;
+
+    constructor(string memory name, string memory symbol, uint8 decimals) public {
+        Secondary.initialize(msg.sender);
+        ERC20Detailed.initialize(name, symbol, decimals);
+    }
+
+    // The primary account (GSNRecipientERC20Fee) can mint tokens
+    function mint(address account, uint256 amount) public onlyPrimary {
+        _mint(account, amount);
+    }
+
+    // The primary account has 'infinite' allowance for all token holders
+    function allowance(address owner, address spender) public view returns (uint256) {
+        if (spender == primary()) {
+            return UINT256_MAX;
+        } else {
+            return super.allowance(owner, spender);
+        }
+    }
+
+    // Allowance for the primary account cannot be changed (it is always 'infinite')
+    function _approve(address owner, address spender, uint256 value) internal {
+        if (spender == primary()) {
+            return;
+        } else {
+            super._approve(owner, spender, value);
+        }
+    }
+
+    function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
+        if (recipient == primary()) {
+            _transfer(sender, recipient, amount);
+            return true;
+        } else {
+            return super.transferFrom(sender, recipient, amount);
+        }
+    }
+}

contracts/GSN/bouncers/GSNBouncerSignature.sol

+pragma solidity ^0.5.0;
+
+import "@openzeppelin/upgrades/contracts/Initializable.sol";
+import "./GSNBouncerBase.sol";
+import "../../cryptography/ECDSA.sol";
+
+contract GSNBouncerSignature is Initializable, GSNBouncerBase {
+    using ECDSA for bytes32;
+
+    // We use a random storage slot to allow proxy contracts to enable GSN support in an upgrade without changing their
+    // storage layout. This value is calculated as: keccak256('gsn.bouncer.signature.trustedSigner'), minus 1.
+    bytes32 constant private TRUSTED_SIGNER_STORAGE_SLOT = 0xe7b237a4017a399d277819456dce32c2356236bbc518a6d84a9a8d1cfdf1e9c5;
+
+    enum GSNBouncerSignatureErrorCodes {
+        INVALID_SIGNER
+    }
+
+    function initialize(address trustedSigner) public initializer {
+        _setTrustedSigner(trustedSigner);
+    }
+
+    function acceptRelayedCall(
+        address relay,
+        address from,
+        bytes calldata encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes calldata approvalData,
+        uint256
+    )
+        external
+        view
+        returns (uint256, bytes memory)
+    {
+        bytes memory blob = abi.encodePacked(
+            relay,
+            from,
+            encodedFunction,
+            transactionFee,
+            gasPrice,
+            gasLimit,
+            nonce, // Prevents replays on RelayHub
+            getHubAddr(), // Prevents replays in multiple RelayHubs
+            address(this) // Prevents replays in multiple recipients
+        );
+        if (keccak256(blob).toEthSignedMessageHash().recover(approvalData) == _getTrustedSigner()) {
+            return _approveRelayedCall();
+        } else {
+            return _rejectRelayedCall(uint256(GSNBouncerSignatureErrorCodes.INVALID_SIGNER));
+        }
+    }
+
+    function _getTrustedSigner() private view returns (address trustedSigner) {
+      bytes32 slot = TRUSTED_SIGNER_STORAGE_SLOT;
+      // solhint-disable-next-line no-inline-assembly
+      assembly {
+        trustedSigner := sload(slot)
+      }
+    }
+
+    function _setTrustedSigner(address trustedSigner) private {
+      bytes32 slot = TRUSTED_SIGNER_STORAGE_SLOT;
+      // solhint-disable-next-line no-inline-assembly
+      assembly {
+        sstore(slot, trustedSigner)
+      }
+    }
+}

