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frangio
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Minimal support for ERC2771 (GSNv2) (#2508)
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
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‎CHANGELOG.md‎

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* `Initializable`: Make initializer check stricter during construction. ([#2531](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2531))
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* `ERC721`: remove enumerability of tokens from the base implementation. This feature is now provided separately through the `ERC721Enumerable` extension. ([#2511](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2511))
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* `AccessControl`: removed enumerability by default for a more lightweight contract. It is now opt-in through `AccessControlEnumerable`. ([#2512](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2512))
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* Meta Transactions: add `ERC2771Context` and a `MinimalForwarder` for meta-transactions. ([#2508](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2508))
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## 3.4.0 (2021-02-02)
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‎contracts/cryptography/ECDSA.sol‎

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@@ -72,9 +72,9 @@ library ECDSA {
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/**
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* @dev Returns an Ethereum Signed Message, created from a `hash`. This
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* replicates the behavior of the
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* https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign[`eth_sign`]
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* JSON-RPC method.
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* produces hash corresponding to the one signed with the
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* https://eth.wiki/json-rpc/API#eth_sign[`eth_sign`]
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* JSON-RPC method as part of EIP-191.
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*
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* See {recover}.
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*/
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// enforced by the type signature above
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return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
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}
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/**
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* @dev Returns an Ethereum Signed Typed Data, created from a
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* `domainSeparator` and a `structHash`. This produces hash corresponding
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* to the one signed with the
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* https://eips.ethereum.org/EIPS/eip-712[`eth_signTypedData`]
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* JSON-RPC method as part of EIP-712.
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*
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* See {recover}.
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*/
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function toTypedDataHash(bytes32 domainSeparator, bytes32 structHash) internal pure returns (bytes32) {
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return keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
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}
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}

‎contracts/drafts/EIP712.sol‎

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pragma solidity ^0.8.0;
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import "../cryptography/ECDSA.sol";
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/**
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* @dev https://eips.ethereum.org/EIPS/eip-712[EIP 712] is a standard for hashing and signing of typed structured data.
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*
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* ```
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*/
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function _hashTypedDataV4(bytes32 structHash) internal view virtual returns (bytes32) {
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return keccak256(abi.encodePacked("\x19\x01", _domainSeparatorV4(), structHash));
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return ECDSA.toTypedDataHash(_domainSeparatorV4(), structHash);
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}
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}

‎contracts/metatx/ERC2771Context.sol‎

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// SPDX-License-Identifier: MIT
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pragma solidity ^0.8.0;
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import "../utils/Context.sol";
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/*
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* @dev Context variant with ERC2771 support.
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*/
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abstract contract ERC2771Context is Context {
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address immutable _trustedForwarder;
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constructor(address trustedForwarder) {
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_trustedForwarder = trustedForwarder;
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}
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function isTrustedForwarder(address forwarder) public view virtual returns(bool) {
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return forwarder == _trustedForwarder;
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}
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function _msgSender() internal view virtual override returns (address sender) {
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if (isTrustedForwarder(msg.sender)) {
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// The assembly code is more direct than the Solidity version using `abi.decode`.
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assembly { sender := shr(96, calldataload(sub(calldatasize(), 20))) }
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} else {
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return super._msgSender();
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}
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}
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function _msgData() internal view virtual override returns (bytes calldata) {
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if (isTrustedForwarder(msg.sender)) {
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return msg.data[:msg.data.length-20];
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} else {
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return super._msgData();
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}
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}
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}

‎contracts/metatx/MinimalForwarder.sol‎

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// SPDX-License-Identifier: MIT
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pragma solidity ^0.8.0;
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import "../cryptography/ECDSA.sol";
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import "../drafts/EIP712.sol";
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/*
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* @dev Simple minimal forwarder to be used together with an ERC2771 compatible contract. See {ERC2771Context}.
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*/
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contract MinimalForwarder is EIP712 {
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using ECDSA for bytes32;
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struct ForwardRequest {
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address from;
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address to;
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uint256 value;
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uint256 gas;
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uint256 nonce;
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bytes data;
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}
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bytes32 private constant TYPEHASH = keccak256("ForwardRequest(address from,address to,uint256 value,uint256 gas,uint256 nonce,bytes data)");
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mapping(address => uint256) private _nonces;
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constructor() EIP712("MinimalForwarder", "0.0.1") {}
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function getNonce(address from) public view returns (uint256) {
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return _nonces[from];
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}
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function verify(ForwardRequest calldata req, bytes calldata signature) public view returns (bool) {
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address signer = _hashTypedDataV4(keccak256(abi.encode(
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TYPEHASH,
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req.from,
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req.to,
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req.value,
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req.gas,
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req.nonce,
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keccak256(req.data)
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))).recover(signature);
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return _nonces[req.from] == req.nonce && signer == req.from;
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}
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function execute(ForwardRequest calldata req, bytes calldata signature) public payable returns (bool, bytes memory) {
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require(verify(req, signature), "MinimalForwarder: signature does not match request");
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_nonces[req.from] = req.nonce + 1;
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// solhint-disable-next-line avoid-low-level-calls
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(bool success, bytes memory returndata) = req.to.call{gas: req.gas, value: req.value}(abi.encodePacked(req.data, req.from));
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// Validate that the relayer has sent enough gas for the call.
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// See https://ronan.eth.link/blog/ethereum-gas-dangers/
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assert(gasleft() > req.gas / 63);
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return (success, returndata);
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}
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}

