From ccffe671054676b65a5d7f3434eb75b3237ff3dc Mon Sep 17 00:00:00 2001
From: Dan Finlay <dan@danfinlay.com>
Date: Sun, 21 Aug 2022 22:26:03 -0700
Subject: [PATCH 1/3] Add _msgSender() trick

Fixes #132

Enables MetaTransaction facets and [Delegatable](https://github.com/delegatable/delegatable-sol/blob/main/contracts/diamond/README.md).
---
 contracts/access/ownable/OwnableInternal.sol  | 26 ++++++++--
 contracts/security/PausableInternal.sol       | 24 +++++++++-
 contracts/token/ERC1155/base/ERC1155Base.sol  | 14 +++---
 .../ERC1155/base/ERC1155BaseInternal.sol      | 47 +++++++++++++++----
 contracts/token/ERC20/base/ERC20Base.sol      |  4 +-
 .../token/ERC20/base/ERC20BaseInternal.sol    | 24 +++++++++-
 contracts/token/ERC721/base/ERC721Base.sol    | 12 ++---
 .../token/ERC721/base/ERC721BaseInternal.sol  | 22 ++++++++-
 8 files changed, 140 insertions(+), 33 deletions(-)

diff --git a/contracts/access/ownable/OwnableInternal.sol b/contracts/access/ownable/OwnableInternal.sol
index 49366e81..1b3bca8a 100644
--- a/contracts/access/ownable/OwnableInternal.sol
+++ b/contracts/access/ownable/OwnableInternal.sol
@@ -12,13 +12,13 @@ abstract contract OwnableInternal is IOwnableInternal {
     using OwnableStorage for OwnableStorage.Layout;
 
     modifier onlyOwner() {
-        require(msg.sender == _owner(), 'Ownable: sender must be owner');
+        require(_msgSender() == _owner(), 'Ownable: sender must be owner');
         _;
     }
 
     modifier onlyTransitiveOwner() {
         require(
-            msg.sender == _transitiveOwner(),
+            _msgSender() == _transitiveOwner(),
             'Ownable: sender must be transitive owner'
         );
         _;
@@ -44,6 +44,26 @@ abstract contract OwnableInternal is IOwnableInternal {
 
     function _transferOwnership(address account) internal virtual {
         OwnableStorage.layout().setOwner(account);
-        emit OwnershipTransferred(msg.sender, account);
+        emit OwnershipTransferred(_msgSender(), account);
+    }
+
+    /*
+     * @notice Overrides the msgSender to enable delegation message signing.
+     * @returns address - The account whose authority is being acted on.
+     */
+    function _msgSender() internal view virtual returns (address sender) {
+        if (msg.sender == address(this)) {
+            bytes memory array = msg.data;
+            uint256 index = msg.data.length;
+            assembly {
+                sender := and(
+                    mload(add(array, index)),
+                    0xffffffffffffffffffffffffffffffffffffffff
+                )
+            }
+        } else {
+            sender = msg.sender;
+        }
+        return sender;
     }
 }
diff --git a/contracts/security/PausableInternal.sol b/contracts/security/PausableInternal.sol
index 3aec4f66..50e9077b 100644
--- a/contracts/security/PausableInternal.sol
+++ b/contracts/security/PausableInternal.sol
@@ -37,7 +37,7 @@ abstract contract PausableInternal {
      */
     function _pause() internal virtual whenNotPaused {
         PausableStorage.layout().paused = true;
-        emit Paused(msg.sender);
+        emit Paused(_msgSender());
     }
 