contracts/mocks/ContextMock.sol

+pragma solidity ^0.5.0;
+
+import "../GSN/Context.sol";
+
+contract ContextMock is Context {
+    event Sender(address sender);
+
+    function msgSender() public {
+        emit Sender(_msgSender());
+    }
+
+    event Data(bytes data, uint256 integerValue, string stringValue);
+
+    function msgData(uint256 integerValue, string memory stringValue) public {
+        emit Data(_msgData(), integerValue, stringValue);
+    }
+}
+
+contract ContextMockCaller {
+    function callSender(ContextMock context) public {
+        context.msgSender();
+    }
+
+    function callData(ContextMock context, uint256 integerValue, string memory stringValue) public {
+        context.msgData(integerValue, stringValue);
+    }
+}

contracts/mocks/GSNBouncerERC20FeeMock.sol

+pragma solidity ^0.5.0;
+
+import "@openzeppelin/upgrades/contracts/Initializable.sol";
+import "../GSN/GSNRecipient.sol";
+import "../GSN/bouncers/GSNBouncerERC20Fee.sol";
+
+contract GSNBouncerERC20FeeMock is GSNRecipient, GSNBouncerERC20Fee {
+    constructor(string memory name, string memory symbol, uint8 decimals) public {
+        GSNBouncerERC20Fee.initialize(name, symbol, decimals);
+        GSNRecipient.initialize();
+    }
+
+    function mint(address account, uint256 amount) public {
+        _mint(account, amount);
+    }
+
+    event MockFunctionCalled(uint256 senderBalance);
+
+    function mockFunction() public {
+        emit MockFunctionCalled(token().balanceOf(_msgSender()));
+    }
+}

contracts/mocks/GSNBouncerSignatureMock.sol

+pragma solidity ^0.5.0;
+
+import "@openzeppelin/upgrades/contracts/Initializable.sol";
+import "../GSN/GSNRecipient.sol";
+import "../GSN/bouncers/GSNBouncerSignature.sol";
+
+contract GSNBouncerSignatureMock is GSNRecipient, GSNBouncerSignature {
+    constructor(address trustedSigner) public {
+        GSNBouncerSignature.initialize(trustedSigner);
+        GSNRecipient.initialize();
+    }
+
+    event MockFunctionCalled();
+
+    function mockFunction() public {
+        emit MockFunctionCalled();
+    }
+}

contracts/mocks/GSNContextMock.sol

+pragma solidity ^0.5.0;
+
+import "./ContextMock.sol";
+import "../GSN/GSNContext.sol";
+import "../GSN/IRelayRecipient.sol";
+
+// By inheriting from GSNContext, Context's internal functions are overridden automatically
+contract GSNContextMock is ContextMock, GSNContext, IRelayRecipient {
+    constructor() public {
+        GSNContext.initialize();
+    }
+
+    function getHubAddr() public view returns (address) {
+        return _getRelayHub();
+    }
+
+    function acceptRelayedCall(
+        address,
+        address,
+        bytes calldata,
+        uint256,
+        uint256,
+        uint256,
+        uint256,
+        bytes calldata,
+        uint256
+    )
+        external
+        view
+        returns (uint256, bytes memory)
+    {
+        return (0, "");
+    }
+
+    function preRelayedCall(bytes calldata) external returns (bytes32) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    function postRelayedCall(bytes calldata, bool, uint256, bytes32) external {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    function getRelayHub() public view returns (address) {
+        return _getRelayHub();
+    }
+
+    function upgradeRelayHub(address newRelayHub) public {
+        return _upgradeRelayHub(newRelayHub);
+    }
+}

contracts/mocks/GSNRecipientMock.sol

+pragma solidity ^0.5.0;
+
+import "../GSN/GSNRecipient.sol";
+
+contract GSNRecipientMock is GSNRecipient {
+    constructor() public {
+        GSNRecipient.initialize();
+    }
+
+    function withdrawDeposits(uint256 amount, address payable payee) public {
+        _withdrawDeposits(amount, payee);
+    }
+
+    function acceptRelayedCall(address, address, bytes calldata, uint256, uint256, uint256, uint256, bytes calldata, uint256)
+        external
+        view
+        returns (uint256, bytes memory)
+    {
+        return (0, "");
+    }
+
+    function preRelayedCall(bytes calldata) external returns (bytes32) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    function postRelayedCall(bytes calldata, bool, uint256, bytes32) external {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+}