‎contracts/metatx/README.adoc‎

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= Meta Transactions
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[.readme-notice]
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NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/math
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== Core
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{{ERC2771Context}}
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== Utils
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{{MinimalForwarder}}

‎contracts/mocks/ERC2771ContextMock.sol‎

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// SPDX-License-Identifier: MIT
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pragma solidity ^0.8.0;
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import "./ContextMock.sol";
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import "../metatx/ERC2771Context.sol";
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// By inheriting from ERC2771Context, Context's internal functions are overridden automatically
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contract ERC2771ContextMock is ContextMock, ERC2771Context {
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constructor(address trustedForwarder) ERC2771Context(trustedForwarder) {}
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function _msgSender() internal override(Context, ERC2771Context) view virtual returns (address) {
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return ERC2771Context._msgSender();
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}
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function _msgData() internal override(Context, ERC2771Context) view virtual returns (bytes calldata) {
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return ERC2771Context._msgData();
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}
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}

‎test/metatx/ERC2771Context.test.js‎

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const ethSigUtil = require('eth-sig-util');
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const Wallet = require('ethereumjs-wallet').default;
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const { EIP712Domain } = require('../helpers/eip712');
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const { expectEvent } = require('@openzeppelin/test-helpers');
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const { expect } = require('chai');
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const ERC2771ContextMock = artifacts.require('ERC2771ContextMock');
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const MinimalForwarder = artifacts.require('MinimalForwarder');
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const ContextMockCaller = artifacts.require('ContextMockCaller');
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const { shouldBehaveLikeRegularContext } = require('../utils/Context.behavior');
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const name = 'MinimalForwarder';
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const version = '0.0.1';
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contract('ERC2771Context', function (accounts) {
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beforeEach(async function () {
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this.forwarder = await MinimalForwarder.new();
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this.recipient = await ERC2771ContextMock.new(this.forwarder.address);
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this.domain = {
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name,
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version,
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chainId: await web3.eth.getChainId(),
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verifyingContract: this.forwarder.address,
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};
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this.types = {
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EIP712Domain,
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ForwardRequest: [
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{ name: 'from', type: 'address' },
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{ name: 'to', type: 'address' },
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{ name: 'value', type: 'uint256' },
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{ name: 'gas', type: 'uint256' },
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{ name: 'nonce', type: 'uint256' },
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{ name: 'data', type: 'bytes' },
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],
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};
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});
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it('recognize trusted forwarder', async function () {
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expect(await this.recipient.isTrustedForwarder(this.forwarder.address));
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});
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context('when called directly', function () {
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beforeEach(async function () {
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this.context = this.recipient; // The Context behavior expects the contract in this.context
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this.caller = await ContextMockCaller.new();
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});
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shouldBehaveLikeRegularContext(...accounts);
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});
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context('when receiving a relayed call', function () {
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beforeEach(async function () {
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this.wallet = Wallet.generate();
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this.sender = web3.utils.toChecksumAddress(this.wallet.getAddressString());
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this.data = {
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types: this.types,
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domain: this.domain,
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primaryType: 'ForwardRequest',
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};
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});
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describe('msgSender', function () {
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it('returns the relayed transaction original sender', async function () {
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const data = this.recipient.contract.methods.msgSender().encodeABI();
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const req = {
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from: this.sender,
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to: this.recipient.address,
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value: '0',
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gas: '100000',
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nonce: (await this.forwarder.getNonce(this.sender)).toString(),
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data,
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};
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const sign = ethSigUtil.signTypedMessage(this.wallet.getPrivateKey(), { data: { ...this.data, message: req } });
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// rejected by lint :/
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// expect(await this.forwarder.verify(req, sign)).to.be.true;
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const { tx } = await this.forwarder.execute(req, sign);
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await expectEvent.inTransaction(tx, ERC2771ContextMock, 'Sender', { sender: this.sender });
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});
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});
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describe('msgData', function () {
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it('returns the relayed transaction original data', async function () {
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const integerValue = '42';
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const stringValue = 'OpenZeppelin';
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const data = this.recipient.contract.methods.msgData(integerValue, stringValue).encodeABI();
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const req = {
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from: this.sender,
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to: this.recipient.address,
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value: '0',
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gas: '100000',
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nonce: (await this.forwarder.getNonce(this.sender)).toString(),
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data,
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};
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const sign = ethSigUtil.signTypedMessage(this.wallet.getPrivateKey(), { data: { ...this.data, message: req } });
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// rejected by lint :/
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// expect(await this.forwarder.verify(req, sign)).to.be.true;
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const { tx } = await this.forwarder.execute(req, sign);
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await expectEvent.inTransaction(tx, ERC2771ContextMock, 'Data', { data, integerValue, stringValue });
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});
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});
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});
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});

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