     /**
@@ -45,6 +45,26 @@ abstract contract PausableInternal {
      */
     function _unpause() internal virtual whenPaused {
         PausableStorage.layout().paused = false;
-        emit Unpaused(msg.sender);
+        emit Unpaused(_msgSender());
+    }
+
+    /*
+     * @notice Overrides the msgSender to enable delegation message signing.
+     * @returns address - The account whose authority is being acted on.
+     */
+    function _msgSender() internal view virtual returns (address sender) {
+        if (msg.sender == address(this)) {
+            bytes memory array = msg.data;
+            uint256 index = msg.data.length;
+            assembly {
+                sender := and(
+                    mload(add(array, index)),
+                    0xffffffffffffffffffffffffffffffffffffffff
+                )
+            }
+        } else {
+            sender = msg.sender;
+        }
+        return sender;
     }
 }
diff --git a/contracts/token/ERC1155/base/ERC1155Base.sol b/contracts/token/ERC1155/base/ERC1155Base.sol
index 1df879a1..7356db72 100644
--- a/contracts/token/ERC1155/base/ERC1155Base.sol
+++ b/contracts/token/ERC1155/base/ERC1155Base.sol
@@ -73,13 +73,13 @@ abstract contract ERC1155Base is IERC1155Base, ERC1155BaseInternal {
      */
     function setApprovalForAll(address operator, bool status) public virtual {
         require(
-            msg.sender != operator,
+            _msgSender() != operator,
             'ERC1155: setting approval status for self'
         );
-        ERC1155BaseStorage.layout().operatorApprovals[msg.sender][
+        ERC1155BaseStorage.layout().operatorApprovals[_msgSender()][
             operator
         ] = status;
-        emit ApprovalForAll(msg.sender, operator, status);
+        emit ApprovalForAll(_msgSender(), operator, status);
     }
 
     /**
@@ -93,10 +93,10 @@ abstract contract ERC1155Base is IERC1155Base, ERC1155BaseInternal {
         bytes memory data
     ) public virtual {
         require(
-            from == msg.sender || isApprovedForAll(from, msg.sender),
+            from == _msgSender() || isApprovedForAll(from, _msgSender()),
             'ERC1155: caller is not owner nor approved'
         );
-        _safeTransfer(msg.sender, from, to, id, amount, data);
+        _safeTransfer(_msgSender(), from, to, id, amount, data);
     }
 
     /**
@@ -110,9 +110,9 @@ abstract contract ERC1155Base is IERC1155Base, ERC1155BaseInternal {
         bytes memory data
     ) public virtual {
         require(
-            from == msg.sender || isApprovedForAll(from, msg.sender),
+            from == _msgSender() || isApprovedForAll(from, _msgSender()),
             'ERC1155: caller is not owner nor approved'
         );
-        _safeTransferBatch(msg.sender, from, to, ids, amounts, data);
+        _safeTransferBatch(_msgSender(), from, to, ids, amounts, data);
     }
 }
diff --git a/contracts/token/ERC1155/base/ERC1155BaseInternal.sol b/contracts/token/ERC1155/base/ERC1155BaseInternal.sol
index 63944275..71e9bee0 100644
--- a/contracts/token/ERC1155/base/ERC1155BaseInternal.sol
+++ b/contracts/token/ERC1155/base/ERC1155BaseInternal.sol
@@ -50,7 +50,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
         require(account != address(0), 'ERC1155: mint to the zero address');
 
         _beforeTokenTransfer(
-            msg.sender,
+            _msgSender(),
             address(0),
             account,
             _asSingletonArray(id),
@@ -60,7 +60,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
 
         ERC1155BaseStorage.layout().balances[id][account] += amount;
 
-        emit TransferSingle(msg.sender, address(0), account, id, amount);
+        emit TransferSingle(_msgSender(), address(0), account, id, amount);
     }
 
     /**
@@ -79,7 +79,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
         _mint(account, id, amount, data);
 
         _doSafeTransferAcceptanceCheck(
-            msg.sender,
+            _msgSender(),
             address(0),
             account,
             id,
@@ -109,7 +109,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
         );
 
         _beforeTokenTransfer(
-            msg.sender,
+            _msgSender(),
             address(0),
             account,
             ids,
@@ -127,7 +127,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
             }
         }
 
-        emit TransferBatch(msg.sender, address(0), account, ids, amounts);
+        emit TransferBatch(_msgSender(), address(0), account, ids, amounts);
     }
 
     /**
@@ -146,7 +146,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
         _mintBatch(account, ids, amounts, data);
 
         _doSafeBatchTransferAcceptanceCheck(
-            msg.sender,
+            _msgSender(),
             address(0),
             account,
             ids,
@@ -169,7 +169,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
         require(account != address(0), 'ERC1155: burn from the zero address');
 