package.json

@@ -42,8 +42,11 @@
   "homepage": "https://github.com/OpenZeppelin/openzeppelin-contracts-ethereum-package",
   "devDependencies": {
     "@openzeppelin/cli": "2.5.0",
+    "@openzeppelin/gsn-helpers": "^0.1.5",
+    "@openzeppelin/gsn-provider": "^0.1.5",
     "@openzeppelin/upgrades": "2.5.0",
     "chai": "^4.1.2",
+    "chai-bn": "^0.1.1",
     "coveralls": "^3.0.1",
     "eslint": "^4.19.1",
     "eslint-config-standard": "^10.2.1",
@@ -61,7 +64,7 @@
     "pify": "^4.0.1",
     "solhint": "^1.5.0",
     "solidity-coverage": "https://github.com:rotcivegaf/solidity-coverage.git#5875f5b7bc74d447f3312c9c0e9fc7814b482477",
-    "truffle": "^5.0.0"
+    "truffle": "^5.0.18"
   },
   "peerDependencies": {
     "@openzeppelin/upgrades": "^2.5.0"

scripts/test.sh

@@ -23,9 +23,13 @@ ganache_running() {
   nc -z localhost "$ganache_port"
 }
 
+relayer_running() {
+  nc -z localhost "$relayer_port"
+}
+
 start_ganache() {
-  # We define 10 accounts with balance 1M ether, needed for high-value tests.
   local accounts=(
+    # 10 accounts with balance 1M ether, needed for high-value tests.
     --account="0x2bdd21761a483f71054e14f5b827213567971c676928d9a1808cbfa4b7501200,1000000000000000000000000"
     --account="0x2bdd21761a483f71054e14f5b827213567971c676928d9a1808cbfa4b7501201,1000000000000000000000000"
     --account="0x2bdd21761a483f71054e14f5b827213567971c676928d9a1808cbfa4b7501202,1000000000000000000000000"
@@ -36,10 +40,14 @@ start_ganache() {
     --account="0x2bdd21761a483f71054e14f5b827213567971c676928d9a1808cbfa4b7501207,1000000000000000000000000"
     --account="0x2bdd21761a483f71054e14f5b827213567971c676928d9a1808cbfa4b7501208,1000000000000000000000000"
     --account="0x2bdd21761a483f71054e14f5b827213567971c676928d9a1808cbfa4b7501209,1000000000000000000000000"
+    # 3 accounts to be used for GSN matters.
+    --account="0x956b91cb2344d7863ea89e6945b753ca32f6d74bb97a59e59e04903ded14ad00,1000000000000000000000000"
+    --account="0x956b91cb2344d7863ea89e6945b753ca32f6d74bb97a59e59e04903ded14ad01,1000000000000000000000000"
+    --account="0x956b91cb2344d7863ea89e6945b753ca32f6d74bb97a59e59e04903ded14ad02,1000000000000000000000000"
   )
 
   if [ "$SOLIDITY_COVERAGE" = true ]; then
-    npx ganache-cli-coverage --emitFreeLogs true --allowUnlimitedContractSize true --gasLimit 0xfffffffffff --port "$ganache_port" "${accounts[@]}" > /dev/null &
+    npx ganache-cli-coverage --emitFreeLogs true --allowUnlimitedContractSize true --gasLimit 0xfffffffffffff --port "$ganache_port" "${accounts[@]}" > /dev/null &
   else
     npx ganache-cli --gasLimit 0xfffffffffff --port "$ganache_port" "${accounts[@]}" > /dev/null &
   fi
@@ -55,6 +63,12 @@ start_ganache() {
   echo "Ganache launched!"
 }
 
