Add ERC721 Wrapper

contracts/token/ERC721/extensions/ERC721Wrapper.sol

@@ -17,6 +17,10 @@ import "../utils/ERC721Holder.sol";
 abstract contract ERC721Wrapper is ERC721, ERC721Holder {
     IERC721 private immutable _underlying;
 
+    // Kept as bytes12 so it can be packed with an address
+    // Equal to 0xb125e89df18e2ceac5fd2fa8
+    bytes12 public constant WRAPPER_ACCEPT_MAGIC = bytes12(keccak256("WRAPPER_ACCEPT_MAGIC"));
+
     constructor(IERC721 underlyingToken) {
         _underlying = underlyingToken;
     }
@@ -25,7 +29,7 @@ abstract contract ERC721Wrapper is ERC721, ERC721Holder {
      * @dev Allow a user to deposit underlying tokens and mint the corresponding tokenIds.
      */
     function depositFor(address account, uint256[] memory tokenIds) public virtual returns (bool) {
-        bytes memory data = abi.encode(account);
+        bytes memory data = abi.encodePacked(WRAPPER_ACCEPT_MAGIC, account);
 
         uint256 length = tokenIds.length;
         for (uint256 i = 0; i < length; ++i) {
@@ -57,6 +61,10 @@ abstract contract ERC721Wrapper is ERC721, ERC721Holder {
      * @dev Overrides {IERC721Receiver-onERC721Received} to allow minting on direct ERC721 transfers to
      * this contract.
      *
+     * In case there's data attached, it validates that the sender is aware of this contract's existence and behavior
+     * by checking a magic value (`WRAPPER_ACCEPT_MAGIC`) in the first 12 bytes. If it also matches, the rest 20
+     * bytes are used as an address to send the tokens to.
+     *
      * WARNING: Doesn't work with unsafe transfers (eg. {IERC721-transferFrom}). Use {ERC721Wrapper-_recover}
      * for recovering in that scenario.
      */
@@ -66,8 +74,11 @@ abstract contract ERC721Wrapper is ERC721, ERC721Holder {
         uint256 tokenId,
         bytes memory data
     ) public override returns (bytes4) {
-        require(msg.sender == address(underlying()), "ERC721Wrapper: caller is not underlying");
-        _safeMint(data.length == 0 ? from : abi.decode(data, (address)), tokenId);
+        require(address(underlying()) == _msgSender(), "ERC721Wrapper: caller is not underlying");
+        if (data.length == 32 && WRAPPER_ACCEPT_MAGIC == bytes12(data)) {
+            from = address(bytes20(bytes32(data) << 96));
+        }
+        _safeMint(from, tokenId);
         return IERC721Receiver.onERC721Received.selector;
     }
 

test/token/ERC721/extensions/ERC721Wrapper.test.js

@@ -1,5 +1,6 @@
 const { BN, expectEvent, constants, expectRevert } = require('@openzeppelin/test-helpers');
 const { expect } = require('chai');
+const { keccakFromString, bufferToHex } = require('ethereumjs-util');
 
 const { shouldBehaveLikeERC721 } = require('../ERC721.behavior');
 
@@ -219,11 +220,31 @@ contract('ERC721Wrapper', function (accounts) {
   });
 
   describe('onERC721Received', function () {
-    it('mints a token upon receival', async function () {
+    const WRAPPER_ACCEPT_MAGIC = bufferToHex(keccakFromString('WRAPPER_ACCEPT_MAGIC')).slice(0, 26); // Include 0x
+
+    const magicWithAddresss = address =>
+      web3.utils.encodePacked(
+        {
+          value: WRAPPER_ACCEPT_MAGIC,
+          type: 'bytes12',
+        },
+        {
+          value: address,
+          type: 'address',
+        },
+      );
+
+    it('mints a token to sender with arbitrary data', async function () {
       // `safeTransferFrom` guarantees `onERC721Received` check
-      const { tx } = await this.underlying.safeTransferFrom(initialHolder, this.token.address, firstTokenId, {
-        from: initialHolder,
-      });
+      const { tx } = await this.underlying.methods['safeTransferFrom(address,address,uint256,bytes)'](
+        initialHolder,
+        this.token.address,
+        firstTokenId,
+        '0x0123',
+        {
+          from: initialHolder,
+        },
+      );
 
       await expectEvent.inTransaction(tx, this.token, 'Transfer', {
         from: constants.ZERO_ADDRESS,
@@ -232,12 +253,12 @@ contract('ERC721Wrapper', function (accounts) {
       });
     });
 
-    it('mints token to specific holder', async function () {
+    it('mints token to specific holder with address after magic value', async function () {
       const { tx } = await this.underlying.methods['safeTransferFrom(address,address,uint256,bytes)'](
         initialHolder,
         this.token.address,
         firstTokenId,
-        web3.eth.abi.encodeParameters(['address'], [anotherAccount]),
+        magicWithAddresss(anotherAccount),
         {
           from: initialHolder,
         },
@@ -256,7 +277,7 @@ contract('ERC721Wrapper', function (accounts) {
           initialHolder,
           this.token.address,
           firstTokenId,
-          web3.eth.abi.encodeParameters(['address'], [anotherAccount]),
+          magicWithAddresss(anotherAccount), // Correct data
           { from: anotherAccount },
         ),
         'ERC721Wrapper: caller is not underlying',