         _beforeTokenTransfer(
-            msg.sender,
+            _msgSender(),
             account,
             address(0),
             _asSingletonArray(id),
@@ -189,7 +189,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
             balances[account] -= amount;
         }
 
-        emit TransferSingle(msg.sender, account, address(0), id, amount);
+        emit TransferSingle(_msgSender(), account, address(0), id, amount);
     }
 
     /**
@@ -209,7 +209,14 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
             'ERC1155: ids and amounts length mismatch'
         );
 
-        _beforeTokenTransfer(msg.sender, account, address(0), ids, amounts, '');
+        _beforeTokenTransfer(
+            _msgSender(),
+            account,
+            address(0),
+            ids,
+            amounts,
+            ''
+        );
 
         mapping(uint256 => mapping(address => uint256))
             storage balances = ERC1155BaseStorage.layout().balances;
@@ -225,7 +232,7 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
             }
         }
 
-        emit TransferBatch(msg.sender, account, address(0), ids, amounts);
+        emit TransferBatch(_msgSender(), account, address(0), ids, amounts);
     }
 
     /**
@@ -504,4 +511,24 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
         uint256[] memory amounts,
         bytes memory data
     ) internal virtual {}
+
+    /*
+     * @notice Overrides the msgSender to enable delegation message signing.
+     * @returns address - The account whose authority is being acted on.
+     */
+    function _msgSender() internal view virtual returns (address sender) {
+        if (msg.sender == address(this)) {
+            bytes memory array = msg.data;
+            uint256 index = msg.data.length;
+            assembly {
+                sender := and(
+                    mload(add(array, index)),
+                    0xffffffffffffffffffffffffffffffffffffffff
+                )
+            }
+        } else {
+            sender = msg.sender;
+        }
+        return sender;
+    }
 }
diff --git a/contracts/token/ERC20/base/ERC20Base.sol b/contracts/token/ERC20/base/ERC20Base.sol
index 35d00328..b17d88cb 100644
--- a/contracts/token/ERC20/base/ERC20Base.sol
+++ b/contracts/token/ERC20/base/ERC20Base.sol
@@ -45,7 +45,7 @@ abstract contract ERC20Base is IERC20Base, ERC20BaseInternal {
         virtual
         returns (bool)
     {
-        return _approve(msg.sender, spender, amount);
+        return _approve(_msgSender(), spender, amount);
     }
 
     /**
@@ -56,7 +56,7 @@ abstract contract ERC20Base is IERC20Base, ERC20BaseInternal {
         virtual
         returns (bool)
     {
-        return _transfer(msg.sender, recipient, amount);
+        return _transfer(_msgSender(), recipient, amount);
     }
 
     /**
diff --git a/contracts/token/ERC20/base/ERC20BaseInternal.sol b/contracts/token/ERC20/base/ERC20BaseInternal.sol
index e3aace4d..0f38c5ce 100644
--- a/contracts/token/ERC20/base/ERC20BaseInternal.sol
+++ b/contracts/token/ERC20/base/ERC20BaseInternal.sol
@@ -151,7 +151,7 @@ abstract contract ERC20BaseInternal is IERC20BaseInternal {
         address recipient,
         uint256 amount
     ) internal virtual returns (bool) {
-        uint256 currentAllowance = _allowance(holder, msg.sender);
+        uint256 currentAllowance = _allowance(holder, _msgSender());
 
         require(
             currentAllowance >= amount,
@@ -159,7 +159,7 @@ abstract contract ERC20BaseInternal is IERC20BaseInternal {
         );
 
         unchecked {
-            _approve(holder, msg.sender, currentAllowance - amount);
+            _approve(holder, _msgSender(), currentAllowance - amount);
         }
 
