EIP712MetaTransaction.sol

//SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

import "./EIP712Base.sol";

abstract contract EIP712MetaTransaction is EIP712Base {
  string internal constant DOMAIN_NAME = "mydapp.app";
  string internal constant DOMAIN_VERSION = "1";

  bytes32 private constant META_TRANSACTION_TYPEHASH =
    keccak256(
      bytes(
        "MetaTransaction(uint256 nonce,address from,bytes functionSignature)"
      )
    );

  event MetaTransactionExecuted(
    address userAddress,
    address payable relayerAddress,
    bytes functionSignature
  );

  mapping(address => uint256) nonces;

  /*
   * Meta transaction structure.
   * No point of including value field here as if user is doing value transfer then he has the funds to pay for gas
   * He should call the desired function directly in that case.
   */
  struct MetaTransaction {
    uint256 nonce;
    address from;
    bytes functionSignature;
  }

  function executeMetaTransaction(
    address userAddress,
    bytes memory functionSignature,
    bytes32 sigR,
    bytes32 sigS,
    uint8 sigV
  ) public payable returns (bytes memory) {
    MetaTransaction memory metaTx = MetaTransaction({
      nonce: nonces[userAddress],
      from: userAddress,
      functionSignature: functionSignature
    });

    require(
      verify(userAddress, metaTx, sigR, sigS, sigV),
      "Signer and signature do not match"
    );

    // increase nonce for user (to avoid re-use)
    nonces[userAddress] = nonces[userAddress] + 1;

    emit MetaTransactionExecuted(
      userAddress,
      payable(msg.sender),
      functionSignature
    );

    // Append userAddress and relayer address at the end to extract it from calling context
    (bool success, bytes memory returnData) = address(this).call(
      abi.encodePacked(functionSignature, userAddress)
    );
    require(success, "Function call not successful");

    return returnData;
  }

  function hashMetaTransaction(MetaTransaction memory metaTx)
    internal
    pure
    returns (bytes32)
  {
    return
      keccak256(
        abi.encode(
          META_TRANSACTION_TYPEHASH,
          metaTx.nonce,
          metaTx.from,
          keccak256(metaTx.functionSignature)
        )
      );
  }

  function msgSender() internal view returns (address payable sender) {
    if (msg.sender == address(this)) {
      bytes memory array = msg.data;
      uint256 index = msg.data.length;
      assembly {
        // Load the 32 bytes word from memory with the address on the lower 20 bytes, and mask those.
        sender := and(
          mload(add(array, index)),
          0xffffffffffffffffffffffffffffffffffffffff
        )
      }
    } else {
      sender = payable(msg.sender);
    }

    return sender;
  }

  function getNonce(address user) public view returns (uint256 nonce) {
    nonce = nonces[user];
  }

  function verify(
    address signer,
    MetaTransaction memory metaTx,
    bytes32 sigR,
    bytes32 sigS,
    uint8 sigV
  ) internal view returns (bool) {
    require(signer != address(0), "NativeMetaTransaction: INVALID_SIGNER");
    return
      signer ==
      ecrecover(
        toTypedMessageHash(hashMetaTransaction(metaTx)),
        sigV,
        sigR,
        sigS
      );
  }
}