Initial GSN support (beta) (#1844)

* 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

* Fix gsn dependencies in package.json

* Rhub address slot reduced by 1

* Rename relay hub changed event

* Use released gsn-provider

* Run relayer with short sleep of 1s instead of 100ms

* update package-lock.json

* clear circle cache

* use optimized gsn-provider

* update to latest @openzeppelin/gsn-provider

* replace with gsn dev provider

* remove relay server

* rename arguments in approveFunction

* fix GSNBouncerSignature test

* change gsn txfee

* initialize development provider only once

* update RelayHub interface

* adapt to new IRelayHub.withdraw

* update @openzeppelin/gsn-helpers

* update relayhub singleton address

* fix helper name

* set up gsn provider for coverage too

* lint

* Revert "set up gsn provider for coverage too"

This reverts commit 8a7b5be5f9.

* remove unused code

* add gsn provider to coverage

* move truffle contract options back out

* increase gas limit for coverage

* remove unreachable code

* add more gas for GSNContext test

* fix test suite name

* rename GSNBouncerBase internal API

* remove onlyRelayHub modifier

* add explicit inheritance

* remove redundant event

* update name of bouncers error codes enums

* add basic docs page for gsn contracts

* make gsn directory all caps

* add changelog entry

* lint

* enable test run to fail in coverage

contracts/mocks/ContextMock.sol

@@ -0,0 +1,27 @@
+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

@@ -0,0 +1,20 @@
+pragma solidity ^0.5.0;
+
+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(name, symbol, decimals) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    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

@@ -0,0 +1,16 @@
+pragma solidity ^0.5.0;
+
+import "../GSN/GSNRecipient.sol";
+import "../GSN/bouncers/GSNBouncerSignature.sol";
+
+contract GSNBouncerSignatureMock is GSNRecipient, GSNBouncerSignature {
+    constructor(address trustedSigner) public GSNBouncerSignature(trustedSigner) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    event MockFunctionCalled();
+
+    function mockFunction() public {
+        emit MockFunctionCalled();
+    }
+}

contracts/mocks/GSNContextMock.sol

@@ -0,0 +1,46 @@
+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 {
+    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

@@ -0,0 +1,25 @@
+pragma solidity ^0.5.0;
+
+import "../GSN/GSNRecipient.sol";
+
+contract GSNRecipientMock is GSNRecipient {
+    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
+    }
+}