Agent: add ERC721Receiver support (aragon#1058)

* Agent: add ERC721Receiver support

* Lint

* Test

* Address review comments

* cosmetic: small whitespace changes

Co-authored-by: Brett Sun <qisheng.brett.sun@gmail.com>

apps/agent/contracts/Agent.sol

@@ -7,13 +7,14 @@ pragma solidity 0.4.24;
 import "./SignatureValidator.sol";
 import "./standards/IERC165.sol";
 import "./standards/ERC1271.sol";
+import "./standards/IERC721Receiver.sol";
 
 import "@aragon/apps-vault/contracts/Vault.sol";
 
 import "@aragon/os/contracts/common/IForwarder.sol";
 
 
-contract Agent is IERC165, ERC1271Bytes, IForwarder, IsContract, Vault {
+contract Agent is IERC165, IERC721Receiver, ERC1271Bytes, IForwarder, IsContract, Vault {
     /* Hardcoded constants to save gas
     bytes32 public constant EXECUTE_ROLE = keccak256("EXECUTE_ROLE");
     bytes32 public constant SAFE_EXECUTE_ROLE = keccak256("SAFE_EXECUTE_ROLE");
@@ -35,6 +36,7 @@ contract Agent is IERC165, ERC1271Bytes, IForwarder, IsContract, Vault {
     uint256 public constant PROTECTED_TOKENS_CAP = 10;
 
     bytes4 private constant ERC165_INTERFACE_ID = 0x01ffc9a7;
+    bytes4 private constant ERC721_RECEIVED_INTERFACE_ID = 0x150b7a02; // bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))
 
     string private constant ERROR_TARGET_PROTECTED = "AGENT_TARGET_PROTECTED";
     string private constant ERROR_PROTECTED_TOKENS_MODIFIED = "AGENT_PROTECTED_TOKENS_MODIFIED";
@@ -56,6 +58,7 @@ contract Agent is IERC165, ERC1271Bytes, IForwarder, IsContract, Vault {
     event RemoveProtectedToken(address indexed token);
     event PresignHash(address indexed sender, bytes32 indexed hash);
     event SetDesignatedSigner(address indexed sender, address indexed oldSigner, address indexed newSigner);
+    event ReceiveERC721(address indexed token, address indexed operator, address indexed from, uint256 tokenId, bytes data);
 
     /**
     * @notice Execute '`@radspec(_target, _data)`' on `_target``_ethValue == 0 ? '' : ' (Sending ' + @tokenAmount(0x0000000000000000000000000000000000000000, _ethValue) + ')'`
@@ -197,6 +200,12 @@ contract Agent is IERC165, ERC1271Bytes, IForwarder, IsContract, Vault {
         emit SetDesignatedSigner(msg.sender, oldDesignatedSigner, _designatedSigner);
     }
 
+    function onERC721Received(address _operator, address _from, uint256 _tokenId, bytes _data) external returns (bytes4) {
+        emit ReceiveERC721(msg.sender, _operator, _from, _tokenId, _data);
+
+        return ERC721_RECEIVED_INTERFACE_ID;
+    }
+
     // Forwarding fns
 
     /**
@@ -208,6 +217,19 @@ contract Agent is IERC165, ERC1271Bytes, IForwarder, IsContract, Vault {
         return true;
     }
 
+    /**
+     * @notice Tells whether this contract supports a given ERC-165 interface
+     * @dev Implements conformance to ERC-165
+     * @param _interfaceId Interface bytes to check
+     * @return True if this contract supports the interface
+     */
+    function supportsInterface(bytes4 _interfaceId) external pure returns (bool) {
+        return
+            _interfaceId == ERC1271_INTERFACE_ID ||
+            _interfaceId == ERC721_RECEIVED_INTERFACE_ID ||
+            _interfaceId == ERC165_INTERFACE_ID;
+    }
+
     /**
     * @notice Execute the script as the Agent app
     * @dev IForwarder interface conformance. Forwards any token holder action.
@@ -233,19 +255,6 @@ contract Agent is IERC165, ERC1271Bytes, IForwarder, IsContract, Vault {
         return canPerform(_sender, RUN_SCRIPT_ROLE, arr(_getScriptACLParam(_evmScript)));
     }
 
-    // ERC-165 conformance
-
-    /**
-     * @notice Tells whether this contract supports a given ERC-165 interface
-     * @param _interfaceId Interface bytes to check
-     * @return True if this contract supports the interface
-     */
-    function supportsInterface(bytes4 _interfaceId) external pure returns (bool) {
-        return
-            _interfaceId == ERC1271_INTERFACE_ID ||
-            _interfaceId == ERC165_INTERFACE_ID;
-    }
-
     // ERC-1271 conformance
 
     /**

apps/agent/contracts/standards/IERC721Receiver.sol

@@ -0,0 +1,20 @@
+pragma solidity 0.4.24;
+
+
+interface IERC721Receiver {
+    /**
+     * @notice Handle the receipt of an NFT
+     * @dev The ERC721 smart contract calls this function on the recipient
+     * after a {IERC721-safeTransferFrom}. This function MUST return the function selector,
+     * otherwise the caller will revert the transaction. The selector to be
+     * returned can be obtained as `this.onERC721Received.selector`. This
+     * function MAY throw to revert and reject the transfer.
+     * Note: the ERC721 contract address is always the message sender.
+     * @param operator The address which called `safeTransferFrom` function
+     * @param from The address which previously owned the token
+     * @param tokenId The NFT identifier which is being transferred
+     * @param data Additional data with no specified format
+     * @return bytes4 `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
+     */
+    function onERC721Received(address operator, address from, uint256 tokenId, bytes data) external returns (bytes4);
+}

apps/agent/test/agent_shared.js

@@ -36,6 +36,7 @@ module.exports = (
   const NO_DATA = '0x'
   const ERC165_SUPPORT_INVALID_ID = '0xffffffff'
   const ERC165_SUPPORT_INTERFACE_ID = '0x01ffc9a7'
+  const ERC721_RECEIVED_INTERFACE_ID = '0x150b7a02'
 
   const AgentLike = artifacts.require(agentName)
 
@@ -759,6 +760,10 @@ module.exports = (
           assert.isTrue(await agent.supportsInterface(ERC1271_INTERFACE_ID))
         })
 
+        it('supports ERC721Receiver interface', async () => {
+          assert.isTrue(await agent.supportsInterface(ERC721_RECEIVED_INTERFACE_ID))
+        })
+
         it('doesn\'t support any other interface', async () => {
           assert.isFalse(await agent.supportsInterface('0x12345678'))
           assert.isFalse(await agent.supportsInterface('0x'))