Closes #161: Add EIP-165 support in DefaultCallbackHandler (#285)

Author: rmeissner

contracts/handler/DefaultCallbackHandler.sol

@@ -4,10 +4,11 @@ pragma solidity >=0.7.0 <0.9.0;
 import "../interfaces/ERC1155TokenReceiver.sol";
 import "../interfaces/ERC721TokenReceiver.sol";
 import "../interfaces/ERC777TokensRecipient.sol";
+import "../interfaces/IERC165.sol";
 
 /// @title Default Callback Handler - returns true for known token callbacks
 /// @author Richard Meissner - <richard@gnosis.pm>
-contract DefaultCallbackHandler is ERC1155TokenReceiver, ERC777TokensRecipient, ERC721TokenReceiver {
+contract DefaultCallbackHandler is ERC1155TokenReceiver, ERC777TokensRecipient, ERC721TokenReceiver, IERC165 {
 
     string public constant NAME = "Default Callback Handler";
     string public constant VERSION = "1.0.0";
@@ -48,4 +49,17 @@ contract DefaultCallbackHandler is ERC1155TokenReceiver, ERC777TokensRecipient,
         // We implement this for completeness, doesn't really have any value
     }
 
+    
+    function supportsInterface(bytes4 interfaceId) 
+        virtual 
+        override 
+        external 
+        view 
+        returns (bool) 
+    {
+        return interfaceId == type(ERC1155TokenReceiver).interfaceId
+            || interfaceId == type(ERC721TokenReceiver).interfaceId
+            || interfaceId == type(IERC165).interfaceId;
+    }
+
 }

contracts/interfaces/IERC165.sol

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+pragma solidity >=0.7.0 <0.9.0;
+
+/// @notice More details at https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/introspection/IERC165.sol
+interface IERC165 {
+    /**
+     * @dev Returns true if this contract implements the interface defined by
+     * `interfaceId`. See the corresponding
+     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
+     * to learn more about how these ids are created.
+     *
+     * This function call must use less than 30 000 gas.
+     */
+    function supportsInterface(bytes4 interfaceId) external view returns (bool);
+}

test/handlers/DefaultCallbackHandler.spec.ts

@@ -10,6 +10,13 @@ describe("DefaultCallbackHandler", async () => {
     });
 
     describe("ERC1155", async () => {
+        it('should supports ERC1155 interface', async () => {
+            const handler = await getDefaultCallbackHandler()
+            await expect(
+                await handler.callStatic.supportsInterface("0x4e2312e0")
+            ).to.be.eq(true)
+        })
+
         it('to handle onERC1155Received', async () => {
             const handler = await getDefaultCallbackHandler()
             await expect(
@@ -26,6 +33,13 @@ describe("DefaultCallbackHandler", async () => {
     })
 
     describe("ERC721", async () => {
+        it('should supports ERC721 interface', async () => {
+            const handler = await getDefaultCallbackHandler()
+            await expect(
+                await handler.callStatic.supportsInterface("0x150b7a02")
+            ).to.be.eq(true)
+        })
+
         it('to handle onERC721Received', async () => {
             const handler = await getDefaultCallbackHandler()
             await expect(
@@ -40,4 +54,13 @@ describe("DefaultCallbackHandler", async () => {
             await handler.callStatic.tokensReceived(AddressZero, AddressZero, AddressZero, 0, "0x", "0x")
         })
     })
+
+    describe("ERC165", async () => {
+        it('should not support random interface', async () => {
+            const handler = await getDefaultCallbackHandler()
+            await expect(
+                await handler.callStatic.supportsInterface("0xbaddad42")
+            ).to.be.eq(false)
+        })
+    })
 })