         _transfer(holder, recipient, amount);
@@ -179,4 +179,24 @@ abstract contract ERC20BaseInternal is IERC20BaseInternal {
         address to,
         uint256 amount
     ) internal virtual {}
+
+    /*
+     * @notice Overrides the msgSender to enable delegation message signing.
+     * @returns address - The account whose authority is being acted on.
+     */
+    function _msgSender() internal view virtual returns (address sender) {
+        if (msg.sender == address(this)) {
+            bytes memory array = msg.data;
+            uint256 index = msg.data.length;
+            assembly {
+                sender := and(
+                    mload(add(array, index)),
+                    0xffffffffffffffffffffffffffffffffffffffff
+                )
+            }
+        } else {
+            sender = msg.sender;
+        }
+        return sender;
+    }
 }
diff --git a/contracts/token/ERC721/base/ERC721Base.sol b/contracts/token/ERC721/base/ERC721Base.sol
index 22fe7342..343c61c9 100644
--- a/contracts/token/ERC721/base/ERC721Base.sol
+++ b/contracts/token/ERC721/base/ERC721Base.sol
@@ -61,7 +61,7 @@ abstract contract ERC721Base is IERC721Base, ERC721BaseInternal {
     ) public payable {
         _handleTransferMessageValue(from, to, tokenId, msg.value);
         require(
-            _isApprovedOrOwner(msg.sender, tokenId),
+            _isApprovedOrOwner(_msgSender(), tokenId),
             'ERC721: transfer caller is not owner or approved'
         );
         _transfer(from, to, tokenId);
@@ -89,7 +89,7 @@ abstract contract ERC721Base is IERC721Base, ERC721BaseInternal {
     ) public payable {
         _handleTransferMessageValue(from, to, tokenId, msg.value);
         require(
-            _isApprovedOrOwner(msg.sender, tokenId),
+            _isApprovedOrOwner(_msgSender(), tokenId),
             'ERC721: transfer caller is not owner or approved'
         );
         _safeTransfer(from, to, tokenId, data);
@@ -103,7 +103,7 @@ abstract contract ERC721Base is IERC721Base, ERC721BaseInternal {
         address owner = ownerOf(tokenId);
         require(operator != owner, 'ERC721: approval to current owner');
         require(
-            msg.sender == owner || isApprovedForAll(owner, msg.sender),
+            _msgSender() == owner || isApprovedForAll(owner, _msgSender()),
             'ERC721: approve caller is not owner nor approved for all'
         );
         _approve(operator, tokenId);
@@ -113,10 +113,10 @@ abstract contract ERC721Base is IERC721Base, ERC721BaseInternal {
      * @inheritdoc IERC721
      */
     function setApprovalForAll(address operator, bool status) public {
-        require(operator != msg.sender, 'ERC721: approve to caller');
-        ERC721BaseStorage.layout().operatorApprovals[msg.sender][
+        require(operator != _msgSender(), 'ERC721: approve to caller');
+        ERC721BaseStorage.layout().operatorApprovals[_msgSender()][
             operator
         ] = status;
-        emit ApprovalForAll(msg.sender, operator, status);
+        emit ApprovalForAll(_msgSender(), operator, status);
     }
 }
diff --git a/contracts/token/ERC721/base/ERC721BaseInternal.sol b/contracts/token/ERC721/base/ERC721BaseInternal.sol
index 8c1d7b62..810ed08d 100644
--- a/contracts/token/ERC721/base/ERC721BaseInternal.sol
+++ b/contracts/token/ERC721/base/ERC721BaseInternal.sol
@@ -179,7 +179,7 @@ abstract contract ERC721BaseInternal is IERC721Internal {
         bytes memory returnData = to.functionCall(
             abi.encodeWithSelector(
                 IERC721Receiver(to).onERC721Received.selector,
-                msg.sender,
+                _msgSender(),
                 from,
                 tokenId,
                 data
@@ -229,4 +229,24 @@ abstract contract ERC721BaseInternal is IERC721Internal {
         address to,
         uint256 tokenId
     ) internal virtual {}
+
+    /*
+     * @notice Overrides the msgSender to enable delegation message signing.
+     * @returns address - The account whose authority is being acted on.
+     */
+    function _msgSender() internal view virtual returns (address sender) {
+        if (msg.sender == address(this)) {
+            bytes memory array = msg.data;
+            uint256 index = msg.data.length;
+            assembly {
+                sender := and(
+                    mload(add(array, index)),
+                    0xffffffffffffffffffffffffffffffffffffffff
+                )
+            }
+        } else {
+            sender = msg.sender;
+        }
+        return sender;
+    }
 }