+setup_relayhub() {
+  npx oz-gsn deploy-relay-hub \
+    --ethereumNodeURL "http://localhost:$ganache_port" \
+    --from "0xbb49ad04422f9fa6a217f3ed82261b942f6981f7"
+}
+
 if ganache_running; then
   echo "Using existing ganache instance"
 else
@@ -64,6 +78,8 @@ fi
 
 npx truffle version
 
+setup_relayhub
+
 if [ "$SOLIDITY_COVERAGE" = true ]; then
   npx solidity-coverage
 else

test/GSN/Context.behavior.js

+const { BN, expectEvent } = require('openzeppelin-test-helpers');
+
+const ContextMock = artifacts.require('ContextMock');
+
+function shouldBehaveLikeRegularContext (sender) {
+  describe('msgSender', function () {
+    it('returns the transaction sender when called from an EOA', async function () {
+      const { logs } = await this.context.msgSender({ from: sender });
+      expectEvent.inLogs(logs, 'Sender', { sender });
+    });
+
+    it('returns the transaction sender when from another contract', async function () {
+      const { tx } = await this.caller.callSender(this.context.address, { from: sender });
+      await expectEvent.inTransaction(tx, ContextMock, 'Sender', { sender: this.caller.address });
+    });
+  });
+
+  describe('msgData', function () {
+    const integerValue = new BN('42');
+    const stringValue = 'OpenZeppelin';
+
+    let callData;
+
+    beforeEach(async function () {
+      callData = this.context.contract.methods.msgData(integerValue.toString(), stringValue).encodeABI();
+    });
+
+    it('returns the transaction data when called from an EOA', async function () {
+      const { logs } = await this.context.msgData(integerValue, stringValue);
+      expectEvent.inLogs(logs, 'Data', { data: callData, integerValue, stringValue });
+    });
+
+    it('returns the transaction sender when from another contract', async function () {
+      const { tx } = await this.caller.callData(this.context.address, integerValue, stringValue);
+      await expectEvent.inTransaction(tx, ContextMock, 'Data', { data: callData, integerValue, stringValue });
+    });
+  });
+}
+
+module.exports = {
+  shouldBehaveLikeRegularContext,
+};

test/GSN/Context.test.js

+require('openzeppelin-test-helpers');
+
+const ContextMock = artifacts.require('ContextMock');
+const ContextMockCaller = artifacts.require('ContextMockCaller');
+
+const { shouldBehaveLikeRegularContext } = require('./Context.behavior');
+
+contract('Context', function ([_, sender]) {
+  beforeEach(async function () {
+    this.context = await ContextMock.new();
+    this.caller = await ContextMockCaller.new();
+  });
+
+  shouldBehaveLikeRegularContext(sender);
+});

