feat: make StarknetTokenBridge ERC2771 compliant

Author: achab

README.md

@@ -35,6 +35,10 @@ Note: the frontend implementation of the bridges, can be found [here](https://gi
 
 This project contains scripts written in Python 3.9.
 
+## EIP2771 compliance
+
+We made the L1 bridge EIP2771 compliant by inheriting from [ERC2771Recipient.sol](https://github.com/opengsn/gsn/blob/master/packages/contracts/src/ERC2771Recipient.sol).
+
 
 ## Getting Started
 

src/solidity/ERC2771Recipient.sol

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: MIT
+// solhint-disable no-inline-assembly
+pragma solidity >=0.6.9;
+
+import "./IERC2771Recipient.sol";
+
+/**
+ * @title The ERC-2771 Recipient Base Abstract Class - Implementation
+ *
+ * @notice Note that this contract was called `BaseRelayRecipient` in the previous revision of the GSN.
+ *
+ * @notice A base contract to be inherited by any contract that want to receive relayed transactions.
+ *
+ * @notice A subclass must use `_msgSender()` instead of `msg.sender`.
+ */
+abstract contract ERC2771Recipient is IERC2771Recipient {
+
+    /*
+     * Forwarder singleton we accept calls from
+     */
+    address private _trustedForwarder;
+
+    /**
+     * :warning: **Warning** :warning: The Forwarder can have a full control over your Recipient. Only trust verified Forwarder.
+     * @notice Method is not a required method to allow Recipients to trust multiple Forwarders. Not recommended yet.
+     * @return forwarder The address of the Forwarder contract that is being used.
+     */
+    function getTrustedForwarder() public virtual view returns (address forwarder){
+        return _trustedForwarder;
+    }
+
+    function _setTrustedForwarder(address _forwarder) internal {
+        _trustedForwarder = _forwarder;
+    }
+
+    /// @inheritdoc IERC2771Recipient
+    function isTrustedForwarder(address forwarder) public virtual override view returns(bool) {
+        return forwarder == _trustedForwarder;
+    }
+
+    /// @inheritdoc IERC2771Recipient
+    function _msgSender() internal override virtual view returns (address ret) {
+        if (msg.data.length >= 20 && isTrustedForwarder(msg.sender)) {
+            // At this point we know that the sender is a trusted forwarder,
+            // so we trust that the last bytes of msg.data are the verified sender address.
+            // extract sender address from the end of msg.data
+            assembly {
+                ret := shr(96,calldataload(sub(calldatasize(),20)))
+            }
+        } else {
+            ret = msg.sender;
+        }
+    }
+
+    /// @inheritdoc IERC2771Recipient
+    function _msgData() internal override virtual view returns (bytes calldata ret) {
+        if (msg.data.length >= 20 && isTrustedForwarder(msg.sender)) {
+            return msg.data[0:msg.data.length-20];
+        } else {
+            return msg.data;
+        }
+    }
+}

src/solidity/IERC2771Recipient.sol

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: MIT
+pragma solidity >=0.6.0;
+
+/**
+ * @title The ERC-2771 Recipient Base Abstract Class - Declarations
+ *
+ * @notice A contract must implement this interface in order to support relayed transaction.
+ *
+ * @notice It is recommended that your contract inherits from the ERC2771Recipient contract.
+ */
+abstract contract IERC2771Recipient {
+
+    /**
+     * :warning: **Warning** :warning: The Forwarder can have a full control over your Recipient. Only trust verified Forwarder.
+     * @param forwarder The address of the Forwarder contract that is being used.
+     * @return isTrustedForwarder `true` if the Forwarder is trusted to forward relayed transactions by this Recipient.
+     */
+    function isTrustedForwarder(address forwarder) public virtual view returns(bool);
+
+    /**
+     * @notice Use this method the contract anywhere instead of msg.sender to support relayed transactions.
+     * @return sender The real sender of this call.
+     * For a call that came through the Forwarder the real sender is extracted from the last 20 bytes of the `msg.data`.
+     * Otherwise simply returns `msg.sender`.
+     */
+    function _msgSender() internal virtual view returns (address);
+
+    /**
+     * @notice Use this method in the contract instead of `msg.data` when difference matters (hashing, signature, etc.)
+     * @return data The real `msg.data` of this call.
+     * For a call that came through the Forwarder, the real sender address was appended as the last 20 bytes
+     * of the `msg.data` - so this method will strip those 20 bytes off.
+     * Otherwise (if the call was made directly and not through the forwarder) simply returns `msg.data`.
+     */
+    function _msgData() internal virtual view returns (bytes calldata);
+}

src/solidity/StarknetTokenBridge.sol

@@ -9,6 +9,7 @@ import "starkware/solidity/libraries/Transfers.sol";
 import "starkware/solidity/tokens/ERC20/IERC20.sol";
 import "starkware/solidity/tokens/ERC20/IERC20Metadata.sol";
 import "starkware/starknet/solidity/IStarknetMessaging.sol";
+import "src/solidity/ERC2771Recipient.sol";
 import "src/solidity/Fees.sol";
 import "src/solidity/IStarkgateBridge.sol";
 import "src/solidity/IStarkgateManager.sol";
@@ -25,7 +26,8 @@ contract StarknetTokenBridge is
     IStarkgateService,
     Identity,
     StarknetTokenStorage,
-    ProxySupport
+    ProxySupport,
+    ERC2771Recipient
 {
     using Addresses for address;
     using Felt252 for string;
@@ -125,7 +127,7 @@ contract StarknetTokenBridge is
     }
 
     modifier onlyManager() {
-        require(manager() == msg.sender, "ONLY_MANAGER");
+        require(manager() == _msgSender(), "ONLY_MANAGER");
         _;
     }
 