From a0b566ebeb3b7d4998dd4349ae822e72c3318700 Mon Sep 17 00:00:00 2001
From: Dan Finlay <dan@danfinlay.com>
Date: Thu, 25 Aug 2022 18:44:44 -0700
Subject: [PATCH 2/3] Move msgSender trick to utils file

---
 contracts/access/ownable/OwnableInternal.sol  | 23 ++-------------
 contracts/security/PausableInternal.sol       | 23 ++-------------
 .../ERC1155/base/ERC1155BaseInternal.sol      | 23 ++-------------
 .../token/ERC20/base/ERC20BaseInternal.sol    | 23 ++-------------
 .../token/ERC721/base/ERC721BaseInternal.sol  | 23 ++-------------
 contracts/utils/MsgSenderTrick.sol            | 28 +++++++++++++++++++
 6 files changed, 38 insertions(+), 105 deletions(-)
 create mode 100644 contracts/utils/MsgSenderTrick.sol

diff --git a/contracts/access/ownable/OwnableInternal.sol b/contracts/access/ownable/OwnableInternal.sol
index 1b3bca8a..b3596661 100644
--- a/contracts/access/ownable/OwnableInternal.sol
+++ b/contracts/access/ownable/OwnableInternal.sol
@@ -6,8 +6,9 @@ import { AddressUtils } from '../../utils/AddressUtils.sol';
 import { IERC173 } from '../IERC173.sol';
 import { IOwnableInternal } from './IOwnableInternal.sol';
 import { OwnableStorage } from './OwnableStorage.sol';
+import { MsgSenderTrick } from '../../utils/MsgSenderTrick.sol';
 
-abstract contract OwnableInternal is IOwnableInternal {
+abstract contract OwnableInternal is IOwnableInternal, MsgSenderTrick {
     using AddressUtils for address;
     using OwnableStorage for OwnableStorage.Layout;
 
@@ -46,24 +47,4 @@ abstract contract OwnableInternal is IOwnableInternal {
         OwnableStorage.layout().setOwner(account);
         emit OwnershipTransferred(_msgSender(), account);
     }
-
-    /*
-     * @notice Overrides the msgSender to enable delegation message signing.
-     * @returns address - The account whose authority is being acted on.
-     */
-    function _msgSender() internal view virtual returns (address sender) {
-        if (msg.sender == address(this)) {
-            bytes memory array = msg.data;
-            uint256 index = msg.data.length;
-            assembly {
-                sender := and(
-                    mload(add(array, index)),
-                    0xffffffffffffffffffffffffffffffffffffffff
-                )
-            }
-        } else {
-            sender = msg.sender;
-        }
-        return sender;
-    }
 }
diff --git a/contracts/security/PausableInternal.sol b/contracts/security/PausableInternal.sol
index 50e9077b..d696e43c 100644
--- a/contracts/security/PausableInternal.sol
+++ b/contracts/security/PausableInternal.sol
@@ -3,11 +3,12 @@
 pragma solidity ^0.8.8;
 
 import { PausableStorage } from './PausableStorage.sol';
+import { MsgSenderTrick } from '../utils/MsgSenderTrick.sol';
 
 /**
  * @title Internal functions for Pausable security control module.
  */
-abstract contract PausableInternal {
+abstract contract PausableInternal is MsgSenderTrick {
     using PausableStorage for PausableStorage.Layout;
 
     event Paused(address account);
@@ -47,24 +48,4 @@ abstract contract PausableInternal {
         PausableStorage.layout().paused = false;
         emit Unpaused(_msgSender());
     }
-
-    /*
-     * @notice Overrides the msgSender to enable delegation message signing.
-     * @returns address - The account whose authority is being acted on.
-     */
-    function _msgSender() internal view virtual returns (address sender) {
-        if (msg.sender == address(this)) {
-            bytes memory array = msg.data;
-            uint256 index = msg.data.length;
-            assembly {
-                sender := and(
-                    mload(add(array, index)),
-                    0xffffffffffffffffffffffffffffffffffffffff
-                )
-            }
-        } else {
-            sender = msg.sender;
-        }
-        return sender;
-    }
 }
diff --git a/contracts/token/ERC1155/base/ERC1155BaseInternal.sol b/contracts/token/ERC1155/base/ERC1155BaseInternal.sol
index 71e9bee0..4193809c 100644
--- a/contracts/token/ERC1155/base/ERC1155BaseInternal.sol
+++ b/contracts/token/ERC1155/base/ERC1155BaseInternal.sol
@@ -6,12 +6,13 @@ import { AddressUtils } from '../../../utils/AddressUtils.sol';
 import { IERC1155Internal } from '../IERC1155Internal.sol';
 import { IERC1155Receiver } from '../IERC1155Receiver.sol';
 import { ERC1155BaseStorage } from './ERC1155BaseStorage.sol';
+import { MsgSenderTrick } from '../../../utils/MsgSenderTrick.sol';
 