test/GSN/GSNBouncerERC20Fee.test.js

+const { BN, ether, expectEvent } = require('openzeppelin-test-helpers');
+const gsn = require('@openzeppelin/gsn-helpers');
+
+const { expect } = require('chai').use(require('chai-bn')(web3.utils.BN));
+
+const GSNBouncerERC20FeeMock = artifacts.require('GSNBouncerERC20FeeMock');
+const ERC20Detailed = artifacts.require('ERC20Detailed');
+const IRelayHub = artifacts.require('IRelayHub');
+
+contract('GSNBouncerERC20Fee', function ([_, sender, other]) {
+  const name = 'FeeToken';
+  const symbol = 'FTKN';
+  const decimals = new BN('18');
+
+  beforeEach(async function () {
+    this.recipient = await GSNBouncerERC20FeeMock.new(name, symbol, decimals);
+    this.token = await ERC20Detailed.at(await this.recipient.token());
+  });
+
+  describe('token', function () {
+    it('has a name', async function () {
+      expect(await this.token.name()).to.equal(name);
+    });
+
+    it('has a symbol', async function () {
+      expect(await this.token.symbol()).to.equal(symbol);
+    });
+
+    it('has decimals', async function () {
+      expect(await this.token.decimals()).to.be.bignumber.equal(decimals);
+    });
+  });
+
+  context('when called directly', function () {
+    it('mock function can be called', async function () {
+      const { logs } = await this.recipient.mockFunction();
+      expectEvent.inLogs(logs, 'MockFunctionCalled');
+    });
+  });
+
+  context('when relay-called', function () {
+    beforeEach(async function () {
+      await gsn.fundRecipient(web3, { recipient: this.recipient.address });
+      this.relayHub = await IRelayHub.at('0xD216153c06E857cD7f72665E0aF1d7D82172F494');
+    });
+
+    it('charges the sender for GSN fees in tokens', async function () {
+      // The recipient will be charged from its RelayHub balance, and in turn charge the sender from its sender balance.
+      // Both amounts should be roughly equal.
+
+      // The sender has a balance in tokens, not ether, but since the exchange rate is 1:1, this works fine.
+      const senderPreBalance = ether('2');
+      await this.recipient.mint(sender, senderPreBalance);
+
+      const recipientPreBalance = await this.relayHub.balanceOf(this.recipient.address);
+
+      const { tx } = await this.recipient.mockFunction({ from: sender, useGSN: true });
+      await expectEvent.inTransaction(tx, IRelayHub, 'TransactionRelayed', { status: '0' });
+
+      const senderPostBalance = await this.token.balanceOf(sender);
+      const recipientPostBalance = await this.relayHub.balanceOf(this.recipient.address);
+
+      const senderCharge = senderPreBalance.sub(senderPostBalance);
+      const recipientCharge = recipientPreBalance.sub(recipientPostBalance);
+
+      expect(senderCharge).to.be.bignumber.closeTo(recipientCharge, recipientCharge.divn(10));
+    });
+  });
+});

test/GSN/GSNBouncerSignature.test.js

+const { expectEvent } = require('openzeppelin-test-helpers');
+const gsn = require('@openzeppelin/gsn-helpers');
+const { fixSignature } = require('../helpers/sign');
+const { utils: { toBN } } = require('web3');
+
+const GSNBouncerSignatureMock = artifacts.require('GSNBouncerSignatureMock');
+
+contract('GSNBouncerSignature', function ([_, signer, other]) {
+  beforeEach(async function () {
+    this.recipient = await GSNBouncerSignatureMock.new(signer);
+  });
+
+  context('when called directly', function () {
+    it('mock function can be called', async function () {
+      const { logs } = await this.recipient.mockFunction();
+      expectEvent.inLogs(logs, 'MockFunctionCalled');
+    });
+  });
+
+  context('when relay-called', function () {
+    beforeEach(async function () {
+      await gsn.fundRecipient(web3, { recipient: this.recipient.address });
+    });
+
+    it('rejects unsigned relay requests', async function () {
+      await gsn.expectError(this.recipient.mockFunction({ value: 0, useGSN: true }));
+    });
+
+    it('rejects relay requests where some parameters are signed', async function () {
+      const approveFunction = async (data) =>
+        fixSignature(
+          await web3.eth.sign(
+            web3.utils.soliditySha3(
+              // the nonce is not signed
+              data.relayerAddress, data.from, data.encodedFunctionCall, data.txFee, data.gasPrice, data.gas
+            ), signer
+          )
+        );
+
+      await gsn.expectError(this.recipient.mockFunction({ value: 0, useGSN: true, approveFunction }));
+    });
+
+    it('accepts relay requests where all parameters are signed', async function () {
+      const approveFunction = async (data) =>
+        fixSignature(
+          await web3.eth.sign(
+            web3.utils.soliditySha3(
+              // eslint-disable-next-line max-len
+              data.relayerAddress, data.from, data.encodedFunctionCall, toBN(data.txFee), toBN(data.gasPrice), toBN(data.gas), toBN(data.nonce), data.relayHubAddress, data.to
+            ), signer
+          )
+        );
+
+      const { tx } = await this.recipient.mockFunction({ value: 0, useGSN: true, approveFunction });
+
+      await expectEvent.inTransaction(tx, GSNBouncerSignatureMock, 'MockFunctionCalled');
+    });
+
+    it('rejects relay requests where all parameters are signed by an invalid signer', async function () {
+      const approveFunction = async (data) =>
+        fixSignature(
+          await web3.eth.sign(
+            web3.utils.soliditySha3(
+              // eslint-disable-next-line max-len
+              data.relay_address, data.from, data.encodedFunctionCall, data.txfee, data.gasPrice, data.gas, data.nonce, data.relayHubAddress, data.to
+            ), other
+          )
+        );
+
+      await gsn.expectError(this.recipient.mockFunction({ value: 0, useGSN: true, approveFunction }));
+    });
+  });
+});