@@ -152,7 +154,7 @@ contract StarknetTokenBridge is
         Fees.checkDepositFee(msg.value);
         uint256 currentBalance = IERC20(token).balanceOf(address(this));
         require(currentBalance + amount <= getMaxTotalBalance(token), "MAX_BALANCE_EXCEEDED");
-        Transfers.transferIn(token, msg.sender, amount);
+        Transfers.transferIn(token, _msgSender(), amount);
         return msg.value;
     }
 
@@ -320,10 +322,10 @@ contract StarknetTokenBridge is
         uint256 fee
     ) internal {
         if (selector == HANDLE_TOKEN_DEPOSIT_SELECTOR) {
-            emit Deposit(msg.sender, token, amount, l2Recipient, nonce, fee);
+            emit Deposit(_msgSender(), token, amount, l2Recipient, nonce, fee);
         } else {
             require(selector == HANDLE_DEPOSIT_WITH_MESSAGE_SELECTOR, "UNKNOWN_SELECTOR");
-            emit DepositWithMessage(msg.sender, token, amount, l2Recipient, message, nonce, fee);
+            emit DepositWithMessage(_msgSender(), token, amount, l2Recipient, message, nonce, fee);
         }
     }
 
@@ -339,15 +341,15 @@ contract StarknetTokenBridge is
      */
     function enableWithdrawalLimit(address token) external onlySecurityAgent {
         tokenSettings()[token].withdrawalLimitApplied = true;
-        emit WithdrawalLimitEnabled(msg.sender, token);
+        emit WithdrawalLimitEnabled(_msgSender(), token);
     }
 
     /**
         Unset withdrawal limit for a token.
      */
     function disableWithdrawalLimit(address token) external onlySecurityAdmin {
         tokenSettings()[token].withdrawalLimitApplied = false;
-        emit WithdrawalLimitDisabled(msg.sender, token);
+        emit WithdrawalLimitDisabled(_msgSender(), token);
     }
 
     /**
@@ -397,7 +399,7 @@ contract StarknetTokenBridge is
             : N_DEPOSIT_PAYLOAD_ARGS;
         uint256[] memory payload = new uint256[](MESSAGE_OFFSET + message.length);
         payload[0] = uint256(uint160(token));
-        payload[1] = uint256(uint160(msg.sender));
+        payload[1] = uint256(uint160(_msgSender()));
         payload[2] = l2Recipient;
         payload[3] = amount & (UINT256_PART_SIZE - 1);
         payload[4] = amount >> UINT256_PART_SIZE_BITS;
@@ -499,7 +501,7 @@ contract StarknetTokenBridge is
     }
 
     function withdraw(address token, uint256 amount) external {
-        withdraw(token, amount, msg.sender);
+        withdraw(token, amount, _msgSender());
     }
 
     /*
@@ -525,7 +527,7 @@ contract StarknetTokenBridge is
             nonce
         );
 
-        emit DepositCancelRequest(msg.sender, token, amount, l2Recipient, nonce);
+        emit DepositCancelRequest(_msgSender(), token, amount, l2Recipient, nonce);
     }
 
     /*
@@ -552,7 +554,7 @@ contract StarknetTokenBridge is
         );
 
         emit DepositWithMessageCancelRequest(
-            msg.sender,
+            _msgSender(),
             token,
             amount,
             l2Recipient,
@@ -581,8 +583,8 @@ contract StarknetTokenBridge is
             nonce
         );
 
-        transferOutFunds(token, amount, msg.sender);
-        emit DepositWithMessageReclaimed(msg.sender, token, amount, l2Recipient, message, nonce);
+        transferOutFunds(token, amount, _msgSender());
+        emit DepositWithMessageReclaimed(_msgSender(), token, amount, l2Recipient, message, nonce);
     }
 
     function depositReclaim(
@@ -598,7 +600,18 @@ contract StarknetTokenBridge is
             nonce
         );
 
-        transferOutFunds(token, amount, msg.sender);
-        emit DepositReclaimed(msg.sender, token, amount, l2Recipient, nonce);
+        transferOutFunds(token, amount, _msgSender());
+        emit DepositReclaimed(_msgSender(), token, amount, l2Recipient, nonce);
+    }
+
+
+    // EIP2771 related functions
+
+    function setTrustedForwarder(address _forwarder) public onlyManager {
+        _setTrustedForwarder(_forwarder);
+    }
+
+    function versionRecipient() external view override returns (string memory) {
+        return "1";
     }
 }