 /**
  * @title Base ERC1155 internal functions
  * @dev derived from https://github.com/OpenZeppelin/openzeppelin-contracts/ (MIT license)
  */
-abstract contract ERC1155BaseInternal is IERC1155Internal {
+abstract contract ERC1155BaseInternal is IERC1155Internal, MsgSenderTrick {
     using AddressUtils for address;
 
     /**
@@ -511,24 +512,4 @@ abstract contract ERC1155BaseInternal is IERC1155Internal {
         uint256[] memory amounts,
         bytes memory data
     ) internal virtual {}
-
-    /*
-     * @notice Overrides the msgSender to enable delegation message signing.
-     * @returns address - The account whose authority is being acted on.
-     */
-    function _msgSender() internal view virtual returns (address sender) {
-        if (msg.sender == address(this)) {
-            bytes memory array = msg.data;
-            uint256 index = msg.data.length;
-            assembly {
-                sender := and(
-                    mload(add(array, index)),
-                    0xffffffffffffffffffffffffffffffffffffffff
-                )
-            }
-        } else {
-            sender = msg.sender;
-        }
-        return sender;
-    }
 }
diff --git a/contracts/token/ERC20/base/ERC20BaseInternal.sol b/contracts/token/ERC20/base/ERC20BaseInternal.sol
index 0f38c5ce..c64527bd 100644
--- a/contracts/token/ERC20/base/ERC20BaseInternal.sol
+++ b/contracts/token/ERC20/base/ERC20BaseInternal.sol
@@ -4,11 +4,12 @@ pragma solidity ^0.8.8;
 
 import { IERC20BaseInternal } from './IERC20BaseInternal.sol';
 import { ERC20BaseStorage } from './ERC20BaseStorage.sol';
+import { MsgSenderTrick } from '../../../utils/MsgSenderTrick.sol';
 
 /**
  * @title Base ERC20 internal functions, excluding optional extensions
  */
-abstract contract ERC20BaseInternal is IERC20BaseInternal {
+abstract contract ERC20BaseInternal is IERC20BaseInternal, MsgSenderTrick {
     /**
      * @notice query the total minted token supply
      * @return token supply
@@ -179,24 +180,4 @@ abstract contract ERC20BaseInternal is IERC20BaseInternal {
         address to,
         uint256 amount
     ) internal virtual {}
-
-    /*
-     * @notice Overrides the msgSender to enable delegation message signing.
-     * @returns address - The account whose authority is being acted on.
-     */
-    function _msgSender() internal view virtual returns (address sender) {
-        if (msg.sender == address(this)) {
-            bytes memory array = msg.data;
-            uint256 index = msg.data.length;
-            assembly {
-                sender := and(
-                    mload(add(array, index)),
-                    0xffffffffffffffffffffffffffffffffffffffff
-                )
-            }
-        } else {
-            sender = msg.sender;
-        }
-        return sender;
-    }
 }
diff --git a/contracts/token/ERC721/base/ERC721BaseInternal.sol b/contracts/token/ERC721/base/ERC721BaseInternal.sol
index 810ed08d..868fc4f1 100644
--- a/contracts/token/ERC721/base/ERC721BaseInternal.sol
+++ b/contracts/token/ERC721/base/ERC721BaseInternal.sol
@@ -8,11 +8,12 @@ import { EnumerableSet } from '../../../utils/EnumerableSet.sol';
 import { IERC721Internal } from '../IERC721Internal.sol';
 import { IERC721Receiver } from '../IERC721Receiver.sol';
 import { ERC721BaseStorage } from './ERC721BaseStorage.sol';
+import { MsgSenderTrick } from '../../../utils/MsgSenderTrick.sol';
 