test/GSN/GSNContext.test.js

+const { BN, constants, expectEvent, shouldFail } = require('openzeppelin-test-helpers');
+const { ZERO_ADDRESS } = constants;
+const gsn = require('@openzeppelin/gsn-helpers');
+
+const GSNContextMock = artifacts.require('GSNContextMock');
+const ContextMockCaller = artifacts.require('ContextMockCaller');
+
+const { shouldBehaveLikeRegularContext } = require('./Context.behavior');
+
+contract('GSNContext', function ([_, deployer, sender, newRelayHub]) {
+  beforeEach(async function () {
+    this.context = await GSNContextMock.new();
+    this.caller = await ContextMockCaller.new();
+  });
+
+  describe('get/set RelayHub', function () {
+    const singletonRelayHub = '0xD216153c06E857cD7f72665E0aF1d7D82172F494';
+
+    it('initially returns the singleton instance address', async function () {
+      expect(await this.context.getRelayHub()).to.equal(singletonRelayHub);
+    });
+
+    it('can be upgraded to a new RelayHub', async function () {
+      const { logs } = await this.context.upgradeRelayHub(newRelayHub);
+      expectEvent.inLogs(logs, 'RelayHubChanged', { oldRelayHub: singletonRelayHub, newRelayHub });
+    });
+
+    it('cannot upgrade to the same RelayHub', async function () {
+      await shouldFail.reverting(
+        this.context.upgradeRelayHub(singletonRelayHub)
+        //, 'GSNContext: new RelayHub is the current one'
+      );
+    });
+
+    it('cannot upgrade to the zero address', async function () {
+      await shouldFail.reverting(
+        this.context.upgradeRelayHub(ZERO_ADDRESS)
+        //, 'GSNContext: new RelayHub is the zero address'
+      );
+    });
+
+    context('with new RelayHub', function () {
+      beforeEach(async function () {
+        await this.context.upgradeRelayHub(newRelayHub);
+      });
+
+      it('returns the new instance address', async function () {
+        expect(await this.context.getRelayHub()).to.equal(newRelayHub);
+      });
+    });
+  });
+
+  context('when called directly', function () {
+    shouldBehaveLikeRegularContext(sender);
+  });
+
+  context('when receiving a relayed call', function () {
+    beforeEach(async function () {
+      await gsn.fundRecipient(web3, { recipient: this.context.address });
+    });
+
+    describe('msgSender', function () {
+      it('returns the relayed transaction original sender', async function () {
+        const { tx } = await this.context.msgSender({ from: sender, useGSN: true });
+        await expectEvent.inTransaction(tx, GSNContextMock, 'Sender', { sender });
+      });
+    });
+
+    describe('msgData', function () {
+      it('returns the relayed transaction original data', async function () {
+        const integerValue = new BN('42');
+        const stringValue = 'OpenZeppelin';
+        const callData = this.context.contract.methods.msgData(integerValue.toString(), stringValue).encodeABI();
+
+        // The provider doesn't properly estimate gas for a relayed call, so we need to manually set a higher value
+        const { tx } = await this.context.msgData(integerValue, stringValue, { gas: 1000000, useGSN: true });
+        await expectEvent.inTransaction(tx, GSNContextMock, 'Data', { data: callData, integerValue, stringValue });
+      });
+    });
+  });
+});