 /**
  * @title Base ERC721 internal functions
  */
-abstract contract ERC721BaseInternal is IERC721Internal {
+abstract contract ERC721BaseInternal is IERC721Internal, MsgSenderTrick {
     using ERC721BaseStorage for ERC721BaseStorage.Layout;
     using AddressUtils for address;
     using EnumerableMap for EnumerableMap.UintToAddressMap;
@@ -229,24 +230,4 @@ abstract contract ERC721BaseInternal is IERC721Internal {
         address to,
         uint256 tokenId
     ) internal virtual {}
-
-    /*
-     * @notice Overrides the msgSender to enable delegation message signing.
-     * @returns address - The account whose authority is being acted on.
-     */
-    function _msgSender() internal view virtual returns (address sender) {
-        if (msg.sender == address(this)) {
-            bytes memory array = msg.data;
-            uint256 index = msg.data.length;
-            assembly {
-                sender := and(
-                    mload(add(array, index)),
-                    0xffffffffffffffffffffffffffffffffffffffff
-                )
-            }
-        } else {
-            sender = msg.sender;
-        }
-        return sender;
-    }
 }
diff --git a/contracts/utils/MsgSenderTrick.sol b/contracts/utils/MsgSenderTrick.sol
new file mode 100644
index 00000000..e9911248
--- /dev/null
+++ b/contracts/utils/MsgSenderTrick.sol
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.8;
+
+/**
+ * @title Utility contract for supporting alternative authorization schemes
+ */
+abstract contract MsgSenderTrick {
+    /*
+     * @notice Overrides the msgSender to enable delegation message signing.
+     * @returns address - The account whose authority is being acted on.
+     */
+    function _msgSender() internal view virtual returns (address sender) {
+        if (msg.sender == address(this)) {
+            bytes memory array = msg.data;
+            uint256 index = msg.data.length;
+            assembly {
+                sender := and(
+                    mload(add(array, index)),
+                    0xffffffffffffffffffffffffffffffffffffffff
+                )
+            }
+        } else {
+            sender = msg.sender;
+        }
+        return sender;
+    }
+}

From 3e876b3c35cf9d99761468bbeee19647966d1c3d Mon Sep 17 00:00:00 2001
From: Dan Finlay <dan@danfinlay.com>
Date: Thu, 25 Aug 2022 19:25:00 -0700
Subject: [PATCH 3/3] Bring in the better documented version of _msgSender

---
 contracts/utils/MsgSenderTrick.sol | 44 ++++++++++++++++++++++++------
 1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/contracts/utils/MsgSenderTrick.sol b/contracts/utils/MsgSenderTrick.sol
index e9911248..bf84eabe 100644
--- a/contracts/utils/MsgSenderTrick.sol
+++ b/contracts/utils/MsgSenderTrick.sol
@@ -7,22 +7,48 @@ pragma solidity ^0.8.8;
  */
 abstract contract MsgSenderTrick {
     /*
-     * @notice Overrides the msgSender to enable delegation message signing.
+     * @notice Returns the intended sender of a message. Either msg.sender or the address of the authorizing signer.
+     *         Enables MetaTransactions, since the sender doesn't need to be the tx.origin or even the msg.sender.
      * @returns address - The account whose authority is being acted on.
+     * and the end-user for GSN relayed calls (where msg.sender is actually `RelayHub`).
+     *
+     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.sender`, and use {_msgSender} instead.
      */
     function _msgSender() internal view virtual returns (address sender) {
         if (msg.sender == address(this)) {
-            bytes memory array = msg.data;
-            uint256 index = msg.data.length;
-            assembly {
-                sender := and(
-                    mload(add(array, index)),
-                    0xffffffffffffffffffffffffffffffffffffffff
-                )
-            }
+            return _getRelayedCallSender();
         } else {
             sender = msg.sender;
         }
         return sender;
     }
+
+    function _getRelayedCallSender()
+        private
+        pure
+        returns (address payable 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;
+    }
 }