test/GSN/GSNRecipient.test.js

+const { balance, ether, shouldFail } = require('openzeppelin-test-helpers');
+const gsn = require('@openzeppelin/gsn-helpers');
+
+const { expect } = require('chai');
+
+const GSNRecipientMock = artifacts.require('GSNRecipientMock');
+
+contract('GSNRecipient', function ([_, payee]) {
+  beforeEach(async function () {
+    this.recipient = await GSNRecipientMock.new();
+  });
+
+  it('returns the RelayHub address address', async function () {
+    expect(await this.recipient.getHubAddr()).to.equal('0xD216153c06E857cD7f72665E0aF1d7D82172F494');
+  });
+
+  it('returns the compatible RelayHub version', async function () {
+    expect(await this.recipient.relayHubVersion()).to.equal('1.0.0');
+  });
+
+  context('with deposited funds', async function () {
+    const amount = ether('1');
+
+    beforeEach(async function () {
+      await gsn.fundRecipient(web3, { recipient: this.recipient.address, amount });
+    });
+
+    it('funds can be withdrawn', async function () {
+      expect(await balance.difference(payee, () =>
+        this.recipient.withdrawDeposits(amount, payee))
+      ).to.be.bignumber.equal(amount);
+    });
+
+    it('partial funds can be withdrawn', async function () {
+      expect(await balance.difference(payee, async () =>
+        this.recipient.withdrawDeposits(amount.divn(2), payee))
+      ).to.be.bignumber.equal(amount.divn(2));
+    });
+
+    it('reverts on overwithdrawals', async function () {
+      await shouldFail.reverting(
+        this.recipient.withdrawDeposits(amount.addn(1), payee)
+        // , 'insufficient funds'
+      );
+    });
+  });
+});

truffle-config.js

+require('chai/register-should');
+const { GSNDevProvider } = require('@openzeppelin/gsn-provider');
+
+const solcStable = {
+  version: '0.5.7',
+};
+
+const solcNightly = {
+  version: 'nightly',
+  docker: true,
+};
+
+const useSolcNightly = process.env.SOLC_NIGHTLY === 'true';
+
 module.exports = {
   networks: {
     development: {
-      host: 'localhost',
-      port: 8545,
+      provider: new GSNDevProvider('http://localhost:8545', {
+        txfee: 70,
+        useGSN: false,
+        // The last two accounts defined in test.sh
+        ownerAddress: '0x26be9c03ca7f61ad3d716253ee1edcae22734698',
+        relayerAddress: '0xdc5fd04802ea70f6e27aec12d56716624c98e749',
+      }),
       network_id: '*', // eslint-disable-line camelcase
     },
     coverage: {
-      host: 'localhost',
-      network_id: '*', // eslint-disable-line camelcase
-      port: 8555,
+      provider: new GSNDevProvider('http://localhost:8555', {
+        txfee: 70,
+        useGSN: false,
+        // The last two accounts defined in test.sh
+        ownerAddress: '0x26be9c03ca7f61ad3d716253ee1edcae22734698',
+        relayerAddress: '0xdc5fd04802ea70f6e27aec12d56716624c98e749',
+      }),
       gas: 0xfffffffffff,
       gasPrice: 0x01,
+      network_id: '*', // eslint-disable-line camelcase
     },
 
     mainnet: {
@@ -45,8 +69,6 @@ module.exports = {
   },
 
   compilers: {
-    solc: {
-      version: '0.5.2',
-    },
+    solc: useSolcNightly ? solcNightly : solcStable,
   },
 };